Liquid nitrogen wash cold energy utilization device

Abstract

The utility model relates to a liquid nitrogen wash cold energy utilization device, which comprises the following steps that: medium-pressure nitrogen is throttled to enter a nitrogen wash tower to prepare liquid nitrogen, low-pressure nitrogen is reduced to-60 DEG C by the liquid nitrogen in a jet mixer, and then enters a liquid nitrogen wash molecular sieve adsorber and a low-temperature methanol wash hydrogen sulfide concentration tower to realize the cooling of a molecular sieve and methanol; and the driving time of low-temperature methanol washing and liquid nitrogen washing is shortened. During normal production, a liquid medium in the nitrogen washing tower is discharged into the liquid collecting tank, the bottom of the liquid collecting tank is communicated with the nitrogen cooler, low-pressure nitrogen enters the nitrogen cooler to be cooled to-60 DEG C and then enters the low-temperature methanol washing hydrogen sulfide concentration tower, the temperature of methanol is reduced, and cold energy recovery is achieved. The device can effectively reduce the start-up time of low-temperature methanol washing and liquid nitrogen washing, improve the utilization efficiency of cold energy, reduce consumption and create economic benefits.

Description

Technical Field

[0001] The utility model relates to a gas purification technology for a coal chemical plant, in particular to a liquid nitrogen washing cold capacity utilization device. Background Art

[0002] When the synthetic ammonia unit is started, the temperature of the molecular sieve washed with liquid nitrogen needs to be reduced from room temperature to below -55°C. In order to prevent the temperature from dropping sharply and damaging the molecular sieve and equipment, the temperature drop needs to be controlled to be less than 15°C / h, and the whole process lasts for 4 hours. After receiving the process gas, the low-temperature methanol washing unit needs to gradually reduce the process gas temperature to -59°C, and the purified gas index can be qualified, which takes 12 hours. During this period, the coal gasification load is 75%, the air separation load is 80%, and a large amount of effective gas process gas and medium-pressure nitrogen are vented, resulting in huge economic losses. During normal production, the low-temperature methanol washing supplements part of the cooling capacity through the ammonia cooler, but the liquid nitrogen washing has excess cooling capacity. The excess cooling capacity is discharged to the liquid collection tank and then volatilized by steam and discharged to the torch, resulting in a waste of cooling capacity. The temperature of the nitrogen entering the low-temperature methanol washing hydrogen sulfide concentration tower is between -60°C and 25°C. The cooling capacity of the liquid collection tank can be used to reduce the nitrogen temperature to -60°C, supplement the cooling capacity for the low-temperature methanol washing, reduce the load of the ammonia cooler, and realize the recycling of cooling capacity. Summary of the invention

[0003] The utility model provides a liquid nitrogen cold washing utilization device, comprising a nitrogen washing tower, wherein the nitrogen washing tower is connected with a liquid collecting tank and a jet mixer; the right end of the jet mixer is connected with a low-pressure nitrogen main pipe through a low-pressure nitrogen flow regulating valve, and the left end is connected with a gas-liquid separation tank; the gas-liquid separation tank is connected with a molecular sieve adsorber above, and the liquid collecting tank below; the molecular sieve adsorber is connected with a liquid nitrogen cold washing box above, and the low-temperature methanol washing low-pressure nitrogen pipeline below; a blind plate is arranged between the molecular sieve adsorber and the gas-liquid separation tank; the liquid collecting tank is connected with a nitrogen cooler, and the low-pressure nitrogen main pipe and the low-temperature methanol washing low-pressure nitrogen pipeline below the nitrogen cooler are connected; the liquid collecting tank and the nitrogen cooler are respectively connected with a flare pipeline.

[0004] A second nitrogen washing tower liquid nitrogen discharge regulating valve, an external liquid nitrogen supplement pipeline, a liquid nitrogen cut-off valve, and a liquid nitrogen regulating valve are sequentially arranged between the nitrogen washing tower and the jet mixer.

[0005] A nitrogen temperature gauge at the outlet of the gas-liquid separation tank is arranged at the outlet above the gas-liquid separation tank. The nitrogen temperature gauge at the outlet of the gas-liquid separation tank is interlocked with a liquid nitrogen cut-off valve and a liquid nitrogen regulating valve. When the temperature is lower than -70°C, the liquid nitrogen cut-off valve is automatically cut off, and the liquid nitrogen regulating valve automatically adjusts the flow rate of liquid nitrogen added to the injection mixer to control the indication drop rate of the molecular sieve adsorber inlet temperature gauge to be less than 15°C / h and the nitrogen temperature at the outlet of the gas-liquid separation tank to be not lower than -60°C.

[0006] The liquid nitrogen spraying direction inside the spray mixer is consistent with the nitrogen flow direction.

[0007] The nitrogen cooler adopts a shell-and-tube heat exchanger inside, with liquid nitrogen running through the shell side and low-pressure nitrogen running through the tube side; a nitrogen cooler outlet temperature gauge is arranged on the pipeline for low-pressure nitrogen to exit the nitrogen cooler; the low-pressure nitrogen flowing through the second low-pressure nitrogen flow regulating valve has two branches, one of which flows into the nitrogen cooler through the nitrogen inlet regulating valve, and the other passes through the nitrogen cooler secondary line regulating valve and is mixed with the low-pressure nitrogen flowing out of the nitrogen cooler to enter the low-temperature methanol washing low-pressure nitrogen pipeline; the nitrogen cooler outlet temperature gauge is interlocked with the nitrogen inlet regulating valve and the nitrogen cooler secondary line regulating valve to automatically control the temperature of the low-pressure nitrogen exiting the nitrogen cooler to be -60°C.

[0008] The pressure of the liquid collection tank is greater than the pressure of the nitrogen cooler, and the liquid nitrogen automatically flows into the nitrogen cooler.

[0009] The liquid nitrogen pressure of the external liquid nitrogen supplement pipeline is higher than the pressure of the low-pressure nitrogen gas flowing into the jet mixer.

[0010] The beneficial effects of the utility model are as follows:

[0011] 1. Use a jet mixer to fully mix nitrogen and liquid nitrogen. At the same time, set a gas-liquid separator at the outlet of the jet mixer to promptly separate and discharge the liquid nitrogen entrained in the gas phase to prevent the liquid nitrogen from being unevenly mixed and brought to the molecular sieve adsorber, damaging the molecular sieve and equipment pipelines.

[0012] 2. The liquid nitrogen flow added to the injection mixer is controlled by a regulating valve to control the temperature drop rate of the molecular sieve adsorber inlet to be less than 15°C / h and the nitrogen temperature at the outlet of the gas-liquid separation tank to be no less than -60°C; a liquid nitrogen cut-off valve interlock is set in front of the liquid nitrogen regulating valve, and it is automatically cut off when the temperature is lower than -70°C to prevent damage to the molecular sieve.

[0013] 3. A nitrogen cooler is installed at the outlet of the liquid collection tank, a regulating valve is installed on the low-pressure nitrogen inlet pipeline of the nitrogen cooler, and a secondary regulating valve is installed on the low-pressure nitrogen outlet pipeline of the nitrogen cooler. By adjusting the opening of the two regulating valves, the temperature of the low-pressure nitrogen outlet of the nitrogen cooler is automatically controlled at -60°C, which can prevent the nitrogen temperature entering the low-temperature methanol washing hydrogen sulfide concentration tower from being too low, causing damage to the equipment pipeline and affecting the normal operation of the working conditions.

[0014] 4. The utility model can be applied to most synthetic ammonia devices with liquid nitrogen washing and low-temperature methanol washing processes, can be implemented on existing devices and can be isolated for maintenance at any time without affecting the safe and stable operation of the production device. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Device diagram of the utility model.

[0016] Figure 2 Schematic diagram of the internal structure of the jet mixer.

[0017] Figure 1 Each label description: 1. Nitrogen washing tower, 2. Medium-pressure nitrogen inlet, 3. Nitrogen washing tower liquid nitrogen discharge regulating valve 1, 4. Liquid collecting tank pressure gauge, 5. Gas phase regulating valve, 6. Flare pipeline, 7. Liquid collecting tank, 8. Nitrogen cooler, 9. Low-pressure nitrogen pipeline for low-temperature methanol washing, 10. Nitrogen cooler outlet temperature gauge, 11. Nitrogen cooler inlet regulating valve, 12. Nitrogen cooler sub-line regulating valve, 13. Low-pressure nitrogen main pipe, 14. Liquid-liquid separation tank liquid phase regulating valve, 15. Gas-liquid separation tank, 16. Jet mixer, 17. Low-pressure nitrogen flow regulating valve 1, 18. External liquid nitrogen pipeline, 19. Liquid nitrogen cut-off valve, 20. Liquid nitrogen regulating valve, 21. Gas-liquid separation tank outlet nitrogen temperature gauge, 22. Liquid nitrogen washing cold box, 23. Molecular sieve adsorber, 24. 2. Liquid nitrogen discharge regulating valve 2 of nitrogen washing tower, 25. Low-pressure nitrogen flow regulating valve 2, 26. Molecular sieve adsorber inlet temperature gauge, 27. Blind plate. DETAILED DESCRIPTION

[0018] The utility model is further described below in conjunction with the embodiments.

[0019] Example 1

[0020] A liquid nitrogen washing cold utilization device, such as Figure 1 As shown, it includes a nitrogen washing tower 1, which is connected to a liquid collecting tank 7 and a jet mixer 16; the right end of the jet mixer 16 is connected to a low-pressure nitrogen main pipe 13 through a low-pressure nitrogen flow regulating valve 17, and the left end is connected to a gas-liquid separation tank 15; the gas-liquid separation tank 15 is connected to a molecular sieve adsorber 23 at the top and to a liquid collecting tank 7 at the bottom; the molecular sieve adsorber 23 is connected to a liquid nitrogen washing cold box 22 at the top and to a low-temperature methanol washing low-pressure nitrogen pipeline 9 at the bottom; a blind plate 27 is arranged between the molecular sieve adsorber 23 and the gas-liquid separation tank 15; the liquid collecting tank 7 is connected to a nitrogen cooler 8, and the nitrogen cooler 8 is connected to two pipelines, the low-pressure nitrogen main pipe 13 and the low-temperature methanol washing low-pressure nitrogen pipeline 9 at the bottom; the liquid collecting tank 7 and the nitrogen cooler 8 are respectively connected to a flare pipeline 6.

[0021] A nitrogen washing tower liquid nitrogen discharge regulating valve 24, an external liquid nitrogen supplement pipeline 18, a liquid nitrogen cut-off valve 19, and a liquid nitrogen regulating valve 20 are sequentially arranged between the nitrogen washing tower 1 and the jet mixer 16.

[0022] A nitrogen temperature gauge 21 at the outlet of the gas-liquid separation tank is arranged at the outlet above the gas-liquid separation tank 15. The nitrogen temperature gauge 21 at the outlet of the gas-liquid separation tank is interlocked with the liquid nitrogen cut-off valve 19 and the liquid nitrogen regulating valve 20. When the temperature is lower than -70°C, the liquid nitrogen cut-off valve 19 is automatically cut off, and the liquid nitrogen regulating valve 20 automatically adjusts the flow rate of liquid nitrogen added to the injection mixer to control the indication drop rate of the molecular sieve adsorber inlet temperature gauge 26 to be less than 15°C / h and the nitrogen temperature at the outlet of the gas-liquid separation tank 15 to be not lower than -60°C.

[0023] The liquid nitrogen spraying direction inside the spray mixer 16 is consistent with the nitrogen flow direction.

[0024] The nitrogen cooler 8 adopts a shell-and-tube heat exchanger inside, with liquid nitrogen running through the shell side and low-pressure nitrogen running through the tube side; a nitrogen cooler outlet temperature gauge 10 is provided for the pipeline of low-pressure nitrogen out of the nitrogen cooler 8; the low-pressure nitrogen flowing through the low-pressure nitrogen flow regulating valve 25 has two branches, one of which flows into the nitrogen cooler 8 through the nitrogen inlet regulating valve 11, and the other passes through the nitrogen cooler by-line regulating valve 12 to mix with the low-pressure nitrogen flowing out of the nitrogen cooler 8 and enter the low-temperature methanol washing low-pressure nitrogen pipeline 9; the nitrogen cooler outlet temperature gauge 10 is interlocked with the nitrogen inlet regulating valve 11 and the nitrogen cooler by-line regulating valve 12 to automatically control the temperature of the low-pressure nitrogen out of the nitrogen cooler 8 to be -60°C.

[0025] The pressure of the liquid collecting tank 7 is greater than the pressure of the nitrogen cooler 8 , and the liquid nitrogen automatically flows into the nitrogen cooler 8 .

[0026] The pressure of the liquid nitrogen in the external supplementary liquid nitrogen pipeline 18 is higher than the pressure of the low-pressure nitrogen gas flowing into the jet mixer 16 .

[0027] Example 2

[0028] Using the device of Example 1, the working process of the utility model is as follows:

[0029] (1) Medium-pressure nitrogen is introduced into the nitrogen washing tower 1 through the medium-pressure nitrogen pipeline 2. When the nitrogen washing tower 1 is filled with liquid to 100%, the nitrogen washing tower liquid nitrogen discharge regulating valve 24 is opened. If the start-up time is insufficient, the external liquid nitrogen pipeline 18 can be opened to replenish liquid nitrogen.

[0030] (2) On the premise of ensuring the stability of the low-pressure nitrogen flow rate in the low-pressure nitrogen pipeline 9 for low-temperature methanol washing, gradually open the low-pressure nitrogen flow regulating valve 17 and close the low-pressure nitrogen flow regulating valve 25 at the same time until the low-pressure nitrogen flow regulating valve 25 is completely closed, thereby opening the process flow of the low-pressure nitrogen into the injection mixer 16, the gas-liquid separation tank 15, the molecular sieve adsorber 23, and into the low-temperature methanol washing low-pressure nitrogen pipeline 9.

[0031] (3) First open the liquid nitrogen shut-off valve 19, then slowly open the liquid nitrogen regulating valve 20, and the liquid nitrogen slowly enters the injection mixer 16. After the liquid nitrogen is mixed with the low-pressure nitrogen, the nitrogen temperature is reduced. The liquid nitrogen and the low-pressure nitrogen flow in the same direction, such as Figure 2The liquid nitrogen flow rate added to the injection mixer 16 is automatically controlled by the liquid nitrogen regulating valve 20, so that the rate of decrease of the reading of the molecular sieve adsorber inlet temperature gauge 26 is less than 15°C / h and the nitrogen temperature at the outlet of the gas-liquid separation tank 15 is not less than -60°C. A liquid nitrogen cut-off valve 19 is set before the liquid nitrogen regulating valve 20. When the nitrogen temperature at the outlet of the gas-liquid separation tank 15 is lower than -70°C, the interlock is automatically cut off to prevent the nitrogen temperature from being too low to damage the molecular sieve and equipment pipelines.

[0032] (4) The low-temperature nitrogen gas flowing out of the jet mixer 16 enters the gas-liquid separation tank 15 to separate the liquid nitrogen entrained in the low-pressure nitrogen gas to prevent the liquid nitrogen from being carried to the molecular sieve adsorber 23 due to uneven gas-liquid mixing, thereby damaging the molecular sieve and equipment pipelines; the separated liquid nitrogen enters the liquid collection tank 7.

[0033] (5) After the inlet temperature of the molecular sieve adsorber drops to -55°C, the liquid nitrogen regulating valve 20 starts to self-regulate, and the temperature setting value is -60°C, continuously supplying cold capacity for low-temperature methanol washing.

[0034] (6) After the low-temperature methanol washing gas index is qualified and before the liquid nitrogen washing cold box 22 is connected to the gas, close the liquid nitrogen regulating valve 20 and the low-pressure nitrogen regulating valve 17 in turn, and open the low-pressure nitrogen flow regulating valve 25. During the degassing process, the reading of the nitrogen temperature gauge 21 at the outlet of the gas-liquid separation tank should be kept at -60℃~-50℃. After the degassing is completed, close the nitrogen washing tower liquid nitrogen discharge regulating valve 24 and the liquid nitrogen cut-off valve 19, and turn the blind plate 27 upside down.

[0035] (7) Open the nitrogen washing tower liquid nitrogen discharge regulating valve 3, discharge the liquid nitrogen to the liquid collection tank 7 and the nitrogen cooler 8 according to the liquid level of the nitrogen washing tower 1, and adjust the gas phase regulating valve 5 to make the pressure of the liquid collection tank 50-100kPa.

[0036] (8) Open the nitrogen cooler inlet regulating valve 11, adjust the nitrogen cooler secondary line regulating valve 12, and gradually adjust the reading of the nitrogen cooler outlet temperature gauge 10 to -60°C. The nitrogen cooler outlet temperature gauge 10 is interlocked with the nitrogen cooler regulating valve 11 and the nitrogen cooler secondary line regulating valve 12. The nitrogen cooler regulating valve 11 and the nitrogen cooler secondary line regulating valve 12 are put into self-adjustment, and the temperature is set to -60°C. The low-pressure nitrogen enters the pipe side of the nitrogen cooler 8 through the low-pressure nitrogen flow regulating valve 25 and the nitrogen cooler inlet regulating valve 11 in turn. The low-pressure nitrogen exchanges heat with the liquid nitrogen in the shell side, and the steam is discharged from the flare pipeline 6. The low-temperature liquid nitrogen with qualified temperature flows to the low-pressure nitrogen pipeline 9 for low-temperature methanol washing.

Claims

1. A liquid nitrogen washing cold utilization device, characterized in that: The invention comprises a nitrogen washing tower (1), wherein the nitrogen washing tower (1) is connected to a liquid collecting tank (7) and a jet mixer (16); the right end of the jet mixer (16) is connected to a low-pressure nitrogen main pipe (13) through a low-pressure nitrogen flow regulating valve (17), and the left end is connected to a gas-liquid separation tank (15); the gas-liquid separation tank (15) is connected to a molecular sieve adsorber (23) at the top and to a liquid collecting tank (7) at the bottom; the molecular sieve adsorber (23) is connected to a liquid nitrogen washing cold box (22) at the top and to a low-temperature methanol washing low-pressure nitrogen pipeline (9) at the bottom; a blind plate (27) is arranged between the molecular sieve adsorber (23) and the gas-liquid separation tank (15); the liquid collecting tank (7) is connected to a nitrogen cooler (8), and the bottom of the nitrogen cooler (8) is connected to two pipelines, namely, a low-pressure nitrogen main pipe (13) and a low-temperature methanol washing low-pressure nitrogen pipeline (9); the liquid collecting tank (7) and the nitrogen cooler (8) are respectively connected to a flare pipeline (6).

2. A liquid nitrogen washing cold utilization device according to claim 1, characterized in that: A second nitrogen washing tower liquid nitrogen discharge regulating valve (24), an external liquid nitrogen supply pipeline (18), a liquid nitrogen shut-off valve (19), and a liquid nitrogen regulating valve (20) are sequentially arranged between the nitrogen washing tower (1) and the jet mixer (16).

3. The liquid nitrogen washing cold utilization device according to claim 1, characterized in that: A nitrogen temperature gauge (21) at the outlet of the gas-liquid separation tank is provided at the outlet above the gas-liquid separation tank (15). The nitrogen temperature gauge (21) at the outlet of the gas-liquid separation tank is interlocked with a liquid nitrogen cut-off valve (19) and a liquid nitrogen regulating valve (20). When the temperature is lower than -70°C, the liquid nitrogen cut-off valve (19) is automatically cut off, and the liquid nitrogen regulating valve (20) automatically adjusts the flow rate of liquid nitrogen added to the injection mixer to control the reading drop rate of the molecular sieve adsorber inlet temperature gauge (26) to be less than 15°C / h and the nitrogen temperature at the outlet of the gas-liquid separation tank (15) to be not lower than -60°C.

4. The liquid nitrogen washing cold utilization device according to claim 1, characterized in that: The liquid nitrogen spraying direction inside the spray mixer (16) is consistent with the nitrogen flow direction.

5. The liquid nitrogen washing cold utilization device according to claim 1, characterized in that: The nitrogen cooler (8) uses a shell-and-tube heat exchanger inside, with liquid nitrogen flowing through the shell side and low-pressure nitrogen flowing through the tube side; a nitrogen cooler outlet temperature gauge (10) is provided on the pipeline for the low-pressure nitrogen to exit the nitrogen cooler (8); the low-pressure nitrogen flowing through the second low-pressure nitrogen flow regulating valve (25) has two branches, one of which flows into the nitrogen cooler (8) through the nitrogen cooler inlet regulating valve (11), and the other flows through the nitrogen cooler secondary line regulating valve (12) and is mixed with the low-pressure nitrogen flowing out of the nitrogen cooler (8) to enter the low-temperature methanol washing low-pressure nitrogen pipeline (9); the nitrogen cooler outlet temperature gauge (10) is interlocked with the nitrogen cooler inlet regulating valve (11) and the nitrogen cooler secondary line regulating valve (12) to automatically control the temperature of the low-pressure nitrogen exiting the nitrogen cooler (8) to be -60°C.

6. The liquid nitrogen washing cold utilization device according to claim 1, characterized in that: The pressure of the liquid collection tank (7) is greater than the pressure of the nitrogen cooler (8), and the liquid nitrogen automatically flows into the nitrogen cooler (8).

7. The liquid nitrogen washing cold utilization device according to claim 1, characterized in that: The pressure of the liquid nitrogen in the external supplementary liquid nitrogen pipeline (18) is higher than the pressure of the low-pressure nitrogen gas flowing into the jet mixer (16).

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