FIELD OF THE INVENTION
The subject matter disclosed herein relates to gas turbines. More specifically, the disclosure pertains to a system and method for establishing a liquid fuel purge credit for a gas turbine.
BACKGROUND OF THE INVENTION
A gas turbine generates mechanical energy by compressing ambient air in its compressor, mixing the compressed air with a combustible fuel, then igniting the mixture in the combustor, and finally expand the hot combustion gas in the turbine to generate mechanical power. Certain gas turbine engines include multi-fuel systems that use, for example, both gas and liquid fuels, where the multi-fuel system allows the transfer from one fuel to the other. During the transfer from one fuel (e.g., a first fuel) to another fuel (e.g., a second fuel), use of the first fuel is terminated. The gas turbine engines may also be shut down between operating with the different fuels. Once the gas turbine engine is shut down, it undergoes a series of purging steps prior to restarting the gas turbine engine. The series of purging steps may be time consuming.
BRIEF DESCRIPTION OF THE INVENTION
Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below.
In a first embodiment, a system includes a liquid fuel system for a multi-fuel gas turbine including a liquid fuel circuit. The liquid fuel system further includes a fuel flow divider configured to distribute liquid fuel flow to associated fuel nozzles of the multi-fuel gas turbine, a liquid fuel control valve

disposed along the liquid fuel circuit upstream of the fuel flow divider, a first valve disposed along the liquid fuel circuit downstream of the liquid fuel control valve and upstream of the fuel flow divider, a check valve disposed along the liquid fuel circuit downstream of the fuel flow divider, and a third valve disposed along the liquid fuel circuit downstream of the check valve and upstream of a respective fuel nozzle of the associated fuel nozzles. During shutdown of the multi-fuel gas turbine, a first block cavity free of liquid fuel is formed along the liquid fuel circuit between the liquid fuel control valve and the stop valve when the liquid fuel control valve and the stop valve are closed, a second block cavity free of liquid fuel is formed along the liquid fuel circuit between the check valve and the third valve when the third valve is closed, and the second block cavity is pressurized with a liquid.
In a second embodiment, a system includes a liquid fuel purge credit system for a multi-fuel gas turbine that further includes a first block cavity, a second block cavity, and a water pressurization system. The first block cavity is free of liquid fuel and is formed along a first portion of a liquid fuel circuit coupled to the multi-fuel gas turbine, where the first block cavity is located upstream of a fuel flow divider between a liquid control valve and a first valve when the liquid control valve and the first valve are closed. The second block cavity is free of liquid fuel and is formed along a second portion of a liquid fuel circuit downstream of the fuel flow divider and between a check valve and a third valve upstream of a respective fuel nozzle of the multi-fuel gas turbine when the third valve is closed. The water pressurization system is coupled to the second portion of the liquid fuel circuit between the check valve and the third valve, where the water pressurization system is configured to pressurize the second block cavity. The maintenance of the first and second block cavities provides a liquid fuel purge credit to be utilized during startup of operation of the multi-fuel gas turbine with liquid fuel.
In a third embodiment, a method includes establishing a liquid fuel purge credit after shutdown of liquid fuel operation of a multi-fuel gas turbine that includes

forming a first block cavity free of liquid fuel and forming a second block cavity free of liquid fuel. The first block cavity is formed along a first portion of a liquid fuel circuit coupled to the multi-fuel gas turbine, where the first block cavity is located upstream of a fuel flow divider between a liquid control valve and a first valve by closing the liquid control valve and the first valve once the first block cavity is free of liquid fuel. The second block cavity is formed along a second portion of the liquid fuel circuit downstream of the fuel flow divider and between a check valve and a third valve upstream of a respective fuel nozzle of the multi-fuel gas turbine by closing the third valve once the first block cavity is free of liquid fuel and pressurizing, via a water pressurization system, the second block cavity to a set pressure range.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
FIG. 1 is a schematic of an embodiment of a fuel circuit system for a gas turbine, in accordance with an aspect of the present disclosure;
FIG. 2 is a schematic of an embodiment of a fuel circuit system in a gas turbine which uses a water pressurization system to establish a purge credit, in accordance with an aspect of the present disclosure;
FIG. 3 is flowchart of an embodiment of a process for the fuel circuit system of FIG. 2 to establish a purge credit during shutdown of liquid fuel operation, in accordance with an aspect of the present disclosure;
FIG. 4 is a flowchart of an embodiment of a logic process for the fuel circuit system of FIG. 2 to maintain conditions of a purge credit, in accordance with an aspect of the present disclosure;

FIG. 5 is a flowchart of an embodiment of a process for the fuel circuit system of FIG. 2 to start liquid fuel operations, in accordance with an aspect of the present disclosure;
FIG. 6 is a schematic of an embodiment of a fuel circuit system in a gas turbine which uses a water pressurization system and/or a compressed gas system to establish a purge credit, in accordance with an aspect of the present disclosure; and
FIG. 7 is a schematic of an embodiment of a fuel circuit system in a gas turbine which uses a water pressurization system and a system configured to monitor liquid levels, in accordance with an aspect of the present disclosure; and
FIG. 8 is a schematic of an embodiment of a fuel circuit system in a gas turbine which uses a water pressurization system, in accordance with an aspect of the present disclosure.
DETAILED DESCRIPTION
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

The present disclosure is directed to systems and methods for purging a gas turbine system to meet the criteria for a purge credit (e.g., liquid fuel purge credit). In some embodiments, the gas turbine system is a multi-fuel system and may use either liquid fuel or gas fuel. In such systems, the fuel circuit may be flushed with a water pressurization system to minimize coking and/or backflow of combustion products into the fuel circuit and fuel nozzles, such as during transfer between liquid fuel operation and gas fuel operation. As such, this minimizes deterioration of engine components (e.g., the fuel circuit) to maintain performance of the gas turbine system. Embodiments of this disclosure may modify the water pressurization system to establish a liquid fuel purge credit as set forth by regulatory standards (e.g., by the National Fire Protection Agency [NFPA]) to ensure safe operations of the gas turbine. In particular, during shutdown of the gas turbine, the water pressurization system may purge the fuel circuit to establish the purge credit. The disclosed system may satisfy the liquid fuel purge credit with minimum adjustments to the system (e.g., installation of additional pieces of equipment or modification of current equipment). As such, the system may save on costs and more easily establish a purge credit.
Turning to the drawings, FIG. 1 is a schematic block diagram of a gas turbine system 10 that uses a purge system 12 to purge a fuel circuit 14. The gas turbine system 10 may be multi-fuel and thereby, may contain a liquid fuel supply 16 and a gas fuel supply 18 in fluid communication with the fuel circuit 14. In some embodiments, the liquid fuel may include distillate oils, light crude, bio-liquid fuels, and other liquid fuels. Additionally, the gas fuel may include syngas, synthetic gas, synthetic natural gas, refinery off-gas, refinery flue gas, blast furnace gas, coke oven gas, or other combustible gases. The fuel circuit 14 may also be in fluid communication with the purge system 12. Although the following disclosure discusses the fuel circuit 14 as a single fuel circuit connected to the liquid fuel supply 16, the gas fuel 18, and the purge system 12, in certain embodiments, the liquid fuel supply 16 and the gas fuel supply 18

may each be in fluid communication with a respective fuel circuit and a respective purge system. Moreover, in some embodiments, the fuel circuit 14 may include a flow divider that divides the fuel circuit 14 into several fuel lines.
To control the operation of the liquid fuel supply 16 and the gas fuel supply 18, the gas turbine system 10 may use a controller 20. For example, the controller 20 may control the amount of fuel entering the fuel circuit 14 from either the liquid fuel supply 16 or the gas fuel supply 18. Furthermore, the controller 20 may be configured to transition operations between operating the gas turbine power plan system 10 using liquid fuel to gas fuel. The controller 20 may also control the purge system 12 to establish a purge credit by running a purge sequence. For example, the controller 20 may be configured to run the purge sequence via the purge system 12 prior to shutdown of a fuel supply and/or before the transition between using liquid fuel and gas fuel. In some embodiments, the purge system 12 may supply a fluid (e.g., water) into the fuel circuit 14 to purge the fuel circuit 14 of fuel and the controller 20 may control the amount of fluid supplied by the purge system 12. Additionally, the controller 20 may use the purge system 12 to flush the fuel circuit 14 with the fluid to minimize coking and/or backflow of combustion products into the fuel circuit and fuel nozzles. The controller 20 may also control components within the fuel circuit 14 (e.g., valves) to further control the flow of fluid and/or fuel during operations.
Moreover, the controller 20 may include a memory 36 storing instructions to perform the aforementioned processes and a processor 38 to execute the instructions. The processor 38 may include a microprocessor or microcontroller, such as a reduced instruction set computer (RISC) or other suitable processors. The memory 36 may include non-transitory, computer-readable medium configured to store the instructions. The memory 36 may include volatile memory such as randomly accessible memory (RAM) and/or non-volatile memory such as hard disc memory, flash memory, and/or other suitable memory formats.

As illustrated in FIG. 1, the fuel circuit 14 leads to one or more fuel nozzles 22 that may be located within a combustor 24. Within the fuel nozzle 22, fuel from the fuel circuit 14 may mix with air flowing from an air supply 26. The air flow may first enter a compressor 28 before being directed to the fuel nozzle 22. As such, the air may be pressurized by the compressor 28 to mix with the fuel in the fuel nozzle 22 or the combustor 24. The fuel nozzle 22 may direct the mixture into the combustor 24 in a suitable ratio for optimal combustion, emissions, fuel consumption, and power output. In the combustor 24, the air and fuel mixture ignites and combusts to produce exhaust gas that passes through a turbine 30. The turbine 30 may contain blades such that the exhaust gases pass through the turbine 30 and force the blades and thereby the turbine 30 to rotate. The turbine 30 may be coupled with a shaft 32 that couples the turbine with a generator 34. The rotation of the turbine 30 may drive the rotation of the shaft 32. The generator 34 may be powered by the rotation of the shaft 32 to generate energy (e.g., electrical energy). Furthermore, the shaft 32 may couple the turbine 30 with the compressor 28 such that rotation of the shaft 32 drives the rotation of the compressor 28. The compressor 28 may also contain blades to facilitate the intake of air from the air supply 26 during rotation of the compressor 28.
The present disclosure may use the gas turbine system 10 to purge the fuel lines of the fuel system (e.g., using the purge system 12). Furthermore, the disclosure may also use the purge system 12 to establish a liquid fuel purge credit. By using the existing purge system 12 to also establish the liquid fuel purge credit, there may be minimum modifications to the gas turbine system 10 to enable the system to establish the liquid fuel purge credit.
FIG. 2 is an embodiment of a liquid fuel circuit system 50 in a gas turbine that may use water to establish purge credit. As illustrated in FIG. 2, liquid fuel enters the liquid fuel circuit system 50 via a fuel circuit 54. The fuel circuit 54 may contain a liquid fuel control valve 56 (e.g., three-way valve) and further downstream, a first valve 58 (e.g., stop valve such as a two-way valve). In

between the liquid fuel control valve 56 and the first valve 58 may be a first block cavity 60. The first block cavity 60 may also be connected to a first block cavity drain valve 62 via a drain line 63. The first block cavity drain valve 62 may be opened to drain the fuel circuit 54 of liquid fuel to atmosphere (i.e., when the liquid fuel control valve 56 and/or the first valve 58 are closed to avoid pressure buildup in the first block cavity 60) to form the block cavity during the establishment of the liquid fuel purge credit. When establishing the liquid fuel purge credit, the first block cavity 60 is maintained at or near atmospheric pressure (e.g., < 0.5 bar). Together, the liquid fuel control valve 56, the first valve 58, the first block cavity drain valve 62, and the first block cavity 60 form the first portion of the required triple block and double bleed system utilized to establish a liquid fuel purge credit.
As depicted, the first block cavity 60 may be connected to a set of triple redundant pressure transmitters 64. The triple redundant pressure transmitters 64 may be configured to monitor the pressure within the first block cavity 60 when the liquid fuel purge credit is established to maintain the liquid fuel circuit 50 in conditions to sustain the purge credit. The triple redundant pressure transmitters 64 may include three pressure transmitters that independently measure the pressure of the first block cavity drain 60 and compare the values to one another to produce a single measured output value. In this manner, the triple redundant pressure transmitters 64 reduces the chance of producing a faulty reading. In some embodiments, the pressure transmitters in the triple redundant pressure transmitters 64 may be the same type of pressure transmitter.
In some embodiments, the liquid fuel control valve 56 may be a three-way stop valve and may control the amount of liquid fuel flowing into the first block cavity 60. For example, the liquid fuel control valve 56 may include a gate disposed in the outlet to the recirculation circuit 66 and another gate disposed in the outlet towards the first block cavity 60. The liquid fuel control valve 56 may open and/or close the gates to direct the liquid fuel towards the first block cavity 60 or a recirculation circuit 66. The recirculation circuit 66 may direct

the liquid fuel away from the first block cavity 60 and/or a flow divider 68. For example, when the gas turbine is in gas fuel operation and the liquid fuel is not in use, the liquid fuel control valve 56 may keep liquid fuel from flowing into the first block cavity 60 by closing the gate disposed in the outlet to the first block cavity 60 and instead permit flow to the recirculation circuit 66. The recirculation circuit 66 may bring the liquid fuel back to a liquid fuel supply line (not shown), where the liquid fuel may be processed and directed back to the fuel circuit 54. In some embodiments, when the liquid fuel circuit is in operation, the gate disposed in the outlet to the recirculation circuit 66 may close completely, thereby only permitting flow to the first block cavity 60. In addition, the first valve 58 may also open to permit liquid fuel to flow through the first block cavity 60 and to the flow divider 68.
Furthermore, in some embodiments, the first valve 58 may be a stop valve that may close to keep liquid fuel from entering the flow divider 68. For example, when liquid fuel within the first block cavity 60 is to be removed, the first valve 58 may close, thereby keeping more liquid fuel from flowing through the first valve 58. The first block cavity drain valve 62 may be another stop valve that may open to drain liquid fuel from the first block cavity 60.
If the first valve 58 is open, liquid fuel may be directed to the flow divider 68. The flow divider 68 may regulate the incoming liquid fuel to flow into separate fuel lines 70 of the fuel circuit 54. Downstream of the flow divider 68, each fuel line 70 may lead to a second valve 72. In some embodiments each second valve 72 is a check valve enabled to permit liquid fuel to only flow downstream, thereby keeping liquid fuel from flowing back towards the flow divider 68. Each fuel line 70 may direct liquid fuel to flow into a respective fuel nozzle 74 and then to a combustor 78. There may be a third valve 82 disposed in the fuel nozzle 74 that permits liquid fuel to enter the fuel nozzle 74. In some embodiments, the third valve 82 may be a stop valve and may be configured to close prior to shutdown of the liquid fuel operation to keep liquid fuel from entering the fuel nozzle 74. The fuel nozzle 74 may also be connected with a

purge air 76. The purge air 76 may direct air flow through the fuel nozzle 74 during gas fuel operation (i.e., when the liquid fuel supply is cut off) to stop backflow of combustion gas into the fuel nozzle 74. In some embodiments, there may be a purge air valve 80 that is a stop valve disposed within each fuel nozzle 74 that may open to permit the purge air 76 to flow into the fuel nozzle 74, such as during gas fuel operation..
In between the second valve 72 and the third valve 82 at each fuel line 70 may be a second block cavity 84. Each second block cavity 84 may be connected a water pressurization system 86 via a water pressurization system line 88. The water pressurization system line 88 may also contain a water tank 90 that provides water to flush the fuel line 70 within the second block cavity 84. In some embodiments, the water pressurization system 86 may use a liquid other than water, but for purposes of discussion, this disclosure will refer to the liquid as water. The water pressurization system 86 may use a variable frequency drive 92 to pump water from the water tank 90 towards the fuel line 70 at different flow rates. For example, when flushing out liquid fuel, the variable frequency drive 92 may pump water at a high rate, whereas during maintenance of pressure within the second block cavity 84, the variable frequency drive 92 may pump water at a lower rate to enable adjusting the pressure in the second block cavity 84 without placing too much stress on the components. Each second block cavity 84 may also include a multiport injection valve 94 that allows water to flow from each water pressurization system line 88 into the corresponding second block cavity 84. In some embodiments, when the liquid fuel system is operating (i.e., the system is not being purged), the multiport injection valve 94 is closed, thereby keeping water from flowing through the injection line 88 from flowing into the liquid fuel circuit system 50. When the liquid fuel system is to be purged, the multiport injection valve 94 may open to allow water to flow through the multiport injection valve 94 and into the second block cavity 84 of the liquid fuel circuit system 50.

To facilitate the operation, the water pressurization system 86 may use a flowmeter 96. The flowmeter 96 may detect the flowrate of water flowing through the water pressurization system line 88. The flowmeter 96 may be in communication with the variable frequency drive 92 to adjust the flow rate of water being pumped into the water pressurization system line 88. Furthermore, a water pressurization system valve 98 may be located downstream of the flowmeter 96 to permit water to flow through to the water pressurization system line 88. In some embodiments, when the water pressurization system 86 is not in use, the water pressurization system valve 98 may be closed. Further downstream, the water pressurization system line 88 may be connected with a water pressurization system drain valve 100. The water pressurization system drain valve 100 may open to drain any unwanted water in the water pressurization system line 88. In some embodiments, the water pressurization system drain valve 100 may recirculate water back to the water tank so the water may be pumped back through the water pressurization system line 88. In some embodiments, the liquid fuel circuit system 50 may contain one water pressurization system 86 that has multiple water pressurization system lines 88, where each water pressurization system line 88 connects to a respective third valve 82. In alternate embodiments, the liquid fuel circuit system 50 may contain multiple water pressurization systems 86 such that each water pressurization system 86 may be connected to one or more second block cavities 82.
The water pressurization system 86 may be utilized to flush the fuel line 70 of liquid fuel to avoid coking. In one embodiment, the water pressurization system 86 may flush the fuel line 70 downstream towards the third valve 82 leading up to the combustor 78. For example, the third valve 82, the multiport injection valve 94, and the water pressurization system valve 98 may open and the variable frequency drive 92 may pump water at a high flow rate through the water pressurization system line 88 to the third valve 82 into the fuel nozzle 74. Further, the water pressurization system 86 may flush the second block cavity

84 towards the second valve 72. For example, the third valve 82 may close to keep fluid from entering the fuel nozzle and the water pressurization system 86 may deliver water into the second block cavity 84, which may fill the second block cavity 84. A multiport drain valve 104 may open to enable water to flow out of the second block cavity 84. In either embodiment, the water may flush the inside of the corresponding sections of the fuel line 70. In this manner, liquid fuel is removed and is kept from coking the inside of the liquid fuel lines 70. In addition to flushing out the fuel line 70, the water pressurization system 86 may also be utilized to pressurize the second block cavity 84 to establish the liquid fuel purge credit. In some embodiments, the water pressurization system 86 may fill the second block cavity 84 with a liquid (e.g., water) after the flushing sequence and pressurize the second block cavity 84 via hydraulic pressure. Further details regarding establishing the liquid fuel purge credit will be discussed. Together, the third valve 82 and the multiport drain valve 104 form the second portion of the required triple block and double bleed system utilized to establish a liquid fuel purge credit.
Each second block cavity 84 may also be connected with a respective pressure transmitter 102. The pressure transmitter 102 may measure the pressure within the second block cavity 84. In some embodiments, the pressure transmitter 102 may be a pressure transmitter system similar to the triple redundant pressure transmitters 64. Furthermore, each second block cavity 84 may be connected to a multiport drain valve 104. The multiport drain valve 104 may open to drain fluid from the second block cavity 84. For example, when the pressure transmitter 102 determines the pressure within the second block cavity 84 is too high, the multiport drain valve 104 may open to remove fluid from the second block cavity 84, thereby reducing hydraulic pressure exerted by the fluid onto the second block cavity 84. In some embodiments, the pressure transmitter 102 and the triple redundant pressure transmitters 64 may be used to monitor the pressures of the first block cavity 60 and the second block cavity 84, respectively, and send the measurements to the controller 106. To maintain the

liquid fuel purge credit, the pressure of the second block cavity 84 is to be kept at least 3 bar above the pressure of the first block cavity 60. Thus, the controller 106 may compare pressure measurements of the triple redundant pressure transmitters 64 and that of the pressure transmitter 102 to determine if the pressures are at the desired levels. If the pressures are not at the desire levels, the controller 106 may adjust the system to obtain desired pressures measurements.
As mentioned above, the liquid fuel circuit system 50 may use the water pressurization system 86 along with several valves and drains during operation. The liquid fuel circuit system 50 may employ a controller 106 that is communicatively coupled to the components of the liquid fuel circuit system 50 (e.g., the drains and valves). For example, the controller 106 may control the actuators of the valves to control the opening and/or closing of the valve. The controller 106 may be similar to the aforementioned controller 20 and may contain a memory 108 that stores instructions to operate the liquid fuel circuit system 50 and a processor 110 to execute the instructions. Likewise to the memory 36, the memory 108 may include non-transitory, computer-readable medium configured to store the instructions and may include volatile memory such as randomly accessible memory (RAM) and/or non-volatile memory such as hard disc memory, flash memory, and/or other suitable memory formats. The processor 110 may include a microprocessor or microcontroller, such as a reduced instruction set computer (RISC) or other suitable processors. In some embodiments, the controller 106 may control the pressure in both the first block cavity 60 and the second block cavity 84 by adjusting the corresponding valves and drains. Further, the controller 106 may control the amount of water being pumped by the water pressurization system 86 during flushing or purging sequences. Further details regarding such sequences will be discussed below.
As previously noted, establishing a liquid fuel purge is required by the NFPA during certain procedures. Such procedures include shutdown of the gas turbine the liquid fuel system and transferring from liquid fuel operation to gas fuel

operation. It should be appreciated that some or all of the steps of the procedures may be performed by the controller 106.
FIG. 3 illustrates a flushing sequence to establish a liquid fuel purge credit. As shown in FIG. 3, the method 150 is an embodiment of a process for a gas turbine system to shut down the liquid fuel operation and establish the liquid fuel purge credit after shutdown. Prior to the initiation of the method 150, the liquid fuel circuit system 50 is in liquid fuel operation. That is, liquid fuel flows through the fuel circuit 54 and liquid fuel lines 70. To facilitate operating with liquid fuel, the first valve 58 and the third valve 82 may open to allow liquid fuel to flow to the flow divider and the fuel nozzle, respectively. Furthermore, the liquid fuel control valve 56 may open in a manner to allow liquid fuel to enter the first block cavity 60. As such, no portion or a small portion of the liquid fuel entering the liquid fuel control valve 56 may enter the recirculation circuit 66. Furthermore, the purge air valve 80 may be closed and the purge air 76 may not enter the fuel nozzle 74.
Method 150 may begin with shutting down the liquid fuel supply system that may be delivering liquid fuel to the liquid fuel circuit system 50, as shown at block 152. In some embodiments, the controller 106 may be communicatively coupled with the liquid fuel supply system and when receiving a signal associated with the cease of liquid fuel operations, the processor 110 of the controller 106 may execute instructions to close the liquid fuel control valve 56 to keep liquid fuel from flowing into the liquid fuel circuit system 50. The first valve 58 may also close to entrap the liquid fuel within the first block cavity 60 and keep liquid fuel from flowing into the fuel line 70. In addition, the controller 106 may also shut down other components, such as the combustor 78 to prepare for the transition to gas fuel supply. As a result of the shutdown of the liquid fuel supply system, liquid fuel may cease to enter the fuel circuit 54. The liquid fuel that was already present in the liquid fuel circuit system 50 prior to shutdown of the liquid fuel supply system may begin to cease from further flowing into the combustor 78 via closing of the third valve 82.

After the liquid fuel supply system is shut down, a forward water flush may performed, as shown at block 154. The third valve 82, the water pressurization system valve 98, and the multiport injection valve 94 may be opened and the variable frequency drive 92 may be turned on to pump water through the fuel line 70. The water pressurization system drain valve 100 may close to ensure accurate flow control to the second block cavity 84. Water then may flow through the water pressurization system line 88 into the second block cavity 84 downstream into the fuel nozzle 74. The water flow may flush liquid fuel out of the fuel line 70. In some embodiments, prior to running water into the liquid fuel circuit system 50, the liquid fuel in the second block cavity 84 may be drained by opening the multiport drain valve 104, the multiport injection valve 94, and the water pressurization system drain valve 100.
After the forward water flush, the liquid fuel circuit system 50 may undergo a backward water flush at block 156. In this step, the third valve 82 may be closed to keep water from flowing into the fuel nozzle. As a result, water may flow towards the second valve 72. The multiport drain valve 104 may be opened to allow water to drain out of the second block cavity 84. Furthermore, the variable frequency drive 92 may adjust to pump water at a higher flow rate to rid the fuel line 70 of liquid fuel. In some embodiments, the purge air valve 80 may be opened and purge air 76 may flow into the fuel nozzle 74 to remove water that remained in the fuel nozzle prior to closing the third valve 82 as a result of block 152.
When the liquid fuel has been removed from the second block cavity 84, the multiport drain valve 104 may be closed to enable water to fill the second block cavity 84. The filling of the second block cavity 84 with water may pressurize the second block cavity 84. As discussed above, establishing a liquid fuel purge credit involves maintaining the first block cavity 60 and the second block cavity 84 to contain a pressure differential above 3 bar. As such, the water pressurization system 86 may continue to pump water into the second block cavity 84 to fill until the pressure in the second block cavity 84 reaches a desired

pressure (e.g., 5 bar). In response, the multiport injection valve 94 and the water pressurization system valve 98 may be closed and the water pressurization system 86 may shut down to keep water from further flowing into the second block cavity 84. Additionally, the first block cavity drain valve 62 may be opened to release liquid fuel from the first block cavity 60 to maintain pressure in the first block cavity 60 at around atmospheric pressure (e.g., less than 0.5 bar). In some embodiments, the controller 106 may be communicatively coupled to the triple redundant pressure transmitters 64, the pressure transmitter 102, and the water pressurization system 86. The controller 106 may receive measurements of pressure in the second block cavity 84 via the pressure transmitter 102 and measurements of the pressure in the first block cavity 60 to compare the measured pressures with one another. The controller 106 may compare the pressure measured by the triple redundant pressure transmitters 64 for the first block cavity 60 with the pressure measured by the pressure transmitter 102 to determine if the pressures of the respective block cavities are at the desired values. As mentioned above, the pressure within the second block cavity 84 (i.e., downstream of the second valve 72) is to be maintained at a pressure at least 3 bar above the liquid fuel circuit system 50 upstream of the second valve 72 to fulfill the conditions for a liquid fuel purge credit. In some embodiments, the pressure of the first block cavity 60 may be around 0.5 bar and the pressure in the second block cavity 84 may be kept at around 4-6 bar.
To complete method 150, at block 160, the liquid fuel circuit system 50 may be configured to maintain the liquid fuel purge credit established at block 158. That is, the multiport drain valve 104, the multiport flush valve 94, and the water pressurization system drain valve 100 may be closed so that no fluids enter or exit from the second block cavity 84. The liquid fuel control valve 56 and the first valve 58 may also both be closed, keeping liquid fuel from entering the first block cavity 60 and the flow divider 68, respectively. Thus, no liquid fuel enters liquid fuel circuit system 50. In addition, the pressurized water may be maintained in the second block cavity 84 to sustain the pressures required for

the liquid fuel purge credit. In some embodiments, an alarm may trigger if the pressure in the second block cavity 84 goes below 4 bar and/or the pressure in the first block cavity 60 significantly deviates from atmospheric pressure. The alarm may also trigger if the pressure difference between the first block cavity 60 and the second block cavity 84 becomes lower than 3 bar. When the pressure in the second block cavity 84 is below the desired value, the controller 106 may adjust the pressure in the second block cavity 84 by pumping more water into the second block cavity 84 via the water pressurization system 86. Moreover, the controller 106 may also be configured to monitor the position of the valves (e.g. the third valve 82 and the multiport drain valve 104). As discussed above, maintaining the purge credit further involves monitoring the stop and drain valve positions. As such, at block 160, the controller 106 may also monitor the valves in the liquid fuel circuit system 50 to maintain the system at the liquid fuel purge credit state to ensure the valve positions do not change.
The method 150 may also be performed with additional steps. For example, the steps in block 154 and block 156 may be performed with several additional iterations to better flush the second block cavity 84. Furthermore, the method 150 may be performed in conjunction with other processes. For example, when operation of the gas turbine transfers from liquid fuel operation to gas fuel operation, the method 150 may be utilized to shut down the liquid fuel operation and a different method for the startup of the gas fuel operation may proceed after completion of the method 150.
The benefit of establishing the liquid purge credit is that it enables faster startup. Typically, a purge sequence involves preparing the turbine system, bringing the combustion turbine to purge speed, exchanging the entire volume of fuel system lines several times, starting the fuel addition and ignition sequence, and then synchronizing all of the systems and components to operating speed. The sequence may extend the time of startup by several minutes (e.g., over 15 minutes) and may also affect performance and reliability of equipment since the system runs during the purge sequence. The method 150 establishes the purge

credit to meet safety conditions of ridding combustible fuel in the fuel circuit. As such, the gas turbine may bypass running a purge sequence prior to startup, enabling the gas turbine to a faster startup time.
FIG. 4 illustrates in detail an embodiment of a method 200 for the liquid fuel circuit system 50 to maintain the liquid fuel purge credit as described by block 160 of FIG. 3. The method 200 may monitor pressure in the first block cavity 60 and/or the second block cavity 84 and steps of the method 200 may be implemented by the processor 110 of the controller 106.
In some embodiments, the method 200 may begin at block 202 with measuring the pressure of the first block cavity 60 via the triple redundant pressure transmitters 64 and measuring the pressure of the second block cavity 84 via the pressure transmitter 102 when the gas turbine has established the liquid fuel purge credit. At block 210, the controller 106 may determine if the measured pressure in the first block cavity 60 is at or below the desired pressure (e.g., 0.5 bar). If the pressure is at or below the desired pressure, the controller 106 may continue to monitor the pressure. If the pressure in the first block cavity 60 is above the desired pressure, the controller 106 may adjust the drain valve 62 as shown at block 212 to reduce the pressure within the first block cavity 60. After adjustment of the first block cavity, the controller 106 may determine again if the pressure in the first block cavity 60 is at or below the desired pressure, as shown at block 214. If the pressure in the first block cavity 60 is decreased to be at or below the desired pressure, the controller 106 may go back to block 202 and continue to monitor the pressure. At block 216, when the pressure cannot be reduced to be at or below the desire pressure, the controller 106 may provide an indication and/or alarm associated with the pressure of the first block cavity 60 being above the desired pressure value.
In addition, the controller 106 may determine, at block 230, if the pressure in the second block cavity 84 is within a desired pressure range (e.g., 4-6 bar). If the measured pressure is within the desired pressure range, the controller 106

may continue to measure the pressure. If the pressure falls out of the desired pressure range, the controller 106 may adjust the pressure in the second block cavity 84. For example, at block 232, the controller 106 may adjust the multiport drain valve 104 in response to the pressure being above the desired pressure range, or the controller 106 may adjust the water pressurization system 86 in response to the pressure being below the desired pressure range. Adjusting (e.g., opening) the multiport drain valve 104 may enable water to be drained from the second block cavity 84 to reduce pressure in the second block cavity 84. Adjusting the water pressurization system 86 may involve opening the multiport injection valve 94 and the water pressurization system valve 98, then pumping water into the second block cavity 84 to increase pressure in the second block cavity 84. In some embodiments, both adjusting the multiport drain valve 104 and adjusting the water pressurization system 86 may be utilized to adjust the pressure in the second block cavity 84. At block 234, after adjustments to the second block cavity 84 have been made, the controller 106 may again determine if the pressure in the second block cavity 86 is within the desired pressure range. If the pressure in the second block cavity 86 is within the desired pressure range, the controller 106 may continue to monitor the pressure as shown at block 202. If the pressure in the second block cavity 84 continues to be outside of the desired pressure range, at block 236, the controller 106 may provide an indication and/or alarm associated with the pressure in the second block 86 being outside of the desired pressure range.
Furthermore, the controller 106 may compare the measurement of the pressure in the first block cavity 60 with the measurement of the pressure in the second block cavity 84. At block 250, the controller 106 determines if the difference in the pressure measurements is at or above a desired difference (e.g., 3 bar). If the difference is at or above the desired difference, the controller 106 may continue to monitor pressure. If the difference falls below the desired difference, the controller 106 may determine whether the pressure in the first block cavity 60 is above the desired pressure or whether the pressure in the

second block cavity 84 is outside of the desired pressure. If the pressure in the first block cavity 60 is above the desired pressure, the controller may follow the steps shown at blocks 210, 212, 214, and/or 216. If the controller determines that the pressure in the second block cavity 84 is outside of the desired pressure, the controller may follow the steps shown at blocks 230, 232, 234, and/or 236.
Moving to another sequence of operating the liquid fuel circuit system 50, FIG. 5 shows an embodiment of a method 350 to start the gas turbine after establishing liquid fuel purge credit. The steps of the method 350 may be performed by the controller 106. In FIG. 5, the liquid fuel circuit system 50 begins in the liquid purge credit state, as shown at block 352, which may have been established prior to shutdown of gas turbine operations (e.g., via the process in FIG. 3). The second block cavity 84 is filled with water as a result of the established liquid fuel purge credit state and the water may be drained, as seen in block 354. The water may drain from the second block cavity 84 from the openings of the multiport drain valve 104, the multiport injection valve 94, and the water pressurization system drain valve 100. In this manner, water may flow out through the multiport drain valve 104 to drain near the second valve 72 or through the water pressurization system line 88 to drain closer to the fuel nozzle. This may result in the second block cavity 84 only containing air after the drainage.
After water has been drained, the liquid fuel supply system may turn on to flow liquid fuel through the liquid fuel circuit system 50. Turning on the liquid fuel supply system to pre-fills the second block cavity 60 at block 356. In some embodiments, the liquid fuel control valve 56 may open the gate to enable liquid fuel to flow into the first block cavity 60 and the first valve 58 may open to enable liquid fuel to flow to the flow divider 68 and thereby the fuel line 70. Furthermore, the first block cavity drain valve 62 may close to keep liquid fuel from draining from the first block cavity 60. Downstream of the first block cavity 60, the multiport drain valve 104, the multiport injection valve 94, and

the water pressurization system drain valve 100 may close to enable the liquid fuel to fill the second block cavity 84 and pressurize the second block cavity 84.
When a certain pressure has been reached (e.g., up to 5.5 bar) in the second block cavity 84, the liquid fuel circuit system 50 may adjust to fully operate in liquid fuel operation. At block 358, the third valve 82 may open and enable the liquid fuel to flow through to the fuel nozzle 74. At this point, the liquid fuel circuit system 50 may be in liquid fuel operation and the position of the valves may be maintained during the operation.
FIGS. 6 and 7 illustrate additional embodiments of the liquid fuel circuit system 50. In FIG. 6, the liquid fuel circuit system 400 contains an additional compressed air supply system 402. The compressed air supply system 402 may contain compressed inert air or nitrogen that may be connected to the water pressurization system line 88 via a compressed air system line 404. The compressed air system line 404 may consist of a compressed air system line valve 406, a compressed air system vent valve 408, and a compressed air system valve 410. The compressed air system valve 410 may enable compressed air to flow out from the compressed air supply system 402 and the compressed air system line valve 406 may enable compressed air to flow through the compressed air system line 404 to the water pressurization system line 88. The vent valve 408 may enable compressed air to redirect out of the compressed air system line 404, such as to release stagnant compressed air from the compressed air system line 404 resulting from the closing of both the compressed air system line valve 406 and the compressed air system valve 410.
The purpose of the compressed air supply system 402 may be similar to that of the water pressurization system 86 to pressurize the second block cavity 84. For example, in some embodiments, establishing and/or maintaining the liquid fuel purge credit state in method 200, 250, 300, and/or 350 may use the compressed air supply system 402 instead of the water pressurization system 86. In alternate embodiments, the compressed air supply system 402 may be used in

conjunction with the water pressurization system 86 in establishing and/or maintaining the liquid fuel purge credit state. In further embodiments, flushing (e.g., forward or backward flush of the second block cavity 84) may be performed by the compressed air supply system 402 or by the compressed air supply system 402 combined with the water pressurization system 86. Adding the compressed air supply system 402 gives the liquid fuel circuit system 400 additional flexibility in obtaining liquid fuel purge credit and in flushing the second block cavity 84.
Furthermore, FIG. 7 provides an embodiment of a liquid fuel circuit 450 that includes a liquid level monitoring system coupled to the second block cavity 84. As illustrated, the second block cavity 84 may be connected to a liquid level sensor 452. The liquid level sensor 452 may measure the liquid level within the second block cavity 84. In some embodiments, the liquid level sensor 452 may be a level switch communicatively coupled with the controller 106 and when the liquid (e.g., liquid fuel or water) reaches a certain level, the liquid level sensor 452 may output a signal to the controller 106. For example, during the maintaining of the liquid fuel purge credit, liquid fuel may be kept from entering the second block cavity 84. The liquid level sensor 452 may monitor the liquid level in the second block cavity 84 to ensure the liquid level is kept at a minimum in order to maintain the liquid fuel purge credit. If the liquid level rises above a predetermined threshold stored in the memory 108, the controller 106 may provide an alarm indicative of the liquid level. In other embodiments, the liquid level sensor 452 may send an output in other situations. For example, the liquid level sensor 452 may monitor the level of liquid fuel during liquid fuel operations and may detect if the level of liquid fuel falls below a predetermined value in the second block cavity 84 (e.g., due to a leak in the piping). As a result of the detection, the liquid level sensor 452 may send a signal to the controller 106 to trigger an alarm indicative of the low liquid level. Additional embodiments may combine the aforementioned uses of the liquid

level sensor 452 or provide other uses where the liquid level sensor 452 may sense liquid level in the second block cavity 84.
Yet another embodiment of the liquid fuel circuit system 500 is illustrated in FIG. 8. In this embodiment, the liquid fuel circuit system 500 uses a water pressurization system 502 to pressurize the second block cavity 84. The water pressurization system 502 may use a single speed pump 504 to pump water from the water tank 90 into the second block cavity 84 via the water pressurization system line 88. Downstream of the single speed pump 504 is a water pressurization system valve 506. In some embodiments, the water pressurization system valve 506 is a three way valve that may allow water to flow through to the water pressurization system line 88 or to a water pressurization system recirculation line 506 to circulate at least a portion of the pumped water back to the water tank. The controller 106 may control the three way valve and control the flow of water from the water pressurization system 502.
Moreover, further embodiments of the liquid fuel circuit system 50 may combine the aspects of the liquid fuel circuit system 400, the liquid fuel circuit system 450, and the liquid fuel circuit system 500 such as adding the compressed air supply system 402, the liquid level sensor 452, the water pressurization system 502, or any combination thereof to the liquid fuel circuit system 50. In additional embodiments, several components, such as stop valves and drain valves, may also be added to other parts of any of the embodiments of the liquid fuel circuit systems for more precise control of the fluids within the liquid fuel circuit system. Likewise, the valves (e.g., second valve 72) are discussed to be certain types of valves (e.g., a check valve), but in alternate embodiments, the valves may be other types of valves that may still allow the liquid fuel circuit system 50 to operate the discussed sequences.
Technical effects of the disclosed embodiments include providing systems and methods for establishing a liquid fuel purge credit in a gas turbine engine. In

particular, the gas turbine engine may be a multi-fuel system and may use a water pressurization system to establish the liquid fuel purge credit. The gas turbine may include a liquid fuel circuit system that includes a first block cavity and a second block cavity, where the pressures within the first and second block cavities are maintained at certain values to meet the liquid fuel purge credit. For example, the water pressurization system may pressurize the second section. The water pressurization system may further flush the fuel lines in the liquid fuel circuit system to reduce coking and/or backflow of combustion particles into the liquid fuel circuit system. In addition, the liquid fuel circuit system may be configured for both gas fuel and liquid fuel operations. A controller may run the flushing and/or the purging sequences of the liquid fuel circuit system. As a result of the disclosure, the gas turbine that already uses the water pressurization system to flush the liquid fuel circuit may be able to establish a liquid fuel purge credit with few additional components and/or modifications of current components. This may reduce costs on assembly and operations to create a gas turbine that is able to meet the liquid fuel purge credit conditions.
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 invention 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 with insubstantial differences from the literal language of the claims.

WE CLAIM:
1. A system, comprising: a liquid fuel system for a multi-fuel gas turbine comprising a liquid fuel circuit, wherein the liquid fuel system comprises:
a fuel flow divider configured to regulate liquid fuel flow to
associated fuel nozzles of the multi-fuel gas turbine;
a liquid fuel control valve disposed along the liquid fuel circuit
upstream of the fuel flow divider;
a first valve disposed along the liquid fuel circuit downstream
of the liquid fuel control valve and upstream of the fuel flow
divider;
a check valve disposed along the liquid fuel circuit
downstream of the fuel flow divider;
a third valve disposed along the liquid fuel circuit downstream
of the check valve and upstream of a respective fuel nozzle of
the associated fuel nozzles; and wherein, during shutdown of the multi-fuel gas turbine, a first block cavity free of liquid fuel is formed along the liquid fuel circuit between the liquid fuel control valve and the stop valve when the liquid fuel control valve and the stop valve are closed, a second block cavity free of liquid fuel is formed along the liquid fuel circuit between the check valve and the third valve when the third valve is closed, and the second block cavity is pressurized with a liquid.
2. The system as claimed in claim 1, wherein the maintenance of the first and second block cavities provides a liquid fuel purge credit to be utilized during startup of operation of the multi-fuel gas turbine with liquid fuel.
3. The system as claimed in claim 1, comprising a water pressurization system coupled to the liquid fuel circuit between the check valve and the third valve,

wherein the water pressurization system is configured to provide the liquid to pressurize the second block cavity.
4. The system as claimed in claim 3, wherein the water pressurization system is configured to purge the liquid fuel circuit of liquid fuel downstream of the check valve prior to forming the second block cavity free of liquid fuel when the multi-gas turbine switches to operation with the gas fuel.
5. The system as claimed in claim 3, comprising a first drain line coupled to the first block cavity, wherein the first drain line is configured to drain the first block cavity to atmosphere.
6. The system as claimed in claim 5, comprising a second drain coupled to the second block cavity.
7. The system as claimed in claim 6, comprising a first pressure transducer coupled to the first block cavity, wherein the first pressure transducer is configured to measure a pressure of the first block cavity.
8. The system as claimed in claim 7, comprising a second pressure transducer coupled to the second block cavity, wherein the second pressure transducer is configured to measure a pressure of the second block cavity.
9. The system as claimed in claim 8, comprising a controller configured to monitor respective pressures of the first and second block cavities based on feedback from the first and second pressure transducers to maintain a liquid fuel purge credit.
10. The system as claimed in claim 9, wherein the controller is configured to regulate the water pressurization system to maintain the pressure within the second block cavity within a set pressure range.

11. The system as claimed in claim 1, comprising the multi-fuel gas turbine configured to operate on both the liquid fuel system and the gas fuel system, wherein the multi-fuel gas system comprises a compressor, a combustor, and a turbine.
12. A system, comprising:
a liquid fuel purge credit system for a multi-fuel gas turbine comprising: a first block cavity free of liquid fuel formed along a first portion of a liquid fuel circuit coupled to the multi-fuel gas turbine, wherein the first block cavity is located upstream of a fuel flow divider between a liquid control valve and a first valve when the liquid control valve and the first valve are closed;
a second block cavity free of liquid fuel formed along a second portion of a liquid fuel circuit downstream of the fuel flow divider and between a check valve and a third valve upstream of a respective fuel nozzle of the multi-fuel gas turbine when the third valve is closed; and
a water pressurization system coupled to the second portion of the liquid fuel circuit between the check valve and the third valve, wherein the water pressurization system is configured to pressurize the second block cavity; wherein the maintenance of the first and second block cavities provides a liquid fuel purge credit to be utilized during startup of operation of the multi-fuel gas turbine with liquid fuel.
13. The system as claimed in claim 12, wherein the liquid fuel purge credit
system comprises a first pressure transducer coupled to the first block cavity
and wherein the first pressure transducer is configured to measure a pressure of
the first block cavity.

14. The system as claimed in claim 13, wherein the liquid fuel purge credit system comprises a second pressure transducer coupled to the second block cavity and is configured to measure a pressure of the second block cavity.
15. The system as claimed in claim 14, comprising a controller configured to monitor respective pressures of the first and second block cavities based on feedback from the first and second pressure transducers to maintain the liquid fuel purge credit.
16. The system as claimed in claim 14, wherein the controller is configured to regulate the water pressurization system and the third valve to maintain the pressure within the second block cavity within a set pressure range.
17. The system as claimed in claim 12, comprising a first drain line coupled to the first block cavity, wherein the first drain line is configured to drain the first block cavity to atmosphere.
18. The system as claimed in claim 17, comprising a second drain coupled to the second block cavity.
19. A method for establishing a liquid fuel purge credit after shutdown of liquid fuel operation of a multi-fuel gas turbine, comprising:
forming a first block cavity free of liquid fuel along a first portion of a liquid fuel circuit coupled to the multi-fuel gas turbine, wherein the first block cavity is located upstream of a fuel flow divider between a liquid control valve and a first valve by closing the liquid control valve and the first valve once the first block cavity is free of liquid fuel; and forming a second block cavity free of liquid fuel along a second portion of the liquid fuel circuit downstream of the fuel flow divider and between a check valve and a third valve upstream of a respective fuel

nozzle of the multi-fuel gas turbine by closing the third valve once the first block cavity is free of liquid fuel and pressurizing, via a water pressurization system, the second block cavity to a set pressure range.
20. The method as claimed in claim 19, comprising monitoring, via a controller, respective pressures of the first and second block cavities based on feedback from pressure transducers to maintain the liquid fuel purge credit.