GE Power Systems

Design Considerationsfor Heated Gas Fuel

D.M. EricksonS.A. DayR. DoyleGE Power SystemsGreenville, SC

GER-4189B

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Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Gas Fuel Performance Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Gas Compressor Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

General System Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Gas Fuel Cleanliness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Gas Fuel Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Gas Fuel Supply Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Gas Fuel Supply Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Combustion Specific System Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

DLN-1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

DLN-2.0 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

DLN-2+ Requirements (PG9351FA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

DLN-2+ FB Requirements (PG7251FB & PG9371FB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

DLN-2.6 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

DLN-2.5H Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Typical GE Gas Fuel Heating System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Design Considerations for Heated Gas Fuel

GE Power Systems GER-4189B (03/03) i

Design Considerations for Heated Gas Fuel

GE Power Systems GER-4189B (03/03) ii

Introduction

Gas Fuel Performance HeatingAs the need for higher efficiency power plantsincreases, a growing number of combined-cyclepower plants are incorporating performancegas fuel heating as a means of improving overallplant efficiency. This heating, typically increas-ing fuel temperatures in the range of365F/185C, improves gas turbine efficiencyby reducing the amount of fuel needed toachieve desired firing temperatures. For fuelheating to be a viable method of performanceenhancement, feedwater has to be extractedfrom the heat recovery steam generator(HRSG) at an optimum location. Boiler feed-water leaving the intermediate pressure econo-mizer is commonly used. Using gas-fired, oil-fired or electric heaters for performance gasfuel heating will not result in a power plantthermal efficiency improvement.

Proper design and operation of the Gas FuelHeating System is critical in insuring reliableoperation of the gas turbine. Improper selec-tion of components, controls configurationand/or overall system layout could result inhardware damage, impact plant availability andcreate hazardous conditions for plant person-nel. This paper addresses the critical design cri-teria that should be considered during thedesign and construction of these systems.

Also included in this paper is the design of a"typical" GE Gas Fuel Heating System. This sys-tem has been developed taking into considera-tion the system requirements defined within.

Gas Compressor HeatingGas compressors may be needed to meet speci-fied minimum gas supply pressures levels. Theuse of a compressor adds heat to the gas andraises its operational temperature. The temper-

ature level of the gas at the exit of the gas com-pressor is a function of its inlet conditions. Thistemperature may vary from site to site andshould be evaluated against any combustionspecific requirements defined in this docu-ment.

General System RequirementsThe following section identifies general systemrequirements that apply to all gas fuel heatingsystems. These requirements, in addition tothose described in the Combustion SpecificSystem Requirements section shall be followedduring the design and development of the sys-tem.

Gas Fuel CleanlinessGas fuel supplied to the gas turbine shall meetthe particulate requirements as specified in thelatest revision of GEI-41040, "ProcessSpecification Gas Fuels for Combustion inHeavy Duty Gas Turbines," (Reference 1). If thecomponents in the Gas Fuel Heating System areconstructed of materials susceptible to corro-sion, a method of final filtration upstream ofthe gas turbine interface is required. Particulatecarryover greater than that identified in GEI-41040 can plug fuel nozzle passages, erode com-bustion hardware and gas valve internals andcause damage to first stage turbine nozzles. Thenew gas piping system must be properly cleanedprior to initial gas turbine operation. Additionaldesign considerations related to gas fuel clean-liness may be found in GER-3942, Gas FuelClean-Up System Design Considerations for GEHeavy Duty Gas Turbines," (Reference 2).

Gas Fuel QualityAs defined in GEI-41040, the fuel delivered tothe gas turbine must be liquid free and containa specified level of superheat above the higherof the hydrocarbon or moisture dewpoints.

Design Considerations for Heated Gas Fuel

GE Power Systems GER-4189B (03/03) 1

Saturated fuels, or fuels containing superheatlevels less than specified, can result in the for-mation of liquids as the gas expands and coolsacross the gas turbine control valves. Theamount of superheat provides margin to com-pensate for temperature decrease due to pres-sure reduction, and is directly related to incom-ing gas supply pressure. (Note: Within thisdocument, gas fuel heating strictly for dewpointconsiderations is still considered to be in a"cold" state. Heating for performance purposesis considered "heated" fuel.)

The design of the Gas Fuel Heating System shallprevent carryover of moisture or water to thegas turbine in the event of a heat exchangertube failure. Water entrained in the gas cancombine with hydrocarbons causing the forma-tion of solid hydrocarbons or hydrates. Thesehydrates, when injected into the combustionsystem, can lead to operability problems,including increased exhaust emissions andmechanical hardware damage. Proper meansof turbine protection, including heat exchang-er leak detection, shall be provided.

Gas Fuel Supply PressureGas being supplied to the gas turbine interfacepoint (customer connection FG1) shall meetthe minimum gas fuel supply pressure require-ments as defined in the proposal documenta-tion. These minimum pressure requirementsare established to insure proper gas fuel flowcontrollability and to maintain required pres-sure ratios across the combustion fuel nozzles.The Gas Fuel Heating System shall be designedto insure that these requirements are met dur-ing all modes of operation over the entireambient temperature range.

The design of the Gas Fuel Heating System shallinsure that the design pressure of the gas tur-bine gas fuel system is not exceeded.

Overpressure protection, as required by appli-cable codes and standards, shall be furnished.In addition to minimum and maximum pres-sures, the gas turbine is also sensitive to gas fuelpressure variations. Sudden drops in supplypressure may destabilize gas pressure and flowcontrol. Sudden increases in supply pressuremay potentially trip the turbine due to a hightemperature condition. Limitations on pressurefluctuations are defined in the gas turbine pro-posal documentation.

Gas Fuel Supply TemperatureThe Gas Fuel Heating System shall be designedto produce the desired gas fuel temperature atthe interface with the gas turbine equipment.Guaranteed performance is based on thedesign fuel temperature at the inlet to the gasturbine gas fuel module (FG1). The gas fuelheating and supply systems shall compensatefor heat losses through the system.Compensation shall include but not be limitedto elevated heater outlet temperatures, use ofpiping and equipment insulation, and mini-mization of piping length from heater outlet toturbine inlet.

The Gas Fuel Heating System shall be designedto support specified gas fuel temperature set-points required by the gas turbine. These set-points include high and low temperaturealarms, gas turbine controls permissives, andgas turbine controls functions. These setpointsare derived by GE Gas Turbine Engineeringand are based on operability requirementsand/or design limitations of components with-in the gas tur