Method for solving pipeline blockage of liquid nitrogen washing device

Abstract

The invention discloses a method for solving pipeline blockage of a liquid nitrogen washing device, which comprises the following steps of: adding a stream of impermeable gas with the pressure of 5-8MPa from a hydrogen recovery device at a safety valve at the top of an ammonia washing tower, and changing the molar concentration of blockage substances by mainly utilizing methane in the impermeable gas, and after the pressure is controlled to be 3.1-3.3 MPa by a valve, the gas is mixed with process gas and sent to a subsequent working section. The pressure of the impermeable gas is controlled by a valve, the impermeable gas is sent to an outlet of the ammonia washing tower through a check valve and a valve, is mixed with process gas, enters a shift gas cooler and a separator to be cooled and separated, enters a washing tower and a molecular sieve to be washed and adsorbed, and is sent to a liquid nitrogen washing device. According to the method, the problems that the inlet and outlet process air pressure difference of the liquid nitrogen washing device is too high and the heat exchanger end face temperature is too low are solved, and the stability and safety of a production device are effectively guaranteed. The method can be widely applied to large-scale ammonia synthesis factories using liquid nitrogen washing devices.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, in particular to a method for solving the blockage of pipelines of a liquid nitrogen washing device. Background Art

[0002] The function of the liquid nitrogen washing device is to use low-temperature liquid nitrogen to wash methane, carbon monoxide and other substances in the process gas. After the high-concentration hydrogen absorbs carbon dioxide, methanol, hydrogen sulfide and other substances in the process gas through the molecular sieve, it enters the liquid nitrogen washing device. The process gas pressure is 2.96MPa, the temperature is -54℃, the pressure difference with the outlet of the liquid nitrogen washing device is 50KPa, the pressure difference with the nitrogen washing tower is 150KPa, the temperature between the synthesis gas precooler is -112℃, and the temperature after the nitrogen washing tower and the synthesis gas precooler is -120℃; after the coal gasification unit changes the raw coal, the pressure difference between the inlet process gas of the liquid nitrogen washing device and the outlet of the liquid nitrogen washing device is 150KPa, the pressure difference with the nitrogen washing tower is 200KPa, and the temperature after the nitrogen washing tower is -180℃. After analysis, it is found that: the conversion catalyst enters the final stage, the side reactions increase, and the by-products block part of the process gas pipeline at this temperature and pressure, affecting the heat exchange effect of the heat exchanger, resulting in an increase in pressure difference and overcooling of the heat exchanger end face, affecting safe production. Summary of the invention

[0003] The object of the present invention is to solve the above-mentioned problem and provide a method for changing the concentration of components, thereby reducing the freezing point of the substance at this temperature and pressure so that the substance will not freeze, thereby reducing the process gas pressure difference between the inlet and outlet of the liquid nitrogen washing device and the supercooling of the end surface temperature of the heat exchanger.

[0004] The technical solution of the present invention is: add a stream of non-permeate gas (pressure 5-8MPa, temperature 50°C) from a hydrogen recovery device at the process gas outlet pipe at the top of the ammonia scrubbing tower, the main components of which are: <![CDATA[N2]]> CO <![CDATA[CO2]]> <![CDATA[H2]]> <![CDATA[CH4]]> <![CDATA[CH3OH]]> <![CDATA[AR+O2]]> % % % % % ppm % 36.79 28.39 5.07 25.46 1.03 219 3.22 The method of the present invention utilizes methane in non-permeate gas to change the molar concentration of the blocking substance. Preferably, the pressure is controlled to be 3.1-3.3 MPa by a valve and then mixed with the process gas and sent to the subsequent process section.

[0005] Preferably, in the above method, the temperature of the non-permeate gas from the hydrogen recovery device is 50°C.

[0006] A device for solving the blockage of pipelines of a liquid nitrogen washing device, wherein a pipeline is added at the outlet pipe of the top of an ammonia washing tower of the liquid nitrogen washing device to connect with a hydrogen recovery device, a stop valve, a gate valve and a check valve are arranged in sequence on the pipeline connecting the hydrogen recovery device to the inlet of a conversion gas cooler, a process gas outlet of the conversion gas cooler is connected to the inlet of a methanol-water separator through a pipeline, the methanol-water separator is connected to a conversion gas methanol washing tower through a pipeline, the top outlet of the conversion gas methanol washing tower is connected to the inlet of a molecular sieve through a pipeline, the bottom outlet of the molecular sieve is connected to the inlet of a filter through a pipeline, and the bottom outlet of the filter is connected to the inlet of a nitrogen washing tower through a switch valve and a synthesizer precooler.

[0007] The methane in the non-permeable gas is mainly used to change the molar concentration of the blocking substance. After the pressure is controlled to 3.2MPa by a valve, it is mixed with the process gas and sent to the subsequent process section.

[0008] The device for implementing the present invention comprises a conversion gas cooler, a conversion gas methanol-water separator, a conversion gas methanol washing tower, a molecular sieve, a filter and a nitrogen washing tower. A pipeline is added at the safety valve at the top of the ammonia washing tower of the liquid nitrogen washing device to connect the hydrogen recovery device. A stop valve, a gate valve and a check valve are arranged in sequence on the pipeline connecting the hydrogen recovery device to the inlet of the conversion gas cooler. The process gas outlet of the conversion gas cooler is connected to the inlet of the methanol-water separator through a pipeline. The methanol-water separator is connected to the conversion gas methanol washing tower through a pipeline. The top outlet of the conversion gas methanol washing tower is connected to the inlet of the molecular sieve through a pipeline. The bottom outlet of the molecular sieve is connected to the inlet of the filter through a pipeline. The bottom outlet of the filter is connected to the inlet of the nitrogen washing tower through a switch valve and a synthesizer precooler.

[0009] Compared with the prior art, the method of the present invention uses a non-permeate gas that is pressure-controlled by a valve and then sent to the outlet of the ammonia washing tower through a check valve and a valve, mixed with the process gas and then sent to the conversion gas cooler and separator for cooling and separation, then sent to the washing tower and molecular sieve for washing and adsorption, and then sent to the liquid nitrogen washing device. The method reduces the problem of excessively high process gas pressure difference between the inlet and outlet of the liquid nitrogen washing device and the overcooling of the end surface temperature of the heat exchanger, and effectively ensures the stability and safety of the production device. The method can be widely used in large-scale synthetic ammonia plants using liquid nitrogen washing devices.

[0010] In addition, the present invention has low cost, and only one stop valve, one check valve, one gate valve and a carbon steel pipeline are used to transform the relevant devices; the present invention can solve the irreversible damage to equipment and pipelines caused by parameter deviation, and effectively ensure production safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the process flow of the present invention; Figure 2 This is a process flow chart of Example 1 in which the present invention is not implemented; In the figure: 1-stop valve, 2-gate valve, 3-check valve, 4-pipeline after non-permeate gas and process gas are mixed, 5-conversion gas cooler, 6-conversion gas methanol water separator, 7-conversion gas methanol washing tower, 8-process gas inlet molecular sieve pipeline, 9-molecular sieve, 10-filter, 11-liquid nitrogen washing device inlet process gas pressure measuring point, 12-temperature measuring point between synthesis gas precoolers, 13-nitrogen washing tower pressure measuring point, 14-temperature measuring point after nitrogen washing tower and synthesis gas precooler, 15-process gas pressure measuring point out of liquid nitrogen washing device; 16-hydrogen recovery device. DETAILED DESCRIPTION Example

[0012] See also Figure 1 A certain company adopts the method and device of the present invention, including a conversion gas cooler 5, a conversion gas methanol water separator 6, a conversion gas methanol washing tower 7, a molecular sieve 9, a filter 10 and a nitrogen washing tower. The non-permeated gas enters the conversion gas cooler 5 inlet pipeline from the hydrogen recovery device. The pipeline is provided with a stop valve 1, a gate valve 2, and a check valve 3. The process gas outlet of the conversion gas cooler 5 is connected to the methanol water separator 6 inlet, and enters the conversion gas methanol washing tower 7 through a pipeline. The top outlet of the conversion gas methanol washing tower 7 is connected to the molecular sieve 9 inlet by a pipeline 8, and the bottom outlet of the molecular sieve 9 is connected to the filter 10 inlet by a pipeline. The bottom outlet of the filter 10 is connected to the nitrogen washing tower inlet through a switch valve and a synthesizer precooler, and is sent to the synthesis gas compressor after being washed with low-temperature liquid nitrogen.

[0013] When the device of the present invention is in use, the non-permeate gas is controlled by the gate valve on the non-permeate gas pipeline of the hydrogen recovery device 16 at a pressure between 3.1 and 3.3 MPa, enters the conversion gas washing ammonia tower safety valve root valve through the pipeline, gate valve and check valve, and is mixed with the process gas in the pipeline. The mixed pressure is 2.9 to 3.1 MPa and the temperature is about 28 to 32°C. It is cooled to -13 to -15°C by the conversion gas cooler and enters the conversion gas methanol water separator and the conversion gas methanol washing After the tower, the pressure is 2.9~3.1MPa. After entering the molecular sieve for adsorption, the temperature is -50~-54℃ and the pressure is 2.9~3.0MPa. After being cooled to -110~-114℃ by the heat exchanger, it enters the heat exchanger to cool to -185~-188℃ and the pressure is 2.9~3.0MPa. After entering the nitrogen washing tower for washing, the synthesis gas is -191~-194℃. After pre-cooling the synthesis gas through the heat exchanger, it is -118~-122℃ and then sent to the synthesis gas compressor.

[0014] By comparing the data before and after the company adopted the method and device of the present invention, the normal pressure difference between the inlet process gas pressure measuring point 11 of the liquid nitrogen washing device and the pressure measuring point 13 of the nitrogen washing tower under normal conditions before changing the raw coal is about 50KPa. After changing the coal, the side reactions increase and the pipeline blockage pressure difference rises to 150KPa. After the implementation of the present invention, the pressure difference is restored to 50KPa under normal conditions after the introduction of hydrogen to recover methane in the non-permeated gas to change the concentration of the blocking substance component; under normal conditions, the pressure difference between the inlet process gas pressure measuring point 11 of the liquid nitrogen washing device and the process gas pressure measuring point 15 of the liquid nitrogen washing device is 150KPa. After that, the pressure difference rises to more than 200KPa. After the implementation of the present invention, the temperature of the temperature measuring point 12 between the synthesis gas precooler drops from -112°C to -170°C after the coal is replaced, and the temperature of the temperature measuring point 14 after the nitrogen washing tower and the synthesis gas precooler drops from -120°C to -180°C. After the implementation of the present invention, the temperature of the temperature measuring point 12 returns to the normal operating condition of -112°C after the introduction of methane into the non-permeable gas to change the concentration of the blockage substance component, and the temperature of the temperature measuring point 14 returns to the normal operating condition of -120°C.

[0015] By adopting the method and device of the present invention, the deviated parameters are restored to normal, which greatly reduces the harm to the equipment and ensures safe production.

Claims

1. A method for solving the blockage of pipeline of liquid nitrogen washing device, characterized in that: A stream of non-permeate gas from the hydrogen recovery unit is added to the process gas outlet pipe at the top of the ammonia scrubbing tower. The pressure is controlled at 5-8 MPa. The main components of the non-permeate gas are: 。 2. The method for solving the blockage of the pipeline of the liquid nitrogen washing device according to claim 1 is characterized in that: The methane in the non-permeate gas is used to change the molar concentration of the blocking material, and after the pressure is controlled to 3.1-3.3MPa by a valve, it is mixed with the process gas and sent to the subsequent process section.

3. The method for solving the blockage of the pipeline of the liquid nitrogen washing device according to claim 1 is characterized in that: The non-permeate gas temperature from the hydrogen recovery unit was 50°C.

4. The method for solving the blockage of the pipeline of the liquid nitrogen washing device according to claim 1 is characterized in that: The methane in the non-permeate gas is used to change the molar concentration of the icing material, and after the pressure is controlled to 3.2MPa by a valve, it is mixed with the process gas and sent to the subsequent process section.

5. A device for solving the blockage of pipelines in liquid nitrogen washing devices, characterized in that: A pipeline is added at the outlet pipe of the ammonia washing tower of the liquid nitrogen washing device to connect to the hydrogen recovery device (16). A stop valve (1), a gate valve (2), and a check valve (3) are provided in sequence on the pipeline connecting the hydrogen recovery device to the inlet of the conversion gas cooler. The process gas outlet of the conversion gas cooler (5) is connected to the inlet of the methanol water separator (6) through a pipeline. The methanol water separator is connected to the conversion gas methanol washing tower through a pipeline. The top outlet of the conversion gas methanol washing tower (7) is connected to the inlet of the molecular sieve (9) through a pipeline. The bottom outlet of the molecular sieve (9) is connected to the inlet of the filter (10) through a pipeline. The bottom outlet of the filter (10) is connected to the inlet of the nitrogen washing tower through a switch valve and a synthesizer precooler.

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