Systems and methods for operating a combustor with multiple liquid fuels - Patents.com

Abstract

The systems and methods presented herein are configured to transition from a first liquid fuel (38a) supplied to a combustor (14) of a gas turbine system (10) to a second liquid fuel (38b) supplied to the combustor (14) without shutting down the gas turbine system (10) using a fuel pump (42) configured to supply both fuels (38a, 38b) from the fuel pump (42) during the transition. By utilizing the fuel pump (42) to coordinate the operation of the fuel pump (42) during the transition, the additional cost, size, and operational complexity associated with multiple liquid fuel trains to facilitate operation of the gas turbine system (10) with multiple liquid fuels (38) can be avoided. Utilizing multiple liquid fuels (38) during operation of the gas turbine system (10) increases the operational flexibility of the gas turbine system (10) by enabling the utilization of various and / or localized liquid fuel sources during steady-state operation and further utilizing a standardized fuel source for startup or shutdown procedures.

Description

[Technical field]

[0001] The subject matter disclosed herein relates to gas turbine systems and, more particularly, to gas turbine systems that burn multiple liquid fuels. [Background technology]

[0002] A gas turbine system typically includes a compressor, a combustor, and a turbine. The combustor combusts a mixture of compressed air and one or more fuels to generate hot combustion gases that are channeled to a turbine to generate work, such as to drive a generator or other load. The compressor compresses a flow of oxidant (e.g., air) and subsequently channels the compressed oxidant to the combustor. Gas turbine systems can be configured to operate with a variety of fuels. For efficiency, availability, and / or cost reasons, it may be desirable to use some fuels during a first period of operation of the gas turbine system and other fuels during a second period of operation of the gas turbine system. However, separate fuel supply systems for the separate fuels may increase the cost and footprint of the gas turbine system. Additionally, it may be undesirable to shut down the gas turbine system to change the fuel source of the gas turbine system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2017 / 184111 Summary of the Invention

[0004] Certain embodiments commensurate in scope with the initially claimed subject matter are summarized below. These embodiments are not intended to limit the scope of the claims, but rather, these embodiments are intended only to provide a brief summary of possible forms of embodiments of the present disclosure. Indeed, the present disclosure may encompass a variety of forms that may be similar to or different from the embodiments set forth below.

[0005] In one embodiment, a system includes a fuel supply system. The fuel supply system includes a fuel pump having an inlet and an outlet. The fuel supply system also includes a first fuel supply valve configured to control a first flow of a first liquid fuel to the inlet based at least in part on a first supply valve control signal. The fuel supply system further includes a second fuel supply valve configured to control a second flow of a second liquid fuel to the inlet based at least in part on a second supply valve control signal.

[0006] Additionally, the fuel supply system includes a motor coupled to the fuel pump. The motor includes a variable frequency drive configured to drive the motor. The motor is configured to drive the fuel pump based at least in part on the pump speed control signal. The fuel supply system also includes a main fuel control valve configured to regulate a fuel flow to a fuel manifold / nozzle of the gas turbine system based at least in part on the main fuel valve control signal. The main fuel valve control signal is based at least in part on a load demand of the gas turbine system. The fuel supply system further includes a controller coupled to the motor, the first fuel supply valve, the second fuel supply valve, and the main fuel control valve. The controller is configured to generate the first supply valve control signal, the second supply valve control signal, the pump speed control signal, and the main fuel valve control signal based at least in part on a first fuel parameter of the first liquid fuel and a second fuel parameter of the second liquid fuel. The controller is also configured to control a transition from a first flow to the inlet at a first time to a second flow to the inlet at a second time.

[0007] In one embodiment, a method for transitioning a liquid fuel flow supplied to a gas turbine system during operation of the gas turbine system includes supplying a first liquid fuel to an inlet of a fuel pump through a first fuel supply valve opened to a first liquid fuel threshold. The first liquid fuel threshold is based at least in part on a first fuel parameter of the first liquid fuel. The method also includes directing the first liquid fuel from an outlet of the fuel pump to a combustor of the gas turbine system. The method further includes combusting the first liquid fuel with an oxidizer in the combustor to generate exhaust gases. In addition, the method includes expanding the exhaust gases through a turbine of the gas turbine system to drive a shaft coupled to the turbine and a load. The method also includes transitioning over a transition period from combustion of the first liquid fuel in the combustor to combustion of a second liquid fuel in the combustor. The transitioning includes opening a second liquid fuel supply valve to a second liquid fuel threshold and supplying the first liquid fuel to the inlet while supplying the second liquid fuel to the inlet of the fuel pump. The second liquid fuel threshold is based at least in part on a second fuel parameter of the second liquid fuel. The transitioning also includes closing the first fuel supply valve to stop supplying the first liquid fuel to the inlet from the first liquid fuel threshold in response to opening the second fuel supply valve to the second liquid fuel threshold. The transitioning further includes controlling a speed of a motor configured to drive the fuel pump to maintain a discharge pressure of the liquid fuel stream at the outlet within a range of the transition pressure. The liquid fuel stream includes the first liquid fuel, the second liquid fuel, or any combination thereof.

[0008] In one embodiment, the fuel supply system includes a processor configured to control a first fuel supply valve configured to direct a first liquid fuel to a fuel pump. The fuel pump is configured to supply the first liquid fuel to the combustor via a main fuel control valve during a startup period of the gas turbine system. The processor is also configured to determine a second liquid fuel threshold value for the second fuel supply valve based at least in part on a first fuel parameter of the first liquid fuel and a second fuel parameter of the second liquid fuel. The processor is further configured to control the second fuel supply valve to the second liquid fuel threshold value during a transition period to direct the first liquid fuel to the fuel pump while directing the second liquid fuel to the fuel pump. Additionally, the processor is configured to control the first fuel supply valve to stop directing the first liquid fuel to the fuel pump in response to controlling the second fuel supply valve to the second liquid fuel threshold value during the transition period. The processor is also configured to control a speed of a motor configured to drive the fuel pump to maintain a discharge pressure of a fuel flow from the fuel pump at the main fuel control valve within a range of transition pressures during the transition period, the fuel flow including a first liquid fuel, a second liquid fuel, or any combination thereof. The processor is further configured to control a speed of the motor to drive the fuel pump to supply the second liquid fuel to the combustor via the main fuel control valve during a steady state period of the gas turbine system.

[0009] These and other features, aspects, and advantages of the present disclosure will become better understood from the following detailed description when taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts throughout. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic block diagram of an embodiment of a gas turbine system including a fuel delivery system having multiple fuels. [Diagram 2] 4 is a chart of the speed of a compressor shaft of a gas turbine system and a pump shaft of a number of fuel supply systems during operation of the gas turbine system. [Diagram 3] 4 is a flow chart of an embodiment of a transition of a fuel source supplied to a gas turbine system from a fuel supply system. [Figure 4] 4 is a chart illustrating control of a fuel valve during a transition of a fuel source in a fuel supply system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] One or more specific embodiments of the present disclosure are described below. In order to provide a concise description of these embodiments, not all features of an actual implementation are described herein. It should be understood that in the development of an actual implementation, such as an engineering or design project, many implementation-specific decisions must be made to achieve the developer's particular objectives, such as compliance with system-related and business-related constraints, and that these constraints may vary from implementation to implementation. It should also be understood that such development efforts may be complex and time-consuming, but are nevertheless a routine undertaking of design, fabrication, and manufacture for those skilled in the art having the benefit of this disclosure.

[0012] When introducing elements of various embodiments of the disclosure, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the element. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0013] A gas turbine system expands combustion gases through a turbine to generate work capable of driving one or more loads. Fuels provided to the gas turbine system may be provided to combustors to generate combustion gases based on the chemical and physical parameters of the fuel, the cost of the fuel, and the availability of the fuel. Standardized fuels, such as diesel oil, natural gas, gasoline, and jet fuel, may be available with consistent fuel parameters that are desirable for start-up and shutdown operations. However, these standardized fuels may be more expensive or unavailable than other fuel sources, such as fuel sources that may possibly be flared near the site of the gas turbine system, unless they are provided to the gas turbine system to generate the combustion gases. Separate fuel pumps and / or compressors that deliver fuel from other fuel sources for steady-state operation of the gas turbine system may increase the footprint of the fuel supply system. However, the analysis of fuel parameters of the fuel sources described herein allows the fuel supply system to provide different fuels to the combustors while avoiding multi-phase fuel flow. When operating with multiple liquid fuels, through the control of a variable speed motor driving the fuel pump, and a fuel control valve, the fuel supply system may maintain the discharge pressure of the liquid fuel from the fuel pump while transitioning the liquid fuel sources of the fuel supply system. The systems and methods for controlling a liquid fuel supply system described herein maintain operational stability of a gas turbine system throughout a transition of liquid fuel sources.

[0014] Referring now to the drawings, FIG. 1 illustrates a block diagram of one embodiment of a gas turbine system 10. The diagram includes a compressor 12, a turbine combustor 14, and a turbine 16. The turbine combustor 14 includes one or more fuel manifolds / nozzles 18 that route liquid and / or gaseous fuel (e.g., natural gas, syngas, or any other gaseous fuel) from a fuel supply system 30 to the turbine combustor 14. The turbine combustor 14 ignites and combusts an air-fuel mixture to generate hot pressurized combustion gases 24, which are subsequently channeled to the turbine 16. While FIG. 1 illustrates one turbine combustor 14, it will be understood that certain embodiments of the gas turbine system 10 may include multiple turbine combustors 14 that channel the combustion gases 24 to the turbine 16. The turbine blades of the turbine 16 are coupled to one or more shafts 26 that may also be coupled to several other components overall of the gas turbine system 10, such as the compressor 12 having a compressor shaft 26c. As the combustion gases 24 flow against turbine blades in the turbine 16, they drive the turbine 16 in rotation, which in turn rotates a turbine shaft 26t. Ultimately, the combustion gases 24 exit the gas turbine system 10 as exhaust gases 28. The turbine shaft 26t may be coupled to a load 32 that is powered via the rotation of the turbine shaft 26t. For example, the load 32 may be any suitable device capable of generating power via the rotational output of the turbine system 10, such as a power plant or an external mechanical load. In certain embodiments, the load 32 may include an electrical generator, a marine propeller (e.g., in marine applications), or the like.

[0015] In one embodiment of the gas turbine system 10, the compressor blades are included as components of the compressor 12. The blades in the compressor 12 are coupled to a compressor shaft 26c and rotate when the compressor shaft 26c is driven by the turbine 16, as described above. The rotation of the blades in the compressor 12 causes compression of the airflow 20 received by the compressor 12 from an air intake 34, thereby forming a compressed airflow 36. For example, in certain embodiments, a first stream of the compressed airflow 36a may be provided to one or more combustors 14, where the compressed airflow 36a is used to oxidize fuel from one or more fuel sources 38 of a fuel supply system 30 in the combustors 14. In certain embodiments, a second stream of the compressed airflow 36b may be provided to a fuel manifold / nozzle 18, where the compressed airflow 36b is premixed with fuel from one or more fuel sources 38 of the fuel system 30 to generate an air-fuel mixture 40 suitable for combustion so as not to waste fuel or generate excessive emissions.

[0016] The fuel delivery system 30 of the present disclosure delivers fuel from one or more fuel sources 38 to one or more fuel manifolds / nozzles 18. The fuel delivery system 30 may deliver one or more liquid fuels to the fuel manifolds / nozzles 18 via a fuel pump 42. The fuel pump 42 may be a centrifugal or positive displacement pump coupled to a motor 44 via a pump shaft 46 and controlled in speed with a variable frequency control device 48, such as a variable frequency drive (VFD) motor, a switched reluctance (SR) motor, or a pump that controls the discharge pressure by adjusting the geometry of its discharge side. In certain embodiments, the fuel delivery system 30 has only one fuel pump 42 configured to couple the one or more fuel sources 38 to a fuel control valve 50 to direct the appropriate fuel flow to the one or more fuel manifolds / nozzles 18, thereby reducing the footprint of the fuel delivery system 30 compared to a fuel delivery system having multiple liquid fuel pumps in parallel.

[0017] In certain embodiments, the VFD / SR 48 of the motor 44, which is used to control the variable speed of the motor 44 and control the discharge pressure to the fuel control valve 50, may be monitored and controlled by a gas turbine controller 52. In certain embodiments, the controller 52 may regulate the discharge pressure by controlling the pump shaft 46 and the output speed of the fuel pump 42 by continuously monitoring the discharge pressure via a pressure transmitter 54 located near the discharge of the fuel pump 42, which provides feedback to the controller 52 to close the control loop for pressure regulation. A processor 56 of the controller 52 may execute instructions stored in a memory 58 of the controller 52 to control signals on the motor control lines 60. In certain embodiments, the controller 52 may perform the control functions described herein automatically without human intervention, based solely on feedback from the sensors and transmitters described herein.

[0018] The fuel pump 42 delivers fuel received at an inlet 62 of the fuel pump 42 to one or more fuel manifolds / nozzles 18 via an outlet 64 of the fuel pump 42. The controller 52 may control which liquid fuel of one or more liquid fuel sources 38 is directed to the inlet 62 via control of one or more respective fuel supply valves 66 via signals (e.g., valve control signals) communicated on supply valve control lines 68. For example, in certain embodiments, the supply of a first fuel source 38a (e.g., diesel oil) to the inlet 62 is controlled by a first fuel supply valve 66a, the supply of a second fuel source 38b (e.g., liquid butane) to the inlet 62 is controlled by a second fuel supply valve 66b, and the supply of a third fuel source 38c (e.g., naphtha) to the inlet 62 is controlled by a third fuel supply valve 66c. As shown in FIG. 1, any number of fuel sources 38 (eg, Nth fuel source 38d shown in FIG. 1) and corresponding fuel valves 66 may be used.

[0019] In certain embodiments, one or more transfer pumps 70 may be disposed between the fuel source 38 and the inlet 62 of the fuel pump 42. Each transfer pump 70 may increase the pressure of the liquid fuel from a respective liquid fuel source 38 to reduce or eliminate two-phase flow to the inlet 62 of the fuel pump 42. The controller 52 may control the operation of the one or more transfer pumps 70 in conjunction with controlling the fuel supply valves 66. For example, the controller 52 may stop the transfer pump 70 when the respective fuel supply valve 66 is closed and start the transfer pump 70 when the respective fuel supply valve 66 is open.

[0020] Additionally, in certain embodiments, the fuel delivery system 30 of the present disclosure may supply gaseous fuel from one or more gaseous fuel sources 72. The controller 52 may direct start-up, stop, or steady state operation with gaseous fuel, as well as command transfer to or from any of a number of liquid fuel sources 38.

[0021] In certain embodiments, the liquid fuel may have a specific gravity ranging from, for example, 0.2 to 2.0, a vapor pressure at 20° C. ranging from, for example, 0.015 psi to 35 psi, a lubricity ranging from, for example, 350 μm to 1000 μm by High Frequency Reciprocating Rig (HFRR), and a lower heating value ranging from, for example, 8,000 BTU / lbm to 20,000 BTU / lbm. Included in this classification are liquid hydrocarbons at ambient conditions, liquid alcohols at ambient conditions, liquid biofuels at ambient conditions, liquid fatty acids at ambient conditions, and the like. The gas fuel may have a specific gravity ranging from, for example, 0.2 to 2.5, a hydrocarbon dew point at 14.696 psia (1 atm) ranging from, for example, -100 to 100F, a Modified Wobbe Index (MWI) ranging from, for example, 10 to 80, a lower heating value by mass ranging from, for example, 5,000 to 22,000 BTU / lbm, and a lower heating value by volume ranging from, for example, 290 BTU / scf to 3700 BTU / scf.

[0022] As described in more detail below, the processor 56 of the controller 52 may execute instructions from the memory 58 of the controller 52 to control the amount of one or more fuel sources provided to the liquid fuel pump 42 according to various control schemes. For example, the controller 52 may control the fuel supply valve 66 to provide fuel to the inlet 62 from only one fuel source 38, mix fuel in the liquid fuel pump 42 from two or more fuel sources 38, and transition the fuel or fuel mixture provided to the inlet 62. While the embodiments described below describe a transition between a first liquid fuel and a second liquid fuel, it is understood that the fuel supply system 30 may be controlled to control a transition from the first liquid fuel to a mixture of liquid fuel including the first liquid fuel, to control a transition from the first liquid fuel to a mixture of liquid fuel excluding the first liquid fuel, to control a transition from a mixture of liquid fuel to only the first liquid fuel in the mixture, or to control a transition from a mixture of liquid fuel to only the first liquid fuel that was not in the mixture. For such a transfer, the controller may receive feedback from sensors, actuators, and / or input from an operator regarding fuel parameters for each of the liquid fuel sources 38 of the fuel supply system 30. The fuel parameters for the liquid fuel sources 38 facilitate operation of the controller to determine liquid fuel transfer values, which may affect fuel supply valve thresholds, motor speed, speed of the gas turbine system, load on the gas turbine system, or any combination thereof.

[0023] The controller 52 of the fuel supply system 30 may receive feedback from one or more sensors 74 throughout the fuel supply system 30 and the gas turbine system 10. The sensors 74 may include, but are not limited to, pressure sensors, composition sensors, flow meters, temperature sensors, load sensors, rotational sensors, or any combination thereof. The sensors 74 may provide feedback to the controller 52 regarding the temperature of the liquid fuel source 38, the pressure of the liquid fuel source 38, the discharge pressure at the outlet 64 of one or more fuels derived from the liquid fuel pump 42 as indicated by the pressure transmitter 54, the position of the fuel control valve 50, the speed of the pump shaft 46, the speed of the compressor shaft 26c of the gas turbine system 10, the speed of the turbine shaft 26t of the gas turbine system 10, the load 32 on the gas turbine system 10, or any combination thereof. The controller 52 may control the liquid fuel pump 42, the fuel supply valve 66, and the fuel control valve 50 based at least in part on the feedback from the one or more sensors 74.

[0024] 2 illustrates a chart 75 showing the speed of the compressor shaft 26c of an embodiment of the gas turbine system 10 of FIG. 1 during operation of the gas turbine system 10, and a chart 76 showing the speed of the pump shaft 46 during operation of the gas turbine system 10 of FIG. 1. During a start-up period 78, the gas turbine system 10 starts up by combusting a first liquid fuel 38a (e.g., diesel oil) in the combustor 14 while the compressor shaft 26c is driven at a starter speed 80. During the start-up period 78, components of the gas turbine system 10 heat up through operation. For example, the combustion of the first fuel heats the combustor 14 and the turbine 16, the compression of the air 20 in the compressor 12 heats the compressor 12, and friction can warm the lubricating oil in the compressor shaft 26c, the turbine shaft 26t, and the driven load 32. The load of the gas turbine system during startup and shutdown operations may be less than approximately 50, 40, 30, 25, 20, or 10% of the rated load of the gas turbine system. The compressor shaft 26c may be initially driven by the starter at a starter speed until combustion of fuel in the combustor 14 generates sufficient combustion gases to drive the turbine 16 and the compressor shaft 26c at a speed faster than the starter speed 80.

[0025] The controller 52 may control the VFD / SR 48 of the motor 44 to drive the fuel pump 42 at an initial pump speed 82. The starter speed 80 of the compressor shaft 26c may be about 2400 RPM. In a particular embodiment, the fuel pump 42 directs the first liquid fuel 38a (e.g., diesel oil) to the fuel manifold / nozzle 18 at about 600 psig by driving the pump shaft 46 at an initial pump speed 82 of about 3500 RPM. After the combustion gases drive the turbine 16 and rotate the compressor shaft 26c at an idle speed 84 at T1, the controller 52 may control the VFD / SR 48 of the motor 44 at T2 to increase the pump speed from the initial pump speed 82 to a starter fuel speed 86 at T3. In a particular embodiment, the idle speed 84 of the compressor shaft 26c of the gas turbine system 10 is 6800-7000 RPM. In a particular embodiment, the fuel pump 42 directs the first liquid fuel 38a to the fuel manifold / nozzle 18 at a transition pressure (e.g., about 1200 psig) by driving the pump shaft 46 at a starting fuel speed 86 of about 5150 RPM. The shaft speed can increase from an idle speed 84 at T1 to a minimum load speed 88 of 7100-7500 RPM at T2 depending on the control of fuel from the pump to the combustor 14 at T2.

[0026] Combustion gases from the combustion of the first liquid fuel 38a in the combustor 14 may continue to increase the speed of the compressor shaft 26c from a minimum load speed 88 of 7100-7500 RPM at T2 to a fuel delivery speed 90 at T4. At the fuel delivery speed 90, the gas turbine system 10 may be configured to operate stably and drive fuel delivery with the first liquid fuel 38a, the second liquid fuel 38b, or any combination thereof. In certain embodiments, the fuel delivery speed 90 for stable operation of the gas turbine system 10 is between 8200-10000 RPM. In certain embodiments, the pressure of the first liquid fuel 38a provided by the variable speed fuel pump 42 at the starting fuel speed 86 is determined based on the vapor pressure of the second liquid fuel 38b added to the first liquid fuel 38a during the first transition period 92. That is, the controller 52 may control the VFD / SR 48 linked to the fuel pump 42 to a starting fuel rate 86 with the first liquid fuel 38a during the start-up period 78 to facilitate the transfer from the first liquid fuel 38a to the second liquid fuel 38b during the first transition period 92 without changing the phase of the first liquid fuel 38a or the second liquid fuel 38b. It will be appreciated that if the fuel pump 42 receives the first liquid fuel 38a at a pressure lower than the vapor pressure of the second liquid fuel 38b, the fuel pump 42 may receive a two-phase flow in which the first liquid fuel 38a is received as a liquid and the second liquid fuel 38b is received as a gas. The controller 52 may control the VFD / SR 48 linked to the fuel pump 42 and the starting fuel rate 86 to avoid providing a two-phase flow to the fuel pump 42 from either of the fuel sources. The controller 52 may determine the starting fuel rate 86 based at least in part on feedback from sensors of the fuel pressure of the fuel source, the fuel temperature of the fuel source, fuel properties input by an operator, or any combination thereof.

[0027] During the transition period, the controller 52 may maintain the first flow of the first liquid fuel 38a to the fuel pump 42 and increase the second flow of the second liquid fuel 38b to the fuel pump 42. The controller 52 may control the VFD / SR 48 of the motor 44 to increase the speed of the fuel pump 42 during the transition period from the starting fuel speed 86 at T4 to the primary fuel speed 94 at T5 to facilitate directing additional second liquid fuel 38b to the fuel pump 42 without adjusting the pressure (e.g., discharge pressure) of the fuel provided by the fuel pump 42. That is, the controller 52 may control the VFD / SR 48 of the motor 44 to adjust the speed of the fuel pump 42 during the transition period to maintain the discharge pressure within a desired pressure (e.g., transition pressure). In one embodiment where the first liquid fuel 38a is diesel liquid fuel and the second liquid fuel 38b is liquid butane fuel, the primary fuel speed 94 may be approximately 6060 RPM. The controller 52 may determine the primary fuel rate 94 of the fuel pump 42 based at least in part on fuel parameters of one or more fuels directed to the combustor during the ramp-up period 96, the steady state period 100, and / or the ramp-down period 102. In certain embodiments, the controller 52 determines the primary fuel rate 94 of the fuel pump based at least in part on the lower heating value of the second liquid fuel 38b, the lubricity of the second liquid fuel 38b, the specific gravity of the second liquid fuel 38b, or the vapor pressure of the second liquid fuel 38b, or any combination thereof. In certain embodiments, the controller 52 may determine the composition of the fuel from feedback of the sensors 74 and the pressure transmitter 54 and then determine the one or more parameters of the fuel from a table stored in the memory 58 or accessible by the processor 56 of the controller 52. During the first transition period 92, the controller 52 may control the fuel supply valve 66 to increase the amount of the second liquid fuel 38b provided to the fuel pump 42 and decrease the amount of the first liquid fuel 38a provided to the fuel pump 42. In certain embodiments, the first transition period 92 is between 15 and 180 seconds, between 30 and 150 seconds, or between 60 and 120 seconds.As described in more detail below, the controller 52 may first increase the amount of the second liquid fuel 38b provided to the fuel pump 42 from zero to a second amount and then decrease the amount of the first liquid fuel 38a provided to the fuel pump 42 from the first amount to zero. Generally, through the controls described herein, the controller 52 is configured to ensure that the first liquid fuel 38a and the second liquid fuel 38b each remain in a liquid phase during the first transition period 92.

[0028] In certain embodiments, the fuel transfer process described above may be performed gradually with a predetermined ramp-up from gas turbine shaft speed 88 to speed 90 without having to hold the gas turbine shaft speed at 90, i.e., opening the second fuel supply valve 38b to a second threshold and closing the first fuel supply valve 38a from the first threshold to zero. In certain embodiments, this process may be performed in part by adjusting the speed of the pump 42 based on the fuel properties of the first and second fuels, ambient properties, and the gas turbine shaft ramp-up rate.

[0029] After the first transition period 92 at T5, the controller 52 may control the gas turbine system 10 during a ramp-up period 96 to increase the speed of the compressor shaft 26c from the fuel delivery speed 90 to an operating load speed 98 at T6. In a particular embodiment, the operating load speed 98 is between 9,500 and 15,000 RPM. At the operating load speed 98, the gas turbine system 10, powered by the second liquid fuel 38b, is configured to drive a load during a steady state period 100. The gas turbine system 10 may be configured to operate in the steady state period 100 for hours, days, weeks, or longer. At T7, the controller 52 may control the gas turbine system 10 during a ramp-down period 102 to decrease the speed of the compressor shaft 26c from the operating load speed 98 to the fuel delivery speed 90 at T8. At T8, the controller 52 controls the fuel supply valve 66 to decrease the amount of the second liquid fuel 38b provided to the fuel pump 42 and increase the amount of another liquid fuel of the fuel supply system 30 provided to the fuel pump 42 during a second transition period 104. Although the charts 75, 76 of FIG. 2 illustrate one embodiment of a transition between the first liquid fuel 38a and the second liquid fuel 38b, the controller 52 may control the transition of more than two liquid fuels. During the second transition period 104, the controller 52 may control the supply valve 66 to increase the amount of the first liquid fuel 38a provided to the fuel pump 42 from zero to a first amount and then decrease the amount of the second liquid fuel 38b provided to the fuel pump 42 from a second amount to zero. At T9, the controller 52 controls the gas turbine system 10 during a shutdown period 106, and 10 The speed of the compressor shaft 26c may be reduced from the fuel delivery speed 90 to the minimum load speed 88 at T 11 In T 10 The speed of the pump shaft 46 at the start-up fuel speed 86 can be reduced to the initial pump speed 82, thereby preparing the fuel delivery system 30 for shutdown. 11 In the above, the controller 52 12The speed of the compressor shaft 26c and the pump speed 76 can be reduced so that the speeds are reduced to zero RPM at T 12 While the speed of the compressor shaft 26c and the speed of the pump shaft 46 are shown at zero RPM at , it is understood that in certain embodiments of the gas turbine system 10, the speed of the compressor shaft 26c and the speed of the pump shaft 46 may decrease at different rates and decrease to zero RPM at different times during the shutdown period 106. Generally, through the controls described herein, the controller 52 is configured to ensure that the first liquid fuel 38a and the second liquid fuel 38b each remain in a liquid phase during the second transition period 104.

[0030] The availability and cost of the liquid fuel sources 38 may vary depending on the location of the gas turbine system 10. For example, diesel fuel, kerosene, or gasoline may be utilized for standardized start-up and shutdown procedures of the gas turbine system 10. However, some liquid fuels, such as diesel oil, may have lower availability, higher cost, or both, compared to other liquid fuels, such as distillate fuels, jet fuel, naphtha, liquid butane, liquid propane, liquefied petroleum gas (LPG), and other hydrocarbons or hydrocarbon mixtures, or biofuels. Furthermore, because the heating values ​​of the liquid fuels differ, it may be desirable to operate a first liquid fuel having a higher heating value at a higher load than a second liquid fuel having a lower heating value. Thus, the controller 52 may control the fuel supply valve 66, the VFD / SR 48, and the fuel control valve 50 to transition from a first flow of one or more liquid fuels of the fuel supply system 30 to a second flow of one or more liquid fuels of the fuel supply system 30 based on the availability of the one or more liquid fuels, the cost of the one or more liquid fuels, and / or the desired load to be driven through the combustion of the one or more liquid fuels. Starting and shutting down can be accomplished with any gaseous fuel through the gas fuel system train if available and convenient to the operator.

[0031] FIG. 3 illustrates a flow chart of an embodiment of a method 120 for operating a gas turbine system from start-up on a first liquid fuel to driving a full load on a second liquid fuel or liquid fuel mixture. A controller of the fuel supply system controls a VFD / SR linked to a fuel pump to direct the first liquid fuel toward one or more fuel manifolds or nozzles of the fuel supply system (block 122). The controller also opens a fuel supply control valve to allow flow of the first liquid fuel to an inlet of the fuel pump (block 124). The controller may execute blocks 122 and 124 approximately simultaneously (e.g., within 1-10 seconds). The gas turbine system starts a compressor and a turbine of the gas turbine system (block 126), thereby commencing rotation of a shaft of the gas turbine system. In certain embodiments, the controller that starts the gas turbine system (block 126) also controls the fuel supply system. Once the first liquid fuel is delivered to the combustor from the fuel pump by the main fuel control valve and the oxidizer from the compressor is delivered to the combustor, the controller may control the combustion of the oxidizer-fuel mixture in the combustor (block 128). As discussed above during the start-up period 78, the controller controls the fuel and oxidizer delivered to the combustor to warm the gas turbine engine components (block 130), thereby increasing the stability of the gas turbine system.

[0032] The controller determines a fuel transition value based at least in part on fuel parameters of a fuel source of the fuel supply system (block 132). In certain embodiments, the controller determines a fuel transition value based at least in part on fuel parameters and environmental parameters (e.g., temperature, pressure, humidity) of the ambient environment of the gas turbine system (block 132). The fuel transition value may include, but is not limited to, a start-up fuel speed for the fuel pump to initiate a transition from the first liquid fuel to the second liquid fuel, a transmission load on the gas turbine system during the transition from the first liquid fuel to the second liquid fuel, a transition threshold of one or more fuel supply valves of the fuel supply system, a mixture of liquid fuels of the second liquid fuel provided to the combustor after the transition, or any combination thereof. The controller then controls a VFD / SR linked to the fuel pump to the start-up fuel speed based at least in part on fuel parameters of the first liquid fuel and the second liquid fuel (block 134). As described above, the start-up fuel speed may be determined based on the vapor pressure of the second liquid fuel added to the first liquid fuel during the transition period. The controller may control the VFD / SR linked to the fuel pump to a start-up fuel speed that facilitates the transfer of the first liquid fuel to the second liquid fuel without providing a multiphase fuel flow to the fuel pump or one or more fuel manifolds / nozzles (block 134).For any of these scenarios, the main fuel control valve regulates the start-up fuel flow, the flow of the liquid fuel mixture during the transition, and the second liquid fuel flow to the manifolds / nozzles as a supplement to the variable speed fuel pump for purposes of liquid fuel flow control.

[0033] The controller controls the load on the gas turbine system to a transfer load at which the controller can stably transition the fuel supplied to the combustor by the main fuel control valve and the individual fuel supply valves from the first liquid fuel to the second liquid fuel (block 136). The starting fuel may be diesel, kerosene, or gasoline, respectively, or a gaseous fuel. The second fuel may be a liquid fuel such as butane, kerosene, or jet fuel, among others. As described above, the controller may determine a fuel transfer value, such as a transfer load, based at least in part on a fuel parameter of the second liquid fuel (block 132). For example, if a first idle load supported by the combustion of the first liquid fuel is less than a second idle load supported by the combustion of the second liquid fuel, the transfer load may be a second idle load such that the gas turbine can stably provide the transfer load during the transition from the first liquid fuel to the second liquid fuel. After the gas turbine system supports the transfer load, the controller transitions from the first liquid fuel to the second liquid fuel (block 138). To transfer the fuel, the controller opens a second fuel supply valve for the second liquid fuel (block 140) while maintaining stable operation of the gas turbine system. Once the second fuel supply valve is opened to the second liquid fuel transfer threshold, the controller closes the first fuel supply valve for the first liquid fuel (block 142) while maintaining stable operation of the gas turbine system. To maintain stable operation of the gas turbine system, the controller may gradually open (block 140) and gradually close (block 142) the fuel supply valves over the respective transfer periods.

[0034] The transition to open and close the fuel supply valve may be 5, 10, 15, 20, 30, 45, or 60 seconds or more, such that the controller executes blocks 140 and 142 for a period of 10, 20, 30, 40, 60, 90, or 120 seconds or more. In certain embodiments, the controller may pause for 5, 10, 15, 30, or 60 seconds or more between opening (block 140) and closing (block 142) the fuel supply valve during the transition (block 138). The second liquid fuel transition threshold for opening (block 140) the second fuel supply valve may be approximately 50, 60, 70, 80, 90, or 100% open. During the liquid fuel transition (block 138), the controller may adjust the speed of the fuel pump through the VFD / SR while controlling the fuel supply valve and the main fuel control valve over the transition period (block 144). For example, the controller may increase the speed of the fuel pump during a transition to a second liquid fuel having a higher vapor pressure than the first liquid fuel while adjusting the position of the main fuel control valve to maintain the gas turbine load. The controller may increase the speed of the fuel pump, maintain the discharge pressure of the fuel delivered to the combustor from the pump outlet within a range of transition pressures (e.g., 0.5-10%) during the transition period, and adjust the position of the main fuel control valve to maintain the gas turbine load. Maintaining the discharge pressure of the liquid fuel delivered to the combustor within the transition pressure range may facilitate stable combustion in the combustor during the transition period. In some examples, the gas turbine system may be started and shut down using a gaseous fuel and transition to a liquid fuel source may be performed, and the gas turbine system may be enabled to perform a transition to the second liquid fuel or other liquid fuel mixture at steady state or at a load higher than the transition load for the start-up and shutdown process.

[0035] After the controller closes the first fuel supply valve (block 142) and the gas turbine system operates completely through the combustion of the second liquid fuel, the controller may control the gas turbine system based on a desired load while operating the gas turbine system on the second liquid fuel (block 146). As can be appreciated, the controller may adjust the amount and / or pressure of the second liquid fuel delivered to the combustor during steady state operation of the gas turbine system in response to changes in the load of the gas turbine system due to the main fuel control valve. The controller may repeat blocks 132-144 described above to transition from the second liquid fuel to the first liquid fuel, a third liquid fuel, or a mixture of one or more liquid fuels in the fuel supply system.

[0036] FIG. 4 illustrates a chart 160 of one embodiment of the control of the fuel supply valve for the liquid fuel transition described above. Prior to the fuel transition 162, a first position 164 of a first fuel supply valve configured to supply a first liquid fuel to a fuel pump is opened to a first liquid fuel threshold 166. The first liquid fuel threshold 166 may be determined by a controller of the fuel supply system based on a determined transmission load for the gas turbine system. As described above, the transmission load may be determined based on fuel parameters of the first liquid fuel and the second liquid fuel and ambient conditions for the gas turbine system. For example, the controller of the fuel supply system may determine from an analysis of the fuel parameters of the first liquid fuel and the second liquid fuel that a stable transition from the first liquid fuel to the second liquid fuel may occur at a transmission load supported by combustion of a first amount of the first liquid fuel supplied when the first fuel supply valve is opened to the first liquid fuel threshold. The controller may also determine from the analysis of the fuel parameters of the first liquid fuel and the second liquid fuel that the transmission load may be supported by combustion of a second amount of the second liquid fuel when the second position 168 of the second fuel supply valve is opened to a second liquid fuel threshold 170. The controller may analyze the fuel parameters of the first liquid fuel and the second liquid fuel based on feedback from sensors monitoring the respective liquid fuels, feedback from inputs to the controller related to the fuel parameters of the respective liquid fuels, or any combination thereof. In certain embodiments, the first liquid fuel threshold 166 is approximately 25, 30, 40, 50, 60, 70, 75, 80, 90, or 100% open. In certain embodiments, the second liquid fuel threshold 170 is approximately 25, 30, 40, 50, 60, 70, 75, 80, 90, or 100% open. For example, the first liquid fuel threshold 166 may be approximately 40% open and the second liquid fuel threshold may be approximately 75% open.

[0037] To initiate the fuel transfer 162, the controller Aand adjusts the second position 168 of the second fuel supply valve at the second liquid fuel threshold 170 to open the second fuel supply valve. The second rate 172 of opening the second fuel supply valve can be controlled based at least in part on the valve type of the second fuel supply valve (e.g., butterfly, ball, gate, globe), the stability of the gas turbine system, and the parameters of the second liquid fuel (e.g., viscosity, vapor pressure, specific gravity, lubricity), or any combination thereof. The second transition period 174 for opening the second position 168 of the second fuel supply valve to the second liquid fuel threshold 170 may be about 5, 10, 15, 20, 30, 45, or 60 seconds. The controller opens the second fuel supply valve to the second liquid fuel threshold 170 while the first supply valve remains open to the first liquid fuel threshold 166. T B In the fuel transfer 162, the second fuel supply valve is opened until the second liquid fuel threshold 170 and the first fuel supply valve remains open until the first liquid fuel threshold 166. Thus, the first liquid fuel and the second liquid fuel are supplied to the fuel pump during the fuel transfer 162. As described above, the speed of the fuel pump may be controlled by the VFD / SR during the fuel transfer 162 based on fuel parameters of the first liquid fuel and the second liquid fuel, as well as based on the discharge pressure from the pressure transmitter, to avoid two-phase flow in the fuel pump and / or downstream of the fuel pump. The gas turbine system combusts a mixture of the first liquid fuel and the second liquid fuel during the fuel transfer 162.

[0038] In certain embodiments, the controller may be configured to adjust T to close the first fuel supply valve as soon as the second fuel supply valve is opened to the second liquid fuel threshold 170. B In a particular embodiment, the controller adjusts the first position 164 of the first fuel supply valve at T for a stabilization interval (e.g., 1 to 60 seconds) to ensure combustion stability of the gas turbine system before adjusting the first position 164 of the first fuel supply valve. BThe first rate 176 of closing the first fuel supply valve can be controlled based at least in part on a valve type (e.g., butterfly, ball, gate, globe) of the first fuel supply valve, the stability of the gas turbine system, and a parameter (e.g., viscosity, vapor pressure, specific gravity, lubricity) of the first liquid fuel, or any combination thereof. A first transition period 178 for closing the first position 164 of the first fuel supply valve from the first liquid fuel threshold 166 to the fully closed position 180 can be approximately 5, 10, 15, 20, 30, 45, or 60 seconds. The controller closes the first fuel supply valve while the second supply valve remains open until the second liquid fuel threshold 170. T C In T, the second fuel supply valve remains open until the second liquid fuel threshold 170 and the first fuel supply valve is commanded to a fully closed position 180. Thus, after the fuel transfer 162, only the second liquid fuel is supplied to the fuel pump. C The controller can then adjust the position of the main fuel control valve and the speed of the fuel pump through the VFD / SR to supply the desired quantity and pressure of the second liquid fuel to the combustor of the gas turbine system to drive the desired load.

[0039] Technical effects of the present disclosure include transitioning from a first liquid fuel supplied to a combustor of a gas turbine system to a second liquid fuel supplied to the combustor utilizing a single fuel pump configured to supply both fuels from a single fuel pump during transition without shutting down the gas turbine system. By utilizing a single fuel pump and coordinating operation of the pump during transition, additional cost, size, and operational complexity associated with multiple liquid fuel trains to facilitate operation of the gas turbine system with multiple liquid fuels may be avoided. Utilizing multiple liquid fuels during operation of a gas turbine system increases the operational flexibility of the gas turbine system by enabling utilization of various and / or localized liquid fuel sources during steady state operation, and further utilizing standardized fuel sources (e.g., diesel oil, kerosene, gasoline, and in some cases gaseous fuels) for start-up or shutdown procedures.

[0040] This specification uses examples to disclose embodiments of the disclosure, including the best mode, and to enable any person skilled in the art to practice the disclosure, including making and using any device or system 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 have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not have substantial differences from the literal language of the claims. [Explanation of symbols]

[0041] 10 Gas Turbine System 12 Compressor 14 Combustor 16 Turbine 18 Fuel manifold / nozzle 20. Air 24 Combustion Gas 26c compressor shaft 26t gas turbine shaft 28 Exhaust Gas 30 Fuel Supply System 32 Load 34 Air Intake 36 Pressurized Air Flow 38 Liquid Fuel Source 40 Fuel or air-fuel mixture 42 Fuel pump 44 Motor 46 Pump shaft 48 Variable Frequency Driver (VFD) or Switched Reluctance (SR) Motor Speed ​​Variation Device 50 Main fuel control valve 52 Controller 54 Pressure Transmitter 56 processors 58 Memory 60 Motor Control Lines 62 Pump inlet 64 Pump outlet 66 Fuel supply valve 68 Supply valve control line 70 Transfer Pump 72 Gas Fuel Sources 74 Sensors 75 Gas Turbine Compressor Shaft Speed 76 Fuel Pump Shaft Speed 78 Start-up Period 80 Starter Speed 82 Initial pump speed 84 Idle speed (gas turbine shaft) 86 Starting fuel speed (pump) 88 Minimum Load Speed ​​(Gas Turbine Shaft) 90 Transmission load speed (gas turbine shaft) 92 First Transition Period 94 Primary fuel speed (pump) 96 Ramp-up Period 98 Operating Load Speed ​​(Gas Turbine Shaft) 100 Steady State Period 102 Ramp-down period 104 Second Transition Period 106 Suspension Period 120 methods 122 Controls the fuel pump to direct the first fuel to the fuel manifold / nozzle 124 Open fuel supply control valve 126 Starting up a gas turbine system 128 Combusting Liquid Fuel Mixtures 130 Warming up the gas turbine system 132 Determine the fuel transfer value 134 Control fuel pump to starting fuel speed 136 Controlling and transferring loads on gas turbine systems 138 Fuel transition during transition period 140 Open the fuel supply valve to increase the second liquid fuel 142 Close the fuel supply valve to reduce the first liquid fuel 144 Adjusting the fuel pump speed 146 Load-Based Control of Gas Turbine Systems 160 Charts 162 Fuel Transition Period 164 First fuel supply valve position 166 First Liquid Fuel Threshold 168 Second fuel supply valve position 170 Second Liquid Fuel Threshold 172 Second Velocity (Second Liquid Fuel) 174 Second transition period (Second fuel supply valve open) 176 First Velocity (First Liquid Fuel) 178 First transition period (first fuel supply valve closed) 180 Fully closed position (first fuel supply valve)

Claims

1. 1. A system comprising: A fuel supply system (30), comprising: a fuel pump (42) having an inlet (62) and an outlet (64); a first fuel supply valve (66a) configured to control a first flow of a first liquid fuel (38a) to the inlet (62) based at least in part on a first supply valve control signal; a second fuel supply valve (66b) configured to control a second flow of a second liquid fuel (38b) to the inlet (62) based at least in part on a second supply valve control signal; and a motor (44) coupled to the fuel pump (42), the motor (44) comprising a variable frequency drive (48) configured to drive the motor (44), the motor (44) configured to drive the fuel pump (42) based at least in part on a pump speed control signal; a main fuel control valve (50) configured to regulate fuel flow to a fuel manifold / nozzle (18) of a gas turbine system (10) based at least in part on a main fuel valve control signal, the main fuel valve control signal being based at least in part on a load demand of the gas turbine system (10) and at least in part on a cost and availability of the first liquid fuel (38a) and the second liquid fuel (38b); a controller (52) coupled to the motor (44), the first fuel supply valve (66a), the second fuel supply valve (66b), and the main fuel control valve (50), the controller (52) configured to generate the first supply valve control signal, the second supply valve control signal, the pump speed control signal, and the main fuel valve control signal based at least in part on a first fuel parameter of the first liquid fuel (38a) and a second fuel parameter of the second liquid fuel (38b), and the controller (52) is configured to generate the first supply valve control signal, the second supply valve control signal, the pump speed control signal, and the main fuel valve control signal based at least in part on a first fuel parameter of the first liquid fuel (38a) and a second fuel parameter of the second liquid fuel (38b) at a first time while maintaining the load demand of the gas turbine system (10) during operation of the gas turbine system (10). a controller configured to control a transition from the first flow into the inlet at a second time to a second flow into the inlet at a second time, the controller controlling a speed of the motor by determining a first speed of the motor based at least in part on the first fuel parameter of the first liquid fuel, determining a second speed of the motor based at least in part on the second fuel parameter of the second liquid fuel, and controlling the speed of the motor from the first speed to the second speed during the transition; A fuel supply system (30) comprising: A system comprising:

2. The system of claim 1, wherein the controller (52) is configured to ensure that the first liquid fuel (38a) and the second liquid fuel (38b) each remain in a liquid phase during the transition.

3. The system of claim 1 , wherein the pump speed control signal is configured to control a speed of the motor (44), and the fuel pump (42) comprises a centrifugal pump.

4. 2. The system of claim 1, further comprising a pump discharge pressure sensor coupled to the outlet of the fuel pump, the pump discharge pressure sensor configured to provide discharge pressure feedback to the controller, the controller configured to generate the first supply valve control signal, the second supply valve control signal, and the pump speed control signal during the transition based at least in part on the discharge pressure feedback from the pump discharge pressure sensor.

5. The system of claim 4, wherein the controller (52) is configured to generate the pump speed control signal during the transition to control the discharge pressure at the outlet (64) within a transition pressure range.

6. 2. The system of claim 1, further comprising: one or more fuel sensors configured to provide feedback of the first fuel parameter, the second fuel parameter, or any combination thereof to the controller, the controller configured to generate the first supply valve control signal, the second supply valve control signal, and the pump speed control signal during the transition based at least in part on the feedback from the one or more fuel sensors.

7. The gas turbine system (10) includes: a combustor (14) configured to receive a flow from the outlet (64) of the fuel pump (42), combust a mixture of the flow and an oxidizer to generate exhaust gases (24), and expand the exhaust gases (24) through a turbine (16); the turbine (16) configured to expand the exhaust gases (24) to drive a shaft (26); the shaft (26) coupled to the turbine (16) and a load (32), the controller (52) configured to generate the first supply valve control signal, the second supply valve control signal, the pump speed control signal, and the main fuel valve control signal during the transition based at least in part on a speed of the shaft (26), the load (32) on the shaft (26), or any combination thereof; The system of claim 1 , comprising:

8. 1. A method for transitioning a liquid fuel stream (38) supplied to a gas turbine system (10) during operation of the gas turbine system (10), the method comprising: supplying a first liquid fuel (38a) to an inlet (62) of a fuel pump (42) through a first fuel supply valve (66a) opened to a first liquid fuel threshold (166), the first liquid fuel threshold (166) being based at least in part on a first fuel parameter of the first liquid fuel (38a); directing the first liquid fuel (38a) from an outlet (64) of the fuel pump (42) to a combustor (14) of the gas turbine system (10); combusting the first liquid fuel (38a) with an oxidizer in the combustor (14) to generate exhaust gases (24); expanding the exhaust gases (24) through a turbine (16) of the gas turbine system (10) to drive a shaft (26) coupled to the turbine (16) and a load (32); transitioning over a transition period from combustion of the first liquid fuel in the combustor to combustion of a second liquid fuel in the combustor, the transitioning being performed by a processor; and opening a second fuel supply valve (66b) to a second liquid fuel threshold (170) to supply the first liquid fuel (38a) to the inlet (62) of the fuel pump (42) while supplying the second liquid fuel (38b) to the inlet (62), the second liquid fuel threshold (170) being based at least in part on a second fuel parameter of the second liquid fuel (38b); in response to opening the second fuel supply valve (66b) to the second liquid fuel threshold (170), closing the first fuel supply valve (66a) from the first liquid fuel threshold (166) to stop supplying the first liquid fuel (38a) to the inlet (62); controlling a main fuel control valve (50) to regulate fuel flow in the gas turbine system (10) based at least in part on load demand of the gas turbine system (10) and based at least in part on cost and availability of the first liquid fuel (38a) and the second liquid fuel (38b); and controlling a speed of a motor (44) configured to drive the fuel pump (42) to maintain a discharge pressure of a liquid fuel stream at the outlet (64) within a transition pressure range, the liquid fuel stream including the first liquid fuel (38a), the second liquid fuel (38b), or any combination thereof. The steps include: and controlling the speed of the motor (44) comprises: determining a first speed of the motor (44) based at least in part on the first fuel parameter of the first liquid fuel (38a); determining a second speed of the motor (44) based at least in part on the second fuel parameter of the second liquid fuel (38b); and controlling the speed of the motor (44) from the first speed to the second speed prior to transitioning from burning the first liquid fuel (38a) in the combustor (14) to burning the second liquid fuel (38b) in the combustor (14). The method includes:

9. monitoring the second liquid fuel (38b) with a sensor (74) and determining the second fuel parameter of the second liquid fuel (38b); determining the second liquid fuel threshold (170); The method of claim 8 , comprising:

10. The method of claim 8 , wherein the transition period is 120 seconds or less.

11. determining a transition load based at least in part on a first fuel parameter of the first liquid fuel (38a) and a second fuel parameter of the second liquid fuel (38b); controlling the load during the transition period based at least in part on the transition load; The method of claim 8 , comprising:

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