19149328-Heat-Recovery-Steam-Generator-Operation-Procedure.pdf

MIRANT- KENDALL REPOWERING PROJECT

Cambridge. MA

OPERATING MANUAL

HEAT RECOVERY STEAM GENERATOR

Section 13.1


Table of Contents

1.0 Simplified Diagram......................................................................3

2.0 System Purpose..........................................................................4

3.0 System Components...................................................................43.1 Control Loop Narratives......................................................10

4.0 System Description...................................................................154.1 Primary System Flow Path..................................................164.2 Normal Operating Parameters............................................174.3 Secondary Systems.............................................................17

5.0 System Startup .........................................................................185.1 Precautions..........................................................................205.2 Prerequisites........................................................................235.3 Startup.................................................................................26

6.0 Normal Operation......................................................................286.1 Valve Alignment...................................................................28

7.0 Normal Shutdown......................................................................357.1 Precautions..........................................................................357.2 Shutdown.............................................................................36

Date of Issue: 12/20/01 Revision: 0

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8.0 Abnormal Shutdown..................................................................398.1 Power Failure......................................................................398.2 Instrument Air Failure..........................................................398.3 Steam Turbine Generator Trip.............................................40

9.0 Alarm Summary and Response................................................40

10.0 References..............................................................................4410.1 Drawings............................................................................4410.2 Vendors..............................................................................45

1.0 SIMPLIFIED DIAGRAM


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Duct Burner

HP Superheater #3

HP Superheater #2

HP Evaporator

IP Evaporator

HP Economizer #3

IP Superheater

CO Reducer / SCR

LP Evaporator

HP Economizer #2

IP Economizer

Feedwater Heater

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2.0 SYSTEM PURPOSE


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The purpose of the heat recovery steam generator is to pre-heat boiler feedwater and generate two pressure levels of steam by the circulation of this water through superheat steam tubes that cross pattern the gas turbine's hot exhaust.

3.0 SYSTEM COMPONENTS

The heat recovery steam generator (HRSG) is a fabricated, horizontal, metal duct that connects to the combustion turbine exhaust and directs the hot exhaust gas through a series of metal tubes to the exhaust stack. Inside the metal tubes, feedwater is circulated and heated to produce steam in the steam drums. Steam produced in the two steam drums supplies the HP and LP steam systems.

Heat Recovery Steam Generator

Mfg: Foster WheelerHP steam: Flow rate – 500-900 kpphPressure 1360-1370 psiaTemperature 895-905°FIP steam: Flow rate - 28 – 50 kpph

Pressure - 195-235 psiaTemperature 500-550°F

The HRSG is comprised of several major sections and components, which collectively produce steam for delivery to the Kendall Station steam.


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The major sections of the HRSG from the exhaust gas inlet looking toward the stack are as follows:

• Expansion joint• HRSG casing• Duct Burner• HP superheater #3• HP superheater #2• HP superheater #1• HP evaporator• CO, SCR, and Ammonia injection grid• IP superheater• IP evaporator• HP economizer 2• HP economizer 3• IP Economizer / HP economizer 1• LP evaporator• Feedwater heater • Exhaust stack

HRSG Casing

A carbon steel casing encloses the heat transfer sections. The casing is lined with stainless steel from the HRSG inlet through the HP Evaporator section, then a carbon steel liner to the main exhaust stack. The gas path is completely gas tight to prevent leakage.

A carbon monoxide (CO) catalyst section and selective catalytic reduction (SCR) System is located downstream from the HP evaporator section of the HRSG.


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Steam Drums

Steam drums are provided in each section of the HRSG to maintain an interface between the water and the steam. The drums have internals that separate the water from the steam and provide for a storage volume of water. Water level is maintained in the drums by means of level control valves controlled by the DCS based on information from steam flow and feedwater flow elements and drum level transmitters. The HP and IP drums are designed with 3 minutes of retention time from normal water level to low-level trip water level based on maximum steam production with no duct firing. The LP drum is designed with 5 minutes of retention time from normal water level to low-level trip water level based on maximum steam production with no duct firing.

Each drum is provided with internal distributors, baffles, shields, separators and internal piping. The separators maintain steam quality and prevent the carry-over of water into tube sections that contain steam. The drums also have provisions for chemical feed, sampling, and continuous blowdown.

Heat Transfer Surfaces

Heat transfer surfaces consist of vertical banks of tubes. The tube material varies in order to be compatible with the pressure and temperature of steam and with the temperature of the exhaust gas that comes in contact with the tubes. The gas temperature is highest at the HRSG inlet and decreases through successive sections of the HRSG as heat is transferred to the water. The coolest gas is at the exit of the HRSG. The coolest water (condensate) is introduced at the exhaust gas exit end of the HRSG. This arrangement is referred to as a countercurrent flow path.

The various sections of the HRSG include the condensate preheater, economizer, evaporator and superheater sections. The economizer is the first section in the water flow path and contains no steam. There are several evaporator sections where steam generation takes place.


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The evaporator sections of each HRSG consist of a steam drum, downcomers, feeder tubes, modules, and riser tubes to create a natural circulation effect. Natural circulation ensures that water is continuously moving within the HRSG tubes to remove and replace the steam produced due to the difference in density between the water and steam. Water is supplied from the drum to the bottom of the unit through the downcomer. As the gas turbine exhaust gas, supplemented with the duct burner, heats the evaporator tubes, a steam/water mixture is formed in the tubes that is less dense than the water in the downcomers; thus, the mixture rises up to the steam drum and ultimately is sent to the superheater as saturated vapor. The circulation process continues with a steam/water mixture generated in the tubes and replaced with heavier water from the downcomers. As more heat is added to the HRSG tubes, the steam quality of the fluid increases. Up to a point, circulation will naturally increase with increased heat input and provide more flow to keep the HRSG tubes cooled as more steam is generated. Beyond a certain level, friction in the tubes overcomes the difference in density and circulation is reduced with additional heat input.

The saturated steam from the drum enters the superheater sections before leaving the HRSG as either HP Steam or IP Steam. LP steam from the LP drum goes directly to the deaerator and is not superheated.

Continuous Blowdown System

The system is a continuous cascading system from the HP steam drum to the IP steam drum and from the IP drum to a continuous blowdown tank. Flash steam from the continuous blowdown tank is vented to the LP Drum.

Desuperheaters

HP desuperheater provides temperature control for the HP steam. The desuperheater is spray type and uses feedwater to cool the steam to achieve the desired outlet temperature. The HP desuperheater is located between the second and third stage of HP superheater. All controls for the desuperheater are furnished with the HRSG and are controlled


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through the DCS. The controls include control valves, automatic block valves, temperature sensing elements and transducers.

Condensate Preheater

Condensate from the existing plant’s condenser, together with demineralized water make-up from the water treatment system, enters the HRSG’s condensate preheater prior to entering the deaerator and LP evaporator section. The preheater is constructed of stainless steel tubes. Two condensate recirculation water pumps draw a portion of heated condensate from the discharge of the condensate preheater and return it to the preheater inlet to maintain the condensate at a minimum of 120°F to prevent exhaust gas from condensing on the outside of the tubes.

Insulation

The inlet ductwork, inlet transition section, and the HRSG are internally insulated to minimize heat loss and for personnel protection. The insulation is attached to the internal wall surfaces and is protected by an internal stainless steel liner. The outlet transition duct and stack are provided with thermal insulation barriers for personnel protection.

Insulation materials are asbestos free and non-corrosive. Piping equipment operating between 140°F and 500°F are insulated with heavy density fiberglass. All piping operating at temperatures above 500°F is insulated with high temperature mineral wool or calcium silicate. Calcium silicate is also installed where piping and equipment, operating below 500°F, is subject to mechanical damage or people walking, leaning, sitting, etc. on it.


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Support Steel, Stairs and Platforms

Stair towers, caged ladders, platforms and walkways are provided for access to the HRSG trim.

Ducts, Silencers and Stack

The 18 foot diameter stack extends to a height of 250 feet above grade. A caged ladder is provided to access the 360-degree platform that serves the continuous emission monitoring (CEM) ports and sample test ports and the platform that serves the FAA lighting. Expansion joints are provided in the ducts at the HRSG inlet and outlet.

Duct Burners

The duct burner system is designed to provide supplemental heat to the combustion turbine exhaust gas in order to increase steam production in the HRSG. The duct burner system is designed to burn natural gas and is located upstream of the HP superheater sections in the HRSG gas path. The duct burner system consists of the following components and is discussed further in Section 13.2.

• Duct burners • Natural gas fuel train• Burner management system• Ignitor system• Scanner system

Selective Catalytic Reduction System

The selective catalytic reduction (SCR) system is used to chemically react the NOx emissions from the combustion turbine exhaust and HRSG duct burner with injected ammonia to produce environmentally neutral nitrogen and water, thereby reducing the NOx emissions to the environment. The SCR system is composed of a set of ammonia injection nozzles; a catalyst bed and an in-line air heater used vaporize ammonia provided by the


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ammonia storage and supply system. The SCR catalyst is designed for a 5-year catalyst life and can be replaced when required. The SCR and ammonia injection system are discussed in Section 13.3.

CO Reduction System

The CO catalyst system is an emission control device designed to oxidize carbon monoxide (CO) from the combustion turbine exhaust and HRSG duct burner into carbon dioxide. The catalyst is supplied in modules that can be replaced when required. The carbon monoxide reduction system is are discussed in Section 13.3

3.1 Control Loop Narratives

PCV-10227 LP Pegging Steam Control Valve

Operation: The LP Steam Drum Pegging Steam Pressure Control Valve is controlled and monitored remotely at the DCS.

LP Steam Drum Pegging Steam Pressure Control Valve regulates flow of pegging steam to the low-pressure steam drum. LP Steam Drum Pegging Steam Pressure Control Valve is controlled as follows:

The control valve is equipped with a typical AUTO/MANUAL station at the DCS. Once the HRSG LP Drum is placed in service, the valve is placed in the AUTO mode.

When in AUTO the valve modulates to maintain LP Steam Drum pressure at the setpoint. As the pressure decreases the valve opens to allow more steam to the steam drum.

Upon loss of compressed air the valve fails in the closed position.

The DCS will indicate the following about the LP Steam Drum Pegging Steam Pressure Control Valve:


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• AUTO/MANUAL operation• % OPEN

LCV-10013 HP Steam Drum Level Control

Note: This description also applies in principle to IP and LP control valves LV-10131 and LV-10213 respectively.

Operation: The level indicating controller is preset to maintain HP steam drum level. The controller provides a signal to the boiler feedwater single and three element control loops to open and close LV-10013 on the supply side of HP economizer 1.

The HP Steam Drum Level Control Valve is controlled and monitored remotely at the DCS.

HP Steam Drum Level Control Valve regulates flow of water from the HP Feedwater system to the HP Steam drum, to maintain HP Steam Drum water level. The HP Steam Drum Level Control Valve is controlled as follows:

The control valve is equipped with a typical AUTO/MANUAL station at the DCS.

The operator at the DCS selects SINGLE or 3-ELEMENT control.

During unit startup and low load conditions, drum level is controlled by single element control; based on drum level only. The process variable used during single element control is solely from Level Transmitter.


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During three-element control, the level controller uses the computed value (summary) of the following input signals as the process variable.

• Drum Level• Feedwater Flow• Steam Flow (pressure and temperature compensated)

During normal operation, the valve is in AUTO, 3-ELEMENT operation.

Upon loss of compressed air the valve fails in the closed position.

The DCS will indicate the following about the HP Steam Drum Level Control Valve:

• AUTO/MANUAL operation• % OPEN• SINGLE or 3-ELEMENT Level Control

LP Feedwater Economizer Bypass Block Valve

Operation: The HRSG LP Economizer Bypass Valve is controlled and monitored remotely from the DCS. The valve operates based on signals generated from the DCS. The signals are OPEN and CLOSE.

The valve can be placed in AUTO or MANUAL at the DCS.

During normal operation the valve is placed in AUTO and OPENS/CLOSES based on the following conditions:

• Valve will automatically CLOSE, when valve is in AUTO, if the CT FIRING ON GAS signal is activated.


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• Valve will automatically OPEN, when valve is in AUTO, if the CT FIRING ON OIL signal is activated.

When changes in system occur, the DCS will indicate either HRSG ECONOMIZER REQUIRED or HRSG ECON BYPASS REQUIRED.

The following can change in the MANUAL valve position:

• Valve will CLOSE when the LP economizer is placed in service from the DCS.

• Valve will OPEN when the LP economizer bypass is activated from the DCS.

If valve does not meet open or closed limits in a specified time period there will be a VALVE TRAVEL FAILURE at the DCS.

The DCS will indicate the following for the HRSG LP Economizer No. 1 Block Valve:

• AUTO/MANUAL• CLOSED• OPEN

Gas Turbine Trip

The Gas Turbine should trip on any of the following:

• HP Drum level low-low (LSLL-10014) @ NWL – 52.5”• IP Drum level low-low (LSLL-10114) @ NWL – 9”• LP Drum level low-low (LSLL-10214) @ NWL – 63”• HP Drum steam pressure high-high (PT-10011) @ 1585 psig (2nd safety

valve)


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• IP Drum steam pressure high-high (PT-10111) @ 345 psig (2nd safety valve)

Pre-alarms as follows:

• HP Drum level low (LSL-10014) @ NWL –25.5”• IP Drum level low (LSL-10114) @ NWL –5”• LP Drum level low (LSL-10214) @ NWL –59”

High Steam Temperature

If the HP Superheater outlet steam temperature becomes high (TE-10022 @ 920 deg F) the duct burners should be run back to minimum load.

The Gas Turbine should be run back to minimum load and the duct burners tripped if this temperature reaches 930 deg F.

Gas Turbine loading rate must not allow an increase in any HP drum metal temperatures (TE-11002A-D) to exceed 600 deg F per hour.

The Gas Turbine should not be started, re-started after a trip, or re-loaded after a runback, unless all drum levels and pressures, and HP steam temperature, are within their normal operating range (i.e. all alarms and trips have been reset). The re-start or re-load should be an operator action.

Process Alarm

In addition to those listed in the preceding sections, the following process conditions will be alarmed:

• LP Drum level low (LSL-10214) @ NWL – 59”• LP Drum steam pressure high (DCS alarm from PT-10211) @ 56 psig• IP Drum steam pressure high (DCS alarm from PT-10111) @ 307 psig


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• HP Drum steam pressure high (DCS alarm from PT-10011) @ 1546 psig

• LP Drum level high (LSH-10214) @ NWL +6”• IP Drum level high (LSH-10114) @ NWL +10”• HP Drum level high (LSH-10114) @ NWL +4.5”

Steam Turbine

The Steam Turbine HP admission valve should trip on HP Drum level high-high (LSHH-10014 @ NWL +10.5”). There should be a pre-alarm at HP Drum level high (LSH-10014 @ NWL +4.5”).

Re-loading of the steam turbine will follow operating procedures for the ST.

4.0 SYSTEM DESCRIPTION

This section provides a general understanding of the Heat Recovery Steam Generator (HRSG) by tracing flow paths, identifying and describing major components, and locating and describing the system instrumentation and controls.

The HRSG utilizes the exhaust gases from the combustion turbine (CT) to produce HP and IP steam for use in the existing plant’s steam turbines. IP steam produced is combined with extraction steam from the steam turbines to export to various customers. The HRSG is a natural circulation water tube, three pressure level unit. Heat transfer is accomplished by convection through banks of finned tubes. Duct burners that use natural gas provide supplemental firing.


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4.1 Primary System Flow Path

The HRSG has three sections: a high pressure (HP) section, an intermediate pressure (IP) section, and a low pressure (LP) section. LP steam is not exported, but is used to deaerate the incoming condensate makeup to the LP steam drum or boiler feedwater storage tank. HP steam may also be used for deaeration when LP steam quantities are not sufficient. Steam is produced when the combustion turbine generator (CTG) exhaust gas enters the HRSG and flows through each section of the HRSG. The feedwater to the HRSG is supplied from the condensate system and circulated by the boiler feedwater system. The exhaust gas discharges to atmosphere through the stack at the low temperature end of the HRSG.

High Pressure (HP) Steam: High-pressure boiler feedwater is supplied to the economizers of the HRSG’s HP sections. The water is heated, and then passed through the evaporators and superheaters. The superheated HP steam exits HP superheater #3 at approximately 1365 psia and 960º F.

Intermediate Pressure (IP) Steam: IP steam is produced in the same manner as the HP steam, except utilizing IP boiler feedwater in the IP sections of the HRSG. IP steam exits the IP superheater at approximately 255 psia and 524º F.


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4.2 Normal Operating Parameters

HP Normal Operating Parameters

Tag No. Description ParameterFE-02001 HP steam flow 500-900

kpphTE-02001 HP steam temperature 895-905ºFPT-02001 HP steam pressure 1360-1370

psiaTE-02010A/B CT power augmentation steam

temperature700ºF

PT-02003 CT power augmentation steam pressure

405 psia

IP Normal Operating Parameters

Tag No. Description ParameterTE-03001 IP Steam Temperature from HRSG 528°FFE-03002 IP Steam Flow 28 – 50 kpphTE-03002 IP Steam Temperature to tie-in 500 – 550 °FPT-03002 IP Steam Pressure to tie-in 195-235 psia

4.3 Secondary systems

The following systems interface with the HRSG during normal operation:

• Boiler Feedwater System• HP Steam System• IP Steam System• Condensate System• Chemical Feed System• Combustion Turbine• Fuel Gas System


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• Aqueous Ammonia System• Continuous Emissions Monitoring System (CEMS)• Boiler Blowdown System

5.0 SYSTEM STARTUP

Note: Startup time depends on the length of shutdown of each HRSG and steam turbine generator. There are three different starting conditions:

• Hot Start - The steam turbine generator has been shut down for a short period of time, the first stage metal temperature is 900 °F or greater, and the steam turbine generator is on turning gear with steam to the steam seals.

• Warm Start - The steam turbine generator has been shut down for more than a day, and the first-stage metal temperature is between 400 °F and 900 °F.

• Cold Start - The steam turbine generator has been shut down for several days, and the first-stage metal temperature is less than 400 °F.

Startup procedures for the three different starting conditions are similar except for the warm-up times required for the piping and steam turbine generator, which increase as the steam turbine generator first-stage metal temperature decreases. Steam line warm-up from a cold start is accomplished with steam from the existing boilers.

Before starting the combustion turbine generator, the HP, IP, and LP HRSG steam drums are set at a low level (just above the low-low level) to account for the drum water expansion that occurs during initial startup. The vent valve on each drum is open until steam is established in the HP, IP, and LP steam lines. These vent valves are then closed when the drum pressure typically reaches


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3.45 bara (50 psia) (HP and IP) and 2.07 bara (30 psia) (LP). The HP, IP, and LP evaporator intermittent blowdown valves are closed. These blowdown valves are operated for immediate blowdown in the event of a high level in the HP and IP steam drums. The HP, IP, and LP superheater drain valves are open to discharge any condensate into the HRSG blowdown flash tank. The HP and IP steam line drain valves are all open.

The combustion turbine generator is started, synchronized, and loaded at a controlled rate until a predetermined load is reached, which provides the HP steam temperature acceptable for steam turbine generator admission. This predetermined load on the combustion turbine generator is selected by the operator before startup. Typically, the gas turbine generator is started and loaded to the spinning reserve mode (5 percent load). The gas turbine generator load ramp rate is limited to approximately 8 percent per minute up to 40 percent steam flow (HRSG in startup). At this load, the HP steam pressure will increase to the steam turbine generator floor pressure. When sufficient pressure is reached, the HRSG HP steam atmospheric vent valve (HP sky valve) opens to maintain this pressure.

The warm-up rate for the HP steam drum is approximately 25 minutes; 15 minutes for warming the water inventory from ambient to 212 °F and then approximately 10 minutes to ramp to a soak temperature of 482 °F. This ramp rate precludes the HP steam drum maximum allowable thermal fatigue stress from being exceeded. Fatigue stresses on the IP and LP steam drums during startup are not a concern.


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5.1 Precautions

WARNING: VERIFY ALL MAINTENANCE PERSONNEL HAVE EXITED THE BOILER AND THAT ALL INSPECTION PORTS AND MANWAYS ARE SECURELY FASTENED.

WARNING: VERIFY THAT MAINTENANCE ACTIVITIES ARE COMPLETE BEFORE SAFETY TAGS AND LOCKING DEVICES ARE REMOVED.

WARNING: DO NOT ATTEMPT TO OPERATE THE HRSG AND STEAM SYSTEMS WITHOUT THOROUGH FAMILIARIZATION OF OPERATIONAL INSTRUCTIONS.

CAUTION: DO NOT ALLOW STEAM PRESSURE TO BUILD IN "DEAD LEGS" AND/OR SECTIONS OF PIPE THAT CANNOT BE DRAINED. THIS IS TO PREVENT HYDRAULIC HAMMER FROM CONDENSATE BUILDUP IN STEAM PRESSURE ENVIRONMENT.

CAUTION: ONCE THE COMBUSTION TURBINE HAS BEEN STARTED AND TEMPERATURES IN THE HRSG BEGIN RISING, STEAM PRODUCTION IN THE DRUMS WILL QUICKLY FOLLOW. IT IS AT THIS CRITICAL POINT THAT THE OPERATOR MUST BE ACUTELY AWARE OF ALL OPERATING PARAMETERS, AS THE CONTROL OF THE SYSTEM SHOULD BE IN THE MANUAL MODE.

CAUTION: ON STARTUP OF THE BOILER IT IS CRITICAL TO MAINTAIN STEAM FLOW THROUGH THE SUPERHEATERS TO PREVENT TUBE DAMAGE.

CAUTION: DURING A COLD START, THE STARTUP VENTS SHOULD BE OPENED PRIOR TO FIRING THE COMBUSTION TURBINE AND CLOSED ONCE ALL DANGER OF EXCEEDING THE STARTUP RAMP RATE HAS PASSED.


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THESE CONTROL VALVES SHOULD NOT BE OPERATED AT LESS THAN 10% OPEN TO AVOID EROSION OF THE SEATS.

General Notes:

Maintaining proper steam drum level is critical during startup and operation of the HRSG. An excessively high water level can cause water carryover into the superheater and result in an automatic trip of the steam turbine. A low-low water level can result in thermal damage to the evaporator tubes and will result in an automatic trip of the combustion turbine.

Thermal stresses are induced in the HRSG during startup and shutdown. The greater the rate of change during these periods, the greater the stress. If ignored, these stresses can cause fatigue and premature mechanical problems.

During startup, failure to expel a continuous purge of steam from the steam drums will result in stagnation of natural circulation within the circuit. Therefore, it is necessary to vent steam through the superheater vent valves until the unit goes online supplying steam to the respective header through the non-return valves.

Never operate the HRSG without all of the safety valves in place, calibrated, and in good working condition.

The economizers should be periodically vented during HRSG operation to prevent the accumulation of air in the high points of the tube bundles.


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The steam drum water column isolation valves should be open at all times. Closing the valves can bypass the protective functions of the drum level switches by holding a false level in the column.

The reliability of the steam drum level transmitters should be periodically checked against the actual level using the corresponding gauge glass.

The steam drum gauge glass must be periodically blown down to prevent the accumulation of contaminates and sludge.

The heat input to the HRSG should be controlled by monitoring the rate at which the saturation temperature rises in the steam drums. The rate of temperature increase should be limited by releasing steam through the startup vents and/or controlling the rate at which heat enters the HRSG by limiting combustion turbine loading.

Proper boiler water chemistry must be maintained at all times. Improper chemistry can lead to fouling or corrosion of internal surfaces, reduced unit efficiency, and possible damage and/or failure of the boiler tubes.

If solids carryover is being caused by excessive boiler water solids concentration, adjustment of the continuous blowdown valve may be required.

1_____ VERIFY proper communications are established between floor Operators and the Control Room.

2_____ VERIFY operations personnel are rehearsed with the startup procedures and are prepared with emergency response actions.

3_____ VERIFY that all personnel involved with the operation of this system are familiar with the equipment manufacturer’s startup and operating procedures.

4_____ VERIFY safety tags and locking devices have been removed as required.


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5_____ WARNING: VERIFY THAT MAINTENANCE ACTIVITIES ARE COMPLETE BEFORE SAFETY TAGS AND LOCKING DEVICES ARE REMOVED.

6_____ REVIEW operations logbook for any condition prohibiting safe startup or need for resetting of controls or instrumentation.

7_____ VERIFY all applicable safety practices and procedures are in place.

5.2 Prerequisites

1_____ VERIFY 125VDC control voltage is available to system instrumentation.

2_____ VERIFY 24VDC control voltage is available to system instrumentation.

3_____ VERIFY the associated DCS control functions and interlocks are ready for service.

4_____ VERIFY the instrument air system is in service.

5_____ VERIFY the raw water system is in service.

6_____ VERIFY the fire protection system is in service and local portable extinguishers are fully charged.

7_____ INSPECT boiler lagging and insulation for damage or loose sections. Notify maintenance of necessary repairs.

8_____ VERIFY that the blowdown system mechanically operable and ready for service.


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9_____ VERIFY that the boiler feedwater system is mechanically operable and ready for service.

10_____ VERIFY that the HRSG chemical feed system is mechanically operable and ready for service.

11_____ VERIFY that the demineralized water system is mechanically operable and ready for service.

12_____ VERIFY that HP BFW system block valves are aligned to establish flow from the HP BFW pumps to the #1 HP economizer and to the HP steam drum.

13_____ VERIFY LP BFW system block valves are aligned to establish flow from the LP BFW pumps to the IP economizer and IP steam drum.

14_____ VERIFY HP steam drum level control valve LV-10013 is in MANUAL mode and CLOSED.

15_____ VERIFY IP steam drum level control valve LV-10113 is in MANUAL mode and CLOSED.

16_____ VERIFY HP BFW isolation MOV YV-10031 is CLOSED.

17_____ VERIFY IP BFW isolation MOV YV-10131 is CLOSED.

18_____ VERIFY the HP and IP desuperheater spray water control valves are in AUTO.

19_____ VERIFY the desuperheater spray control valve isolation valves are CLOSED.

20_____ VERIFY all boiler feedwater pump HOA control switches in AUTO.


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21_____ START one BFW pump with recirculation OPEN to the LP steam drum, in accordance with the guidelines in Section 9.0, Boiler Feedwater System.

22_____ START one condensate pump and one condensate header booster pump with makeup to the system in accordance with the guidelines in Section 14, Condensate System.

23_____ PARTIALLY OPEN HP steam drum level control valve to fill the HP steam drum to just above the LO level alarm setpoint.

Note: As temperature and pressure within the boiler and steam drums increase, water level will rise. Therefore, allow for this expansion in setting the working levels. If the level rises above the working level it may be necessary to blow down some water in order to maintain the level.

24_____ COMPARE local sight glass and level indicating to DCS level indicator.

25_____ As the HP drum level reaches the desired level, PLACE the level control valve in single element AUTO control and monitor feedwater flow shutoff on the associated BFW flow indicator.

26_____ From the DCS, OPEN IP BFW level control valve and repeat the process.

27_____ CHECK the boiler feedwater chemistry for proper quality.

5.3 Startup


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Note: It is recommended that start-up of the boiler be manually controlled; however controllers should be placed in automatic position as soon as possible.

Note: The normal shutdown condition of the boiler is a wet lay-up with minimal operator involvement returning it to full operation.

1_____ START the combustion turbine in accordance with guidelines in Section 12.0, Combustion Turbine Generator

2_____ MONITOR the level in the HP, IP and LP steam drums.

3_____ CLOSE LP steam drum vent valves when drum pressure reaches 25-30 psig.

4_____ CLOSE HP and IP steam drum vent valves when drum pressure reaches 50 psig.

5_____ Once steam drum pressures have reached 50 psig, the Operator may place the boiler feedwater control system in AUTO single element control mode.

Note: Verify that boiler feedwater supply and steam flows are stabilized and correspond before placing in three element control.

6_____ OPEN HP and LP intermittent blowdown valves on the steam drums to prevent high drum levels, if necessary.

Note: It may be necessary to first drain down the blowdown tank prior to opening the intermittent blowdown drains.


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7_____ ADJUST combustion turbine heat output to the boiler or regulate superheater startup vent valving to produce 8%/minute maximum temperature increase during start-up.

8_____ PARTIALLY OPEN the existing steam isolation valve and begin warming the HP steam system.

9_____ PARTIALLY OPEN the existing steam isolation valve and begin warming the IP steam system.

10_____ VERIFY HP and IP desuperheaters are in service.

11_____ ENSURE that low point drains on steam headers remain OPEN during low-pressure warm-up only.

12_____ ADJUST the continuous blowdown rate from the steam drums to the minimum acceptable level to maintain boiler water quality.

CAUTION: DO NOT START THE DUCT BURNER UNTIL STEAM PRESSURE AND TEMPERATURE HAVE STABILIZED AND THE COMBUSTION TURBINE GENERATOR IS AT BASE LOAD.

13_____ OPERATE the intermittent blowdown at 1/2-hour intervals for three blows to rid the system of any residual silt or sludge collected during shutdown.

14_____ OPEN the economizer vents for 2 minutes to ensure that all air is out of the economizers.


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6.0 NORMAL OPERATION

During normal operation, the main steam system operates at various loads dictated by ambient conditions and the steam turbine generator and combustion turbine generator’s electrical demand. As the electrical demand changes, the HRSG high pressure steam pressure is kept constant by varying duct burner firing, which in turn maintains steady HP steam pressure to the steam turbine generator.

6.1 Valve Alignment

HP Steam System

Valve Tag Description PositionYV-10040 Startup vent ClosedYV-10041 HP steam outlet valve OpenTIC-10019 HP desuperheater BFW control VariablePCV-10227 Pegging steam pressure

controlVariable

YV-02013 Existing STG steam supply OpenYV-02002 CT steam injection supply MOV OpenPV-02003 CT steam injection pressure

controlVariable

YV-02004 HP steam line drip leg drain Closed/AutoYV-02009 HP steam line drip leg drain Closed/AutoYV-02014 HP steam line drip leg drain Closed/AutoYV-10039 HP steam line drip leg drain Closed/AutoYV-10037 HP 1 superheater drain Closed/AutoYV-10036 HP 2/3 superheater drain Closed/Auto


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IP Steam System

Valve Tag Description PositionYV-10140 Startup vent ClosedYV-10141 IP steam outlet valve OpenTY-10119 IP desuperheater BFW control VariableYV-03101 CT injection steam control valve VariableYV-03102 CT steam injection stop valve OpenYV-03007 IP steam line drip leg drain Closed/AutoYV-03009 IP steam line drip leg drain Closed/AutoYV-03010 IP steam line drip leg drain Closed/Auto

WARNING: EXERCISE EXTREME CAUTION WHEN WORKING ON OR NEAR EQUIPMENT THAT GENERATES STEAM WITH HIGH PRESSURE AND TEMPERATURE.

CAUTION: NEVER DEPEND ENTIRELY UPON AUTOMATIC ALARMS OR FEEDWATER INSTRUMENTATION FOR CONTROL OF BOILER LEVELS. PERIODICALLY INSPECT LOCAL PRESSURE, TEMPERATURE, AND LEVEL INDICATORS FOR COMPARATIVE READINGS ON THE DCS.

Note: The following checks and inspections should be accomplished at least once per shift.

Note: During normal operation, Operators should periodically visit the HRSG to check local instrument readings. During these walk-downs, the operator should look for potential equipment problems. If a problem is observed, it should be quickly evaluated for its severity and a corrective plan be developed.

1_____ INSPECT boiler equipment, valves and piping for steam, water and hot air leaks.


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2_____ RECORD system parameters. INVESTIGATE all abnormal readings.

Note: DCS trends of operating parameters indicate problems such as fouling or turbine degradation. A review of this data should be made regularly, looking for any changes in unit performance

3_____ Periodically BLOW DOWN steam pressure gages, level columns and gages periodically to ensure proper flushing.

4_____ CHECK the overall condition of the HRSG. Steam or water leaks from any source should be investigated and repaired as soon as possible.

Note: Gas side leaks should be noted and scheduled for repair. In particular, casing penetrations at inlet and outlet headers and drain lines should be checked for leaks.

Note: The bottom of the HRSG casing is equipped with drain valves. A rupture or leak within the steam/water circuits of the HRSG will be indicated by the presence of water at the drain connections.

5_____ CHECK the HP and IP superheater vent valves for steam leakage. Due to their service, these valves may require more frequent attention than others.

6_____ INSPECT expansion joints for discoloration of fabric belt due to leak or high heat waves

Note: Expansion joints may have heat waves due to hot flange connections to CTG flange and diffuser duct.

7_____ Inspect casing for paint discoloration or peeling hot spots.


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8_____ INSPECT casing for water leakage (particularly at the rear of the HRSG.

9_____ INSPECT casing for smoke or plume due to casing leak heat waves

10_____ CHECK for signs of manway cover leakage.

11_____ LISTEN to piping for water hammer.

12_____ INSPECT platforms for loose grating or bolting on handrails.

13_____ MONITOR vent stack for excessive steam plume.

14_____ INSPECT safety valves for "sizzling" valve due to poor seating.

15_____ CHECK for steam plume from vent stacks when valve should be closed.

16_____ LISTEN to deaerator for signs of “rumbling”.

17_____ MONITOR carryover (steam purity) from steam drum to superheater.

18_____ ANALYZE total solids concentration and silica values. Intermittent blowoff shall be used to reduce boiler water TDS in order to improve steam purity.

19_____ MONITOR oxygen content of the boiler.

20_____ MONITOR DCS for indications of abnormal conditions.

21_____ MONITOR tube metal surface temperature to verify temperature is within design limits.


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Note: If the temperature limit is exceeded, it must be immediately investigated for problems like steam/water flow, localized hot gas temperature, etc.

22_____ MONITOR gas side pressure drop across HRSG. Increased pressure drop may indicate fouling possibility.

23_____ LISTEN for unusual noises coming from HRSG inlet duct.

24_____ On a periodic schedule, manually BLOW DOWN the HP steam system line drip legs and gage glasses.

25_____ MONITOR steam drum level gages for operating water levels.

Note: it may be necessary for the operator to blow down the water column and gage drains. More frequent blowdown may be necessary when trouble is experienced with boiler compounds, foaming, priming, and other feedwater problems.

Make provisions to by-pass any low water cutouts while blowing down the gage glasses and water columns. Experience may indicate that less frequent blowdown is desirable. This should be coordinated with the boiler operator, and water treatment consultant.

26_____ MONITOR boiler feedwater pumps for excessive noise, vibration, or heat buildup.


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27_____ BLOW DOWN the boiler drums as required, by OPENING the bottom, or intermittent blowdown valves.

Note: Better cleaning is obtained with multiple short blows than one long blow. The valve farthest from the boiler should be completely opened before the valve closest to the drum is opened.

Open the second valve fully and quickly, leaving it open for only a few seconds. If possible, watch the flow of water coming from the bottom of the drum. If there are solids in the water, perform a second bottom blow and repeat this process until the water is clear.

The frequency of performing this procedure should be between once per shift and once per week, depending on the quality of the feedwater. To ensure the valves work when needed, always bottom blow at least once per week.

28_____ MONITOR boiler feedwater chemistry by periodically taking water samples from the grab sample outlets and comparing to water/steam analyzers.

29_____ COMPARE DCS indicating controllers with local readings.

30_____ REVIEW HP boiler conditions on three-element control by RECALLING the HISTORICAL TREND feature on the DCS.

31_____ REVIEW LP boiler conditions on three-element control by RECALLING the HISTORICAL TREND feature on the DCS.

32_____ MONITOR HRSG skin temperatures for possible "hot spots".


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33_____ MONITOR DCS for indications of abnormal conditions.

34_____ MONITOR HP steam drum level gages and EYE-HYES for operating water levels.

35_____ MONITOR DCS for indications of abnormal steam temperature, pressure and flow conditions.

36_____ MONITOR steam parameters by RECALLING the historical trends from the DCS.

37_____ VERIFY HP steam pressure to Kendall Station is between 1360 and 1370 psia

38_____ VERIFY HP steam temperature to Kendall Station is between 895 and 905ºF.

39_____ VERIFY that HP steam flow is 500 to 900 kpph.

40_____ VERIFY HP steam pressure to CT steam injection is approximately 405 psia

41_____ VERIFY HP steam temperature to CT steam injection is approximately 700ºF.

42_____ VERIFY HP steam blowdown temperature to the HRSG intermittent blowdown drum is normal.

43_____ MONITOR IP steam drum level gages and EYE-HYES for operating water levels.

44_____ VERIFY IP steam flow at FI-03002 is 28 – 50 kpph.

45_____ VERIFY IP steam pressure at PI-03002 is approximately 255 psia.

46_____ VERIFY IP steam temperature at TI-03002 is normal.


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7.0 NORMAL SHUTDOWN

7.1 Precautions

WARNING: HP STEAM HEADER COMPONENTS BECOME EXTREMELY HOT DURING OPERATION. SOME AREAS MAY RETAIN RESIDUAL HEAT FOR LONG PERIODS AFTER SHUTDOWN. WEAR PROTECTIVE APPAREL TO PREVENT SERIOUS BURNS TO EXPOSED SKIN.

MANY LINES AND FITTINGS ON THE BOILER CONTAIN STEAM AND HOT FLUIDS UNDER HIGH PRESSURE. USE EXTREME CAUTION WHEN LOOSENING PIPING AND FITTINGS. WEAR SAFETY GOGGLES AND GLOVES WHEN PERFORMING MAINTENANCE TO PREVENT EYE INJURY OR BURNED SKIN.

WARNING: FOLLOW LOCKOUT PROCEDURES PRIOR TO WORKING ON THIS EQUIPMENT.

WARNING: EXTREME CAUTION SHOULD BE EXERCISED BEFORE ENTERING THE STEAM DRUMS AS THEY MAY CONTAIN OXYGENLESS GASSES THAT CAN CAUSE SEVERE ILLNESS OR DEATH IF INHALED.

ENSURE THE APPROPRIATE CONFINED SPACE ENTRY PERMIT IS FILLED WITH THE DESIGNATED SAFETY OFFICER.

Note: During unit operation, feedwater sludge and other matter are kept in suspension by circulation of the boiler water. When the circulation stops due to shutdown, solids will tend to settle and adhere to internal surfaces. This can inhibit heat transfer and promote corrosion. To avoid these


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problems, perform the following several hours or more prior to unit shutdown:

• Increase continuous blowdown by 10% and double the frequency of bottom blowdown.

• Increase the boiler water alkalinity treatment based on the guidelines of the plant’s Boiler Water Treatment Program.

1_____ COORDINATE stopping the boiler feedwater pumps and steam systems with the Control Room Operator, as shutdown of the boiler requires a prior orderly shutdown of the duct burner and combustion turbine.

2_____ Prior to shutdown, CHECK drum chemistry to ensure that pH, the oxygen scavenger and phosphate inhibitor residuals are at the proper level.

7.2 Shutdown

1_____ If the duct burner is operating, TURN DOWN the burner control by lowering the setting on the DCS gradually until the controls are at the minimum fire position.

2_____ SHUTDOWN the duct burner from the DCS, following the Forney operating procedures.

3_____ Following GE operating procedures, SLOWLY REDUCE combustion turbine to minimum load before shutdown.

4_____ At the DCS, PLACE HP steam controllers and valves in the MANUAL mode.

5_____ REMOVE the HP and IP desuperheaters from service by CLOSING the associated temperature control valve.


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6_____ MAINTAIN load at minimum level for an additional 15 minutes if conditions permit. TRIP the turbine.

7_____ MONITOR steam drum levels. Add boiler feedwater as needed to maintain levels between the LO level setpoint and normal operating level.

8_____ CLOSE HP and IP steam drum continuous blowdown.

9_____ STOP HRSG chemical injection into the steam drums.

10_____ At the DCS, CLOSE combustion turbine HP steam injection isolation MOV valve.

11_____ Once steam pressure in the HP steam line diminishes, CLOSE HP steam header isolation MOV.

Note: If the boiler is to be shutdown, isolate the HP steam header when line pressure decreases to approximately 15 psig.

12_____ OPEN HP steam header startup vent.

Note: Opening the startup vent is not required if the HRSG is to be bottled up for temporary shutdown.

13_____ OPEN HP and IP steam header vents when drum pressure decreases to less than 25 psig to avoid drawing a vacuum on the system.

14_____ OPEN HP steam header low point drains.

15_____ CLOSE boiler feedwater level control valves when no further makeup water is required.

Note: If the HRSG is to be shut down for a period of less than 24 hours, the unit can be bottled up by closing


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the steam header isolation valves, boiler feedwater supply valves and the continuous blowdown valves.

16_____ DETERMINE lay-up considerations and prepare accordingly.

Note: Depending on ambient conditions, the HRSG will remain warm for up to 24 hours after unit shutdown. If the combustion turbine is scheduled for restart within that period of time, the system can be left as is, ready for an immediate return to service.

If the unit is to remain idle for a week or more, a wet lay-up must be performed in accordance with the manufacturer’s procedures and recommendations.

If the boiler is to be placed in wet storage open all boiler feedwater pump circuit breakers.

Fill the steam drums completely full to the top by opening the makeup valve bypass with the block valves closed. This action will minimize the corrosion attack in the unit and prevent the presence of oxygen within the system.

When water has reached the uppermost position as evidenced by seepage from the vent valves, close the makeup by-pass valve.

For longer outage periods it is recommended that a "nitrogen blanket" be applied to each steam drum through the nitrogen fill and bleed valves fitted on each drum.

17_____ ISOLATE any equipment requiring maintenance.


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18_____ ENSURE necessary work permits have been issued prior to beginning maintenance on the system.

19_____ PERFORM all pre-start inspections before placing the system back in service.

8.0 ABNORMAL SHUTDOWN

8.1 Power Failure

Other than instrumentation 24VDC control voltage and 125VDC control valve voltage, the HRSG does not require electrical power to operate.

8.2 Instrument Air Failure

Loss of instrument air to the control valves would prevent automatic control of the steam system pressure and temperature and shutdown the combustion turbine and all steam production. Manual regulation of steam by a qualified Operator can maintain steam production and boiler feedwater supply by monitoring pressure, flow and temperature. The system can function until instrument air is restored to the affected component(s) or an orderly shutdown can be accomplished.

All control valves would go to their design fail position.


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8.3 Steam Turbine Generator Trip

In the event of a steam turbine generator trip, the following devices are actuated closed by either the DCS or the steam turbine generator control system:

• Main steam stop and control valves

• HRSG HP steam isolation valves (only in the event all STGs tripped).

A single turbine trip would only require a runback to minimum turbine load.

9.0 ALARM SUMMARY AND RESPONSE

The following chart is provided to assist an experienced Operator in identifying and resolving abnormal conditions associated with the Heat Recovery Steam Generators. It is not intended as a substitute for a thorough understanding of the system equipment, common sense, and safe operating practices and techniques.

Alarm Probable Cause Response Action

LAH-xxxx

Steam drum HI level alarm

Feedwater valve malfunction

Feedwater valve setpoint incorrect

Feedwater valve operation incorrect

Drum level instrument failure

Remove water from the drum through the intermittent blowdown valves.

Verify the level control valve or feedwater pump is in AUTO.

Check control valve for possible binding; i.e., stuck in the open position. Use manual bypass valve if necessary.

Check the drum level controller for failure. If the controller fails to operate in AUTO, place in MANUAL and control level as necessary.

Check level transmitter signal quality. Date of Issue: 12/20/01 Revision: 0

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Compare remote level indications against the local sight glass.

Swelling of water during startup

Level control loop malfunction or incorrect setpoint.

LAHH-xxxx

Steam drum HI HI level alarm





Check for HI level alarm LAH-xxxx

Check steam drum level gage

Check DCS level control setpoint

Check if HP boiler feedwater level control valve stuck open

Check for possible sudden pressure loss on HP steam system or vent opening

Check that feedwater and steam outlet flow correspond - switch to single element control in the event they vary noticeably

Note: HI HI Steam drum alarm results in an automatic trip of the steam turbine and duct burner.

As appropriate, restore steam turbine operation when drum level is restored.

LAL-xxxx

Steam drum LO level alarm





Verify the level control valve or feedwater pump is in AUTO.

Check control valve for possible binding; i.e., stuck in the closed position. Use manual bypass valve if necessary.

Check the drum level controller for failure. If the controller fails to operate in AUTO, place in MANUAL and


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control level as necessary.

Check level transmitter signal quality. Compare remote level indications against the local sight glass.

Add makeup to bring level to normal operation level.

LALL-xxxx

Steam drum LO LO level alarm





Check for LO level alarm

Check steam drum level gage

Check DCS level control setpoint

Check if the gas turbine tripped

Check if duct burner tripped to the low fire position

Check if boiler feedwater level control valve is stuck closed

Check for sudden pressure increase in steam system

NOTE: Alarm results in an automatic TRIP of the combustion turbine.

Address the unit trip. Perform all functions associated with a unit shutdown.

Make repairs or adjustments to the system as required.

Restore drum level.

Restore unit operation.

PAH-xxxx

Steam drum HI pressure alarm

Gas turbine load to high

Duct burner firing rate too high

Check pressure gage

Check the pressure setpoint in DCS

Open steam drum vent


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Pressure relief valve failure

Pressure instrument failure

Steam drum vent misalignment

Decrease duct burner firing temperature

Decrease gas turbine load

Check for sudden decrease in HP steam flow

TAH-xxxx

Steam drum HI temperature alarm

Gas turbine load to high

Duct burner firing rate too high

Temperature instrument failure

Check DCS temperature indicator

Check alarm setpoint

Check HI temperature switch operation and setpoint

Reduce duct burner firing temperature

Check for abnormally high steam drum pressure

TAL-xxxx

LO temperature alarm for steam exiting the steam drum

Duct firing rate too low

Turbine load minimum

Instrument failure

Temperature setpoint

incorrect

Check DCS pressure indicator


Increase duct burner firing temperature

Check for abnormally low steam drum pressure

TAH-xxxx

HI temperature alarm for the HP

Steam desuperheater

flow control valve

malfunction

Check DCS pressure indicator TI-10019

Compare to temperature indicating


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steam header from the desuperheater

Low feedwater flow to

attemporator

Temperature controller

setpoint incorrect

Instrument failure

transmitter TIC-10019


Check if temperature control valve is stuck closed

Check DCS temperature controller setpoint

Check desuperheater operation

Check duct burner firing temperatures

10.0 REFERENCES

10.1 Piping and Instrument Diagrams

• 20-078-1-PS-050 – Condensate• 20-078-1-PS-060 – Boiler Feedwater• 20-078-1-PS-090 – Blowdown, Traps, and Drains• 20-078-1-PS-500, 501, 502 - Sampling• 20-078-1-PS-520 – Chemical Feed Steam Cycle• 20-078-1-PS-650 – Fuel Gas • 20-078-1-PS-780 – Aqueous Ammonia Storage and Supply• 3595-0201 – Low Pressure (Foster Wheeler)• 3595-0202 – Intermediate Pressure (Foster Wheeler)• 3595-0203 – High Pressure (Foster Wheeler)• 3595-0204 – Gas Flow (Foster Wheeler)


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• 61-7723-5-6101 – Selective Catalytic Reduction (Foster Wheeler)• 400851-01 – Multiple Gas Element Duct Burner (Forney)

10.2 Vendor Manuals

• Foster Wheeler HRSG• Forney


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19149328-Heat-Recovery-Steam-Generator-Operation-Procedure.pdf

Documents

system startup

ipsteam steam outyv

system purpose

system components

system description

normal operating parameters

steam turbine generator

abnormal shutdown