Page 1 of 33

Administrative Order by Consent 

Alternative Method Proposal for Furnace Line 2

As indicated in the February 19, 2008 Administrative Order by Consent, effective March 3, 

2008, signed by the Minnesota Pollution Control Agency (MPCA) and Hibbing Taconite 

Company (HTC), item # 8 states: 

“Hibtac agrees to undertake the testing and analyses set forth 

below to provide the MPCA with data to determine whether an 

Alternative NOx Emissions Measurement Method is approvable by 

the MPCA and agrees to implement the Alternative Method, if it is 

approved by the MPCA.” 

This document serves as the Alternative Method Proposal for Furnace Line 2, as explained in 

items # 10-12 of the Administrative Order by Consent and contains the following information in 

each respective Appendix: 

Appendix A: Data Points for Operating Parameters during 150-hour NOx Test 

Administrative Order Requirement: “The data points recorded during emissions testing 

conducted for these parameters at a minimum: ferrous iron content of the feed materials, pellet 

type, production rate, heat input, stack gas flow rate, and combustion zone temperature. Data for 

other parameters shall be submitted if Hibtac determines they are relevant to NOx formation. If 

the MPCA determines that any further parameters that are currently measured are relevant to 

NOx formation, those parameters shall be added to the list of operating parameters recorded and 

submitted.” 

Appendix B: Stack Testing Results with Validated Data 

Administrative Order Requirement: “Hibtac shall submit all results of the testing to the MPCA. 

If Hibtac believes that any data resulting from the testing is not valid, Hibtac shall include an 

explanation of why it believes the data is not valid with the test report and test data. All data 

shall be provided in an unlocked electronic spreadsheet.” 

Appendix C: Relative Variability Index (RVI) Determination 

Administrative Order Requirement: “Hibtac shall analyze the calculated hourly NOx 

concentration for each furnace weighted by stack flow rate and determine the relative variability 

index (RVI) for the data set. The variability of the stack-flow weighted NOx concentration for 

each furnace will be quantified by a RVI, which is defined by the MPCA as the ratio of the width 

of a 95 percent prediction interval to the center of the interval. The stack-flow weighted NOx 

concentration for each hourly data point shall be calculated as follows: 
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If the RVI for the [NOx]Fj data is less than or equal to 0.20, then variability will be considered to 

be “low”. If the relative variability is greater than 0.20, then variability will be considered to be

“high”.” 

Appendix D: Predictive Equation Supporting Data and Calculations 

Administrative Order Requirement: “If the RVI for the data is high, then Hibtac may evaluate 

whether operating parameters (predictors) can be used to predict NOx concentration for each 

stack, from which hourly mass rate emissions in pounds per hour can be calculated using hourly 

stack gas flow rate measurement. The MPCA will accept a multiple regression-based predictive 

equation for each stack for NOx emission calculation, if: 1) the residual standard deviation of the 

random differences between the actual measured concentration and the regression equation 

predicted value divided by the average NOx concentration is less than or equal to 0.09 at the 

midpoint of the predicted concentration; 2) the predictors used in the regression equations 

incorporate, either directly or by proxy, significant plant parameters that could affect the NOx 

concentration; and 3) the leverage is not large, as determined by the MPCA (leverage is a 

measure used by statisticians to identify the extent to which the predictors are extrapolations). 

All supporting calculations and data used in developing the predictive equation shall be provided 

to the MPCA.” 

Appendix E: Quality Assurance and Control 

Administrative Order Requirement: “A description of and schedule for quality assurance and 

quality control methods by which Hibtac will ensure the continuing validity of the data collected 

for RVI determination or for the calibration of the predictive equation. The description shall 

include at a minimum: annual extended method 7E emissions testing with justification for the 

proposed duration of testing, and the quarterly submittal of relevant hourly operating parameters 

to demonstrate that operating conditions continue to be 1) within the range of the data collected 

during testing under Part 10, if the RVI is low or 2) within the range of data collected during 

calibration testing of a predictive equation, if the RVI is high. If the RVI is high and a predictive

equation is used, Hibtac shall provide a protocol consistent with US EPA’s monitoring protocol 

for an industrial furnace Predictive Emission Monitoring System. The protocol is available at: 

http://www.epa/gov/ttn/emc/furnace.pdf.”

Appendix F: Stack Gas Flow Monitor Schedule 

Administrative Order Requirement: “A schedule for installation and certification of permanent 

stack gas flow monitors such that installation and certification occurs no later than November 30, 

2008.” 
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Appendix G: Pellet Plant hourly NOx Emissions Readout Installation 

Administrative Order Requirement: “If the RVI is high and a predictive equation is used, a 

schedule for installation of a readout in the pellet furnace operator control room with the 

predicted hourly NOx emissions such that installation occurs no later than November 30, 2008.” 

It is understood by Hibbing Taconite Company that the MPCA will either approve or disapprove 

the use of this Alternative Method Proposal by August 31, 2008. 
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Appendix A 

Data Points for Operating Parameters during 150-hour NOx Test

The enclosed CD-ROM contains a folder titled “Furnace Line 2 Alternative Method Proposal.” 

This folder contains Barr Engineering’s Microsoft Excel spreadsheet titled “Copy of 60 minute 

file 11-19-07(Values).xls”. The spreadsheet’s highlighted regions indicate time periods when 

Barr Engineering personnel were completing periodic calibrations, moisture checks, and other 

minor equipment maintenance, as well as all time periods that were determined to be invalid for 

NOx calculation purposes. HTC used only validated data in the development of a Predictive 

Emission Monitoring System (PEMS) for Pellet Indurating Furnace Line 2. 

During the stack test, operating parameters were measured and recorded by HTC’s Distributive 

Control System (DCS) and retrieved using PI Historian. A Microsoft Excel spreadsheet titled 

“Furnace Line 2 Hourly Validated Process Data.xls” contains the retrieved, validated data. 
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Appendix B 

Stack Testing Results with Validated Data 

As noted in Appendix A, the validated operating parameters in the spreadsheet titled “Furnace 

Line 2 Hourly Validated Process Data.xls” does not include the highlighted cells in Barr 

Engineering’s spreadsheet titled “Copy of 60 minute file 11-19-07(Values).xls”. In order to 

obtain the hourly averages, HTC delineated the start and end times of each 60 minute test 

segment, and then averaged all of the operating data required by the MPCA (ferrous iron content 

of the feed material, pellet type, production rate, heat input, stack gas flow rate, and combustion 

zone temperature), in addition to operating parameters that HTC believed may affect NOx 

variability in the furnace. The operating parameters listed below were used to determine both the 

relative variability index (RVI), as well as a predictive equation for each stack vent, as required. 

Barr Engineering’s stack test report for the April 9-April 17, 2008 NOx testing for Furnace Line 

1 has been submitted concurrently with this Alternative Method Proposal. 

 Indurating Furnace Line 2 Monitored Operating Parameters

1. Airflow Rates for Scrubber Houses 1 through 4 (standard cubic feet per minute) 

2. Furnace Feed Rate (wet long tons per hour) 

3. South and North Chamber gas usage (million cubic feet per hour) 

4. Demist Differential Pressure for Scrubber Houses 1 through 4 (inches of water) 

5. Venturi Differential Pressure for Scrubber Houses 1 through 4 (inches of water) 

6. Water Flow Rate for Scrubber Houses 1 through 4 (gallons per minute) 

7. Hearth Layer Depth (inches) 

8. Machine Speed (feet per minute) 

9. UDD, WEX, WBR, CAF Pressures (inches of water)* 

10. UDD Discharge Temperature (degrees Fahrenheit)* 

11. Burn Thru Temperature (degrees Fahrenheit) 

12. 2

nd Cooling and Firing Zone Hood Pressures (in. H2O) 

13. Hoods 18 and 22 Temperatures (degrees Fahrenheit) 

14. Machine Discharge Temperature (degrees Fahrenheit) 

15. Fired Pellet – Total Fe (percent) 

16. Fired Pellet – Fe++ (percent) 

17. Fired Pellet – Silica (percent) 

18. Green Ball Moisture (percent) 

19. Fired Pellet – CaO (percent) 

20. Satmagan and Wet Fe++ of Plant Concentrate (percent) 

*UDD: Updraft Drying; WEX: Windbox Exhaust; WBR: Windbox Recoup; CAF: Cooling Air Fan 

During the 7-day performance test conducted on Indurating Furnace Line 2, HTC developed a 

schedule of 12 test runs, each with specific, predetermined operating conditions. HTC selected 

the various operating conditions in an attempt to determine the relationship between specific 

furnace operating conditions and NOx emission rates. HTC maintained the respective operating 

conditions for durations of approximately 8 – 16 hours, with transition periods generally required 

between operating conditions in order to achieve furnace stability. The transition periods are 

noted in the submitted spreadsheet. 

HTC’s experience has demonstrated that the time required for furnace stabilization between 

operating condition changes is insignificant with respect to HTC’s actual operation during 

normal production. However, because the changes between conditions occurred frequently 
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during the test, the data from these transition periods became a very significant portion in the 

calculations, and it is believed that these periods would bias the results. 

Because the transition periods are insignificant during normal operating conditions, the transition 

periods have been eliminated from all RVI calculations to better represent normal, stable furnace 

operations that would typically occur. It should be noted that some of the tested furnace 

operating conditions negatively impacted pellet physical quality, resulting in situations where 

HTC’s required fired pellet specifications could not be obtained. As previously stated, the 

overall intent was to test furnace conditions in order to induce NOx emissions variability, in 

order to develop a more valid predictive equation. 
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Appendix C 

Relative Variability Index (RVI) Determination

As stated in Appendix B, HTC removed the transition periods from the RVI determination 

calculations, because these transition periods represent an insignificant portion of normal 

operating conditions. If testing were conducted under normal operating conditions only, over a 

longer time period, the effect of the transition periods would become even more insignificant, 

allowing HTC’s furnace NOx emission results to meet the MPCA’s RVI threshold of 0.20, 

indicating low variability. However, because the test duration was 7 days, only 150 hours of 

valid data, representing multiple furnace operating conditions, was available to determine the 

sources of variation within the NOx emissions. Furthermore, the higher RVI values associated 

with SV025 is in part attributable to the low NOx emission rates for this particular stack vent, 

which causes higher variation. Also, please note that Condition 1 results were not utilized, due 

to instrumentation issues and operating upsets. Average NOx emission rates are displayed in 

parts per million. 

 SV028 SV027 SV026 SV025

 

Table 1: Relative Variability Index for Conditions 1 through 8 
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Appendix D 

Predictive Equation Supporting Data and Calculations 

Using the validated operating data detailed in Appendix B, HTC produced a predictive equation 

using Minitab®. To determine the significant parameters related to NOx formation, HTC 

developed a series of furnace operating test conditions in an effort to induce NOx emission 

variability. These operating conditions were controlled by HTC’s DCS and were selected to 

simulate potential furnace operating conditions. The test operating conditions were as follows: 

 

• Indexing the furnace (reduced temperatures, tonnage, and airflow) to imitate 

reduced tonnage situations 

• Non-realistic situations in which HTC would not choose to operate because of 

reduced quality and/or tonnage 

• Maximum tonnage (approximately 470 tons per hour), airflow, and temperatures 

to simulate a standard compression pellet run when the furnaces are running at 

optimum capacity. 

Even though the operating conditions were changed numerous times during this seven-day test, it 

is more typical that HTC maintains similar furnace operating conditions for several days or 

longer. When low tonnage situations occur, HTC may index for up to several weeks at a time. 

Therefore, the transition periods that were experienced during the seven-day test would actually 

have a very minimal effect on the NOx emissions over an extended period of time, a situation 

which is more representative of how HTC typically operates. When testing each condition for 8 

– 16 hour time periods, the transition periods will have a much larger impact during the test than 

typical transition periods would during periods of normal furnace operation. 

Therefore, a predictive equation without the transition periods included has been developed. To 

begin with, a best subset regression analysis was developed, taking into account the best model 

using 1 to 25 variables. Shown below are the best subsets regression analyses for Stacks 1 

(SV028), 2 (SV027), 3 (SV026), and 4 (SV025). 
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For each respective stack vent’s analysis, the R2

 from a 1 variable model to a 25 variable model 

was calculated. After completing multiple calculations, it was determined that the model’s 

accuracy does not improve significantly when taking into account greater than 5 variables. 

Therefore, it has been determined that 5 significant variables exist for each stack vent, with the 

remaining variables classified as insignificant. 

Shown below are the regression analyses for stacks 1 (SV028), 2 (SV027), 3 (SV026), and 4 

(SV025). 
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The Administrative Order by Consent states the following: “The MPCA will accept a multiple 

regression-based predictive equation for each stack for NOx emission calculation, if: 1) the 

residual standard deviation of the random differences between the actual measured concentration 

and the regression equation predicted value divided by the average NOx concentration is less 

than or equal to 0.09 at the midpoint of the predicted concentration.”. 

For the regression analyses, Minitab® stored the residuals for each data point employed by the 

model. Along with storage of the residuals, the standard deviation of the residuals and the 

average of the actual NOx concentrations have also been calculated. This data allowed 

determinations to be made regarding adherence to the requirement of 0.09. Below is the 

Minitab® output for this calculation: 

Stack 1 (SV028) 6.468 / 50.083 = .1291 

Stack 2 (SV027) 5.685 / 64.819 = .0877 

Stack 3 (SV026) 7.987 / 102.14 = .0782 

Stack 4 (SV025) 10.116 / 123.08 = .0822 
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Appendix E 

Quality Assurance and Control 

1. Applicability 

a. Identify source name, location, and emission unit number(s) 

Hibbing Taconite Company 

Highway 5 North 

P.O. Box 589 

Hibbing, MN 55746-0589 

Pellet Indurating Furnace Line 2 (EU 021) 

Control Equipment (CE) Stack Vent (SV) 

027 025 

028 026 

029 027 

030 028 

b. Identify the type of industry; 

SIC Code: 1011 

NAISC Code: 212210 (Iron Ore Mining) 

c. Identify the process of interest; 

Pellet Indurating Furnace Line 2 

d. Identify the regulations that apply (e.g.; NSPS, NESHAP, SIP); 

Several regulations apply to Pellet Indurating Furnace Line 2. However, only the 

Regional Haze Rule applies to the predictive emission monitoring requirements 

outlined in this protocol. 

e. Identify the pollutant(s) subject to monitoring (information on major/area 

source determination). 

NOx concentrations in parts per million (ppm) are calculated and converted to 

either pounds per hour or pounds per ton using gas flow rates measurements 

recorded by installed stack gas flow monitors. 

f. Provide expected dates of monitor compliance demonstration testing 

Installation, calibration, and certification of stack gas flow monitors will occur by 

November 30, 2008, as per the requirements detailed in the Administrative Order 

by Consent dated March 3, 2008. 
Page 21 of 33

2. Source Description 

a. Provide a simplified block flow diagram with parameter monitoring 

points and emission sampling points identified (e.g.; sampling ports in 

the stack); 

[7] 

[1] 

FURNACE 

FEED RATE 

(LONG 

TONS PER 

HOUR)

 UDD 

 Zone

 DDD 

 Zone

 PREHEAT 

 Zone

 FIRING 

 Zone

GRATE 

MACHINE 

SPEED 

(FEET PER 

MINUTE) 

FIRING HOOD 

PRESSURE [8]

[2] 

 To 

Scrubbers 

[7] 

2

nd

COOLING 

HOOD 

PRESSURE 

Windbox 

Exhaust fan Fresh Air 

Intake 

WIND BOX 

EXHAUST 

HEADER 

PRESSURE 

Cooling Air 

Fan

 UDD 

 Zone

 DDD 

 Zone

 PREHEAT 

 Zone

 FIRING 

 Zone

A. F. 

Zone

 PRI COOLING 

 Zone 

S COOL 

 Zone

COOLING 

AIR FAN 

HEADER 

PRESSURE 

[4] 
Page 22 of 33

 

 

 

Natural Gas Flow (Million Cubic Feet) to 

South Chamber 

Hood Temp 

(Wind Box 18) 

Lower 

Burner 

Typical South Firing Chamber

Natural Gas 

Flow to both 

South and 

North Firing 

Chambers

[2] 

[5] 

Bed

[6] 

BURNTHRU TEMP 

 (AVERAGE OF 

TWO 

TEMPERATURES) 

HOOD TEMP 

(WIND BOX 18) [5]

To DDD 

Hood zone 

Windbox 

Recoup Fan 

Fresh Air 

Intake 

Cooling Air 

Fan 

 UDD 

 Zone

 DDD 

 Zone

 PREHEAT 

 Zone

 FIRING 

 Zone

A. F. 

Zone

 PRI COOLING 

 Zone 

S COOL 

 Zone
Page 23 of 33

b. Provide a discussion of process or equipment operations that are 

known to significantly affect emissions or monitoring procedures 

(e.g., batch operations, plant schedules, product changes). 

HTC produces two types of pellets (standard and high compression). The typical 

split annually is 75 percent standard pellets and 25 percent high compression 

pellets. Limestone is added to each type of pellet to improve the pellet physical 

strength, in particular, the compression strength. For both, less than one percent 

by weight limestone is added to the green (unfired) pellets, with high compression 

addition rates double in comparison to standard pellets. When producing high 

compression pellets, the natural gas burner temperature set points are increased to 

calcinate the increased limestone quantities that are added during a high 

compression production run. 

HTC has developed a process control strategy to optimize process air flow at less 

than 100 percent production rates. This optimization matches process air flow 

with production rate and minimizes excess process air that is not needed. Finally, 

two shutdowns per furnace line occur each calendar year. The length of a 

shutdown is usually between 10 and 21 days and is dependant on the amount of 

scheduled maintenance performed. 

3. Control Equipment Description 

a. Provide a simplified block flow diagram with parameter monitoring 

points and emission sampling points identified (e.g.; sampling ports in 

the stack); 
Page 24 of 33

Hood Exhaust 

Fan (Primary) 

to Scrubber #1 

Process Scrubber Header (Common to both Fans)

Scrubber 

Water 

Flow 

Demist 

Differential 

Pressure 

Venturi 

Differential 

Pressure 

Scrubber #4 (Typical Scrubber) 

Process Air Flow from 

Scrubber Header to 

Scrubber #4 

Wind box Exhaust 

Fan (Primary) 

to Scrubber #4 

Four Header Outlet Ducts 

One for Each Scrubber 

Wind box 

Exhaust 

Multi-Tube 

House 

Windbox 

Exhaust 

Fan 

Hood 

Exhaust 

Fan 

Furnace 

Process Air 

From Updraft 

Drying Zone Multi-Tube 

Differential Pressure 

Future Air Flow 

Monitoring 

Wind Box Exhaust 

Fan (Secondary) 

to Scrubber #3 

Hood Exhaust 

Fan (Secondary) 

to Scrubber #2 

[3] 
Page 25 of 33

b. List monitored operating parameters and normal operating ranges; 

 Pellet Indurating Furnace Line 2 (EU 021) 

CE SV Venturi Differential 

Pressure (inches of water) 

Demist Differential 

Pressure (inches of water) 

Water Flow 

(gallons per 

minute) 

027 025 > 3.3 > 0.4 > 412 

028 026 > 4.5 > 0.3 > 416 

029 027 > 3.7 > 0.7 > 417 

030 028 > 4.1 > 0.9 > 390 

c. Provide a discussion of operating procedures that are known to 

significantly affect emissions (e.g., catalytic bed replacement 

schedules, ESP rapping cycles, fabric filter cleaning cycles). 

Please refer to 2b. 

4. Monitoring System Design 

a. Install, calibrate, operate, and maintain a continuous PEMS; 

The monitoring system will be installed, calibrated, and operational by November 

30, 2008.

b. Provide a general description of the software and hardware components of 

the PEMS including manufacturer, type of computer, name(s) of software 

product(s), monitoring technique (e.g., method of emission correlation). 

Manufacturer literature and other similar information shall also be 

submitted, as appropriate; 

Sick/Maihak FLOWSIC 100 Ultrasonic Flow Meters will be installed on each of 

Pellet Indurating Furnace Line 2 Stack Vents (SV025 – SV028). These flow 

meters calculate stack gas volume flow measurements, with the calculated data 

transmitted to the Fisher Rosemount Distributed Control System (DCS). In 

addition to stack gas flow rates, other process operating parameters relevant to 

NOx formation are collected by the DCS at the intervals specified in 4f. DCS 

readings are transmitted to the OSI Soft PI historian database, which facilitates 

storage and retrieval of historical data. 

NOx predictive models have been developed for each respective stack vent, with 

each model utilizing specific parameters to calculate NOx concentrations in parts 

per million (ppm). Stack gas flow rates are used to convert NOx concentrations 

in ppm to NOx emission rates in pounds per hour. PI historian is configured to 

collect and process all predictive model parameters, with NOx concentrations 

displayed visually in PI ProcessBook. 

c. List all elements used in the PEMS to be measured (e.g., pollutant(s), other 

exhaust constituent(s) such as O for correction purposes, process parameter(s), 

and/or emission control device parameter(s)); 
Page 26 of 33

Pellet Indurating Furnace Line 2 (EU021) 

CE SV Description Predictive Model Variables PI Tag ID 

Furnace Feed Rate [1] ADBI3160 

Total Natural Gas Usage [2] ADBI3108 

ADBI3109 

Venturi Differential Pressure 

[3] ADBI3718 

Cooling Air Fan Header 

Pressure [4] ADBI3122 

027 025 Wind Box Exhaust (Primary) 

Hood 18 Temperature [5] ADBI3199 

Furnace Feed Rate [1] ADBI3160 

Total Natural Gas Usage [2] ADBI3108 

ADBI3109 

Venturi Differential Pressure 

[3] ADBI3715 

Burn Thru Temperature [6] ADBI3196 

028 026 Wind Box Exhaust (Secondary) 

Hood 18 Temperature [5] ADBI3199 

Total Natural Gas Usage [2] ADBI3108 

ADBI3109 

Grate Machine Speed [7] ADBI3123 

Firing Hood Pressure [8] ADBI3194 

Hood 18 Temperature [5] ADBI3199 

029 027 Hood Exhaust (Secondary) 

Satmagan Fe++ in Plant 

Concentrate CLAB0003VL 

Hood 18 Temperature [5] ADBI3199 

Wind Box Exhaust Pressure ADBI3246 

Grate Machine Speed [7] ADBI3123 

Total Natural Gas Usage [2] ADBI3108 

ADBI3109 

030 028 Hood Exhaust (Primary) 

Venturi Differential Pressure 

[3] ADBI3709 

[*] denotes location in diagrams contained in 2a and 3a 

d. List all measurement or sampling locations (e.g., vent or stack location, 

process parameter measurement location, fuel sampling location, work 

stations); 

Please refer to Figure 1. 

 

e. Provide a simplified block flow diagram of the monitoring system overlaying 

process or control device diagram (could be included in Source Description 

and Control Equipment Description); 

Please refer to Figure 1.

f. Provide a description of sensors and analytical devices (e.g., thermocouple 

for temperature, pressure diaphragm for flow rate);
Page 27 of 33

g. Provide a description of the data acquisition and handling system operation 

including sample calculations (e.g., parameters to be recorded, frequency of 

measurement, data averaging time, reporting units, recording process); 

The data acquisition and handling system is described in 4b, and sensors used to 

measure predictive model variables, along with data collection intervals, are listed 

in 4f. 

Predictive 

Model 

Variable 

Description Manufacturer Part 

Number 

HTC Stock 

Code 

Data 

Collection 

Interval 

Scrubber Water 

Flow 

Water Flow 

Transmitter ABB 60 seconds 

Demist 

Differential 

Pressure Pressure 

Transmitter ABB 621DB2H 20067989 60 seconds 

Cooling Air 

Fan Header 

Pressure 

Pressure 

Transmitter ABB 621DB2H 20067989 200 milliseconds 

2

nd Cooling 

Hood Pressure 

Pressure 

Transmitter ABB 621DB2H 20067989 5 seconds 

Hood 18 

Temperature 

Type R 

Thermocouple Dynametrics 

24RSCPT2CN7

11MH2X3/4

BR35 

1108208 5 seconds 

Hood 22 

Temperature 

Type R 

Thermocouple Dynametrics 

24RSCPT2CN7

11MH2X3/4

BR35 

1108208 5 seconds 

Wet Fe++ in 

Plant 

Concentrate 

Wet Chemistry 

Titration N/A N/A Direct Order 8 hours 

Satmagan Fe++ 

in Plant 

Concentrate 

Magnetic 

Balance Satmagan N/A Direct Order 8 hours 

Total Iron in 

Fired Pellet 

X-Ray 

Fluorescence 

Spectrometry 

Panalytical PW 2403 Direct Order 8 hours 

Silica in Fired 

Pellet 

X-Ray 

Fluorescence 

Spectrometry 

Panalytical PW 2403 Direct Order 8 hours 

Updraft Drying 

Discharge 

Temperature 

Type R 

Thermocouple Dynametrics 

24RSCPT2CN7

11MH2X3/4

BR35 

1108208 5 seconds 

Wind Box 

Exhaust 

Pressure 

Pressure 

Transmitter ABB 621DB2H 20067989 5 seconds 
Page 28 of 33

The following sample equations are used to calculate NOx emissions from Pellet 

Indurating Furnace Line 2. The equations reference predictive model variables 

and associated PI Tag IDs listed in 4c. It should be noted that the predictive 

equations calculate NOx concentrations in parts per million, which will be 

converted to NOx emission rates (in pounds per hour) using stack gas flow 

measurements. 

NOx Predictive Equation for EU021, CE027, SV025 (PI Tag ID ADBI3950)

(IF TAGVAL('ADBI3160') > 400 THEN – 602 + 0.207 * 

(TAGVAL('ADBI3160') – 0.739 * (TAGVAL(' ADBI3108') + 

(TAGVAL('ADBI3109')) + 11.8 * TAGVAL('ADBI3718') – 2.92 * 

TAGVAL('ADBI3122') + 0.315 * TAGVAL('ADBI3199') ELSE 0.0) 

NOx Predictive Equation for EU021, CE028, SV026 (PI Tag ID ADBI3951)

(IF TAGVAL('ADBI3160') > 400 THEN – 503 + 0.202 * 

(TAGVAL('ADBI3160') – 0.481 * (TAGVAL(' ADBI3108') + 

(TAGVAL('ADBI3109')) – 12.7 * TAGVAL('ADBI3715') + 0.0532 * 

TAGVAL('ADBI3196') + 0.250 * TAGVAL('ADBI3199') ELSE 0.0) 

NOx Predictive Equation for EU021, CE029, SV027 (PI Tag ID ADBI3952)

(IF TAGVAL('ADBI3160') > 400 THEN – 394 – 0.447 * 

(TAGVAL('ADBI3108') + (TAGVAL('ADBI3109')) + 5.35 * 

TAGVAL('ADBI3123') + 153 * TAGVAL('ADBI3194') + 0.180 * 

TAGVAL('ADBI3199') + 4.16 * TAGVAL('CLAB0003VL') ELSE 0.0) 

NOx Predictive Equation for EU021, CE030, SV028 (PI Tag ID ADBI3953)

(IF TAGVAL('ADBI3160') > 400 THEN – 597 + 0.291 * TAGVAL(' 

ADBI3199') + 2.48 * (TAGVAL('ADBI3246') + 7.32 * TAGVAL('ADBI3123') – 

1.81 * (TAGVAL('ADBI3108') + (TAGVAL('ADBI3109')) + 12.6 * 

TAGVAL('ADBI3709') ELSE 0.0) 

Total NOx Emissions for EU021 (PI Tag ID ADBI3954)

TAGVAL('ADBI3950')+TAGVAL('ADBI3951')+TAGVAL('ADBI3952')+TAG

VAL('ADBI3953') 

h. Provide checklists, data sheets, and report format as necessary for 

compliance determination (e.g., forms for record keeping). 

As indicated in 4b, PI historian is used for storage and retrieval of predictive 

model data. Ellipse functions as HTC’s maintenance information management 

system. Preventive maintenance, repair, and calibration of monitoring equipment 

is planned, scheduled, and maintained using Ellipse. Quarterly reports consisting 

of emissions and operating parameter data will be submitted to the MPCA 30 

days following the end of each calendar quarter. 
Page 29 of 33

5. Support Testing and Data for Protocol Design 

a. Provide a description of field and/or laboratory testing conducted in 

developing the correlation (e.g., measurement interference check, 

parameter/emission correlation test plan, instrument range calibrations): 

Please refer to Appendices A – D. 

b. Provide graphs showing the correlation, and supporting data (e.g., 

correlation test results, predicted versus measured plots, sensitivity plots, 

computer modeling. 

Please refer to Appendices A – D. 

6. Initial Verification Test Procedures 

a. Perform an initial relative accuracy test (RA test) to verify the performance 

of the PEMS over the permitted operating range. The PEMS must meet the 

relative accuracy requirement of the applicable Performance Specification in 

40 CFR Part 60, Appendix B. The test shall utilize the test methods of 40 

CFR Part 60, Appendix A. 

Following the installation and certification of stack gas flow meters, currently 

scheduled for completion by November 30, 2008, HTC will conduct stack testing 

in conformance with the initial verification test procedures. 

b. Identify the most significant independently modifiable parameter affecting 

the emissions. Within the limits of safe unit operation, and typical of the 

anticipated range of operation, test the selected parameter for three RA test 

data sets at the low range, three at the normal operating range and three at 

the high operating range of that parameter, for a total of nine RA test data 

sets. Each RA test data set should be between 21 and 60 minutes in duration: 

Hood 18 temperature will be used as the most significant independently 

modifiable parameter affecting NOx emissions. Low, normal, and high operating 

ranges for this parameter will be selected based upon temperature ranges that 

allow HTC to meet and/or exceed its customers’ fired pellet quality specifications 

for both standard and high compression pellet production operating conditions. 

c. Maintain a log or sampling report for each required stack test listing the 

emission rate in accordance with the applicable emission limitations: 

HTC will adhere to all pre- and post-stack testing notification and recordkeeping 

requirements contained in HTC’s Title V (Part 70) Air Emissions Permit. Each 

subsequent stack testing campaign will be summarized and reported to the MPCA 

using a final stack test report. 

d. Demonstrate the ability of the PEMS to detect excessive sensor failure modes 

that would adversely affect PEMS emission determination. These failure 

modes include gross sensor failure or sensor drift. 
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i. The owner or operator shall demonstrate the ability to detect sensor 

failures that would cause the PEMS emissions determination to drift 

significantly from the original PEMS value. 

The identified predictive emission parameters are also critical parameters 

used to maintain HTC’s fired pellet quality specifications. As a result, 

instances of sensor failure and/or drift are promptly detected and resolved. 

In addition, analytical laboratory analyses allow confirmation of 

conformance to fired pellet quality specifications, thereby ensuring that 

sensor failure or drift has not occurred. 

ii. The owner or operator may use calculated sensor values based upon 

the mathematical relationships established with the other sensors used 

in the PEMS. The owner or operator shall establish and demonstrate 

the number and combination of calculated sensor values which would 

cause PEMS emission determination to drift significantly from the 

original PEMS value. 

Mathematical relationships between various parameters will not be used in 

the predictive emission monitoring system. 

7. Quality Assurance Plan 

a. Provide a list of the input parameters to the PEMS (e.g., transducers, 

sensors, gas chromatograph, periodic laboratory analysis), and a description 

of the sensor validation procedure (e.g., manual or automatic check): 

Please refer to 4f. 

b. Provide a description of routine control checks to be performed during 

operating periods (e.g., preventive maintenance schedule, daily manual or 

automatic sensor drift determinations, periodic instrument calibrations) 

Preventive maintenance, repair, and calibration of monitoring equipment is 

planned, scheduled, and maintained using Ellipse. 

c. Provide minimum data availability requirements and procedures for 

supplying missing data (including specifications for equipment outages for 

QA/QC checks): 

Please refer to 6di. 

d. List corrective action triggers [e.g., response time deterioration limit on 

pressure sensor, use of statistical process control (SPC) determinations of 

problems, sensor validation alarms]: 

Please refer to 6di. 

e. List trouble-shooting procedures and potential corrective actions: 

f. Provide an inventory of replacement and repair supplies for the sensors: 
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Please refer to 4f. 

g. Specify, for each input parameter to the PEMS, the drift criteria for 

excessive error (e.g.: the drift limit of each input sensor that would cause the 

PEMS to exceed relative accuracy requirements): 

Drift criteria for predictive emission monitoring system parameters have been 

established and are maintained using the preexisting specifications for 

maintenance of overall fired pellet quality. 

 

h. Conduct a quarterly electronic data accuracy assessment test of the PEMS. 

A quarterly electronic data accuracy assessment of the PEMS will be conducted 

and reported to the MPCA. 

i. Conduct semiannual RA tests of the PEMS. Annual RA tests may be 

conducted if the most recent RA test result is less than or equal to 7.5%. 

Identify the most significant independently modifiable parameter affecting 

the emissions. Within the limits of safe unit operation and typical of the 

anticipated range of operation, test the selected parameter for three RA test 

data pairs at the low range, three at the normal operating range, and three at 

the high operating range of that parameter for a total of nine RA test data 

sets. Each RA test data set should be between 21 and 60 minutes in duration: 

HTC will conduct annual method 7E testing to verify continuing accuracy of the 

PEMS, using the parameter specified in 6b. 

8. PEMS Tuning 

a. Perform tuning of the PEMS provided that the fundamental mathematical 

relationships in the PEMS model are not changed. 

Annual 7E stack testing, in combination with the quarterly electronic data 

assessments, will allow for tuning of the PEMS, as necessary. 

b. Perform tuning of the PEMS in case of sensor recalibration or sensor 

replacement provided that the fundamental mathematical relationships in 

the PEMS model are not changed. 

Annual 7E stack testing, in combination with the quarterly electronic data 

assessments, will allow for tuning of the PEMS, as necessary. In addition, 

calibration and/or repair procedures for monitoring equipment will ensure that the 

PEMS output retains RA requirements. 
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Appendix G 

Pellet Plant Hourly NOx Emissions Readout Installation 

Furnace Line 2 real-time NOx predictions per individual stack are now recorded in PI Historian. 

The NOx predictions are calculated from the models that were created from the Furnace Line 2 

NOx performance test that occurred on April 9-April 17, 2008. These predictions are accessible 

by staff throughout the property, as well as employees in the Pelletizing control room, where the 

operator can view real-time predicted NOx emissions using PI ProcessBook. The historical data 

can be retrieved and processed using Microsoft Excel’s PI Datalink feature.