Safe purging method for methanol fuel supply system of marine boiler

Abstract

The invention relates to the technical field of fuel system purging, and discloses a specific process and system structure of a safe purging method for a marine boiler methanol fuel supply system.The specific process includes the steps that a nitrogen and purified water flushing device is arranged, after the device shuts down, a pipeline is flushed through purified water, and the flushing water amount is four times of the total volume of the pipeline; it is ensured that methanol in the pipeline is washed clean, and the residual concentration is within a safe range; after clean water flushing is completed, the Npurging mode is switched to, water in the pipeline is purged cleanly, a very small part of residual liquid is diluted residual liquid, the concentration is very low, the human body cannot be injured, and the explosion risk cannot be caused; the purified water used for operation comes from steam generated by the boiler, after the boiler runs to generate steam, the steam is condensed into water through the cooler, purified water is obtained, the part of purified water is stored for pipeline flushing, the stored purified water can be replaced regularly, impurities are prevented from entering the purified water, and the problem that the pipeline is corroded due to the fact that the purified water containing the impurities enters the pipeline for flushing is solved.

Description

Technical Field

[0001] The invention relates to the field of fuel system cleaning, and in particular to a safe cleaning method for a methanol fuel supply system of a marine boiler. Background Art

[0002] Methanol, a hazardous fuel, is toxic, has a low boiling point, is highly volatile, and is flammable. Its vapor can form explosive mixtures with air and is miscible with most organic compounds, including water, alcohols, and ether. Methanol metabolized by the human body produces formaldehyde and formic acid, which can be harmful. Common symptoms of poisoning include headaches, nausea, vomiting, and blurred vision, while severe cases can lead to blindness or even death. The lethal dose of methanol is approximately 70 ml. Given these risks, addressing residual methanol in pipelines is crucial to ensuring its safe use.

[0003] Patent application publication number CN116816562A discloses a marine methanol fuel supply system, comprising a methanol supply module, a nitrogen purge / degassing module, a constant temperature medium supply module, and a discharge module. The methanol supply module includes a first methanol remote control valve connected in series with the methanol daily tank, a methanol filter, a first methanol normally open ball valve, a methanol booster pump, a second methanol normally open ball valve, a methanol check valve, a first methanol shut-off valve, a methanol flowmeter, a second methanol shut-off valve, a methanol thermostat, a fourth methanol shut-off valve, a double-blocking double-drain valve, and a second methanol remote control valve. The nitrogen purge / degassing module includes a methanol pipeline purge line, a methanol thermostat purge line, and a double-blocking double-drain valve purge line.

[0004] The prior art purge system cannot effectively and thoroughly purge the methanol pipeline, and its safety needs to be improved.

[0005] Therefore, a new technical solution is needed to solve the above technical problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a safe purge method for the methanol fuel supply system of a marine boiler, which uses pure water to flush the pipeline and then uses nitrogen to purge the residue after completion, so as to achieve a thorough purge of the methanol pipeline. The distilled water generated by the operation of the boiler itself is used, which is easy to obtain and has a low cost.

[0007] The technical solution adopted in the present invention is: A safe purge method for a methanol fuel supply system of a marine boiler comprises the following steps: Step 1: Prepare pure water: The pure water used for methanol pipeline purging comes from the steam generated by the boiler itself: After the boiler is running to generate steam, open the first manual shut-off valve, and the steam enters the steam cooler through pipe 1. The steam is condensed into pure water by external cooling water in the internal pipe of the steam cooler; the pure water enters the water storage tank through pipe 2. The water storage tank is equipped with a liquid level transmitter. When the water in the water storage tank reaches the maximum liquid level at the set height, the first manual shut-off valve is closed, completing the preparation of pure water; Step 2: Methanol pipeline water flushing: Before pipeline flushing, first open the fourth pneumatic shut-off valve, the sixth pneumatic shut-off valve, the seventh pneumatic shut-off valve, the eighth pneumatic shut-off valve, the tenth pneumatic shut-off valve, and the eleventh pneumatic shut-off valve, open the flow control valve to the maximum opening, keep the third pneumatic shut-off valve, the thirty-fifth pneumatic shut-off valve, and the ninth pneumatic shut-off valve closed, connect pipeline 8 to the purge waste liquid tank, release the pressure, and confirm that there is no pressure in the methanol pipeline through the pressure transmitter before proceeding with the pipeline flushing process; Step 3: After confirming that there is no pressure in the methanol pipeline, open the second manual shut-off valve to allow nitrogen to enter pipeline three. Adjust the pressure to the set value through the first pressure control valve. At the same time, check whether the nitrogen pressure meets the requirements through the pressure switch to ensure that the nitrogen has sufficient pressure to push the water into the pipeline. Nitrogen enters pipeline four. The first check valve is installed on the pipeline to prevent the methanol solution from flowing back into the nitrogen. Step 4: Nitrogen passes through the first three-way switching valve, controlling the nitrogen to enter pipe five, and then enters the top of the water storage tank. Purified water enters pipe six under the action of nitrogen pressure, and then passes through the second three-way switching valve, controlling the purified water to enter pipe seven. A second check valve is also installed on the pipeline to prevent the methanol solution from flowing back into the nitrogen or water. Step 5: Close the eleventh pneumatic shut-off valve, open the third pneumatic shut-off valve, and flush pipes eight and nine with pure water. When the liquid level in the water tank drops to the set value, it proves that there is enough water to flush pipes eight and nine (the total flushing water volume is generally 4 times the total volume of the flushed pipes). Then close the fourth pneumatic shut-off valve, open the eleventh pneumatic shut-off valve, and flush pipe ten. When the liquid level in the water tank drops to the set value, it proves that there is enough water to flush pipe ten. Step 6: After all methanol pipelines are flushed with water, switch the first three-way conversion valve to control nitrogen to enter pipeline 11, switch the second three-way conversion valve to control nitrogen to enter pipeline 7, and purge pipeline 10 with nitrogen. Maintain a certain purge time to ensure that sufficient nitrogen is purged through the pipeline (the total purge nitrogen volume is generally 30 times the total volume of the purged pipeline). Then close the eleventh pneumatic shut-off valve and open the fourth pneumatic shut-off valve to purge pipelines 8 and 9 with nitrogen. Maintain a certain purge time to ensure that sufficient nitrogen is flushed through the pipeline. Step 7: After completing the above flushing and purging, close the second manual shut-off valve, wait for 30 seconds, then close the third pneumatic shut-off valve, the sixth pneumatic shut-off valve, the seventh pneumatic shut-off valve, and the eighth pneumatic shut-off valve, close the flow control valve to the minimum opening, open the eleventh pneumatic shut-off valve, keep the fourth pneumatic shut-off valve and the tenth pneumatic shut-off valve open, check the pressure transmitter to confirm that there is no pressure in the methanol pipeline, check the pressure switch to confirm that there is no pressure in the nitrogen pipeline, and after confirming that all pipelines are pressure-free, you can open the pipeline for maintenance operations.

[0008] By adopting the above process, pure water is used to flush the pipeline, and then N2 is used to purge the residue after completion, so as to achieve a thorough purge of the methanol pipeline. The distilled water generated by the operation of the boiler itself is used, which is easy to obtain and has a low cost.

[0009] Preferably, the system used for purging includes a pure water preparation system, a methanol pipeline system, and a nitrogen purging system. The inlet of the pure water preparation system is the boiler steam inlet, which is connected to the steam cooler and the water tank in sequence. There is pipe one between the boiler steam inlet and the steam cooler, and a first manual shut-off valve is installed on pipe one. There is pipe two between the steam cooler and the water tank, and the water tank is connected to the second three-way conversion valve through pipe six. A liquid level transmitter is provided on the water tank.

[0010] By adopting the above structure, pure water is prepared for purging the methanol pipeline, thereby preventing the corrosion of the pipeline caused by the reaction between impurities in the water and methanol.

[0011] Preferably, the methanol pipeline in the methanol pipeline system is pipeline eight, and the inlet of pipeline eight is the methanol inlet. The ninth pneumatic shut-off valve, the eighth pneumatic shut-off valve, the seventh pneumatic shut-off valve, the sixth pneumatic shut-off valve, and the thirty-fifth pneumatic shut-off valve are sequentially provided on pipeline eight from the methanol inlet. The ninth pneumatic shut-off valve and the eighth pneumatic shut-off valve are connected to the purge waste liquid tank through pipeline nine. The tenth pneumatic shut-off valve is provided on pipeline nine. The sixth pneumatic shut-off valve and the thirty-fifth pneumatic shut-off valve are connected to the second three-way conversion valve through pipeline seven. The purge waste liquid tank is connected to pipeline seven through pipeline ten.

[0012] Preferably, a pressure transmitter is provided between the sixth pneumatic shut-off valve and the thirty-fifth pneumatic shut-off valve, and a flow control valve is provided between the seventh pneumatic shut-off valve and the sixth pneumatic shut-off valve.

[0013] Preferably, pipeline seven is provided with a fourth pneumatic shut-off valve, a third pneumatic shut-off valve, and a second check valve, and the fourth pneumatic shut-off valve and the third pneumatic shut-off valve are connected to pipeline ten.

[0014] By adopting the above structure and coordinating the valves between the pipelines, the pipeline can be preliminarily purged of waste liquid, and the pressure in the methanol pipeline can be confirmed before flushing the pipeline to avoid excessive pressure in the methanol pipeline, which may cause the methanol solution to flow back and cause danger.

[0015] Preferably, the nitrogen purging system includes pipeline three, pipeline four, pipeline five, and pipeline eleven. The inlet of pipeline three is the nitrogen inlet. A second manual shut-off valve, a first pressure control valve, and a pressure switch are provided on pipeline three in sequence from the nitrogen inlet. Pipeline three is connected to the pipe body of pipeline four. Pipeline four is connected to the first three-way conversion valve. The first three-way conversion valve is connected to the water tank and the second three-way conversion valve through pipeline five and pipeline eleven respectively.

[0016] Preferably, a first check valve is provided on pipeline four.

[0017] By adopting the above structure, nitrogen purge is added to blow out the water in the pipeline. At this time, even if there is residue caused by factors such as pipeline layout or equipment structure, it will not cause harm to the operator.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The process of the present invention uses pure water to flush the pipeline, and then uses N2 to purge the residue after completion, so as to achieve a thorough purge of the methanol pipeline. The distilled water generated by the operation of the boiler itself is easily available and has a low cost.

[0019] 2. After the water flushing is completed, the device of the present invention can switch to the N2 purge mode to purge the water in the pipeline. A very small amount of residual liquid is diluted, and the concentration is extremely low. It will not cause harm to the human body and will not cause the risk of explosion.

[0020] 3. The pure water for flushing the device of the present invention comes from the steam generated by the boiler itself. After the boiler is running and producing steam, the steam is condensed into water through a cooler to obtain pure water. This part of the pure water is stored for use in pipeline flushing, which saves costs and is convenient to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the system of the present invention; Figure 2 Schematic diagram of the structure of the nitrogen purge system of the present invention; Figure 3 Schematic diagram of the structure of the pure water preparation system of the present invention.

[0022] Among them: 1. First manual shut-off valve; 2. Second manual shut-off valve; 3. First pressure control valve; 4. First check valve; 5. First three-way conversion valve; 6. Second three-way conversion valve; 7. Second check valve; 8. Third pneumatic shut-off valve; 9. Fourth pneumatic shut-off valve; 10. Third and fifth pneumatic shut-off valves; 11. Sixth pneumatic shut-off valve; 12. Flow control valve; 13. Seventh pneumatic shut-off valve; 14. Eighth pneumatic shut-off valve; 15. Ninth pneumatic shut-off valve; 16. Tenth pneumatic shut-off valve; 17. Eleventh pneumatic shut-off valve; 18. Liquid level transmitter; 19. Pressure switch; 20. Pressure transmitter; 21. Steam cooler; 22. Water storage tank; 23. Purge waste liquid tank; 24. Pipeline 1; 25. Pipeline 2; 26. Pipeline 3; 27. Pipeline 4; 28. Pipeline 5; 29. ​​Pipeline 6; 30. Pipeline 7; 31. Pipeline 8; 32. Pipeline 9; 33. Pipeline 10; 34. Pipeline 11; 35. Methanol inlet; 36. Nitrogen inlet; 37. Boiler steam inlet. DETAILED DESCRIPTION

[0023] like Figure 1-3 As shown, a safe purge method for a methanol fuel supply system for a marine boiler comprises the following steps: Step 1: Prepare pure water: The pure water used for methanol pipeline purging comes from the steam generated by the boiler itself: After the boiler is running to generate steam, the first manual shut-off valve 1 is opened, and the steam enters the steam cooler 21 through the pipe 1 24. The steam is condensed into pure water by the external cooling water in the internal pipe of the steam cooler 21; the pure water enters the water storage tank 22 through the pipe 2 25. The water storage tank 22 is equipped with a liquid level transmitter 18. When the water tank in the water storage tank 22 reaches the maximum liquid level at the set height, the first manual shut-off valve 1 is closed, completing the preparation of pure water; Step 2: Methanol pipeline water flushing: Before pipeline flushing, first open the fourth pneumatic shut-off valve 9, the sixth pneumatic shut-off valve 11, the seventh pneumatic shut-off valve 13, the eighth pneumatic shut-off valve 14, the tenth pneumatic shut-off valve 16, and the eleventh pneumatic shut-off valve 17, open the flow control valve 12 to the maximum opening, keep the third pneumatic shut-off valve 8, the thirty-fifth pneumatic shut-off valve 10, and the ninth pneumatic shut-off valve 15 closed, connect the methanol pipeline pipe 8 31 to the purge waste liquid tank 23 to release the pressure, and confirm through the pressure transmitter 20 that there is no pressure in the methanol pipeline before proceeding with the pipeline flushing process to avoid excessive pressure in the methanol pipeline, which may cause the methanol solution to flow back and cause danger; Step 3: After confirming that there is no pressure in the methanol pipeline, open the second manual shut-off valve 2 to allow nitrogen to enter the third pipeline 26. The pressure is adjusted to the set value through the first pressure control valve 3. At the same time, check whether the nitrogen pressure meets the requirements through the pressure switch 19 to ensure that the nitrogen has sufficient pressure to push the water into the pipeline. The nitrogen enters the fourth pipeline 27. A first check valve 4 is set on the pipeline to prevent the methanol solution from flowing back into the nitrogen. Step 4: Nitrogen passes through the first three-way switching valve 5, controlling the nitrogen to enter the fifth pipe 28, and then enters the top of the water storage tank 22. Purified water enters the sixth pipe 29 under the action of nitrogen pressure, and then passes through the second three-way switching valve 6, controlling the purified water to enter the seventh pipe 30. A second check valve 7 is also provided on the pipe to prevent the methanol solution from flowing back into the nitrogen or water. Step 5: Close the eleventh pneumatic shut-off valve 17, open the third pneumatic shut-off valve 8, and flush the eighth and ninth pipes 31 and 32 with pure water. The liquid level in the water storage tank 22 drops to the set value (intermediate level), proving that there is sufficient water to flush the eighth and ninth pipes 31 and 32 (the total flushing water volume is generally four times the total volume of the flushed pipes). Then, close the fourth pneumatic shut-off valve 9, open the eleventh pneumatic shut-off valve 17, and flush the tenth pipe 33. The liquid level in the water storage tank 22 drops to the set value (minimum level), proving that there is sufficient water to flush the tenth pipe 33. Step 6: After all methanol pipelines are flushed with water, switch the first three-way switching valve 5 to control nitrogen to enter the eleventh pipeline 34. Switch the second three-way switching valve 6 to control nitrogen to enter the seventh pipeline 30. Pipeline ten 33 is purged with nitrogen for a certain time to ensure that sufficient nitrogen is purged through the pipeline (the total purging nitrogen volume is generally 30 times the total volume of the purged pipeline). Then, close the eleventh pneumatic shut-off valve 17 and open the fourth pneumatic shut-off valve 9 to purge pipeline eight 31 and pipeline nine 32 with nitrogen. Maintain the purge time to ensure that sufficient nitrogen is flushed through the pipeline. Step 7: After completing the above flushing and purging, close the second manual shut-off valve 2, wait for 30 seconds, then close the third pneumatic shut-off valve 8, the sixth pneumatic shut-off valve 11, the seventh pneumatic shut-off valve 13, and the eighth pneumatic shut-off valve 14, close the flow control valve 12 to the minimum opening, open the eleventh pneumatic shut-off valve 17, keep the fourth pneumatic shut-off valve 9 and the tenth pneumatic shut-off valve 16 open, check the pressure transmitter 20, confirm that there is no pressure in the methanol pipeline, check the pressure switch 19, confirm that there is no pressure in the nitrogen pipeline, and after confirming that all pipelines are pressure-free, the pipeline can be opened for maintenance operations.

[0024] The systems used for purging include a pure water preparation system, a methanol pipeline system, and a nitrogen purging system. The inlet of the pure water preparation system is the boiler steam inlet 37, which is connected to the steam cooler 21 and the water tank 22 in sequence. There is a pipeline 1 24 between the boiler steam inlet 37 and the steam cooler 21, and a first manual shut-off valve 1 is installed on the pipeline 1 24. There is a pipeline 25 between the steam cooler 21 and the water tank 22. The water tank 22 is connected to the second three-way conversion valve 6 through the pipeline 6 29, and a liquid level transmitter 18 is provided on the water tank 22.

[0025] The methanol pipeline in the methanol pipeline system is pipeline 8 31, and the inlet of pipeline 8 31 is methanol inlet 35. Pipeline 8 31 is provided with, in order from methanol inlet 35, a ninth pneumatic shut-off valve 15, an eighth pneumatic shut-off valve 14, a seventh pneumatic shut-off valve 13, a sixth pneumatic shut-off valve 11, and a thirty-fifth pneumatic shut-off valve 10. Pipeline 9 32 connects the ninth and eighth pneumatic shut-off valves 15 and 14 to a purge waste liquid tank 23. Pipeline 9 32 is provided with a tenth pneumatic shut-off valve 16. Pipeline 7 30 connects the sixth and thirty-fifth pneumatic shut-off valves 11 and 10 to a second three-way switching valve 6. The purge waste liquid tank 23 is connected to pipeline 7 30 via pipeline 10 33. A pressure transmitter 20 is provided between the sixth and thirty-fifth pneumatic shut-off valves 11 and 10, and a flow control valve 12 is provided between the seventh and sixth pneumatic shut-off valves. A fourth pneumatic shut-off valve 9, a third pneumatic shut-off valve 8, and a second check valve 7 are provided on pipeline seven 30. The fourth pneumatic shut-off valve 9 and the third pneumatic shut-off valve 8 are connected to pipeline ten 33.

[0026] The nitrogen purge system includes pipeline 3 26 , pipeline 4 27 , pipeline 5 28 , and pipeline 11 34 . The inlet of pipeline 3 26 is nitrogen inlet 36 . Pipeline 3 26 is provided with a second manual shutoff valve 2 , a first pressure control valve 3 , and a pressure switch 19 in this order, starting from nitrogen inlet 36 . Pipeline 3 26 is connected to the body of pipeline 4 27 , which is connected to a first three-way switching valve 5 . The first three-way switching valve 5 is connected to the water tank 22 and the second three-way switching valve 6 via pipeline 5 28 and pipeline 11 34 , respectively. Pipeline 4 27 is provided with a first check valve 4 .

[0027] The system of the present invention is provided with a nitrogen + pure water flushing device. After the device is shut down, the pipeline is first flushed with pure water. The flushing water volume is 4 times the total volume of the pipeline, ensuring that the methanol in the pipeline is flushed clean and the residual concentration is within a safe range; after the clean water flushing is completed, the mode is switched to N2 purge mode to purge the water in the pipeline clean. A very small amount of residue is diluted residual liquid with an extremely low concentration, which will not cause harm to the human body and will not cause explosion risk; the pure water used in the operation comes from steam generated by the boiler itself. After the boiler is running and producing steam, the steam is condensed into water through a cooler to obtain pure water, which is stored for use in pipeline flushing, saving costs, and the stored pure water can be replaced regularly to prevent impurities from entering it, thereby avoiding the problem of pipeline corrosion due to flushing with pure water containing impurities.

[0028] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by those skilled in the art should be included in the scope of protection determined by the claims of the present invention.

Claims

1. A safe purge method for a methanol fuel supply system of a marine boiler, characterized in that: The following steps are involved: Step 1: Prepare pure water: The pure water used for methanol pipeline purging comes from the steam generated by the boiler itself: After the boiler is running to generate steam, open the first manual shut-off valve, and the steam enters the steam cooler through pipe 1. The steam is condensed into pure water by external cooling water in the internal pipe of the steam cooler; the pure water enters the water storage tank through pipe 2. The water storage tank is equipped with a liquid level transmitter. When the water tank in the water storage tank reaches the highest liquid level of the set height, the first manual shut-off valve is closed to complete the preparation of pure water; Step 2: Methanol pipeline water flushing: Before pipeline flushing, first open the fourth pneumatic shut-off valve, the sixth pneumatic shut-off valve, the seventh pneumatic shut-off valve, the eighth pneumatic shut-off valve, the tenth pneumatic shut-off valve, and the eleventh pneumatic shut-off valve, open the flow control valve to the maximum opening, keep the third pneumatic shut-off valve, the thirty-fifth pneumatic shut-off valve, and the ninth pneumatic shut-off valve closed, connect pipeline eight with the purge waste liquid tank, release the pressure, and confirm that there is no pressure in the methanol pipeline through the pressure transmitter before proceeding with the pipeline flushing process; Step 3: After confirming that there is no pressure in the methanol pipeline, open the second manual shut-off valve to allow nitrogen to enter pipeline three. Adjust the pressure to the set value through the first pressure control valve. At the same time, check whether the nitrogen pressure meets the requirements through the pressure switch to ensure that the nitrogen has sufficient pressure to push the water into the pipeline. Nitrogen enters pipeline four. The first check valve is set on the pipeline to prevent the methanol solution from flowing back into the nitrogen. Step 4: Nitrogen passes through the first three-way conversion valve to control nitrogen to enter pipeline five, and then enter the top of the water storage tank. Purified water enters pipeline six under the pressure of nitrogen. Purified water passes through the second three-way conversion valve to control purified water to enter pipeline seven. A second check valve is also set on the pipeline to prevent methanol solution from flowing back into nitrogen or water. Step 5: Close the eleventh pneumatic shut-off valve, open the third pneumatic shut-off valve, flush the pipe eight and the pipe nine with pure water, and the liquid level of the water storage tank drops to the set value, which proves that there is enough water to flush the pipe eight and the pipe nine, and then close the fourth pneumatic shut-off valve, open the eleventh pneumatic shut-off valve, flush the pipe ten, and the liquid level of the water storage tank drops to the set value, which proves that there is enough water to flush the pipe ten; Step 6: After all methanol pipelines are flushed with water, switch the first three-way conversion valve to control nitrogen to enter pipeline 11, switch the second three-way conversion valve to control nitrogen to enter pipeline 7, purge pipeline 10 with nitrogen, maintain a certain purge time, ensure that there is enough nitrogen to purge the pipeline, then close the eleventh pneumatic shut-off valve, open the fourth pneumatic shut-off valve, purge pipelines 8 and 9 with nitrogen, maintain a certain purge time, ensure that there is enough nitrogen to flush the pipeline; Step 7: After completing the above flushing and purging, close the second manual shut-off valve, wait for 30 seconds, then close the third pneumatic shut-off valve, the sixth pneumatic shut-off valve, the seventh pneumatic shut-off valve, and the eighth pneumatic shut-off valve, close the flow control valve to the minimum opening, open the eleventh pneumatic shut-off valve, keep the fourth pneumatic shut-off valve and the tenth pneumatic shut-off valve open, check the pressure transmitter, confirm that there is no pressure in the methanol pipeline, check the pressure switch, confirm that there is no pressure in the nitrogen pipeline, and after confirming that all pipelines are pressure-free, the pipeline can be opened for maintenance operations.

2. A safe purge method for a marine boiler methanol fuel supply system according to claim 1, characterized in that: The system used for the purge includes a pure water preparation system, a methanol pipeline system, and a nitrogen purge system. The inlet of the pure water preparation system is the boiler steam inlet, which is connected to a steam cooler and a water tank in sequence. A pipeline one is provided between the boiler steam inlet and the steam cooler, and a first manual shut-off valve is installed on the pipeline one. A pipeline two is provided between the steam cooler and the water tank, and the water tank is connected to a second three-way conversion valve via a pipeline six. A liquid level transmitter is provided on the water tank.

3. A safe purge method for a marine boiler methanol fuel supply system according to claim 2, characterized in that: The methanol pipeline in the methanol pipeline system is pipeline eight, and the entrance of pipeline eight is the methanol entrance. The ninth pneumatic shut-off valve, the eighth pneumatic shut-off valve, the seventh pneumatic shut-off valve, the sixth pneumatic shut-off valve, and the thirty-fifth pneumatic shut-off valve are arranged on pipeline eight in sequence from the methanol entrance. The ninth pneumatic shut-off valve and the eighth pneumatic shut-off valve are connected to the purge waste liquid tank via pipeline nine. The tenth pneumatic shut-off valve is arranged on pipeline nine. The sixth pneumatic shut-off valve and the thirty-fifth pneumatic shut-off valve are connected to the second three-way conversion valve via pipeline seven. The purge waste liquid tank is connected to pipeline seven via pipeline ten.

4. A safe purge method for a methanol fuel supply system for a marine boiler according to claim 3, characterized in that: A pressure transmitter is provided between the sixth pneumatic shut-off valve and the thirty-fifth pneumatic shut-off valve, and a flow control valve is provided between the seventh pneumatic shut-off valve and the sixth pneumatic shut-off valve.

5. A safe purge method for a marine boiler methanol fuel supply system according to claim 3, characterized in that: The pipeline seven is provided with a fourth pneumatic shut-off valve, a third pneumatic shut-off valve and a second check valve, and the connection point with the pipeline ten is between the fourth pneumatic shut-off valve and the third pneumatic shut-off valve.

6. A safe purge method for a methanol fuel supply system for a marine boiler according to claim 2, characterized in that: The nitrogen purge system comprises pipeline three, pipeline four, pipeline five and pipeline eleven. The inlet of pipeline three is the nitrogen inlet. The pipeline three is provided with a second manual shut-off valve, a first pressure control valve and a pressure switch in sequence from the nitrogen inlet. The pipeline three is connected with the pipe body of pipeline four. The pipeline four is connected with the first three-way conversion valve. The first three-way conversion valve is connected with the water storage tank and the second three-way conversion valve through pipeline five and pipeline eleven respectively.

7. A safe purge method for a methanol fuel supply system for a marine boiler according to claim 6, characterized in that: The pipeline 4 is provided with a first check valve.

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