Coronado Emissions Control Project SRP Doc #:1700- 02-M-SZZ-6435

SRP PO #: SRP - 0000322042 Dist: G91, SRP Rev A

Project No. Plant and Unit No. Document No. 100551 Salt River Project Coronado Generating Station Unit 2 100551-090220000-04

Document 

## FUNCTIONAL DESCRIPTION The SCR Reactor

Note:

1st Issue Phone No. Date Name Signature Written by X1178 4/26/11 Kellie Bresnahan Kellie Br esnahan Reviewed by X3877 4/27/11 Kenneth Hurlburt Kenneth Hurlburt Approved by X1192 4/29/11 Michael Jasinski Michael Jasinski Approved by X1174 5/3/11 William Braband William Br aband Rev. Date Item Changed by Approved

by 01 10/24/11 Updates per SRP / S&L Comments KSB MLJ 02 3/26/12 Update section 2.2, 3.1 KSB MLJ 03 2/4/13 Remove reference to Alarm & Setpoint List KSB MLJ 04 9/4/13 Update Figures 1 and 2 KSB MLJ
Distribution list no. pages 

# 10

This document and the information, design and mater ial contained and/or illustrated therein (hereinaft er “proprietary material”), is the pro perty of BABCOCK POWER Inc., P.O. Box 15040, Worcester, MA 01615-0040, and is su bmitted, lent and furnished to recipient in strict confidence with the express understanding that the recipient shall not reproduce, copy, loan, dispose of, or disclose to a nyone outside recipient’s organization, directly or indirectly, or use sai d proprietary material for any purpose other than t hat for which it is furnished and submitted. Recipient by receiving said proprietary material agrees not t o use the same in any way in jurious to the interest or BABCOCK POWER Inc., and agrees to return same upon request. Copyr ight  BABCOCK POWER Inc., 2011. All Rights Reserved.Salt River Project Coronado Generating Station Unit 2

Selective Catalytic Reduction System

SCR Operating and Maintenance Manual September 04 , 2013 SCR Reactor Functional Description Page 2 of 10 Rev ision 04



## The Selective Catalytic Reduction Reactor

Table of Contents

1.0 GENERAL INFORMATION AND REFERENCES 3

2.0 SCR REACTOR PROCESS DESCRIPTION 4

2.1 The NOx Reduction Chemical Reaction 4

2.2 SCR Reactors 4

3.0 SCR REACTOR OPERATION AND CONTROL 7

3.1 SCR Reactor Startup 7

3.2 Normal Operation 8

3.3 Normal Shutdown 9

3.4 Emergency Shutdown (SCR Reactor Trip) 10

3.5 SCR Reactor Purge 10Salt River Project Coronado Generating Station Unit 2

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### 1.0 General Information and References The design of the SCR Reactor system complies with the following codes:

• American National Standard Institute (ANSI)

• American Society of Mechanical Engineers (ASME)

• National Fire Protection Association (NFPA)

• American Institute of Steel Construction (AISC)

• American Welding Society (AWS)

• Occupational Safety and Health Administration Stan dards (OSHA)

• American Society of Civil Engineers (ASCE)

• American Society for Testing and Materials (ASTM) Refer to the following documents for detailed infor mation such as the process flow rates, instrument t ag numbers, DCS I/O points and alarm setpoints.

Reference No. RPI Doc. Number SRP Doc. Number Title 1 100551-093000100 1700-02-M-SZF-6435 Process Flow Diagram 2 100551-093001040 1700-02-M-SZM-6435 SCR Material Balance – 450 MW 3 100551-093001041 1700-02-M-SZM-6436 SCR Material Balance – 200 MW 4 100551-093001042 1700-02-M-SZM-6437 SCR Material Balance – 50 MW 5 100551-094900050 1700-02-M-BAD-6435 P&ID – SCR R eactor 2-N 6 100551-094900051 1700-02-M-BAD-6436 P&ID – SCR R eactor 2-S 7 100551-094751001 1700-02-M-SZL-6435 Manual Valve List 8 100551-094752001 1700-02-M-SZL-6436 Actuated Val ve List 9 100551-094904200 1700-02-J-SZZ-6436 Instrument L ist 10 100551-094915000 – 1700-02-J-XXF-6435 – Analo g Logic Diagrams 100551-094917088 1700-02-J-SHF-6438 11 100551-094920000 – 1700-02-J-XXL-6435 – Binar y Logic Diagrams 100551-094928022 1700-02-J-SHL-6440 12 100551-094904600 1700-02-J-SZZ-6437 Input/Outpu t ListSalt River Project Coronado Generating Station Unit 2

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### 2.0 SCR Reactor Process Description
2.1 The NOx Reduction Chemical Reaction The SCR System is designed to reduce nitrogen oxide s (NOx) in the boiler flue gas to nitrogen gas (N 2 ) and water vapor (H 2 O). The reduction is accomplished using ammonia as the reducing agent in the presence of a catalyst. The catalyst allows the ex othermic reactions to take place in the SCR reactor

.

As long as a mixture of NO and NO 2 is present, the following faster reaction happens in parallel,



### 2.2 SCR Reactors Installed on the boiler of the Salt River Project (SRP) Coronado Unit 2 are two SC R reactors operating in parallel at the hot gas side ESP outlet. Anhydrous ammonia is the reducing reagent for the SCR reacto rs. The initial charge of reactor catalyst is a honeyco mb design. Figure 1 is a schematic of one of the SCR reactors. Each SCR reactor is comprised of the following equipment:

• Four layer reactor with three layers of catalyst i nstalled and one empty layer for future catalyst

• Redundant inlet (2-BA-AE-6451N / S, 2-BA-AE-6452N / S) and outlet (2-BA-AE-6491N / S, 2-BAAE-6492N / S) NOx / CO 2 Analyzer (See Figure 1)

• Outlet ammonia slip analyzer (2-BA-AE-6490N / S)

• Expansion joints (2-M-BA-M-6435N / S, 2-M-BA-M-643 6N / S, 2-M-BA-M-6437N / S, 2-M-BA-M6438N / S)

• Pressure instrumentation located throughout the sy stem (See Figure 1): 2-BA-PIT-6440NA / NB / NC, SA / SB / SC 2-BA-PIT-6464NA / NB / NC, SA / SB / SC 2-BA-PIT-6470N / S 2-BA-PIT-6481NA / NB / NC, SA / SB / SC 2-BA-PIT-6510NA / NB / NC, SA / SB / SC

• Temperature instrumentation located throughout the system (See Figure 1): 2-BA-TE-6443NA / NB / NC, SA / SB / SC 2-BA-TE-6461NA / NB / NC, SA / SB / SC 2-BA-TE-6472NA / NB, SA / SB 

### O H N NH NO O H N O NH NO

2 2 3 2 2 2 2 3 

### + → + +

→ + +

O

H N NH NO NO 2 2 3 2 

### + → + +Salt River Project Coronado Generating Station Unit 2

Selective Catalytic Reduction System

SCR Operating and Maintenance Manual September 04 , 2013 SCR Reactor Functional Description Page 5 of 10 Rev ision 04 2-BA-TE-6473NA / NB, SA / SB 2-BA-TE-6474NA / NB, SA / SB 2-BA-TE-6494NA / NB / NC, SA / SB / SC

• Permanently installed temperature measurement grid at inlet

• Permanently installed temperature measurement grid at outlet for initial testing

• Delta Wing  mixers with locations for injecting ammonia vapor

• Four sonic horns on each layers two (2-M-SH-B-6435 N / S – 6438N / S), three (2-M-SH-B-6439N / S – 6442N / S), and four (2-M-SH-B-6443N / S – 64 46N / S) of catalyst (See Sonic Horn and Sootblower Functional Description)

• Three sootblowers on catalyst layer one (2-M-SS-B- 6435N / S, 6436N / S, 6437N / S)

• Manual test ports
In the case of three redundant instruments in a row , RPI uses median select which uses only good signa ls as determined by the DCS. During boiler operation, flue gas flows from the ou tlet of the economizer through a hot gas side ESP a nd on to the inlet of the SCR reactor. Ammonia vapo r diluted with warm air is injected at the Delta Wi ng  mixers at the SCR reactor inlet to thoroughly mix t he ammonia with the flue gas. Turning vanes and crossmixers are located throughout the SCR system d uctwork to aid with flow and ash distribution and NH 3 / NO x

mixing. After mixing with ammonia, the flue gas e nters the reactor and first layer of catalyst. The SCR initially contains three layers of honeycom b type catalyst and one empty layer to be filled in the future. Each layer of catalyst contains 66 modules in a 6 x 11 arrangement. The catalytic reaction between the NOx and NH 3 occurs in the reactor. Once the flue gas passes t hrough the active reactor layers, it flows to the inlet of the Air Heater. In cases where there are multiple instruments insta lled in one location, the median select using only good signals is used.Salt River Project Coronado Generating Station Unit 2

Selective Catalytic Reduction System

SCR Operating and Maintenance Manual September 04 , 2013 SCR Reactor Functional Description Page 6 of 10 Rev ision 04 FIGURE 1: SCR Reactor System Schematic

P1 – HESP Outlet Pressure x 3
P2 – SCR Reactor Inlet Pressure x 3
P3 – SCR Reactor Inlet Pressure x 1
P4 – SCR Reactor Outlet Pressure x 3
P5 – Air Heater Inlet Pressure x 3
A1 – SCR Reactor Inlet NOx and CO 2 x 2 A2 – SCR Reactor Outlet NOx and CO 2 x 2
A3 – NH 3 Slip T1 – HESP Outlet Temperature x 3 T2 – SCR Reactor Inlet Temperature x 3 T3 – Permanently Installed Temperature Grid T4 – Catalyst Layer N-1 Temperature x 2 T5 – Catalyst Layer N-2 Temperature x 2 T6 – Catalyst Layer N-3 Temperature x 2 T7 – Catalyst Layer N-4 Temperature x 2 T8 – Permanently Installed Temperature Grid for Tes ting T9 – SCR Reactor Outlet Temperature x 3Salt River Project Coronado Generating Station Unit 2

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### 3.0 SCR Reactor Operation and Control 3.1 SCR Reactor Startup The objective of the SCR start-up is to warm the re actor in a controlled procedure to the minimum cata lyst operating temperature before injecting ammonia. SCR warm up is controlled manually by the DCS operator by limiting the boiler ramp up rate. Ammo nia cannot be injected below the minimum temperatur e because ammonia sulfates would condense in the cata lyst pores and prematurely reduce the activity of the catalyst. The catalyst minimum continuous oper ating temperature (T mincot ) is calculated based on an analysis of the fuels. The catalyst maximum contin uous operating temperature (T maxcot ) is set to avoid thermal sintering of the catalyst. Based on the specified fuel and the catalyst design the catalyst minimum and maximum continuous operating temperatures at Coronado Unit 2 are:



### F T F T

° = ° = 800 599

cot max cot min

The SCR reactor starts along with the boiler. It i s important to monitor and control the SCR reactor temperature ramp-up rate during start-up. It is th e responsibility of the DCS operator to limit boile r ramp up rate to avoid exceeding the limitations. There a re two limitations that must be considered: a) The maximum allowed temperature ramp up rate for the catalyst: The catalyst manufacturer defines this temperature. The supplier supplied st art up temperature ramping rate up to the desired catalyst temperature is 18°F per minute. O nce the catalyst reaches the desired temperature, the ramp rate is increased to 180°F pe r minute. b) The maximum allowed temperature ramp up rate of the SCR reactor steel structure: Riley Power, Inc. defines the maximum temperature ramp up rate a s 3°F per minute (180°F/hr) when measured with gas thermocouples in the inlet, react or, and outlet ductwork. If the maximum allowed temperature rise for the cat alyst is exceeded, the catalyst pores may be damage d due to the quick evaporation of moisture. If the m aximum allowed temperature rise for the steel struc ture is exceeded, serious thermal stress damage of the r eactor steel structure may occur. The maximum allowed steel structure temperature rise of 3°F per minute and is the limiting temperature ramp-up rat e. Figure 2 illustrates a typical temperature trend fo r the SCR reactor during start-up. At a reactor in let temperature (T2) above ambient, a temperature rise of 2.5°F per minute (150°F/hr) produces an alarm to the operator. The operator receives a second alarm at 3°F per minute (180°F/hr). At the second alarm , the operator must take steps to lower the temperatu re rise rate in the SCR such as limiting the firing rate in the boiler. Alarms also occur for high catalyst temperatures or high SCR reactor differential pres sure. The logic diagrams provide the values of the alarm setpoints. At a reactor outlet temperature (T9) abo ve 500°F, the reactor steel structure is close to the normal operating temperature and with reduced therm al stresses there are no temperature rise alarms, but other alarms remain active. When the temperature of the SCR reactor outlet and the last catalyst layer reaches the minimum continuous operating temperature for ammonia inject ion, the ammonia injection trip valve is permitted to open.Salt River Project Coronado Generating Station Unit 2

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### 3.2 Normal Operation Figure 3 shows the SCR temperature as a function of load. The reactor operates in a temperature range between the catalyst minimum continuous operating t emperature and the maximum continuous operating temperature. A low temperature alarm is generated for the operator at an SCR inlet temperature of T mincot + 15 ° F. A low-low temperature alarm occurs at T mincot . If the SCR inlet temperature falls below T mincot - 15 ° F, the ammonia injection trip valves close. The amm onia injection trip valve will not close if the SCR temperature exceeds T maxcot , however catalyst deactivation can occur. If T maxcot is exceeded, it is necessary for the operator to limit firing rate on the boiler to bring the temperature back into the o perating range. The ammonia injection trip valve also closes when the SCR reactor outlet temperature or the catalyst temperature falls below T mincot - 15 ° F. A high alarm occurs at T maxcot - 25 ° F and at T maxcot for any SCR reactor temperature element. Alarms are also g enerated for high-pressure drop across the SCR reactor and high outlet NOx concentration. The log ic diagrams provide the temperature setpoints and alarms to aid the operator. FIGURE 2: SCR Reactor Start-up Temperature TrendSalt River Project Coronado Generating Station Unit 2

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### 3.3 Normal Shutdown A normal shutdown occurs when the temperature of th e SCR reactor inlet, SCR reactor outlet or lowest filled catalyst layer drops below T mincot - 15 ° F. The SCR reactor cool down rate is not monitored or controlled, as the insulation and heat capacity of the reactor and structure will not allow the SCR re actor to exceed a maximum cool down rate. A normal shutdown results in the following action:

• The ammonia injection trip valves (2-SN-V6496NA / SA, NB / SB) for both reactors close

• The ammonia injection flow control valves (2-SN-V6 506NA / NB, SA / SB) for both reactors close and transfer to manual mode The operating ammonia pump isolation valve remains open, the ammonia pump remains on, and the ammonia tank supply remains selected. The operator shuts down the dilution air system app roximately 30 minutes after ammonia injection has ceased in order to purge the ammonia injection pipi ng. The presence of residual ammonia can be determined based on inlet and outlet NOx meter valu es. Once the boiler is shut down standard NPFA purge requirements clear the SCR reactor and ductwo rk of any potential explosive gases. (See the SCR System Operating Procedure and the Catalyst Manual)

. FIGURE 3: SCR Reactor Temperature versus LoadSalt River Project Coronado Generating Station Unit 2

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### 3.4 Emergency Shutdown (SCR Reactor Trip) An emergency shutdown occurs in response to a Maste r Fuel Trip (MFT). The MFT signal from the BMS will result in the following actions in the SCR con trol system logic:

• The ammonia double block valves (2-SN-V6501NA / NB , SA / SB, 2-SN-V6504NA / NB, SA / SB) close and vent valves (2-SN-V6503NA / NB, SA / SB) open

• The ammonia injection trip valves (2-SN-V6496NA / SA, NB / SB) for both reactors close

• The ammonia injection flow control valves (2-SN-V6 506NA / NB, SA / SB) for both reactors close after delay (Delay is required to bleed ammonia int o reactor)

• Sonic horns and soot blowers shutdown. Catalyst c leaning not required when there is no flue gas flowing The dilution air system remains in service in order to purge the ammonia injection piping of residual ammonia. A time period of 30 minutes is recommended to ensure the residual ammonia has been vaporized. In addition hard-wired MFT relay contacts will clos e the double block valves and open the vent valve o n all of the ammonia injection headers preventing injecti on of ammonia while the unit is shutdown. 

### 3.5 SCR Reactor Purge After a Master Fuel Trip or normal shutdown, a unit purge should be completed according to NFPA 85 and plant procedures.