CIRCUIT-LEVEL HEATING FOR WIDE WOBBE FUELS IN DLN GAS TURBINE COMBUSTION

Abstract

A gas turbine fuel heating system is disclosed having at least one coalescing filter configured to accept a main fuel supply and a plurality of fuel circuit heaters. Each fuel circuit heater can be configured to accept an independent fuel circuit portion of the main fuel supply leaving the at least one coalescing filter and also configured to accept a heating medium circuit portion of a heating medium. The system can have a plurality of scrubbers, a plurality of fuel circuit manifolds, and a plurality of fuel premix tubes. A controller circuit determines the MWI for each independent fuel circuit portion and adjusts the heating medium circuit portion passed to the corresponding fuel circuit heater to maintain at least one parameter selected from the group consisting of a baseline independent fuel circuit portion MWI setpoint and a predetermined independent fuel circuit portion nozzle gas injector pressure ratio.

Claims

1. A gas turbine fuel heating system, comprising; at least one coalescing filter configured to accept a main fuel supply; a plurality of fuel circuit heaters, each fuel circuit heater configured to accept an independent fuel circuit portion of the main fuel supply leaving the at least one coalescing filter and configured to accept a heating medium circuit portion of a heating medium; a plurality of scrubbers, each scrubber configured to accept the independent fuel circuit portion corresponding with a specific fuel circuit heater; a plurality of fuel circuit manifolds, each manifold configured to accept the independent fuel circuit portion corresponding with a specific scrubber; a plurality of fuel premix tubes, each premix tube configured to accept the independent fuel circuit portion corresponding with a specific manifold; and a controller circuit comprising at least one MWI sensor configured to determine the MWI for each independent fuel circuit portion and adjust the heating medium circuit portion passed to the corresponding fuel circuit heater thereby maintaining at least one parameter selected from the group consisting of a baseline independent fuel circuit portion MWI setpoint and a predetermined independent fuel circuit portion nozzle gas injector pressure ratio.

2. The fuel heating system of claim 1, further comprising an electric startup heater.

3. The fuel heating system of claim 1, wherein the plurality of fuel circuit heaters comprise shell and tube heat exchangers.

4. The fuel heating system of claim 1, wherein the controller circuit further comprises a plurality of operating modes supporting different portions of an operational range of the gas turbine.

5. The fuel heating system of claim 4, wherein the controller circuit maintains the at least one parameter in operating modes above about 25% load.

6. The fuel heating system of claim 1, wherein the MWI sensors comprise at least one optical diagnostic device selected from the group consisting of tunable diode laser absorption spectroscope, emissions spectroscope, and fiber pyrometer.

7. A gas turbine system, comprising: an air compressor; one or more fuel combustors comprising air/fuel mixers and a fuel heating system; a gas turbine to expand combusted fuel into fuel exhaust; and a heat recovery steam generator, comprising; a steam generator comprising a heat exchanger to generate steam from the gas turbine fuel exhaust, a steam turbine configured to generate a heating medium for the fuel heating system; wherein the fuel heating system comprises; at least one coalescing filter configured to accept a main fuel supply; a plurality of fuel circuit heaters, each fuel circuit heater configured to accept an independent fuel circuit portion of the main fuel supply leaving the at least one coalescing filter and configured to accept a heating medium circuit portion of a heating medium; a plurality of scrubbers, each scrubber configured to accept the independent fuel circuit portion corresponding with a specific fuel circuit heater; a plurality of fuel circuit manifolds, each manifold configured to accept the independent fuel circuit portion corresponding with a specific scrubber; a plurality of fuel premix tubes, each premix tube configured to accept the independent fuel circuit portion corresponding with a specific manifold; and a controller circuit comprising at least one MWI sensor configured to determine the MWI for each independent fuel circuit portion and adjust the heating medium circuit portion passed to the corresponding fuel circuit heater thereby maintaining at least one parameter selected from the group consisting of a baseline independent fuel circuit portion MWI setpoint and a predetermined independent fuel circuit portion nozzle gas injector pressure ratio.

8. The gas turbine system of claim 7, further comprising an electric startup heater.

9. The gas turbine system of claim 7, wherein the plurality of fuel circuit heaters comprise shell and tube heat exchangers.

10. The gas turbine system of claim 7, wherein the controller circuit further comprises a plurality of operating modes supporting different portions of an operational range of the gas turbine.

11. The gas turbine system of claim 10, wherein the controller circuit maintains the at least one parameter in operating modes above about 25% load.

12. The gas turbine system of claim 7, wherein the at least one MWI sensor comprises at least one optical diagnostic device selected from the group consisting of tunable diode laser absorption spectroscope, emissions spectroscope, and fiber pyrometer.

13. A method for heating gas turbine fuel comprising the steps of: supplying a heating medium to a plurality of fuel circuit heaters; supplying fuel to the plurality of fuel circuit heaters, each fuel circuit heater configured to accept an independent fuel circuit portion of a main fuel supply and exchanging heat with a heating medium circuit portion of the heating medium; and measuring the MWI of each independent fuel circuit portion using MWI sensors configured as part of a controller circuit; and adjusting the heating medium flow through each corresponding heating medium circuit portion to maintain at least one parameter selected from the group consisting of a baseline independent fuel circuit portion MWI setpoint and a predetermined independent fuel circuit portion nozzle gas injector pressure ratio.

14. The method of claim 13, wherein said heating medium is generated by a heat recovery steam generator.

15. The method of claim 14, wherein the heating medium is generated by an intermediate pressure economizer of the heat recovery steam generator.

16. The method of claim 13, further comprising the initial step of heating the fuel during startup with an electric startup heater.

17. The method of claim 13, wherein the plurality of fuel circuit heaters comprise shell and tube heat exchangers.

18. The method of claim 13, wherein the controller circuit further comprises a plurality of operating modes supporting different portions of an operational range of the gas turbine.

19. The method of claim 18, wherein the controller circuit maintains the at least one parameter in operating modes above about 25% load.

20. The method of claim 13, wherein the MWI sensors comprise at least one optical diagnostic device selected from the group consisting of tunable diode laser absorption spectroscope, emissions spectroscope, and fiber pyrometer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] A full and enabling disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

[0014] FIG. 1 is a schematic diagram of a combined-cycle power plant having a gas turbine and heat recovery steam generator (HRSG) for circuit-level fuel heating as may incorporate at least one embodiment of the present disclosure;

[0015] FIG. 2 is a schematic of the fuel side of a circuit-level fuel heating system as may incorporate at least one embodiment of the present disclosure;

[0016] FIG. 3 is a forward end view of a combustion liner cap assembly;

[0017] FIG. 4 is a graph of the gas turbine operating modes when using MWI fuel heating control;

[0018] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0019] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0020] As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location, or importance of the individual components. The terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example, “upstream” refers to the direction from which the fluid flows, and “downstream” refers to the direction to which the fluid flows. The term “radially” refers to the relative direction that is substantially perpendicular to an axial centerline of a particular component and/or substantially perpendicular to an axial centerline of the turbomachine, and the term “axially” refers to the relative direction that is substantially parallel and/or coaxially aligned to an axial centerline of a particular component and/or to an axial centerline of the turbomachine, and the term “circumferentially” refers to the relative direction that is substantially parallel to the circumference of a particular component and/or substantially parallel to the turbomachine annular casing element.

[0021] Although an industrial, marine, or land based gas turbine is shown and described herein, the present disclosure as shown and described herein is not limited to a land based and/or industrial, and/or marine gas turbine unless otherwise specified in the claims. For example, the disclosure as described herein may be used in any type of turbine including but not limited to an aero-derivative turbine or marine gas turbine.

[0022] Two fuel parameters used herein that are defined for the incoming gas are the Wobbe Number (WN) and the Modified Wobbe Index (MWI) of the gas supplied to the turbine. The WN is defined as:

[00001]$\mathrm{WN}=\frac{\mathrm{HHV}}{\sqrt{\mathrm{SG}}}$

where HHV is the higher heating value of the gas fuel and SG is the specific gravity of the gas fuel mixture relative to air. The WN is used as an interchangeability index to permit gas fuels of various heating values to be utilized in the same combustion system without changing hardware. Temperature is not included in this equation for WN because gas is typically delivered at approximately ground temperature with little variation throughout the year. The MWI is defined as:

[00002]$\mathrm{MWI}=\frac{\mathrm{LHV}}{\sqrt{(\left(\mathrm{SG}\times \left(460+\mathrm{Tg}\right)\right)}}$

where LHV is the lower heating value of the gas fuel and Tg is the gas fuel temperature in degrees F. MWI more accurately measures the energy delivered through a fuel nozzle at a given injector pressure ratio than WN. This distinction between MWI and WN becomes very important when gas fuel is heated before delivery to the gas turbine.

[0023] Any change in the fuel compositions may result in unacceptable levels of combustion dynamics as it has been determined that combustion dynamics are a function of MWI. Decreasing the MWI also results in increasing the pressure drop across the fuel injection holes resulting in changes to the fuel system impedance characteristics. One method to control the dynamics is to determine the baseline MWI which has favorable combustion instabilities. Then, the incoming fuel composition MWI is compared with the baseline MWI and adjusted to at least one of the baseline MWI or a predetermined independent fuel circuit portion gas injector pressure ratio, either by increasing or decreasing the fuel temperatures using independent fuel heaters mounted on the respective fuel circuits, and the amount of individual premix circuit fuel flow. With this method of fuel utilization, fuel nozzle impedance characteristics can now be varied or modified not only by changing the fuel splits but also by changing/adjusting the fuel temperature in the individual premix circuits which can produce a more favorable acoustic response from individual flames. This provides capability to independently adjust the fuel temperature and flow in each of the fuel circuits, and effectively altering the fuel flow and injector pressure ratio conditions in fuel circuits which produces a more favorable acoustic response from individual premixed flames. The resulting variation in the individual circuit's impedance and heat release provides the capability to effectively dampen unfavorable combustion dynamics. Independent fuel circuit portion heating provides ability to maintain baseline MWI in each circuit, and provides ability to adjust both fuel flow and gas fuel pressure ratio for each fuel circuit, thus providing an extra tuning knob for dynamics. Previously, fuel flow could be adjusted, but pressure ratio was done for all fuel circuits simultaneously by adjusting fuel temperature for all circuits in one large performance heater.

[0024] Referring now to the drawings, FIG. 1 illustrates a schematic diagram of one embodiment of a combined-cycle power plant having a gas turbine 10 with circuit-level fuel heating provided by a heat recovery steam generator 40. The gas turbine 10 generally includes an inlet section 12, a compressor section 14 disposed downstream of the inlet section 12, a plurality of combustors (not shown) within a combustor section 16 disposed downstream of the compressor section 14, a turbine section 18 disposed downstream of the combustor section 16 and an exhaust section 20 disposed downstream of the turbine section 18. The combustor section 16 fuel is supplied from a circuit-level heating system 80. Additionally, the gas turbine 10 may include one or more shafts 22 coupled between the compressor section 14 and the turbine section 18.

[0025] The turbine section 18 may generally include a rotor shaft 24 having a plurality of rotor disks 26 (one of which is shown) and a plurality of rotor blades 28 extending radially outwardly from and being interconnected to the rotor disk 26. Each rotor disk 26 in turn, may be coupled to a portion of the rotor shaft 24 that extends through the turbine section 18. The turbine section 18 further includes an outer casing 30 that circumferentially surrounds the rotor shaft 24 and the rotor blades 28, thereby at least partially defining a hot gas path 32 through the turbine section 18.

[0026] During operation, a working fluid such as air flows through the inlet section 12 and into the compressor section 14 where the air is progressively compressed, thus providing pressurized air to the combustors of the combustion section 16. The pressurized air is mixed with fuel and burned within each combustor to produce combustion gases 34. The combustion gases 34 flow through the hot gas path 32 from the combustor section 16 into the turbine section 18, where the energy (kinetic and/or thermal) is transferred from the combustion gases 34 to the rotor blades 28, thus causing the rotor shaft 24 to rotate. The mechanical rotational energy may then be used to power the compressor section 14 and/or to generate electricity. The combustion gases 34 exiting the turbine section 18 may then be exhausted from the gas turbine 10 via the exhaust section 20, into a heat recovery steam generator (HRSG) 40. Steam from the HRSG 40 is expanded through a high pressure turbine(HP) section 42, then an intermediate pressure turbine (IP) section 44, and finally through a low pressure turbine (LP) section 46 before exhausting to a condenser 49. The turbine shaft rotates a power generator 48.

[0027] The circuit-level fuel gas heating system 80 is typically heated by hot water 50 supplied from the HRSG IP economizer. The hot water 50 passes through circuit-level hot water control valves 51-54 in route to corresponding circuit-level fuel heaters 72-74. Fuel conditions leaving each fuel heater 72-74 are measured by MWI sensors 92-94 that provide input to a controller circuit 86 that conditions a control signal for each hot water control valve 51-54 to maintain a baseline circuit MWI setpoint as determined by the gas turbine controller circuit 86. The MWI sensors 92-94 can be an optical diagnostic device of at least one type selected from the group consisting of tunable diode laser absorption spectroscope, emissions spectroscope, and fiber pyrometer as taught in commonly-owned U.S. Pat. No. 9,249,737, titled “METHODS AND APPARATUS FOR RAPID SENSING OF FUEL WOBBE INDEX” issued Feb. 2, 2016.

[0028] Referring now to FIG. 2 schematic showing the fuel side of a circuit-level fuel heating system 80, as the incoming main gas fuel supply 79 enters the plant facility, it first passes through at least one coalescing filter 75. These coalescing filter(s) 75 are required to remove both liquids and particulate from the customer's gas supply. Downstream of the coalescing filter(s) 75, the gas fuel supply enters the electric startup heater 70. This startup heater 70 is required when the gas supply 79 does not meet the minimum superheat requirement. The electric heater 70 is turned off and then bypassed at the point when the circuit-level heaters 72-74 are capable of maintaining gas temperatures above the minimum superheat requirement. When the electric heater 70 is off, fuel enters the circuit-level heaters 72-74. The circuit-level heaters 72-74 can incorporate a shell & tube heater arrangement with the gas on the shell side and the hot water on the tube side. The gas fuel exiting the circuit-level heaters 72-74 enters the gas fuel scrubbers 82-84. This “dry” scrubber performs two functions in that it provides the final level of particulate filtration upstream of the gas turbine, and removes gas entrained water droplets present as the result of a possible minor tube leak (i.e., pinhole). Gas fuel exiting the fuel scrubbers 82-84 enters gas fuel supplying manifolds 56, 57, and 58 to supply fuel that is ultimately introduced to a combustor. As seen in FIGS. 2 and 3, premix 1 (PM1) manifold 56 supplies fuel to center fuel nozzle 33. Premix 2 (PM2) manifold 57 supplies fuel for premixing to two of the five outer fuel nozzles 36 arranged relative to combustion liner cap assembly 25 as shown in FIG. 3. Premix 3 manifold 58 supplies fuel for premixing to three of five outer fuel nozzles 36 arranged relative to combustion liner cap assembly 25. Purge air for passages which do not receive a fuel supply in all modes of operation is supplied to the five outer fuel nozzles via purge air manifold 60.

[0029] In FIG. 3, combustion liner cap assembly 38 includes openings for outer fuel nozzles 36 and their premix tubes, and an opening for center fuel nozzle 33 and its premix tube, all openings disposed in forward support plate 29. In some configurations, forward support covers 35 are included and are mounted to forward support plate 29. Forward support covers 35 aid in securing each of the outer premix tubes on the forward end.

[0030] Referring to the mode graph of FIG. 4, exemplary configurations of each combustor can have a plurality of normal operating modes on gas fuel. These modes are configured to support different portions of the operational range of gas turbine 10. A combustor is ignited in mode3, and a gas turbine rotor accelerated to 95% speed in Mode 2. Mode2 has gas fuel supplied by the PM2 manifold 57 to the PM2 fuel nozzles. Mode3 has gas fuel supplied by PM1 manifold 56 to the PM1 fuel nozzle, and gas fuel supplied by the PM2 manifold 57 to the PM2 fuel nozzles. At approximately 95% turbine rotor speed condition, a transition to the Mode 1 premix mode occurs. This transition initiates fuel flow in premix 1 (PM1) fuel circuit or manifold 56, and terminates fuel flow to gas manifold 57 and the PM2 fuel nozzles, allowing the rotor to achieve a full speed condition (100% speed) with minimal or reduced load application to the turbine rotor. This operational sequence provides constant fueling of premix 1 fuel manifold 56 for all rotor speeds and loads greater than the 95% speed, no load condition. As a result, premix 1 fuel manifold 56 does not require purge air at any time during operation. During Mode 1, purge air is supplied to premix 2 fuel manifold 57 and premix 3 fuel manifold 58. At a preselected gas turbine reference firing temperature condition between 100% rotor speed up to a minimal load condition, a mode transition to premix mode 3 is initiated as premix 2 manifold 57 begins fueling the combustor while premix 3 manifold 58 continues to be air purged. In mode 3 premix mode, premix 1 manifold 56, and premix 2 manifold 57 are all fueled. The mode 3 premix mode is a very stable, non-low emissions mode that can use either hot or cold fuel.

[0031] At approximately 25% load or higher, a mode transition to mode 4 premix circuit-level heating mode is scheduled, where the PM1 gas manifold 56 continues to supply gas to the PM1 fuel nozzle, the PM3 gas manifold 58 supplies gas fuel to the PM3 fuel nozzle, and the PM2 gas manifold 57 gas fuel flow is terminated. In this circuit-level heating mode of the operation sequence, the controller circuit 86 uses the circuit modified Wobbe index measured by MWI sensors 92-94 to modulate the hot water control valves 51-54 to maintain a baseline MWI setpoint that is mode-specific. In mode 4 premix mode, combustion dynamics are improved by maintaining the baseline MWI which has less combustion instabilities. The incoming fuel composition MWI is compared with the baseline MWI and adjusted to the baseline MWI either by increasing or decreasing the fuel temperatures using independent fuel heaters 72-74 and premix circuits 56-58 mounted on the respective fuel circuits. In mode 4 premix mode, as the split of total fuel flow is modulated as a function of reference firing temperature to the premix fuel manifolds 56, and 58. Above approximately 50% load, mode 6 is scheduled where gas fuel is supplied from manifold 56, 57, 58 to fuel nozzles PM1, PM2 and PM3 respectively. Acceptable flame stability and low dynamic pressures are simultaneously realized as a result of the ability of the fuel system to control axisymmetric fuel staging within combustion burning zone, and independently heat fuel supplied to each fuel circuit to maintain a baseline MWI setpoint and/or a targeted fuel nozzle gas injection pressure ratio.

[0032] Hot fuel (>120° F.) is permitted in modes 1, 2 and 3 from ignition up to about 10% load, but hot fuel is not recommended in this operating range for long term operation. Between about 10% and 25% load, mode 3 can use either hot or cold fuel and the independent fuel circuit portion temperatures can be controlled in accordance with this disclosure. Above about 25% load, the gas temperature of each independent fuel circuit portion is adjusted to satisfy design MWI specifications and maintain at least one of a baseline independent fuel circuit portion MWI setpoint and a predetermined independent fuel circuit portion nozzle gas injector pressure ratio. Additionally, independent fuel circuit portion temperatures can be controlled for any operating mode during startup or shutdown.

[0033] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.