GEK 117019

g GEK 117019

January 2012

GE Energy

These instructions do not purport to cover all details or variations in equipment nor to provide for every possible contingency to be met in connection with installation, operation or maintenance. Should further information be desired or should particular problems arise which are not covered sufficiently for the purchaser's purposes the matter should be referred to General Electric Company. These instructions contain proprietary information of General Electric Company, and are furnished to its customer solely to assist that customer in the installation, testing, operation, and/or maintenance of the equipment described. This document shall not be reproduced in whole or in part nor shall its contents be disclosed to any third party without the written approval of General Electric Company.

2012 General Electric Company. All Rights Reserved. This material may not be copied or distributed in whole or in part, without prior permission of the copyright owner.

Fuel Gas System DLN I, Independent Control Valve Configuration

GEK 117019 Fuel Gas System

The following notices will be found throughout this publication. It is important that the significance of each is thoroughly understood by those using this document. The definitions are as follows:

NOTE

Highlights an essential element of a procedure to assure correctness.

CAUTION

Indicates a potentially hazardous situation, which, if not avoided, could result in minor or moderate injury or equipment damage.

WARNING

INDICATES A POTENTIALLY HAZARDOUS SITUATION, WHICH, IF NOT AVOIDED, COULD RESULT IN DEATH OR SERIOUS INJURY

***DANGER***

INDICATES AN IMMINENTLY HAZARDOUS SITUATION, WHICH, IF NOT AVOIDED WILL RESULT IN DEATH OR SERIOUS INJURY.

2 2012 General Electric Company. All Rights Reserved. This material may not be copied or distributed in whole or in part, without prior permission of the copyright owner.

Fuel Gas System GEK 117019

TABLE OF CONTENTS

I. GENERAL .................................................................................................................................................. 4 II. GAS FUEL SYSTEM................................................................................................................................. 4 III. FLAME DETECTION............................................................................................................................... 6 IV. IGNITION SYSTEM ................................................................................................................................. 6 V. GAS FUEL SYSTEM................................................................................................................................. 6 VI. GAS FUEL OPERATION......................................................................................................................... 8

A. Primary................................................................................................................................................. 10 B. Lean-Lean ............................................................................................................................................ 10 C. Secondary............................................................................................................................................. 10 D. Premix.................................................................................................................................................. 10

VII. DLN LOADING/TRIPS........................................................................................................................... 11 A. Auto Raise System Summary .............................................................................................................. 11 B. DLN Trip System Summary ................................................................................................................ 11 C. Auto Lower System Summary............................................................................................................. 12

VIII. MAINTENANCE OF FUEL GAS COMPONENTS ............................................................................ 12

LIST OF FIGURES

Figure 1. DLN I Multi-Nozzle Staged Combustor Cross-Section. ........................................................................ 4 Figure 2. DLN I Fuel System. ................................................................................................................................ 5 Figure 3. DLN I MK VI* / MK VIe* Control Software Schematic. ....................................................................... 9 Figure 4. Fuel Staged Dry Low NOx I Gas Fuel Operating Modes....................................................................... 9 Figure 5. Typical DLN I Control Gas Fuel Split Schedule. ................................................................................. 11

2012 General Electric Company. All Rights Reserved. This material may not be copied or distributed in whole or in part, without prior permission of the copyright owner. 3


I. GENERAL

The purpose of the Dry Low NOx (DLN I) control system is to regulate the distribution of the fuel and the location of flame in the staged multi-nozzle combustors around the gas turbine. A diagram of a DLN I combustor is provided in Figure 1.

Figure 1. DLN I Multi-Nozzle Staged Combustor Cross-Section.

II. GAS FUEL SYSTEM

A schematic of the DLN I fuel delivery systems is shown in Figure 2. The gas fuel system is made up of the gas fuel stop/ratio valve, the gas control valves.



DLN 1 FUEL GAS SYSTEM

Figure 2. DLN I Fuel System.

The stop/speed ratio valve (VSR-1) is designed to maintain a predetermined pressure, P2, at the control valve inlet. The Stop/Speed Ratio valve (VSR-1) in conjunction with Gas Control Valves (VGC-1, 2, 3) regulates the total fuel flow delivered to the gas turbine. This arrangement uses three separate Gas Control Valves to control the distribution of the fuel flow to a DLN I combustion system. VGC-1 ports fuel to the Primary Fuel Nozzles. VGC-2 ports fuel to Secondary Fuel Nozzles and VGC-3 ports fuel Transfer Fuel Nozzles. The Transfer Fuel Nozzles are only fueled during a Lean-Lean to Premix mode transfer.

A gas control valve operating off a supply manifold controls fuel flow to the combustion system. This manifold is supplied by the stop/ speed ratio valve, and maintains a controlled pressure (P2). The controlled supply pressure and the critical pressure drop design of the gas control valve ensure that the percentage valve stroke is proportional to percentage fuel flow.

The Fuel Stroke Reference is the overall fuel control for the gas turbine. The Fuel Stroke Reference (FSR) controls the rate of fuel (liquid or gas) into the combustion chambers based upon running conditions such as startup, warm-up, base load, shut down etc. The Fuel Splitter BBL (FSR1V1) then splits FSR to FSR1, liquid fuel % stroke reference or FSR2, gas fuel % stroke reference. The gas control valve uses this fuel stroke % reference (FSR2) to position the valve.



III. FLAME DETECTION

Reliable detection of the flame location in the DLN I system is critical to the control of the combustion process and to the protection of the gas turbine hardware. Four flame detectors in separate combustion chambers around the gas turbine are mounted to detect primary zone flame. Also, four flame detectors in separate combustion chambers are dedicated to detect the presence secondary flame. The signals from these flame detectors are processed in control logic and used for various control and protection functions including the DLN I combustion mode determination.

IV. IGNITION SYSTEM

Two spark plugs located in different combustion chambers are used to ignite the fuel flow in the primary zone of the combustors. These spark plugs are energized to ignite the fuel during startup and during certain DLN I mode changes that require re-ignition of the primary combustion zone. Flame is propagated to those combustion chambers without spark plugs through crossfire tubes that connect the primary zones of adjacent combustion chambers around the gas turbine. Flame is introduced in the secondary zone of the combustion chambers by igniting the secondary fuel flow with flame from the primary zone.

V. GAS FUEL SYSTEM

Following is the list of major equipment on the fuel gas module:

1. Y-Strainer: The High Efficiency type includes a seal at the screen to prevent leakage. The application of the High Efficiency Y-Strainer is dependent upon the level of upstream filtration. A strainer is provided in gas supply lines to remove any foreign particles from the gas fuel before it is admitted to the speed/ratio valve assembly. There is a blowdown connection on the bottom of the strainer body which should be utilized periodically for cleaning the strainer screen. The frequency of cleaning will depend upon the quality of the fuel gas used. The strainer should be cleaned shortly after full load has been attained for the first time, and after any disassembly of the purchasers fuel gas lines.

2. Low Pressure Switch, 63FG: This pressure switch is installed in the gas piping upstream of the gas stop/speed ratio valve and control valve assembly and initiates an alarm on the annunciation panel whenever the gas pressure drops below a specified setting. On dual fuel units, this switch or a second 63FG pressure switch set below alarm set point is used to initiate a transfer to liquid fuel.

3. Pressure Transmitter (96FG-1): The 96FG-1 pressure transmitter is installed upstream of Stop/ Speed Ratio Valve for pressure monitoring and action capability.

4. Stop/ Speed Ratio Valve (VSR-1): The stop/ratio valve is a dual function valve. It serves as a stop valve and is therefore an integral part of the protection system. Any emergency trip or normal shutdown will trip the valve to its closed position shutting off gas fuel flow to the turbine. This is done either by dumping hydraulic oil from the SRV hydraulic cylinder or driving the position control closed electrically. The valve also serves as a pressure regulating valve to hold a known fuel gas pressure ahead of the gas control valve and because of these dual functions the valve is sometimes called a stop/speed ratio valve.

a. Speed Ratio Function

The stop/speed ratio valve has two control loops. There is a position control loop similar to that for the gas control valve and there is a pressure control loop, Fuel gas pressure P2 at the inlet to the gas control valve is controlled by the pressure loop as a function of turbine speed. This is



done by proportioning the turbine speed signal TNH, and comparing it with the pressure feedback signal from transducer 96FG, at the summing junction of a controlling amplifier, see Figure 4. Any error between signals causes the amplifier to generate a pressure control signal to reposition the valve. The valve will be modulated continuously to hold this pressure.

The pressure control signal commands a servo-drive amplifier to control the ratio valve position loop in the same way the gas control valve drives its position loop in response to FSR. Many of the values used in these algorithms are also sent to modules to be displayed on the CRT (e.g. fuel gas pressure, valve stroke, FSROUT, and FPRG).

b. Stop Valve Function

The stop/ratio valve provides a shutoff of the fuel gas flow when required by either normal operation or emergency conditions. A solenoid dump valve is located between the electrohydraulic servo valve 90SR, and the hydraulic cylinder. This dump valve is operated by electric trip system. When dump valve (solenoid) is energized, it allows the electrohydraulic servo valve 90SR to control the cylinder position. When the dump valve (solenoid) is de-energized (as in the case of normal or emergency shutdown), the dump valve spring shifts a spool to a position which dumps high pressure hydraulic oil (OH) in the stop/speed ratio valve actuating cylinder to the lube oil reservoir. The closing spring, atop the valve plug, instantly shuts the valve, thereby shutting off fuel gas flow to the turbine combustors.

5. Vent Solenoid 20VG-1: The gas bleed (vent) valve is a solenoid-operated valve. This solenoid valve vents the volume between the stop/speed ratio valve and the gas control valve when the solenoid is deenergized. The solenoid is energized and the vent valve closed when the master control protection circuit is energized. When a turbine starts signal is given the valve, therefore, will be closed and remain closed during gas fuel operation. The vent is open when the turbine is shut down because the stop/speed ratio and gas control valves have metal plugs and metal seats and therefore, are not leak tight. The vent insures that during the shutdown period, fuel gas pressure will not build up between the stop/speed ratio and gas control valves, and that no fuel gas will leak past the closed gas control valve to collect in the combustors or exhaust.

6. Fuel Gas Thermocouples (FT_GC_1A, 1B, 2A, 2B): Fuel gas thermocouples provide the fuel gas temperature upstream of the Stop/Speed Ratio Valve to confirm that the fuel temperature is within specified requirements during startup and throughout turbine operation.

7. Gas Fuel Control valves (VGC-1, 2, 3) regulate the flow of gas into the combustion chambers during different DLN1 modes of operation. The position of the gas control valve plug is intended to be proportional to FSR which represents the total called-for fuel flow.

When the turbine is to run on gas fuel the permissive must be true. This enables the GCV to open. The stroke of the valve will then be proportional to FSR.

The gas control valve stem position is sensed by the output of a linear variable differential transducer (LVDT), rectified, and fed back to an operational amplifier. There are two LVDTs, so it will select the highest output and this is compared to the FSROUT input signal at the summing junction. If the feedback is in error with FSROUT, the operational amplifier will increase the signal to the hydraulic servo valve to drive the gas control valve in a direction to decrease the error. In this way the desired relationship between position and FSR is maintained, and the control valve meters the correct gas fuel. Actuation of the spring-loaded gas control valve is by a hydraulic cylinder controlled by the electrohydraulic servo valve.



The plug in the gas control valve is contoured to provide the proper flow area in relation to valve stroke. The gas control valve uses a skirted valve disc and venturi seat to obtain adequate pressure recovery. High pressure recovery occurs at overall valve pressure ratios substantially less than the critical pressure ratio. The net result is that flow through the control valve is independent of valve pressure drop. Gas flow then is a function of valve inlet pressure, P2, and valve area only.

An open or a short circuit in one of the servo coils or the signal to one coil does not cause a trip. The GCV has two LVDTs and can run correctly on one.

8. Pressure Transmitters (96FG-2A, B, C): The fuel gas pressure transducer, 96FG, is a pressure transducer with a dc voltage output directly proportional to pressure input in psig. It incorporates solid state circuits and an amplifier in the transducer case. A diode is connected across the output of the transducer. This prevents any possibility of a spurious signal driving the transducer amplifier negative, out of its normal operating range. The transducer is normally factory adjusted and calibrated; however, the calibration must be checked in the field and necessary readjustment made to meet the voltsoutput versus pressureinput requirements, as specified in the Control specifications. These pressure transmitters are used to calculate flow for use in a prefill timer for the critical pressure drop control scheme, and are used to calculate reference flow and fuel split for the non-critical pressure drop control scheme.

9. Temporary Strainer (MLI A179): Temporary strainers have been added to all fuel circuits and are to be used during unit commissioning and after any outages. Model List Item A179 covers the installation and use.

VI. GAS FUEL OPERATION

The gas turbine firing temperature is defined as the temperature at the inlet to the first turbine stage. Due to the extreme temperatures in this region of the gas turbine, it is impractical to measure the firing temperature directly. The MK VI* / MK VIe* control software calculates a turbine firing temperature through known thermodynamic relationships by measuring the gas turbine exhaust temperature, the compressor discharge pressure and the ambient temperature.

The fuel flow split between the DLN I combustion chamber fuel nozzles and the location of the flame is regulated as a function of the calculated turbine firing temperature signal (TTRF).

Figure 3 is a flow chart relationship of the DLN I control panel software functions. There are four basic modes of distributing the fuel to the DLN I combustor (See Figure 4):

* Trademark of the General Electric Company.



Figure 3. DLN I MK VI* / MK VIe* Control Software Schematic.

Figure 4. Fuel Staged Dry Low NOx I Gas Fuel Operating Modes.



A. Primary Only the p ode of operation is

nite, accelerate and operate the machine over low to mid loads, up to a pre-selected n reference temperature (similar to a firing temperature).

B. ame exists in both the primary

y zones. This mode of operation is used for intermediate loads during start-up and shut- between two pre-selected combustion reference temperatures.

C. mode is a transition

n lean-lean and premix modes. This mode is necessary for extinguishing the flame in the , after which fuel maybe reintroduced into what becomes the primary fuel/air premixing

D. injected through both the primary and secondary nozzles. Flame is in the secondary zone only.

the fuel is injected through the primary fuel nozzles, and this fuel premixes with air in the bustion zone without igniting. This fuel/air mixture then accelerates through the venturi,

will go

w to the secondary zone in the combustor. The gas transfer

rimary nozzles inject fuel. Flame is in the primary stage only. This mused to igcombustio

Lean-Lean

Fuel is injected through both the primary and secondary nozzles. Fland secondardown events,

Secondary

Only the secondary nozzles inject fuel. Flame is in the secondary zone only. This state betweeprimary zonezone.

Premix

Fuel isMost of first comwhich prevents flame propagation into the first zone. The fuel from the secondary fuel nozzles also premixes with air. Premix mode is the mode of minimum NOx emissions. Emissions of CO are minimized when the combustion temperature is up near the design combustion temperature.

Figure 5 is a plot of the DLN I operation modes as a function of firing temperature. During normal loading of a unit operating on gas fuel, the system will progress through Primary, Lean-Lean, Secondary and Premix modes. Normal unloading of the machine from high loads on gas fuelfrom Premix to Lean-Lean after the spark plugs re-ignite the primary combustion zone. Further unloading will cause Primary mode operation to be initiated which will continue through breaker opening until turbine shutdown.

In certain operational situations, such as load rejection, the fuel gas control system may divert all fuel to either the primary or secondary zones depending upon the operational mode and firing temperature.

The gas primary valve (VGC-1) regulates the distribution of the fuel flow to the primary zone in the combustor. Refer to Figure 1 for a diagram of the DLN 1 combustor. The secondary valve (VGC-2) regulates the distribution of the fuel flovalve (VGC-3) regulates the distribution of the fuel flow to the secondary zone of the combustor for fuel transfers to premix. The secondary fuel nozzle assembly contains a flow passage that mixes air and fuel (secondary nozzle) and a normal diffusion type passage (transfer nozzle).During the transfer from Lean-Lean to Premix, the gas fuel flows in the combustors secondary stage fuel nozzle through the premixing secondary passage and the diffusion transfer passage. It is necessary to route some of the secondary fuel flow through the diffusion section of the secondary nozzle during this transfer period in order to lower combustion dynamics and stabilize the secondary flame. The gas primary valve will normally be in the 0% stroke position, meaning that 100% of the secondary fuel flow will be to the secondary premixing passage in the secondary nozzle assembly. During transfer to the Secondary mode of operation, flame is extinguished in the primary zone. In premixed mode, the gas fuel flows through both the gas primary valve (VGC-1) and gas secondary valve (VGC-2), with majority of fuel flowing the primary nozzles.



% Primary

100 (Loading toPremix)%

0%TTRF1

FXSFXSP3

L

Extended Lean-lean

PremixLean-lean

Loading

Primary

FXKTL1 FXKTS1 FXKTL3

Figure 5. Typical DLN I Control Gas Fuel Split Schedule.

II. DLN LOADING/TRIPS

related unit trips, unloads, fired shutdowns and loading rates. With DLN e load and unload functions are necessary for turbine protection as well as unit

The auto raise function is used in DLN 1 systems, through the turbine control raise load sequencing. ry transfer and remains active until the premix steady state mode is

B. Two types of DLN turbine trips exist in the DLN 1 system.

leave a particular mode. Failure to leave mode. This is not desirable for extended

LOADING FROM PIMARY TO PREMIX MODE

V

This summarizes DLN 1 systems, a number of uniqutrips. Refer to document control specification for complete information.

A. Auto Raise System Summary

The raise is initiated at secondareached. This function selects a unique load rate and continually loads the turbine through a premix transfer.

DLN Trip System Summary

L4DLNT1 is associated with mode sequencing or failure tosecondary transfer indicates that the split is in full secondaryperiods of time due to damage that could be caused to the combustion liner. This occurs with a failure to flame out the primary zone. A similar turbine trip can occur with an attempted primary re-ignition. If flame is not detected within a set period of time the turbine is tripped. Compressor discharge pressure failures are also tied in with this fault.

L4DLNT2 is associated with a loss of compressor discharge pressure (L3TFLT) trip. On dual fuel units (L86P_FLT) loss of purge trip is added.



C. Auto Lower System Summary The auto lower function is used in DLN 1 systems through the turbine control lower load sequencing. If the liquid fuel shear valve fails closed indicated by the limit switch (L33FK1C), the unit will also be lowered into liquid primary mode and inhibit a raise into Lean-Lean. For combustor protection an auto load function is added if the unit is above a certain megawatt; this is for turbine hardware protection. If purge air is not reaching the transfer fuel nozzles, load will be reduced until primary mode, which is considered a safe operating region.

VIII. MAINTENANCE OF FUEL GAS COMPONENTS

The fuel gas and purge systems should be isolated and vented prior to any maintenance.

Use proper lock-out tag-out procedure when working on any of this equipment.

Regularly inspect the fuel gas and purge piping for any leakage, and rectify any leaks as immediately. Refer to Equipment Service Manual & manufacturers manual for detailed instruction on operation & maintenance. Refer to Spare Parts List for maintaining the spares & procurement cycle.

1. Fuel Gas Strainer:

A differential pressure switch across the Y-strainer is used to monitor the differential pressure across strainer to indicate when strainer needs cleaning.

2. Fuel Gas Vent Valves

Periodically check for proper control air pressure. Also check for leakage from the tubing to the regulator, 3-way solenoid valve and valve actuator.

3. Auxiliary Stop and Purge Gas Block Valves

Periodically check for proper control air pressure. Also check for leakage from the tubing to the regulator, 3-way solenoid valve, spool valve and valve actuator.

4. Fuel Gas Control Valves

Periodically check the servo for calibration. Examine the servo valve for hydraulic fluid leakage at the pressure, drain, and trip ports. Replace the hydraulic oil filter on a scheduled basis.

5. General Maintenance

a. Periodically check for air, gas or oil leakage as appropriate.

b. Check switch set point calibrations in accordance with the Device Summary List.

c. Check gauge calibrations.

d. Isolation valves and test ports for the pressure switches and gauges are provided for this purpose so that the calibration can be performed as installed during turbine non-operation periods.

Idle is defined as a period of time less than or equal to six weeks. During a shutdown special maintenance procedures are required to prevent deterioration of system components. Operation of the fuel oil pumps is recommended to circulate oil throughout the piping system ensuring a protective coat of oil on the oil pipes to prevent corrosion.



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