A gas turbine dual fuel system and control method

Abstract

The application belongs to the field of fuel system design, and particularly relates to a gas turbine dual fuel system and a control method, which comprises a natural gas system and a fuel system, the fuel supercharging pump is driven by an independent motor, and can be controlled to stop when burning natural gas; the fuel regulating device is directly driven by a limited angle torque motor to drive a metering valve, and the anti-fuel pollution ability is improved; a double fuel filter is arranged on the fuel side, and the filter element can be replaced online. The application adopts a blow cleaning scheme for different working conditions: in the medium and low working conditions, the compressor outlet gas is used to blow clean the natural gas pipeline, and in the medium and high working conditions, the natural gas is used to blow clean the fuel pipeline. The fuel switching adopts equal heat control, open loop control of the fuel reduction and closed loop control of the fuel increment, the upper limit of the flow and the switching termination threshold are set, and the valve action, pipeline blow cleaning and pump body start and stop are completed according to the predetermined time sequence. The application simplifies the structure of the blow cleaning system, reduces the equipment cost, improves the service life and maintainability of the components, and ensures the safe and stable operation of the offshore platform gas turbine dual fuel.

Description

Technical Field

[0001] This application belongs to the field of fuel system design, and specifically relates to a dual-fuel system for gas turbines and its control method. Background Technology

[0002] When gas turbines are used on offshore platforms, they require both liquid and gaseous fuels. Liquid fuels are chosen for startup, shutdown preparation, and low-operational-condition operation, resulting in shorter operating times. Gaseous fuels are chosen for medium- to high-operational-condition operation, resulting in longer operating times. Compared to single-fuel systems, dual-fuel systems are more complex to design, involving key technologies such as dual-fuel system design methods, bleed air methods for the purge system, control methods for bleed air from the idle main pipe after dual-fuel switching, and control methods for the dual-fuel switching process.

[0003] Traditional liquid single-fuel systems typically use a booster pump integrated into the accessory housing to further pressurize the liquid fuel. The fuel conditioning system's metering module is driven and controlled by an electro-hydraulic servo valve, and oil filters with a certain filtration precision are installed before and after the pump. For conventional dual-fuel systems, the purge system typically obtains gas by pressurizing air through a compressor, supplying nitrogen through a nitrogen cylinder, or obtaining it from the compressor outlet. The dual-fuel switching process generally uses open-loop control; at the start of the switch, the liquid fuel and gaseous fuel are increased or decreased at a certain slope until the switch is complete.

[0004] Traditional designs have the following drawbacks:

[0005] 1. For dual-fuel systems, if the fuel booster pump is integrated into the accessory system, the pressure of liquid fuel is increased by extracting power from the gas turbine rotor. This means that the booster pump must keep running as long as the gas turbine is running, which requires a constant supply of fuel. This not only affects the lifespan and reliability of the booster pump, but also the operating efficiency of the gas turbine.

[0006] 2. Offshore gas turbines operate for long periods, in rough seas, and are difficult to resupply and maintain. The quality of imported fuel for gas turbines is hard to guarantee, and poor fuel quality can easily cause electro-hydraulic servo valves to jam, resulting in the fuel metering feedback not following.

[0007] 3. If the purging system uses compressor-pressurized air as the purging gas, it requires a compressor, cooler, and 220V power supply of appropriate power according to the gas turbine compressor outlet pressure. The main disadvantages are complex equipment, high power consumption, high cost, large space occupation, and poor maintainability. Purging with nitrogen supplied by nitrogen cylinders can only meet short-term commissioning needs and is not suitable for long-term use. When purging with bleed air at the compressor outlet, as the gas turbine operating conditions increase, the compressor outlet pressure and outlet temperature also rise. Especially at medium and high operating conditions of the gas turbine, the compressor outlet bleed air temperature will be higher than the allowable temperature. Directly leading the purging liquid fuel pipeline and nozzles can easily cause coking, and also affect the service life of the pipeline system, valves, and instruments. Therefore, a cooler is needed for heat dissipation. However, configuring a cooler will increase space occupation, cost, and bleed air pressure loss, and may also create a risk of leakage.

[0008] 4. The disadvantages of using open-loop fuel slope control in the dual-fuel switching process are unstable power generation control, easy combustion instability, and large deviations in operating conditions before and after switching.

[0009] Therefore, how to design a more effective dual-fuel system is a problem that needs to be solved. Summary of the Invention

[0010] To address the aforementioned issues, this application provides a dual-fuel gas turbine system and control method to resolve the problem of low design efficiency in existing dual-fuel systems.

[0011] The technical solution of this application is: a gas turbine dual-fuel system, including a natural gas system and an oil fuel system;

[0012] The natural gas system includes a booster device, parameter monitoring instruments, a shut-off valve and a vent valve for pre-start sealing checks, a shutdown shut-off valve, a vent valve, a fuel control valve with a drive motor, a purge shut-off valve at the compressor outlet, a vent valve, a backflow prevention check valve, a natural gas main, and a purge gas throttle nozzle.

[0013] The fuel system includes a dual fuel filter, a differential pressure alarm, a ball valve, an electric fuel booster pump, a parameter monitoring instrument, an adjustment device with a drive motor, a main and auxiliary fuel line separator, a stop valve, a drain valve, a purge stop valve that draws gas from the natural gas pipeline, a backflow prevention check valve, a fuel main pipe, and a purge gas throttle nozzle.

[0014] The electric fuel booster pump is independently driven by a motor and can be shut down by controlled power-off when the gas turbine switches to gaseous fuel; the fuel system regulating device adopts a metering valve directly driven by a motor with limited rotation angle torque.

[0015] The dual-fuel system is configured with condition-specific purging control logic: when the gas turbine is in a low-to-medium operating condition and burning liquid fuel, it takes low-temperature gas from the compressor outlet and purifies the idle natural gas main and nozzles through the throttle nozzle; when the gas turbine is in a high-to-medium operating condition and burning natural gas, it draws some natural gas from the natural gas fuel outlet valve and introduces it into the main and auxiliary fuel lines through the throttle nozzle to purify the idle fuel main and nozzles.

[0016] Preferably, the gas turbine dual-fuel system is further configured with dual-fuel switching control logic, and the switching process adopts isothermal control, satisfying the following relationship: ,in For fuel flow rate, This refers to the calorific value of fuel oil. For natural gas flow rate, The calorific value of natural gas;

[0017] During fuel switching, the fuel to be reduced is controlled by open-loop rate control, and the fuel to be increased is controlled by closed-loop rate control. The upper limit of the fuel flow to be increased is set to 110% of the target flow. When the fuel flow to be increased reaches 95% of the target flow, the original fuel supply is cut off.

[0018] Preferably, the dual oil filter is installed on the pipeline in front of the electric fuel booster pump. The dual oil filter is equipped with a differential pressure alarm and a ball valve for switching the flow path, which enables online replacement of the filter element without shutting down the pump. Pressure and temperature measuring points are also installed on the natural gas main pipeline to monitor the purge gas parameters and the hot gas return status.

[0019] Preferably, in the natural gas system, the output end of the booster unit is connected in sequence to a parameter monitoring instrument, a shut-off valve for pre-start sealing check, a shutdown valve, and a fuel control valve with a drive motor before being connected to the natural gas main pipe; the vent valve is connected in parallel to the pipeline downstream of the sealing check shut-off valve; one end of the purge shut-off valve at the compressor outlet is connected to the gas turbine compressor outlet, and the other end is split into two paths, one of which is connected to the vent valve, and the other path is connected to the natural gas main pipe in sequence through the purge gas throttle nozzle and the anti-backflow check valve;

[0020] In the fuel system, external fuel input sequentially passes through a dual fuel filter, an electric fuel booster pump, a parameter monitoring instrument, an adjustment device with a drive motor, and a main and auxiliary fuel line separator before connecting to the fuel main line. The dual fuel filter is equipped with a differential pressure alarm and a path switching ball valve. A stop valve and a drain valve are connected in parallel on the fuel main line. A purge valve that draws gas from the natural gas pipeline is connected to the natural gas system at one end, and the other end is connected to the fuel main line sequentially through a purge gas throttle nozzle and an anti-backflow check valve.

[0021] Preferably, the shut-off valve includes a first shut-off valve to a fifth shut-off valve, the cut-off valve includes a first cut-off valve to a fourth cut-off valve, the vent valve includes a first vent valve to a third vent valve, the purge shut-off valve includes a first purge shut-off valve to a third purge shut-off valve, and the drain valve includes a first drain valve and a second drain valve.

[0022] When switching from fuel oil to natural gas, the following control steps are executed:

[0023] S1. Determine that the high-pressure converted speed of the gas turbine is greater than the threshold C1, and receive the instruction from the host computer to switch to natural gas;

[0024] S2. Detect that the natural gas pipeline pressure has reached the normal value, and control the natural gas electric valve to open to the minimum open position; after waiting for 5 control cycles, connect the first shut-off valve, the first cut-off valve and the second shut-off valve, and disconnect the venting valve, the first venting valve, the second venting valve, the third venting valve, the second shut-off valve, the third shut-off valve, the fourth shut-off valve and the fifth shut-off valve.

[0025] S3. Calculate the target natural gas flow rate corresponding to the current power generation capacity based on the fuel combustion heat before the switchover, and limit the upper limit of the natural gas flow rate to 110% of the target flow rate; the fuel oil decreases in an open loop at a set rate, and the natural gas increases in a closed loop at a set rate;

[0026] S4. When the natural gas flow reaches 95% of the target flow, disconnect the third and fourth shut-off valves, close the fuel regulating device metering valve; connect the second and third purge shut-off valves to purge the main and auxiliary fuel lines, fuel main pipe and nozzles, disconnect the electric fuel booster pump motor power, and complete the switch from fuel to natural gas.

[0027] Preferably, when switching from natural gas to fuel oil, the following control steps are performed:

[0028] S1. Determine that the high-pressure converted speed of the gas turbine is greater than the threshold C1, and receive the instruction from the host computer to switch to fuel oil.

[0029] S2. Power on the electric fuel booster pump motor and set the fuel regulating device metering valve to the minimum position; check that the fuel line pressure reaches the normal value, wait for 5 control cycles, then connect the third and fourth shut-off valves and disconnect the first and second drain valves; if the second and third purge shut-off valves are in the connected state, disconnect them.

[0030] S3. Based on the current natural gas combustion heat, calculate the target fuel flow rate corresponding to the current power generation capacity, and limit the upper limit of the fuel flow rate to 110% of the target flow rate; natural gas decreases in an open loop at a set rate, and fuel increases in a closed loop at a set rate;

[0031] S4. When the fuel flow reaches 95% of the target flow, disconnect the first shut-off valve, the first cut-off valve and the second cut-off valve, and close the natural gas fuel electric valve; connect the vent valve and the first vent valve; connect the fourth shut-off valve and the fifth shut-off valve, disconnect the second vent valve and the third vent valve, purge the natural gas main and nozzles, stop the natural gas booster device, and complete the switch from natural gas to fuel oil.

[0032] Another technical solution of this application is: a dual-fuel control method for a gas turbine, comprising:

[0033] During the low- and medium-operating-condition phase of the gas turbine when burning liquid fuel, the gas from the compressor outlet is used to purge the idle natural gas main and nozzles after passing through the throttle nozzle.

[0034] During the high-performance phase of the gas turbine when burning natural gas, a portion of natural gas is drawn from the natural gas fuel outlet valve and fed into the main and auxiliary fuel oil circuits through the throttle nozzle to purge the idle fuel oil main and nozzles.

[0035] When switching fuels, isothermal control is used. The open-loop flow rate of fuel is reduced and the closed-loop flow rate of fuel is increased. The upper limit of the fuel flow rate to be increased is set to 110% of the target flow rate. When the increased fuel flow rate reaches 95% of the target flow rate, the supply of raw fuel is cut off.

[0036] Preferably, switching from fuel oil to natural gas includes:

[0037] After determining that the high-pressure conversion speed is greater than C1 and confirming that the natural gas pipeline pressure is normal, set the natural gas electric valve to the minimum opening. After the valve status switch is completed, calculate the target natural gas flow rate based on the fuel heat before the switch. Calculate the fuel open-loop decrease and the natural gas closed-loop increase. After the natural gas flow rate reaches 95% of the target flow rate, cut off the fuel supply, start the fuel pipeline purging, and stop the electric fuel booster pump.

[0038] Preferably, switching from natural gas to fuel oil includes:

[0039] If the high-pressure conversion speed is greater than C1, power on the electric fuel booster pump, confirm that the fuel line pressure is normal, and close the fuel line purging circuit; calculate the target fuel flow rate based on the current natural gas heat; reduce the natural gas flow rate in the open loop and increase the fuel flow rate in the closed loop; once the fuel flow rate reaches 95% of the target flow rate, cut off the natural gas, start the natural gas line purging, and stop the natural gas booster device.

[0040] The dual-fuel gas turbine system and control method of this application have the following advantages:

[0041] An electric fuel booster pump is selected to pressurize the fuel and is separated from the accessory casing. When natural gas is selected for operation, the fuel booster pump can be stopped, which is beneficial for maintaining the long life and high reliability of the fuel booster pump.

[0042] A set of dual fuel filters, differential pressure alarms, and ball valves is installed at the fuel inlet and placed outside the enclosure. This enables fuel filter differential pressure alarms and online fuel filter replacement, avoiding unnecessary shutdowns and improving maintenance efficiency.

[0043] The liquid fuel regulating device uses a metering valve driven by a limited angle torque motor. Compared with the metering valve driven by an electro-hydraulic servo valve, the rotary metering valve driven by the angle torque motor has a stronger resistance to fuel pollution.

[0044] The cleaning and purging method does not require compressors, coolers, or power supply equipment. The cleaning and purging system has advantages such as simple structure, low cost, high safety, small footprint, and good maintainability.

[0045] When switching between fuel oil and natural gas, the method uses equal heat control. This method can calculate the target flow rate of the fuel to be switched in advance, and then set the maximum flow limit protection and the switching end point in advance according to the target flow rate. At the same time, the planned reduction of fuel is controlled in open loop, and the planned increase of fuel is controlled in closed loop. The main advantages of this method are that the control target parameters and the switching end point are clear, the switching control is stable, the operating condition deviation is small, and it is not easy to have problems such as flameout or abnormal temperature rise. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the overall structure of this application.

[0047] 1. First shut-off valve; 2. First cut-off valve; 3. Second cut-off valve; 4. Vent valve; 5. First vent valve; 6. Second vent valve; 7. Third vent valve; 8. Second shut-off valve; 9. Third shut-off valve; 10. Fourth shut-off valve; 11. Fifth shut-off valve; 12. Third cut-off valve; 13. Fourth cut-off valve; 14. First drain valve; 15. Second drain valve; 16. Natural gas main; 17. Dual oil filter; 18. Electric fuel booster pump; 19. Boosting device; 20. Regulating device; 21. Fuel main. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0049] The first aspect of this application provides a dual-fuel gas turbine system, such as... Figure 1 As shown, it includes a natural gas system and a fuel oil system.

[0050] The natural gas system includes a booster unit 19, parameter monitoring instruments, a shut-off valve and a vent valve 4 for pre-start sealing checks, a shutdown valve, a vent valve, a fuel control valve with a drive motor, a purge shut-off valve at the compressor outlet, a vent valve, a backflow prevention check valve, a natural gas main 16, and a purge gas throttle nozzle.

[0051] The fuel system includes a dual oil filter 17, a differential pressure alarm, a ball valve, an electric fuel booster pump 18, a parameter monitoring instrument, an adjustment device 20 with a drive motor, a main and auxiliary fuel line separator, a stop valve, a drain valve, a purge stop valve that draws gas from the natural gas pipeline, a backflow prevention check valve, a fuel main pipe 21, and a purge gas throttle nozzle.

[0052] The electric fuel booster pump 18 is independently driven by an electric motor and can be shut down by controlled power-off when the gas turbine switches to gaseous fuel; the fuel system regulating device 20 adopts a metering valve directly driven by a motor with limited rotation angle torque.

[0053] The dual-fuel system is configured with a condition-specific purging control logic: when the gas turbine is in a low-to-medium operating condition and burning liquid fuel, it takes low-temperature gas from the compressor outlet and purifies the idle natural gas main 16 and nozzles through the throttle nozzle; when the gas turbine is in a high-to-medium operating condition and burning natural gas, it draws some natural gas from the natural gas fuel outlet valve and introduces it into the main and auxiliary fuel oil circuits through the throttle nozzle to purify the idle fuel oil main 21 and nozzles.

[0054] An electric fuel booster pump 18 driven by an independent motor is installed, which can be shut down in a controlled manner when the gas turbine is burning natural gas, avoiding the booster pump from running continuously with the main unit, thus improving the service life of the booster pump and the overall reliability of the machine.

[0055] The metering valve is driven directly by a motor with limited rotation angle torque, replacing the traditional electro-hydraulic servo valve drive scheme. This improves the system's resistance to fuel oil pollution, adapts to the unstable fuel quality conditions on offshore platforms, and reduces the risk of metering valve jamming.

[0056] The system is configured with different purging logic for different operating conditions: for low and medium operating conditions, the system uses low-temperature gas from the compressor outlet to purge idle natural gas pipelines; for medium and high operating conditions, it directly extracts natural gas to purge idle fuel pipelines, eliminating the need for additional compressors, nitrogen cylinders, and coolers. This simplifies the purging system hardware, reduces equipment costs and space requirements, and avoids the risk of leakage in the cooling circuit.

[0057] Preferably, the gas turbine dual-fuel system is further configured with dual-fuel switching control logic, and the switching process adopts isothermal control, satisfying the following relationship: ,in For fuel flow rate, This refers to the calorific value of fuel oil. For natural gas flow rate, The calorific value of natural gas;

[0058] During fuel switching, the fuel to be reduced is controlled by open-loop rate control, and the fuel to be increased is controlled by closed-loop rate control. The upper limit of the fuel flow to be increased is set to 110% of the target flow. When the fuel flow to be increased reaches 95% of the target flow, the original fuel supply is cut off.

[0059] The target flow rate for switching fuel is calculated based on the isothermal conservation relationship to ensure the stability of the total output heat during the switching process. A combination of reduced open-loop control and incremental closed-loop control is adopted, while setting a flow limit protection and clear switching termination conditions.

[0060] Preferably, the dual oil filter 17 is installed on the pipeline in front of the electric fuel booster pump 18. The dual oil filter 17 is equipped with a differential pressure alarm and a ball valve for switching the circuit, which can realize online replacement of the filter element without stopping the machine. Pressure and temperature measuring points are also installed on the natural gas main pipe 16 to monitor the purge gas parameters and the hot gas return status.

[0061] The dual oil filter 17 is located upstream of the electric fuel booster pump 18. Together with the differential pressure alarm and the channel switching ball valve, the filter element can be switched and replaced online during unit operation without stopping the machine, reducing unplanned downtime on the offshore platform and improving equipment maintenance efficiency and unit availability.

[0062] Preferably, in the natural gas system, the output end of the booster device 19 is connected in sequence to a parameter monitoring instrument, a shut-off valve for pre-start sealing check, a shutdown shut-off valve, and a fuel control valve with a drive motor before being connected to the natural gas main pipe 16; the vent valve 4 is connected in parallel to the downstream pipeline of the sealing check shut-off valve; one end of the purge shut-off valve at the compressor outlet is connected to the gas turbine compressor outlet, and the other end is split into two paths, one of which is connected to the vent valve, and the other path is connected to the natural gas main pipe 16 in sequence through the purge gas throttle nozzle and the anti-backflow check valve;

[0063] In the fuel system, the external fuel input passes sequentially through a dual fuel filter 17, an electric fuel booster pump 18, a parameter monitoring instrument, a regulating device 20 with a drive motor, and a main and auxiliary fuel line separator before being connected to the fuel main pipe 21. The dual fuel filter 17 is equipped with a differential pressure alarm and a path switching ball valve. A stop valve and a drain valve are connected in parallel on the fuel main pipe 21. One end of the purge shut-off valve, which draws gas from the natural gas pipeline, is connected to the natural gas system, and the other end passes sequentially through a purge gas throttle nozzle and an anti-backflow check valve to the fuel main pipe 21.

[0064] Clearly define the main fuel passage, purging branch, and parallel connection structure of valves in the natural gas system to ensure reliable natural gas fuel delivery and realize the compressor priming and purging function; the vent valve and vent valve 4 realize pipeline depressurization and depressurization for sealing test.

[0065] Preferably, the shut-off valve includes a first shut-off valve 1 to a fifth shut-off valve 11, the cut-off valve includes a first cut-off valve 2 to a fourth cut-off valve 13, the vent valve includes a first vent valve 5 to a third vent valve 7, the purge shut-off valve includes a first purge shut-off valve to a third purge shut-off valve, and the oil drain valve includes a first oil drain valve 14 and a second oil drain valve 15.

[0066] When switching from fuel oil to natural gas, the following control steps are executed:

[0067] S1. Determine that the high-pressure converted speed of the gas turbine is greater than the threshold C1, and receive the instruction from the host computer to switch to natural gas;

[0068] S2. Detect that the natural gas pipeline pressure has reached the normal value, and control the natural gas electric valve to open to the minimum open position; after waiting for 5 control cycles, connect the first shut-off valve 1, the first cut-off valve 2 and the second cut-off valve 3, and disconnect the venting valve 4, the first venting valve 5, the second venting valve 6, the third venting valve 7, the second shut-off valve 8, the third shut-off valve 9, the fourth shut-off valve 10 and the fifth shut-off valve 11.

[0069] S3. Calculate the target natural gas flow rate corresponding to the current power generation capacity based on the fuel combustion heat before the switchover, and limit the upper limit of the natural gas flow rate to 110% of the target flow rate; the fuel oil decreases in an open loop at a set rate, and the natural gas increases in a closed loop at a set rate;

[0070] S4. When the natural gas flow reaches 95% of the target flow, disconnect the third shut-off valve 12 and the fourth shut-off valve 13, and close the metering valve of the fuel regulating device 20; connect the second and third purge shut-off valves to purge the main and auxiliary fuel lines, the fuel main pipe 21 and the nozzles, and disconnect the power supply of the electric fuel booster pump 18 motor to complete the switch from fuel to natural gas.

[0071] When switching from fuel oil to natural gas, the speed condition is first judged and the gas source pressure is verified. Then, the valve opening and closing, fuel addition and reduction, pipeline purging and pump shutdown are completed step by step. The timing constraints of the whole set of steps are clear to avoid accidental switching. After the switching is completed, the idle fuel pipeline is purged in time to prevent fuel residue from coking and to protect the fuel nozzle and pipeline.

[0072] Preferably, when switching from natural gas to fuel oil, the following control steps are performed:

[0073] S1. Determine that the high-pressure converted speed of the gas turbine is greater than the threshold C1, and receive the instruction from the host computer to switch to fuel oil.

[0074] S2. When the electric fuel booster pump 18 is powered on, the fuel regulating device 20 metering valve is set to the minimum position; the fuel line pressure is checked and it reaches the normal value. After waiting for 5 control cycles, the third shut-off valve 12 and the fourth shut-off valve 13 are connected, and the first drain valve 14 and the second drain valve 15 are disconnected; if the second purge valve and the third purge valve are in the connected state, they are disconnected.

[0075] S3. Based on the current natural gas combustion heat, calculate the target fuel flow rate corresponding to the current power generation capacity, and limit the upper limit of the fuel flow rate to 110% of the target flow rate; natural gas decreases in an open loop at a set rate, and fuel increases in a closed loop at a set rate;

[0076] S4. When the fuel flow reaches 95% of the target flow, disconnect the first shut-off valve 1, the first cut-off valve 2 and the second cut-off valve 3, and close the natural gas fuel electric valve; connect the vent valve 4 and the first vent valve 5; connect the fourth shut-off valve 10 and the fifth shut-off valve 11, disconnect the second vent valve 6 and the third vent valve 7, purge the natural gas main pipe 16 and the nozzle, and stop the natural gas booster device 19 from working, thus completing the switch from natural gas to fuel oil.

[0077] Clearly define the complete control sequence for switching from natural gas to fuel oil. First, verify the speed conditions, start the fuel booster pump in advance, and perform the fuel switch after completing the pressure verification to avoid fuel shortage faults. Before switching, close the fuel side purging circuit to prevent purging gas from interfering with the fuel supply.

[0078] A second aspect of this application provides a dual-fuel control method for a gas turbine, comprising:

[0079] During the low- and medium-operating-condition liquid fuel combustion stage of the gas turbine, the compressor outlet gas is taken and purged through the throttle nozzle to purge the idle natural gas main 16 and nozzles.

[0080] During the high-performance phase of the gas turbine when burning natural gas, a portion of natural gas is drawn from the natural gas fuel outlet valve and fed into the main and auxiliary fuel oil circuits through the throttle nozzle to purge the idle fuel oil main pipe 21 and nozzles.

[0081] When switching fuels, isothermal control is used. The open-loop flow rate of fuel is reduced and the closed-loop flow rate of fuel is increased. The upper limit of the fuel flow rate to be increased is set to 110% of the target flow rate. When the increased fuel flow rate reaches 95% of the target flow rate, the supply of raw fuel is cut off.

[0082] By using differentiated purging methods based on different operating conditions, the system can effectively purge 16 nozzles in the idle natural gas main and 21 nozzles in the idle fuel oil main, without the need to add complex purging gas source equipment, thus reducing system costs.

[0083] An isothermal switching control method is adopted, with flow limit protection and switching termination conditions set. Reduced open-loop and incremental closed-loop coordinated control is used to maintain thermal stability during the switching process, reduce power fluctuations, improve the control stability of dual-fuel switching, and reduce the risk of abnormal combustion.

[0084] Preferably, switching from fuel oil to natural gas includes:

[0085] After determining that the high-pressure conversion speed is greater than C1 and confirming that the natural gas pipeline pressure is normal, set the natural gas electric valve to the minimum opening degree; after the valve state switch is completed, calculate the target natural gas flow rate based on the fuel heat before the switch; the fuel open-loop decrease and the natural gas closed-loop increase; after the natural gas flow rate reaches 95% of the target flow rate, cut off the fuel supply, start the fuel pipeline purging, and stop the electric fuel booster pump 18.

[0086] The complete control process for switching from fuel oil to natural gas is defined, and pre-verification conditions for speed and gas source pressure are added. The valve timing, flow control, purging, and pump shutdown steps are coordinated to ensure that the process of switching from fuel oil to natural gas is carried out in an orderly and safe manner, and to prevent flameout and coking of residual fuel oil in the pipeline during the switching process.

[0087] Preferably, switching from natural gas to fuel oil includes:

[0088] If the high-pressure conversion speed is greater than C1, power on the electric fuel booster pump 18, confirm that the fuel line pressure is normal, and close the fuel line purging circuit; calculate the target fuel flow rate based on the current natural gas heat; reduce the natural gas flow rate in the open loop and increase the fuel flow rate in the closed loop; cut off the natural gas flow rate after the fuel flow rate reaches 95% of the target flow rate, start the natural gas line purging, and stop the natural gas booster device 19.

[0089] The complete control process for switching from natural gas to fuel oil is defined. Before switching, the fuel pump is started and pressure is checked, and the fuel side purging circuit is closed to avoid interfering with the fuel supply. After switching, the natural gas pipeline is purged and the booster device 19 is shut down to ensure stable operation during the natural gas to fuel oil switching process and eliminate safety hazards caused by residual gas in the pipeline.

[0090] In summary, this application has the following advantages:

[0091] The electric fuel booster pump, driven by an independent motor, can be directly shut down when the gas turbine is running on natural gas. This eliminates the need for the traditional booster pump structure driven by the gas turbine rotor and continuously operating during unit operation, reducing ineffective pump losses. The fuel regulating mechanism uses a metering valve directly driven by a limited-angle torque motor, replacing the electro-hydraulic servo valve which is prone to jamming due to fuel contamination. This significantly improves resistance to fuel contamination, making it suitable for offshore platform applications where fuel quality is difficult to guarantee, and reducing the probability of control failures.

[0092] The upstream fuel line is equipped with a dual oil filter, along with a differential pressure alarm and a flow switching ball valve, enabling online filter element replacement without shutting down the turbine. Given the harsh sea conditions and challenging replenishment and maintenance on offshore platforms, this design allows for filter element maintenance without unit shutdown, effectively reducing unplanned downtime and improving the overall availability of the gas turbine. Pressure and temperature monitoring points are installed on the natural gas main pipeline to monitor the purge gas status and the risk of hot gas backflow in real time, facilitating early fault identification.

[0093] An adaptive purging gas scheme based on operating conditions is adopted: when fuel oil is used in low and medium operating conditions, the low-temperature gas from the compressor outlet is used to purge idle natural gas pipelines; when natural gas is used in medium and high operating conditions, natural gas is directly extracted as the purging gas source to purge fuel oil pipelines. This eliminates the need for high-power compressors, coolers, and supporting power supply equipment, and also avoids reliance on nitrogen cylinders that can only be used for short periods. It reduces equipment space requirements, lowers hardware costs, eliminates pressure loss and potential media leakage risks caused by cooling circuits, and the purging system has a simple structure and good maintainability.

[0094] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A dual-fuel gas turbine system, characterized in that, Including natural gas systems and fuel oil systems; The natural gas system includes a booster (19), parameter monitoring instruments, a shut-off valve and a vent valve (4) for pre-start sealing checks, a shutdown valve, a vent valve, a fuel control valve with a drive motor, a purge shut-off valve at the compressor outlet, a vent valve, a backflow prevention check valve, a natural gas main (16), and a purge gas throttle nozzle. The fuel system includes a dual oil filter (17), a differential pressure alarm, a ball valve, an electric fuel booster pump (18), a parameter monitoring instrument, an adjustment device (20) with a drive motor, a main and auxiliary oil circuit separator, a stop valve, a drain valve, a purge stop valve that draws gas from the natural gas pipeline, a backflow prevention check valve, a fuel main pipe (21), and a purge gas throttle nozzle. The electric fuel booster pump (18) is driven independently by a motor and can be shut down by controlled power-off when the gas turbine switches to gaseous fuel; the fuel system regulating device (20) adopts a metering valve driven by a motor with limited rotation angle torque; The dual-fuel system is configured with a working condition-specific purging control logic: when the gas turbine is in a medium-low working condition and burning liquid fuel, the low-temperature gas from the compressor outlet is used to purge the idle natural gas main (16) and nozzles after passing through the throttle nozzle; When the gas turbine is operating under medium to high conditions and burning natural gas, a portion of natural gas is drawn from the natural gas fuel outlet valve and fed into the main and auxiliary fuel lines through the throttle nozzle to purge the idle fuel main pipe (21) and nozzles.

2. The gas turbine dual-fuel system as described in claim 1, characterized in that, The gas turbine dual-fuel system is also equipped with dual-fuel switching control logic. The switching process uses isothermal control and satisfies the following relationship: ,in For fuel flow rate, This refers to the calorific value of fuel oil. For natural gas flow rate, The calorific value of natural gas; During fuel switching, the fuel to be reduced is controlled by open-loop rate control, and the fuel to be increased is controlled by closed-loop rate control. The upper limit of the fuel flow to be increased is set to 110% of the target flow. When the fuel flow to be increased reaches 95% of the target flow, the original fuel supply is cut off.

3. The gas turbine dual-fuel system as described in claim 1, characterized in that, The dual oil filter (17) is installed on the pipeline in front of the electric fuel booster pump (18). The dual oil filter (17) is equipped with a differential pressure alarm and a ball valve for switching the circuit, which can realize online replacement of the filter element without stopping the machine. Pressure and temperature measuring points are also installed on the natural gas main pipe (16) to monitor the purge gas parameters and the hot gas return status.

4. The gas turbine dual-fuel system as described in claim 1, characterized in that, In the natural gas system, the output end of the booster device (19) is connected in sequence to the parameter monitoring instrument, the shut-off valve for pre-start sealing check, the shutdown valve, and the fuel control valve with drive motor, and then connected to the natural gas main pipe (16); the vent valve (4) is connected in parallel to the pipeline downstream of the sealing check shut-off valve; one end of the purge shut-off valve at the compressor outlet is connected to the gas turbine compressor outlet, and the other end is divided into two paths, one of which is connected to the vent valve, and the other path is connected to the natural gas main pipe (16) in sequence through the purge gas throttle nozzle and the anti-backflow check valve; In the fuel system, the external fuel input passes through a dual oil filter (17), an electric fuel booster pump (18), a parameter monitoring instrument, an adjustment device (20) with a drive motor, and a main and auxiliary oil circuit separator before being connected to the fuel main pipe (21). The dual oil filter (17) is equipped with a differential pressure alarm and a path switching ball valve. The stop valve and the drain valve are connected in parallel on the fuel main pipe (21). The purge valve, which takes gas from the natural gas pipeline, is connected to the natural gas system at one end, and the other end is connected to the fuel main pipe (21) in sequence through a purge gas throttle nozzle and an anti-backflow check valve.

5. The gas turbine dual-fuel system as described in claim 1, characterized in that, The shut-off valve includes a first shut-off valve (1) to a fifth shut-off valve (11), the cut-off valve includes a first cut-off valve (2) to a fourth cut-off valve (13), the vent valve includes a first vent valve (5) to a third vent valve (7), the purge shut-off valve includes a first purge shut-off valve to a third purge shut-off valve, and the oil drain valve includes a first oil drain valve (14) and a second oil drain valve (15). When switching from fuel oil to natural gas, the following control steps are executed: S1. Determine that the high-pressure converted speed of the gas turbine is greater than the threshold C1, and receive the instruction from the host computer to switch to natural gas; S2. When the pressure of the natural gas pipeline reaches the normal value, control the natural gas electric valve to open to the minimum open position; after waiting for 5 control cycles, connect the first shut-off valve (1), the first cut-off valve (2), and the second cut-off valve (3), and disconnect the vent valve (4), the first vent valve (5), the second vent valve (6), the third vent valve (7), the second shut-off valve (8), the third shut-off valve (9), the fourth shut-off valve (10), and the fifth shut-off valve (11). S3. Calculate the target natural gas flow rate corresponding to the current power generation capacity based on the fuel combustion heat before the switchover, and limit the upper limit of the natural gas flow rate to 110% of the target flow rate; the fuel oil decreases in an open loop at a set rate, and the natural gas increases in a closed loop at a set rate; S4. When the natural gas flow reaches 95% of the target flow, disconnect the third shut-off valve (12) and the fourth shut-off valve (13), and close the metering valve of the fuel regulating device (20); connect the second purge shut-off valve and the third purge shut-off valve to purge the main and auxiliary fuel lines, the fuel main pipe (21) and the nozzles, and disconnect the power supply of the electric fuel booster pump (18) motor to complete the switch from fuel to natural gas.

6. The gas turbine dual-fuel system as described in claim 1, characterized in that, When switching from natural gas to fuel oil, the following control steps are executed: S1. Determine that the high-pressure converted speed of the gas turbine is greater than the threshold C1, and receive the instruction from the host computer to switch to fuel oil. S2. Power on the electric fuel booster pump (18) motor and set the fuel regulating device (20) metering valve to the minimum position; check that the fuel line pressure reaches the normal value, wait for 5 control cycles and then connect the third shut-off valve (12) and the fourth shut-off valve (13), and disconnect the first drain valve (14) and the second drain valve (15); if the second purge shut-off valve and the third purge shut-off valve are in the connected state, disconnect them; S3. Based on the current natural gas combustion heat, calculate the target fuel flow rate corresponding to the current power generation capacity, and limit the upper limit of the fuel flow rate to 110% of the target flow rate; natural gas decreases in an open loop at a set rate, and fuel increases in a closed loop at a set rate; S4. When the fuel flow reaches 95% of the target flow, disconnect the first shut-off valve (1), the first cut-off valve (2), and the second cut-off valve (3), and close the natural gas fuel electric valve; connect the vent valve (4) and the first vent valve (5); connect the fourth shut-off valve (10) and the fifth shut-off valve (11), disconnect the second vent valve (6) and the third vent valve (7), purge the natural gas main pipe (16) and the nozzle, and stop the natural gas booster device (19) from working, thus completing the switch from natural gas to fuel oil.

7. A dual-fuel control method for a gas turbine, employing the dual-fuel gas turbine system as described in any one of claims 16, characterized in that, include: During the low- and medium-operating-condition liquid fuel combustion stage of the gas turbine, the compressor outlet gas is taken and purged through the throttle nozzle to purge the idle natural gas main (16) and nozzles. During the high-performance phase of the gas turbine, when natural gas is used, a portion of natural gas is drawn from the natural gas fuel outlet valve and fed into the main and auxiliary fuel oil circuits through the throttle nozzle to purge the idle fuel main pipe (21) and nozzles. When switching fuels, isothermal control is used. The open-loop flow rate of fuel is reduced and the closed-loop flow rate of fuel is increased. The upper limit of the fuel flow rate to be increased is set to 110% of the target flow rate. When the increased fuel flow rate reaches 95% of the target flow rate, the supply of raw fuel is cut off.

8. The gas turbine dual-fuel control method as described in claim 7, characterized in that, Switching from fuel oil to natural gas includes: After determining that the high pressure conversion speed is greater than C1 and confirming that the natural gas pipeline pressure is normal, set the natural gas electric valve to the minimum opening degree; after the valve state is switched, calculate the target flow rate of natural gas based on the fuel heat before switching; the fuel open-loop decrease and the natural gas closed-loop increase; after the natural gas flow rate reaches 95% of the target flow rate, cut off the fuel, start the fuel pipeline purging, and stop the electric fuel booster pump (18).

9. The gas turbine dual-fuel control method as described in claim 7, characterized in that, Switching from natural gas to fuel oil includes: If the high pressure conversion speed is greater than C1, the electric fuel booster pump (18) is powered on, the fuel line pressure is confirmed to be normal, and the fuel line purging circuit is closed. The target fuel flow rate is calculated based on the current natural gas heat. The natural gas flow rate decreases in the open loop and the fuel flow rate increases in the closed loop. After the fuel flow rate reaches 95% of the target flow rate, the natural gas is cut off, the natural gas line purging is started, and the natural gas booster device (19) is stopped.

Images