Nitrogen purging method for dual-fuel systems of medium-power gas turbines

Abstract

This invention discloses a nitrogen purging method for a dual-fuel system of a medium-power gas turbine, belonging to the field of gas turbine technology. It solves the defect of fluctuations in gas turbine speed and power caused by traditional nitrogen purging in existing technologies. Its main structure includes the following steps: S1: nitrogen purging before start-up; S2: nitrogen purging during fuel switching; S3: nitrogen purging after fuel switching; S4: nitrogen purging during shutdown of gaseous fuel operation. This invention is mainly used in medium-power gas turbines.

Description

Technical Field

[0001] This invention belongs to the field of gas turbine technology, and more specifically, relates to a nitrogen purging method for a dual-fuel system of a medium-power gas turbine. Background Technology

[0002] Nitrogen purging of gas turbines, especially for medium-power dual-fuel gas turbine systems, uses diesel and coke oven gas as fuels. Because coke oven gas has a low calorific value and is difficult to ignite directly, high-calorific-value fuels (diesel or natural gas) must be used for ignition. Since coke oven gas contains over 65% hydrogen by volume, medium-pressure nitrogen must be used as the purging gas source to prevent backfire in the fuel system. The fuel lines, fuel nozzles, and combustion chamber of the gas turbine dual-fuel system are purged before ignition and before and after fuel switching, thereby achieving the goal of safe and stable operation of the gas turbine dual-fuel system.

[0003] After the fuel switching of the current medium-power gas turbine is completed, nitrogen is introduced into the liquid fuel main pipe and coke oven gas is introduced into the liquid fuel auxiliary pipe. However, the residual liquid fuel in the main and auxiliary pipes is transported to the combustion chamber, causing fluctuations in the gas turbine speed and power. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a nitrogen purging method for a medium-power gas turbine dual-fuel system. In order to reduce liquid fuel consumption, lower operating costs, and reduce the gas turbine power during fuel switching, considering that the low-power fuel switching speed and power fluctuation are greater than those of the high-power fuel switching speed and power fluctuation, after the low-power fuel switching is completed, the liquid fuel main pipeline and the liquid fuel auxiliary pipeline are purged separately. First, the liquid fuel main pipeline is purged with a small flow of nitrogen for a period of time. After the liquid fuel main pipeline is purged, the liquid fuel auxiliary pipeline is then purged with a small flow of nitrogen for a period of time.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A nitrogen purging method for a dual-fuel system of a medium-power gas turbine includes the following steps:

[0007] S1: Nitrogen purging before starting the machine;

[0008] S2: Fuel switching and nitrogen purging;

[0009] S3: Nitrogen purging after fuel switching;

[0010] S4: Nitrogen purging during gas fuel operation shutdown.

[0011] Preferably, step S1 includes the following steps:

[0012] Open the following valves in sequence: the first shut-off valve on the nitrogen purging line upstream of the gaseous fuel control valve; the vent valve on the nitrogen vent line upstream of the gaseous fuel control valve; the second shut-off valve on the nitrogen purging line downstream of the gaseous fuel control valve; the third shut-off valve on the nitrogen purging line of the liquid fuel main pipe; and the fourth shut-off valve on the nitrogen purging line of the liquid fuel auxiliary pipe. After the set purging time (approximately 10 seconds) is met, close the first shut-off valve, vent valve, second shut-off valve, third shut-off valve, and fourth shut-off valve in sequence to complete the nitrogen purging before startup. The purpose of the nitrogen purging before startup is to check whether the first shut-off valve, vent valve, second shut-off valve, third shut-off valve, and fourth shut-off valve can open and close normally, and also to achieve the effect of purging the fuel lines.

[0013] Preferably, step S2 includes the following steps:

[0014] S21: Before switching from liquid fuel to gaseous fuel, purge the upstream and downstream gaseous fuel lines with nitrogen.

[0015] The specific operation of step S21 is as follows: First, open the first shut-off valve on the nitrogen purging pipeline upstream of the gas fuel fuel control valve and the vent valve on the nitrogen venting pipeline upstream of the gas fuel fuel control valve. The nitrogen purging supply pipeline purges the upstream pipeline of the gas fuel pipeline through the first shut-off valve, the first orifice plate, and the first check valve. The nitrogen in the upstream pipeline of the gas fuel pipeline is discharged through the vent valve. After the purging is completed according to the set time, close the first shut-off valve and the vent valve. Then, open the second shut-off valve on the nitrogen purging pipeline downstream of the gas fuel fuel control valve. Before the gas fuel is supplied, the gas fuel fuel control valve is in the closed state. The nitrogen purging supply pipeline purges the downstream pipeline of the gas fuel pipeline through the second shut-off valve, the second orifice plate, and the second check valve. The nitrogen in the downstream pipeline of the gas fuel pipeline is discharged through the gas turbine fuel nozzle.

[0016] Preferably, step S3 includes the following steps:

[0017] After the fuel switch is completed, first open the third shut-off valve on the nitrogen purging pipeline of the liquid fuel main pipe. The nitrogen purging supply pipeline purges the liquid fuel main pipe for a period of time through the third shut-off valve, the third orifice plate, and the third check valve. After purging is completed, the third shut-off valve is closed, and coke oven gas is introduced into the liquid fuel main pipe. Then open the fourth shut-off valve on the nitrogen purging pipeline of the liquid fuel auxiliary pipe. The nitrogen purging supply pipeline purges the liquid fuel auxiliary pipe for a period of time through the fourth shut-off valve, the fourth orifice plate, and the fourth check valve. After purging is completed, the fourth shut-off valve is closed, and coke oven gas is introduced into the liquid fuel auxiliary pipe.

[0018] Preferably, step S4 includes the following steps:

[0019] When the gas turbine is shut down while the fuel is gaseous, the following steps are taken: First, open the first shut-off valve on the nitrogen purging line upstream of the gaseous fuel fuel control valve, the vent valve on the nitrogen vent line upstream of the gaseous fuel fuel control valve, the third shut-off valve on the nitrogen purging line of the liquid fuel main pipe, and the fourth shut-off valve on the nitrogen purging line of the liquid fuel auxiliary pipe. This purging process purges the upstream gaseous fuel pipeline, the main liquid fuel pipeline, and the auxiliary liquid fuel pipeline. After the set purging time is met, the first shut-off valve, the vent valve, the third shut-off valve, and the fourth shut-off valve are closed, stopping the purging of the upstream gaseous fuel pipeline, the main liquid fuel pipeline, and the auxiliary liquid fuel pipeline. Then, open the second shut-off valve on the nitrogen purging line downstream of the gaseous fuel fuel control valve and purge the downstream gaseous fuel pipeline according to the set time.

[0020] The flow sequence of nitrogen in the nitrogen purging supply pipeline is as follows: nitrogen passes through the pressure control valve, the inlet nitrogen purging shut-off valve, the Y-type filter, and the check valve in sequence.

[0021] Preferably, the nitrogen purging supply line includes a pressure control valve, an inlet nitrogen purging shut-off valve, a Y-type filter, a pressure safety valve, a check valve, a pressure sensor, and a nitrogen pipeline vent valve connected in sequence. The outlet of the check valve is connected to the first shut-off valve, the second shut-off valve, the third shut-off valve, the fourth shut-off valve, and the nitrogen pipeline vent valve, respectively. The pressure safety valve is installed on the supply line between the Y-type filter and the check valve.

[0022] Preferably, the nitrogen purging line upstream of the gaseous fuel regulating valve includes a first shut-off valve, a first orifice plate, a first differential pressure transmitter, and a first check valve. The first shut-off valve is connected to the first check valve through the first orifice plate, and the first differential pressure transmitter is connected in parallel with the first orifice plate. That is, one end of the first differential pressure transmitter is connected to the air inlet of one end of the first orifice plate, and the other end of the first differential pressure transmitter is connected to the air outlet of the other end of the first orifice plate. The differential pressure transmitter detects the pressure difference between the inlet and outlet on both sides of the first orifice plate.

[0023] Preferably, the nitrogen purging line downstream of the gaseous fuel control valve includes a second shut-off valve, a second orifice plate, a second differential pressure transmitter, and a second check valve. The second shut-off valve is connected to the second check valve through the second orifice plate, and the second differential pressure transmitter is connected in parallel with the second orifice plate. That is, one end of the second differential pressure transmitter is connected to the air inlet of one end of the second orifice plate, and the other end of the second differential pressure transmitter is connected to the air outlet of the other end of the second orifice plate. The differential pressure transmitter detects the pressure difference between the inlet and outlet on both sides of the second orifice plate.

[0024] Preferably, the liquid fuel main nitrogen purging line includes a third shut-off valve, a third orifice plate, a third differential pressure transmitter, and a third check valve. The third shut-off valve is connected to the third check valve through the third orifice plate, and the third differential pressure transmitter is connected in parallel with the third orifice plate. That is, one end of the third differential pressure transmitter is connected to the air inlet of one end of the third orifice plate, and the other end of the third differential pressure transmitter is connected to the air outlet of the other end of the third orifice plate. The differential pressure transmitter detects the pressure difference between the inlet and outlet on both sides of the third orifice plate.

[0025] Preferably, the nitrogen purging line of the liquid fuel auxiliary pipe includes a fourth shut-off valve, a fourth orifice plate, a fourth differential pressure transmitter, and a fourth check valve. The fourth shut-off valve is connected to the fourth check valve through the fourth orifice plate, and the fourth differential pressure transmitter is connected in parallel with the fourth orifice plate. That is, one end of the fourth differential pressure transmitter is connected to the air inlet of one end of the fourth orifice plate, and the other end of the fourth differential pressure transmitter is connected to the air outlet of the other end of the fourth orifice plate. The differential pressure transmitter detects the pressure difference between the inlet and outlet on both sides of the fourth orifice plate.

[0026] Preferably, the nitrogen venting pipeline upstream of the gaseous fuel control valve includes a fifth orifice plate and a venting valve, with the venting valve connected to the gaseous fuel pipeline through the fifth orifice plate.

[0027] Preferably, a gaseous fuel control valve is installed on the gaseous fuel pipeline between the upstream nitrogen vent line and the downstream nitrogen purging line of the gaseous fuel control valve. When gaseous fuel is not supplied, the gaseous fuel control valve is in the closed state, and the gaseous fuel control valve acts as a barrier to the upstream and downstream nitrogen purging of the gaseous fuel control valve. Therefore, the upstream nitrogen purging of the gaseous fuel control valve is discharged through the vent valve, and the downstream nitrogen purging of the gaseous fuel control valve is discharged through the gas turbine fuel nozzle.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. Improve the nitrogen purging according to step S3 to reduce the impact of nitrogen system failure on gas turbine operation. This is reflected in the fact that after fuel switching, nitrogen is no longer used to purge the liquid fuel main pipe for a long time, and both the liquid fuel main pipe and the liquid fuel auxiliary pipe are connected to coke oven gas.

[0030] 2. To reduce the cost of liquid fuel, the fuel switching is set to be performed at low power. However, after the fuel switching, if the residual liquid fuel in the main liquid fuel pipeline and the auxiliary liquid fuel pipeline is simultaneously supplied to the combustion chamber along with the coke oven gas in the gas fuel pipeline, the gas turbine speed and power will fluctuate greatly, resulting in unstable gas turbine operation. The nitrogen purging is improved according to step S3. After the fuel switching is completed at low power, the main liquid fuel pipeline and the auxiliary liquid fuel pipeline are purged separately. First, the main liquid fuel pipeline is purged with a small flow of nitrogen for a period of time. After the main liquid fuel pipeline is purged, the auxiliary liquid fuel pipeline is purged with a small flow of nitrogen for a period of time, which reduces the fluctuation of gas turbine speed and power.

[0031] 3. During the purging process, a suitable orifice plate must be selected to control the nitrogen purging flow rate. If the orifice plate size is too large, the nitrogen flow rate will be too large, resulting in too much fuel being purged into the gas turbine combustion chamber, which will cause fluctuations in the gas turbine speed and power. The first, second, third, and fourth orifice plates are used to limit the nitrogen flow rate required for purging. Differential pressure transmitters are installed on both sides of each orifice plate to monitor the orifice plate flow rate in real time.

[0032] 4. The function of the pressure relief valve is to release pressure from the nitrogen purging supply line when the nitrogen pressure in the nitrogen purging supply line is higher than the set pressure of the pressure relief valve.

[0033] 5. Check valve is used to prevent fuel from entering the nitrogen purging supply line;

[0034] 6. The gas fuel fuel control valve acts as a barrier to the upstream and downstream nitrogen purging of the gas fuel fuel control valve. The upstream nitrogen purging is discharged through the vent valve, and the downstream nitrogen purging is discharged through the gas turbine fuel nozzle. Attached Figure Description

[0035] Figure 1 This is a system schematic diagram of the present invention.

[0036] In the diagram: 1. Pressure control valve; 2. Inlet nitrogen purging shut-off valve; 3. Y-type filter; 4. Pressure safety valve; 5. Check valve; 6. Pressure sensor; 7. First shut-off valve; 8. First orifice plate; 9. First differential pressure transmitter; 10. First check valve; 11. Fifth orifice plate; 12. Vent valve; 13. Second shut-off valve; 14. Second orifice plate; 15. Second differential pressure transmitter; 16. Second check valve; 17. Third shut-off valve; 18. Third orifice plate; 19. Third differential pressure transmitter; 20. Third check valve; 21. Fourth shut-off valve; 22. Fourth orifice plate; 23. Fourth differential pressure transmitter; 24. Fourth check valve; 25. Nitrogen pipeline vent valve; 26. Gaseous fuel control valve; 29. ​​Gaseous fuel pipeline; 30. Liquid fuel main pipeline; 31. Liquid fuel auxiliary pipeline. Detailed Implementation

[0037] The present invention will be further described below through specific embodiments and in conjunction with the accompanying drawings.

[0038] Example 1:

[0039] Medium-power gas turbine dual-fuel systems, especially those involving liquid fuel ignition, have three nozzles: a gas fuel nozzle, a main liquid fuel nozzle, and a secondary liquid fuel nozzle. Because coke oven gas has a low calorific value and a low ignition success rate, liquid fuel is used for ignition. Once the turbine reaches high power, the fuel is switched back to coke oven gas. During the operation of a medium-power gas turbine, nitrogen purging is mainly divided into four stages: nitrogen purging before start-up, nitrogen purging before fuel switching, nitrogen purging after fuel switching, and nitrogen purging during gas fuel shutdown. Specifically, before starting the machine, nitrogen is used to purge one gaseous fuel pipeline 29 and two liquid fuel pipelines; before fuel switching, nitrogen is used to purge the gaseous fuel pipeline 29; after fuel switching, nitrogen is used to purge the main liquid fuel pipeline 30 and the auxiliary liquid fuel pipeline 31 in sequence. After purging, coke oven gas is introduced into the main liquid fuel pipeline 30 and the auxiliary liquid fuel pipeline 31. When the gaseous fuel operation is stopped, nitrogen is used to purge one gaseous fuel pipeline 29 and two liquid fuel pipelines.

[0040] like Figure 1 As shown, a nitrogen purging method for a medium-power gas turbine dual-fuel system includes the following steps:

[0041] S1: Nitrogen purging before starting the machine;

[0042] S2: Fuel switching and nitrogen purging;

[0043] S3: Nitrogen purging after fuel switching;

[0044] S4: Nitrogen purging during gas fuel operation shutdown.

[0045] Example 2:

[0046] A nitrogen purging method for a dual-fuel system of a medium-power gas turbine, wherein the nitrogen purging shut-off valve 2 at the inlet is opened and the nitrogen pipeline vent valve 25 is closed before the gas turbine is started normally;

[0047] Step S1 includes the following steps:

[0048] The first shut-off valve 7 on the upstream nitrogen purging line of the gaseous fuel fuel control valve, the vent valve 12 on the upstream nitrogen vent line of the gaseous fuel fuel control valve, the second shut-off valve 13 on the downstream nitrogen purging line of the gaseous fuel fuel control valve, the third shut-off valve 17 on the main nitrogen purging line of the liquid fuel, and the fourth shut-off valve 21 on the secondary nitrogen purging line of the liquid fuel are opened sequentially. After the set purging time is met, the first shut-off valve 7, the vent valve 12, the second shut-off valve 13, the third shut-off valve 17, and the fourth shut-off valve 21 are then closed sequentially to complete the nitrogen purging before startup. The purpose of the nitrogen purging before startup is to check whether the first shut-off valve 7, the vent valve 12, the second shut-off valve 13, the third shut-off valve 17, and the fourth shut-off valve 21 can open and close normally, and also to achieve the effect of purging the fuel lines.

[0049] Step S2 includes the following steps:

[0050] S21: Before switching from fuel oil to gaseous fuel, purge the upstream and downstream lines of gaseous fuel line 29 with nitrogen.

[0051] The specific operation of step S21 is as follows: First, open the first shut-off valve 7 on the nitrogen purging pipeline upstream of the gas fuel fuel control valve and the vent valve 12 on the nitrogen venting pipeline upstream of the gas fuel fuel control valve. The nitrogen purging supply pipeline purges the upstream pipeline of the gas fuel pipeline 29 through the first shut-off valve 7, the first orifice plate 8, and the first check valve 10. The nitrogen in the upstream pipeline of the gas fuel pipeline 29 is discharged through the vent valve 12. After the purging is completed according to the set time, close the first shut-off valve 7 and the vent valve 12. Then, open the second shut-off valve 13 on the nitrogen purging pipeline downstream of the gas fuel fuel control valve. The nitrogen purging supply pipeline purges the downstream pipeline of the gas fuel pipeline 29 through the second shut-off valve 13, the second orifice plate 14, and the second check valve 16. The nitrogen in the downstream pipeline of the gas fuel pipeline 29 is discharged through the gas turbine fuel nozzle.

[0052] Step S3 includes the following steps:

[0053] After the fuel switch is completed, first open the third shut-off valve 17 on the nitrogen purging pipeline of the liquid fuel main pipe. The nitrogen purging supply pipeline purges the liquid fuel main pipe 30 for a period of time through the third shut-off valve 17, the third orifice plate 18, and the third check valve 20. After purging is completed, the third shut-off valve 17 is closed, and coke oven gas is introduced into the liquid fuel main pipe 30. Then open the fourth shut-off valve 21 on the nitrogen purging pipeline of the liquid fuel auxiliary pipe. The nitrogen purging supply pipeline purges the liquid fuel auxiliary pipe 31 for a period of time through the fourth shut-off valve 21, the fourth orifice plate 22, and the fourth check valve 24. After purging is completed, the fourth shut-off valve 21 is closed, and coke oven gas is introduced into the liquid fuel auxiliary pipe 31.

[0054] Step S4 includes the following steps:

[0055] When the gas turbine is shut down while the fuel is gaseous, the first shut-off valve 7 on the upstream nitrogen purging line of the gaseous fuel fuel control valve, the vent valve 12 on the upstream nitrogen vent line of the gaseous fuel fuel control valve, the third shut-off valve 17 on the main nitrogen purging line of the liquid fuel, and the fourth shut-off valve 21 on the secondary nitrogen purging line of the liquid fuel are opened to purge the upstream pipeline of the gaseous fuel pipeline 29, the main liquid fuel pipeline 30, and the secondary liquid fuel pipeline 31. After the set purging time is met, the first shut-off valve 7, the vent valve 12, the third shut-off valve 17, and the fourth shut-off valve 21 are closed to stop purging the upstream pipeline of the gaseous fuel pipeline 29, the main liquid fuel pipeline 30, and the secondary liquid fuel pipeline 31. Then, the second shut-off valve 13 on the downstream nitrogen purging line of the gaseous fuel fuel control valve is opened to purge the downstream pipeline of the gaseous fuel pipeline 29 for the set time.

[0056] The flow sequence of nitrogen in the nitrogen purging supply pipeline is as follows: nitrogen passes through pressure control valve 1, inlet nitrogen purging shut-off valve 2, Y-type filter 3 and check valve 5 in sequence.

[0057] The nitrogen purging supply line includes a pressure control valve 1, an inlet nitrogen purging shut-off valve 2, a Y-type filter 3, a pressure safety valve 4, a check valve 5, a pressure sensor 6, and a nitrogen pipeline vent valve 25 connected in sequence. The outlet of the check valve 5 is connected to the first shut-off valve 7, the second shut-off valve 13, the third shut-off valve 17, the fourth shut-off valve 21, and the nitrogen pipeline vent valve 25, respectively. The pressure safety valve 4 is located on the supply line between the Y-type filter 3 and the check valve 5.

[0058] Example 3:

[0059] A nitrogen purging method for a dual-fuel system of a medium-power gas turbine includes a nitrogen purging supply pipeline and a nitrogen venting pipeline upstream of a gas fuel fuel control valve. The nitrogen purging supply pipeline is connected to a nitrogen purging pipeline upstream of the gas fuel fuel control valve, a nitrogen purging pipeline downstream of the gas fuel fuel control valve, a nitrogen purging pipeline for the main liquid fuel line, and a nitrogen purging pipeline for the secondary liquid fuel line. The nitrogen purging pipeline upstream of the gas fuel fuel control valve, the nitrogen purging pipeline downstream of the gas fuel fuel control valve, and the nitrogen venting pipeline upstream of the gas fuel fuel control valve are all connected to a gas fuel pipeline 29. The nitrogen purging pipeline for the main liquid fuel line is connected to a main liquid fuel line 30, and the nitrogen purging pipeline for the secondary liquid fuel line is connected to a secondary liquid fuel line 31.

[0060] The upstream nitrogen purging line of the gas fuel control valve includes a first shut-off valve 7, a first orifice plate 8, a first differential pressure transmitter 9, and a first check valve 10. The first shut-off valve 7 is connected to the first check valve 10 through the first orifice plate 8, and the first differential pressure transmitter 9 is connected in parallel with the first orifice plate 8. That is, one end of the first differential pressure transmitter 9 is connected to one end of the air inlet of the first orifice plate 8, and the other end of the first differential pressure transmitter 9 is connected to the other end of the air outlet of the first orifice plate 8. The differential pressure transmitter 9 detects the pressure difference between the inlet and outlet on both sides of the first orifice plate 8.

[0061] The nitrogen purging line downstream of the gas fuel control valve includes a second shut-off valve 13, a second orifice plate 14, a second differential pressure transmitter 15, and a second check valve 16. The second shut-off valve 13 is connected to the second check valve 16 through the second orifice plate 14, and the second differential pressure transmitter 15 is connected in parallel with the second orifice plate 14. That is, one end of the second differential pressure transmitter 15 is connected to the air inlet of one end of the second orifice plate 14, and the other end of the second differential pressure transmitter 15 is connected to the air outlet of the other end of the second orifice plate 14. The differential pressure transmitter 15 detects the pressure difference between the inlet and outlet on both sides of the second orifice plate 14.

[0062] The liquid fuel main nitrogen purging line includes a third shut-off valve 17, a third orifice plate 18, a third differential pressure transmitter 19, and a third check valve 20. The third shut-off valve 17 is connected to the third check valve 20 through the third orifice plate 18, and the third differential pressure transmitter 19 is connected in parallel with the third orifice plate 18. That is, one end of the third differential pressure transmitter 19 is connected to one end of the air inlet of the third orifice plate 18, and the other end of the third differential pressure transmitter 19 is connected to the other end of the air outlet of the third orifice plate 18. The differential pressure transmitter 19 detects the pressure difference between the inlet and outlet on both sides of the third orifice plate 18.

[0063] The nitrogen purging line for the liquid fuel auxiliary pipe includes a fourth shut-off valve 21, a fourth orifice plate 22, a fourth differential pressure transmitter 23, and a fourth check valve 24. The fourth shut-off valve 21 is connected to the fourth check valve 24 through the fourth orifice plate 22, and the fourth differential pressure transmitter 23 is connected in parallel with the fourth orifice plate 22. That is, one end of the fourth differential pressure transmitter 23 is connected to the air inlet of one end of the fourth orifice plate 22, and the other end of the fourth differential pressure transmitter 23 is connected to the air outlet of the other end of the fourth orifice plate 22. The differential pressure transmitter 23 detects the pressure difference between the inlet and outlet on both sides of the fourth orifice plate 22.

[0064] The nitrogen venting line upstream of the gas fuel control valve includes a fifth orifice plate 11 and a venting valve 12. The venting valve 12 is connected to the gas fuel pipeline 29 through the fifth orifice plate 11.

[0065] A gaseous fuel control valve 26 is installed on the gaseous fuel pipeline 29 between the upstream nitrogen vent line and the downstream nitrogen purging line of the gaseous fuel control valve. The gaseous fuel control valve 26 acts as a barrier between the upstream and downstream nitrogen purging processes. The upstream nitrogen purging is discharged through the vent valve 12, and the downstream nitrogen purging is discharged through the gas turbine fuel nozzle. The rest of the process is the same as in Example 1.

[0066] In this embodiment, the first orifice plate 8, the second orifice plate 14, the third orifice plate 18, and the fourth orifice plate 22 are used to limit the nitrogen flow rate required for purging. Differential pressure transmitters are installed on both sides of each orifice plate to monitor the orifice plate flow rate in real time.

[0067] Pressure control valve 1 is used to stabilize the nitrogen purging supply pressure; pressure sensor 6 is used to monitor the supply pressure on the nitrogen purging supply pipeline in real time, and the pressure value is uploaded to the nitrogen purging control system. When the pressure exceeds or falls below the normal nitrogen purging pressure, the inlet nitrogen purging shut-off valve 2 is shut off in time, and the nitrogen pipeline vent valve 25 is opened to protect the nitrogen purging system.

[0068] The function of pressure safety valve 4 is to release pressure from the nitrogen purging supply line when the nitrogen pressure in the nitrogen purging supply line is higher than the set pressure of pressure safety valve 4.

[0069] Check valve 5 is used to prevent fuel from entering the nitrogen purging supply line.

Claims

1. A nitrogen purging method for a dual-fuel system of a medium-power gas turbine, characterized in that: Includes the following steps: S1: Nitrogen purging before starting the machine; S2: Fuel switching and nitrogen purging; S3: Nitrogen purging after fuel switching; S4: Nitrogen purging during gas fuel operation shutdown; Step S2 includes the following steps: S21: Before switching from liquid fuel to gaseous fuel, purge the upstream and downstream lines of the gaseous fuel line (29) with nitrogen. The specific operation of step S21 is as follows: First, open the first shut-off valve (7) on the nitrogen purging pipeline upstream of the gas fuel fuel control valve and the vent valve (12) on the nitrogen venting pipeline upstream of the gas fuel fuel control valve. The nitrogen purging supply pipeline purges the upstream pipeline of the gas fuel pipeline (29) through the first shut-off valve (7), the first orifice plate (8) and the first check valve (10). The nitrogen in the upstream pipeline of the gas fuel pipeline (29) is discharged through the vent valve (12). After the purging is completed according to the set time, Close the first shut-off valve (7) and the vent valve (12); then open the second shut-off valve (13) on the nitrogen purging pipeline downstream of the gas fuel fuel control valve. Before the gas fuel is supplied, the gas fuel fuel control valve (26) is closed. The nitrogen purging supply pipeline purges the downstream pipeline of the gas fuel pipeline (29) through the second shut-off valve (13), the second orifice plate (14), and the second check valve (16). The nitrogen in the downstream pipeline of the gas fuel pipeline (29) is discharged through the gas turbine fuel nozzle. Step S3 includes the following steps: After the fuel switching is completed, the third shut-off valve (17) on the nitrogen purging pipeline of the liquid fuel main pipe is opened first. The nitrogen purging supply pipeline purges the liquid fuel main pipe (30) for a period of time through the third shut-off valve (17), the third orifice plate (18) and the third check valve (20). After the purging is completed, the third shut-off valve (17) is closed and coke oven gas is introduced into the liquid fuel main pipe (30). Then the fourth shut-off valve (21) on the nitrogen purging pipeline of the liquid fuel auxiliary pipe is opened. The nitrogen purging supply pipeline purges the liquid fuel auxiliary pipe (31) for a period of time through the fourth shut-off valve (21), the fourth orifice plate (22) and the fourth check valve (24). After the purging is completed, the fourth shut-off valve (21) is closed and coke oven gas is introduced into the liquid fuel auxiliary pipe (31).

2. The nitrogen purging method for a medium-power gas turbine dual-fuel system according to claim 1, characterized in that: Step S1 includes the following steps: The first shut-off valve (7) on the nitrogen purging pipeline upstream of the gas fuel fuel control valve, the vent valve (12) on the nitrogen venting pipeline upstream of the gas fuel fuel control valve, the second shut-off valve (13) on the nitrogen purging pipeline downstream of the gas fuel fuel control valve, the third shut-off valve (17) on the nitrogen purging pipeline of the liquid fuel main pipe, and the fourth shut-off valve (21) on the nitrogen purging pipeline of the liquid fuel auxiliary pipe are opened in sequence. After the set purging time is met, the first shut-off valve (7), the vent valve (12), the second shut-off valve (13), the third shut-off valve (17), and the fourth shut-off valve (21) are closed in sequence to complete the nitrogen purging before starting the machine.

3. The nitrogen purging method for a medium-power gas turbine dual-fuel system according to claim 2, characterized in that: Step S4 includes the following steps: When the gas turbine is shut down, the first shut-off valve (7) on the nitrogen purging pipeline upstream of the gas fuel fuel control valve, the vent valve (12) on the nitrogen vent pipeline upstream of the gas fuel fuel control valve, the third shut-off valve (17) on the nitrogen purging pipeline of the liquid fuel main pipe, and the fourth shut-off valve (21) on the nitrogen purging pipeline of the liquid fuel auxiliary pipe are opened to purge the upstream pipeline of the gas fuel pipeline (29), the liquid fuel main pipe (30), and the liquid fuel auxiliary pipe (31). After the set purging time is met, the first shut-off valve (7), the vent valve (12), the third shut-off valve (17), and the fourth shut-off valve (21) are closed to stop purging the upstream pipeline of the gas fuel pipeline (29), the liquid fuel main pipe (30), and the liquid fuel auxiliary pipe (31). Then, the second shut-off valve (13) on the nitrogen purging pipeline downstream of the gas fuel fuel control valve is opened to purge the downstream pipeline of the gas fuel pipeline (29) according to the set time. The flow sequence of nitrogen in the nitrogen purging supply pipeline is as follows: nitrogen passes through the pressure control valve (1), the inlet nitrogen purging shut-off valve (2), the Y-type filter (3), and the check valve (5) in sequence.

4. The nitrogen purging method for a medium-power gas turbine dual-fuel system according to any one of claims 1-3, characterized in that: The nitrogen purging supply line includes a pressure control valve (1), an inlet nitrogen purging shut-off valve (2), a Y-type filter (3), a pressure safety valve (4), a check valve (5), a pressure sensor (6), and a nitrogen pipeline vent valve (25) connected in sequence. The outlet of the check valve (5) is connected to the first shut-off valve (7), the second shut-off valve (13), the third shut-off valve (17), the fourth shut-off valve (21), and the nitrogen pipeline vent valve (25), respectively. The pressure safety valve (4) is located on the supply line between the Y-type filter (3) and the check valve (5).

5. The nitrogen purging method for a medium-power gas turbine dual-fuel system according to claim 4, characterized in that: The upstream nitrogen purging pipeline of the gas fuel ignition control valve includes a first shut-off valve (7), a first orifice plate (8), a first differential pressure transmitter (9) and a first check valve (10). The first shut-off valve (7) is connected to the first check valve (10) through the first orifice plate (8), and the first differential pressure transmitter (9) is connected in parallel with the first orifice plate (8).

6. The nitrogen purging method for a medium-power gas turbine dual-fuel system according to claim 5, characterized in that: The nitrogen purging pipeline downstream of the gas fuel ignition control valve includes a second shut-off valve (13), a second orifice plate (14), a second differential pressure transmitter (15), and a second check valve (16). The second shut-off valve (13) is connected to the second check valve (16) through the second orifice plate (14), and the second differential pressure transmitter (15) is connected in parallel with the second orifice plate (14).

7. The nitrogen purging method for a medium-power gas turbine dual-fuel system according to claim 6, characterized in that: The liquid fuel main nitrogen purging pipeline includes a third shut-off valve (17), a third orifice plate (18), a third differential pressure transmitter (19), and a third check valve (20). The third shut-off valve (17) is connected to the third check valve (20) through the third orifice plate (18), and the third differential pressure transmitter (19) is connected in parallel with the third orifice plate (18).

8. The nitrogen purging method for a medium-power gas turbine dual-fuel system according to claim 7, characterized in that: The liquid fuel auxiliary nitrogen purging pipeline includes a fourth shut-off valve (21), a fourth orifice plate (22), a fourth differential pressure transmitter (23), and a fourth check valve (24). The fourth shut-off valve (21) is connected to the fourth check valve (24) through the fourth orifice plate (22), and the fourth differential pressure transmitter (23) is connected in parallel with the fourth orifice plate (22).

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