PNM email 12-8-10.txt

RE: Questions on CD contract dates, cost of electricity, and implosion 

study

Norem, Nancy 

to:

Joe Kordzi

12/08/2010 01:54 PM

Cc:

"Gannon, Maureen", mack.mcguffey, "Alvidrez, Richard (Miller)", "Fischer, 

Diane M.", "Lucas, Kyle J.", "Williams, Mark A."

Show Details

History: This message has been replied to and forwarded.

Joe,

Attached is the response to the questions you sent on November 12, 2010.

Nancy

From: Kordzi.Joe@epamail.epa.gov [mailto:Kordzi.Joe@epamail.epa.gov] 

Sent: Friday, November 12, 2010 10:36 AM

To: Norem, Nancy

Cc: Gannon, Maureen

Subject: Questions on CD contract dates, cost of electricity, and 

implosion study

Hi Nancy, 

I wanted to followup on a few remaining questions. 

Have you been able to locate the dates of the contracts for the consent 

decree work? 

Can you provide the current cost to PNM to produce electricity (busbar 

cost)? 

Can you provide the implosion study, which was part of the boiler 

stiffening study? 

Regards,

Joe

" ... and miles to go before I sleep."

-- Robert Frost

Page 1
Response to Question 1 in email dated November 12, 2010: 

PNM has undertaken a more detailed review of the project design records for the boiler 

stiffening work previously performed at SJGS as part of the installation of baghouses in 

compliance with the 2005 Consent Decree. Although the following provides additional 

clarification of our prior responses, it does not alter the recommendation of PNM’s experts that 

additional boiler stiffening will be needed as part of any plan to install SCR at SJGS. 

As an initial matter, PNM must correct its prior response to your questions, in which we 

indicated that SJGS only complied with the 2004 version of the National Fire Protection 

Association (NFPA) Code 85 during the installation of the pollution control equipment required 

by the Consent Decree. On the contrary, SJGS did in fact consider the newer 2007 version of 

NFPA 85 when it completed the Consent Decree work. 

The confusion was caused in part by the structure of NFPA 85 itself. NFPA 85 contains a broad, 

generally-applicable standard that requires all boilers with downstream fans to be capable of 

withstanding a pressure differential of +/- 35 inches w.g. (or the maximum capability of the fans, 

whichever is less; in this case, +/- 35 inches is less than the capability of the fans). Because this 

standard is applicable to a wide range of boilers, and does not take into account site-specific 

circumstances, it is designed to be relatively conservative, particularly given the catastrophic 

consequences and safety concerns associated with a boiler implosion or explosion. However, 

recognizing that the safety concerns underlying the “one-size-fits-all” standard can be addressed 

by other means in some instances, NFPA 85 allows “[a] designer capable of applying a more 

complete and rigorous analysis to special or unusual problems [to] have latitude in the 

development of [boiler] designs.” NFPA 85 Section 1.2.3.1. In essence, boiler owners have two 

methods of complying with NFPA 85 – implement the generally-applicable standard of +/- 35 

inches w.g., or conduct “a more complete and rigorous analysis” to determine whether other 

safety precautions and specifications will suffice. 

In light of the latitude allowed by NFPA 85, the engineers hired by PNM to help complete the 

SJGS Consent Decree work, Sargent & Lundy (S&L), asked boiler designer Babcock and 

Wilcox (B&W) to determine whether SJGS could sufficiently protect its boilers without meeting 

the generally-applicable NFPA 85 standard of +/- 35 inches w.g. B&W in turn asked TRAX 

Corporation to develop implosion studies (attached) to determine the best means of protecting 

the boiler. Those studies required a rigorous, time-consuming analysis that cost over $300,000, 

not including costs associated with the review and approval of those studies. 

With the implosion studies, PNM’s experts were able to demonstrate that the SJGS boilers would 

be adequately protected from implosion during a master fuel trip if stiffened to withstand 

negative pressure differentials of 15 inches w.g. (for Units 3 and 4) and 12 inches w.g. (for Units 

1 and 2), instead of the generally applicable NFPA 85 standard of +/- 35 w.g. These conclusions 

were provided to the insurance carrier for SJGS, FM Global, as evidence of compliance with 

NFPA 85. However, FM Global required PNM to be more conservative and stiffen the boilers 

further so that all four units would be able to withstand a negative pressure differential of up to 

18 inches w.g. PNM complied with that request and stiffened the boilers to that specification. 
Although SJGS fully complied with NFPA 85 (2007) during the Consent Decree work, the 

installation of SCR at the plant will place increased implosion potential on the boilers by 

increasing the negative pressure on the draft system by 10 more inches w.g. As a result, a 

requirement to install SCR at SJGS will trigger the need to once again perform a costly, timeconsuming analysis to determine whether PNM will qualify for an exception from the generallyapplicable implosion protection standard of NFPA 85. To date, neither PNM nor its consultants 

have attempted to determine whether an alternative to the +/- 35 inches w.g. standard would 

suffice following installation of an SCR, due to the significant amount time and expense that 

would be associated with that analysis. However, based on the information that is currently 

available, and the added pressures associated with an SCR, PNM’s expert Black and Veatch 

remains concerned that it may not be possible to successfully develop other means for protecting 

the boilers without stiffening them to the NFPA 85 standard. As such, Black and Veatch 

recommends stiffening the boilers to +/- 35 inches w.g. 

Without a successful demonstration that the boilers could be adequately protected without 

stiffening them to the NFPA 85 standard (and approval of that approach by PNM’s insurance 

carrier), PNM cannot assume that additional boiler stiffening will not be required. Quite the 

opposite, PNM must instead assume that stiffening will be required unless (and until) 

demonstrated otherwise. The mere existence of a possible exception from the generally 

applicable NFPA 85 standard, even if successfully obtained in the past, does not change the fact 

that PNM’s experts currently believe significant boiler stiffening will be necessary to protect the 

boilers from implosion following installation of an SCR. 

Response to Question 1 in email dated November 12, 2010: 

PNM’s average cost of generation is $47.83/MWh. 

Response to Question 3 in email dated November 12, 2010: 

The implosion studies are attached. 
Public Service Company of New Mexico

San Juan Generating Station Units 1 & 2

Furnace Draft Analysis

FINAL REPORT FINAL REPORT

Report Number EA0711–0103

March 27, 2008

Prepared by:

107 Vista Centre Drive Forest, Virginia 24551

Voice: 434.385.7250 Fax: 434.385.8233

www.traxcorp.com
PUBLIC SERVICE COMPANY OF NEW MEXICO 

SAN JUAN GENERATING STATION UNITS 1 & 2 

FURNACE DRAFT ANALYSIS 

FINAL REPORT 

Prepared for: 

The Babcock & Wilcox Company 

P.O. No. BAX080393

Report Number EA0711–0103

Prepared by: 

Satish Perivilli, Simulation Engineer 

Engineering Applications Business Unit 

Reviewed by Kent Kozak, Senior Engineer 

TRAX, LLC 

107 Vista Centre Drive Forest, VA 24551 

Voice: (434) 385-7250, Ext. 271 Fax: (434) 385-8233 

Email: sperivilli@traxcorp.com 

Approved by: 

 Gregory M. Kosowski, Vice President
 

TRAX, LLC shall not be liable for any losses or for damages resulting from the use of any 

information, apparatus, method, or process disclosed in this report. 

Copyright © TRAX LLC, 2007. All rights reserved. 

ProTRAX is a trademark of TRAX, LLC. 

All other brand and product names are trademarks or registered trademarks 

of their respective companies. 

 
PNM – San Juan Generating Station Unit 1 Page i 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

TABLE OF CONTENTS 

LIST OF FIGURES.......................................................................................................... ii

LIST OF TABLES .......................................................................................................... iv

EXECUTIVE SUMMARY ................................................................................................ v

1.0 INTRODUCTION.................................................................................................. 1

2.0 NOMENCLATURE ............................................................................................... 3

3.0 EXISTING CONFIGURATION MODEL AND VALIDATION ................................ 4

3.1 Existing Configuration Process Model..................................................... 4

3.2 Existing Configuration Control Model ...................................................... 5

3.3 Steady-State Conditions ............................................................................ 6

3.3.1 Full Load Steady-State ....................................................................... 6

3.3.2 Low Load Steady-State ...................................................................... 9

3.3.3 Validation Load Steady-State ........................................................... 11

3.4 Transient Validation ................................................................................. 13

3.4.1 Unit 1 MFT Procedure ...................................................................... 13

3.4.2 Unit 1 Validation Parameters............................................................ 13

3.4.3 Unit 1 Validation Results .................................................................. 14

3.5 Validation Conclusion.............................................................................. 16

4.0 FUTURE CONFIGURATION MODEL AND TRANSIENT TESTING ................. 17

4.1 Future Configuration Process Model...................................................... 17

4.2 Future Configuration Control Model....................................................... 18

4.3 Steady-State Conditions .......................................................................... 20

4.3.1 Full Load Steady-State ..................................................................... 20

4.3.2 Low Load Steady-State .................................................................... 22

4.4 Transient Events and Mitigations ........................................................... 23

4.4.1 T1: Full Load MFT ............................................................................ 24

4.4.2 T2: Full Load All Booster Fans Trip .................................................. 28

4.4.3 T3: Full Load Both FD Fans Trip ...................................................... 35

4.4.4 T4: Low Load Two Booster Fans Runaway...................................... 38

4.4.5 T5: Full Load All Fans Trip................................................................ 41

4.4.6 T6: Full Load Single Booster Fan Trips ............................................ 45

4.4.7 T7: Full Load Baghouse Cleaning System Failure............................ 50

4.5 Transient Events Summary Table........................................................... 54

5.0 CONCLUSIONS AND RECOMMENDATIONS.................................................. 55
PNM – San Juan Generating Station Unit 1 Page ii 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

LIST OF FIGURES 

Figure 1 Unit 1 Pressure Profile at Full Load............................................................ 8

Figure 2 Unit 1 Pressure Profile at Low Load ......................................................... 10

Figure 3 Unit 1 Pressure Profile at Validation Point (97.2% Load)........................ 12

Figure 4 San Juan Future Configuration................................................................. 18

Figure 5 Booster Fan IGV Controls.......................................................................... 19

Figure 6 Steady-State Pressure Profile for 100% Load.......................................... 21

Figure 7 Steady-State Pressure Profile for 30% Load............................................ 23

Figure 8 T1 Unit Pressures....................................................................................... 25

Figure 9 T1 Fan Inlet Guide Vane Positions............................................................ 26

Figure 10 T1 Baghouse and Scrubber Pressures................................................... 27

Figure 11 T1 Flows.................................................................................................... 28

Figure 12 T2 Unit Pressures..................................................................................... 29

Figure 13 T2 Fan Inlet Guide Vane Positions.......................................................... 30

Figure 14 T2 Fan Speeds .......................................................................................... 30

Figure 15 T2 Baghouse and Scrubber Pressures................................................... 31

Figure 16 T2 Flows.................................................................................................... 32

Figure 17 T2 and MT2 Transient Maximum Pressure Profile................................. 33

Figure 18 T2 and MT2 Furnace Pressure Comparison........................................... 33

Figure 19 MT2 and MT2A Transient Maximum Pressure Profile ........................... 34

Figure 20 MT2 and MT2A Furnace Pressure Comparison ..................................... 35

Figure 21 T3 Unit Pressures..................................................................................... 36

Figure 22 T3 Fan Inlet Guide Vane Positions.......................................................... 36

Figure 23 T3 Baghouse and Scrubber Pressures................................................... 37

Figure 24 T3 Flows.................................................................................................... 38

Figure 25 T4 Unit Pressures..................................................................................... 39

Figure 26 T4 Fan Inlet Guide Vane Positions.......................................................... 39

Figure 27 T4 Baghouse and Scrubber Pressures................................................... 40

Figure 28 T4 Flows.................................................................................................... 41

Figure 29 T5 Unit Pressures..................................................................................... 42

Figure 30 T5 Fan Speeds .......................................................................................... 42

Figure 31 T5 Fan Inlet Guide Vane Positions.......................................................... 43
PNM – San Juan Generating Station Unit 1 Page iii 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Figure 32 T5 Baghouse and Scrubber Pressures................................................... 44

Figure 33 T5 Flows.................................................................................................... 45

Figure 34 T6 Unit Pressures..................................................................................... 46

Figure 35 T6 Fan Speeds .......................................................................................... 47

Figure 36 T6 Baghouse and Scrubber Pressures................................................... 47

Figure 37 T6 Flows.................................................................................................... 48

Figure 38 T6 Fan Inlet Guide Vane Positions.......................................................... 48

Figure 39 T6 Transient Maximum Pressure Profile ................................................ 49

Figure 40 T6 Furnace Pressure Comparison .......................................................... 50

Figure 41 T7 Unit Pressures..................................................................................... 51

Figure 42 T7 Baghouse and Scrubber Pressures................................................... 52

Figure 43 T7 Fan Inlet Guide Vane Positions.......................................................... 52

Figure 44 T7 Flows.................................................................................................... 53
PNM – San Juan Generating Station Unit 1 Page iv 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

LIST OF TABLES 

Table 1 List of Transients ........................................................................................... 2

Table 2 Unit 1 Critical Plant Parameters at Full Load (100%) .................................. 7

Table 3 Stack Calculations ......................................................................................... 9

Table 4 Unit 1 Critical Plant Parameters at Low Load (55.5%) .............................. 10

Table 5 Unit 1 Critical Plant Parameters at Validation Point (97.2% Load) .......... 12

Table 6 100% Load Initial Condition Parameters.................................................... 21

Table 7 30% Load Initial Condition Parameters...................................................... 22

Table 8 Transient Descriptions ................................................................................ 24

Table 9 Transient Event Summary Table ................................................................ 54

Table 10 Transient Event Summary Table .............................................................. 54

Table 11 Kick Values................................................................................................. 56
PNM – San Juan Generating Station Unit 1 Page v 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

EXECUTIVE SUMMARY 

TRAX, LLC has been retained by The Babcock and Wilcox Company (B&W) to perform a 

furnace draft analysis for the Public Service Company of New Mexico (PNM) San Juan 

Generating Station Units 1 and 2. This study analyzed the effect of ductwork and equipment 

changes related to the addition of environmental equipment. These modifications included the 

addition of a baghouse and related ductwork, the replacement of existing booster fans with new 

upgraded booster fans, and the redirection all the flue gas flow through the baghouse, the booster 

fans, and the scrubbers before entering the stack. The primary goal of this study was to 

determine the effects of these plant modifications on pressures and flows throughout the furnace 

draft system during normal and abnormal operation. 

In the initial phase of this analysis, a model of the existing plant configuration for Unit 1 was 

built. The plant model was validated against plant data to ensure accuracy and to establish a 

baseline for the subsequent investigation of the equipment addition. The validation effort 

consisted of running the Unit 1 model through a severe transient similar to one previously 

experienced at the plant, and comparing the model results to historical plant data. The results 

from this validation were delivered in Validation Report EA0711–0101, dated September 25, 

2007. 

The existing configuration was then modified to the future configuration by making process and 

control changes as necessitated by the additional equipment. The future configuration model 

was then tested through seven severe transients. TRAX implemented the basic proposed control 

logic for the new environmental equipment as provided by PNM. This control logic was then 

enhanced by tuning the controllers and adding mitigating measures to improve the control 

system performance and protect the equipment during pressure excursions. 

The results obtained during the transient analysis of the future configuration are summarized 

below: 

• Holding the booster fan kicker circuit for 15 seconds following a master fuel trip (MFT) 

promoted stable process and control behavior during recovery. 

Furnace Pressure

• During a full load MFT, the quick adjustment of booster fan inlet guide vanes (IGV) via a 

kicker circuit was essential to prevent further furnace pressure excursions. 

• Prior to applying any mitigating measures, the “Full Load All Booster Fans Trip,” “Full 

Load Single Booster Fan Trips,” and “Full Load Baghouse Cleaning System Failure” 

transients resulted in positive furnace pressure excursions, while all the other transients 

resulted in negative furnace pressure excursions. 

• Prior to applying any mitigating measures, the “Full Load Single Booster Fan Trips” and 

the “Full Load All Booster Fans Trip” transients caused the highest positive furnace 

pressure excursions of +21.1 inwc and +18.6 inwc respectively. 
PNM – San Juan Generating Station Unit 1 Page vi 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

− Reduction of mass flow through the system via a runback from 100% to 70%, at a 

rate of 30 MW/min, mitigated the furnace pressure to a maximum of +17.4 inwc 

during the “Full Load Single Booster Fan Trips” transient. 

− Tripping both forced draft (FD) fans on a high pressure limit following the MFT 

mitigated the furnace pressure to a maximum of +15.1 inwc during the “Full Load All 

Booster Fans Trip” transient. Note that the +15 inwc high pressure limit caused the 

FD fan trip to occur 59 seconds after the MFT. 

− Tripping both FD fans immediately following the MFT mitigated the furnace pressure 

to a maximum of +9.9 inwc during the “Full Load All Booster Fans Trip” transient. 

Note that this transient was run to compare the results of an immediate FD fan trip 

with the results of a delayed FD fan trip, as described above. 

• The “Full Load Both FD Fans Trip” transient caused the lowest furnace pressure 

excursion of –6.9 inwc. 

• The overriding booster fan runback controller was responsible for limiting the furnace 

pressure to only –3.7 inwc during the “Low Load Two Booster Fans Runaway” transient. 

Booster Fan Inlet Pressure

• Prior to applying any mitigating measures, the “Full Load All Booster Fans Trip” 

transient caused the highest booster fan inlet pressure excursion of +8.3 inwc, while the 

“Full Load Baghouse Cleaning System Failure” transient caused the lowest booster fan 

inlet pressure excursion of –14.7 inwc. 

− Tripping both FD fans on a high pressure limit following the MFT mitigated the 

booster fan inlet pressure to a maximum of +5.5 inwc during the “Full Load All 

Booster Fans Trip” transient. 

Air Heater Gas Outlet Pressure

• Prior to applying any mitigating measures, the “Full Load All Booster Fans Trip” 

transient caused the highest air heater gas outlet pressure excursion of +14.6 inwc, while 

the “Full Load Both FD Fans Trip” transient caused the lowest air heater gas outlet 

pressure excursion of –7.7 inwc. 

− Tripping both FD fans on a high pressure limit following MFT mitigated the air 

heater gas outlet pressure to a maximum of +11.4 inwc during the “Full Load All 

Booster Fans Trip” transient. 

Based on the results of the transient runs, TRAX recommends the following control strategies 

and mitigating measures be implemented in the future plant configuration controls: 

1. During normal operation, the booster fan IGV should be controlled by a feed-forward 

signal from the FD fan IGV added to a trim control that monitors air heater gas outlet 

pressure. 

2. A kicker circuit should be used to immediately run back booster fan inlet guide vanes for 

15 seconds following an MFT. 
PNM – San Juan Generating Station Unit 1 Page vii 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

3. An overriding booster fan runback controller should be used to help mitigate negative 

furnace pressure excursions during MFT and fan transients. 

4. If all operating booster fans are tripped, immediately triggering an MFT, then both FD 

fans should also be tripped to avoid high furnace pressure excursions. 

5. In the event of a single booster fan trip at full load, the load should be reduced in order to 

avoid high positive furnace pressure excursions. 

The model construction, validation, transient testing, results, and conclusions are detailed in the 

following report. The transient analysis modeling selected as described in this report was used to 

estimate the magnitude of possible events. Some of the cases modeled are worst-case scenarios 

that have a low probability of occurrence. This report does not attempt to predict the likelihood 

of any of these events occurring. 
PNM – San Juan Generating Station Unit 1 Page 1 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

1.0 INTRODUCTION 

TRAX, LLC has been retained by The Babcock & Wilcox Company to perform an engineering 

analysis on Units 1 and 2 at the Public Service Company of New Mexico San Juan Generating 

Station. This study analyzed the effect of proposed plant modifications, which included addition 

of a baghouse and related ductwork changes and replacement of existing booster fans with new 

upgraded booster fans while allowing no bypass flow directly to the stack. 

The primary goal of the study was to help answer the following questions: 

1. What is the impact of the process modifications on furnace and ductwork pressure 

excursions during normal and abnormal plant operation? 

2. How does the proposed control system design behave during severe pressure excursions? 

3. What, if any, corrective actions are necessary? 

The approach used in this study consisted of the following basic steps: 

1. A dynamic model of Unit 1 in its existing configuration was constructed and validated 

against historical plant data. 

2. A baghouse was added, booster fans were upgraded, and ductwork was modified to 

represent the plant in its future configuration. 

3. The future configuration model was run through selected transients, and pressure 

excursions in the furnace and ductwork were recorded. 

4. The results were analyzed, and mitigating measures designed to minimize pressure 

excursions were identified and tested. 

The existing furnace draft system for San Juan Unit 1 was modeled using ProTRAX, a 

commercially available dynamic simulation system. The ProTRAX system is based on modular 

components, allowing interconnecting of modules representing furnaces, fans, dampers, ducts, 

etc., into any physically realistic configuration. All of the module formulations are based on 

first-principle conservation relations, the Second Law of Thermodynamics, and well-established 

constitutive relations for heat transfer and fluid mechanics. The resulting executable models are 

operated from a graphics-based environment that provided extensive capability for controlling 

the models and displaying the results in various formats. 

B&W, PNM, and TRAX selected a total of seven transients to be tested with the new plant 

configuration. The goal was to identify conditions that would create large pressure excursions in 

the furnace and ductwork. Each transient consisted of an initial event followed by the response 

of the controls, which could eventually lead to a master fuel trip and/or individual fan trips. The 

transients selected for the study are shown in Table 1. 
PNM – San Juan Generating Station Unit 1 Page 2 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

No. Transient Name 

T1 Full Load MFT 

T2 Full Load All Booster Fans Trip 

T3 Full Load Both FD Fans Trip 

T4 Low Load Two Booster Fans Runaway 

T5 Full Load All Fans Trip 

T6 Full Load Single Booster Fan Trips 

T7 Full Load Baghouse Cleaning System Failure 

Table 1 List of Transients 

This report describes the results of these transient runs. A Reference Section is provided at the 

end of this report containing schematics, plots for validation runs, and plots for transient runs 

pertinent to each named transient. 
PNM – San Juan Generating Station Unit 1 Page 3 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

2.0 NOMENCLATURE 

The naming convention used throughout this report is described below: 

1st Quadrant Fan Operation 

Fan operation where the fan has flow in the direction of fan suction to discharge, with a 

discharge pressure greater than the suction pressure. Operation in this region is governed 

by manufacturers’ fan curves (developed head versus volumetric flow). 

2nd Quadrant Fan Operation 

Flow through the fan has reversed and is now from discharge to suction. Head is positive 

with the discharge pressure greater than the suction pressure. In this quadrant the fan is 

acting as a resistance with flow from higher (discharge) to lower (suction) pressure. 

Operation in this region starts at the fan dead head pressure (zero flow) and is based on 

an assumed flow resistance. Fan operation in the 2nd quadrant typically occurs during fan 

trips or other equipment malfunctions. 

4th Quadrant Fan Operation 

Flow is in the direction of fan suction to discharge with a discharge head less than the 

suction head (i.e., the pressure drops across the fan rather than rising). Operation in this 

region is governed by the run out portion of the fan curve and assumed flow resistance 

behavior. Typically, fan operation in the 4th quadrant occurs during a fan trip. 

MFT 

Master fuel trip (MFT) is the procedure in which all fuel to the furnace is completely shut 

off. 

Water Seal Venting 

Water seal venting refers to the water seal at the bottom of the furnace. At sufficiently 

low furnace pressure (–28 inwc below ambient), the water seal can rupture, allowing 

ambient air into the furnace. This additional flow of ambient air into the furnace will 

help minimize any negative furnace pressure transient. 

 
PNM – San Juan Generating Station Unit 1 Page 4 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

3.0 EXISTING CONFIGURATION MODEL AND VALIDATION 

TRAX, PNM, and B&W worked together to analyze plant historian data, equipment 

configurations, and control schemes to determine if Unit 1 and Unit 2 required separate 

validations. It was determined by the project team that the simulation of Unit 1 was sufficient to 

represent both Unit 1 and Unit 2. All subsequent references to Unit 1 should be considered 

representative of Unit 1 or Unit 2. 

The dynamic model representing San Juan Generating Station Unit 1 consisted of a process 

model, which simulated the existing process configuration; and a controls model, which was 

built from a subset of existing plant controls. TRAX prepared the process model based on 

drawings provided by PNM, a plant walkdown, and discussions with plant personnel. The 

process and control model configuration drawings were reviewed and approved by B&W and 

PNM. 

Validation is the process of comparing steady-state and dynamic model predictions with plant 

data. The process and controls models were run to full and low load steady-state conditions, and 

the results were compared with plant data. For this study, an MFT event was picked as the 

validation transient, and the San Juan Unit 1 model was run to a steady-state at this load. The 

model was run through the event, and the results were compared with plant data provided. 

3.1 Existing Configuration Process Model 

The process model included the following components: 

• Air path through and including FD fans, air heaters, and furnace 

• Fuel (coal) and primary air path including primary air (PA) fans, pulverizers, and feeders 

• Flue gas path from the furnace including superheaters, reheaters, economizer, air heaters, 

booster fans, and stack 

• Pollution control systems including precipitator and flue gas desulphurization (FGD) 

equipment 

As the focus of the study involved relatively fast furnace pressure transients, slower steam-side 

components, such as steam drums and desuperheaters, were not modeled. Only the metal mass 

for the walls and heated surfaces was modeled, along with the energy stored in the metal during 

the transient. 

Centrifugal fan operation was modeled by incorporating the actual fan head curves. In addition, 

shutdown flow effects (4th quadrant behavior) were simulated and combined the run-out portion 

of the fan curve, and assumed flow resistance behavior. 

Pulverized coal combustion was simulated in the furnace module. Coal combustion was 

represented as a two-stage reaction, with the first stage being the rapid devolatilization of the 

coal particles, and the second stage being the combustion of the remaining coal char. Char 
PNM – San Juan Generating Station Unit 1 Page 5 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

combustion was a function of temperature, particle size, and availability of oxygen. The amount 

and size of the char particles would strongly affect the rate of fireball collapse during a fuel trip. 

The furnace module calculated the exiting flue gas composition based on the rate of fuel and air 

flow into the furnace, the chemistry of combustion, and furnace leakage. 

3.2 Existing Configuration Control Model 

As the controls for a unit play an important role in the behavior of the plant through any 

transient, a detailed model of the San Juan Unit 1 control system was also constructed. Note that 

only those portions of the controls that affect any of the final control elements in the model were 

included in the control system simulation. Control loops for the existing configuration plant 

model included: 

• Furnace pressure 

• Primary air heater (PAH) air outlet pressure 

• Primary air heater air outlet temperature 

• Secondary airflow 

• Economizer excess air 

• Fuel flow 

• Pulverizer coal air temperature 

• Pulverizer primary airflow 

• Stack flue gas temperature 

• Master fuel trip 

These control loops manipulated the following final control elements (not necessarily in the 

order listed above): 

• FD fan IGV demand 

• PA fan IGV demand 

• Booster fan IGV demand 

• Feeder speed 

• Primary air control dampers 

• Hot air dampers 

• Tempering air dampers 

• PAH gas inlet dampers 
PNM – San Juan Generating Station Unit 1 Page 6 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

3.3 Steady-State Conditions 

An overall heat balance is achieved and the models are parameterized to a full load condition. 

The process and control models are then integrated and run to a steady-state condition to observe 

stability within the models. The three steady-state conditions used to ensure model stability are: 

1. Full load steady-state 

2. Low load steady-state 

3. Validation load steady-state 

The steps must be completed in the above order, as each step was dependent upon the successful 

completion of the previous step. All three steps involved a comparison of model output with 

plant data, and the combination of all three comparisons resulted in a high level of confidence 

that the model provided reliable predictions for the current plant configuration. 

The following sections describe the steps used for the validation of the San Juan Unit 1 model. 

 

3.3.1 Full Load Steady-State 

Each furnace draft component was simulated and connected in the same configuration as the 

plant using ProTRAX modules. Where there were parallel components in the plant, such as FD 

fans, each fan was modeled separately to assure any effects of multiple component operations 

were incorporated in the study. This was the “configuration” process. 

The physical characteristics of each component were input through fill-in-the-blank forms in the 

modeling system. This included data such as damper sizes, fan head curves, and physical 

dimensions of ducts, stacks, and vessels. This was the “parameterization” process. The 

parameterization process also included operating data based on a full load heat balance created 

from plant data, manufacturer’s heat balances, discussions with plant personnel, and visual 

observations during the plant walkdown. Where plant data was not available, such as pressure 

profiles through the convection pass of the furnace, estimates of pressure drops were made based 

on the physical drawings showing tube densities, flow cross sectional areas, and gas 

temperatures. Plant data itself is generally not sufficient due to instrumentation errors and 

unavailable signals. Therefore, the full load heat balance data comes from a variety of sources 

and is adjusted to ensure mass and energy balance. 

At this point, the model had the three requirements of a high-fidelity model: 

• Module equations were based on conservation of mass, energy, momentum, and wellaccepted correlations for heat transfer and mass flow. 

• The configuration of the model was the same as the plant based on the scope of this 

study. 

• The physical characteristics of each component were programmed into the corresponding 

modules. 
PNM – San Juan Generating Station Unit 1 Page 7 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Step 1 was performed at full load, as most design data required for model parameterization was 

available at that load. Most dampers and fans were operated at known design conditions at full 

load. This helped to determine the size and performance of these components, and thereby 

identified inherent plant operational limits such as fan runout and damper flow limits. 

The full load model was run at steady-state for several minutes and tested for stability and 

accuracy. That is, the model was initialized to full load conditions, and then allowed to run to 

equilibrium. If properly parameterized, the model should show little or no movement from the 

parameterization point and should come to a solid, steady-state in just a few seconds. Since all 

the module equations calculated an absolute heat balance at steady-state, any deviation from the 

full load conditions by the model would be immediately obvious and indicate an error in 

parameterization of the model. Once the model had demonstrated a reliable, stable match to the 

plant data at full load, it was ready to run to a lower load condition. 

In this case, at the full load steady-state point the San Juan Unit 1 model was immediately stable 

and no further corrections were required. Critical parameters for the full load steady-state are 

listed in Table 2. The corresponding model pressure profile at full load for Unit 1 is shown in 

Figure 1. 

Parameter Plant Data Model Unit 

Gross Load 360 360 MW 

Load Level 100 100 Percent 

Heat Rate 9,033 9,033 BTU/kWh 

Coal Flow Rate 346 342 kpph 

Number of Mills Grinding 3 3 

Economizer Oxygen 3.2–3.5 3.33 % By Vol. 

Total Secondary Air Flow 2,393 2,462 kpph 

Pulverizer Air Flow 178 178 kpph 

FD Fan Discharge Pressure +22.8 +22.8 inwc 

PA Fan Discharge Pressure +74.3 +76.6 inwc 

Primary Air Duct Pressure +72.2 +72.2 inwc 

Windbox Pressure +15.1 +15.1 inwc 

Furnace Pressure +10.2 +10.2 inwc 

Ambient Air Temperature 73 70 °F 

Primary Air Heater Air Inlet Temperature 138 139 °F 

Secondary Air Heater Air Inlet Temperature 110 110 °F 

Coal Air Temperature 157 157 °F 

Primary Air Heater Air Outlet Temperature 505 505 °F 

Secondary Air Heater Air Outlet Temperature 514 514 °F 

Table 2 Unit 1 Critical Plant Parameters at Full Load (100%) 
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Figure 1 Unit 1 Pressure Profile at Full Load 

Stack Calculations

Pressure difference along the height of the stack is made up of three parts: 

• Density head of the column of flue gas 

• Fluid frictional losses 

• Exit losses due to unrecoverable kinetic energy (flue gas velocity) at the stack exit 

Table 3 summarizes these calculations for the full load plant configuration. 

Having demonstrated a reliable, stable match to the plant data at full load, the San Juan Unit 1 

model was ready to run to the lower load condition. 
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Description Value 

Plant Load 100% 

Gauge Pressure at the Stack Base –0.53 inwc 

Ambient Gauge Pressure at the Top of the Stack –4.57 inwc 

Elevation Difference: Stack Breeching to Top of Stack 309 ft 

Flue Gas Temperature Entering Stack 135.4 °F 

Density Head of Flue Gas 3.55 inwc 

Fluid Frictional Losses 0.09 inwc 

Kinetic Energy (Exit) Losses 0.40 inwc 

Total Pressure Difference: Bottom to Top of Stack 4.04 inwc 

Table 3 Stack Calculations 

Note that the total stack draft loss is the sum of the frictional and kinetic energy losses. 

3.3.2 Low Load Steady-State 

The control system was used to run the plant model down in load. Pulverizers and/or other 

equipment were turned off as necessary to represent the plant condition at the lower load. The 

model was then tested at this lower load for stability and accuracy. Typically, the primary causes 

of variations at this point would be the following: 

1. Missing, incomplete, or erroneous data 

2. Different operational procedures of the model compared to the plant 

3. Fouling and soot buildup on various surfaces that alter pressure distribution 

4. Significantly different conditions at the plant during the low load compared to the full 

load data set (e.g., winter versus summer operation) 

For Unit 1, the low load data available from the plant was at 200 MW during plant start-up. All 

the control setpoints were applied as observed from the historian data for a 55.5% load. The 

number of pulverizers operating was reduced from three to two, the excess oxygen percentage 

was adjusted to 4.1%, and the model was run to a steady-state. A comparison of model and plant 

parameters for the lower load steady-state is shown in Table 4. The corresponding model 

pressure profile at full load for Unit 1 is shown in Figure 2. 
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Parameter Plant Data Model Unit 

Gross Load 200 200 MW 

Load Level 55.5 55.5 Percent 

Heat Rate 9,375 9,375 BTU/kWh 

Coal Flow Rate 194 194 kpph 

Number of Mills Grinding 2 2 

Economizer Oxygen 4.0–4.3 4.11 % By Vol. 

Total Secondary Air Flow 1,320 1,425 kpph 

Pulverizer Air Flow 185 185 kpph 

FD Fan Discharge Pressure +7.4 +7.7 inwc 

PA Fan Discharge Pressure +62.0 +62.6 inwc 

Primary Air Duct Pressure +60.8 +60.2 inwc 

Windbox Pressure +5.0 +5.0 inwc 

Furnace Pressure +4.0 +3.4 inwc 

Ambient Air Temperature 86 86 °F 

Primary Air Heater Air Inlet Temperature 156 143 °F 

Secondary Air Heater Air Inlet Temperature 127 127 °F 

Coal Air Temperature 154 154 °F 

Primary Air Heater Air Outlet Temperature 422 422 °F 

Secondary Air Heater Air Outlet Temperature 467 455 °F 

Table 4 Unit 1 Critical Plant Parameters at Low Load (55.5%) 

Figure 2 Unit 1 Pressure Profile at Low Load 
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Project Number EA0711 

The Unit 1 model was stable and accurate at low load condition, and no further actions were 

required. 

3.3.3 Validation Load Steady-State 

As a part of the dynamic testing, it was important to establish a steady-state condition at the 

validation load. Normally, a MFT would be the best choice for dynamic testing, provided that 

the trip was not caused by a component failure in the gas path such as a fan or damper. Multiple 

events made it more difficult to identify and duplicate the actual driving forces on the plant, and 

hence the model. A transient that was both severe enough to test the model, yet had only one 

cause was selected. It was also important to begin the transient at a high load when most plant 

equipment was operational. 

B&W provided TRAX with historian spreadsheet exports of two MFT events. TRAX chose the 

validation event based on the following criteria: 

• Near full load condition 

• Steady state condition prior to the trip 

• Single event as the cause of the trip 

• Normal operation of components in the flue gas path 

• Adequate data during the trip from the plant historian 

The event data selected by TRAX to validate models against was from an MFT that occurred on 

February 25, 2006 at 9:48 a.m. with a unit load of 97.2%. The historian data was provided in 10 

second intervals. 

The validation load model was run at steady-state for several minutes and tested for stability and 

accuracy. Critical plant parameters obtained at this steady state were compared with plant data 

as shown in Table 4. 
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Parameter Plant Data Model Unit 

Gross Load 350 350 MW 

Load Level 97.2 97.2 Percent 

Heat Rate 9,028 9,028 BTU/kWh 

Coal Flow Rate 350 335 kpph 

Number of Mills Grinding 3 3 

Economizer Oxygen 2.8–3.9 3.05 % By Vol. 

Total Secondary Air Flow 2,307 2,313 kpph 

Pulverizer Air Flow 182 183 kpph 

FD Fan Discharge Pressure +19.8 +19.7 inwc 

PA Fan Discharge Pressure +76.7 +79.0 inwc 

Primary Air Duct Pressure +74.4 +73.8 inwc 

Windbox Pressure +13.2 +13.0 inwc 

Furnace Pressure +9.3 +8.7 inwc 

Ambient Air Temperature 36 36 °F 

Primary Air Heater Air Inlet Temperature 113 123 °F 

Secondary Air Heater Air Inlet Temperature 113 106 °F 

Coal Air Temperature 155 155 °F 

Primary Air Heater Air Outlet Temperature 481 464 °F 

Secondary Air Heater Air Outlet Temperature 486 498 °F 

Table 5 Unit 1 Critical Plant Parameters at Validation Point (97.2% Load) 

The model pressure profile generated from the steady-state at validation load for Unit 1 is shown 

in Figure 3. 

Figure 3 Unit 1 Pressure Profile at Validation Point (97.2% Load) 
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3.4 Transient Validation 

To perform the transient validation, the model was first moved to the steady-state operating point 

corresponding to 97.2% load to be consistent with the plant data. The transient event was then 

initiated and all known plant variables, (i.e. damper positions, fan and feeder speeds) were 

maneuvered by the control system to mimic plant movements as closely as possible based on the 

available plant data. 

The behavior of a number of variables during this transient was analyzed and compared to the 

plant data, over a period of 120 seconds, for validation. One of the major variables of interest 

was the furnace pressure. In comparing the model response to the plant, the criterion was the 

time required for the furnace pressure to reach a minimum, the magnitude of the minimum, and 

the rate of decrease of the furnace pressure. The most important factors that affected these 

results were: 

• Timing and speed of fuel shutoff to the furnace 

• Control of airflow to the furnace 

A significant level of effort was invested to assure that the timing of movement for the burner 

coal valves, fan inlet vane position, and the shutdown of pulverizers, PA fans, and feeders was 

duplicated as closely as possible. 

3.4.1 Unit 1 MFT Procedure 

During the MFT, the following control elements were driven as described based on the historian 

data: 

• All pulverizers and associated feeders were tripped 

• Burner coal valves for all pulverizers were closed 

• Primary air shutoff and control dampers for each pulverizer were closed 

• Hot air dampers and tempering air dampers were closed 

• FD fan inlet guide vanes were frozen in place 

• Both PA fans were tripped and their inlet guide vanes were closed 

• All three booster fans were tripped 

All other control elements remained in auto for the duration of the MFT event. 

3.4.2 Unit 1 Validation Parameters 

To validate the models, TRAX compared the model-generated values for the following 

parameters to plant data as recorded by the historian: 

• Furnace pressure 

• Windbox pressure 
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• Coal feeder flow 

• Secondary airflow 

• FD fan discharge pressure 

• PA fan discharge pressure 

• Economizer oxygen 

3.4.3 Unit 1 Validation Results 

Validation comparisons of the ProTRAX Unit 1 model versus plant data are shown in the 

Reference Section. 

Furnace Pressure

The Unit 1 model was initialized to the validation condition load (350 MW) and allowed to run 

for 10 seconds to ensure steady-state operation. At 10 seconds, an MFT was initiated by tripping 

all pulverizers, associated feeders, and both PA fans. As a result of the MFT, controls 

instantaneously set the PA fan guide vanes to zero and fully closed the PA control dampers, 

burner coal valves, pulverizer hot air dampers, and tempering air damper for each pulverizer. 

Although all dampers in the primary air path associated with each pulverizer were closed, it was 

the fast-acting burner coal valve (with a seven-second stroke time) that decided the magnitude 

and timing of the furnace pressure minimum by stopping fuel flow to the furnace. 

Upon loss of the PA fans, the amount of pulverized coal being transported to the burners began 

to drop rapidly due to the decreasing primary air flow. When the burner coal valves closed 

completely at 17 seconds, the fireball collapse began due to the fuel being shut off and furnace 

pressure dropped to its minimum of –0.15 inwc once the available fuel was totally consumed. 

The furnace then began to respond to the additional inflow of air caused by the continuous 

operation of the FD fans, and recovered to +7.3 inwc by 120 seconds. 

The plant data, as shown in the furnace pressure plot, indicated a maximum pressure drop of only 

+1.5 inwc and an eventual steady-state recovery pressure. Since an MFT is a fast transient, and 

the fuel is rapidly cut off due to the coal valve shutoff, the fireball collapse is usually severe and 

a much greater drop in furnace pressure was expected. PNM indicated that this data behavior 

was likely the result of a partially plugged tap that did not respond to the expected pressure dip. 

This lack of response is further illustrated by the windbox pressure plot, which is discussed in the 

following section. 

Windbox Pressure

The windbox pressure at the beginning of the transient was +13.0 inwc. The fireball collapse led 

windbox pressure to decrease to a minimum of +6.6 inwc at 17 seconds. Freezing the FD fan 

guide vanes while they remained in operation caused the pressure to increase to +13.1 inwc by 

the end of the transient. 
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The windbox pressure plot illustrates that the windbox pressure minimum predicted by the model 

was +3.3 inwc lower than the corresponding plant measurement. However, the shape of the 

plant data curve indicates that the minimum windbox pressure probably occurred between 

recorded measurements and was likely lower than the given +9.9 inwc. Since furnace and 

windbox pressures generally behave in accordance with one another, this reinforces the 

probability of a plugged furnace pressure tap, as discussed above. 

Coal Feeder Flow 

Prior to the MFT, a total of 335 kpph of coal was supplied to the furnace through the feeders. 

During the MFT, the coal feeders were tripped and fuel flow stopped. The plot of coal flow into 

the mills agrees well with the plant data. 

Secondary Airflow

Prior to the MFT, 2,313 kpph of secondary air was flowing into the furnace through the flow 

control sleeves and registers. Following the MFT, the controls froze both FD fan inlet vanes. 

The increased pressure differential between the FD fans and the furnace (due to the drop in 

furnace pressure) led to an increase in the secondary airflow to a maximum of 2,954 kpph by 23 

seconds. As the system pressures stabilized, the secondary air flow dropped slightly to a steady 

value of approximately 2,776 kpph. The secondary airflow plot shows a close match in shape, 

magnitude, and timing between the model and plant data. 

The sharp increase in airflow was not seen in the plant data most likely because of the ten second 

historian frequency and signal filtering. 

FD Fan Discharge Pressure

The FD fan discharge pressure was steady at +19.7 inwc at the beginning of the transient. Upon 

initiation of the MFT, the controls locked both FD fan inlet vanes and all secondary air dampers 

in place. The 8.85 inwc drop in furnace pressure during the MFT only caused a 2.8 inwc drop in 

FD fan discharge pressure because of the resistance of the secondary air heaters and registers. 

The minimum FD fan discharge pressure corresponds to the minimum furnace pressure during 

the fireball collapse. As the furnace pressure recovered, the FD fans’ discharge pressure reached 

a steady value of +22.3 inwc by the end of the transient. The FD fans’ discharge pressure plot 

illustrates a close match between the model and the plant historian data. 

PA Fan Discharge Pressure

The PA fans were operating steadily with a discharge pressure of +79.0 inwc prior to the MFT. 

The loss of primary air due to the PA fan trip and shutoff during the MFT resulted in a decrease 

of discharge pressure, as illustrated by the PA fan discharge pressure plot. As the system 

pressures recovered, the PA fan discharge pressure recovered to +21.0 by 120 seconds. The 

decay in discharge pressure as predicted by the model matched the plant data well. 

Economizer Oxygen

A range for economizer oxygen was established by two corresponding measurements (2.8% and 

3.9%) provided by the historian for this particular transient. Based on the plant controls, a value 

for economizer oxygen (within this range) that provided the closest match to the historian 

secondary air flow was determined. This value was established as 3.05% for the validation case. 
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The complete loss of fuel due to the MFT resulted in an increase of economizer oxygen, as 

illustrated by the corresponding plot. The plant economizer oxygen measurements do not show 

this significant increase from their steady-state values. This indicates significant filtering in the 

oxygen transmitter signals. Filtered model data, represented by the dashed line in the plot, shows 

a closer agreement with the plant data. 

3.5 Validation Conclusion 

A dynamic model of the Unit 1 furnace draft system was constructed. Controls were installed on 

the process model consistent with existing plant logic. The process plus control system model 

was tested for both steady state and dynamic accuracy. Dynamic testing consisted of running the 

model through a severe furnace pressure excursion and comparing the model generated data to 

historical plant data. This comparison of data showed that the model generated data matched 

both the timing and magnitude of the plant data. Therefore, the Unit 1 model is considered 

sufficiently accurate to provide a meaningful basis for further draft analysis. Note that the model 

can also provide excellent relative results, which are particularly important in the planned study. 
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4.0 FUTURE CONFIGURATION MODEL AND TRANSIENT TESTING 

The existing process and controls models were updated to reflect the changes necessary for the 

addition of the environmental equipment. Note that while the existing controls scheme was 

retained for the most part, modifications were made as necessary. These controls may change as 

a part of the proposed mitigations. The models were then run to obtain full and low load steadystate initial conditions. Once the steady-state conditions were obtained, the future configuration 

model was run through the seven selected transients and the results were analyzed. The selected 

transients were run at their respective operating conditions and any controls mitigations 

necessary to limit extreme pressure excursions through the system were tested. 

4.1 Future Configuration Process Model 

The proposed future configuration process model included all of the components in the San Juan 

Unit 1 process models, plus the proposed environmental equipment. Modifications to represent 

the future configuration included: 

• Addition of a baghouse and related controls 

• Replacement of existing booster fans with new upgraded booster fans 

• Related ductwork changes 

• Elimination of bypass flow directly to the stack; that is, the total flue gas flow from the 

air heaters will pass through the new baghouse, new booster fans, and scrubbers before 

reaching the stack 

Parameterization data for the new process equipment such as fan head curves, pressure drops, 

etc. was based on proposed design information provided by B&W and PNM. The proposed 

configuration schematics for the process model are given in the Reference Section. A block 

diagram of the future configuration is shown in Figure 4. 
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Figure 4 San Juan Future Configuration 

4.2 Future Configuration Control Model 

The control logic for the new equipment included various control loops for the booster fans. In 

the booster fan IGV control loop, an error signal was calculated by comparing the air heater gas 

outlet duct pressure to a setpoint. The controller output was then added to a characterized feedforward signal from the FD fan inlet guide vane demand and a kicker circuit signal activated for 

15 seconds upon initiation of an MFT. The sum of these outputs was then used to adjust booster 

fan inlet guide vanes’ demand. This control scheme also included an overriding controller that 

would cause the booster fan inlet guide vanes to run back in an attempt to maintain a furnace 

pressure of +1 inwc if the furnace pressure dropped below –1 inwc or an MFT occurred. A 

functional diagram of this control loop is shown in Figure 5. 

Flue Gas from 

Primary Air 

Heaters 

Flue Gas from 

Secondary Air 

Heaters 

Baghouse 

Booster Fan A 

Booster Fan B 

Booster Fan C 

Scrubber A 

Scrubber B 

Scrubber C 

Stack 
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Furnace Draft Analysis – Final Report 

Project Number EA0711 

Figure 5 Booster Fan IGV Controls 
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In addition, the following controls logic was used: 

• When the furnace pressure dropped below –7 inwc for three seconds, a low furnace 

pressure MFT was triggered. 

• During an MFT, no FD fans or booster fans were tripped by the controls unless specified 

as a failed component for transient testing. 

• During transient testing, the booster fan inlet guide vanes’ stroke time was 17 seconds. 

The proposed configuration schematics for the controls model are given in the Reference 

Section. 

Several other control solutions were developed to mitigate the severity of pressure excursions. 

These measures are discussed in Section 4.4. 

4.3 Steady-State Conditions 

All transient runs were initiated with the model at a steady-state condition, with all pressures, 

flows, temperatures, and controlled variables constant. While there were seven transient events 

tested during this phase, there were only two unique initial conditions: 

• Full load (100%) 

• Low load (30%) 

The models were run to steady-states corresponding to these loads to establish initial conditions 

for the transient runs. 

4.3.1 Full Load Steady-State 

The model was re-parameterized at full load to account for the addition of the environmental 

equipment and associated ductwork changes. While the parameterization of most of the modules 

was retained from the existing configuration, only the necessary changes as required by the 

addition of the new equipment were made. Critical parameters for the steady-state condition at 

full load are shown in Table 6. Figure 6 graphically shows the steady-steady pressure profiles. 
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Parameter 100% Load Unit 

Gross Load 360 MW 

Load Level 100 Percent 

Heat Rate 9,033 BTU/kWh 

Coal Flow Rate 342 kpph 

Number of Mills Grinding 3 

Economizer Oxygen 3.33 % By Vol. 

Total Secondary Air Flow 2,460 kpph 

Pulverizer Airflow 178 kpph 

FD Fan Discharge Pressure +22.4 inwc 

PA Fan Discharge Pressure +76.4 inwc 

Primary Air Duct Pressure +71.9 inwc 

Windbox Pressure +14.7 inwc 

Furnace Pressure +9.9 inwc 

Ambient Air Temperature 70 °F 

Primary Air Heater Air Inlet Temperature 139 °F 

Secondary Air Heater Air Inlet Temperature 110 °F 

Coal Air Temperature 157 °F 

Primary Air Heater Air Outlet Temperature 500 °F 

Secondary Air Heater Air Outlet Temperature 509 °F 

Table 6 100% Load Initial Condition Parameters 

Figure 6 Steady-State Pressure Profile for 100% Load 
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4.3.2 Low Load Steady-State 

The model was then used to generate a low load steady-state condition. The operation of the 

plant on two pulverizers and two booster fans with both FD fans in operation was simulated for 

this load condition. Critical parameters for the steady-state condition at low load are shown in 

Table 7. Figure 7 graphically shows the steady-steady pressure profiles. 

Parameter 30% Load Unit 

Gross Load 108 MW 

Load Level 30 Percent 

Heat Rate 10,516 BTU/kWh 

Coal Flow Rate 120 kpph 

Number of Mills Grinding 2 

Economizer Oxygen 9.21 % By Vol. 

Total Secondary Air Flow 1,315 kpph 

Pulverizer Airflow 148 kpph 

FD Fan Discharge Pressure +5.8 inwc 

PA Fan Discharge Pressure +53.9 inwc 

Primary Air Duct Pressure +53.0 inwc 

Windbox Pressure +3.6 inwc 

Furnace Pressure +2.2 inwc 

Ambient Air Temperature 70 °F 

Primary Air Heater Air Inlet Temperature 141 °F 

Secondary Air Heater Air Inlet Temperature 115 °F 

Coal Air Temperature 157 °F 

Primary Air Heater Air Outlet Temperature 492 °F 

Secondary Air Heater Air Outlet Temperature 454 °F 

Table 7 30% Load Initial Condition Parameters 
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Figure 7 Steady-State Pressure Profile for 30% Load 

The combination of both comparisons resulted in a high level of confidence that the model 

provided reliable predictions for the future plant configuration. 

4.4 Transient Events and Mitigations 

To evaluate the performance of the plant in its new configuration, seven transients were run with 

the new control logic and the results analyzed. This process consisted of the following steps: 

• Initially run the selected transients with the new control logic to obtain baseline 

(unmitigated) results for analysis 

• Analyze the baseline results and find areas that need improvement (typically pressures, 

flows, and fan IGV) 

• Go through each transient and determine process/controls mitigations required for 

individual transients 

• Implement the mitigations for all transients 

The goal in selecting the transients was to define conditions that would create large pressure 

excursions in the furnace and ductwork. Transient descriptions are listed in Table 8. 
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No. Transient Name Unit 

Load Description 

T1 Full Load MFT 100% With the unit at full load, an operator initiates an MFT. All controls 

remain in auto. 

T2 Full Load All Booster 

Fans Trip 100% With the unit at full load, all three booster fans trip and immediately trigger an MFT. 

T3 Full Load Both FD Fans 

Trip 100% 

With the unit at full load, both FD fans trip and immediately initiate 

an MFT. All three booster fans will run back, but no booster fan will 

be tripped. 

T4 Low Load Two Booster 

Fans Runaway 30% With the unit at low load, the inlet guide vanes on both operating booster fans will ramp open. 

T5 Full Load All Fans Trip 100% With the unit at full load, an electrical bus failure causes all fans to 

trip. An MFT is immediately initiated. All controls remain in auto. 

T6 Full Load Single 

Booster Fan Trips 100% 

With the unit at full load, a single booster fan is tripped. A 30-

second stroke time is assumed for the booster fan inlet damper. 

The tripped fan is isolated and the unit continues to operate at full 

load on the remaining two booster fans. All controls remain in auto. 

T7 

Full Load Baghouse 

Cleaning System 

Failure 

100% 

With the unit at full load, the baghouse cleaning system failure 

increases the baghouse differential pressure from 10 inwc to 14 

inwc over a period of one minute. All controls remain in auto. 

Table 8 Transient Descriptions 

As part of this study, TRAX proposed and tested several mitigating measures to help control the 

extent of furnace and ductwork pressure excursions. Mitigating measures added to the control 

model included: 

• If all the three operating booster fans tripped at full load operation, the controls should 

wait 20 seconds following the MFT and the FD fans should be tripped once the furnace 

pressure reached +15 inwc. 

• On a single booster fan trip, the load should be run back from 100% to 70% to avoid 

severe pressure excursions in the furnace. 

The graphs, presented under each transient heading, are results obtained from the unmitigated 

runs. Any results obtained from mitigated transient runs are presented under the mitigations 

subsection of each transient. All the graphs are shown in the Reference Section. Among the 

plots shown for each transient is a graphical profile of the maximum and minimum pressure 

measurements at various positions along the air-gas path. Points on each maximum and 

minimum profile did not necessarily occur at the same time. 

The baseline transient runs are designated with a “T” and are then given sequential numbers 

according to their order in Table 8. Each mitigated run designation matches the corresponding 

baseline transient designation, but is preceded by an “M.” 

4.4.1 T1: Full Load MFT 

This transient consisted of the following steps: 

• Initialized the model to the 100% load condition 

• Ran the model for 10 seconds to establish steady-state conditions 
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• MFT initiated by an operator at 10 seconds 

• All controls remained in auto throughout the transient 

The control system triggered a series of events immediately following the MFT. The control 

actions are listed below: 

• Froze FD inlet guide vanes at their current position 

• Tripped pulverizers and their feeders 

• Shut coal valves 

• Tripped, shut off, and isolated PA fans 

• Closed hot air, tempering air, and primary air control dampers 

• Booster fan IGV demand controlled by a kicker circuit for 15 seconds following the MFT 

• Transferred control of the booster fan IGV demand to a runback controller from 25 

seconds to the end of the transient 

The Unit 1 model was initialized to the full load condition (360 MW) and allowed to run for 10 

seconds to ensure steady-state operation. At 10 seconds, an operator initiated an MFT, which 

shut down the coal valves and shut off the pulverizer feeders, causing the amount of pulverized 

coal being transported to the burners to drop rapidly. Due to this rapid fuel shutoff, the fireball 

collapsed and the furnace pressure dropped to a minimum of –1.2 inwc upon total consumption 

of available fuel, as shown in Figure 8. The continuous operation of the FD fans and the action 

of the booster runback control logic triggered at 25 seconds led furnace pressure recovery to 

reach +3.2 inwc by 120 seconds. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet

Figure 8 T1 Unit Pressures 
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During this and all the other transients, a kicker circuit for controlling the booster fan IGV was 

active for 15 seconds following an MFT signal. It is important to include this kicker circuit in 

the controls in order to prevent more severe negative furnace pressure excursions during an 

MFT. As an example, the furnace pressure would have dropped by an additional 9 inwc in the 

absence of the kicker circuit during this transient. The kicker was held active until after the 

completion of the fireball collapse and into the beginning of furnace pressure recovery to provide 

a more stable and over-dampened response when the booster fan IGV control was transferred to 

the runback logic. 

The booster fan IGV closed from 64% open (initial condition) to 18% open in eight seconds 

during this transient, as shown in Figure 9. For the remaining seven seconds of the kicker 

operation, the IGV position remained constant with only a minor adjustment from the air heater 

gas outlet pressure controller. At 25 seconds, the kicker was released and the runback controller 

opened the booster fan IGV in an attempt to maintain a +1 inwc furnace pressure. 

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120

Time (seconds)

Position (percent open)

FD Fans Booster Fans

Figure 9 T1 Fan Inlet Guide Vane Positions 
PNM – San Juan Generating Station Unit 1 Page 27 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Figure 10 shows the baghouse, FGD, and booster fan inlet pressures during the transient. The 

baghouse inlet pressure decreased from +0.1 inwc to –3.2 inwc during the fireball collapse. 

Following the rise in furnace pressure after the MFT, the baghouse inlet pressure increased to 

–1.0 inwc at 25 seconds, and eventually decreased to –4.8 inwc as the booster fan IGV continued 

to open because of the runback controller action. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet

Figure 10 T1 Baghouse and Scrubber Pressures 

The immediate impact of closing the booster fan IGV during the fireball collapse can be seen on 

the booster fan inlet pressure plot. The reduction in flow being transported across the booster 

fan, due to the closing of its IGV, led to an increase of the inlet pressure from an initial –11.0 

inwc to –3.8 inwc while the kicker was active. Following the opening of the booster fan IGV, 

the booster fan inlet pressure decreased to –14.5 inwc by the end of the transient. 

Also, during the closing of booster fan IGV from 10 seconds to 18 seconds, the FGD inlet 

pressure dropped by 11.4 inwc due to reduction in flow being transported across it. The FGD 

inlet pressure then remained nearly constant at around +2.5 inwc (for seven seconds) while the 

booster fan IGV was held in place by the kicker circuit. Following the transfer of control to the 

booster fan runback logic, the FGD inlet pressure started increasing and eventually reached 

+12.3 inwc by the end of the transient. 

Flows corresponding to the FD fans, furnace exhaust, and FGD inlet are shown in Figure 11. 

The rapid fuel shutoff, combined with loss of primary air due to the MFT, led to a 43% decrease 

in furnace exhaust flow in seven seconds, and a corresponding decrease in FGD inlet flow. 

During this time, the FD fans’ IGVs were frozen in place while the fans continued to operate. 

The increased differential between the FD discharge and furnace pressures led to the increased 

transportation of air, as shown in Figure 11. The total FGD inlet flow remained nearly constant 
PNM – San Juan Generating Station Unit 1 Page 28 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

from 18 seconds to 25 seconds, during which the FGD inlet pressure remained nearly constant. 

The loss of primary air and fuel (due to the MFT) caused the furnace exhaust and FGD inlet 

flows to steady out at values lower than their initial conditions. 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 20 40 60 80 100 120

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet

Figure 11 T1 Flows 

Mitigations

During this transient, process pressures did not reach values that required additional control 

mitigations. Since the booster fans did not trip, the mitigations listed on page 24 had no effect on 

this transient. 

4.4.2 T2: Full Load All Booster Fans Trip 

This transient consisted of the following steps and control actions: 

• Initialized the model to the 100% load condition 

• Ran the model for 10 seconds to establish steady-state conditions 

• Tripped all three operating booster fans, immediately causing an MFT and associated 

control actions as listed in Section 4.4.1 

• All controls remained in auto throughout the transient 
PNM – San Juan Generating Station Unit 1 Page 29 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Following the MFT initiated by the loss of all booster fans, the furnace pressure dropped to a 

minimum of +1.8 inwc by 18 seconds. This fall in furnace pressure was not as great as in the 

“Full Load MFT” transient because of the reduction in furnace exhaust flow due to the booster 

fans’ trip. This behavior was reflected in the FD discharge and air heater gas outlet pressures, as 

shown in Figure 12, which were also measured upstream of the tripped booster fans. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet

Figure 12 T2 Unit Pressures 

Following the kicker release at 25 seconds, the booster fan IGV opened up continuously, as 

shown in Figure 13. Despite the opening IGV position, the tripped booster fans operated only at 

constantly decreasing speeds, as shown in Figure 14. The reduction in flow through the tripped 

booster fans resulted in inadequate relief of pressures upstream, and the furnace, FD discharge, 

and air heater gas outlet pressures increased correspondingly upon completion of the fireball 

collapse. The rate of increase of these pressures slowed with time, as shown in Figure 12, once 

the booster fan IGV was completely open. 
PNM – San Juan Generating Station Unit 1 Page 30 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120

Time (seconds)

Position (percent open)

FD Fans Booster Fans

Figure 13 T2 Fan Inlet Guide Vane Positions 

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120

Time (seconds)

Speed (rpm)

FD Fans Booster Fans

Figure 14 T2 Fan Speeds 

While the booster fan IGVs were closing (due to the kicker action from 10 seconds to 25 

seconds), the baghouse inlet pressure increased by about 1.8 inwc. The inadequate pressure 

relief provided by the tripped booster fans resulted in a baghouse inlet pressure increase to +13.9 

inwc by the end of the transient. The booster fan inlet pressure increased during the fireball 

collapse, as shown in Figure 15, and continued to increase at a lesser rate following the opening 

of booster fan IGV. 
PNM – San Juan Generating Station Unit 1 Page 31 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet

Figure 15 T2 Baghouse and Scrubber Pressures 

The FGD inlet pressure dropped by about 13.2 inwc during the fireball collapse, and stayed 

nearly constant from 17 seconds to 25 seconds as the booster fan IGV was held constant by the 

kicker. The pressure started to increase following the transition of controls to the booster fan 

runback controller, and eventually steadied out at 48% of the initial condition. Figures 12 and 15 

show that, compared to their initial values, the pressures upstream of the tripped booster fans 

recovered to a higher value while the downstream pressures approached a lower value. 

Figure 16 shows the behavior of the flows during this transient. The total FD fan flow increased 

by only 2% during the fireball collapse, and decreased to 83% of the initial value by the end of 

the transient. This was a result of the continuous operation of the FD fans, even though the 

booster fans were tripped. Following the fireball collapse, the FGD inlet flow fell to about 1,570 

kpph, from an initial value of 3,823 kpph. The flow stayed constant for about eight seconds, due 

to the constant FGD inlet pressure during this time. The tripped booster fans did not transport as 

much air, which resulted in FGD inlet flow recovery to only 73% of the initial flow by the end of 

the transient. 
PNM – San Juan Generating Station Unit 1 Page 32 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 20 40 60 80 100 120

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet

Figure 16 T2 Flows 

Mitigations

MT2: Mitigated Full Load All Booster Fans Trip– Delayed FD Trip

The high positive pressures obtained during this transient were prevented by tripping the FD fans 

simultaneously with the operating booster fans. For this mitigation, the MFT was allowed to 

continue for 20 seconds, and the FD fans were tripped once the furnace pressure exceeded +15 

inwc. The results of the mitigated transient are presented in the Reference Section. Figure 17 

shows a comparison of the maximum system pressures obtained with and without mitigations, 

showing an improvement of all pressures upstream of the booster fan outlets. 
PNM – San Juan Generating Station Unit 1 Page 33 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

-4.6

+2.9

+14.9

+17.6

0.0

+8.3 +9.0

+14.6

+18.6

+24.9

+30.5

+29.2

+23.1

+16.9

+13.9

 -0.3

+6.2 +5.5

+10.7 +11.4

+13.5 +15.1 +14.2

+20.3

+22.4

+27.3 +28.8

-40

-30

-20

-10

0

+10

+20

+30

+40

Ambient

FD Fan Outlet

SAH Air Inlet

SAH Air Outlet

Windbox

Furnace

Economizer Outlet

Precip Outlet

SAH Gas Outlet

Baghouse Inlet

Baghouse Outlet

Booster Fan Inlet

Booster Fan Outlet

Scrubber Outlet

Stack Base

Top of Stack

Pressure (inwc)

Maximum (Unmitigated) Maximum with FD Fan Trip (Mitigated)

Figure 17 T2 and MT2 Transient Maximum Pressure Profile 

Figure 18 shows a comparison of the mitigated and unmitigated furnace pressures. For this 

mitigation, both FD fans were tripped at about 59 seconds, when the furnace pressure reached 

+15 inwc. The mitigated furnace pressure recovered to about 18.6 inwc lower than the 

unmitigated pressure at the end of this transient. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

Furnace (Unmitigated) Furnace with FD Fan Trip (Mitigated)

Figure 18 T2 and MT2 Furnace Pressure Comparison 
PNM – San Juan Generating Station Unit 1 Page 34 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

MT2A: Mitigated Full Load All Booster Fans Trip – Immediate FD Trip

During discussion between members of the project team, the merits of immediately tripping the FD 

fans were considered. It was agreed that the “Full Load All Booster Fans Trip” transient should 

be tested to compare a delayed FD fan trip against an immediate FD fan trip. Letter Report 

0817-0101, which contains a comparison of the “MT2: Mitigated Full Load All Booster Fans 

Trip – Delayed FD Trip” and “MT2A: Mitigated Full Load All Booster Fans Trip – Immediate 

FD Trip” transients, is included in the Reference Section. Figure 19 shows a comparison of the 

maximum system pressures obtained with the delayed and immediate FD fan trips. 

0.0

+28.8 +27.3

+22.4

+20.3

+15.1 +14.2 +13.5

+11.4 +10.7

+6.2 +5.5

+14.9

+2.9

 -0.3

 -4.6

0.0

+22.4 +20.9

+16.6

+14.7

+9.9

+7.5 +6.1

+1.5 +0.2 -0.7

+14.9

 -0.7 -0.5

-40

-30

-20

-10

0

+10

+20

+30

+40

Ambient

FD Fan Outlet

SAH Air Inlet

SAH Air Outlet

Windbox

Furnace

Economizer Outlet

Precip Outlet

SAH Gas Outlet

Baghouse Inlet

Baghouse Outlet

Booster Fan Inlet

Booster Fan Outlet

Scrubber Outlet

Stack Base

Top of Stack

Pressure (inwc)

Maximum with MT2 Maximum with MT2A

Figure 19 MT2 and MT2A Transient Maximum Pressure Profile 

Figure 20 shows a comparison of the furnace pressures for the MT2 and MT2A runs. At 10 

seconds, an MFT occurred and fuel was shut off to the furnace. The resulting fireball collapse 

caused a sharp drop in furnace pressure. Pressure for the MT2A run continued to drop as the FD 

fans were immediately tripped and reduced mass flow into the furnace. Furnace pressure for run 

MT2A eventually reached a minimum of -3.3 inwc. Conversely, pressure for the MT2 run began 

to rise at about 20 seconds as the FD fans continued to run and pressurize the furnace. 

Eventually, furnace pressure rose above +15 inwc at about 60 seconds and the FD fans tripped. 

Furnace pressure for both transients then trended to ambient as the FD fans spun down. 
PNM – San Juan Generating Station Unit 1 Page 35 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

MT2 Furnace MT2A Furnace 

Figure 20 MT2 and MT2A Furnace Pressure Comparison 

4.4.3 T3: Full Load Both FD Fans Trip 

This transient consisted of the following steps and control actions: 

• Initialized the model to the 100% load condition 

• Ran the model for 10 seconds to establish steady-state conditions 

• Tripped both operating FD fans immediately causing an MFT and associated control 

actions as listed in Section 4.4.1. 

• All controls remained in auto throughout the transient 

Figure 21 shows the FD discharge, furnace, and air heater gas outlet pressures during this 

transient. At 10 seconds, an MFT was initiated following the loss of both FD fans. Reduced 

airflow through the tripped FD fans resulted in a reduction in FD discharge pressure by about 

21.6 inwc in 18 seconds following the MFT. The furnace pressure decreased by 16.8 inwc to a 

minimum of –6.9 inwc and recovered to –2.2 inwc by the end of the transient. The recovery of 

the furnace pressure was limited by the lack of flow through the FD fans. 
PNM – San Juan Generating Station Unit 1 Page 36 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet

Figure 21 T3 Unit Pressures 

Following the MFT at 10 seconds, the booster fans’ inlet guide vanes closed from 64% to 12% 

over nine seconds, as shown in Figure 22. In the next six seconds, the active kicker circuit 

further reduced the position to 7%, after which the control was transferred to the booster fan 

runback logic. At this point, the booster fan IGV closed further in an attempt to bring the 

furnace pressure up to its setpoint of +1 inwc. The FD fan IGVs froze in place following 

initiation of the MFT at 10 seconds. 

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120

Time (seconds)

Position (percent open)

FD Fans Booster Fans

Figure 22 T3 Fan Inlet Guide Vane Positions 
PNM – San Juan Generating Station Unit 1 Page 37 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

The baghouse inlet pressure decreased by about 8 inwc following the MFT and eventually 

recovered to 3.2 inwc lower than its initial value by the end of the transient. The reduction in air 

being transported through the FD fans, combined with the closing of booster fan IGV (triggered 

at 25 seconds), led to lower baghouse inlet pressure at the end of the transient. Corresponding to 

the movement of the fan IGV position, the booster fan inlet pressure increased from 10 seconds 

to 19 seconds, and then increased gradually over the remainder of the transient. 

The FGD inlet pressure fell from an initial value of +14.5 inwc to +0.6 inwc over nine seconds 

following the MFT at 10 seconds. The pressure then remained nearly constant for six seconds, 

as shown in Figure 23, due to the restricted movement of the booster fan IGV. Further closing of 

the booster fan IGV led the FGD inlet pressure to stabilize at a pressure lower than the initial 

condition by the end of the transient. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet

Figure 23 T3 Baghouse and Scrubber Pressures 
PNM – San Juan Generating Station Unit 1 Page 38 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Following the MFT at 10 seconds, furnace exhaust flow dropped by 40% in eight seconds, as shown 

in Figure 24. The loss of the FD fans resulted in a gradual decrease of the flow transported through 

the fans, and this loss of airflow, combined with the loss of fuel due to the MFT, caused the furnace 

exhaust flow to drop from an initial value of 3,263 kpph to 1,000 kpph by the end of the transient. 

Closing the booster fan IGV caused the decrease in FGD flow. The rate of decrease of the FGD inlet 

flow was similar to the FGD inlet pressure, as was the case in the previous transients. 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 20 40 60 80 100 120

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet

Figure 24 T3 Flows 

Mitigations

During this transient, process pressures did not reach values that required additional control 

mitigations. Since the booster fans did not trip, the mitigations listed on page 24 had no effect on 

this transient. 

4.4.4 T4: Low Load Two Booster Fans Runaway 

This transient consisted of the following steps and control actions: 

• Initialized the model to the 30% load condition (only two booster fans were in operation 

at this load) 

• Ran the model for 10 seconds to establish steady-state conditions 

• Manually opened the inlet guide vanes of the two operating booster fans 

• All controls remained in auto throughout the transient 

Following the opening of the booster fan IGV at 10 seconds, the furnace pressure decreased to a 

minimum of –3.7 inwc at 27 seconds, as shown in Figure 25. By 17 seconds, the furnace 

pressure decreased below –1 inwc, triggering the runback controller, which ramped back the 

inlet guide vanes on both operating booster fans. The booster fan IGV position changed from an 
PNM – San Juan Generating Station Unit 1 Page 39 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

initial 37% at 10 seconds to 79% at 18 seconds, and then closed to 49% at 25 seconds due to the 

runback controller, as shown in Figure 26. The FD fan IGV gradually closed during the course 

of the transient to facilitate transport of less air due to the closing of the booster fan IGV. As a 

result, the unit pressures did not recover to their initial values, even though the booster fan IGV 

recovered to nearly the initial value at the end of the transient. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet

Figure 25 T4 Unit Pressures 

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120

Time (seconds)

Position (percent open)

FD Fans Booster Fans

Figure 26 T4 Fan Inlet Guide Vane Positions 
PNM – San Juan Generating Station Unit 1 Page 40 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Figure 27 shows the baghouse and scrubber pressures during this transient. The booster fans’ 

runaway at 10 seconds caused an immediate decrease in the baghouse inlet pressure by 5.6 inwc 

in eight seconds. The baghouse inlet pressure reached –4 inwc after the booster fans’ IGVs 

closed due to the runback control action initiated at 18 seconds (and maintained throughout the 

transient). 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet

Figure 27 T4 Baghouse and Scrubber Pressures 

A qualitatively similar behavior was observed in the booster fan inlet pressure profile. In 

summary, the booster fans’ runaway at 10 seconds caused an immediate decrease in pressures 

upstream of the booster fans, as reflected in the baghouse and booster fan inlet pressures. The 

combined effect of the booster fan IGVs closing to their initial value and the FD fan IGVs 

closing caused the baghouse and booster fan inlet pressures to drop lower than their initial values 

by the end of the transient. 

Figure 27 also shows the close correspondence of the FGD inlet pressure to the booster fans’ IGV 

position. As the inlet guide vanes opened from 10 seconds to 18 seconds, thereby transporting 

more flow, the FGD inlet pressure increased by 10.1 inwc. The FGD inlet pressure then fell by 

7.7 inwc in the next seven seconds due to the closing of IGV caused by the runback controller. 

The booster fans transported more flow into the scrubbers as they opened, which reflected an 

increase of the total FGD inlet flow from 2,031 kpph to 2,960 kpph in a period of eight seconds 

following the runaway at 10 seconds, as shown in Figure 28. Once the runback controller took 

over at 18 seconds, the flow decreased to 2,319 kpph by 25 seconds, which corresponded to the 

closing of the booster fan IGV. While the booster fan IGVs opened, the decrease in furnace 

pressure led to a 14% increase in furnace exhaust flow. 
PNM – San Juan Generating Station Unit 1 Page 41 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 20 40 60 80 100 120

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet

Figure 28 T4 Flows 

Mitigations

During this transient, process pressures did not reach values that required additional control 

mitigations. It is, however, important to realize that the transfer of the booster fans’ IGV control 

to the runback controller at 18 seconds was essential in preventing further negative furnace 

pressure excursions. In the case of no runback controller or IGV runaway caused by an actuator 

failure, the continuous opening of the booster fans’ IGV would have resulted in a further 

decrease of upstream pressures and could have led to a possible low pressure MFT. Since the 

booster fans did not trip, the mitigations listed on page 24 had no effect on this transient. 

4.4.5 T5: Full Load All Fans Trip 

This transient consisted of the following steps and control actions: 

• Initialized the model to the 100% load condition 

• Ran the model for 10 seconds to establish steady-state conditions 

• Manually tripped both operating FD fans and all three operating booster fans immediately 

causing an MFT and associated control actions as listed in Section 4.4.1. 

• All controls remained in auto throughout the transient 

The furnace pressure reached a minimum of –3.3 inwc at about 21 seconds before recovering to 

–0.3 inwc at the end of the transient. Figure 29 shows that the FD discharge and air heater gas 

outlet pressures also recovered to values less than their initial values. This occurred because the 
PNM – San Juan Generating Station Unit 1 Page 42 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

air pushed by the FD fans decreased with time, since the tripped FD fans operated at decreasing 

speeds, which in turn reduced the downstream pressures, as shown in Figure 30. A comparison 

of Figures 29 and 21 revealed that the final pressures were higher than those in the “Full Load 

Both FD Fans Trip” transient due to the additional tripping of booster fans. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet

Figure 29 T5 Unit Pressures 

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120

Time (seconds)

Speed (rpm)

FD Fans Booster Fans

Figure 30 T5 Fan Speeds 
PNM – San Juan Generating Station Unit 1 Page 43 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Following the MFT at 10 seconds, the booster fans’ IGVs closed from 64% to 17% in eight 

seconds, as shown in Figure 31. In the next seven seconds, the active kicker circuit further 

reduced the position to 14%, after which control was transferred to the booster fan runback logic. 

The later movement in the booster fans’ IGV position was a result of the runback controller 

attempting to attain the furnace pressure setpoint of +1 inwc. The FD fan IGV froze in place 

following the MFT. 

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120

Time (seconds)

Position (percent open)

FD Fans Booster Fans

Figure 31 T5 Fan Inlet Guide Vane Positions 

The baghouse inlet pressure decreased by 4.2 inwc in 10 seconds, following the loss of the FD 

fans at 10 seconds, before recovering to a value closer to its initial condition. The booster fan 

inlet pressure increased by 6.3 inwc during the 15 seconds of kicker circuit operation. A 

comparison of Figures 32 and 15 reveals that the magnitude of increase was less for this transient 

than the “Full Load All Booster Fans Trip” transient because of the simultaneous trip of the FD 

fans. The FGD inlet pressure, as shown in Figure 32, decreased from +14.5 inwc to +0.3 inwc 

by 18 seconds. As the rate of change in the booster fans’ IGV slowed down, the inlet pressure 

remained nearly constant over the next seven seconds before eventually steadying out at -0.7 

inwc by the end of the transient. 
PNM – San Juan Generating Station Unit 1 Page 44 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet

Figure 32 T5 Baghouse and Scrubber Pressures 

By 18 seconds, the furnace exhaust flow decreased to about 34% of its initial value during the 

fireball collapse associated with the MFT. As shown in Figure 33, the flow continued to 

decrease further, due to the loss of air from the FD fans and fuel flow caused by the MFT, and 

reached about 11% of its initial value by the end of the transient. A similar behavior was 

observed in the total flow to the FGD inlet during this transient. The tripped FD fans continued 

to transport air at a lesser rate due to their decreasing speed. This resulted in a continuous 

decrease of the total air pushed by the FD fans throughout the transient. 
PNM – San Juan Generating Station Unit 1 Page 45 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 20 40 60 80 100 120

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet

Figure 33 T5 Flows 

Mitigations

During this transient, process pressures did not reach values that required additional control 

mitigations. Since the booster fans did not trip, the mitigations listed on page 24 had no effect on 

this transient. 

4.4.6 T6: Full Load Single Booster Fan Trips 

This transient consisted of the following steps and control actions: 

• Initialized the model to the 100% load condition 

• Ran the model for 10 seconds to establish steady-state conditions 

• Manually tripped an operating booster fan 

• Isolated the tripped booster fan by closing the associated inlet and outlet dampers 

• All controls remained in auto throughout the transient 

• MFT was not triggered during this event 

• Booster fan runback control did not occur as the furnace pressure never reached -1 inwc 

during the transient 

Note that this transient alone was tested for a period of 300 seconds to capture all events. 
PNM – San Juan Generating Station Unit 1 Page 46 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Figure 34 shows the FD discharge, furnace, and air heater gas outlet pressures during this transient. 

The loss of a single booster fan at 10 seconds led to an increase in pressures upstream of the 

booster fans. By 40 seconds, the furnace pressure increased by 7.5 inwc from its initial value. At 

this point, the gradual reduction of the tripped fan’s speed, combined with the continuous operation 

of the remaining two boosters, as shown in Figure 35, caused pressures to steady out. All the 

pressures upstream of the booster fans recovered to values higher than their initial values. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 50 100 150 200 250 300

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet

Figure 34 T6 Unit Pressures 

Figure 35 also shows the speed profile of the tripped booster fan (Booster Fan A). In addition to 

being tripped during this transient, Booster Fan A was isolated by closing the associated inlet and 

outlet dampers. The inertial losses resulted in a rapid decrease of speed by 47% in the first 15 

seconds of the transient. As the flow through the fan went to zero due to its isolation, the work 

done by the fan went to zero, resulting in a sudden change in direction of the Booster Fan A speed 

at 25 seconds. The frictional losses in the fan caused a more gradual decrease of speed thereafter, 

and the operating speed of the tripped booster fan decreased to about 115 rpm by 300 seconds. 
PNM – San Juan Generating Station Unit 1 Page 47 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

0

200

400

600

800

1000

1200

1400

0 50 100 150 200 250 300

Time (seconds)

Speed (rpm)

FD Fans Booster Fan A Booster Fans B & C

Figure 35 T6 Fan Speeds 

The effect of a single booster fan loss on the upstream pressures was also reflected in the baghouse 

and booster fan inlet pressures, as shown in Figure 36. The baghouse inlet pressure increased by 9 

inwc in the first 30 seconds, and eventually steadied out at +10.7 inwc by the end of the transient. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 50 100 150 200 250 300

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet

Figure 36 T6 Baghouse and Scrubber Pressures 

The booster fan inlet pressure similarly recovered to 10.6 inwc higher than the initial value. The FGD 

inlet pressure increased by 77% by 40 seconds and attained almost twice the initial values by the end 

of the transient. The isolation of the tripped booster fan and subsequent redistribution of the total flue 

gas flow to two scrubbers resulted in steady, but higher, pressures at the end of the transient. 
PNM – San Juan Generating Station Unit 1 Page 48 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

At 10 seconds, tripping and isolating a single booster fan led to a sudden 17% decrease in FGD 

inlet flow in the first 15 seconds of the transient. As the IGVs of the remaining two booster fans 

opened in an effort to decrease furnace pressure, the flow was redistributed to the two scrubbers in 

operation and eventually recovered to the initial value, as shown in Figure 37. The reduction in the 

total flow through the FD fans at the start of the transient resulted in a decrease of the oxygen 

percentage at the economizer outlet, which caused the FD fan IGV to open, as shown in Figure 38. 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 50 100 150 200 250 300

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet

Figure 37 T6 Flows 

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300

Time (seconds)

Position (percent open)

FD Fans Booster Fans

Figure 38 T6 Fan Inlet Guide Vane Positions 
PNM – San Juan Generating Station Unit 1 Page 49 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

MT6: Mitigated Full Load Single Booster Fan Trips

The high positive pressures measured throughout the system could be prevented by reducing the 

mass flowing through the system via a runback. For this mitigation, TRAX tested a load 

reduction from 100% to 70% at the rate of 30 MW/min. This rate was obtained from the original 

control logic supplied to TRAX. The time taken for the desired load reduction at the specified 

rate was calculated to be approximately 216 seconds (3.6 minutes). Thus it was necessary to run 

the transient, with and without mitigations, for 300 seconds to allow additional time for 

stabilization. The results of the mitigated transient are presented in the Reference Section. 

Figure 39 shows a comparison of the maximum system pressures obtained with and without 

mitigations. There is an improvement in all pressures upstream of the stack base. 

-4.6

+11.5

+17.4

+25.9

+32.1 +33.6

+27.8

+21.1

+12.9

+2.2

0.0 +0.2

+18.8

+30.0

+3.5

+1.0

+9.1

+28.9 +27.5

+23.4

+21.7

+17.4 +15.4

+14.2 +10.3

+28.0

+3.2 -0.4

 -0.6

-40

-30

-20

-10

0

+10

+20

+30

+40

Ambient

FD Fan Outlet

SAH Air Inlet

SAH Air Outlet

Windbox

Furnace

Economizer Outlet

Precip Outlet

SAH Gas Outlet

Baghouse Inlet

Baghouse Outlet

Booster Fan Inlet

Booster Fan Outlet

Scrubber Outlet

Stack Base

Top of Stack

Pressure (inwc)

Maximum (Unmitigated) Maximum with Load Runback (Mitigated)

Figure 39 T6 Transient Maximum Pressure Profile 

A comparison of the mitigated and unmitigated furnace pressures is shown in Figure 40. The 

mitigated value of the maximum furnace pressure was 3.7 inwc lower than the case without 

mitigation. The furnace pressure following the mitigation recovered to about 15.3 inwc lower 

than the unmitigated pressure at the end of this transient. 
PNM – San Juan Generating Station Unit 1 Page 50 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 50 100 150 200 250 300

Time (seconds)

Pressure (inwc)

Furnace (Unmitigated) Furnace with Load Runback (Mitigated)

Figure 40 T6 Furnace Pressure Comparison 

4.4.7 T7: Full Load Baghouse Cleaning System Failure 

This transient consisted of the following steps and control actions: 

• Initialized the model to the 100% load condition 

• Ran the model for 10 seconds to establish steady-state conditions 

• Increased the pressure drop across the baghouse by 4 inwc, from 9.7 inwc to 13.7 inwc, 

in 10 seconds to simulate its cleaning system failure (for testing a severe transient) 

• All controls remained in auto throughout the transient 

• MFT was not triggered during this event 

• Booster fan runback control did not occur as the furnace pressure never reached -1 inwc 

during the transient 

At 10 seconds, the pressure drop across the baghouse was increased by 4 inwc to begin the 

transient. This led to an increase in pressures upstream of the baghouse to allow for more flow 

through the system. This increase in pressure was small in magnitude compared to the other 

transients. Also, the rise in pressure due to increased baghouse pressure differential was more 

prominent closer to the baghouse, and the effect grew less pronounced away from it, as shown in 

Figure 41. The air heater gas outlet pressure increased by about 1.3 inwc, while the FD fan 

discharge pressure increased by 0.7 inwc by 20 seconds. The rate at which the upstream pressures 

increased gradually slowed over the next 40 seconds before the pressures eventually recovered to 

their initial values. The rate of change for these pressures was dependent on their relative position 

with respect to the baghouse. The pressures elsewhere in the system responded proportionately, as 

shown in Figure 42. 
PNM – San Juan Generating Station Unit 1 Page 51 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet

Figure 41 T7 Unit Pressures 

The baghouse inlet pressure increased by 1.5 inwc from 10 seconds to 20 seconds, and gradually 

increased through the next 40 seconds, before recovering to its initial value by the end of the 

transient, as shown in Figure 42. As shown in Figure 43, the booster fan IGV opened by 8% 

during the first 40 seconds of the transient and subsequently remained nearly constant at this 

position to support the additional flow transported by the increased baghouse differential. The 

opening of the IGV corresponded with an initial 1.3 inwc decrease of the booster fan inlet 

pressure for the first 10 seconds of the transient. Booster fan inlet pressure eventually settled at 

about 3.6 inwc lower than the initial value. The movement of the booster fan IGV, followed by 

the adjustment in booster fan inlet pressures, led to a nearly constant FGD inlet pressure 

throughout the transient. Overall, the booster fan IGV movement was able to compensate for the 

additional 4 inwc pressure drop across the baghouse. 
PNM – San Juan Generating Station Unit 1 Page 52 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet

Figure 42 T7 Baghouse and Scrubber Pressures 

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120

Time (seconds)

Position (percent open)

FD Fans Booster Fans

Figure 43 T7 Fan Inlet Guide Vane Positions 

No significant changes were observed in the flows of interest as the pressures measured at the 

FD outlet, furnace, and FGD inlet remained nearly constant throughout the transient, as shown in 

Figure 44. 
PNM – San Juan Generating Station Unit 1 Page 53 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 20 40 60 80 100 120

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet

Figure 44 T7 Flows 

Mitigations

During this transient, process pressures did not reach values that required additional control 

mitigations. Since the booster fans did not trip, the mitigations listed on page 24 had no effect on 

this transient. 
PNM – San Juan Generating Station Unit 1 Page 54 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

4.5 Transient Events Summary Table 

A summary of the unmitigated transient results is shown in Table 9. 

Furnace 

Pressure 

(inwc) 

Air Heater 

Gas Outlet 

Duct (inwc) 

Booster Fan 

No. Transient Name Inlet (inwc) 

No. of 

Booster 

Fans in 

Service

Gross 

Load

% Min Max Min Max Min Max 

T1 Full Load MFT 3 100 -1.2 +9.9 -3.6 +1.5 -14.4 -3.8 

T2 Full Load All Booster Fans Trip 3 100 +1.8 +18.6 +0.4 +14.6 -11.0 +8.3 

T3 Full Load Both FD Fans Trip 3 100 -6.9 +9.9 -7.7 +1.5 -11.0 -4.4 

T4 Low Load Two Booster Fans Runaway 2 30 -3.7 +2.2 -6.8 +0.0 -12.1 -3.5 

T5 Full Load All Fans Trip 3 100 -3.3 +9.9 -4.0 +1.5 -11.0 -0.7 

T6 Full Load Single Booster Fan Trips 2 100 +9.9 +21.1 +1.5 +12.9 -11.0 +0.2 

T7 Full Load Baghouse Cleaning System Failure 3 100 +9.5 +11.5 +1.4 +3.1 -14.7 -11.0 

Table 9 Transient Event Summary Table 

A summary of the mitigated transient results is shown in Table 10. 

Furnace 

Pressure 

(inwc) 

Air Heater 

Gas Outlet 

Duct (inwc) 

Booster Fan 

No. Transient Name Inlet (inwc) 

No. of 

Booster 

Fans in 

Service

Gross 

Load

% Min Max Min Max Min Max 

MT2 Mitigated Full Load All Booster Fans Trip – 

Delayed FD Trip 3 100 -0.0 +15.1 -0.3 +11.4 -11.0 +5.5 

MT2A Mitigated Full Load All Booster Fans Trip – 

Immediate FD Trip 3 100 -3.3 +9.9 -4.0 +1.5 -11.0 -0.7 

MT6 Mitigated Full Load Single Booster Fan 

Trips 2 100* +1.2 +17.4 -3.4 +10.3 -11.0 -0.6 

Table 10 Transient Event Summary Table 

*As a part of the mitigated run, the load changed from 100% to 70%. 
PNM – San Juan Generating Station Unit 1 Page 55 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

5.0 CONCLUSIONS AND RECOMMENDATIONS 

During transient testing, unmitigated furnace pressures were held within the range of –6.9 inwc 

to +21.1 inwc. The “Full Load All Booster Fans Trip” and “Full Load Single Booster Fan Trips” 

transients led to high furnace pressure maximums of +18.6 inwc and +21.1 inwc respectively. A 

delayed trip of the FD fans mitigated the furnace pressure to a maximum of +15.1 inwc for the 

former transient, and an immediate trip of the FD fans mitigated the furnace pressure to a 

maximum of +9.9 inwc, but a furnace pressure minimum of -3.3 inwc was experienced. 

Reducing the load from 100% to 70%, at a rate of 30 MW/min, mitigated the maximum furnace 

pressure to +17.4 inwc for the “Full Load Single Booster Fan Trips” transient. The remaining 

transients led to negative furnace pressure excursions, with the most severe being –6.9 inwc 

measured during the “Full Load Both FD Fans Trip” transient. 

The rapid movement of the booster fan inlet guide vanes to prevent furnace pressure excursions 

often caused sharp downstream pressure excursions. The booster fans’ inlet pressure was found 

to vary within -14.7 inwc and +8.3 inwc for all the transients. Again, the indicated maximum 

pressure was obtained for the “Full Load All Booster Fans Trip” transient. The proposed 

mitigation of tripping both the FD fans when all booster fans trip mitigated the booster fan inlet 

pressure to a maximum of +5.5 inwc. 

Pressure excursions at the flue gas outlet of the air heaters were within –7.7 inwc and +14.6 

inwc. The indicated maximum air heater gas outlet pressure was obtained during the “Full Load 

All Booster Fans Trip” transient. Tripping both the FD fans on a high pressure limit following 

the MFT mitigated the air heater gas outlet pressure to a maximum of +11.4 inwc. 

During the “Full Load MFT” transient, the fireball collapse resulted in the furnace pressure 

dropping by 11.1 inwc in about eight seconds. During this period of time, closing booster fan 

inlet guide vanes by 46% reduced flow to the scrubbers and caused inlet pressure to the FGD to 

drop by about 12.6 inwc. Over a period of 15 seconds following the release of the kicker at 25 

seconds, the FGD inlet pressure improved by 7.2 inwc while the boosters opened by 24%. 

 

The fast-adjusting booster fan inlet guide vanes were a key factor in moderating the furnace 

pressure drop associated with a MFT fireball collapse. On an MFT, controls closed the burner 

shutoff valves, which rapidly cut off fuel to the furnace and caused a sharp fireball collapse. 

With the FD fan IGV frozen in place, the only response available to the controls was to cut 

furnace exhaust by decreasing the flow transported by the downstream booster fans. The 17 

second full stroke time of the booster fan inlet guide vanes enabled controls to reduce furnace 

exhaust by 43% in seven seconds. This flow reduction limited the negative furnace pressure 

excursion during the fireball collapse. 
PNM – San Juan Generating Station Unit 1 Page 56 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

Because the MFT fireball collapse happened so quickly, a kicker circuit was necessary to 

reduce the booster fan inlet guide vane position demand. The air heater gas outlet pressure 

controls alone were not fast enough to close booster fan inlet guide vanes to achieve the 43% 

reduction in furnace exhaust necessary to mitigate the MFT. Upon initiation of an MFT, a 

kicker circuit immediately reduced demand to the booster fan inlet guide vanes by 46%. This 

quick change in demand closed the booster fan inlet guide vanes sufficiently to reduce the 

furnace exhaust flow and hold the furnace pressure excursion to –1.2 inwc during a full load 

MFT. 

A fast-acting booster fan runback control was critical to mitigating the “Low Load Two Booster 

Fans Runaway” transient. When the furnace pressure dropped below –1 inwc, the booster fan 

runback controller overrode normal controls and adjusted booster fan inlet guide vanes to 

maintain +1 inwc furnace pressure. During the “Low Load Two Booster Fans Runaway” 

transient, the booster fan runback controls began to decrease booster fan inlet guide vane 

positions after the runaway had opened the vanes to 79%. If the booster fan inlet guide vanes 

had driven full open, the furnace pressure excursion would have been more severe than the –3.7 

inwc measured during the transient. 

Based on the results of the transient runs, TRAX recommends the following control strategies 

and mitigating measures be implemented in the future plant configuration controls: 

1. During normal operation, adjust the booster fan inlet guide vanes via a control that uses 

an FD inlet guide vane demand feed-forward, added to a trim controller that monitors air 

heater gas outlet pressure. 

2. For mitigating MFT events, a kicker circuit should be used to immediately run back 

booster fan inlet guide vanes. The kicker would be activated by the MFT circuit and 

should last 15 seconds. The kick value is a function of a feed forward signal of the FD 

fan demand and the relation is shown in Table 10. 

FD Fan Feed-Forward Signal (%) Kick Value (%) 

0 0 

50 –20 

100 –60 

Table 11 Kick Values 

The extent of the booster fan runback should be load dependent—i.e. at lower loads, the 

extent of the booster fan runback would be less than a runback during an MFT at full 

load. 

3. An overriding booster fan runback controller should be used to help mitigate negative 

furnace pressure excursions. The runback controller should take precedence over normal 

controls and operator auto/manual stations. When active, the runback controller would 

adjust booster fan inlet guide vanes to maintain a positive furnace pressure. The 

controller should go active if furnace pressure drops below –1 inwc without an MFT 

occurrence. 
PNM – San Juan Generating Station Unit 1 Page 57 of 57 

Furnace Draft Analysis – Final Report 3/27/2008 

Project Number EA0711 

4. On an all booster fan trip, there are two alternate control strategies that have merit for 

mitigating positive and negative pressure excursions: 

a. Trip FD fans on a high furnace pressure limit 

b. Trip FD fans immediately 

Tripping both FD fans if the furnace pressure exceeded +15 inwc prevented overpressurizing the furnace following an MFT. However, by immediately tripping the FD 

fan, high positive pressures were avoided, but a furnace pressure minimum of –3.3 inwc 

was experienced. Note that tripping the FD fans immediately upon loss of all booster 

fans is in compliance with a strict interpretation of the NFPA guidelines. 

5. If a single booster fan is tripped, the mass flowing through the system should be reduced 

in order to prevent over-pressurize the furnace via a runback. A load reduction from 

100% to 70% at a rate of 30 MW/min reduced the maximum furnace pressure value by 

3.7 inwc as compared to the unmitigated transient. 
REFERENCE SECTION 

This Reference Section is a supplement to the San Juan Generating Station Units 1 & 2 Final 

Report Number EA0711-0103. 

The following additional reference information is provided in this section, subdivided into the 

following categories, each containing a list of contents: 

1. Schematics 

2. Validation Runs 

3. Transient Runs 

4. Letter Report 
1. SCHEMATICS 

The Unit 1 Process Schematics contain the following pages: 

• INDEX 1–1 

• FANS AND AIR HEATERS 2–1 

• FURNACE 3–1 

• PULVERIZERS A–D 1–2 

• BAGHOUSE AND BOOSTER FANS 2–2 

• SCRUBBERS AND STACK 3–2 
1

1

22

33

44

55

66

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B C D Prepared bySVP

Drawing No.EA0711.02 - 01 - 001 page 1-1

Date26 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft Analysis Process Model - Proposed Configuration 

PROCESS MODEL

SAN JUAN GENERATING STATION UNIT 1

FURNACE DRAFT ANALYSIS

2-2

Key:

ProTRAX Modu

Module ID

Flow Stream ID

FSID FSID

Connector Coordinates of mat

Page number of matching connector

p-p (xy)

'MID'

FAN

PUBLIC SERVICE COMPANY OF NEW MEXICO

1-1

INDEX

1-2

PULVERIZERS A-D

2-1

FANS AND

AIR HEATERS 

3-1

FURNACE

BAGHOUSE AND

BOOSTER FANS

3-2

SCRUBBERS AND

STACK
1

1

22

33

44

55

66

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B C D Prepared bySVP

Drawing No.EA0711.02 - 01 - 001 page 2-1

Date26 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft Analysis Process Model - Proposed Configuration 

LB_1 EPS_1

LB2_1 EPS2_1

EPAHLB_1

EBPAHB_1 LPSCAHB_1EPAHB_1

EPAHLA_1

EBPAHA_1 LPSCAHA_1 EPAHA_1

ESAHLA_1

LBSAHA_1 ESAHA_1

GLSAHB_1

ESAHLB_1

LBSAHB_1 ESAHB_1

LTA2_1

LTA_1

ETA2_1

LPAOSB_1

ETA_1

LPAOSA_1

ESOFA_1

EOFA_1

EBSAHA_1

EBSAHB_1

LFDA_1 EFDOSA_1

LDWB_1

LDWA_1

EPAGCDB_1

EPAB_1

LFDXO_1EFDXO_1

LPAHB_1

LPAHLB_1

LPAGSOB_1

GLPAHB_1 GEPAHB_1

LSCASO_1 EDWA_1

LSAHB_1 LSCBSO_1

EHP

LPAHA_1

LPAGSOA_1 GLPAHA_1

GEPAHA_1 EPAGCDA_1

GESAHB_1 ESBGSO_1

GESAHA_1 ESAGSO_1

LSAHA_1

EDWB_1

GLSAHA_1

EFDB_1

EFDA_1

LPAB_1

LFDB_1

LPAA_1 EPAA_1

LPAHLA_1

LSAHLB_1

LSAHLA_1

EPAOSB_1

EPAOSA_1

EFDOSB_1 LFDOSB_1

LFDOSA_1

3-2 (D7)

To Stack

FANS AND AIR HEATERS

DAMPER

'FDOSA_1'

'J5_1'

DAMPER

'FDOSB_1'

'J11_1'

DAMPER

'PAOSA_1'

FD Fan A

'J12_1'

DAMPER

'PAOSB_1'

Primary Air Fan A

3-1 (B5)

From ESP

3-1 (B5)

3-2 (D7)

3-2 (B7)

SCAH

SAH B

Outlet

Shutoff

Atmosphere

Atmosphere

'J16_1'

'J17_1'

DUCT

'TA_1'

Outlet

Shutoff

DUCT

'SAHLA_1'

DUCT

'SAHLB_1' 3-2 (A7)

To Stack

3-2 (C7) DUCT 'PAHLA_1' 3-1 (A5)

3-2 (C7)

From ESP

From ESP

PAH B

To Booster Fans

To Booster Fans

Primary Air Fan B

Outlet

Shutoff

DUCT

'DWA_1'

FD Fan B

FANTAB

'PAA_1'

FANTAB

'FDA_1'

FANTAB

'FDB_1'

FANTAB

'PAB_1'

BC

'BCA_1'

BC

'BCB_1'

RHTRFD

'PAHA_1'

RHTRFD

'SAHA_1'

RHTRFD

'SAHB_1'

PLNMRV

'PN20_1'

DAMP

'SAF_1

Air Sleeves 

DUCT

'DWB_1'

PLNMRV

'PN29_1' SCAH

DAMPER

'SCASO_1'

DAMPER

'SAGSO_1'

DAMPER

'SCBSO_1'

DAMPER

'SBGSO_1'

DAMPER

'PAGCDA_1'

DAMPER

'PAGSOA_1'

DUCT

'PSCAHA_1'

'JHP_1'

SAH A

To Stack

DAMP

'OFA_

NOX Po

RHTRFD

'PAHB_1'

DUCT

'PSCAHB_1'

3-2 (C7)

DAMPER

'PAGSOB_1'

DAMPER

'PAGCDB_1'

3-2 (B7) DUCT 'PAHLB_1'

PAH Lkg

PAH A

DAMPER

'FDXO_1'

3-1 (A5)

From ESP

'JA21_1'

'J4_1'

BANK

'BSAHB_1'

BANK

'BSAHA_1'

'J32_1'

'J33_1'

DUCT

'TA2_1'

'J22_1'

'J23_1'

BANK

'BPAHA_1'

'J24_1'

BANK

'BPAHB_1'

'J25_1'

PAH Lkg

To Stack

'J29_1'

'J30_1'

Outlet

Shutoff SAH Lkg

SAH Lkg
1

1

22

33

44

55

66

A 

B C D Prepared bySVP

Drawing No.EA0711.02 - 01 - 001 page 3-1

Date26 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft Analysis Process Model - Proposed Configuration 

LBSOD_1LBSOC_1

LBSOB_1LBSOA_1

LOFA_1

LSOFA_1

ESHDIV_1 EPSH_1 LFSH_1 

ERH_1 

LPSH_1 EFSH_1

EPAGCDB_1

BC LBCD

'BCD_1'

FURNMF

'FRN_1'

LESPA_1

EPAGCDA_1

ESAGSO_1

ESBGSO_1 LESPB_1

ELKOUT_1 LLKOUT_1

LFRN_1 LFRND_1

LBRN_1

LSEAL_1

ELKIN_1

LLKIN_1

BANK

'PSH_1'

BANK

'CONVSH_1'

BANK

'RH_1'

BC

'SEAL_1'

Water Seal

Pendant

Superheater

Conv

Superheater

Reheate

FURNACE

Furnace

FurnaceIn-Leakage

'LKIN_1'

DUCT

'LKBC_1'

BCATM

DUCT

'FRND_1'

PLNMRV

'PLK_1'

BC

'L2BC_1'

DUCT

'LKOUT_1'

Atmosphere

 FurnaceOut-Leakage

DUCT

'ESPB_1'

PLNMRV

'ESPR_1'

 Hot-SidPrecipita

2-1 (C5)

To Secondary Air Heater A

2-1 (A5)

To Secondary Air Heater B

2-1 (D6)

To Primary

 Air Heater A

DUCT

'ESPA_1'

BURNMF

'BRN_1'

2-1 (C6)

To Primary

 Air Heater B

'JFB2'

BANK

'SHDIV_1'

Division walls

2-1 (B7)

2-1 (A7)

From Windbox

1-2 (D7)

From WindboxPrim Air & Coal From Pulverizer A

1-2 (C8)

1-2 (B8)1-2 (A8)From Pulverizer BFrom Pulverizer C

From Pulverizer D
1

1

22

33

44

55

66

A 

B C D Prepared bySVP

Drawing No.EA0711.02 - 01 - 001 page 1-2

Date26 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft Analysis Process Model - Proposed Configuration 

EBSOD_1

EHDD_1

ETDD_1

LHDD_1 EPASOD_1 EPACD_1

LTDD_1

LPACD_1 EPVD_1

LPVD_1

LPVC_1

EPVC_1

EPVB_1

LPACC_1

LPACB_1

LPACA_1 EPVA_1

EHPAH1_1 LHAH1_1

EPASOC_1

EPASOB_1

EPACC_1

EPACB_1

EPASOA_1 EPACA_1

EHDC_1

EHDB_1

EHDA_1

ETDC_1

ETDA_1

ETDB_1

LHDA_1

LTDA_1 LPVA_1 EBSOA_1

LTDB_1

LHDB_1

LTDC_1

LHDC_1

LPVB_1

EBSOC_1

EBSOB_1

PULVBR

'PVA_1'

2-1 (D8)

DAMPER

'TDA_1'

DAMPER

'HDA_1'

'JBA_1'

'JCA_1'

DAMPRC

'BSOA_1

Tempering Damper

Hot Air Damper

DAMPER

'TDB_1'

DAMPER

'HDB_1'

'JBB_1'

PULVBR

'PVB_1'

'JCB_1'

DAMPRC

'BSOB_1'

DAMPER

'TDC_1'

DAMPER

'HDC_1'

'JBC_1'

'JCC_1'

DAMPRC

'BSOC_1'

2-1 (D8)

Temp Air fromPA Plenum

Temp Air from

PA Plenum

Temp Air fromPA Plenum

Pulverizer A

Pulverizer B

Pulverizer C

PULVERIZERS A - D

PLNMRV

'HP1_1'

2-1 (D7)

2-1 (C8)

Hot Air from Primary Air Heater

DAMPER

'PASOA_1'

DAMPER

'PACA_1'

DAMPER

'PASOB_1'

DAMPER

'PACB_1'

DAMPER

'PASOC_1'

DAMPER

'PACC_1'

Primary Air

Shutoff Damper 

Primary Air 

Control Damper 

Burner Coal Valv

DUCT

'HPAH1_1'

Hot Primary Air 

Header A

'JDA_1'

'JDB_1'

'JDC_1'

PULVBR

'PVC_1'

Primary Air

Shutoff Damper 

Primary Air 

Control Damper 

DAMPER

'TDD_1'

DAMPER

'HDD_1'

'JBD_1'

'JCD_1'

DAMPRC

'BSOD_1'

2-1 (C8)Temp Air from

PA Plenum

DAMPER

'PASOD_1'

DAMPER

'PACD_1'

Burner Coal V

'JDD_1'

PULVBR

'PVD_1'

Pulverizer D
1

1

22

33

44

55

66

A 

B C D Prepared bySVP

Drawing No.EA0711.02 - 01 - 001 page 2-2

Date26 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft Analysis Process Model - Proposed Configuration 

EBHBPD_1 LBHBPD_1

LBBHPL

_

1 LDBBH_1 EBHILD_1 LBHILD_1 LBHD_1 LBHPL_1 LBHOLD_1 LEBFJ_1 LEBFD_1

LSADB_1

L

S

A

D

A_

1

EBFC_1

EBFB

_

1

EBFA_1

LBFIDC_1

LBFIDB

_

1

LBFIDA_1

E

B

F

I

D

C

_

1 EBFIDA_1 EBFIDB_1

BAGHOUSE AND BOOSTER FANS

PLNMRV

'EBFPL_1'

DAMPER

'BFIDA_1'

FAN

'BFA

DAMPER

'BFIDB_1'

FANT

'BFB_

DAMPER

'BFIDC_1'

FAN

'BFC

Booster F

Booster F

Booster F

'BFDJ_1'

'BFEJ_1'

'BLCJ_1'

3-2 (D4)

3-2 (A4)

PLNMRV

'BBHPL_1'

DUCT

'DBBH_1'

'BBHJ_1'

DAMPER

'BHILD_1'

DAMPER

'BHOLD_1'

DUCT

'BHD_1'

PLNMRV

'BHPL_1' 'EBFJ_1' 

DUCT

'EBFD_1'

DAMPER

'BHBPD_1'

Baghouse

 BaghouseInlet Damper

 BaghouseOutlet Damper

 BaghouseBypass Damper

From SAH B

From SAH A
1

1

22

33

44

55

66

A 

B C D Prepared bySVP

Drawing No.EA0711.02 - 01 - 001 page 3-2

Date26 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft Analysis Process Model - Proposed Configuration 

LSBC4C_1 LBFODC_1

LBFODB_1

LBFODA_1

LFE_1

LFGDPL_1

LSADB

_

1

LSADA

_

1

LFGDBD_1

ESTK_1

ED121_1

LSBDB_1

L

S

B

D

A_

1

LSTK_1

L

L

GL

G

ESBDB_1ESBDA_1

LS

LSA

ESADB_1

ESADA

_

1

LPB_1EPB_1LPA_1EPA_1

LSBC3C_1

LSBC2C_1

LSBC1C_1

LWWBCC_1

LSBC4B_1

LSBC3B_1

LSBC2B_1

LSBC1B_1

LWWBCB_1

LSBC4A_1

LSBC3A_1

LSBC2A_1

LSBC1A_1

LWWBCA_1

LFGDCD

_

1

LFGDAD

_

1

FGDSCB

'FGDC_1'

FGDSCB

'FGDB_1'

FGDSCB

'FGDA_1'

LFGDC_1

LFGDB

_

1

LFGDA_1

EFGDC

_

1

EFGDB

_

1

EFGDA

_

1

BC

'ATMSK'

Stack

'BFCJ_1'

'BFBJ_1'

'BFAJ_1'

PLNMRV

'FGDPL_1'

DUCT

'FGDAD_1'

DUCT

'FGDBD_1'

DUCT

'FGDCD_1'

BC

'WWBCA_1'

BC

'SBC1A_1'

BC

'SBC2A_1'

BC

'SBC3A_1'

BC

'SBC4A_1'

BC

'WWBCB_1'

BC

'SBC1B_1'

BC

'SBC2B_1'

BC

'SBC3B_1'

BC

'SBC4B_1'

WashWater

 SlurryEntering

 SlurryEntering

BC

'WWBCC_1'

BC

'SBC1C_1'

BC

'SBC2C_1'

BC

'SBC3C_1'

BC

'SBC4C_1'

 SlurryEntering

'J411_1''J412_1'

'J413_1'

DUCT

'PA_1'

'PB_1'

DUCT

DUCT

'SADA_1'

DUCT

'FE_1'

DUCT

'SADB_1'

'SBDA_1'

DAMPER

DAMPER

'SBDB_1'

Scrubber Module A

Scrubber Module B

Scrubber Module C

STACK'STK_1'

'J44_1'

DUCT

'D121_1'

2-2 (D1)

2-2 (B1)

To Baghouse

To Baghouse

WashWater

WashWater

SCRUBBERS AND STACK

2-2 (D8)

2-2 (C8)2-2 (B8)

From Booster Fan A

From Booster Fan B

From Booster Fan C
The Unit 1 Controls Schematics contain the following pages: 

• INDEX 1–1 

• LEGEND 2–1 

• SEC AIR CNTRL & OXYGEN TRIM 3–1 

• FD DEMAND 4–1 

• PRIMARY AIR PRESSURE 5–1 

• MASTER FUEL TRIP 6–1 

• EQUIPMENT SHUTDOWN 7–1 

• BOOSTER FANS 8–1 

• PULVERIZER/COMPARTMENT A CONTROLS 1–2 

• PULVERIZER/COMPARTMENT B CONTROLS A 2–2 

• PULVERIZER/COMPARTMENT C CONTROLS 3–2 

• PULVERIZER/COMPARTMENT D CONTROLS 4–2 

• AIR HEATER INLET DAMPERS 5–2 

• PRIMARY AIR SHUTOFF DAMPERS 6–2 

• BAGHOUSE DAMPERS 7–2 

• FD FAN TRIPS 1–3 
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 1-1

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

FD DEMAND PRIMARY AIR PRESSURE MASTER FUEL TRIP LEGEND

PULVERIZER/

COMPARTMENT A

CONTROLS

INDEX

1-1

1-2 2-2 3-2

CONTROLS MODEL

2-1

PULVERIZER/

COMPARTMENT B

CONTROLS

PULVERIZER/

COMPARTMENT C

CONTROLS

PULVERIZER/

COMPARTMENT D

CONTROLS

4-2

3-1 4-1 5-1

SEC AIR CNTRL &

OXYGEN TRIM

6-1

EQUIPSHUTD

7

SAN JUAN GENERATING STATION UNIT 1

FURNACE DRAFT ANALYSIS

PUBLIC SERVICE COMPANY OF NEW MEXICO

AIR HEATER

INLET DAMPERS

PRIMARY AIR

SHUTOFF DAMPERS

5-2 6-2

FD FAN TRIPS

1-3

BAGH

DAM

7
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 2-1

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

LEGEND

PROCESS VARIABLE FROMFIELD TRANSMITTER

LEAD-LAGLIMIT HIGH

CYxyz

= Valve 

OUTPUT TOFINAL CONTROL ELEMENT

PROCVAR

*ID

*ID SUM

*ID

TRANSFER

DIFFERENCE

DIVIDEDERIVATIVE

BIAS BIAS

*ID

d

*ID

dt

*ID

f(x)

*ID

~

1 + ks

*ID

1 - 2s

*ID

>

*ID

> < LIMIT HIGH LOW

*ID

< LIMIT LOW

X

*ID

MULTIPLY

K/S/D

*ID PID CONTROLLER

K

*ID

PROPORTIONAL

*ID

RAMP

>

*ID

<

*ID

HIGH SELECT

LOW SELECT

A MANUAL ANALOG SET

MANUAL INTEGER/DISCREET SET

*ID

SQUARE ROOT

f(t)

*ID

do TIME DELAY

FUNCTION GENERATOR

VELOCITY LIMITER

*ID

V<

K/S

*ID

PI CONTROLLER

ACCUM1*ID INTEGRATOR

ACCUM2

*ID

2-INPUT INTEGRATOR

WITH LIMITS

H/

*ID

*ID

H/L

/L

*ID

HIGH SIGNAL MONITORHIGH/LOW SIGNAL MONITORLOW SIGNAL MONITORDIGITAL OUT WHEN INPUT

 IS ABOVE SETPOINT

DIGITAL OUT WHEN INPUT IS BELOW SETPOINTDIGITAL OUT WHEN INPUT IS ABOVE HIGH SETPOINT

OR BELOW LOW SETPOINT

N

*ID

AVERAGE
1

1

22

33

44

55

66

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B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 3-1

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

AVGPVDMD

TOTFUEL

TOTFUEL

HL2

VH2

DB11

LP46_OUT

LIMB

FDIFF

LIMFUEL MB1_2

B9B

SPAIR

WAIR

LIMB5

FUEL_MULT

PIB5DB5

MB1_2

STMFL BTUC

SPAIR

WAIR

SCAT421SUM51D

B10S

PVDMD

PIB11

FMSTR

FGB9BLIMFUEL

DLAIR

LIMAIR

LIMAIR

AIRMIN

AIRBIAS FUELBIAS

GENDMD GENDMD

WEPVD

WEPVC

SUM51E

WEPVB WEDWA 

WEPVA

O

KS51AE51A

MULT51A

WAIRTOTAIR

SUM51A

Fuel Demand

'SUM51A'

'SUM51C'

Primary Air Flow 

f(x)

'FX51A'

X

'MUL51A'

'E51A'

K/S

'KS51A'

'SUM51D'

4-1 (D1)

Pulverizer Demand

Airflow Demand 

to FD Fans

3-1 (C6)

SEC AIR CNTRL & OXYGEN TRIM

1-2 (D1)4-2 (D1)2-2 (D1)3-2 (D1)

'WEPVA'

PROCVAR

'WEPVB'

PROCVAR

'WEPVC'

PROCVAR

'WEPVD'

PROCVAR

'SUM51E'

'WLDWA'

PROCVAR

Secondary Air Flow

0-288

(KPP

(0-100

FD F

3-1 (D3)6-1 (C1)

Total Airflow

BIAS

'AIRBIAS'

BIAS

'FUELBIAS'

>

'LIMAIR'

<

'LIMFUEL'

7-2 (D2) Total Airflow

A

Firing Rate 

Demand

>

'LIMAIR1'

t-to

'DTIM'

B5

B6-

B7

B8-1

B10

B10

B10

B10

B9-2 B9-1

B9-1

B9-2

B23A B24A

Total Fuel Flow

(Add All Fuel to Pulverizers)

(0-100 %)

K/S

'FMSTR'

'B10S'

f(x)

'FGB9B'

B9B

B10B10

B10

B10

Average Pulverizer

Demand

K/S

'PIB11'

Integral Only

B11

B11

'LIMB11'

> <

B11

30%

'LIMB10' >

'LIM51A' >

PROCVAR

'STMFL'

f(x)

'BTUC'

'DB5'

X

'MB1_2'

K/S

'PIB5'

'LIMB5'

> <

BTU Compensator

Integral Only

B5

B5

B5

LOOPA

'LOOP45'

LOOPA

'LOOP46' f(x)

'B9B'

'FDIFF'

'DB11'

A

PROCVAR

'PTOTFUEL'

'PAVGDMD'

PROCVAR
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 4-1

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

LIMB11A

LP2_OUT

FDTV

FDTS

CYFDOSA

CYFX

CYFDB

TR31B TR31A

TR31B

LP1_OUT

TR31A

LIMB18 LIMB18

SA31B SI31B

TR31BBI31BAUT31B

LIMB11A

LIMB14

LIMB14

FX31C

CYFDA

TR31A

LIMB11AKS31A

SCAT421

FDAVGDMD

GROSS_MW

GENDMD

BLRDMD

GENDMD

AUT31A

FDA_TRP 

NFD

SFDA

NFDA

BI31A

SA31A SI31A

E31A

'E31A'

K/S

'KS31A'

BIAS

'BI31A'

'TR31A'

A

CYFDA

FD Fan A

Inlet Guide Vanes

'GENDMD'

PROCVAR

Firing Rate Demand

A

A

'TR61A'

A

FD Fan A Speed 

1-3 (D3) 

'AUT31A'

Firing Demand

3-1 (D8)

f(x)

'FX31B'

1180 RPM

f(x)

'FX31C'

CYFDOSA

FD Fan A

Outlet Shutoff Damper

f(x)

'FX31B1'

FD Fan A 

Demand

4-1 (D2)

FD Fan ADemand

'FDAVGDMD'

4-1 (B2)

4-1 (A6)

FD Fan B

Demand

3-1 (A6)

Airflow

Demand 

B8-2

B11

B11

B14B14

B14

B15

100

0 0 50 100

Out

In

FD FAN SPEED

'LIMB11A'

> <

'LIMB14'

> <

f(x)

'FX120A'

B14 f(x)

'FX120C'

BIAS

'B131B'

'TR31B'

A

CYFDB

FD Fan B

Inlet Guide Vanes

'AUT31B'

f(x)

'FX31D'

CYFDOS

FD Fan B

Outlet Shutoff Da

4-1 (D2)

FD Fan BDemand

B18

B18

B18

'LIMB18'

> <

f(x)

'FX120B'

B18

f(x)

'FX120D'

LOOPA

'LOOP1'

LOOPA

'LOOP2'

A

FD DEMAND

8-1 (C1) FD Fan Demand To Booster Fan
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 5-1

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

PFURNACE

PFURNACE

B511 FX41A MAXPVDMD

NPA 

CYPAOS

TR41H

CYPAOSA

TR41G

CYPAB

TR41B

TR41B

TR41B

CYPAA

TR41A

TR41A

TR41A

LP4_OUT

TR41B

LP3_OUT

TR41A

PADIF

PLPAH

KS41A

SA41D SI41D

AUT41DFX41D

SA41C SI41C

AUT41CFX41C

KS41B

KS41B

AUT41A AUT41B

AVE41A

PAAZERO TRPPAA

NPAA

SA41A SI41A SA41B SI41B

E41B

E41A

'PV41A'

PROCVAR

Pri Air Duct Press Highest 

Feeder

Demand

f(x)

'FX41A'

'E41A'

K/S

'KS41A'

'E41B'

K/S

'KS41B'

N

'AVE41A'

'TR41A' 'TR41B'

A A

CYPAA

CYPAB

PA FAN SPEED

'TR41D'

A

'AUT41A' 'AUT41B'

'TR41G'

A

CYPAOSA

'AUT41C'

f(x)

'FX41C'

'TR41H'

A

'AUT41D'

f(x)

'FX41D'

1790 RPM

PA Fan A

Inlet Guide Vanes

100

0 0 50 100

100

0 0 

B3

B4

B4

5-1 (D3)

5-1 (D4)

5-1 (A2)

5-1 (A5)

Integral Only

B5

B5

B8 B9

B11

B12

'PADIF'

Furnace Pressure

Out

In

Out

LOOPA

'LOOP3'

LOOPA

'LOOP4'

f(x)

'FX121A' f(x)

'FX121B'

f(x)

'FX121C' f(x)

'FX121D'

A

BIAS

'B511'

PRIMARY AIR PRESSURE

'PMAXPVDMD'

PROCVAR

'PFURNACE'

PROCVAR

PA Fan A

Outlet Shutoff Dampers

PA Fan B

Inlet Guide Vanes

P

Outlet S

8-1 (B8)

PA Fan A Speed 

PA Fan Inlet Guide Vane Demand
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 6-1

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

PFURNACE

PFURNACE

TRIP_ALL_BF

BHDELP HBHDP DHBDP

MFTF

WAI

MF

WAIR

RHTBLK

MFTB

A6

TD61A

NO_PA_FANS

MF

WAWA

MF

MFT

MF

MF

M

FDR_NOSTOP

NO_FD_FANS MFTC

MFTF

MFTE

PLPAH LO61A

WA

WA

WA

WAI

MFTA

LO61B

HI61A

MFTD

LO61C

MFTSET

MFTRESET

PROCVAR

'PV61A'

PROCVAR

'PV61C'

OR

'OR61A'

/L

'LO61B'

f(t) pu

'TD61B'

PROCVAR

'PV61B'

H/

'HI61A'

< -7 inwc

f(t) pu

'TD61C'

OR

'SMFT2'

3 s

Primary Air Duct Pressure

Furnace Pressure

< 25%

3 s

f(t) pu

'TD61A'

< +47.7 inwc 5 s

/L

'LO61C'

> +34.4 inwc 3 s

f(t) pu

'TD61D'

Secondary Air Flow

MEM3

'MMFT'

Both PA fans tripped

/L

'LO61A'

Loss of FD fans

MFT Emerg. PB

f(t) pu

'TD61E'

0 s

'A6'

AND

PROCVAR

'PV61F'

All Feeders Not StoppedReheater Blocked

REF : Currentl TRAX ex

3-1 (C6)

7-2 (D2)

To Baghouse Dampers

9-2 (B5) H/ 'HI61A1'

> +14.0 inwc

Baghouse DP

f(t) pu

'TD61C1'

5 s

7-2 (C7)

Trip All Booster Fans

MASTER FUEL TRIP

5-1 (D2)
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 7-1

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

TRIP_PA_FANS

FDB_TRP

FDA_TRP

PAB_TRP

TRIP_PA_FANS

PAA_TRP

YBSO YBSO YBS

NPULV NPULV NPULV NPULV

TRPPULV TRPPULV TRPPULV TRPPULV

NPVA NPVB NPVC NPVD

TRPVA TRPVB TRPVC TRPVD

SA71B SI71B SA71C SI71C SA71D 

CYBSOA CYBSOB CYB

AA

'TRPA15' 'TRPA16'

A

BURNER COAL VALVES

'TR

A

A

'TPVA' 'TPVB' 'TPVC' 'TPVD'

PULVERIZERS

A

MFT

6-1 (D8)

OR

'OR41A' FD Fan A tripped

MFT

6-1 (D8)

OR

'OR41B' FD Fan B tripped

PA Fan B tripped

1-3 (D3)

1-3 (B3)

PA FANS

EQUIPMENT SHUTDOWN

PA Fan A tripped

Pulverizer A

Speed

CYBSOA CYBSOB CYBSOC 

NPVA NPVB NPVC NPVD

Pulverizer B

Speed

Pulverizer C

Speed

Pulverizer D

Speed

Burner A

Coal Valve

Burner C

Coal Valve

Burner B

Coal Valve
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 8-1

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

FDFFS

KICK

MPUL

FDFFSKICK

MFT

PFURNACE

MPUL

MFT

S332 S332 S332

BFRB

PSAD

F

D

F

S

S

MFT

LIMB11A

LIMB11A

PIBF BFRB PIBF BFRB PIBF BFRB

CYBFA CYBFB CYBFCAUT81A AUT81B AUT81C

D312

FDFFS

FDFF

SPSAD

NORM

MPUL

KICK

KVAL

TP6

NT6

BFLP

PID331

NT7

BTRK

Y

B

F

A

'TR81A'

CYBFA

Booster Fan A

Inlet Guide Vanes

'TR81B'

CYBFB

'TR81C'

CYBFC

'AUT81A' 'AUT81B'

'AUT81C'

Normally in Auto

9-2 (B6)

'D331'

Airheater Gas

Outlet Duct Pressure (inwc)

K/S/D

'PID331'

4-1 (C2) K 'S332' 'PP332'

From FD Demand

Setpoint

0.0 inwc

FD Feed Forward X 1.0

High and Low Cl

8-1 (C4)

'M

AN f(x) D

'FX41A1'

A

Normally in Auto Normally in Auto

6-1 (D6)

'TR333'

A

'PUL'

f(x)

'FX41A2'

MFT Kicker Circuit

MFT

20 s 

8-1 (C3)

Normally Zero

6-1 (D6) f(t) pu 'TP6'8-1 (D3) NOT 'NT6'

NOT

5-1 (D2)

6-1 (D6)

NOT

'M

AND

NOT

'NT7'

/L

'BFLP'

8-1 (C8)

8-1 (A8) 8-1 (C8) 8-1 (A8) 8-1 (C8) 8-1 (A8) 8-1 (C8)

8-1 (D4)

5 s

< -1 inwc

MFT in

Progress

BF Kicker

Active

Furnace

Pressure

MFT in

Progress

Booster Fan

Position Feedbac

Booster Fan

Runback Controll

Active

8-1 (C3)

'D811' 8-1 (C8)

Tracking Signal

BF RunbackController Active

P = 1I = 10 s

X Y0 050 -20100 -60

X Y

 0 0

100 50

PROCVAR

'P1'

BOOSTER FANS 

Booster Fan B

Inlet Guide Vanes

Booster Fan C

Inlet Guide Vanes

8-1 (C6)

MFT Impulse

8-1 (D6)

Booster Kicker

8-1 (D6)

FD Feed Forward

FD Feed Forward

Booster Fan A MFT Impulse

IGV Position
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 1-2

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

LDGAIN12

FX12A

DIV12

WEPVA

DIV12A

LDLAG12

CYTDATR12D

KS12C

CYHDATR12C

CYPACATR12B

NFPVATR12A

KS12C

KS12C

LIM12A

CASPT

PVDMD TLPVA

LIM12ASUM12A

KS12B

BI12A

E12B

SA12C SI12C SA12D SI12D

SA12A SI12A

SA12B SI12B

PV12B

E12A

PROCVAR

'PV12E'

PROCVAR

'PV12D'

'E12B'

'TR12C'

A

Coal AirTemperature

Pulverizer A 

Tempering Air Damper

CYHDA

'TR12D'

A

CYTDA

PROCVAR

'PV12B'

Pulverizer Bias

Feeder Demand

'SUM12A'

'TR12A'

NFPVA

A

K/S

'KS12B'

'TR12B'

A

CYPACA

Pulverizer A

Primary Air

Control Damper

Feeder A

Speed Control

'PV12C'

PROCVAR

'E12A'

BIAS

'BI12A'

f(x)

'FX12A'

K/S

'KS12C'

Pulverizer A

Hot Air Damper

'LIM12A'

> <

3-1 (A4)

Air Flow STPT

0

100

OUT

0 

B6

B6

B11

B11

B13

B13

5-2 (D2)

Temp Control

Output

Feeder A

REF : 

f(x)

'FXSPD2A'

f(x)

'FX108' f(x)

'FX104A'

f(x)

'FX104B'

~

1 + ks

'LDLAG12'

1 - 2s

'DIV12A'

B7

B2

A

B9

K

'K12'

PULVERIZER/COMPARTMENT A CONTROLS

Coal Air SetpointNormally 160 F

Pulverizer APA Air Flow

Typical For Pulverizer B-D
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 5-2

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

LH3B1

CYPAGCDBTRGID1

CYPAGCDATRGID

SA41D2 SI41D2

LH3B2KS7B1DIFB8

TLAHB

LH3B

SA41D1 SI41D1

KS7BDIFBC

LH3B

KS3BDIF3B

SETPA

MAXPA

KS12C KS42C

KS32C

KS22C

PROCVAR TLAHA

'TLAHA'

Primary Air

Heater A 

Air Out Temp 

'DIFB7'

1-2 (C6)

2-2 (C6)

3-2 (C5)

4-2 (C5)

Temp Control

Output

Feeder A

Temp Control

Output

Feeder B

Temp Control

Output

Feeder C

Temp Control

Output

Feeder D

>

'MAXPA'

'DIF3B' A

80%

K/S

'KS3B'

'LH3B'

> <

Integral Only

K/S

'KS7B'

'LH3B1'

> <

'TRGID'

A

PROCVAR

'TLAHB'

'DIFB8'

K/S

'KS7B1'

'LH3B2'

> <

'TRGID1'

A

Primary Air

Heater B

Air Out Temp 

CYPAGCDA

Primary Air Heater A 

Gas Inlet Damper

CYPAGCDB

Primary Air Heater B 

Gas Inlet Damper

B1

B3

B3

B3

B7

B7B7

B10

B10

B10

f(x)

'FX88'

f(x)

'FX87'

REF : FO

Hi Lim 600 FLo Lim 350 F

AIR HEATER INLET DAMPERS
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 6-2

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

CYPASO CYPASO 

LB101 LB102 LB100

CYPASO

RU190CV RU190CS

CYPASOC

RU190

CYPASOB

RU190BV RU190BS

CYPASOA

RU190AV RU190AS

'RU190A'

A

CYPASOA

Primary Air Shutoff 

Damper A

'RU190B'

A

CYPASOB

'RU190C'

A

CYPASOC

A

PROCVAR

'P11'

BIAS

'B100'

BIAS

'B101'

BIAS

'B102'

Primary Air Shutoff 

Damper B

Primary Air Shutoff 

Damper C

PRIMARY AIR SHUTOFF DAMPERS

Primary Air

Shutoff Damper

Setpoint
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 7-2

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

TLPJFF

MFTF

OR431

OR431

GENDMD

HIACT

IS431

OPENBYP

IS432 OPENINL

IS430

TRIP_ALL_

PEBF

LLIM BFLIM

LOWBFP

OR431

TRBF

OK_TO_TRIP

TRIP_ON_LOW_FURNACE

WAIT9

Ba

9-2 (C5) H/ 'SH431' MEM2

'OPENBYP'

OR

'OR431'

Temperature of

Flue Gas Leaving

Baghouse 

Reset

MEM2

'OPENINL'

Set 

> 345 F

MEM2

Reset 'OPENBYP1'

/L

'BFL'

PROCVAR

'P721'

PROCVAR

'P722'

f(x)

'FX2'

Load-Based Trip (Normally Disabled)

BF InletPressure

ADAPT

'ADP'

OR

'OR432' 6-1 (B5) 'A821' A

ND

Low Furnace Pressure MFT

Unit Load X Y

30 -9.4100 -22.1

PROCVAR

'P2'

BAGHOUSE DAMPERS
1

1

22

33

44

55

66

A 

B C D Prepared byMG

Drawing No.EA0711.02 - 01 - 002 page 1-3

Date18 Sep 2007

No. Date By Description

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 1 Furnace Draft AnalysisControls Model - Proposed Configuration 

ONBFT

PLDWB

WAIT11

TRIP_ALL_BF

FDB_TRP

FDA_TRP

PLDWA

TLSAHA

HI31A

TLSAHB

HI31B

HI31D

TRFD

FDA_TRP_PB

FDB_TRP_PB

HI31C ONBFT

PROCVAR

'PV31A'

Secondary Air A DuctPressure

PROCVAR

'PV31B'

Secondary Air A Temp

H/

'HI31A'

> +47.7 inwc

H/

'HI31B'

> 620 F

OR

'OR31A'

FD Fan A tripped

PROCVAR

'PV31C'

Secondary Air B DuctPressure

PROCVAR

'PV31D'

Secondary Air B Temp

H/

'HI31C'

> +47.7 inwc

H/

'HI31D'

> 620 F

OR

'OR31B'

FD Fan B tripped

PROCVAR

'PV31E'

FD Fan A Operator TripPROCVAR

'PV31F'

FD Fan B Operator Trip

'AD1'

AND

f(t) pu

'DL1' 7-2 (C7)

15 s

Trip all Booster FansFrom Baghouse Dampers

FD FAN TRIPS
2. VALIDATION RUNS 

The Unit 1 Validation Runs contain the following graphs: 

• Furnace Pressure 

• Windbox Pressure 

• Coal Flow 

• Secondary Airflow 

• FD Fans Discharge Pressure 

• PA Fans Discharge Pressure 

• Economizer Oxygen 
Furnace Pressure

-5

0

+5

+10+15+20+25

0 10 20 30 40 50 60 70 80 90 1

Time (seconds)

Pressure (inwc)

Model FURNACE PRESS
Windbox Pressure

0

+5

+10+15+20+25

0 10 20 30 40 50 60 70 80 90 1

Time (seconds)

Pressure (inwc)

Model WINDBOX PRESS
Coal Flow

0

20406080

100120140

0 10 20 30 40 50 60 70 80 90 1

Time (seconds)

Flow (kpph)

Model (per pulverizer) COAL FEEDER 1A FLOW COAL FEEDER 1B COAL FEEDER 1C FLOW COAL FEEDER 1D FLOW
Secondary Airflow

0

200400600800

1000120014001600

0 10 20 30 40 50 60 70 80 90 1

Time (seconds)

Flow (kpph)

Model (Draught Side A) SEC AIR FLOW 1A SEC AIR FLO
FD Fans Discharge Pressure

0

+5

+10+15+20+25

0 10 20 30 40 50 60 70 80 90 1

Time (seconds)

Pressure (inwc)

Model FD FAN 1A DISCH PRESS FD FAN 1B DISCH PRESS
PA Fans Discharge Pressure

0

+10+20+30+40+50+60+70+80+90

0 10 20 30 40 50 60 70 80 90 1

Time (seconds)

Pressure (inwc)

Model PA FAN 1A DISCH PRESS PA FAN 1B DISCH PRESS
Economizer Oxygen

05

10152025

0 10 20 30 40 50 60 70 80 90 10

Time (seconds)

0

2 (percent)

Model Model with filtering ECON FLUE 1A OXYGEN ECON FLUE 1B O
3. TRANSIENT RUNS 

Transient No. 1: “Full Load MFT” contains the following graphs: 

• Transient Max/Min Pressure Profile (Unmitigated) 

• Unit Pressures (Unmitigated) 

• Baghouse and Scrubber Pressures (Unmitigated) 

• Flows (Unmitigated) 

• Fan Inlet Guide Vanes (Unmitigated) 

• Fan Speeds (Unmitigated) 
Full Load MFT (Unmitigated)

Transient Max/Min Pressure Profile

+2.9

+14.9

+7.5

0.0 

-3.8 -3.4

+1.5

+9.9

+16.7

+22.8

+21.3

+14.8

+6.1

+0.1

 -0.7

+1.9

 -13.2 -14.4

 -4.8 -3.6 -1.7 -1.9 -1.2

+6.8

+9.9

+18.8 +16.8

-40-30-20-10

0

+10+20+30+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Windbox FurnaceEconomizer Outlet Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet Scrubber 

Pressure (inwc)

Maximum Minimum
Full Load MFT (Unmitigated)

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load MFT (Unmitigated)

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load MFT (Unmitigated)

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load MFT (Unmitigated)

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load MFT (Unmitigated)

Fan Speeds

0

200400600800

100012001400

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
Transient No. 2: “Full Load All Booster Fans Trip” contains the following graphs: 

• Transient Max/Min Pressure Profile (Unmitigated) 

• Unit Pressures (Unmitigated) 

• Baghouse and Scrubber Pressures (Unmitigated) 

• Flows (Unmitigated) 

• Fan Inlet Guide Vanes (Unmitigated) 

• Fan Speeds (Unmitigated) 

• Mitigated Transient Max/Min Pressure Profile 

• Mitigated Unit Pressures 

• Mitigated Baghouse and Scrubber Pressures 

• Mitigated Flows 

• Mitigated Fan Inlet Guide Vanes 

• Mitigated Fan Speeds 

• Furnace Pressure Comparison 

• Transient Max/Min Pressure Profile Comparison 
Full Load All Booster Fans Trip (Unmitigated)

Transient Max/Min Pressure Profile

+13.9

+16.9

+23.1

+29.2

+30.5

+24.9

+18.6

+14.6

+9.0

+8.3

0.0

+17.6

+14.9

+2.9

+20.4 +18.5

+12.1

+9.2

+1.8 +1.4 +1.2 +0.4 +0.1

 -9.5 -11.0

+1.4

 -0.8 

-40-30-20-10

0

+10+20+30+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Windbox FurnaceEconomizer Outlet Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet Scrubber 

Pressure (inwc)

Maximum Minimum
Full Load All Booster Fans Trip (Unmitigated)

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load All Booster Fans Trip (Unmitigated)

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load All Booster Fans Trip (Unmitigated)

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load All Booster Fans Trip (Unmitigated)

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load All Booster Fans Trip (Unmitigated)

Fan Speeds

0

200400600800

100012001400

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
Mitigated Full Load All Booster Fans Trip

Transient Max/Min Pressure Profile

+10.7

+13.5

+20.3

+27.3

+28.8

+22.4

+15.1

+11.4

+6.2

+5.5

0.0

+14.2 +14.9

+2.9

+0.5 +0.4 +0.2 +0.2 -0.0 -0.1 -0.2 -0.3 -0.3

 -9.5 -11.0

 -0.5 -0.8 

-40-30-20-10

0

+10+20+30+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Windbox FurnaceEconomizer Outlet Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet Scrubber 

Pressure (inwc)

Maximum Minimum
Mitigated Full Load All Booster Fans Trip

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Mitigated Full Load All Booster Fans Trip

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Mitigated Full Load All Booster Fans Trip

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Mitigated Full Load All Booster Fans Trip

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Mitigated Full Load All Booster Fans Trip

Fan Speeds

0

200400600800

100012001400

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
Full Load All Booster Fans Trip

Furnace Pressure Comparison

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

Furnace (Unmitigated) Furnace with FD Fan Trip (Mitigated)
Full Load All Booster Fans Trip

Transient Max/Min Pressure Profile Comparison

+2.9

+14.9

+17.6

0.0

+8.3 +9.0

+14.6

+18.6

+24.9

+30.5

+29.2

+23.1

+16.9

+13.9

+6.2 +5.5

+10.7 +11.4

+13.5 +15.1 +14.2

+20.3

+22.4

+27.3 +28.8

-40-30-20-10

0

+10+20+30+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Windbox FurnaceEconomizer Outlet Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet Scrubber 

Pressure (inwc)

Maximum (Unmitigated) Maximum with FD Fan Trip (Mitigated)
Transient No. 3: “Full Load Both FD Fans Trip” contains the following graphs: 

• Transient Max/Min Pressure Profile (Unmitigated) 

• Unit Pressures (Unmitigated) 

• Baghouse and Scrubber Pressures (Unmitigated) 

• Flows (Unmitigated) 

• Fan Inlet Guide Vanes (Unmitigated) 

• Fan Speeds (Unmitigated) 
Full Load Both FD Fans Trip (Unmitigated)

Transient Max/Min Pressure Profile

+0.1

+6.1

+14.7

+20.9

+22.4

+16.6

+9.9

+1.5

-4.2 -4.4

0.0

+7.5

+14.9

+2.9

 -0.3 -0.6 -2.4 -3.6

 -6.9 -7.2 -7.4 -7.7 -8.0 -9.5

 -11.0

+0.4

 -1.0 

-40-30-20-10

0

+10+20+30+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Windbox FurnaceEconomizer Outlet Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet Scrubber 

Pressure (inwc)

Maximum Minimum
Full Load Both FD Fans Trip (Unmitigated)

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load Both FD Fans Trip (Unmitigated)

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load Both FD Fans Trip (Unmitigated)

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load Both FD Fans Trip (Unmitigated)

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load Both FD Fans Trip (Unmitigated)

Fan Speeds

0

200400600800

100012001400

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
Transient No. 4: “Low Load Two Booster Fans Runaway” contains the following graphs: 

• Transient Max/Min Pressure Profile 

• Unit Pressures 

• Baghouse and Scrubber Pressures 

• Flows 

• Fan Inlet Guide Vanes 

• Fan Speeds 
Low Load Two Booster Fans Runaway (Unmitigated)

Transient Max/Min Pressure Profile

+2.0

+18.7

+1.7

0.0 

-3.5

-3.0

+0.0

+2.2 +4.1

+5.8 +5.4 +3.6

+1.3 -0.4

+0.2

+6.7

 -11.3 -12.1

 -6.8 -7.3 -4.5 -5.0 -3.7

 -1.6 -2.2 +0.2 -0.2

-40-30-20-10

0

+10+20+30+40

Ambient

FD Fan Outlet

SAH Air Inlet

SAH Air Outlet

Windbox

Furnace

Economizer Outlet

Precip Outlet

SAH Gas Outlet

Baghouse Inlet

Baghouse Outlet

Booster Fan Inlet

Booster Fan Outlet

Scrubber 

Pressure (inwc)

Maximum Minimum
Low Load Two Booster Fans Runaway (Unmitigated)

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Low Load Two Booster Fans Runaway (Unmitigated)

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Low Load Two Booster Fans Runaway (Unmitigated)

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Low Load Two Booster Fans Runaway (Unmitigated)

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Low Load Two Booster Fans Runaway (Unmitigated)

Fan Speeds

0

200400600800

100012001400

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
Transient No. 5: “Full Load All Fans Trip” contains the following graphs: 

• Transient Max/Min Pressure Profile (Unmitigated) 

• Unit Pressures (Unmitigated) 

• Baghouse and Scrubber Pressures (Unmitigated) 

• Flows (Unmitigated) 

• Fan Inlet Guide Vanes (Unmitigated) 

• Fan Speeds (Unmitigated) 
Full Load All Fans Trip (Unmitigated)

Transient Max/Min Pressure Profile

+0.2

+6.1

+14.7

+20.9

+22.4

+16.6

+9.9

+1.5 -0.7 -0.7 

0.0

+7.5

+14.9

+2.9

+0.0 -0.0 -0.5 -0.9

 -3.3 -3.6 -3.7 -4.0 -4.1

 -9.5 -11.0

 -0.6 -1.1 

-40-30-20-10

0

+10+20+30+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Windbox FurnaceEconomizer Outlet Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet Scrubber 

Pressure (inwc)

Maximum Minimum
Full Load All Fans Trip (Unmitigated)

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load All Fans Trip (Unmitigated)

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load All Fans Trip (Unmitigated)

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load All Fans Trip (Unmitigated)

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load All Fans Trip (Unmitigated)

Fan Speeds

0

200400600800

100012001400

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
Transient No. 6: “Full Load Single Booster Fan Trips” contains the following graphs: 

• Transient Max/Min Pressure Profile (Unmitigated) 

• Unit Pressures (Unmitigated) 

• Baghouse and Scrubber Pressures (Unmitigated) 

• Flows (Unmitigated) 

• Fan Inlet Guide Vanes (Unmitigated) 

• Fan Speeds (Unmitigated) 

• Mitigated Transient Max/Min Pressure Profile 

• Mitigated Unit Pressures 

• Mitigated Baghouse and Scrubber Pressures 

• Mitigated Flows 

• Mitigated Fan Inlet Guide Vanes 

• Mitigated Fan Speeds 

• Furnace Pressure Comparison 

• Transient Max/Min Pressure Profile Comparison 

 
Full Load Single Booster Fan Trips (Unmitigated)

Transient Max/Min Pressure Profile

+11.5

+17.4

+25.9

+33.6 +32.1

+27.8

+21.1

+12.9

+2.2

+0.2 

0.0

+18.8

+30.0

+3.5

+22.4 +20.9

+16.6

+14.7

+9.9 +7.5 +6.1

+1.5 +0.1

 -9.5 -11.0

+14.9

+1.7

-40-30-20-10

0

+10+20+30+40

Ambient

FD Fan Outlet

SAH Air Inlet

SAH Air Outlet

Windbox

Furnace

Economizer Outlet

Precip Outlet

SAH Gas Outlet

Baghouse Inlet

Baghouse Outlet

Booster Fan Inlet

Booster Fan Outlet

Scrubber 

Pressure (inwc)

Maximum Minimum
Full Load Single Booster Fan Trips (Unmitigated)

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 50 100 150 200 2

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load Single Booster Fan Trips (Unmitigated)

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 50 100 150 200 2

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load Single Booster Fan Trips (Unmitigated)

Flows

0

100020003000400050006000700080009000

10000

0 50 100 150 200 2

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load Single Booster Fan Trips (Unmitigated)

Fan Inlet Guide Vanes

0

102030405060708090

100

0 50 100 150 200 2

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load Single Booster Fan Trips (Unmitigated)

Fan Speeds

0

200400600800

100012001400

0 50 100 150 200 2

Time (seconds)

Speed (rpm)

FD Fans Booster Fan A Booster Fans B & C
Mitigated Full Load Single Booster Fan Trips

Transient Max/Min Pressure Profile

+3.2

+28.0

+15.4

0.0 

-0.6 +1.0

+10.3

+17.4

+23.4

+28.9 +27.5

+21.7

+14.2

+9.1

+0.9

+12.3

 -9.7 -11.0

 -3.4 -4.2

 -0.8 +1.2 -0.1

+3.6 +4.5 +7.3 +6.6

-40-30-20-10

0

+10+20+30+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Windbox FurnaceEconomizer Outlet Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet Scrubber 

Pressure (inwc)

Maximum Minimum
Mitigated Full Load Single Booster Fan Trips

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 50 100 150 200 2

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Mitigated Full Load Single Booster Fan Trips

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 50 100 150 200 2

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Mitigated Full Load Single Booster Fan Trips

Flows

0

100020003000400050006000700080009000

10000

0 50 100 150 200 2

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Mitigated Full Load Single Booster Fan Trips

Fan Inlet Guide Vanes

0

102030405060708090

100

0 50 100 150 200 2

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Mitigated Full Load Single Booster Fan Trips

Fan Speeds

0

200400600800

100012001400

0 50 100 150 200 2

Time (seconds)

Speed (rpm)

FD Fans Booster Fan A Booster Fans B & C
Full Load Single Booster Fan Trips

Furnace Pressure Comparison

-40-30-20-10

0

+10+20+30+40

0 50 100 150 200 2

Time (seconds)

Pressure (inwc)

Furnace (Unmitigated) Furnace with Load Runback (Mitigated
Full Load Single Booster Fan Trips

Transient Max/Min Pressure Profile Comparison

+11.5

+17.4

+25.9

+32.1 +33.6

+27.8

+21.1

+12.9

+2.2

0.0 +0.2

+18.8

+30.0

+3.5

+1.0

+9.1

+28.9 +27.5

+23.4

+21.7

+17.4 +15.4

+14.2 +10.3

+28.0

+3.2 

 -0.6

-40-30-20-10

0

+10+20+30+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Windbox FurnaceEconomizer Outlet Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet Scrubber 

Pressure (inwc)

Maximum (Unmitigated) Maximum with Load Runback (Mitigated)
Transient No. 7: “Full Load Baghouse Cleaning System Failure” contains the following graphs: 

• Transient Max/Min Pressure Profile (Unmitigated) 

• Unit Pressures (Unmitigated) 

• Baghouse and Scrubber Pressures (Unmitigated) 

• Flows (Unmitigated) 

• Fan Inlet Guide Vanes (Unmitigated) 

• Fan Speeds (Unmitigated) 
Full Load Baghouse Cleaning System Failure (Unmitigated)

Transient Max/Min Pressure Profile

+1.7

+7.7

+16.5

+22.8

+24.3

+18.4

+11.5

+3.1

-9.5

-11.0

0.0

+9.1

+15.5

+3.0

+21.7 +20.3

+16.1

+14.3

+9.5

+7.3 +5.9

+1.4 -0.1

 -13.2 -14.7

+14.7

+2.8

-40-30-20-10

0

+10+20+30+40

Ambient

FD Fan Outlet

SAH Air Inlet

SAH Air Outlet

Windbox

Furnace

Economizer Outlet

Precip Outlet

SAH Gas Outlet

Baghouse Inlet

Baghouse Outlet

Booster Fan Inlet

Booster Fan Outlet

Scrubber 

Pressure (inwc)

Maximum Minimum
Full Load Baghouse Cleaning System Failure (Unmitigated)

Unit Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load Baghouse Cleaning System Failure (Unmitigated)

Baghouse and Scrubber Pressures

-40-30-20-10

0

+10+20+30+40

0 20 40 60 80 1

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load Baghouse Cleaning System Failure (Unmitigated)

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load Baghouse Cleaning System Failure (Unmitigated)

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load Baghouse Cleaning System Failure (Unmitigated)

Fan Speeds

0

200400600800

100012001400

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
4. LETTER REPORT 

Letter Report—EA-0817-0101 contains the following sections: 

• Introduction 

• Model Construction 

• Model Validation 

• Future Configuration Model 

• Initial Conditions 

• Transient Testing: MT2 Full Load All Booster Fans Trip – Delayed FD Trip 

• Transient Testing: MT2A Full Load All Booster Fans Trip – Immediate FD Trip 

• Results 

• Transient Events Summary Table 

• Conclusions and Recommendations 
PNM, San Juan Generating Station Units 1 & 2 Page 1 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Letter Report 

To: Public Service Company of New Mexico/The Babcock and Wilcox Company 

From: Satish Perivilli/TRAX LLC

Date: 4 March 2008

Subject: San Juan Generating Station Units 1 & 2/Furnace Draft Analysis

Introduction

TRAX, LLC has been retained by The Babcock and Wilcox Company (B&W) to perform a 

furnace draft analysis for Units 1 & 2 of Public Service Company of New Mexico’s (PNM) San 

Juan Generating Station. This study analyzed the effect of ductwork and equipment changes 

related to the addition of environmental equipment. These modifications included the addition of 

a baghouse and related ductwork, the replacement of existing booster fans with new upgraded 

booster fans, and the redirection of all the flue gas flow through the baghouse, the booster fans, 

and the scrubbers before entering the stack. The study was based on the assumption that San 

Juan Generating Station Units 1 and 2 are identical in construction and operation. 

The primary goal of this study was to determine the effects of these plant modifications on 

pressures and flows throughout the furnace draft system during normal and abnormal operation. 

To accomplish this, TRAX built a model of the existing process and control system for San Juan 

Station Unit 1. This model was validated against plant data and then modified to represent the 

future plant configuration by adding the new equipment and making the corresponding changes 

to the controls model. The future configuration model was then tested through seven severe 

transients. The results of these transient runs were presented in Preliminary Report EA0711-

0102 dated December 12, 2007. 

During the transient runs, the existing controls did not trip the forced draft (FD) fans during a 

booster fan trip, which led to high furnace pressure during the transient. To mitigate this furnace 

pressure excursion, TRAX suggested tripping the FD fans based on high furnace pressure 

following a booster fan trip and resulting master fuel trip (MFT). During discussion between 

members of the project team, the merits of immediately tripping the FD fans vs. a delayed trip 

were discussed. It was agreed that a single transient should be tested to compare a delayed FD 

fan trip against an immediate FD fan trip. The transient selected to test these alternative control 

strategies was the “Full Load All Booster Fans Trip” transient. This letter report presents the 

results of these transient runs. 
PNM, San Juan Generating Station Units 1 & 2 Page 2 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Model Construction

The dynamic model representing San Juan Station Unit 1 consisted of a process model, which 

simulated the existing process configuration; and a controls model, which was built from a 

subset of existing plant controls. TRAX prepared the process model based on drawings provided 

by PNM and discussions with plant personnel. The process and control model configuration 

drawings were reviewed by B&W and PNM. The model was parameterized to a full load 

steady-state condition based on plant data provided from Unit 1. 

Model Validation

Validation is the process of comparing steady-state and dynamic model predictions with plant 

data. The process and controls models were run to high (360 MW) and low (200 MW) load 

steady-state conditions, and the results were compared with plant data. The model was then run 

through an MFT transient similar to one that occurred at the plant and the dynamic data 

generated by the model was compared to the dynamic plant data. The steady state and transient 

comparisons were documented and presented to PNM and B&W in Preliminary Report EA0711-

0102 dated December 12, 2007. 

Future Configuration Model

The validated process and control system models were then modified to reflect the plant 

configuration with the new equipment. These modifications included: 

• Addition of a baghouse and related controls 

• Replacement of existing booster fans with new upgraded booster fans 

• Related ductwork changes 

• Elimination of bypass flow directly to the stack. All flue gas flow from the air heaters 

will pass through the new baghouse, new booster fans, and scrubbers before reaching the 

stack 

A schematic diagram of the proposed plant configuration is shown in Figure 1. 

Figure 1 Proposed Plant Configuration 

Flue Gas from 

Primary Air 

Heaters 

Flue Gas from 

Secondary Air 

Heaters 

Baghouse 

Booster Fan A

Booster Fan B

Booster Fan C

Scrubber A 

Scrubber B 

Scrubber C 

Stack
PNM, San Juan Generating Station Units 1 & 2 Page 3 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Initial Conditions

The transient run was initiated with the model at a full load, steady-state condition, with all 

pressures, flows, temperatures, and controlled variables constant. The full load, steady-state 

pressure profile for this initial condition is shown in Figure 2. 

Figure 2 Initial Condition Pressure Profile for Full Load 

Transient Testing: MT2 Full Load All Booster Fans Trip – Delayed FD Trip

This full load transient run (MT2) tripped all of the booster fans, but delayed the FD fan trip for 

20 seconds. After that delay, a high furnace pressure FD fan trip was enabled and would be 

triggered if furnace pressure rose above +15 inwc. 

This transient consisted of the following steps and control actions: 

• Initialized the model to the 100% load condition 

• Ran the model for 10 seconds to establish steady-state conditions 

• Tripped all three operating booster fans, immediately causing an MFT and the following 

associated control actions: 

− Froze FD inlet guide vanes at their current position 

− Tripped pulverizers and their feeders 

− Shut coal valves 

− Tripped, shut off, and isolated primary air (PA) fans 
PNM, San Juan Generating Station Units 1 & 2 Page 4 of 13 

Letter Report—EA-0817-0101 3/4/2008 

− Closed hot air, tempering air, and primary air control dampers 

− Booster fan IGV demand is controlled by a kicker circuit for 15 seconds after the 

initiation of the MFT. Control of the IGVs is then transferred to a runback controller 

through the end of the transient 

− Waited 20 seconds following the MFT, then enabled the +15 inwc high furnace 

pressure FD fan trip 

• All controls remained in auto throughout the transient 

The model was run for 120 seconds and data was saved. Results are presented below. 

Transient Testing: MT2A Full Load All Booster Fans Trip – Immediate FD Trip

This full load transient run (MT2A) tripped all of the booster fans and immediately tripped all 

FD fans. The transient consisted of the following steps and control actions: 

• Initialized the model to the 100% load condition 

• Ran the model for 10 seconds to establish steady-state conditions 

• Tripped all three operating booster fans, immediately causing an MFT and the following 

associated control actions: 

− Froze FD inlet guide vanes at their current position 

− Tripped pulverizers and their feeders 

− Shut coal valves 

− Tripped, shut off, and isolated PA fans 

− Closed hot air, tempering air, and primary air control dampers 

− Booster fan IGV demand is controlled by a kicker circuit for 15 seconds after the 

initiation of the MFT. Control of the IGVs is then transferred to a runback controller 

through the end of the transient 

− Tripped the FD fans immediately 

• All controls remained in auto throughout the transient 

The model was run for 120 seconds and data was saved. Results are presented below. 
PNM, San Juan Generating Station Units 1 & 2 Page 5 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Results

Figure 3 shows a comparison of the furnace pressures for the MT2 and MT2A runs. At 10 

seconds, an MFT occurred and fuel was shut off to the furnace. The resulting fireball collapse 

caused a sharp drop in furnace pressure. Pressure for the MT2A run continued to drop as the FD 

fans were immediately tripped and reduced mass flow into the furnace. Furnace pressure for run 

MT2A eventually reached a minimum of -3.3 inwc. Conversely, pressure for the MT2 run began 

to rise at about 20 seconds as the FD fans continued to run and pressurize the furnace. 

Eventually, furnace pressure rose above +15 inwc at about 60 seconds and the FD fans tripped. 

Furnace pressure for both transients then trended to ambient as the FD fans spun down. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

MT2 Furnace MT2A Furnace 

Figure 3 T2 Furnace Pressure Comparison
PNM, San Juan Generating Station Units 1 & 2 Page 6 of 13 

Letter Report—EA-0817-0101 3/4/2008 

 

Figure 4 shows system pressures for the two runs. Pressures at the FD fan discharge and air 

heater gas outlet followed predicable paths as the transient proceeded. Pressures for the MT2 run 

initially dropped due to the MFT, and then increased as the FD fans continued to push air into 

the draft system. The pressure plots remained approximately the same distance apart until 60 

seconds, indicating a relatively constant flow of air into the system. Pressures dropped after 60 

seconds as the fans tripped and spun down. 

Pressures for the MT2A run, with the immediate FD fan trip, also followed expected paths as 

they quickly dropped as the fireball collapsed due to the MFT. The pressures then trended 

together and approached ambient as the booster and FD fans spun down. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

MT2 FD Discharge MT2 Furnace MT2 Air Heater Gas Outlet

MT2A FD Discharge MT2A Furnace MT2A Air Heater Gas Outlet

Figure 4 T2 Unit Pressures 
PNM, San Juan Generating Station Units 1 & 2 Page 7 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Figure 5 shows the guide vane position for the booster and FD fans. For both transients, the FD 

fan vane positions were frozen in place after the trip at 10 seconds, and so remained constant 

throughout both runs. 

The booster fan guide vanes were used to control pressure at the regenerative air heater gas 

outlet. Plots of the booster fan guide vane positions showed an initial steep ramp downward as 

the kicker circuit reduced the guide vane position immediately after the booster fan trip. At 

about 18 seconds, the two plots diverged due to the differences in air heater gas outlet pressure 

for the two runs (see Figure 4). At 25 seconds, the kicker circuit was released and control of the 

booster fan guide vanes was transferred to the runback controller, which attempted to control 

furnace pressure at +1 inwc. After 25 seconds, furnace pressure was only slightly negative for 

transient MT2A (since the FD fans had already tripped), so the booster fan guide vanes only 

needed to increase to about 25% to bring furnace pressure back to setpoint. For transient MT2, 

after the release of the kicker circuit, the booster fan guide vanes ramped full open in an attempt 

to control furnace pressure, which had steadily risen above +10 inwc. After the FD fans tripped 

at 60 seconds, furnace pressure began to decrease, and the booster fan guide vane positions 

decreased. 

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120

Time (seconds)

Position (percent open)

MT2 FD Fans MT2 Booster Fans

MT2A FD Fans MT2A Booster Fans

MT2 FD Fans and MT2A FD Fans are identical

Figure 5 T2 Fan Inlet Guide Vane Positions 
PNM, San Juan Generating Station Units 1 & 2 Page 8 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Figure 6 shows the FD and booster fan speeds during this transient. For both runs, the booster 

fans tripped at 10 seconds and immediately began coasting down. The FD fans tripped at 10 

seconds during transient MT2A, and immediately begin coasting down; whereas during run 

MT2, the FD fans did not trip until 60 seconds and then began coasting down. 

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100 120

Time (seconds)

Speed (rpm)

MT2 FD Fans MT2 Booster Fans

MT2A FD Fans MT2A Booster Fans

Figure 6 T2 Fan Speeds 
PNM, San Juan Generating Station Units 1 & 2 Page 9 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Figure 7 shows back end pressures at the baghouse, booster fan, and scrubber. Pressures for run 

MT2A were consistent with the other plots as pressures trended towards ambient immediately 

after the FD and booster fan trips. The pressures for run MT2 also trended as expected, slowly 

rising until 60 seconds when the FD fans tripped and system pressures slowly dropped down to 

ambient. 

-40

-30

-20

-10

0

+10

+20

+30

+40

0 20 40 60 80 100 120

Time (seconds)

Pressure (inwc)

MT2 Baghouse Inlet MT2 Booster Fan Inlet MT2 FGD Inlet

MT2A Baghouse Inlet MT2A Booster Fan Inlet MT2A FGD Inlet

Figure 7 T2 Baghouse and Scrubber Pressures 
PNM, San Juan Generating Station Units 1 & 2 Page 10 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Figure 8 shows the system flows during this transient. Flows for run MT2A dropped off 

immediately as the FD and booster fans tripped and spun down. Furnace and FGD flows 

dropped more sharply due to the MFT, while the FD fan flow dropped more slowly as flow was 

still being transported by the decelerating fans. For run MT2, FD flow initially increased due to 

the lower pressure in the furnace after the MFT. Flows at the back end initially dropped due to 

the kicker circuit, then increased after the kicker circuit released. Flows steadied out until about 

60 seconds, at which time the FD fans tripped and flows slowly decreased as pressures dropped 

to ambient. 

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 20 40 60 80 100 120

Time (seconds)

Flow (kpph)

MT2 Total FD Fans MT2 Furnace Exhaust MT2 Total FGD Inlet

MT2A Total FD Fans MT2A Furnace Exhaust MT2A Total FGD Inlet

Figure 8 T2 Flows 
PNM, San Juan Generating Station Units 1 & 2 Page 11 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Figure 9 shows the maximum pressures experienced during these two transients at various points 

in the flue gas path. As expected, front end pressures for run MT2A were lower, as the FD fans 

had tripped. Back end pressures for the two runs were similar, as the booster fans tripped in both 

cases. Note that draft system pressures for either of the transients as shown in Figure 9 do not 

necessarily occur at the same time. 

0.0

+28.8 +27.3

+22.4

+20.3

+15.1 +14.2 +13.5

+11.4 +10.7

+6.2 +5.5

+14.9

+2.9

 -0.3

 -4.6

0.0

+22.4 +20.9

+16.6

+14.7

+9.9

+7.5 +6.1

+1.5 +0.2 -0.7

+14.9

 -0.7 -0.5

-40

-30

-20

-10

0

+10

+20

+30

+40

Ambient

FD Fan Outlet

SAH Air Inlet

SAH Air Outlet

Windbox

Furnace

Economizer Outlet

Precip Outlet

SAH Gas Outlet

Baghouse Inlet

Baghouse Outlet

Booster Fan Inlet

Booster Fan Outlet

Scrubber Outlet

Stack Base

Top of Stack

Pressure (inwc)

Maximum with MT2 Maximum with MT2A

Figure 9 T2 Transient Maximum Pressure Profile 
PNM, San Juan Generating Station Units 1 & 2 

Letter Report—EA-0817-0101 

Transient Events Summary Table

A summary of the maximum and minimum pressures at various locations in the system are shown in Tapressures are unfiltered values. Note that the pressures in any row do not necessarily occur at the same ti

Furnace 

Pressure 

(inwc) 

Air Heater 

Gas Outlet 

Duct (inwc)

B

No. Transient Name In

No. of 

Booster 

Fans in 

Service

Gross 

Load 

% Min Max Min Max M

MT2 Full Load All Booster Fans Trip – Delayed FD Trip 3 100 -0.0 +15.1 -0.3 +11.4 -1

MT2A Full Load All Booster Fans Trip – Immediate FD Trip 3 100 -3.3 +9.9 -4.0 +1.5 -1

Table 1 Transient Event Summary Table 
PNM, San Juan Generating Station Units 1 & 2 Page 13 of 13 

Letter Report—EA-0817-0101 3/4/2008 

Conclusions and Recommendations

Based on this transient analysis, the following conclusions can be made: 

• The delayed trip of the FD fans results in a furnace pressure that reached a positive value 

of +15.1 inwc. 

• By immediately tripping the FD fan, high positive furnace pressures were avoided, but a 

furnace pressure minimum of -3.3 inwc was experienced. 

• Tripping the FD fans immediately upon loss of all booster fans is in compliance with a 

strict interpretation of the NFPA guidelines. 
PPuubblliicc SSeerrvviiccee CCoommppaannyy ooff NNeeww MMeexxiiccoo 

SSaann JJuuaann GGeenneerraattiinngg SSttaattiioonn UUnniittss 33 && 44 

IImmpplloossiioonn SSttuuddyy 

 

 

FFIINNAALL RREEPPOORRTT 

 

 

Prepared for: 

The Babcock & Wilcox Company 

P.O. NO.: BAX067843 

 

 

 

Report Number EA0624-0301

July 10, 2007 
Public Service Company of New Mexico 

San Juan Generating Station Units 3 & 4 

Implosion Study 

FINAL REPORT

Prepared for: 

The Babcock & Wilcox Company 

P.O. NO.: BAX067843 

Report Number EA0624-0301

Prepared by: 

Kent Kozak, Senior Engineer 

TRAX, LLC 

107 Vista Centre Drive Forest, VA 24551 

Voice: (434) 385-7250, Ext. 228 Fax: (434) 385-8233 

Email: kmkozak@traxcorp.com

Approved by: 

 Gregory M. Kosowski, Vice President

Prepared by: 

Kent Kozak, Senior Engineer 

TRAX, LLC 

107 Vista Centre Drive Forest, VA 24551 

Voice: (434) 385-7250, Ext. 250 Fax: (434) 385-8233 

Email: kmkozak@traxcorp.com

Approved by: 

 Gregory M. Kosowski, Vice President
TRAX shall not be liable for any losses or for damages resulting from the use of any information, 

apparatus, method, or process disclosed in this report. 

Copyright © TRAX, LLC, 2007. All rights reserved. 

ProTRAX is a trademark of TRAX, LLC. 

All other brand and product names are trademarks or registered 

 trademarks of their respective companies. 

 
PNM, San Juan Generating Station Units 3 & 4 Page i of iii 

Implosion Study – Final Report 7/10/2007 

Project Number EA0624

TABLE OF CONTENTS 

LIST OF APPENDICES ................................................................................................... I

EXECUTIVE SUMMARY ................................................................................................ II

1.0 INTRODUCTION.................................................................................................. 1

2.0 NOMENCLATURE ............................................................................................... 3

3.0 DYNAMIC MODEL CONSTRUCTION ................................................................. 4

4.0 VALIDATION OF EXISTING CONFIGURATION MODEL................................... 7

5.0 TRANSIENT EVENT TESTING.......................................................................... 14

6.0 CONCLUSIONS................................................................................................. 24

 LIST OF APPENDICES 

APPENDIX A Model Process Schematics 

APPENDIX B Model Control Schematics 

APPENDIX C Validation Results 

APPENDIX D Full Load MFT 

APPENDIX E Full Load All Booster Fans Trip 

APPENDIX F Full Load Both FD Fans Trip 

APPENDIX G Low Load Two Booster Fans Runaway 

APPENDIX H Full Load All Fans Trip 
PNM, San Juan Generating Station Units 3 & 4 Page ii of iii 

Implosion Study – Final Report 7/10/2007 

Project Number EA0624 

EXECUTIVE SUMMARY 

TRAX, LLC has been retained by The Babcock & Wilcox Company (B&W) to perform an 

implosion study for San Juan Generating Station Units 3 and 4. This study analyzed the effect of 

ductwork and equipment changes related to the addition of a baghouse. Model simulation 

performed as part of this study predicted the behavior of the units in their future configuration, 

and determined the extent of furnace and ductwork pressure excursions through several severe 

transient events. 

In the initial phase of this project, the project team analyzed plant data to determine the 

differences between Units 3 and 4. Following this analysis, the team agreed that the two units 

are almost identical. For the purposes of this report, all references to Unit 4 apply equally to 

Unit 3. 

After determining a single unit was sufficient to represent both Units 3 and 4, a model of the 

current plant configuration for Unit 4 was built. The plant model was validated against plant 

data to ensure accuracy and to establish a baseline for the investigation of the subsequent flue gas 

desulphurization (FGD) changes. The validation effort consisted of running the Unit 4 model 

through a severe transient similar to one previously experienced at the plant, and comparing the 

model results to historical plant data. The results from this validation were delivered in 

Validation Report EA0624-0401, dated November 6, 2006. 

Following the validation of the Unit 4 current configuration model, ductwork was modified and 

emission controls equipment was added to represent the plant in its future configuration. These 

modifications included addition of a baghouse, replacement of existing booster fans with new 

upgraded booster fans, removal of the existing stack dampers and air heater gas outlet to stack 

breaching ducts, and de-energizing (but not removing) the existing hot-side precipitator. The 

future configuration model was then tested through five severe transients. 

TRAX implemented the basic proposed control logic for the new environmental equipment as 

provided by PNM. This control logic was then enhanced by tuning the controllers and adding 

mitigating measures to improve the control system performance and protect the equipment 

during pressure excursions. 

The results obtained during the study are summarized below: 

• The controls as designed were able to mitigate all negative furnace pressure excursions to 

within -11 inwc. 

• During transient testing, pressure excursions downstream of the flue gas outlet of the air 

heaters were within +25 inwc and -20 inwc. 

• The “Full Load Both FD Fans Trip” transient caused the lowest furnace pressure 

excursions. During this transient, furnace pressures decreased to -10.3 inwc. 

• The lowest booster fan inlet duct pressures measured were during the “Full Load MFT” 

transient. The inlet pressure dropped to -19.9 inwc during this transient. 
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• The highest pressure excursions occurred during the “Full Load All Booster Fans Trip” 

transient. Following the booster fans trip, the lack of exhaust capability caused furnace 

pressure to rise to +24.8 inwc, and booster fan inlet pressure to rise to +21.0 inwc. 

Tripping both forced draft (FD) fans on a high furnace pressure limit following the 

master fuel trip (MFT) easily mitigated the high pressures. 

• During a full load MFT, the quick adjustment of booster fan inlet guide vanes via the 

kicker circuit prevented an additional 7 inwc of furnace pressure excursion. 

• Holding the booster fan kicker circuit for 20 seconds during an MFT promoted stable, 

over-dampened process and control behavior during furnace pressure recovery. 

• The overriding booster fan runback controller was responsible for limiting the furnace 

pressure excursion to only -3.2 inwc during the “Low Load Two Booster Fans Runaway” 

transient. 

Based on the results of the transient runs, TRAX recommends the following control strategies 

and mitigating measures be implemented in the future plant configuration controls: 

1. During normal operation, the booster fan inlet guide vanes should be controlled by a 

feed-forward signal from the FD inlet guide vanes, added to a trim control that monitors 

air heater gas outlet pressure. 

2. For mitigating MFT events, a kicker circuit should be used to immediately run back 

booster fan inlet guide vanes. 

3. An overriding booster fan runback controller should be used to help mitigate negative 

furnace pressure excursions during MFT and fan transients. 

4. During an MFT, if both booster fans are tripped, both FD fans should be tripped if the 

furnace pressure exceeds a high furnace pressure limit. This will help prevent overpressurizing the furnace. 

5. Should the booster fan runback controller fail to mitigate a booster fan runaway event, 

the controls should trip the fan. One such measure would be to trip the booster fans on a 

load-indexed, low booster fan inlet pressure. 

The model construction, validation, transient testing, results, and conclusions are detailed in the 

following report. The transient analysis modeling selected as described in this report was used to 

estimate the magnitude of possible events. Some of the cases modeled are worst-case scenarios 

that have a low probability of occurrence. This report does not attempt to predict the likelihood 

of any of these events occurring. 
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1.0 INTRODUCTION 

TRAX, LLC has been retained by The Babcock & Wilcox Company to perform an implosion 

study for San Juan Generating Station Units 3 and 4. This study analyzed the effect of proposed 

plant modifications related to the addition of a new baghouse. These modifications included 

addition of a baghouse, replacement of existing booster fans with new upgraded booster fans, 

removal of the existing stack dampers and air heater gas outlet to stack breaching ducts, and deenergizing (but not removing) the existing hot-side precipitator. 

The primary goals of the study were to help answer the following questions: 

1. What is the impact of the process modifications on furnace and ductwork pressure 

excursions during normal and abnormal plant operation? 

2. How does the proposed control system design behave during severe pressure excursions? 

3. What, if any, corrective actions are necessary? 

The approach used in this study consisted of the following basic steps: 

1. Compare data for Units 3 and 4 to determine if a single model would be sufficient to 

represent both units. 

2. A dynamic model of Unit 4 in its existing configuration was constructed and validated 

against historical plant data. 

3. A baghouse was added, booster fans were upgraded, and ductwork was modified to 

represent the plant in its future configuration. 

4. The future configuration model was run through selected transients, and pressure 

excursions in the furnace and ductwork were recorded. 

5. The results were analyzed, and mitigating measures designed to minimize pressure 

excursions were identified and tested. 

The existing furnace draft system for San Juan Unit 4 was modeled using ProTRAX, a 

commercially available dynamic simulation system. The ProTRAX system is based on modular 

components, allowing interconnecting of modules representing furnaces, fans, dampers, ducts, 

etc., into any physically realistic configuration. All of the module formulations are based on 

first-principle conservation relations, the Second Law of Thermodynamics, and well-established 

constitutive relations for heat transfer and fluid mechanics. The resulting executable models are 

operated from a graphics-based environment that provided extensive capability for controlling 

the models and displaying the results in various formats. 

A workgroup with representatives from Babcock & Wilcox, Sargent and Lundy (S&L), and 

TRAX selected a total of five transients to be tested with the new plant configuration. The goal 

was to identify conditions that would create large pressure excursions in the furnace and 

ductwork. Each transient consisted of an initial event followed by the response of the controls, 

which could eventually lead to a master fuel trip and/or individual fan trips. The transients 

selected for the study are shown below in Table 1. 
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No. Transient Name 

1 Full Load MFT 

2 Full Load All Booster Fans Trip 

3 Full Load Both FD Fans Trip 

4 Low Load Two Booster Fans Runaway 

5 Full Load All Fans Trip 

Table 1 List of Transients 

This report describes the results of these transient runs. 
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2.0 NOMENCLATURE 

The naming convention used throughout this report is described below: 

 

1st Quadrant Fan Operation 

Fan operation where the fan has flow in the direction of fan suction to discharge, with a 

discharge pressure greater than the suction pressure. Operation in this region is governed 

by manufacturers fan curves (developed head versus volumetric flow). 

2nd Quadrant Fan Operation 

Flow through the fan has reversed and is now from discharge to suction. Head is positive 

with the discharge pressure greater than the suction pressure. In this quadrant the fan is 

acting as a resistance with flow from higher (discharge) to lower (suction) pressure. 

Operation in this region starts at the fan dead head pressure (zero flow) and is based on 

an assumed flow resistance. Fan operation in the 2nd quadrant typically occurs during fan 

trips or other equipment malfunctions. 

4th Quadrant Fan Operation 

Flow is in the direction of fan suction to discharge with a discharge head less than the 

suction head (i.e., the pressure drops across the fan rather than rising). Operation in this 

region is governed by the run out portion of the fan curve and assumed flow resistance 

behavior. Typically, fan operation in the 4th quadrant occurs during a fan trip. 

MFT 

Master fuel trip (MFT) is the procedure in which all fuel to the furnace is completely shut 

off. 

Water Seal Venting 

Water seal venting refers to the water seal at the bottom of the furnace. At sufficiently 

low furnace pressure (-19 inwc below ambient), the water seal can rupture allowing 

ambient air into the furnace. This additional flow of ambient air into the furnace will 

help minimize any negative furnace pressure transient. 
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3.0 DYNAMIC MODEL CONSTRUCTION 

3.1 Existing Configuration Model 

The dynamic model representing San Juan Unit 4 consisted of a process model, which simulated 

the existing process configuration; and a controls model, which was built from a subset of 

existing plant controls. 

TRAX prepared the process model based on drawings provided by PNM, a plant walkdown, and 

discussions with plant personnel. The process and control model configuration drawings were 

reviewed and approved by B&W, S&L, and PNM. 

During the initial phase of the project, the project team compared process and controls data for 

both Unit 3 and Unit 4. It was determined, during the comparison of data between the units, that 

there were only subtle differences between the overall process and controls systems for Units 3 

and 4. The team determined that a single model would be sufficient to accurately represent the 

two units as they are almost identical. For the purposes of this report all references to Unit 4 

apply equally to Unit 3. 

3.1.1 Existing Configuration Process Model 

The process model for each of the units included the following components: 

• Air path through and including FD fans, air heaters, and furnace 

• Fuel (coal) and primary air path including PA fans, pulverizers, and feeders 

• Flue gas path from the furnace including superheaters, reheaters, economizer, air 

preheater, and stack 

• Pollution control systems including precipitator and FGD equipment 

As the focus of the study involved relatively fast furnace pressure transients, slower steam-side 

components, such as steam drums and desuperheaters, were not modeled. Only the metal mass 

for the walls and heated surfaces was modeled, along with the energy stored in the metal during 

the transient. 

Centrifugal fan operation was modeled by incorporating the actual fan head curves. In addition, 

shutdown flow effects (4th quadrant behavior) were simulated and combined the run-out portion 

of the fan curve, and assumed flow resistance behavior. 

Pulverized coal (PC) combustion was simulated in the furnace. Coal combustion was 

represented as a two-stage reaction, with the first stage being the rapid devolatilization of the 

coal particles, and the second stage being the combustion of the remaining coal char. Char 

combustion was a function of temperature, particle size, and availability of oxygen. The amount 

and size of the char particles would strongly affect the rate of fireball collapse during a fuel trip. 

The furnace calculated the exiting flue gas composition based on the rate and chemistry of 

combustion and furnace leakage. 
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3.1.2 Existing Configuration Control Model 

Note that only those portions of the controls that affected any of the final control elements in the 

model were included in the control system simulation. Control loops for the existing 

configuration plant model included: 

• Secondary air duct pressure 

• Primary air heater (PAH) air outlet pressure 

• Secondary airflow 

• Economizer excess air 

• Fuel flow 

• Pulverizer coal air temperature 

• Pulverizer primary airflow 

• Stack flue gas temperature 

• Master fuel trip 

3.2 Future Configuration Model 

3.2.1 Future Configuration Process Model 

The proposed future configuration process model included all of the components in the San Juan 

process models, plus the proposed emission control equipment. Modifications to represent the 

future configuration included: 

• Addition of a baghouse 

• Replacement of existing booster fans with new upgraded booster fans 

• Removal of the existing stack dampers and air heater gas outlet stack breeching ducts 

• De-energizing (but not removing) the existing hot-side precipitator 

Parameterization data for the new process equipment such as fan head curves, vessel volumes, 

pressure drops, etc. was based on proposed design information provided by B&W, S&L, and 

PNM. 

3.2.2 Future Configuration Control Model

The control logic for the new equipment included various control loops for the booster fans. In 

the booster fan control loop, an error signal was calculated by comparing the air heater gas outlet 

duct pressure to a setpoint, which remained constant for all loads. The controller output was then 

added to a characterized feed-forward signal, which was developed from the FD fan inlet guide 

van demand. The total was then used to adjust booster fan inlet guide vane demand. A 

functional diagram of this control loop is shown in Figure 1. 
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Figure 1 Booster Fan Inlet Guide Vane Controls 

This control scheme also included overriding controllers to protect the furnace and associated 

ductwork. The booster fan runback controller superseded any booster fan demand by adjusting 

booster fan inlet guide vane to maintain a -1 inwc furnace pressure. Either of the following 

activated the override: 

• A MFT was in progress for at least five seconds and the booster fan kicker circuit was 

completed 

• A MFT was not in progress and the furnace pressure had dropped below -1 inwc 
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4.0 VALIDATION OF EXISTING CONFIGURATION MODEL 

Model validation is the process of running the model through a transient and comparing the data 

produced by the model to data gathered from the plant for a similar transient event. 

There are three basic steps to validating a dynamic model for an implosion study: 

1. Configure and parameterize the process model at full load 

2. Run the model to a lower load and compare to plant data 

3. Compare model to plant data during a severe transient 

These steps must be completed in the above order, as each step is dependent upon the successful 

completion of the previous step. All three steps involve a comparison of model output with plant 

data, and the combination of all three comparisons result in a high level of confidence that the 

model provides reliable predictions for current and future plant configurations. 

The following sections describe the steps used for the validation of the San Juan Unit 4 model. 

 

Step 1: Configure and Parameterize Model at Full Load

Each furnace draft component in the plant was simulated and connected in the same 

configuration as the plant using ProTRAX modules. Where there are parallel components in the 

plant, such as FD fans, each fan was modeled separately to ensure any effects of multiple 

component operations were incorporated in the study. This was the “configuration” process. 

The physical characteristics of each component were input through fill-in-the-blank forms in the 

modeling system. This included data such as damper sizes, fan head curves, and physical 

dimensions of ducts, stacks, and vessels. This was the “parameterization” process. The 

parameterization process also included operating data based on a full load heat balance 

performed by TRAX using plant data, manufacturer’s heat balances, discussions with plant 

personnel, and visual observations during the plant walkdown. Where plant data was not 

available, such as pressure profiles through the convection pass of the furnace, estimates of 

pressure drops were made based on the physical drawings showing tube densities, flow cross 

sectional areas, and gas temperatures. Plant data itself is generally not sufficient due to 

instrumentation errors and unavailable signals. Therefore, the full load heat balance data comes 

from plant and design data, and is adjusted to ensure mass and energy balance. 

At this point, the model had the three requirements of a high-fidelity model: 

• Module equations were based on conservation of mass, energy, momentum, and wellaccepted correlations for heat transfer and mass flow. 

• The configuration of the model was the same as the plant for the scope under consideration. 

• The physical characteristics of each component were programmed into the corresponding 

modules. 
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Model parameterization was performed at full load, as most design data was available at that 

point and not at other points. Also, at full load most plant equipment is in service and is 

operating at a substantial load where losses and inefficiencies play a minor role in the 

component’s performance. 

The full load model was run at steady-state for several minutes and tested for stability and 

accuracy. That is, the model was initialized to full load conditions, and then allowed to run to 

equilibrium. If properly parameterized, the model should show little or no movement from the 

parameterization point and should come to a solid, steady state in just a few seconds. Since all 

the module equations calculate an absolute heat balance at steady-state, any deviations from the 

full load conditions by the model are immediately obvious and indicate an error in 

parameterization of the model. If there are instabilities, the model will not reach a smooth 

steady-state, and the model must be corrected. 

In this case, at the full load steady-state point the San Juan Unit 4 model was immediately stable 

and no further corrections were required. Critical parameters for the full load steady-state are 

listed in Table 2. 

Parameter Plant Data Model Unit 

Gross Load 550 550 MW 

Load Level 100 100 Percent 

Coal Flow Rate 552 552 kpph 

Number of Mills Grinding 6 6 

Total Secondary Airflow 4,400 4,400 kpph 

Total Compartmental Airflow 3,700 3,700 kpph 

Pulverizer Airflow (per mill) 190 190 kpph 

FD Fan Discharge Pressure 30 30 inwc 

PA Fan Discharge Pressure 74 74 inwc 

Secondary Air Heater Air Outlet Pressure 25 25 inwc 

Primary Air Heater Air Outlet Pressure 70 70 inwc 

Secondary Air Duct Pressure 23 23 inwc 

Furnace Pressure 10.2 10.1 inwc 

Secondary Air Heater Gas Outlet Pressure 0.7 0.5 inwc 

Economizer Gas Outlet Temperature 704 696 Degree F 

Table 2 Unit 4 Critical Plant Parameters at Full Load (100%)

Having demonstrated a reliable, stable match to the plant data at full load, the San Juan Unit 4 

model was ready to run to the lower load condition. 

Step 2: Run Model to Lower Load and Compare to Plant Data

The control system was used to run the plant model to a lower load. The model was tested at this 

lower load for stability and accuracy. Typically, the primary causes of variations at this point are 

the following: 

1. Missing, incomplete or erroneous data for full load parameterization 

2. Different operation of the model compared to the plant 
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3. Fouling and soot buildup on various surfaces that alter pressure distribution 

4. Significantly different conditions at the plant during the low load compared to the full 

load data set (e.g., winter versus summer operation) 

For Unit 4, the low load data available from the plant was at 300 MW. All the control setpoints 

were applied as observed from the historian data for a 54.5% load. The number of mills 

operating was reduced from six to four, excess oxygen trim percentage was increased from 

2.03% to 6.3%, and the model was run to a steady-state. A comparison of model and plant 

parameters for the lower load steady state is shown in Table 3. 

Parameter Plant Data Model Unit 

Gross Load 300 300 MW 

Load Level 54.5 54.5 Percent 

Coal Flow Rate 341 341 kpph 

Number of Mills Grinding 4 4 

Total Secondary Airflow 3,400 3,320 kpph 

Total Compartmental Airflow 2,500 2,500 kpph 

Pulverizer Airflow (per mill) 186 186 kpph 

FD Fan Discharge Pressure 22 23 inwc 

PA Fan Discharge Pressure 72 72 inwc 

Secondary Air Heater Air Outlet Pressure 19 20 inwc 

Primary Air Heater Air Outlet Pressure 70 70 inwc 

Secondary Air Duct Pressure 18 19 inwc 

Furnace Pressure 5.0 4.0 inwc 

Secondary Air Heater Gas Outlet Pressure 0.1 -0.7 inwc 

Economizer Gas Outlet Temperature 570 587 Degree F 

Table 3 Unit 4 Critical Plant Parameters at Low Load (54.5%)

The Unit 4 model was stable and accurate at low load condition, and no further actions were 

required. 

Step 3: Compare Model to Plant Data/Historical Data During Severe Transient

The first two steps in the validation process addressed the steady-state characterization and 

operation of the model. The third step addresses the dynamic behavior. Step 3 cannot begin 

without the successful completion of the first two steps. The third step is the focus and essence 

of the validation report, and is therefore described in more detail than the previous two steps. 

It is important to select a transient for validation that is both severe enough to test the model, yet 

has only one cause. In most cases, a master fuel trip (MFT) is the best choice providing that the 

trip was not caused by a component failure in the gas path such as a fan or damper. Multiple 

failures make it more difficult to identify and duplicate the actual driving forces on the plant and 

the model. 

To perform the validation, the model was first moved to a steady-state operating point consistent 

with the plant data for the selected event. The control system was again used to run the plant 

model to this load, and the model was allowed to reach a steady-state. A short run of ten seconds 

was made at the beginning of the transient to show that the models were at the proper steady-
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state. The MFT was initiated and all known plant variables, (i.e. damper positions, feeder 

speeds, etc.) were maneuvered by the control system to mimic plant movements as closely as 

possible based on the available plant data. 

The primary variable of interest in model validation was the furnace pressure. The model 

furnace pressure was compared to plant furnace pressure for a period of one minute. In 

comparing the model response to the plant, the criterion was the time required for the furnace 

pressure to reach a minimum, the magnitude of the minimum, and the rate of decrease of the 

furnace pressure. The most important factors that affected results were: 

• Timing and speed of fuel shutoff to the furnace 

• Control of airflow to the furnace 

A significant level of effort was invested to assure the timing of movement for the burner coal 

valves, fan inlet vane position, and the shutdown of pulverizers, PA fans, and feeders were 

duplicated as closely as possible. 

4.1.1 Unit 4 Initial Conditions 

PNM provided TRAX with plant historian data for an MFT at 98% load. The MFT occurred 

May 4, 2006 at 11:39 a.m. Although the historian data had a five second sampling rate, TRAX 

identified that in every 15 seconds of data, two measurements were identical, leading to the 

conclusion that the data was actually recorded at 10 second intervals. TRAX took this into 

account during the model validation, by tuning the model to produce a slightly more 

conservative estimate of system pressures during the transient. The larger the time span between 

recorded data, the more likely stored data missed the furnace pressure minimum. 

Critical plant parameters for the 98% load at the beginning of the MFT are listed in Table 4. 

Parameter Plant Data Model Unit 

Gross Load 539 539 MW 

Load Level 98 98 Percent 

Coal Flow Rate 524 526 kpph 

Number of Mills Grinding 6 6 

Total Secondary Air Flow 4,300 4,300 kpph 

Total Compartmental Airflow 3,400 3,500 kpph 

Pulverizer Airflow (per mill) 193 195 kpph 

FD Fan Discharge Pressure 28.0 27.5 inwc 

PA Fan Discharge Pressure 72 74 inwc 

Secondary Air Heater Air Outlet Pressure 24 23 inwc 

Primary Air Heater Air Outlet Pressure 70 70 inwc 

Secondary Air Duct Pressure 21 21 inwc 

Furnace Pressure 9.6 9.4 inwc 

Secondary Air Heater Gas Outlet Pressure 0.8 0.4 inwc 

Economizer Gas Outlet Temperature 670 691 Degree F 

Table 4 Unit 4 Critical Plant Parameters at Validation Point (98% Load) 
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At steady-state conditions, a pressure profile plot for the air/gas path from the FD fan inlet to the 

stack outlet was generated for Unit 4, and compared with the available historian data for the 

validation case. Model pressure profile at validation condition for Unit 4 is shown in Figure 2. 

Figure 2 Unit 4 Pressure Profile at Validation Conditions (98% Load)

4.1.2 Unit 4 MFT Procedure 

During the MFT, the following control elements were driven as described based on historian data: 

• All pulverizers, associated feeders and both PA fans were tripped 

• Burner coal valve for all pulverizers were closed 

• Primary air shutoff and control dampers for each pulverizer were closed 

• Hot air dampers were closed and tempering air dampers were opened fully 

• All secondary air dampers were locked in place 

• FD fan inlet vanes were frozen in place 

• Booster fan inlet guide vane control remained in manual 
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4.1.3 Unit 4 Validation Parameters 

To validate the models, TRAX selected several critical parameters that were measured and 

archived in plant data. The model results were then compared to plant historical data for the 

selected MFT. The following measured values were selected for comparison: 

• Furnace pressure 

• Total secondary airflow 

• FD fan discharge pressure 

• Primary air heater air outlet pressure 

4.1.4 Unit 4 Validation Results 

Validation comparisons of the ProTRAX Unit 4 model versus plant data are shown in Appendix C. 

Furnace Pressure

The Unit 4 model was initialized to the validation condition load (536 MW) and allowed to run 

for ten seconds to ensure steady-state operation. At 10 seconds, an MFT was initiated by 

tripping all pulverizers, associated feeders and both PA fans. As a result of the MFT, controls 

instantaneously closed the PA shutoff dampers, PA control dampers, burner coal valves, 

pulverizer hot air dampers, and opened the tempering air damper fully for each pulverizer. 

Although all dampers in the primary air path associated with each pulverizer were closed, it was 

the fast acting burner coal valve (with a 14 second stroke time) that decided the magnitude and 

the timing of furnace pressure minimum. 

Upon loss of the PA fans, the amount of pulverized coal being transported to the burners began 

to drop rapidly due to the decreasing primary airflow. When the burner coal valves closed 

completely at 24 seconds, the fireball collapsed and furnace pressure dropped to its minimum of 

+1.9 inwc. The furnace then began to respond to the additional air flowing in, and consequently 

furnace pressure began to increase and recovered to +5.6 inwc by 80 seconds. 

The furnace pressure plot illustrates that the furnace pressure minimum predicted by the model 

was +1.4 inwc lower than the corresponding plant measurement. However, from the shape of the 

plant data curves, it is likely that the minimum furnace pressure occurred between recorded 

measurements and was likely lower than 3 inches. 

Total Secondary Airflow

Prior to the master fuel trip, 4,300 kpph of secondary air was flowing into the furnace through 

overfire air dampers and six windbox compartments. Following the MFT, the controls froze 

both FD fan inlet vanes and all secondary air dampers in place. The drop in furnace pressure 

increased the differential pressure between the FD fans and the furnace, which led to an increase 

in the secondary airflow up to a maximum of 5,110 kpph by 26 seconds. As the system 

pressures stabilized, the secondary airflow dropped slightly to a steady value of approximately 

5,000 kpph. This increased airflow helped the furnace pressure recover from its minimum. The 

Total Secondary Airflow plot shows a close match in shape, magnitude, and timing between the 

model and plant data. 
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FD Fan Discharge Pressure

Prior to the MFT, the FD fans were controlling secondary air duct pressure at +21 inwc and 

hence the FD fan discharge pressure was steady at +27.5 inwc. Upon initiation of the MFT, the 

controls locked both FD fan inlet vanes and all secondary air dampers in place. The 7.5 inwc 

drop in furnace pressure resulting from the MFT only caused a 1.0 inwc drop in FD fan 

discharge pressure because of the resistance of the secondary air heaters and secondary air 

dampers. As the furnace pressure recovered, the FD fans discharge pressure reached a steady 

value of +29.2 inwc by 50 seconds. The FD Fans Discharge Pressure plot illustrates a close 

match between the model and the plant historian data. 

Primary Air Heater Air Outlet Pressure 

The PA fan inlet dampers were controlling the primary air heater air outlet pressure at +70 inwc 

before the MFT was triggered. Immediately following the MFT, the controls tripped both PA 

fans and locked both PA fan inlet dampers in place. This caused the primary air heater air outlet 

pressure to drop from +70 inwc to +35.8 inwc by 80 seconds. The plot of primary air heater 

outlet pressure in Appendix C shows a close match between the model and historian data. 

4.3 Validation Conclusion 

A dynamic model of the San Juan Unit 4 furnace draft process equipment was constructed. 

Controls were installed on the process model consistent with existing plant logic. The models 

were tested for both steady state and dynamic accuracy. Dynamic testing consisted of running 

the model through a severe furnace pressure excursion, and comparing the model-generated data 

to plant historian data. This comparison showed that the model data matched both the timing 

and magnitude of the plant data to a high degree of accuracy. Therefore, the San Juan Unit 4 

model is considered sufficiently accurate to provide a meaningful basis for further draft analysis. 

Note that the model can also provide excellent relative results, which are particularly important 

in the planned study. 
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5.0 TRANSIENT EVENT TESTING 

This section describes the transient testing procedure and analyzes the results of that testing in 

detail. 

5.1 Initial Conditions 

All transient runs were initiated with the model at a steady-state condition, with all pressures, 

flows, temperatures, and controlled variables constant. While there were five transient events 

tested during this phase, there were only two unique initial conditions. 

• 100% Load – Unit 4 was operating at base load with 7 pulverizers active. Three booster 

fans were in operation. 

• 30% Unit – Unit 4 was operating at 30% load with 2 pulverizers active. Two booster 

fans were in operation. 

Critical parameters for the initial conditions listed above are shown in Table 5. Figures 3 and 4 

graphically show the steady-steady pressure profiles. 

Parameter 100% 

Load

30% 

Load Unit 

Gross Load 550 165 MW 

Load Level 100 30 Percent 

Coal Flow Rate 552 191 kpph 

Number of Mills Grinding 6 2 

Total Secondary Airflow 4,401 2,107 kpph 

Economizer Oxygen 5.5 9.2 % Vol 

Pulverizer Airflow (Per Mill) 190 197 kpph 

FD Fan Discharge Pressure 30.0 16.6 inwc 

PA Fan Discharge Pressure 73.9 70.7 inwc 

Secondary Air Heater Air Outlet Pressure 25.0 15.4 inwc 

Primary Air Heater Air Outlet Pressure 70.0 70.0 inwc 

Secondary Air Duct Pressure 23.0 15.0 inwc 

Furnace Pressure 9.6 1.9 inwc 

Secondary Air Heater Gas Outlet Pressure 0.0 0.0 inwc 

Baghouse Differential Pressure 11.6 2.5 inwc 

Number of Booster Fans in Service 3 2 

Booster Fan Pressure Rise 33.6 9.3 inwc 

Booster Fan Inlet Guide Vane Position 100 29 Percent 

 Table 5 100% and 30% Load Initial Condition Parameters 
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Figure 3 100% Load Initial Condition Pressure Profile 

Figure 4 30% Load Initial Condition Pressure Profile 
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5.2 Transient Events 

To evaluate the performance of the plant in its new configuration and with the new control logic, 

as described in Section 3.2.1 “Future Configuration Process Model” and Section 3.2.2 “Future 

Configuration Control Model,” five transients were run and the results analyzed. The goal in 

selecting the transients was to define conditions that would create large pressure excursions in 

the furnace and ductwork. Transient descriptions for each of the five runs are listed in Table 6. 

No. Transient name Unit Load Description 

1 Full Load MFT 100% With the unit at full load, an MFT is initiated manually. 

All controls remain in auto. 

2 Full Load All Booster Fans Trip 100% With the unit at full load, all three-booster fans trip 

and immediately trigger an MFT. 

3 Full Load Both FD Fans Trip 100% 

With the unit at full load, both FD fans trip and 

immediately initiate an MFT. All three booster fans 

will runback, but no booster fans will be tripped. 

4 Low Load Two Booster Fans 

Runaway 30% With the unit at low load, the inlet guide vanes on both operating booster fans ramp open. 

5 Full Load All Fans Trip 100% 

With the unit at full load, an electrical bus failure 

causes all fans to trip. An MFT is immediately 

initiated. All controls remain in auto. 

Table 6 Transient Descriptions 

Transient results are shown in Appendices D through H. Among the plots shown for each 

transient is a graphical profile of maximum and minimum pressure measurements at various 

positions along the air-gas path. Points on each maximum and minimum profile did not 

necessarily occur at the same time. 

5.2.1 Full Load MFT 

This transient consisted of the following steps: 

• Initialize the model to the 100% load condition, as shown in Figure 3 

• Run the model for five seconds to establish steady-state conditions 

• Manually initiate an MFT 

• All controls remain in auto throughout the transient 

Transient results are presented in Appendix D. 

Unit 4

At five seconds an MFT was initiated on Unit 4. Rapid fuel shutoff via burner coal valves led to 

a quick fireball collapse. Eleven seconds following the MFT, the furnace pressure dropped 11.1 

inwc to a minimum value of -1.7 inwc. Furnace pressure recovered to 2.0 inwc by 27 seconds, 

and slowly decreased to +1.2 inwc by the end of the transient. 
PNM, San Juan Generating Station Units 3 & 4 Page 17 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

At 5 seconds, the kicker circuit reduced the demand to the booster fan inlet guide vanes by 43%. 

The subsequent inlet guide vane movement brought about a 25% decrease in furnace exhaust 

flow. It is important to include the kicker circuit in the controls because without the kicker 

circuit movement of the booster fan inlet guide vanes, furnace pressure would have dropped 

another 7 inwc during the transient. 

To promote process stability, the kicker circuit was active for 20 seconds. The runback 

controller was tuned aggressively, and during initial testing, it was found that a kicker circuit 

duration less than 20 seconds caused oscillatory behavior during furnace pressure recovery. 

Holding the kicker circuit until after the completion of the fireball collapse and into the 

beginning seconds of furnace pressure recovery led to more stable over-dampened process 

response when the booster fan runback controller became active. 

During the MFT, the inlet guide vanes on the FD fans were held in place to maintain airflow to 

the furnace. FD fans were not tripped during the transient. 

It took roughly 11 seconds for the booster fan inlet guide vanes to close from 100% to 36%. For 

the remaining nine seconds of the kicker circuit, the kicker circuit demand remained constant 

with only a 1% adjustment of the booster fan inlet guide vanes from the air heater gas outlet 

pressure controller. 

At 25 seconds into the transient, the kicker circuit was released, and the booster fan runback 

controller attempted to maintain a +1 inwc furnace pressure. In the first two seconds of the 

transfer, the booster fan runback controller opened inlet guide vanes by 8% to 43%, keeping 

furnace pressure at about +2 inwc. The slope of the furnace pressure curve flattened near this 

point, and for the remainder of the transient, the runback controller gradually increased the 

booster fan inlet guide vane opening to bring furnace pressure to setpoint. 

Baghouse and Scrubbers

During the fireball collapse in Unit 4, baghouse inlet pressure decreased by 4.5 inwc, from -2.8 

inwc to -7.5 inwc. As furnace pressure rose following the fireball collapse, baghouse inlet pressure 

recovered to -4.1 inwc by 27 seconds. As the booster fan runback controller opened booster fan 

inlet guide vanes, pressure at the baghouse inlet gradually decreased to -8.5 inwc by 120 seconds. 

Booster fan inlet pressure rose 5.4 inwc during the fireball collapse as the rapid closing of 

booster fan inlet guide vanes results in a 2,230 kpph (or 35%) drop in flow through the fans. 

After 27 seconds, the booster fan runback controller opened booster fan inlet guide vanes, 

resulting in higher flows transported by the fans and a decrease in booster fan inlet pressure to 

-20 inwc by the end of the transient. 

The rapid closing of booster fan inlet guide vanes lessened furnace exhaust to limit the furnace 

pressure excursion, but caused a 35% drop in FGD inlet flow and a corresponding 11.7 inwc 

drop of FGD inlet pressure. This was the largest pressure excursion experienced during the MFT 

transient. From 16 to 25 seconds, the FGD inlet pressure remained nearly constant at +5.8 inwc 

while the booster fan inlet guide vanes were held near 36%. FGD inlet pressure increased to 

14.2 inwc by transient end as flows gradually rose through the scrubbers. 
PNM, San Juan Generating Station Units 3 & 4 Page 18 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

Mitigation

Though the results indicate no immediate need for mitigation, some measures may be taken to 

increase downstream pressures during MFT recovery. Either the setpoint of the furnace pressure 

runback control could be increased, or the control system could revert back to air heater gas 

outlet pressure control after 40 seconds. 

5.2.2 Full Load All Booster Fans Trip 

This transient consisted of the following steps: 

• Initialize the model to the 100% load condition, as shown in Figure 3 

• Run the model for five seconds to establish steady-state conditions 

• Manually trip all three operating booster fans 

• Immediately initiate an MFT 

• All controls remain in auto throughout the transient 

Transient results are presented in Appendix E. In order for pressures to come to a steady-state, 

this transient was conducted for a longer test period of 360 seconds. 

Unit 4

Following the trip of all three operating booster fans at five seconds, the controls immediately 

initiated an MFT. Furnace pressure dropped to +6.5 inwc, 8.2 inwc less change than that 

measured during the “Full Load MFT” transient. Tripping the booster fans increased pressures 

upstream of the booster fan, which helped to offset the fireball collapse. This can be seen in the 

air heater gas outlet pressure. In the “Full Load MFT” transient, the air heater gas outlet pressure 

had dropped to -6 inwc by 16 seconds, while in this transient, the air heater gas outlet pressure 

increased to +4 inwc over the same period. 

After the completion of the fireball collapse at roughly 17 seconds, the lack of furnace exhaust 

capability led to a furnace mass imbalance that caused furnace pressure to ramp up from +4.2 

inwc to +19.6 inwc by 60 seconds. 

After 120 seconds, as the imbalance between furnace airflow and exhaust became less, the rate 

of furnace pressure rise slowed. In the remaining 240 seconds of the transient, furnace pressure 

only increased an additional 3.4 inwc to +26.9 inwc. The +26.9 inwc furnace pressure was the 

highest measured during transient testing. 

Both FD fans remained in operation throughout the transient. However, the increase in 

downstream pressures led to a 33% drop in FD fan throughput by 90 seconds. From 4,000 kpph, 

flow continued a gradual decrease, reaching 57% of the initial flow, or 3,390 kpph, by 360 

seconds. 
PNM, San Juan Generating Station Units 3 & 4 Page 19 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

Baghouse and FGD

By 15 seconds, the trip of all booster fans, combined with the MFT kicker circuit movement of 

the booster fan inlet guide vanes, caused total FGD inlet flow to drop by 39% from 6,280 kpph to 

3,820 kpph. Following a 15 second, 500-kpph flow depression, FGD inlet flow decreased at a 

slower rate over the next 300 seconds and reached 3,320 kpph (50%) by the end of the transient. 

The decrease in flow through the FGD led to increasing pressures upstream of the booster fans. 

Baghouse inlet pressure increased from -2.8 inwc at the beginning of the transient to +24.8 inwc 

by transient end. Likewise, booster fan inlet pressure increased from -16 inwc to +21 inwc as 

flow through the fans decreased. 

Even though the booster fans had tripped, they were still able to transport flue gas for about 30 

seconds as they spun down from 890 to 330 rpm. As the fan speed decreased, the fans no longer 

put work into the flue gas, but instead became a resistive element. The fans eventually slowed 

down to about 65 rpm by 330 seconds. 

Mitigations

The high positive pressures measured throughout the process could be prevented by eventually 

following the booster fan trips with the tripping of both FD fans. In this transient, the tripping of 

all booster fans led to an immediate MFT. Mitigations that tripped FD fans following the MFT 

and after reaching a high furnace pressure limit were tested. Tripping following the MFT 

allowed airflow from the FD fans to at least partially purge combustibles throughout the fireball 

collapse and into furnace pressure recovery. For Unit 4, the controls should wait 20 seconds 

following an MFT prior to enabling a high furnace pressure trip of FD fans. For testing 

purposes, the FD fan trip limit was set to +15 inwc. The improvement in furnace pressure is 

shown on the Furnace Pressure plot. 

When this FD tripping scheme was tested, both FD fans were tripped at 38 seconds when the 

furnace pressure reached +15 inwc. The furnace pressure reached a maximum pressure of +15.3 

inwc, 11.7 inwc lower that without the FD fans trip. As shown in the transient maximum profile 

plot, improvements were observed on all pressures upstream of the scrubbers. 

5.2.3 Full Load Both FD Fans Trip 

This transient consisted of the following steps: 

• Initialize the model to the 100% load condition, as shown in Figure 3 

• Run the model for five seconds to establish steady-state conditions 

• Manually trip both operating FD fans 

• Immediately initiate an MFT 

• Inlet guide vanes on all booster fans were run back, but none of the booster fans tripped 

• All controls remain in auto throughout the transient 

Transient results are presented in Appendix F. 
PNM, San Juan Generating Station Units 3 & 4 Page 20 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

Unit 4

During the MFT, furnace pressure dropped from +9.6 inwc to -10.3 inwc, the lowest furnace 

pressure measured during transient testing, and 8.6 inwc lower than measured during the “Full 

Load MFT” transient. While the MFT booster fan kicker circuit reduced furnace exhaust flow 

by 2,000 kpph, any improvement to the furnace pressure excursion was offset by the tripping of 

both FD fans. Tripping the FD fans decreased flow to the furnace by 1,120 kpph. Despite the 

FD fans tripping, the controls were able to adjust the booster fan inlet guide vanes to keep 

furnace exhaust flow below total FD fan flow throughout the transient. This enabled furnace 

pressure to recover to 0 inwc following the fireball collapse. 

Though the FD fans tripped, the FD fans continued to transport air while coasting down 

throughout the transient, though at a decreasing flow rate. In the first 15 seconds following the 

FD fans trip, FD fan speed reduced 256 rpm to 453 rpm. Correspondingly, FD fan discharge 

pressure dropped from +30 inwc to +9.2 inwc. However, total FD fan flow only decreased by 

17% over the same period, and the slope of the total FD fan flow measurement flattened between 

10 and 16 seconds. The flattening slope was due to the collapse of the fireball lowering furnace 

pressure to maintain a 20 inwc differential between FD fans and furnace. As furnace pressure 

recovered following the completion of the fireball collapse at 18 seconds, the differential 

between FD fans and furnace dropped, aiding in a sharper decrease in total FD fan flow rate. 

Between 20 and 40 seconds, the FD fans coasted down another 153 rpm, which reduced FD fan 

flow by an additional 22% (or 1,650 kpph). During this period, total FD fan flow exceeded 

furnace exhaust by an average of roughly 800 kpph, which enabled the furnace pressure to 

recover to -1 inwc by 40 seconds. 

By the end of the transient, unit pressures were approaching +1 inwc as total FD fan flow and 

furnace exhaust flow were at 9% of the initial flows. FD fan speed decreased from 300 rpm to 

125 rpm over the last 80 seconds of the transient. 

Baghouse and Scrubbers

Immediately following initiation of the MFT, the kicker circuit reduced booster fan inlet guide 

vane demand by 64%. By 18 seconds, total FGD inlet flow reduced to approximately 50% of the 

initial flow. In turn, FGD inlet pressure dropped to +1.5 inwc, 16 inwc lower than that at the 

beginning of the transient. At the same time, pressure at the baghouse inlet dropped from -2.8 

inwc to -13.9 inwc, and booster fan inlet pressure dropped 2.7 inwc to -18.8 inwc. 

Following the conclusion of the fireball collapse at 18 seconds, the booster fan runback 

controller continued to close booster fan inlet guide vanes and decrease flow to the scrubbers. 

By 113 seconds, booster fan inlet guide vanes were fully closed with a total FGD inlet flow of 

550 kpph, roughly one-tenth of the starting total flow. 

Mitigations

During this transient, process pressures did not reach values that required additional control 

mitigations. 
PNM, San Juan Generating Station Units 3 & 4 Page 21 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

5.2.4 Low Load Two Booster Fans Runaway 

This transient consisted of the following steps, and the transient results are presented in 

Appendix G: 

• Initialize the model to the 30% load condition, as shown in Figure 4. Note that at low 

load only two booster fans are in operation. 

• Run the model for five seconds to establish steady-state conditions 

• Manually open the inlet guide vanes for the two operating booster fans 

• When the furnace pressure decreased below -1 inwc, the booster fan runback controller 

began to runback the inlet guide vanes on the two operating booster fans 

• When the furnace pressure dropped below -2 inwc for 3 seconds, a low furnace pressure 

MFT was initiated by the controls 

• All controls remain in auto throughout the transient 

Unit 4

At five seconds into the transient, the booster fan inlet guide vanes for operating Fan A and Fan 

B began to ramp open from 29%. This caused furnace exhaust flow to increase by 300 kpph, or 

roughly 10%. By 9 seconds, the imbalance in furnace draft caused furnace pressure to decrease 

below -1 inwc, triggering operation of the booster fan runback controller, which began to close 

the booster fans blades. Furnace pressure continued to drop until the minimum of -3.2 inwc was 

reached at 12 seconds. 

Furnace pressure stayed below -2 inwc for three seconds, which triggered a lower furnace 

pressure MFT. Because of the lower load and the booster fan runback controller actions, only a 

slight effect of the fireball collapse associated with MFT was observed in furnace pressure from 

13 to 20 seconds. By 60 seconds, the booster fan runback controller was able to maintain 

furnace pressure near its +1 inwc setpoint, and held it near setpoint for the remainder of the 

transient. 

Baghouse and FGD

During the booster fans runaway, total FGD inlet flow increased from 3,000 kpph to 4,140 kpph. 

This burst of flow caused FGD inlet pressure to rise 7.4 inwc to +13.2 inwc, and booster fan inlet 

pressure to decrease 7 inwc to -10.7 inwc. At nine seconds, the booster fan runback controller 

began to ramp back the inlet guide vanes on both booster fans. This decrease in booster fan inlet 

guide vane position dropped total FGD inlet flow to 1,470 kpph by 27 seconds. By the end of 

the transient, as the booster fan runback controller steadied inlet guide van adjustment, total flow 

to the FGD stabilized at 2,580 kpph and baghouse and booster fan inlet pressures approached 

pre-transient values. 

Because of the action of the booster fan runback controller, none of the FD or booster fans were 

tripped during this transient. 
PNM, San Juan Generating Station Units 3 & 4 Page 22 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

Mitigation

The booster fan runback controller overriding adjustment of the inlet guide vanes on all booster 

fans was critical to mitigating the furnace pressure excursion during this transient. After nine 

seconds into the transient, if the booster fan inlet guide vanes continued to ramp open, the 

negative furnace pressure excursion would have been more severe. The last line of defense for 

this transient was to trip the fan(s) that are running away. TRAX recommends using a booster 

fan-tripping scheme based upon low inlet duct pressure with a load-indexed limit. At 30% load, 

the booster fans could be tripped if fan inlet pressures dropped below -18 inwc. At higher loads, 

the trip limit would decrease, at lower loads the trip would increase. 

5.2.5 Full Load All Fans Trip 

This transient consisted of the following steps: 

• Initialize the model to the 100% load condition, as shown in Figure 3 

• Run the model for five seconds to establish steady-state conditions 

• Manually trip both operating FD fans, and all three operating booster fans 

• Immediately initiate an MFT 

• Controls continued to modulate the booster fan inlet guide vanes 

• All controls remain in auto throughout the transient 

Transient results are presented in Appendix H. 

Unit 4

During the MFT, furnace pressure dropped from +9.6 to -1.3 inwc, 0.5 inwc less excursion than 

measured during the “Full Load MFT” transient. The tripping of booster fans, combined with 

the action of the MFT kicker circuit, led to a 50% reduction in furnace exhaust flow by 20 

seconds. This large reduction in furnace exhaust helped to mitigate the effect of the fireball 

collapse. On the other hand, the loss of 35% of flow through the FD fans offset some of the 

change in furnace exhaust. However, the net flow favored airflow to the furnace, and furnace 

pressure recovered to +1 inwc by 60 seconds. By 120 seconds, the lack of airflow led furnace 

pressure to decrease back to ambient pressure. 

Baghouse and Scrubbers

Following the conclusion of the fireball collapse at 17 seconds, the runback furnace pressure 

controller adjusted booster fan inlet guide vanes, which reduced flow through the scrubbers. 

After 60 seconds, the controls gradually closed the booster fan inlet guide vanes, but all the fans 

had decelerated so that flows through the system had reduced. By the end of the transient, FGD 

inlet flow had decreased to roughly 12% of that measured at the start of the transient. 

Mitigations

During this transient, process pressures did not reach values that required additional control 

mitigation measures. 
PNM, San Juan Generating Station Units 3 & 4 Page 23 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

5.3 Transient Events Summary Table 

A summary of the unmitigated runs is shown in Table 7 below. 

Furnace 

Pressure 

(inwc) 

Airheater 

Gas Outlet 

Duct (inwc) 

Booster 

Fan Inlet 

(inwc) Case # Transient Name 

No. of 

Booster 

Fans in 

Service 

Gross 

Load

% 

Min Max Min Max Min Max

1 Full Load MFT 3 100 -1.7 +9.6 -6.1 0.0 -19.9 -10.4

2 Full Load All Booster Fans Trip 3 100 +6.5 +26.9 0.0 +24.8 -16.1 +21.0

3 Full Load Both FD Fans Trip 3 100 -10.3 +9.6 -13.1 +0.7 -18.9 +0.4

4 Low Load Two Booster Fans 

Runaway 2 30 -3.2 +2.0 -5.7 +0.6 -10.7 -0.7 

5 Full Load All Fans Trip 3 100 -1.3 +9.6 -2.7 +0.7 -16.1 -0.3 

Table 7 Unmitigated Transient Event Summary Table 

A summary of the mitigated run is shown in Table 8 below. 

Furnace 

Pressure 

(inwc) 

Airheater 

Gas Outlet 

Duct (inwc) 

Booster 

Fan Inlet 

(inwc) Case # Transient Name 

No. of 

Booster 

Fans in 

Service 

Gross 

Load

% 

Min Max Min Max Min Max

2 Full Load All Booster Fans Trip 3 100 -0.5 +15.3 -0.7 +11.9 -16.1 +6.1

Table 8 Mitigated Transient Event Summary Table
PNM, San Juan Generating Station Units 3 & 4 Page 24 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

6.0 CONCLUSIONS 

During transient testing, furnace pressures were held to within the range of +27 inwc to -11 inwc. 

Only the “Full Load All Booster Fans Trip” transient led to high furnace pressures, but tripping 

the FD fans easily mitigated the high +26.9 inwc measured at the furnace. The remaining 

transients led to negative furnace pressure excursions, with the most severe being -10.3 inwc 

measured during the “Full Load All FD Fans Trip” transient. 

Pressure excursions downstream of the flue gas outlet of the air heaters were within +25 inwc 

and -20 inwc. The rapid movement of booster fan inlet guide vanes to prevent furnace pressure 

excursions often caused sharp downstream pressure excursions. For example, during the “Full 

Load MFT” transient, furnace pressure changed by 11.1 inwc (from +9.6 inwc to -1.7 inwc). 

During the transient, closing booster fan inlet guide vanes by 64% reduced flow to the scrubbers 

and caused inlet pressure to the FGD to drop 11.7 inwc. 

The fast-adjusting booster fan inlet guide vanes were a key factor in moderating the furnace 

pressure drop associated with a MFT fireball collapse. On an MFT, controls closed burner 

shutoff valves that rapidly cut off fuel to the furnace and caused a sharp fireball collapse. With 

FD fan dampers frozen in place (per NFPA requirements), the only response available to the 

controls was to cut furnace exhaust by decreasing the flow transported by the downstream 

booster fans. The 17 second full stroke time of the booster fan inlet guide vanes enabled controls 

to reduce furnace exhaust by 20% in 10 seconds. This flow reduction prevented 7 inwc of 

additional furnace pressure excursion during the fireball collapse. 

Because the MFT fireball collapse was a short duration event, a kicker circuit was necessary to 

reduce the booster fan inlet guide vane position demand. At full load, the fireball collapse was 

complete 12 seconds after MFT initiation. The air heater gas outlet pressure controls alone were 

not fast enough to close booster fan inlet guide vanes to achieve the 20% reduction in furnace 

exhaust necessary to mitigate the MFT. Upon initiation of an MFT, a kicker circuit immediately 

reduced demand to the booster fan inlet guide vanes by 43%. This quick change in demand 

drove close booster fan inlet guide vanes sufficiently reduced furnace exhaust flow and held the 

furnace pressure excursion to -1.7 inwc during a full load MFT. 

A fast acting booster fan runback control was critical to mitigating the “Low Load Two Booster 

Fans Runaway” transient. When the furnace pressure dropped below -1 inwc, the booster fan 

runback controller overrode normal controls and adjusted booster fan inlet guide vanes to 

maintain +1 inwc furnace pressure. During the “Low Load Two Booster Fans Runaway” 

transient, the booster fan runback controls began to decrease booster fan inlet guide vane 

positions after the runaway had opened the vanes to 53%. If the booster fan inlet guide vanes 

had driven full open, the furnace pressure excursion would have been more severe than the -3.2 

inwc measured during the transient. 
PNM, San Juan Generating Station Units 3 & 4 Page 25 of 25 

Implosion Study – Final Report 7/10/2007

Project Number EA0624

Based on the results of the transient runs, TRAX recommends the following control strategies 

and mitigating measures be implemented in the future plant configuration controls: 

1. In normal operation, adjust booster fan inlet guide vanes via a control that uses a FD inlet 

guide vane demand feed-forward, added to a trim controller that monitors air heater gas 

outlet pressure. 

2. For mitigating MFT events, a kicker circuit should be used to immediately run back 

booster fan inlet guide vanes. The kicker would be activated by the MFT circuit and 

should last 20 seconds. The extent of the booster fan runback should be load 

dependent—i.e. at lower loads the extent of the booster fan runback would be less than a 

runback during a MFT at full load. 

3. An overriding booster fan runback controller should be used to help mitigate negative 

furnace pressure excursions. The runback controller should take precedence over normal 

controls and operator auto manual stations. When active, the runback controller would 

adjust booster fan inlet guide vanes to maintain a positive furnace pressure. The 

controller would go active when the furnace pressure dropped below -1 inwc and if the 

furnace MFT kicker circuit was not active. 

4. If the booster fans are tripped, both FD fans should be tripped if the furnace pressure 

exceeds a high furnace pressure limit to prevent over-pressurizing the furnace following 

an MFT. 
APPENDIX A 

Model Process Schematics 
1

1

22

33

44

55

66

A 

B C D Prepared byJB

Drawing No.EA0624.01 - 04 - 001 page 1-1

Date04 Oct 2006

No. 1 2 3

Date25 Oct 200612 Nov 200601 Mar 2007

BySPSPKMK

DescriptionIncorporated client's commentsAdded Baghouse and Upgraded the Booster FansFinal Configuration

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

Public Service Company - San Juan Unit 4 Boiler Implosion Study Process Model - Proposed Configuraion 

PROCESS MODEL

SAN JUAN GENERATING STATION UNIT 4

BOILER IMPLOSION STUDY

3-2

BAGHOUSE AND

BOOSTER FANS

Key:

ProTRA

Module ID

Flow Stream ID

FSID FSID

Connector Coordinates 

Page number of matching connector

p-p (xy)

'MID'

FAN

PUBLIC SERVICE COMPANY OF NEW MEXICO

1-1

INDEX

1-2

PULVERIZERS A-C

2-2

PULVERIZERS D-F

2-1

FANS AND

AIR HEATERS 

3-1

FURNACE

4-2

SCRUBBERS AND

STACK
1

1

22

33

44

55

66

A 

B C D Prepared byJB

Drawing No.EA0624.01 - 04 - 001 page 2-1

Date04 Oct 2006

No. 1 2 3

Date25 Oct 200612 Nov 200601 Mar 2007

BySPSPKMK

DescriptionIncorporated client's commentsAdded Baghouse and Upgraded the Booster FansFinal Configuration

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

Public Service Company - San Juan Unit 4 Boiler Implosion Study Process Model - Proposed Configuraion 

LSCASO_4 EDWA_4

LSAF_4 ERLSAD_4 ERD

LSAC_4 ERC

LSAB_4 ERB

LSAA_4 ER

EOFA_4 

ETA_4

LSAHB_4 LSCBSO_4

EHPAH

EHPA

EPSCAH_4 EPAH_4 LPAH_4

LPAGSO_4 GLPAH_4 GEPAH_4 EPAGCD_4

GESAHB_4 ESBGSO_4

GESAHA_4 ESAGSO_4

LSAHA_4

ESCAHB_4 ESAHB_4

ESCAHA_4 ESAHA_4

EDWB_4 LDWB_4

ESAF_4

ESAE_4

ESAD_4

ESAC_4

ESAB_4

ESAA_4

LSAE_4 ER

LDWA_4

LPAOSB_4

GLSAHB_4

GLSAHA_4

EFDB_4

EFDA_4

LPAB_4

EPAB_4

LFDB_4

LFDA_4

LPAA_4

EPAA_4

LPAHLA_4 EPAHLA_4

LSAHLB_4 ESAHLB_4

LSAHLA_4 ESAHLA_4

LPAOSA_4

EPAOSB_4

EPAOSA_4

EFDOSB_4

EFDOSA_4

LFDOSB_4

LFDOSA_4

LTA

4-2 (C8)

Sec. AH Leakage

FANS AND AIR HEATERS

'J4_4'

DAMPER

'FDOSA_4'

'J5_4'

DAMPER

'FDOSB_4'

'J11_4'

DAMPER

'PAOSA_4'

Forced Draft

Fan A Outlet

Shutoff

'J12_4'

DAMPER

'PAOSB_4'

Primary Air Fan A

3-1 (B5)

From ESP

3-1 (B5)

4-2 (D8)

4-2 (B8)

SCAH

(Out of Service)

Sec. Air Heater B

OutletShutoff

Atmosphere

Atmosphere

PLNMRV

'PN2_4'

'J16_4''J17_4'

DUCT

'TA_4'

Outlet

Shutoff

DUCT

'SAHLA_4'

DUCT

'SAHLB_4' 4-2 (A8)

To Flue Gas Duct

4-2 (B8)

DUCT

'PAHLA_4'

Pri. AH Leakage

4-2 (C8) 3-1 (A5)

From ESP

From ESP

Pri. Air Heater Primary Air Fan B Outlet Shutoff

DUCT

'DWA_4'

Forced Draft

Fan B

FANTAB

'PAA_4'

FANTAB

'FDA_4'

FANTAB

'FDB_4'

FANTAB

'PAB_4'

BC

'BCA_4'

BC

'BCB_4'

RHTRFD

'PAH_4'

RHTRFD

'SAHA_4'

RHTRFD

'SAHB_4'

PLNMRV

'PN20_4'

DAMPRN

'SAA_4'

'JEW_4'

DAMPRN

'SAB_4'

DAMPRN

'SAC_4'

DAMPRN

'SAD_4'

DAMPRN

'SAE_4'

PLNMRV

'CE_4'

DAMPRN

'SAF_4'

Compartments

DUCT

'DWB_4'

PLNMRV

'PN29_4'

R

SCADS

DUCT

'SCAHA_4'

SCAH

(Out of Service)

DUCT

'SCAHB_4'

DAMPER

'SCASO_4'

DAMPER

'SAGSO_4'

DAMPER

'SCBSO_4'

DAMPER

'SBGSO_4'

DAMPER

'PAGCD_4'

DAMPER

'PAGSO_4'

SCAH

(Out of Service)

DUCT

'PSCAH_4'

'JHP_4'

Sec. Air Heater A

DAMPRN

'OFA_4'

OFA

PLNMRV

'CA_4'

PLNMRV

'CB_4'

PLNMRV

'CC_4'

PLNMRV

'CD_4'

PLNMRV

'CF_4'

P XMTRP 'PT408F'

P XMTRP 'PT408E'

P XMTRP 'PT439A'

W XMTRF 'WLSAA'

W XMTRF 'WLSAB'W XMTRF 'WLSAC'

W XMTRF 'WLSAD'

W XMTRF 'WLSAE'

W XMTRF 'WLSAF'

T XMTRT 'TSAHA'

T XMTRT 'TSAHB'

W XMTRF 'WEDWA'

W XMTRF 'WEDWB'

To Flue Gas Duct

To Flue Gas Duct

Windbox

To Flue Gas Duct

To Flue Gas Duct

To Flue Gas Duct

P XMTRP 'PEFDA_4' P XMTRP 'PLFDA_4' P XMTRP 'PESAHA_4'

P XMTRP 'PLSAHA_4'

P XMTRP 'PESAA_4' P XMTRP 'PGLSAHA_4'
1

1

22

33

44

55

66

A 

B C D Prepared byJB

Drawing No.EA0624.01 - 04 - 001 page 3-1

Date04 Oct 2006

No. 1 2 3

Date25 Oct 200612 Nov 200601 Mar 2007

BySPSPKMK

DescriptionIncorporated client's commentsAdded Baghouse and Upgraded the Booster FansFinal Configuration

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

Public Service Company - San Juan Unit 4 Boiler Implosion Study Process Model - Proposed Configuraion 

BC LBCD

'BCD_4'

FURNMF

'FRN_4'

LSECSH_4 

LESPA_4

EPAGCD_4

ESAGSO_4

ESBGSO_4 LESPB_4

LWBDK_4

ELKOUT_4 LLKOUT_4

LFRN_4 LFRND_4 ESHPL_4

LBNRD_4

LBRN_4

LSEAL_4

ELKIN_4

LLKIN_4

LSHPL_4 LRH_4 LP

1-2 (A8)

Primary Air &

Coal Pulv A-F

BANK

'SHPL_4'

BANK

'SECSH_4'

BANK

'RH_4'

BANK

'PSH_4'

BC

'SEAL_4'

Water Seal

Secondary Platen

Superheater

Secondary 

Superheater

Reheater Primary 

Superheate

From Windboxes

FURNACE

Furnace

FurnaceIn-Leakage

'LKIN_4'

DUCT

'LKBC_4'

BCATM

DUCT

'FRND_4'

PLNMRV

'PLK_4'

BC

'L2BC_4'

DUCT

'LKOUT_4'

Atmosphere

 FurnaceOut-Leakage

2-1 (B8)

DUCT

'ESPB_4'

PLNMRV

'ESPR_4'

 Hot-Side

Precipitator 

2-1 (C5)

To Secondary Air Heater A

2-1 (A5)

To Secondary Air Heater B

2-1 (D6)

To Primary Air Heater

DUCT

'ESPA_4'

BURNMF

'BRN_4'

P XMTRP 'PFURN'

(De-energized)

P XMTRP 'PESAGSO_4'
1

1

22

33

44

55

66

A 

B C D Prepared byJB

Drawing No.EA0624.01 - 04 - 001 page 1-2

Date04 Oct 2006

No. 1 2 3

Date25 Oct 200612 Nov 200601 Mar 2007

BySPSPKMK

DescriptionIncorporated client's commentsAdded Baghouse and Upgraded the Booster FansFinal Configuration

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

Public Service Company - San Juan Unit 4 Boiler Implosion Study Process Model - Proposed Configuraion 

LPVC_4

EPVC_4

EPVB_4

LPACC_4

LPACB_4

LPACA_4 EPVA_4

LBSOF_4

EHPAH1_4 LHAH1_4

EPASOC_4

EPASOB_4

EPACC_4

EPACB_4

EPASOA_4 EPACA_4

EHDC_4

EHDB_4

EHDA_4

ETDC_4

ETDA_4

ETDB_4

LBSOD_4

LBSOE_4

LL

LHDA_4

LTDA_4

LPVA_4

EBSOA_4

LTDB_4

LHDB_4

LTDC_4

LHDC_4

LPVB_4

EBSOC_4

EBSO2_4

PULVBR

'PVA_4'

2-1 (C8)

DAMPER

'TDA_4'

DAMPER

'HDA_4'

'JBA_4'

'JCA_4'

DAMPRC

'BSOA_4

Tempering Damper

Hot Air Damper

DAMPER

'TDB_4'

DAMPER

'HDB_4'

'JBB_4'

PULVBR

'PVB_4'

'JCB_4'

DAMPRC

'BSOB_4'

DAMPER

'TDC_4'

DAMPER

'HDC_4'

'JBC_4'

'JCC_4'

DAMPRC

'BSOC_4'

2-1 (C8)

2-2 (D8)

2-2 (C8)

Temp Air fromPA Plenum

Temp Air from

PA Plenum

Temp Air fromPA Plenum

From Pulverizer E

Pulverizer A

Pulverizer BPulverizer C 

PULVERIZERS A - C

PLNMRV

'HP1_4'

2-1 (D7)

2-1 (D8)

Hot Air from Primary Air Heater

DAMPER

'PASOA_4'

DAMPER

'PACA_4'

DAMPER

'PASOB_4'

DAMPER

'PACB_4'

DAMPER

'PASOC_4'

DAMPER

'PACC_4'

Primary Air

Shutoff Damper 

Primary Air 

Control Damper 

Burner Coal Valv

DUCT

'HPAH1_4'

From Pulverizer D

2-2 (B8)

From Pulverizer F

Hot Primary Air 

Header A

'JDA_4'

'JDB_4'

'JDC_4'

T XMTRT 'TPVA'

T XMTRT 'TPVB'

T XMTRT 'TPVC'

W XMTRF 'WEPVA'

W XMTRF 'WEPVB'

W XMTRF 'WEPVC'

PULVBR

'PVC_4'
1

1

22

33

44

55

66

A 

B C D Prepared byJB

Drawing No.EA0624.01 - 04 - 001 page 2-2

Date04 Oct 2006

No. 1 2 3

Date25 Oct 200612 Nov 200601 Mar 2007

BySPSPKMK

DescriptionIncorporated client's commentsAdded Baghouse and Upgraded the Booster FansFinal Configuration

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

Public Service Company - San Juan Unit 4 Boiler Implosion Study Process Model - Proposed Configuraion 

EPVF_4

EPVE_4EPVD_4

LPACF_4

LPACE_4

LPACD_4

EHPAH2_4

EHDF_4

EHDE_4

EHDD_4

LHAH2_4

ETDD_4 LTDD_4 

LHDD_4 EPASOD_4 EPACD_4

EPASOF_4EPASOE_4

EPACF_4

EPACE_4

ETDF_4

ETDE_4

LHDF_4

LTDF_4

LTDE_4

LHDE_4

DAMPER

'TDE_4'

DAMPER

'HDE_4'

'JBE_4'

Tempering Damper

Hot Air Damper

DAMPER

'TDF_4'

DAMPER

'HDF_4'

'JBF_4'

2-1 (D8)2-1 (D8)

Temp Air from

Temp Air from

PA Plenum

PA Plenum

Pulveriz

Pulveri

PULVERIZERS D - F

DAMPER

'PASOE_4'

DAMPER

'PACE_4'

DAMPER

'PASOF_4'

DAMPER

'PACF_4'

Primary Air

Shutoff Damper 

Primary Air 

Control Damper 

DAMPER

'TDD_4'

DAMPER

'HDD_4'

'JBD_4'

2-1 (D8)

Temp Air fromPA Plenum

Pulveriz

DAMPER

'PASOD_4'

DAMPER

'PACD_4'

DUCT

'HPAH2_4'

PLNMRV

'HP2_4'

2-1 (D7)

Hot Air from Primary Air Heater

Hot Primary Air 

Header B

'JDD_4''JDE_4'

'JDF_4'

T 

'

T 

T 

W XMTRF 'WEPVD'

W XMTRF 'WEPVE'

W XMTRF 'WEPVF'

PULV

'PVD

PULV

'PVE_

PULV

'PVF_
1

1

22

33

44

55

66

A 

B C D Prepared byJB

Drawing No.EA0624.01 - 04 - 001 page 3-2

Date04 Oct 2006

No. 1 2 3

Date25 Oct 200612 Nov 200601 Mar 2007

BySPSPKMK

DescriptionIncorporated client's commentsAdded Baghouse and Upgraded the Booster FansFinal Configuration

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

Public Service Company - San Juan Unit 4 Boiler Implosion Study Process Model - Proposed Configuraion 

EBFIDC_4EBFIDA_4

LFFOD_4 EBFIDB_4

LSADB1_4 ESADB1_4 LSADB_4

LSADA1_4 ESADA1_4 LSADA_4

LBHOLD_4 EFFOD_4

EBYBH_4 LBYBH_4

EFFID

_

4 LFFID_4 EBHILD_4 LBHILD_4 EBHOLD

_

4

ESADA

_

4

ESADB_4

LPJFF_4

LBFC_4 EB

LBFB_4 EBF

LBFA_4 EB

EBFC_4

EBFB_4

EBFA_4

LBFIDC_4

LBFIDB_4

LBFIDA_4

BAGHOUSE AND BOOSTER FANS

PLNMRV

'EBFPL_4'

DAMPER

'BFIDA_4'

FANTAB

'BFA_4' 

DAMPER

'BFIDB_4'

FANTAB

'BFB_4' 

DAMPER

'BFIDC_4'

FANTAB

'BFC_4' 

Booster Fan N

'BFAJ_5'

'BFBJ_5'

'BFCJ_5'

'BOAJ_

'BOBJ_4

'BOCJ_4

DUCT

'SADA_4'

DUCT

'SADB_4'

DUCT

'PJFF_4'

PLNMRV

'BHPL_4'

Baghouse

DAMPER

'BYBH_4'

P XMTRP 'PT439A1'

DAMPER

'BHOLD_4'

Baghouse

Outlet Damper

Baghouse Emergency Bypass 

Damper

DAMPER

'BHILD_4'

Baghouse

Inlet Damper

Booster Fan P

Booster Fan R

DUCT

'FFID_4'

DUCT

'FFOD_4'

'BHJ1_4' 'BHJ2_4'

'SAAPL_4'

PLNMRV 'SABPL_4'

PLNMRV

DUCT

'SADA1_4'

DUCT

'SADB1_4'

PLNMRV

'BFPL_4'

P XMTRP 'PT439A2'

P XMTRP 'PT439A3'

P XMTRP 'PT439A4'

P XMTRP 'PLBHOLD_4'

P XMTRP 'PLBFA_4'
1

1

22

33

44

55

66

A 

B C D Prepared byJB

Drawing No.EA0624.01 - 04 - 001 page 4-2

Date04 Oct 2006

No. 1 2 3

Date25 Oct 200612 Nov 200601 Mar 2007

BySPSPKMK

DescriptionIncorporated client's commentsAdded Baghouse and Upgraded the Booster FansFinal Configuration

Revision History

No. Date By 

TRAX LLC, Forest,Virginia

for Public Service Company of New Mexico

Public Service Company - San Juan Unit 4 Boiler Implosion Study Process Model - Proposed Configuraion 

ESADB_4

LPB

FGDSCB

'FGDC_4'

ESADA_4

LBFODC_4

LBFODB_4

LBFODA_4

LFE_4

EFE_4

EPBLPAEPA

LSBC4C_4

LSBC3C_4

LSBC2C_4

LSBC1C_4

LWWBCC_4

LSBC4B_4LSBC3B_4LSBC2B_4LSBC1B_4

LWWBCB_4

LSBC4A_4

LSBC3A_4LSBC2A_4LSBC1A_4

LWWBCA_4

LFGDCD_4

LFGDBD_4

LFGDAD_4

FGDSCB

'FGDB_4'FGDSCB

'FGDA_4'

LFGDC_4

LFGDB_4

LFGDA_4

EFGDC_4

EFGDB_4

EFGDA_4

LSTK_4

ESTK_4

DUCTDW

'STK_4'

BC

'ATMSK'

Stack

'BFCJ_4'

'BFBJ_4'

'BFAJ_4'

PLNMRV

'FGDPL_4'

DUCT

'FGDAD_4'

DUCT

'FGDBD_4'

DUCT

'FGDCD_4'

BC

'WWBCA_4'

BC

'SBC1A_4'

BC

'SBC2A_4'

BC

'SBC3A_4'

BC

'SBC4A_4'

BC

'WWBCB_4'

BC

'SBC1B_4'

BC

'SBC2B_4'

BC

'SBC3B_4'

BC

'SBC4B_4'

Wash Water

 SlurryEntering

Wash Water

 SlurryEntering

BC

'WWBCC_4'

BC

'SBC1C_4'

BC

'SBC2C_4'

BC

'SBC3C_4'

BC

'SBC4C_4'

Wash Water

 SlurryEntering

'J411_4'

'J413_4'

DUCT

'PA_4'

'PB_4'

DUCT

DUCT

'FE_4'

Scrubber Module NScrubber Module PScrubber Module R

PLNMRV

'STKPL_4'

T XMTRT

'TESTK'

3-2 (C8)

3-2 (B8)

3-2 (A8)

3-2 (A8)

3-2 (D7)

SCRUBBERS AND STACK

Flue Gas to

Baghouse Inlet

Flue Gas to

Baghouse Inlet

Flue Gas

From Booster Fan A

Flue Gas

From Booster Fan B

Flue Gas

From Booster Fan C

P XMTRP 'PT408E1'

P XMTRP 'PT408E2'

P XMTRP 'PLFGDA_4'

P XMTRP 'PESTK_4'

P XMTRP 'PLSTK_4'

'J412_
APPENDIX B 

Model Control Schematics 
1

1

22

33

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A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 1-1

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

INDEX

1-1

PULVERIZER / 

1-2 2-2 3-2

CONTROLS MODEL

2-1

COMPARTMENT A

CONTROLS

PULVERIZER / 

COMPARTMENT B

CONTROLS

PULVERIZER / 

COMPARTMENT C

CONTROLS

PULVERIZER / 

4-2 5-2 6-2

COMPARTMENT D

CONTROLS

PULVERIZER / 

COMPARTMENT E

CONTROLS

PULVERIZER / 

COMPARTMENT F

CONTROLS

3-1 4-1 5-1

SEC AIR CNTRL &

6-1

MASTER FUEL

7

EQUIP

SAN JUAN GENERATING STATION UNIT 4

BOILER IMPLOSION STUDY

PUBLIC SERVICE COMPANY OF NEW MEXICO

LEGEND OXYGEN TRIM TRIP SHUTD

PRIMARY AIR

PRESSURE

WINDBOX

PRESSURE

7

PRIMA

SHUTOFF 

FD FANS TRIPS

1-3
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 2-1

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

Legend LEGEND

PROCESS VARIABLE FROMFIELD TRANSMITTER

LEAD-LAGLIMIT HIGH

CYxyz

= Valve 

OUTPUT TOFINAL CONTROL ELEMENT

PROCVAR

*ID

*ID SUM

*ID

TRANSFER

DIFFERENCE

DIVIDEDERIVATIVE

BIAS BIAS

*ID

d

*ID

dt

*ID

f(x)

*ID

~

1 + ks

*ID

1 - 2s

*ID

>

*ID

> < LIMIT HIGH LOW

*ID

< LIMIT LOW

X

*ID

MULTIPLY

K/S/D

*ID PID CONTROLLER

K

*ID

PROPORTIONAL

*ID

RAMP

>

*ID

<

*ID

HIGH SELECT

LOW SELECT

A MANUAL ANALOG SET

MANUAL INTEGER/DISCREET SET

*ID

SQUARE ROOT

f(t)

*ID

do TIME DELAY

FUNCTION GENERATOR

VELOCITY LIMITER

*ID

V<

K/S

*ID

PI CONTROLLER

ACCUM1*ID INTEGRATOR

ACCUM2

*ID

2-INPUT INTEGRATOR

WITH LIMITS

H/

*ID

*ID

H/L

/L

*ID

HIGH SIGNAL MONITORHIGH/LOW SIGNAL MONITORLOW SIGNAL MONITORDIGITAL OUT WHEN INPUT

 IS ABOVE SETPOINT

DIGITAL OUT WHEN INPUT IS BELOW SETPOINTDIGITAL OUT WHEN INPUT IS ABOVE HIGH SETPOINT

OR BELOW LOW SETPOINT

N

*ID

AVERAGE
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 3-1

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

FDTS

FDTV

GROSS_MW

GENDMD

SA31D 

CYFDOSBAUT31DFX31DKS31A KS31A

SA31C SI31C

CYFDOSAAUT31CFX31CKS31A

BLRDMD

GENDMD

AUT31A AUT31BKS31A

FDA_TRP 

NFD

FX31A

SLO31A

GENDMD

PLDWA PLDWB

SFDA

NFDA

BI31A BI31BCYFDA CYFDB

SA31A SI31A SA31B SI31B

E31A

'E31A'

K/S

'KS31A'

BIAS

'BI31A'

'TR31A'

A

CYFDA

FD Fan A

Inlet Guide Vanes

BIAS

'BI31B'

'TR31B'

A

CYFDB

FD Fan B

Inlet Guide Vanes

WINDBOX PRESSURE

f(x)

'FX31A'

'WBOXPA'

PROCVAR

'WBOXPB'

PROCVAR

'GENDMD'

PROCVAR

Firing Rate Demand

A

A

'TR61A'

A

FD Fan A Speed 

<

'SLO31A'

1-3 (D3) 

'AUT31A' 'AUT31B'

Boiler Demand

5-1 (D2)

f(x)

'FX31B'

709 RPM

f(x)

'FX31C'

'AUT31C'

'TR31C'

A

CYFDOSA

FD Fan A

Outlet Shutoff Damper

f(x)

'FX31D'

'AUT31D'

'TR31D'

A

CYFDOSB

FD Fan B

Outlet Shutoff Damper

f(x)

'FX31B1'

Secondary Air Duct Press

A

X Y0 0100 90

X Y0 0100 550

P = 1.0I = 10 Sec

X Y0 0100 100

X 0 100 

X Y0 030 1554.55 19100 23
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 4-1

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

BI41A

P

L

P

A

H

SA41D SI41D

CYPAOSBAUT41DFX41DKS41B

SA41C SI41C

CYPAOSAAUT41CFX41CKS41B

PVDMD

FX41B

KS41A

KS41B KS41B

AUT41A AUT41B

AVE41A

AVE41A

YPAA YPAB

CNPAALO

PAAZERO TRPPAA

NPAAPAASPD

CNPAAHI PAASEL

CYPAA CYPAB

SA41A SI41A SA41B SI41B

E41B

E41A

FX41A

PRIMARY AIR PRESSURE

'PV41A'

PROCVAR

Pri Air Duct Press Coal Demand

f(x)

'FX41A'

BIAS

'BI41A'

'E41A'

K/S

'KS41A'

'E41B'

K/S

'KS41B'

N

'AVE41A'

'TR41A' 'TR41B'

A A

CYPAA

PA Fan A

CYPAB

PA Fan B

A

PA FAN SPEED

'TR41C''TR41D'

A

Hi Spd

Lo Spd

Speed Selector

L

A

'YPAA_4'

PROCVAR

'YPAB_4'

PROCVAR

'AUT41A' 'AUT41B'

f(x)

'FX41B'

PA Fan Inlet Guide Vane Position

5-1 (A1)

'TR41G'

A

CYPAOSA

PA Fan A

Outlet Shutoff Damper

'AUT41C'

f(x)

'FX41C'

'TR41H'

A

CYPAOSB

PA Fan B

Outlet Shutoff Damper

'AUT41D'

f(x)

'FX41D'

Normal 1182 RPM 

887 RPM 88

Inlet Damper Inlet Damper

P = 1.0I = 10 Sec

X Y0 0100 100

P = 0.5I = 20 Sec

X Y0 032.8 100

X Y0 032.8 100
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 5-1

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

WAIR

SUM51E

SUM51B

WEDWA WEDWB

WEPVD WEPVE WEPVF WEPVA WEPVB WEPVC

PVDMD

BLRDMD

BLRDMD

BLRDMD

SEHI51A

TOTFUEL

DIV51A

PV51A

NUMOFPULV

O2TRIM

FX51B

KS51A

SUM51D

E51A

MUL51A

WAIRTOTAIR

SCAT421

SUM51A

'TOTFUEL'

PROCVAR

Total Fuel Flow

(Add All Fuel To Pulverizers) Boiler Demand

'SUM51A'

'SUM51B'

'SUM51C'

Primary Air Flow

f(x)

'FX51A'

X

'MUL51A'

'E51A'

K/S

'KS51A'

'SUM51D'

'LIM51A'

> <

1-2 (D6)

f(x)

'FX51B'

'ECONO2'

OC

'E5

K

'K

'LIM5

< 

f(x)

'PV51A'

A 'DIV51A'

Number of

Pulverizers

Pulverizer Demand

f(x)

'PV51B'

>

'SEHI51A'

Flue Ga

(0.7 - 1.3)

Sec. Air Trim

3-1 (C3)

SEC AIR CNTRL & OXYGEN TRIM

4-2 (D1)

( 0-100 % )

'WEPVA'

PROCVAR

'WEPVB'

PROCVAR

'WEPVC'

PROCVAR

'WEPVD'

PROCVAR

'WEPVE'

PROCVAR

'WEPVF'

PROCVAR

Primary Air Flow

'SUM51E'

'WLDWA'

PROCVAR

'WLDWB'

PROCVAR

Secondary Air Flow

( KPPH )

( 0-100 % )

Air Flow Master

6-1 (C1)

X Y0 027.0 191,00049.0 360,00074.7 460,00090.0 552,200

X Y0 092033.3 80

P = 0.1I = 100 Sec

X Y0 02474 274998 80

P = 1I = 10 Sec

X Y0 090 1
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 6-1

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

TRIP_ALL_BF

BHDELP HBHDP DHBDP

WAI

MF

WAIR

RHTBLK

MFTB

A6

TD61A

NO_PA_FANS

MF

WAWA

MF

MFT

MF

MF

M

FDR_NOSTOP

NO_FD_FANS MFTC

MFTFMFTE

PFURNACE

PFURNACE

PLPAH LO61A

WA

WA

WA

WAI

MFTA

LO61B

HI61A

MFTD

LO61C

MFTSET

MFTRESET

MASTER FUEL TRIP

PROCVAR

'PV61A'

PROCVAR

'PV61C'

OR

'OR61A'

PROCVAR

'PV61E'

/L

'LO61B'

f(t) pu

'TD61B'

PROCVAR

'PV61B'

H/

'HI61A'

< -2 inwc

f(t) pu

'TD61C'

OR

'SMFT2'

3 Sec

Primary Air Duct Pressure

Furnace Pressure

< 25%

3 Sec

f(t) pu

'TD61A'

< +47.7 inwc 5 Sec

/L

'LO61C'

> +34.4 inwc 3 Sec

f(t) pu

'TD61D'

Secondary Air Flow

MEM3

'MMFT'

Both PA fans tripped

/L

'LO61A'

Loss of FD fans

MFT Emerg. PB

f(t) pu

'TD61E'

0 Sec

'A6'

AND

PROCVAR

'PV61F'

All Feeders Not Stopped

Reheater Blocked

5-1 (C5)

9-2 (B5) H/ 'HI61A1'

> +14.0 inwc

Baghouse DP

f(t) pu

'TD61C1'

5 Sec

8-2 (D7)

Trip All Booster Fans
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 7-1

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

TRIP_ALL_BF 

SBA SBB

NBFA NBFB

NBF NBF NBF

TRIP_PA_FANS

FDA_TRP FDB_TRP

PAB_TRP

TRIP_PA_FANS

PAA_TRP

YBSO YBSO YBSO YBSO YBSO

NPULV NPULV NPULV NPULV NPULV NPULV

TRPPULV TRPPULV TRPPULV TRPPULV TRPPULV TRPPULV

NPVA NPVB NPVC NPVD

TRPVA TRPVB TRPVC TRPVD

NPVE NPVF

TRPVE TRPVF

SA71B SI71B SA71C SI71C SA71D SI71D SA71F SI71F SA71G SI71G 

CYBSOA CYBSOB CYBSOC CYBSOD CYBSOE 

EQUIPMENT SHUTDOWN

A

A

'TRPA15' 'TRPA16'

A

BURNER COAL VALVES

'TRPA17'

A

'TRPA18'

A

'TRPA19'

A

A

'TPVA' 'TPVB' 'TPVC' 'TPVD'

PULVERIZERS

A

'TPVE' 'TPVF'

6-1 (D7)

OR

'OR41A' FD Fan A tripped

PA Fan A tripped

6-1 (D7)

OR

'OR41B' FD Fan B tripped

PA Fan B tripped

1-3 (D3) 1-3 (B3)

PA FANS

Trip PA Fans Trip PA Fans

A

A

'TR61A1'

A

'TR61B

Booster Fan A Speed Booster Fan B Spe

890 RPM
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 8-1

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

Y

B

F

A

BFRB

BTRK

F

D

F

F

S

NT7

PIBF BFRB PIBF BFRB PIBF BFRB

PID331

MFT

PFURNACE BFLP

MFT

MPUL NT6

MFT TP6

KVAL

KS31A

KF

KICK

MPUL

NORM

PSAD

SPSAD

S332 S332

S332

KS31A FDFF

FDFFS

D312

AUT81A AUT81B AUT81C

CYBFC CYBFA CYBFB

'TR81A'

CYBFA

Booster Fan A

Inlet Guide Vanes

'TR81B'

CYBFB

Booster Fan B

Inlet Guide Vanes

'TR81C'

CYBFC

Booster Fan C

Inlet Guide Vanes

BOOSTER FANS CONTROL

'AUT81A' 'AUT81B'

'AUT81C'

Normally in Auto

9-2 (B6)

'D331'

Airheater Gas

Outlet Duct Pressure (inwc)

K/S/D

'PID331'

3-1 (B2) K 'S332' 'PP332'

FD Fan Demand

From Airflow Controls

Setpoint

0.0 inwc

Feed Forward

X 1.0

High and L

8-1 (C3)

f(x) 

'FX41A1'

A

Normally in Auto Normally in Auto

6-1 (D6)

'TR333'

A

'PUL'

f(x)

'FX41A2'

MFT Kicker Circuit

MFT

20 Sec 

8-1 (D2)

Normally Zero

6-1 (D6) f(t) pu 'TP6'8-1 (D2) NOT 'NT6'

NOT

9-2 (C1)

6-1 (D6)

NOT

NOT

'NT7'

/L

'BFLP'

8-1 (A8) 8-1 (C8) 8-1 (A8) 8-1 (C8) 8-1 (A8) 8-1 (C8)

5 Seconds

< -1 inwc

MFT in

Progress

BF Kicker

Active

Furnace

Pressure

MFT in

Progress

Booster F

Position Fee

Booster F

Runback Con

Active

8-1 (C3)

'D811' 8-1 (C8)

Tracking Signal

Tracking Switch

P = 1I = 10 Sec

X Y0 050 -20100 -60

X Y0 0100 50

PROCVAR

'P1'
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 1-2

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

TS

CASPT

TLPVA

SUM12D

PVDMD

PVDMD

PVDMD

LIM12ASUM12A

KS12B

KS12B

FX12F

SA12G

SCAT421

BI12A

SA12E 

CYSAABI12C

MUL12A

SUM12C

SUM12C

KS12C

FX12D

E12B

FX12A

SA12C SI12C

CYHDA

SI12D

CYTDA

SA12D

SA12A SI12A

NFPVA

SA12B SI12B

CYPACA

PV12B

FX12E

WEPVAFX12B

E12A

PROCVAR

'PV12E'

PROCVAR

'PV12D'

'E12B'

'TR12C'

A

Pulv A Coal Air

Temperature

Coal Air SetpointNormally 160 F

Pulverizer A 

Tempering Air Damper

CYHDA

'TR12D'

A

CYTDA

PROCVAR

'PV12B'

Pulverizer

Bias

Feeder Demand

'SUM12A'

'TR12A'

NFPVA

Feeder "A"

A

K/S

'KS12B'

'TR12B'

A

CYPACA

Pulverizer A

Primary Air

Control Damper

PULVERIZER/COMPARTMENT A CONTROLS

Speed Control

f(x)

'FX12E'

'PV12C'

PROCVAR

f(x)

'FX12B'

'E12A'

BIAS

'BI12A'

f(x)

'FX12A'

Pulverizer A

PA Air Flow

K/S

'KS12C'

f(x)

'FX12D'

'SUM12C'

Pulverizer A

Hot Air Damper

Feeder "A" Demand

5-1 (A4)

Sec. Air Trim

X

'MUL12A'

'SUM12D'

BIAS

'BI12C

'TR12

A

CYSAA1

SCAD

A

f(x)

'FX12F'

'LIM12A'

> <

5-1 (A1)

5-1 (A1)

Typical For Pulverizer B-F

Air Flow Setpoint

0

100

OUT

IN 0 100

Bias

A

X Y0 0100 100

X Y0 0190,000 80

P = 0.5I = 180 Sec

P = 1.5I = 77 Sec

X Y0 0100 50

X Y0 100100 0

X Y0 080 807465
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 7-2

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

CYPASOF

RU190FV RU190FS

LB105

RU190EV RU190ES

CYPASOELB104

CYPASO CYPASO CYPASO

CYPASO CYPASO

LB103

LB101 LB102 LB100

CYPASO

RU190CV RU190CS

CYPASOC

CYPASOD

RU190DV RU190DS

CYPASOB

RU190BV RU190BS

CYPASOA

RU190AV RU190AS

'RU190A'

A

CYPASOA

Primary Air Shut Off 

Damper A

'RU190B'

A

CYPASOB

'RU190C'

A

CYPASOC

'RU190D'

A

CYPASOD

PROCVAR

'P11'

BIAS

'B100'

BIAS

'B101'

BIAS

'B102'

BIAS

'B103'

'RU190B1'

A

CYPASOE

'RU190C1'

A

CYPASOF

BIAS

'B104'

BIAS

'B105'

Primary Air Shut Off 

Damper B

Primary Air Shut Off 

Damper C

Primary Air Shut Off 

Damper D Primary Air Shut Off Damper E Primary Air Shut Off Damper F

PRIMARY AIR SHUT OFF DAMPERS
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 8-2

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

WAIT9

TRIP_ON_LOW_FURNACE

OK_TO_TRIP

MFTF

TRBF

OR431

LOWBFP

GENDMD LLIM BFLIM

PEBF

TRIP_A

IS430

TLPJFF

OR431

ST43

CYBST4

OPENINL

OR431

IS432

OPENBYP

IS431

HIACT

CYBP

'TR431'

CYBPASS

Baghouse Emerg

Bypass Damp

9-2 (C5)

H/

'SH431'

MEM2

'OPENBYP'

OR

'OR431'

Temperature of

Flue Gas Leaving

Baghouse (oF)

Reset

C

CYBHOLD

Baghouse 

Outlet Dam

MEM2

'OPENINL'

Set 'TR432'

A C

A

> 345 Deg F

BAGHOUSE DAMPERS

MEM2

Reset 'OPENBYP

/L

'BFL'

PROCVAR

'P721'

PROCVAR

'P722'

f(x)

'FX2'

Load-Based Trip (Normally Disabled)

BF Inlet Pressure

ADAPT

'ADP'

OR

'OR432' 6-1 (B3) 'A821' A

ND

Low Furnace Pressure MFT

Unit Load

X Y30 -9.4100 -22.1

PROCVAR

'P2'
1

1

22

33

44

55

66

A 

B C D Prepared byCU

Drawing No.EA0624.01 - 04 - 002 page 1-3

Date04 Oct 2006

No. 1 2 3 4

Date25 Oct 200613 Nov 200601 Mar 200710 Jul 2007

BySPSPKMKSJ

DescriptionIncorporated client's commentsUpdated Booster Fan control logicFinal ConfigurationDisplayed Tuning Parameters and Function Generators

Revision History

No. Date By 

TRAX LLC., Forest, VA

for Public Service of New Mexico

PNM - San Juan Generating Station Unit 4 Boiler Implosion StudyControls Model - Proposed Configuration 

WAIT11

ONBFT

ONBFT

HI31C

FDB_TRP_PB

FDA_TRP_PB

TRIP_ALL_BF TRFD

HI31D

HI31B

FDB_TRP TLSAHB

PLDWB

FDA_TRP

HI31A

TLSAHA

PROCVAR PLDWA

'PV31A'

Secondary Air A Duct Press

PROCVAR

'PV31B'

Secondary Air A Temp

H/

'HI31A'

> +47.7 inwc

H/

'HI31B'

> 620 F

OR

'OR31A'

FD Fan A tripped

PROCVAR

'PV31C'

Secondary Air B Duct Press

PROCVAR

'PV31D'

Secondary Air B Temp

H/

'HI31C'

> +47.7 inwc

H/

'HI31D'

> 620 F

OR

'OR31B'

FD Fan B tripped

PROCVAR

'PV31E'

FD Fan A Operator trip

PROCVAR

'PV31F'

FD Fan B Operator tripFD FANS TRIPS

'AD1'

AND

f(t) pu

'DL1' 8-2 (D7)

15 Sec

9-2 (B4)
APPENDIX C 

Unit 4 Validation Results 
Furnace Pressure

02468

10121416

0 10 20 30 40 50 60 

Time (Seconds)

Pressure (inwc)

A1574 FURNACE PRESS Model
Total Secondary Airflow

0

100020003000400050006000

0 10 20 30 40 50 60 

Time (Seconds)

Flow (kpph)

Plant Model
FD Fans Discharge Pressure

05

101520253035

0 10 20 30 40 50 60 

Time (Seconds)

Pressure (inwc)

A1501 FD FAN A DISCHARGE PRESS A1503 FD FAN B DISCHARGE PRESS M
Primary Air Heater Air Outlet Pressure

0

102030405060708090

100

0 10 20 30 40 50 60 

Time (Seconds)

Pressure (inwc)

A1531 PRI AH AIR OUT PRESS Model
APPENDIX D 

Full Load MFT 
Full Load MFT

Transient Max/Min Pressure Profile

Without Mitigations

0.0

+31.0 +29.8

+25.0 +23.0

+9.6

+7.0 +5.3

0.0

-9.6 -10.4

+17.4

+1.8 

+23.0

-2.8

+28.2 +26.9

+21.2

+18.3 +18.3

-1.7 -2.8 -3.6

-6.1

-8.5

-18.4 -19.9

+5.7

-0.8 -

-40-35-30-25-20-15-10

-5

0

+5

+10+15+20+25+30+35+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Sec. Air Duct Windbox Compartment FurnaceEconomizer Outlet Hot Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet FGD Outl

Pressure (inwc)

Maximum Minimum
Full Load MFT

Unit Pressures

-30-20-10

0

10203040

0 20 40 60 80 10

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load MFT

Baghouse and Scrubber Pressures

-30-20-10

0

10203040

0 20 40 60 80 10

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load MFT

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load MFT

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load MFT

Fan Speeds

0

100200300400500600700800900

1000

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
APPENDIX E 

Full Load All Booster Fans 

Trip 
Full Load All Booster Fans Trip

Transient Max/Min Pressure Profile

Without Mitigations

+24.2

+32.6

+1.8

+17.4

+21.0 +21.4 +24.8 +26.5 +26.1 +26.9

+33.5 +32.6

+35.4 +35.8

0.0

-

-1.2

+2.9

-16.1 -14.4

-2.8

0.0

+5.7 +5.2 +6.5

+22.8 +22.8

+25.0

+30.0 +29.0

-40-35-30-25-20-15-10

-5

0

+5

+10+15+20+25+30+35+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Sec. Air Duct Windbox Compartment FurnaceEconomizer Outlet Hot Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet FGD Outl

Pressure (inwc)

Maximum Minimum
Full Load All Booster Fans Trip

Unit Pressures

-30-20-10

0

10203040

0 40 80 120 160 200 240 280 

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load All Booster Fans Trip

Baghouse and Scrubber Pressures

-30-20-10

0

10203040

0 40 80 120 160 200 240 280 

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load All Booster Fans Trip

Flows

0

100020003000400050006000700080009000

10000

0 40 80 120 160 200 240 280 

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load All Booster Fans Trip

Fan IGV

0

102030405060708090

100

0 40 80 120 160 200 240 280 

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load All Booster Fans Trip

Furnace Pressure

-30-20-10

0

10203040

0 40 80 120 160 200 240 280 

Time (seconds)

Pressure (inwc)

Furnace (Unmitigated) Furnace With FD Fan Trip (Mitigat
Full Load All Booster Fans Trip

Transient Maximum Pressure Profile

0.0

+35.8 +35.4

+33.5 +32.6

+26.9 +26.5 +26.1 +24.8

+21.4 +21.0

+17.4

+1.8

+32.6

+24.2

0.0

+34.0 +33.2

+29.4

+27.6 +27.6

+15.3 +14.6 +13.9

+11.9 +10.9

+6.6 +6.1

-10

-5

0

+5

+10+15+20+25+30+35+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Sec. Air Duct Windbox Compartment FurnaceEconomizer Outlet Hot Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet FGD Outl

Pressure (inwc)

Maximum (Unmitigated) Maximum With FD Fan Trip (Mitigated)
Full Load All Booster Fans Trip

Fan Speeds

0

100200300400500600700800900

1000

0 40 80 120 160 200 240 280 

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
APPENDIX F 

Full Load Both FD Fans 

Trip 
Full Load Both FD Fans Trip

Transient Max/Min Pressure Profile

Without Mitigations

+0.6

+23.0

+1.8

+17.4

+0.5 +0.4 0.0

+5.3 +7.0

+9.6

+23.0 +25.0

+29.0 +30.0

0.0

-

-2.0 -2.2

-18.2 -18.9

-14.0 -13.1

-11.0 -11.5 -10.3

+1.1 +1.1 +1.0 +1.0 +1.0

-40-35-30-25-20-15-10

-5

0

+5

+10+15+20+25+30+35+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Sec. Air Duct Windbox Compartment FurnaceEconomizer Outlet Hot Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet FGD Outl

Pressure (inwc)

Maximum Minimum
Full Load Both FD Fans Trip

Unit Pressures

-30-20-10

0

10203040

0 20 40 60 80 10

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load Both FD Fans Trip

Baghouse and Scrubber Pressures

-30-20-10

0

10203040

0 20 40 60 80 10

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load Both FD Fans Trip

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load Both FD Fans Trip

Fan IGV

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load Both FD Fans Trip

Fan Speeds

0

100200300400500600700800900

1000

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
APPENDIX G 

Low Load Two Booster 

Fans Runaway 
Low Load Two Booster Fans Runaway

Transient Max/Min Pressure Profile

Without Mitigations

+0.3

+17.5

0.0

+13.6

-0.7 -0.5 +1.5 +1.1 0.0 +2.0

+18.0 +17.5

+19.3 +19.0

0.0

-

-1.8 -0.3

-10.0 -10.7

-6.5 -5.7 -3.8 -4.3 -3.2

+13.6 +13.6 +14.1 +15.5 +15.2

-40-35-30-25-20-15-10

-5

0

+5

+10+15+20+25+30+35+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Sec. Air Duct Windbox Compartment FurnaceEconomizer Outlet Hot Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet FGD Outl

Pressure (inwc)

Maximum Minimum
Low Load Two Booster Fans Runaway

Unit Pressures

-30-20-10

0

10203040

0 20 40 60 80 10

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Low Load Two Booster Fans Runaway

Baghouse and Scrubber Pressures

-30-20-10

0

10203040

0 20 40 60 80 10

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Low Load Two Booster Fans Runaway

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Low Load Two Booster Fans Runaway

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Low Load Two Booster Fans Runaway

Fan Speeds

0

100200300400500600700800900

1000

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans
APPENDIX H 

Full Load All Fans Trip 
Full Load All Fans Trip

Transient Max/Min Pressure Profile

Without Mitigations

0.0

+23.0

+1.8

+17.4

-0.3 -0.2 0.0

+5.3 +7.0

+9.6

+23.0 +25.0

+29.0 +30.0

0.0

-

-1.8 -2.1

-16.1 -14.4

-2.7 -3.2 -1.3 -1.7 -1.9 +1.0 +1.0 +0.9 +0.8 +0.8

-40-35-30-25-20-15-10

-5

0

+5

+10+15+20+25+30+35+40

Ambient FD Fan Outlet SAH Air Inlet SAH Air Outlet Sec. Air Duct Windbox Compartment FurnaceEconomizer Outlet Hot Precip Outlet SAH Gas Outlet Baghouse Inlet Baghouse Outlet Booster Fan Inlet Booster Fan Outlet FGD Outl

Pressure (inwc)

Maximum Minimum
Full Load All Fans Trip

Unit Pressures

-30-20-10

0

10203040

0 20 40 60 80 10

Time (seconds)

Pressure (inwc)

FD Discharge Furnace Air Heater Gas Outlet
Full Load All Fans Trip

Baghouse and Scrubber Pressures

-30-20-10

0

10203040

0 20 40 60 80 10

Time (seconds)

Pressure (inwc)

Baghouse Inlet Booster Fan Inlet FGD Inlet
Full Load All Fans Trip

Flows

0

100020003000400050006000700080009000

10000

0 20 40 60 80 1

Time (seconds)

Flow (kpph)

Total FD Fans Furnace Exhaust Total FGD Inlet
Full Load All Fans Trip

Fan Inlet Guide Vanes

0

102030405060708090

100

0 20 40 60 80 1

Time (seconds)

Position (percent open)

FD Fans Booster Fans
Full Load All Fans Trip

Fan Speeds

0

100200300400500600700800900

1000

0 20 40 60 80 1

Time (seconds)

Speed (rpm)

FD Fans Booster Fans