CN106369934B - Anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device and method combined with mixed refrigerant system - Google Patents

Anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device and method combined with mixed refrigerant system Download PDF

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CN106369934B
CN106369934B CN201610933593.6A CN201610933593A CN106369934B CN 106369934 B CN106369934 B CN 106369934B CN 201610933593 A CN201610933593 A CN 201610933593A CN 106369934 B CN106369934 B CN 106369934B
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gas
nitrogen
pneumatic valve
raw material
adsorber
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CN106369934A (en
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章有虎
陈环琴
黄成华
王晋
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Hangzhou Zhongtai Cryogenic Technology Corp
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Hangzhou Zhongtai Cryogenic Technology Corp
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F25JLIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
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    • F25J2205/30Processes or apparatus using other separation and/or other processing means using a washing, e.g. "scrubbing" or bubble column for purification purposes
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Abstract

The invention discloses a combined mixed refrigerant systemThe device and the method for preventing freezing and blocking and co-producing LNG liquid nitrogen washing. The invention mainly comprises a molecular sieve adsorption system, a cold box separation liquefaction system and a mixed refrigerant refrigeration cycle system. The molecular sieve system mainly comprises an adsorber and a regeneration system, and carbon dioxide and methanol in the molecular sieve system are removed by adopting a mature liquid nitrogen molecular sieve washing adsorption technology; the mixed refrigerant system mainly comprises a compressor unit and a refrigerant storage and distribution unit, and the compressor adopts a single MRC centrifugal compressor, so that the energy consumption is low, the equipment is simple, and the stability and reliability are realized; the cold box system mainly comprises a plate-fin heat exchanger group, a nitrogen washing tower and a methane rectifying tower. The invention receives the purified gas from the upstream low-temperature methanol washing process to internally remove CO and CH in the purified gas4And Ar, H2/N2 ═ 3: 1, synthesizing ammonia by using the pure synthesis gas, and separating the separated methane-rich liquid by using a rectifying tower to obtain LNG (liquefied natural gas), and sending the LNG to an LNG tank area outside the battery area.

Description

Anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device and method combined with mixed refrigerant system
Technical Field
The invention relates to a chemical cryogenic purification and separation device, in particular to an anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device and method combined with a mixed refrigerant system.
Background
The natural gas treatment device mostly adopts a low-temperature condensation method to carry out condensation separation on natural gas, a plurality of parts of the device are in a low-temperature state of-20 ℃ to 89 ℃ under normal operation, slight freezing causes blockage of pipelines, the start and normal production of the device are affected, equipment, pipelines and valves are seriously frozen and cracked, a large amount of natural gas leakage is possibly caused, and a series of accidents such as personal poisoning, equipment explosion, ignition and the like are caused.
The formation of natural gas hydrates, in addition to being related to the composition and free water content of the natural gas, requires certain thermodynamic conditions, i.e. certain temperatures and pressures. In summary, natural gas hydrates must have the conditions of 1) having gas molecules capable of forming hydrates, such as small molecule hydrocarbons and acidic components such as H2S, C02; 2) in the presence of liquid water, the temperature of the natural gas must be lower than the water dew point of the natural gas; 3) low temperature, the system temperature is lower than the phase equilibrium temperature of hydrate generation; 4) high pressure, the system pressure is higher than the phase equilibrium pressure of hydrate generation; 5) other auxiliary conditions such as turbulence caused by sudden changes in gas flow rate and direction, fluctuations in pressure and the presence of seeds.
Liquid methane (LNG) is a high-quality energy source, has the characteristics of high heat value, cleanness, small combustion pollution and the like, is convenient to transport, and is a preferred fuel for civil gas in China in the 21 st century. The LNG can be used as high-quality vehicle fuel, compared with gasoline, the LNG has the advantages of high heat value, good anti-explosion performance, complete combustion, small exhaust pollution, long service life of an engine, transportation cost reduction and the like, and even compared with compressed natural gas, the LNG also has the advantages of high storage efficiency, long continuous travel after adding once gas, small pressure of vehicle-mounted steel cylinders, light weight, small quantity, no limitation of a gas supply pipe network for building stations and the like. Is beneficial to environmental protection and reduces urban pollution.
The synthetic ammonia is always an energy-consuming big household in the chemical industry. The purification of synthetic ammonia adopts different methods according to the difference of the overall process, mostly adopts liquid nitrogen washing, the conventional treatment method is to recycle most of hydrogen and nitrogen with higher content, and the washed return gas containing methane and the like is combusted or directly discharged. Thus not only wasting energy and polluting environment, but also reducing the economic benefit of nitrogen fertilizer plants. With the increasing shortage of energy sources, the recovery of methane in the energy sources brings great economic benefits and environmental protection benefits.
Conventional liquid nitrogen washing is to provide cold through throttling of high pressure nitrogen and external feeding of liquid nitrogen, and requires a large consumption of liquid nitrogen. And the conventional nitrogen washing tower does not have a bottom rectifying part, and raw gas directly enters the bottom of the tower, so that the problem of freezing and blocking of condensed gas such as methane, carbon dioxide and the like is easily caused. At present, many enterprises generally divide liquid nitrogen cleaning synthesis gas and liquefied and separated LNG into two systems, so that the occupied space is large, the efficiency is low, and the energy consumption is high.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device and method combined with a mixed refrigerant system.
A freeze-blocking prevention co-production LNG liquid nitrogen washing device combined with a mixed refrigerant system comprises a regeneration gas heater, a first pneumatic valve, a second pneumatic valve, a third pneumatic valve, a fourth pneumatic valve, a fifth pneumatic valve, a sixth pneumatic valve, a seventh pneumatic valve, an eighth pneumatic valve, a ninth pneumatic valve, a first adsorber, a second adsorber and a regeneration gas cooler of a molecular sieve unit, and a high-pressure nitrogen cooler, a first throttling valve, a second throttling valve, a third throttling valve, a fourth throttling valve, a fifth throttling valve, a sixth throttling valve, a seventh throttling valve, an eighth throttling valve, a No. 1 raw material gas cooler, a gas mixer, a raw material gas separator, a No. 2 raw material gas cooler, a nitrogen washing tower, a methane rectifying tower and a methane tower bottom reboiler of the liquid nitrogen washing unit;
one end of a regeneration gas heater is connected with the low-pressure nitrogen through pipe through a pipeline, the other end of the regeneration gas heater is respectively connected with the inlet ends of the first adsorber and the second adsorber, one end of a regeneration gas cooler is connected with a nitrogen leading-out port through a pipeline, the other end of the regeneration gas cooler is divided into two branches and is respectively connected with an eighth pneumatic valve and a ninth pneumatic valve, the eighth pneumatic valve is connected with the interface end of the first adsorber, and the ninth pneumatic valve is connected with the interface end of the second adsorber;
a first pneumatic valve is arranged on a purified gas conveying pipeline of the first adsorber, a fourth pneumatic valve is arranged on a purified gas conveying pipeline of the second adsorber, a regenerative heating nitrogen gas input pipeline is connected with the end of the adsorber and divided into two branches, a second pneumatic valve is arranged between the regenerative heating nitrogen gas input pipeline and the first adsorber, a third pneumatic valve is arranged between the regenerative heating nitrogen gas input pipeline and the second adsorber, and a fifth pneumatic valve is also arranged between the regenerative heating nitrogen gas input pipelines of the two adsorbers;
the methanol washing raw material gas input pipeline is divided into two branches which are respectively connected with a sixth pneumatic valve and a seventh pneumatic valve, the sixth pneumatic valve is connected with the interface end of the first adsorber, and the seventh pneumatic valve is connected with the interface end of the second adsorber;
a purified gas conveying pipeline penetrates through the No. 1 raw material gas cooler and the No. 2 raw material gas cooler and is connected with a raw material gas separator, a pipeline at the lower end of the raw material separator is connected with the methane distillation tower, a fourth throttling valve is arranged between the pipelines, and a pipeline at the upper end of the raw material separator penetrates through the No. 2 raw material gas cooler and is connected with the nitrogen washing tower; the low-pressure liquid-phase refrigerant pipeline inlet section and the liquid-phase mixed refrigerant pipeline inlet section respectively penetrate through the high-pressure nitrogen cooler, a first throttle valve and a second throttle valve are respectively installed after the high-pressure nitrogen cooler and the liquid-phase mixed refrigerant pipeline inlet section penetrate through the high-pressure nitrogen cooler, the No. 1 raw material gas cooler and the No. 2 raw material gas cooler, a fifth throttle valve is installed after the No. 2 raw material gas cooler, and the backflow section of the fifth throttle valve penetrates through the No. 1 raw material gas cooler and the No. 2 raw material gas cooler respectively; three branches of a low-pressure liquid-phase refrigerant reflux section, a liquid-phase mixed refrigerant reflux section and a gas-phase mixed refrigerant reflux section are converged into a pipeline between the high-pressure nitrogen cooler and the No. 1 raw material gas cooler and penetrate through the high-pressure nitrogen cooler to be communicated to a refrigerant compressor; the inlet section of the high-pressure nitrogen pipeline penetrates through the high-pressure nitrogen cooler and the No. 1 raw material gas cooler respectively and then is divided into two paths, one path of the high-pressure nitrogen pipeline penetrates through a third throttling valve and is connected with a gas mixer, the other path of the high-pressure nitrogen pipeline continuously penetrates through the No. 2 raw material gas cooler and is connected with the upper part of a nitrogen washing tower, a sixth throttling valve is further arranged between the No. 2 raw material gas cooler and the nitrogen washing tower, the lower end of the gas mixer is connected with the top end of the nitrogen washing tower, and the upper end of the gas mixer is provided with a synthetic gas conveying pipeline which is connected with a synthetic device; the lower part of the nitrogen tower is provided with two pipelines to be connected with the methane rectifying tower, the top of the methane rectifying tower is provided with a conveying pipeline to be connected with the liquid nitrogen system, a reflux pipeline and two output pipelines, and the bottom of the methane rectifying tower is provided with a methane tower bottom reboiler which is connected with the LNG storage tank through a pipeline.
The first adsorber and the second adsorber are filled with molecular sieves, and are automatically switched by a program controller, so that one adsorber is used for regeneration while the other adsorber is used for regeneration.
The top of the raw material gas separator is connected with the bottom of a nitrogen washing tower, raw material gas in the tower is washed by liquid nitrogen, and CO and CH in the gas4And Ar and other impurity gases are absorbed by liquid nitrogen and can come out from the top of the nitrogen washing tower to enter a gas mixer to ensure that the hydrogen-nitrogen ratio is 3: 1.
the liquid nitrogen cleaning synthesis gas system provided with the gas mixer and the nitrogen washing tower is integrated with the mixed refrigerant circulating refrigeration system and the liquefaction separation system provided with the methane rectifying tower.
The cold insulation materials of the high-pressure nitrogen cooler, the No. 1 raw material gas cooler, the No. 2 raw material gas cooler, the nitrogen washing tower and the methane rectifying tower are expanded perlite, and the heat exchanger is a plate-fin heat exchanger.
A control method of an anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device combined with a mixed refrigerant system comprises the following steps:
1) the raw material gas comes from a low-temperature methanol washing procedure and firstly enters two adsorbers to remove trace methanol and carbon dioxide in the raw material gas so as to prevent the raw material gas from freezing in a cold box to cause the blockage of low-temperature equipment and pipelines. When the first adsorber works and is used, the second adsorber is regenerated, the first pneumatic valve, the third pneumatic valve, the sixth pneumatic valve and the ninth pneumatic valve are opened, the second pneumatic valve, the fourth pneumatic valve, the fifth pneumatic valve, the seventh pneumatic valve and the eighth pneumatic valve are closed, the regeneration gas heater provides nitrogen heated to 200 ℃ for the second adsorber, the regeneration gas cooler cools the nitrogen after the regeneration action of the molecular sieve, the recovery of the nitrogen is facilitated, the first adsorber receives raw material gas for purifying methanol washing, useless waste gas is filtered, and the purified gas enters the next working procedure;
when the first adsorber is regenerated, the second adsorber works and is used, the first pneumatic valve, the third pneumatic valve, the fifth pneumatic valve, the sixth pneumatic valve and the ninth pneumatic valve are closed, the second pneumatic valve, the fourth pneumatic valve, the seventh pneumatic valve and the eighth pneumatic valve are opened, the regeneration gas heater provides nitrogen heated to 200 ℃ for the first adsorber, the regeneration gas cooler cools the nitrogen after the regeneration action of the molecular sieve, the recovery of the nitrogen is facilitated, the second adsorber receives raw material gas for purifying methanol washing, useless waste gas is filtered, and the purified gas enters the next working procedure;
2) the feed gas passes through the first adsorber and the second adsorber to remove CO2、CH3Removing impurities such as OH, entering a No. 1 cooler and a No. 2 cooler, performing countercurrent heat exchange with purified gas from the top of a nitrogen washing tower and tail gas from the top of a methane rectification tower, cooling to a certain temperature, partially condensing, entering a raw material gas separator, continuously cooling the gas at the top of the raw material gas separator, entering the bottom of the nitrogen washing tower, washing the raw material gas in the tower with liquid nitrogen, and removing CO and CH in the gas4Ar and the like are absorbed by liquid nitrogen to obtain refined gas, and the refined gas is discharged from the top of the nitrogen washing tower, subjected to heat exchange and then subjected to gas exchangeNitrogen in the mixer so that the hydrogen-nitrogen ratio is 3: 1, continuously recovering the cold energy and sending the cold energy to a synthesizer;
3) high-pressure nitrogen gas from air separation enters a cold box to be cooled and then is divided into two paths, wherein one path is used for distributing nitrogen and supplementing cold energy to refined gas, and the other path is cooled into liquid nitrogen which enters a nitrogen washing tower to be used as washing liquid;
4) the method comprises the following steps that methane-rich liquid at the bottom of a raw material gas separator and tail liquid at the bottom of a nitrogen washing tower are decompressed and then enter a methane rectifying tower, tail gas at the top of the tower is recovered by a liquid nitrogen system to be reheated to normal temperature and then is discharged out of the device, and LNG obtained at the bottom of the methane rectifying tower is decompressed and enters an LNG product storage tank after being cooled;
5) the cold energy of the system is provided by the mixed refrigerant refrigeration cycle, and the mixed working medium refrigerant from the refrigerant compressor enters the cold box and is precooled and cooled to be used as the refrigerant to provide the cold energy for the liquefaction of the natural gas; the refrigerant is compressed and divided into a gas-phase mixed refrigerant and a liquid-phase mixed refrigerant which respectively enter the cold box, and the gas phase is cooled and then passes through the plate-fin heat exchanger, then returns to the heat exchanger through the fifth throttling valve and provides liquefied cold energy for the raw material natural gas; and after the liquid phase is subcooled in the heat exchanger, the liquid phase passes through the first throttling valve and the second throttling valve and then is mixed with the other returned gas-phase refrigerant, and then the liquid phase returns to the inlet of the compressor for closed circulation after being reheated.
The invention mainly comprises a molecular sieve adsorption system, a cold box separation liquefaction system and a mixed refrigerant refrigeration cycle system. The molecular sieve system mainly comprises an adsorber and a regeneration system, and carbon dioxide and methanol in the molecular sieve system are removed by adopting a mature liquid nitrogen molecular sieve washing adsorption technology; the mixed refrigerant system mainly comprises a compressor unit and a refrigerant storage and distribution unit, and the compressor adopts a single MRC centrifugal compressor, so that the energy consumption is low, the equipment is simple, and the stability and reliability are realized; the cold box system mainly comprises a plate-fin heat exchanger group, a nitrogen washing tower and a methane rectifying tower.
The conventional nitrogen washing tower has no bottom rectifying part, and the raw material gas directly enters the bottom of the tower, so that the bottom rectifying part is added, 2 problems are effectively solved, one problem is that the raw material gas contains methane and is frozen and blocked, the recovery rate of hydrogen is improved, and the recovery rate of H2 of the liquid nitrogen washing device is improved to 99.2%. And the conventional liquid nitrogen washing device is skillfully combined with the mixed refrigerant refrigeration cycle, so that the total efficiency of the device is improved. In the past, the LNG prepared by cleaning and separating the liquid nitrogen into the synthetic gas and liquefying the synthetic gas is divided into two systems, so that the efficiency is low, the energy consumption is high, and the occupied area is large.
Drawings
FIG. 1 is a schematic diagram of a molecular sieve adsorption unit of an anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device combined with a mixed refrigerant system;
FIG. 2 is a schematic diagram of a cold box separation liquefaction unit and a mixed refrigerant refrigeration cycle system of an anti-freezing and blocking co-production LNG liquid nitrogen washing device combined with a mixed refrigerant system;
in the figure, a regeneration gas heater 1, a first pneumatic valve 2, a second pneumatic valve 3, a third pneumatic valve 4, a fourth pneumatic valve 5, a fifth pneumatic valve 6, a sixth pneumatic valve 9a, a seventh pneumatic valve 9b, an eighth pneumatic valve 10, a ninth pneumatic valve 11, a first adsorber 7, a second adsorber 8, a regeneration gas cooler 12, a high-pressure nitrogen cooler 13, a first throttle valve 14, a second throttle valve 15, a third throttle valve 17, a fourth throttle valve 20, a fifth throttle valve 21, a sixth throttle valve 23, a seventh throttle valve 25, an eighth throttle valve 26, a No. 1 raw material gas cooler 16, a gas mixer 18, a raw material gas separator 19, a No. 2 raw material gas cooler 22, a nitrogen scrubber 24, a methane rectifier 27, and a methane column bottom 28 are provided.
Detailed Description
As shown in FIGS. 1 and 2, an anti-freezing and anti-blocking LNG liquid nitrogen washing device combined with a mixed refrigerant system comprises a regeneration gas heater 1, a first pneumatic valve 2, a second pneumatic valve 3, a third pneumatic valve 4, a fourth pneumatic valve 5, a fifth pneumatic valve 6, a sixth pneumatic valve 9a, a seventh pneumatic valve 9b, an eighth pneumatic valve 10, a ninth pneumatic valve 11, a first adsorber 7, a second adsorber 8 and a regeneration gas cooler 12 of a molecular sieve unit, and a high-pressure nitrogen cooler 13, a first throttle valve 14, a second throttle valve 15, a third throttle valve 17, a fourth throttle valve 20, a fifth throttle valve 21, a sixth throttle valve 23, a seventh throttle valve 25, an eighth throttle valve 26, a feed gas cooler No. 1 16, a gas mixer 18, a feed gas separator 19, a feed gas cooler No. 2, a nitrogen scrubber 24, a methane rectifier 27 and a methane column bottom reboiler 28 of the liquid nitrogen scrubbing unit; the regeneration gas heater 1 is connected with a low-pressure nitrogen through pipe at one end through a pipeline, the other end of the regeneration gas heater is respectively connected with the inlet ends of the first adsorber 7 and the second adsorber 8, the regeneration gas cooler 12 is connected with a nitrogen leading-out port at one end through a pipeline, the other end of the regeneration gas cooler is divided into two branches which are respectively connected with the interface ends of the first adsorber 7 and the second adsorber 8, and an eighth pneumatic valve 10 and a ninth pneumatic valve 11 are respectively arranged;
a first pneumatic valve 2 is arranged on a purified gas conveying pipeline of the first adsorber 7, a fourth pneumatic valve 5 is arranged on a purified gas conveying pipeline of the second adsorber 3, a regenerative heating nitrogen gas input pipeline is connected with the end of the adsorber and divided into two branches, a second pneumatic valve 3 is arranged between the regenerative heating nitrogen gas input pipeline and the first adsorber 7, a third pneumatic valve 4 is arranged between the regenerative heating nitrogen gas input pipeline and the second adsorber 8, and a fifth pneumatic valve 6 is also arranged between the regenerative heating nitrogen gas input pipelines of the two adsorbers;
the pipeline for inputting the methanol washing raw material gas into the adsorber is divided into two branches which are respectively connected with the interface ends of the first adsorber 7 and the second adsorber 8, and a sixth pneumatic valve 9a and a seventh pneumatic valve 9b are respectively arranged on the two branches;
a purified gas conveying pipeline penetrates through the No. 1 raw material gas cooler 16 and the No. 2 raw material gas cooler 22 and is connected with a raw material gas separator 19, a pipeline at the lower end of the raw material separator 19 is connected with a methane distillation tower 27, a fourth throttling valve 20 is arranged between the pipeline and the methane distillation tower 27, and a pipeline at the upper end of the raw material separator 19 penetrates through the No. 2 raw material gas cooler 22 and is connected with a nitrogen washing tower 24; the low-pressure liquid-phase refrigerant pipeline inlet section and the liquid-phase mixed refrigerant pipeline inlet section respectively penetrate through the high-pressure nitrogen cooler 13, a first throttle valve 14 and a second throttle valve 15 are respectively installed after the low-pressure liquid-phase refrigerant pipeline inlet section and the liquid-phase mixed refrigerant pipeline inlet section penetrate through the high-pressure nitrogen cooler 13, the No. 1 raw material gas cooler 16 and the No. 2 raw material gas cooler 22, a fifth throttle valve 21 is installed after the No. 2 raw material gas cooler 22, and the return sections of the fifth throttle valve 21 respectively penetrate through the No. 1 raw material gas cooler 16 and the No. 2 raw material gas cooler 22; between the high-pressure nitrogen cooler 13 and the No. 1 raw material gas cooler 16, three branches of a low-pressure liquid-phase refrigerant reflux section, a liquid-phase mixed refrigerant reflux section and a gas-phase mixed refrigerant reflux section are converged into a pipeline and penetrate through the high-pressure nitrogen cooler 13 to be led to a refrigerant compressor; the high-pressure nitrogen pipeline inlet section penetrates through the high-pressure nitrogen cooler 13 and the No. 1 raw material gas cooler respectively and then is divided into two paths, one path passes through the third throttle valve 17 and is connected with the gas mixer 17, the other path continuously penetrates through the No. 2 raw material gas cooler 22 and is connected with the upper part of the nitrogen washing tower, a sixth throttle valve 23 is further arranged between the high-pressure nitrogen pipeline inlet section and the nitrogen washing tower, the lower end of the gas mixer 17 is connected with the top end of the nitrogen washing tower 24, and the upper end of the gas mixer 17 is provided with a synthetic gas conveying pipeline which is connected with a synthetic device; the lower part of the nitrogen tower 24 is provided with two pipelines to connect with a methane rectifying tower 27, the top of the methane rectifying tower 27 is provided with a conveying pipeline to connect with a liquid nitrogen system, a reflux pipeline and two output pipelines, and the bottom of the methane rectifying tower 27 is provided with a methane tower bottom reboiler 28 and is connected with an LNG storage tank through a pipeline.
As shown in figure 1, the molecular sieves are arranged in the first adsorber 7 and the second adsorber 8 of the invention, and the automatic switching is realized by a program controller, so that one adsorber is used for regeneration while the other adsorber is used for regeneration.
As shown in figure 2, the top of the raw material gas separator 19 is connected with the bottom of a nitrogen washing tower 24, raw material gas in the tower is washed by liquid nitrogen, and CO and CH in the gas4And Ar and other impurity gases are absorbed by liquid nitrogen and can come out from the top of the nitrogen washing tower to enter a gas mixer to ensure that the hydrogen-nitrogen ratio is 3: 1.
as shown in fig. 2, the liquid nitrogen-washed synthesis gas system equipped with the gas mixer 18 and the nitrogen scrubber 24 is integrated with a mixed refrigerant circulating refrigeration system and a liquefaction separation system equipped with a methane rectification column 27.
As shown in fig. 2, the cold insulation materials of the high-pressure nitrogen cooler 13, the No. 1 raw material gas cooler 16, the No. 2 raw material gas cooler 22, the nitrogen washing tower 24 and the methane rectifying tower 27 are expanded perlite, and the heat exchanger is a plate-fin heat exchanger.
The control method for the anti-freezing blockage co-production LNG liquid nitrogen washing device combined with the mixed refrigerant system as claimed in claim 1 comprises the following steps:
1) the raw material gas comes from a low-temperature methanol washing procedure and firstly enters two adsorbers to remove trace methanol and carbon dioxide in the raw material gas so as to prevent the raw material gas from freezing in a cold box to cause the blockage of low-temperature equipment and pipelines. When the first adsorber 7 works and is used, the second adsorber 8 is regenerated, the first pneumatic valve 2, the third pneumatic valve 4, the sixth pneumatic valve 9a and the ninth pneumatic valve 11 are opened, the second pneumatic valve 3, the fourth pneumatic valve 5, the fifth pneumatic valve 6, the seventh pneumatic valve 9b and the eighth pneumatic valve 10 are closed, the regeneration gas heater 1 provides nitrogen heated to 200 ℃ for the second adsorber 8, the regeneration gas cooler 12 cools the nitrogen after the regeneration action of the molecular sieve, the recovery of the nitrogen is facilitated, the first adsorber 7 receives raw material gas for purifying methanol washing, useless waste gas is filtered, and the purified gas enters the next process;
when the first adsorber 7 is regenerated, the second adsorber 8 works, the first pneumatic valve 2, the third pneumatic valve 4, the fifth pneumatic valve 6, the sixth pneumatic valve 9a and the ninth pneumatic valve 11 are closed, the second pneumatic valve 3, the fourth pneumatic valve 5, the seventh pneumatic valve 9b and the eighth pneumatic valve 10 are opened, the regeneration gas heater 1 provides nitrogen heated to 200 ℃ for the first adsorber 7, the regeneration gas cooler 12 cools the nitrogen after the regeneration action of the molecular sieve, the recovery of the nitrogen is facilitated, the second adsorber 8 receives raw material gas for purifying methanol washing, useless waste gas is filtered, and the purified gas enters the next process;
2) the raw material gas passes through a first adsorber 7 and a second adsorber 8 to remove CO2、CH3Removing impurities such as OH, entering a No. 1 cooler 16 and a No. 2 cooler 17, performing countercurrent heat exchange with purified gas from the top of a nitrogen washing tower 24 and tail gas from the top of a methane rectifying tower 27, cooling to a certain temperature, partially condensing, entering a raw material gas separator 19, continuously cooling gas at the top of the raw material gas separator 19, entering the bottom of the nitrogen washing tower 24, washing the raw material gas in the tower by liquid nitrogen, and removing CO and CH in the gas4And Ar and the like are absorbed by liquid nitrogen to obtain refined gas, and the refined gas is discharged from the top of the nitrogen washing tower 24, subjected to heat exchange, and subjected to nitrogen treatment in a gas mixer 18 to ensure that the hydrogen-nitrogen ratio is 3: 1, continuously recovering the cold energy and sending the cold energy to a synthesizer;
3) high-pressure nitrogen gas from air separation enters a cold box to be cooled and then is divided into two paths, wherein one path is used for distributing nitrogen and supplementing cold energy to refined gas, and the other path is cooled into liquid nitrogen which enters a nitrogen washing tower to be used as washing liquid;
4) the methane-rich liquid at the bottom of the raw material gas separator 19 and the tail liquid at the bottom of the nitrogen washing tower 24 are decompressed and then enter a methane rectifying tower 27, the tail gas at the top of the tower is recovered by a liquid nitrogen system to be reheated to normal temperature and then is discharged out of the device, and the LNG obtained at the bottom of the methane rectifying tower 27 is decompressed and enters an LNG product storage tank after being cooled;
5) the cold energy of the system is provided by the mixed refrigerant refrigeration cycle, and the mixed working medium refrigerant from the refrigerant compressor enters the cold box and is precooled and cooled to be used as the refrigerant to provide the cold energy for the liquefaction of the natural gas; the refrigerant is compressed and divided into a gas-phase mixed refrigerant and a liquid-phase mixed refrigerant which respectively enter the cold box, and the gas phase is cooled and then goes out of the plate-fin heat exchanger, passes through the fifth throttling valve 21 and then returns to the heat exchanger to provide liquefied cold energy for the raw material natural gas; after being subcooled in the heat exchanger, the liquid phase passes through the first throttling valve 14 and the second throttling valve 15 and then is mixed with the other returned gas-phase refrigerant, and then the liquid phase returns to the inlet of the compressor for closed cycle after being reheated.

Claims (6)

1. The device is characterized by comprising a regeneration gas heater (1) of a molecular sieve unit, a first pneumatic valve (2), a second pneumatic valve (3), a third pneumatic valve (4), a fourth pneumatic valve (5), a fifth pneumatic valve (6), a sixth pneumatic valve (9 a), a seventh pneumatic valve (9 b), an eighth pneumatic valve (10), a ninth pneumatic valve (11), a first adsorber (7), a second adsorber (8) and a regeneration gas cooler (12), and a high-pressure nitrogen cooler (13), a first throttle valve (14), a second throttle valve (15), a third throttle valve (17), a fourth throttle valve (20), a fifth throttle valve (21), a sixth throttle valve (23), a seventh throttle valve (25), an eighth throttle valve (26), a No. 1 raw material gas cooler (16) of a liquid nitrogen washing unit, The system comprises a gas mixer (18), a raw material gas separator (19), a No. 2 raw material gas cooler (22), a nitrogen washing tower (24), a methane rectifying tower (27) and a methane tower bottom reboiler (28); the bottom of the nitrogen washing tower (24) is provided with a bottom rectifying part;
one end of a regeneration gas heater (1) is connected with a low-pressure nitrogen through pipe through a pipeline, the other end of the regeneration gas heater is respectively connected with the inlet ends of a first adsorber (7) and a second adsorber (8), one end of a regeneration gas cooler (12) is connected with a nitrogen leading-out port through a pipeline, the other end of the regeneration gas cooler is divided into two branches and respectively connected with an eighth pneumatic valve (10) and a ninth pneumatic valve (11), the eighth pneumatic valve (10) is connected with the interface end of the first adsorber (7), and the ninth pneumatic valve (11) is connected with the interface end of the second adsorber (8);
a first pneumatic valve (2) is arranged on a purified gas conveying pipeline of the first adsorber (7), a fourth pneumatic valve (5) is arranged on a purified gas conveying pipeline of the second adsorber (8), a regenerative heating nitrogen gas input pipeline is connected with the adsorber end and divided into two branches, a second pneumatic valve (3) is arranged between the regenerative heating nitrogen gas input pipeline and the first adsorber (7), a third pneumatic valve (4) is arranged between the regenerative heating nitrogen gas input pipeline and the second adsorber (8), and a fifth pneumatic valve (6) is also arranged between the regenerative heating nitrogen gas input pipelines of the two adsorbers;
the methanol washing raw material gas input pipeline is divided into two branches which are respectively connected with a sixth pneumatic valve (9 a) and a seventh pneumatic valve (9 b), the sixth pneumatic valve (9 a) is connected with the interface end of the first adsorber (7), and the seventh pneumatic valve (9 b) is connected with the interface end of the second adsorber (8);
a purified gas conveying pipeline penetrates through the No. 1 raw material gas cooler (16) and the No. 2 raw material gas cooler (22) and is connected with a raw material gas separator (19), a pipeline at the lower end of the raw material gas separator (19) is connected with a methane rectifying tower (27), a fourth throttle valve (20) is arranged between the raw material gas cooler and the No. 2 raw material gas cooler, and an upper end pipeline of the raw material gas separator (19) penetrates through the No. 2 raw material gas cooler (22) and is connected with a nitrogen washing tower (24); the low-pressure liquid-phase refrigerant pipeline inlet section and the liquid-phase mixed refrigerant pipeline inlet section respectively penetrate through the high-pressure nitrogen cooler (13), a first throttling valve (14) and a second throttling valve (15) are respectively installed after penetrating through the high-pressure nitrogen cooler (13), the No. 1 raw material gas cooler (16) and the No. 2 raw material gas cooler (22), a fifth throttling valve (21) is installed after the No. 2 raw material gas cooler (22), and the backflow section of the fifth throttling valve respectively penetrates through the No. 1 raw material gas cooler (16) and the No. 2 raw material gas cooler (22); three branches of a low-pressure liquid-phase refrigerant reflux section, a liquid-phase mixed refrigerant reflux section and a gas-phase mixed refrigerant reflux section are converged into a pipeline between the high-pressure nitrogen cooler (13) and the No. 1 raw material gas cooler (16), penetrate through the high-pressure nitrogen cooler (13) and are led to a refrigerant compressor; the high-pressure nitrogen pipeline inlet section penetrates through the high-pressure nitrogen cooler (13) and the No. 1 raw material gas cooler respectively and then is divided into two paths, one path of the high-pressure nitrogen pipeline inlet section passes through the third throttling valve (17) and is connected with the gas mixer (18), the other path of the high-pressure nitrogen pipeline inlet section continues to penetrate through the No. 2 raw material gas cooler (22) and is connected with the upper part of the nitrogen washing tower, a sixth throttling valve (23) is further arranged between the No. 2 raw material gas cooler (22) and the nitrogen washing tower, the lower end of the gas mixer (18) is connected with the top end of the nitrogen washing tower (24), and a synthetic gas conveying pipeline is mounted at the upper end of the gas mixer (18) and is connected with a synthetic device; the lower part of the nitrogen washing tower (24) is provided with two pipelines to be connected with a methane rectifying tower (27), one pipeline is provided with a seventh throttling valve (25), the other pipeline is provided with an eighth throttling valve (26), the top of the methane rectifying tower (27) is provided with a conveying pipeline to be connected with a liquid nitrogen system, a reflux pipeline and two output pipelines, and the bottom of the methane rectifying tower (27) is provided with a methane tower bottom reboiler (28) and is connected with an LNG storage tank through a pipeline.
2. The anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device combined with the mixed refrigerant system is characterized in that the first adsorber (7) and the second adsorber (8) are internally provided with molecular sieves, and one of the two adsorbers is used for regeneration during operation.
3. The anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device combined with the mixed refrigerant system as claimed in claim 1, wherein the top of the raw material gas separator (19) is connected with the bottom of the nitrogen washing tower (24), raw material gas in the tower is washed by liquid nitrogen, impurity gas in the gas is absorbed by the liquid nitrogen and can come out from the top of the nitrogen washing tower and enter the gas mixer to enable the hydrogen-nitrogen ratio to be 3: 1.
4. the anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device combined with the mixed refrigerant system as claimed in claim 1, wherein the liquid nitrogen washing synthesis gas system provided with the gas mixer (18) and the nitrogen washing tower (24) is integrated with the mixed refrigerant circulation refrigeration system and the liquefaction separation system provided with the methane rectification tower (27).
5. The anti-freezing and blocking co-production LNG liquid nitrogen washing device combined with the mixed refrigerant system as claimed in claim 1, wherein the cold insulation materials of the high-pressure nitrogen cooler (13), the No. 1 raw gas cooler (16), the No. 2 raw gas cooler (22), the nitrogen washing tower (24) and the methane rectification tower (27) are expanded perlite, and the heat exchanger is a plate-fin heat exchanger.
6. The control method for the anti-freezing blockage co-production LNG liquid nitrogen washing device combined with the mixed refrigerant system as claimed in claim 1 is characterized by comprising the following steps of:
1) the raw material gas comes from a low-temperature methanol washing process and firstly enters two adsorbers to remove trace methanol and carbon dioxide in the raw material gas so as to prevent the methanol and the carbon dioxide from being frozen in a cold box to cause the blockage of low-temperature equipment and pipelines, when a first adsorber (7) works and is used, a second adsorber (8) is regenerated, a first pneumatic valve (2), a third pneumatic valve (4), a sixth pneumatic valve (9 a) and a ninth pneumatic valve (11) are opened, a second pneumatic valve (3), a fourth pneumatic valve (5), a fifth pneumatic valve (6), a seventh pneumatic valve (9 b) and an eighth pneumatic valve (10) are closed, a regeneration gas heater (1) provides nitrogen heated to 200 ℃ for the second adsorber (8), a regeneration gas cooler (12) cools the nitrogen after the regeneration of a molecular sieve, the recovery of the nitrogen is facilitated, the first adsorber (7) receives the raw material gas for purifying the methanol washing, filtering useless waste gas, and enabling purified gas to enter the next working procedure;
when the first adsorber (7) is regenerated, the second adsorber (8) works and is used, the first pneumatic valve (2), the third pneumatic valve (4), the fifth pneumatic valve (6), the sixth pneumatic valve (9 a) and the ninth pneumatic valve (11) are closed, the second pneumatic valve (3), the fourth pneumatic valve (5), the seventh pneumatic valve (9 b) and the eighth pneumatic valve (10) are opened, the regeneration gas heater (1) provides nitrogen heated to 200 ℃ for the first adsorber (7), the regeneration gas cooler (12) cools the nitrogen after the regeneration of the molecular sieve, the recovery of the nitrogen is facilitated, the second adsorber (8) receives raw material gas for purifying methanol washing, useless waste gas is filtered, and purified gas enters the next process;
2) after impurities are removed from the raw gas through a first adsorber (7) and a second adsorber (8), the raw gas enters a No. 1 raw gas cooler (16) and a No. 2 raw gas cooler (22) and then carries out countercurrent heat exchange with purified gas from the top of a nitrogen washing tower (24) and tail gas from the top of a methane rectifying tower (27), after cooling, part of the raw gas is condensed and enters a raw gas separator (19), the gas at the top of the raw gas separator (19) is continuously cooled and then enters the bottom of the nitrogen washing tower (24), the raw gas is washed by liquid nitrogen in the tower, after the impurities in the gas are absorbed by the liquid nitrogen, refined gas is obtained, after the gas comes out from the top of the nitrogen washing tower (24) and is subjected to heat exchange, and the nitrogen in a gas mixer (18) enables the hydrogen-nitrogen ratio to be 3: 1, continuously recovering the cold energy and sending the cold energy to a synthesizer;
3) high-pressure nitrogen gas from air separation enters a cold box to be cooled and then is divided into two paths, wherein one path is used for distributing nitrogen and supplementing cold energy to refined gas, and the other path is cooled into liquid nitrogen which enters a nitrogen washing tower to be used as washing liquid;
4) the methane-rich liquid at the bottom of the raw material gas separator (19) and the tail liquid at the bottom of the nitrogen washing tower (24) are decompressed and then enter a methane rectifying tower (27), the tail gas at the top of the tower is recovered by a liquid nitrogen system to be reheated to normal temperature and then is discharged out of the device, and LNG obtained at the bottom of the methane rectifying tower (27) is decompressed and enters an LNG product storage tank after being supercooled;
5) the cold energy of the system is provided by the mixed refrigerant refrigeration cycle, and the mixed working medium refrigerant from the refrigerant compressor enters the cold box and is precooled and cooled to be used as the refrigerant to provide the cold energy for the liquefaction of the natural gas; the refrigerant is compressed and divided into a gas-phase mixed refrigerant and a liquid-phase mixed refrigerant which respectively enter the cold box, and the gas phase is cooled and then passes through the plate-fin heat exchanger, then returns to the heat exchanger through a fifth throttling valve (21) and provides liquefied cold energy for the raw material natural gas; and after being subcooled in the heat exchanger, the liquid phase passes through a first throttling valve (14) and a second throttling valve (15) and then is mixed with the other returned gas-phase refrigerant, and then the liquid phase returns to the inlet of the compressor for closed cycle after being reheated.
CN201610933593.6A 2016-10-25 2016-10-25 Anti-freezing and anti-blocking co-production LNG liquid nitrogen washing device and method combined with mixed refrigerant system Active CN106369934B (en)

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