CN115991493A - Open heat pump air separation and high-efficient synthetic ammonia system based on LNG cold energy - Google Patents

Open heat pump air separation and high-efficient synthetic ammonia system based on LNG cold energy Download PDF

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CN115991493A
CN115991493A CN202310125549.2A CN202310125549A CN115991493A CN 115991493 A CN115991493 A CN 115991493A CN 202310125549 A CN202310125549 A CN 202310125549A CN 115991493 A CN115991493 A CN 115991493A
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heat exchanger
ammonia
heat pump
rectification
air separation
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CN115991493B (en
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孙志新
冯捷
黄宏基
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Fuzhou University
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Fuzhou University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04521—Coupling of the air fractionation unit to an air gas-consuming unit, so-called integrated processes
    • F25J3/04563—Integration with a nitrogen consuming unit, e.g. for purging, inerting, cooling or heating
    • F25J3/04587—Integration with a nitrogen consuming unit, e.g. for purging, inerting, cooling or heating for the NH3 synthesis, e.g. for adjusting the H2/N2 ratio
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04012—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling
    • F25J3/0403—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of warm gaseous streams; details of intake or interstage cooling of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04048—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams
    • F25J3/0406—Providing pressurised feed air or process streams within or from the air fractionation unit by compression of cold gaseous streams, e.g. intermediate or oxygen enriched (waste) streams of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04157—Afterstage cooling and so-called "pre-cooling" of the feed air upstream the air purification unit and main heat exchange line
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04151—Purification and (pre-)cooling of the feed air; recuperative heat-exchange with product streams
    • F25J3/04187—Cooling of the purified feed air by recuperative heat-exchange; Heat-exchange with product streams
    • F25J3/04218—Parallel arrangement of the main heat exchange line in cores having different functions, e.g. in low pressure and high pressure cores
    • F25J3/04224—Cores associated with a liquefaction or refrigeration cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
    • F25J3/04333—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams
    • F25J3/04351—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using quasi-closed loop internal vapor compression refrigeration cycles, e.g. of intermediate or oxygen enriched (waste-)streams of nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04406—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system
    • F25J3/04424—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system without thermally coupled high and low pressure columns, i.e. a so-called split columns
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2205/00—Processes or apparatus using other separation and/or other processing means
    • F25J2205/02—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/62—Liquefied natural gas [LNG]; Natural gas liquids [NGL]; Liquefied petroleum gas [LPG]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/04—Compressor cooling arrangement, e.g. inter- or after-stage cooling or condensate removal
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
    • F25J2245/42—Processes or apparatus involving steps for recycling of process streams the recycled stream being nitrogen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
    • F25J2270/904—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration by liquid or gaseous cryogen in an open loop
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Separation By Low-Temperature Treatments (AREA)

Abstract

The invention relates to an open heat pump air separation and high-efficiency synthesis ammonia system based on LNG cold energy, which comprises an LNG cooling system, a two-stage heat pump rectification air separation nitrogen production system, a methane steam reforming hydrogen production system and a synthesis ammonia system, wherein the two-stage heat pump rectification air separation nitrogen production system separates nitrogen from pretreated air and conveys the nitrogen to the synthesis ammonia system; the methane steam reforming hydrogen production system fully reacts methane with water, then separates hydrogen and sends the hydrogen to the synthetic ammonia system, the synthetic ammonia system mixes nitrogen with the hydrogen and then reacts to generate ammonia, and liquid ammonia is separated out through the cooling system; the LNG cooling system is used as a heat exchange cold source of an air separation part in the two-stage heat pump rectification air separation nitrogen production system, and is also used as a cold source of an ammonia separation module heat exchanger in the synthetic ammonia system. By utilizing the cold energy of LNG and an open heat pump rectification technology, the problem of cold energy waste in the LNG gasification process is solved, the problem of serious energy consumption of a rectification tower in an air separation link is solved, and the internal efficient recovery and cascade utilization of energy are realized.

Description

Open heat pump air separation and high-efficient synthetic ammonia system based on LNG cold energy
Technical field:
the invention relates to an open heat pump air separation and high-efficiency ammonia synthesis system based on LNG cold energy.
The background technology is as follows:
the ammonia synthesis industry is a high energy consumption industry of the festuca arundinacea, but the ammonia synthesis industry is one of basic chemical industry at the same time, and the yield is the first place of various chemical products. The ammonia product is an important chemical raw material and is also an important nitrogen fertilizer. Nitrogen fertilizer is generally produced by synthesizing ammonia and then processing into various iron salts or urea, so that the synthetic ammonia industry is indispensable in production and life. Therefore, the existing numerous ammonia synthesizing devices in China are required to be the primary targets for energy conservation. Because the synthesis ammonia needs hydrogen and nitrogen as raw materials, the hydrogen is generally prepared by taking natural gas as raw materials and through water-gas shift; nitrogen is obtained by an air separation process. In the process, a large amount of raw materials mainly containing energy substances are needed, and meanwhile, the cold energy requirement is high in the production process.
The natural gas has the advantages of low carbon, environmental protection, no smell, no toxicity, high heat value and the like. With the remarkable improvement of the requirements on environmental protection and ecological environment, the liquefied natural gas LNG import quantity in China is increased year by year. At the LNG receiving terminal, LNG needs to be heated to gasify to natural gas for later use. Because LNG is usually transported by sea, LNG is gasified at a receiving terminal by using sea water as a heat source, which wastes a great amount of valuable cold energy of LNG, and also causes cold pollution to the sea, thereby affecting the living environment of marine organisms.
The invention comprises the following steps:
the invention aims at improving the problems existing in the prior art, namely the technical problem to be solved by the invention is to provide an open heat pump air separation and high-efficiency ammonia synthesis system based on LNG cold energy.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: an open heat pump air separation and high-efficiency synthesis ammonia system based on LNG cold energy comprises an LNG cooling system, a two-stage heat pump rectification air separation nitrogen production system, a methane steam reforming hydrogen production system and a synthesis ammonia system, wherein the two-stage heat pump rectification air separation nitrogen production system separates nitrogen from pretreated air and conveys the nitrogen to the synthesis ammonia system; the methane steam reforming hydrogen production system fully reacts methane with water to generate hydrogen and sends the hydrogen to the synthetic ammonia system, the synthetic ammonia system mixes nitrogen with the hydrogen to react to generate ammonia, and liquid ammonia is separated out through a cooling system; the LNG cooling system is used as a heat exchange cold source of an air separation part in the two-stage heat pump rectification air separation nitrogen production system, and is also used as a cold source of a heat exchanger in an ammonia separation module in the synthetic ammonia system.
Further, the two-stage heat pump rectification air separation nitrogen production system comprises a first-stage heat pump rectification system and a second-stage heat pump rectification system, wherein the input end of the first-stage heat pump rectification system is connected with a gas treatment component for air pretreatment, a main cooler, a compressor A, a heat exchanger B, a throttle valve A, a flash tank A and a flow divider A are sequentially connected between the liquid nitrogen output end of the first-stage heat pump rectification system and the input end of the second-stage heat pump rectification system, and the oxygen-enriched liquid air output by the first-stage heat pump rectification system is conveyed to a stripping section of the second-stage heat pump rectification system; the LNG cooling system is connected with the heat exchanger B through a circulation loop taking R23 as an intermediate secondary refrigerant and is used as a cold source of the heat exchanger B.
Further, the primary heat pump rectification system comprises a high-pressure rectification tower, a compressor B, a heat exchanger C, a throttle valve B, a heat exchanger D, a flow divider B, a heat exchanger E and a flash tank B, wherein the interior of the high-pressure rectification tower is divided into a rectification section and a stripping section which are distributed up and down through a feeding tower plate, the input end of the high-pressure rectification tower is connected with a gas treatment assembly, a vapor component output from the top of the high-pressure rectification tower is compressed by the compressor B and exchanges heat with a liquid component output from the bottom of the tower at the heat exchanger C, one output port of the heat exchanger C is connected with the input end of the flow divider B in sequence, one output port of the flow divider B is connected with the rectification section of the high-pressure rectification tower, and the other output port of the flow divider B is connected with a main cooler; the other output port of the heat exchanger C is connected with a heat exchanger E between the flash tank B, a gas phase outlet of the flash tank B is connected with a stripping section of the high-pressure rectifying tower, and an input end of a liquid phase outlet secondary heat pump rectifying system of the flash tank B is connected.
Further, the secondary heat pump rectification system comprises a low-pressure rectification tower, a compressor C, a heat exchanger F, a throttle valve C, a throttle valve D, a heat exchanger G, a flow divider C, a heat exchanger H and a flash tank C, wherein the interior of the low-pressure rectification tower is divided into a rectification section and a stripping section which are distributed up and down through a feeding tray, the throttle valve C is connected between the input end of the low-pressure rectification tower and the liquid phase outlet of the flash tank B, a vapor component output from the top of the low-pressure rectification tower is compressed by the compressor C and exchanges heat with a liquid phase component output from the bottom of the tower in the heat exchanger F, one output port of the heat exchanger F is connected with the input end of the flow divider C in sequence, one output port of the flow divider C is connected with the rectification section of the low-pressure rectification tower, and the other output port of the flow divider C is connected with the ammonia synthesis system; the heat exchanger H is connected between the other output port of the heat exchanger F and the flash tank C, and the gas phase output port of the flash tank C is connected with the stripping section of the low-pressure rectifying tower.
Further, the gas treatment assembly comprises a compressor D, a heat exchanger I and a main cooler which are sequentially connected along the air conveying direction, and an output port of the main cooler is connected with an input end of the high-pressure rectifying tower; and a heat exchanger V and a heat exchanger B are arranged between the heat exchanger I and the LNG cooling system, and the LNG cooling system is directly used as a cold source of the heat exchanger I after being cooled by a circulation loop taking R23 as an intermediate secondary refrigerant and the heat exchanger B.
Further, the methane steam reforming hydrogen production system comprises a mixer A, a heat exchange component A, a mixer B, a preheating component, a steam reforming reactor, a heat exchange component B, a shift reactor, a gas-liquid separator and a separation component which are sequentially connected, wherein water input from the mixer A is heated into steam through the heat exchange component A and then mixed with methane gas in the mixer B, the mixture output from the mixer B is sent into the steam reforming reactor to carry out reforming reaction after being preheated by the preheating component, then is sent into the shift reactor to carry out shift reaction after being cooled by the heat exchange component B, liquid water component is separated by the gas-liquid separator and flows back into the mixer A, the residual gaseous component is separated by the separation component, and the obtained hydrogen component flows into the ammonia synthesis system as ammonia synthesis raw material gas.
Further, the heat exchange assembly A comprises a heat exchanger L, a heat exchanger M and a heat exchanger N which are sequentially arranged; the preheating component comprises a preheater A, a preheater B and a preheater C which are sequentially arranged; the heat exchange assembly B comprises a heat exchanger O and a heat exchanger P which are sequentially arranged; a heat exchanger Q for cooling reaction products is connected between the gas-liquid separator and the shift reactor; the separation assembly comprises a separator A and a separator B.
Further, the synthesis ammonia system comprises a raw material mixer, a first-stage synthesis ammonia reactor, a second-stage synthesis ammonia reactor, a third-stage synthesis ammonia reactor, a cooler, a flash tank D and a mixer C which are sequentially connected, gas output by the third-stage synthesis ammonia reactor is cooled by the cooler and then enters the flash tank D to separate out liquid nitrogen, and one output port of the mixer C is connected with the input end of the raw material mixer.
Further, a compressor D, a heat exchanger R, a compressor E and a heat exchanger S are sequentially connected between the raw material mixer and the first-stage synthetic ammonia reactor, a heat exchanger T is connected between the first-stage synthetic ammonia reactor and the second-stage synthetic ammonia reactor, and a heat exchanger U is connected between the second-stage synthetic ammonia reactor and the third-stage synthetic ammonia reactor.
Compared with the prior art, the invention has the following effects: the invention has reasonable design, efficiently utilizes the cold energy of LNG, solves the problem of cold energy waste in the LNG gasification process, uses part of gasified NG as hydrogen production raw material, solves the problem of serious energy consumption of the rectifying tower in the air separation link by an open heat pump rectifying technology, realizes the internal efficient recovery and cascade utilization of energy, and is used for efficiently preparing high-purity nitrogen, hydrogen and ammonia.
Description of the drawings:
fig. 1 is a schematic configuration of an embodiment of the present invention.
In the figure:
1-a two-stage heat pump rectification air separation nitrogen production system; 2 methane steam reforming hydrogen production system; 3-synthesis of ammonia systems; a 4-LNG cooling system; 6-a primary heat pump rectification system; 7-a two-stage heat pump rectification system; 9-compressor a; 10-a heat exchanger B; 11-throttle valve a; 12-flash tank a; 13-shunt a; 14-a high-pressure rectifying tower; 15-compressor B; 16-heat exchanger C; 17-throttle valve B; 18-a heat exchanger D; 19-shunt B; 20-heat exchanger E; 21-flash tank B; 22-a low pressure rectifying tower; 23-compressor C; 24-heat exchanger F; 25-throttle valve C; 26-throttle valve D; 27-heat exchanger G; 28-shunt C; 29-heat exchanger H; 30-flash tank C; 31-compressor D; 32-heat exchanger I; 35-mixer a; 36-a mixer B; a 37-steam reforming reactor; a 38-shift reactor; 39-a gas-liquid separator; 40-heat exchanger L; 41-a heat exchanger M; 42-heat exchanger N; 43-preheater a; 44-preheater B; 45-preheater C; 46-heat exchanger O; 47-heat exchanger P; 48-heat exchanger Q; 49-separator a; 50-separator B; 51-a raw material mixer; 52-a first stage ammonia synthesis reactor; 53-a second stage ammonia synthesis reactor; 54-third stage ammonia synthesis reactor 55-cooler; 56-flash tank D; 57-mixer C; 58-compressor D; 59-heat exchanger R; 60-compressor E; 61-a heat exchanger S; 62-heat exchanger T; 63-heat exchanger U; 64-diverter; 65-a coolant circulation pump; 66-heat exchanger V;67- -main cooler.
The specific embodiment is as follows:
the invention will be described in further detail with reference to the drawings and the detailed description.
In the description of the present invention, it should be understood that the terms "longitudinal," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present invention, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present invention.
As shown in fig. 1, the open heat pump air separation and high-efficiency synthesis ammonia system based on LNG cold energy comprises an LNG cooling system 4, a two-stage heat pump rectification air separation nitrogen production system 1, a methane steam reforming hydrogen production system 2 and a synthesis ammonia system 3, wherein the two-stage heat pump rectification air separation nitrogen production system 1 separates nitrogen from pretreated air and conveys the nitrogen to the synthesis ammonia system 3 to serve as raw material gas; the methane steam reforming hydrogen production system 2 fully reacts methane with water to separate hydrogen and convey the hydrogen to the synthesis ammonia system 3 to be used as raw material gas; the synthetic ammonia system 3 mixes nitrogen and hydrogen to react to generate ammonia, and separates out liquid ammonia through a cooling system; the LNG cooling system 4 is used as a heat exchange cold source of an air separation part in the two-stage heat pump rectification air separation nitrogen making system 1, and the LNG cooling system 4 is simultaneously used as a cold source of a heat exchanger in an ammonia separation module in the synthetic ammonia system 3.
In this embodiment, the two-stage heat pump rectification air separation nitrogen production system 1 includes a first-stage heat pump rectification system 6 and a second-stage heat pump rectification system 7. The input end of the primary heat pump rectification system 6 is connected with a gas treatment component for air pretreatment, a main cooler 67, a compressor A9, a heat exchanger B10, a throttle valve A11, a flash tank A12 and a flow divider A13 are sequentially connected between the liquid nitrogen output end of the primary heat pump rectification system 6 and the input end of the secondary heat pump rectification system 7, the oxygen-enriched liquid air output by the primary heat pump rectification system 6 is conveyed to the rectification section of the secondary heat pump rectification system 7, and the liquid nitrogen output end of the secondary heat pump rectification system 7 is connected with the synthetic ammonia system 3; and an LNG output section of the LNG cooling system 4 is connected with the heat exchanger B10 and serves as a cold source of the heat exchanger B. When the liquid nitrogen heat pump rectifying system works, liquid nitrogen output by the primary heat pump rectifying system 6 is heated in the main cooler 67 and then becomes gaseous, and is compressed by the compressor A9, cooled by the heat exchanger B10, throttled by the throttle valve A11 to be liquefied mostly, and the pressure of the liquid nitrogen is reduced to 0.15bar; and finally, carrying out gas-liquid separation in a flash tank A12, circulating a gas part to an inlet of a compressor A9 for continuous circulation, splitting a liquid part through a splitter A13, and sending most of the gas part to a rectifying section of a secondary heat pump rectifying system 7 for secondary rectification, and sending the small part to a storage tank as a product.
In this embodiment, the primary heat pump rectification system 6 includes a high-pressure rectification tower 14, a compressor B15, a heat exchanger C16, a throttle valve B17, a heat exchanger D18, a flow divider B19, a heat exchanger E20, and a flash tank B21, where the interior of the high-pressure rectification tower 14 is divided into a rectification section and a stripping section, which are distributed up and down, by using a feeding tray as a boundary, and the input end of the high-pressure rectification tower 14 is connected with a gas processing component. In the rectifying section of the high-pressure rectifying tower 14, the steam component rises along a feeding tower plate to enter a compressor B15 for pressurizing to improve the component temperature, the steam component output from the top of the high-pressure rectifying tower 14 is compressed by the compressor B15 and exchanges heat with the liquid phase component output from the bottom of the tower in a heat exchanger C16, a throttle valve B17 and a heat exchanger D18 are sequentially connected between one output port of the heat exchanger C16 and the input end of a flow divider B19, and one output port of the flow divider B19 is connected with the rectifying section of the high-pressure rectifying tower 14 so that part of liquid nitrogen flows back to the rectifying tower; the other output port of the shunt B19 is connected with the main cooler 67; the other output port of the heat exchanger C16 is connected with a heat exchanger E20 between a flash tank B21, a gas phase outlet of the flash tank B21 is connected with a stripping section of the high-pressure rectifying tower 14, and a liquid phase outlet of the flash tank B21 is connected with an input end of the secondary heat pump rectifying system 7.
In this embodiment, the second-stage heat pump rectification system 7 includes a low-pressure rectification column 22, a compressor C23, a heat exchanger F24, a throttle valve C25, a throttle valve D26, a heat exchanger G27, a splitter C28, a heat exchanger H29, and a flash tank C30, wherein the interior of the low-pressure rectification column 22 is divided into a rectification section and a stripping section which are distributed up and down through a feed tray, the throttle valve C25 is connected between the input end of the low-pressure rectification column 22 and the liquid phase outlet of the flash tank B21, the vapor component output from the top of the low-pressure rectification column 22 is compressed by the compressor C23 and exchanges heat with the liquid phase component output from the bottom of the column in the heat exchanger F24, one output port of the heat exchanger F24 and the input end of the splitter C28 are sequentially connected with the throttle valve D26 and the heat exchanger G27, one output port of the splitter C28 is connected with the rectification section of the low-pressure rectification column 14, and the other output port of the splitter C28 is connected with the ammonia synthesis system; and a heat exchanger H29 is connected between the other output port of the heat exchanger F24 and the flash tank C30, and the gas phase output port of the flash tank C30 is connected with the stripping section of the low-pressure rectifying tower 14.
In this embodiment, the gas treatment assembly includes a compressor D31, a heat exchanger I32, and a main cooler 67 connected in this order along the air conveying direction. The output port of the main cooler 67 is connected with the input end of the high-pressure rectifying tower 14; the air in the heat exchanger I32 exchanges heat with the LNG via the intermediate coolant. The method comprises the following steps: an intermediate coolant circulation loop is added between the cold end of heat exchanger I32 and LNG cooling system 4. The intermediate coolant can adopt nonflammable R23 as a medium to isolate direct heat exchange of LNG and air, so that potential risks are avoided. LNG transfers cold energy to R23 in heat exchanger V66, cooled R23 pre-cools the compressed air in heat exchanger I32, the temperature rises and returns to heat exchanger V66, and circulating pump 65 provides power for R23 circulation. Because the boiling point of oxygen is higher than that of nitrogen, the pretreated air is compressed to 0.60MPa by a compressor D31, cooled to be below the boiling point of oxygen (-168 ℃) by a heat exchanger I32 and a main cooler 67, changed into a gas-liquid two-phase mixture, and then is input into a high-pressure rectifying tower as raw material gas.
In this embodiment, the methane-steam reforming hydrogen production system 2 includes a mixer a35, a heat exchange assembly a, a mixer B36, a preheating assembly, a steam reforming reactor 37, a heat exchange assembly B, a shift reactor 38, a gas-liquid separator 39, and a separation assembly that are sequentially connected, water input from the mixer a35 is heated to steam by the heat exchange assembly a and then mixed with methane gas in the mixer B35, the mixture output from the mixer B35 is preheated by the preheating assembly and then sent to the steam reforming reactor 37 for reforming reaction, and then cooled by the heat exchange assembly B and then sent to the shift reactor 38 for shift reaction, separated by the gas-liquid separator 39, liquid water component flows back to the mixer a35, and residual gaseous component is separated by the separation assembly, and the obtained hydrogen component flows into the ammonia synthesis system as raw material gas for synthesizing ammonia. During operation, water in the methane steam reforming hydrogen production system is heated into steam through the heat exchange assembly A and then mixed with methane gas in the mixer B36, the steam is preheated to 800 ℃ through the preheating assembly and then sent into the steam reforming reactor 37 for reforming reaction, then cooled to 400 ℃ through the heat exchange assembly B and then sent into the shift reactor 38 for shift reaction, after the reaction product is cooled, the reaction product is separated through the gas-liquid separator 39, the liquid water component is returned to the mixer A for cyclic reaction again, and the residual gaseous component is separated through the separation assembly, so that the hydrogen component finally flows into the next stage as synthesis ammonia raw gas.
In this embodiment, the heat exchange assembly a includes a heat exchanger L40, a heat exchanger M41, and a heat exchanger N42 sequentially disposed; the preheating component comprises a preheater A43, a preheater B44 and a preheater C45 which are sequentially arranged; the heat exchange assembly B comprises a heat exchanger O46 and a heat exchanger P47 which are sequentially arranged; a heat exchanger Q48 for cooling the reaction products is connected between the gas-liquid separator 39 and the shift reactor 38; the separation assembly includes separator A49 and separator B50.
In this embodiment, the ammonia synthesis system 3 adopts the haber-bosch method, and includes a raw material mixer 51, a first-stage ammonia synthesis reactor 52, a second-stage ammonia synthesis reactor 53, a third-stage ammonia synthesis reactor 54, a cooler 55, a flash tank D56 and a mixer C57 which are sequentially connected, a compressor D58, a heat exchanger R59, a compressor E60 and a heat exchanger S61 are sequentially connected between the raw material mixer 51 and the first-stage ammonia synthesis reactor 52, a heat exchanger T62 is connected between the first-stage ammonia synthesis reactor 52 and the second-stage ammonia synthesis reactor 53, a heat exchanger U63 is connected between the second-stage ammonia synthesis reactor 53 and the third-stage ammonia synthesis reactor 54, the gas output by the third-stage ammonia synthesis reactor 54 is cooled by the cooler 55 and then enters the flash tank D56 to be separated, and an output port of the mixer C57 is connected with an input end of the raw material mixer 51. During operation, the raw material mixer 51 mixes the raw material gas sent by the two-stage heat pump rectification air separation nitrogen making system and the methane steam reforming hydrogen making system, then is cooled and compressed to 15.6MPa in the middle of the two-stage compression (the compressor D58 and the compressor E60), is cooled to 310 ℃ by the heat exchanger S61, enters the first-stage synthetic ammonia reactor 52 for reaction, is cooled to 330 ℃ by the heat exchanger T62, enters the second-stage synthetic ammonia reactor 53 for reaction, is cooled to 340 ℃ by the heat exchanger U63, and enters the third-stage synthetic ammonia reactor 54 for reaction. The gas from the third stage synthesis ammonia reactor 54 is cooled to-23 ℃ by a cooler 55, enters a flash tank D56 to separate out liquid ammonia, and simultaneously, most of the gas is introduced into the inlet of the raw material mixer 51 as recycle gas to be mixed and re-reacted with the raw material gas for subsequent reaction, and the extracted part is discharged as purge gas to prevent the accumulation of inert gas from influencing the subsequent reaction.
In this embodiment, the LNG cooling system 4 is first used as a cold source of the heat exchanger B10 and the heat exchanger I32 of the air separation part, and at this time, the temperature of the LNG is raised to-148 ℃, and the LNG enters the ammonia synthesis system to be used as a cold source of the cooler 55 for cooling the mixed gas at the outlet of the third-stage ammonia synthesis reactor 54.
In this embodiment, the flow from the third stage ammonia synthesis reactor 54 in the cooler 55 is left in and right out; the flow coming out of the LNG cooling system 4 is up-in and down-out, and the NG gas output by the cooler 55 is split by the splitter 64, and part of the NG gas is sent to the storage tank and part of the NG gas is sent to the methane in the mixer B36 to be used as the raw material for hydrogen production by methane reforming.
The specific implementation process comprises the following steps:
in the starting stage, after the pretreated air in the two-stage heat pump rectification air separation nitrogen production system is compressed to 0.60MPa by a compressor D31, as the boiling point of oxygen is higher than that of nitrogen, the air is continuously cooled to be below the boiling point (-168 ℃) of oxygen by a heat exchanger I32 and a main cooler 67, and then the raw material gas is changed into a gas-liquid two-phase mixture, and enters a high-pressure rectifying tower 14. The high-pressure rectifying tower is bounded by a feeding tower plate, a rectifying section is arranged above the feeding tower plate, and a stripping section is arranged below the feeding tower plate. In the rectifying section, the steam component rises along a feeding tower plate to enter a compressor B15 for pressurizing to increase the component temperature, heat exchange is carried out between the steam component and cold flow at the bottom of the tower through a heat exchanger C16, the steam component enters a throttle valve B17 for pressure relief, the steam component is fully condensed into liquid nitrogen through a heat exchanger D18, finally, the liquid reflux flows back to the rectifying section of the high-pressure rectifying tower 14 through a flow divider B19, the reflux liquid exchanges heat with the steam rising subsequently, the steam is partially condensed into liquid after encountering cold, oxygen is more easily condensed into liquid to flow into the stripping section, and the liquid nitrogen with higher concentration is obtained at the outlet of the flow divider B19 through multiple times of condensation. In the stripping section, the liquid phase component flows out from the bottom of the high-pressure rectifying tower along a feeding tower plate, exchanges heat with a heat flow stream of the steam component at the top of the tower through a heat exchanger C16, is heated through a heat exchanger E20, and finally is split in a flash tank B21, wherein liquid nitrogen with higher volatility is evaporated into nitrogen which is returned to the stripping section of the high-pressure rectifying tower 14 again, rises to the top of the tower along the tower bottom and flows out from the upper part of the high-pressure rectifying tower 14, and the liquid phase outlet of the flash tank B21 obtains an oxygen-enriched liquid space.
Liquid nitrogen produced from the top of the high pressure rectifying column is warmed up in the main cooler 67 and then becomes gaseous, and at the same time, compressed by the compressor A9, cooled by the heat exchanger B10, throttled by the throttle valve a11 to be mostly liquefied, and reduced in pressure to 0.15bar. And finally, carrying out gas-liquid separation in a flash tank A12, recycling a gas part to an inlet of a compressor A9 for continuous recycling, splitting a liquid part through a splitter A13, sending most part of the gas part to a low-pressure tower rectifying tower 22 for secondary rectification, and sending the small part of the gas part as a product to a storage tank.
And finally, the oxygen-enriched liquid air at the liquid phase outlet of the flash tank B21 is changed into gas-liquid two phases through throttling and depressurization, the gas-liquid two phases are sent into the low-pressure rectifying tower 22 from the inlet of the 12 th column plate, most of liquid nitrogen separated by the splitter A13 is sent into the low-pressure rectifying tower from the 2 nd column plate, the steam component rises along the column plate and enters the compressor C23 to pressurize and raise the component temperature, the steam component is subjected to heat exchange with cold flow at the bottom of the tower through the heat exchanger F24, enters the throttle valve D26 to decompress, is fully condensed into liquid nitrogen through the heat exchanger G27, finally, the liquid reflux and the steam which rises later are subjected to heat exchange, the steam is partially condensed into liquid after encountering cold, wherein the oxygen is easier to be condensed into liquid to flow into the stripping section, and the liquid nitrogen with higher concentration is obtained at the outlet of the splitter C through multiple condensation. In the stripping section, the liquid phase component flows out from the bottom of the low-pressure rectifying tower 22 along a tower plate, exchanges heat with a hot stream of the steam component at the top of the tower through a heat exchanger F24, is heated through a heat exchanger H29, and finally is split in a flash tank C30, wherein liquid nitrogen with higher volatility is evaporated into nitrogen which is returned to the stripping section of the low-pressure rectifying tower again, rises to the top of the tower along the tower bottom and flows out from the upper part of the low-pressure rectifying tower, and a liquid phase outlet of the flash tank C30 obtains oxygen with higher concentration.
The water in the methane steam reforming hydrogen production system is heated into steam through a heat exchanger L40, a heat exchanger M41 and a heat exchanger N42 and then mixed with methane gas in a mixer B36, the steam is preheated to 800 ℃ through a preheater A43, a preheater B44 and a preheater C45 and then sent into a steam reforming reactor 37 to carry out reforming reaction, then cooled to 400 ℃ through a heat exchanger O46 and a heat exchanger P47 and then sent into a shift reactor to carry out shift reaction, after the reaction product is cooled, the reaction product is separated through a gas-liquid separator, the liquid water component is recirculated and reacted with the methane gas in an inlet of a mixer A35, and the residual gaseous component is finally obtained through a separator A49 and a separator B50 and flows into the next stage as the raw gas of synthetic ammonia.
The synthetic ammonia system adopts a Haber-Bosch method, raw gas sent by a two-stage heat pump rectification air separation nitrogen production system and a methane steam reforming hydrogen production system is mixed and then compressed to 15.6MPa in a two-stage compression intermediate cooling mode, the raw gas is cooled to 310 ℃ through a heat exchanger S61 and then enters a first-stage synthetic ammonia reactor 52 for reaction, then is cooled to 330 ℃ through a heat exchanger T62, then enters a second-stage synthetic ammonia reactor 53 for reaction, is cooled to 340 ℃ through a heat exchanger U63 and then enters a third-stage synthetic ammonia reactor 54 for reaction. The gas from the third stage synthesis ammonia reactor 54 is cooled to-23 ℃ by a cooler 55, enters a flash tank D56 to separate out liquid ammonia, and simultaneously, most of the gas is introduced into the inlet of the raw material mixer 51 as recycle gas to be mixed and re-reacted with the raw material gas for subsequent reaction, and the extracted part is discharged as purge gas to prevent the accumulation of inert gas from influencing the subsequent reaction.
The LNG cooling system 4 is first used as a cold source of the heat exchanger B10 and the heat exchanger I32 of the air separation part, and at this time, the temperature of the LNG is raised to-148 ℃, and the LNG enters the synthesis ammonia system to be used as a cold source of the cooler, so as to cool the mixed gas at the outlet of the third-stage synthesis ammonia reactor 54.
The invention has the advantages that: the LNG gasification process has the advantages that LNG cold energy is efficiently utilized, the problem of cold energy waste in the LNG gasification process is solved, meanwhile, the problem of serious energy consumption of the rectifying tower in an air separation link is solved through an open heat pump rectifying technology, and the efficient recovery and cascade utilization of the energy are realized, so that high-purity nitrogen, hydrogen and ammonia are efficiently prepared.
If the invention discloses or relates to components or structures fixedly connected with each other, then unless otherwise stated, the fixed connection is understood as: detachably fixed connection (e.g. using bolts or screws) can also be understood as: the non-detachable fixed connection (e.g. riveting, welding), of course, the mutual fixed connection may also be replaced by an integral structure (e.g. integrally formed using a casting process) (except for obviously being unable to use an integral forming process).
In addition, terms used in any of the above-described aspects of the present disclosure to express positional relationship or shape have meanings including a state or shape similar to, similar to or approaching thereto unless otherwise stated.
Any part provided by the invention can be assembled by a plurality of independent components, or can be manufactured by an integral forming process.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same; while the invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that: modifications may be made to the specific embodiments of the present invention or equivalents may be substituted for part of the technical features thereof; without departing from the spirit of the invention, it is intended to cover the scope of the invention as claimed.

Claims (9)

1. An open heat pump air separation and high-efficient synthetic ammonia system based on LNG cold energy, its characterized in that: the system comprises an LNG cooling system, a two-stage heat pump rectification air separation nitrogen production system, a methane steam reforming hydrogen production system and a synthetic ammonia system, wherein the two-stage heat pump rectification air separation nitrogen production system separates nitrogen from pretreated air and conveys the nitrogen to the synthetic ammonia system; the methane steam reforming hydrogen production system fully reacts methane with water to generate hydrogen and sends the hydrogen to the ammonia synthesis system; the synthetic ammonia system mixes nitrogen with hydrogen to react to generate ammonia, and separates out liquid ammonia through a cooling system; the LNG cooling system is used as a heat exchange cold source of an air separation part in the two-stage heat pump rectification air separation nitrogen production system, and is also used as a cold source of an ammonia separation module heat exchanger in the synthetic ammonia system.
2. An open heat pump air separation and efficient synthesis ammonia system based on LNG cold energy as claimed in claim 1, wherein: the two-stage heat pump rectification air separation nitrogen production system comprises a first-stage heat pump rectification system and a second-stage heat pump rectification system; the system comprises a primary heat pump rectification system, a secondary heat pump rectification system, a main cooler, a compressor A, a heat exchanger B, a throttle valve A, a flash tank A and a flow divider A, wherein the input end of the primary heat pump rectification system is connected with a gas treatment component for air pretreatment; the liquid nitrogen output end of the secondary heat pump rectification system is connected with the ammonia synthesis system; the LNG cooling system is connected with the heat exchanger B through a circulation loop taking R23 as an intermediate secondary refrigerant and is used as a cold source of the heat exchanger B.
3. An open heat pump air separation and efficient synthesis ammonia system based on LNG cold energy as claimed in claim 2, wherein: the primary heat pump rectification system comprises a high-pressure rectification tower, a compressor B, a heat exchanger C, a throttle valve B, a heat exchanger D, a flow divider B, a heat exchanger E and a flash tank B, wherein the interior of the high-pressure rectification tower is divided into a rectification section and a stripping section which are distributed up and down through a feeding tower plate, the input end of the high-pressure rectification tower is connected with a gas treatment assembly, the vapor component output from the top of the high-pressure rectification tower is compressed by the compressor B and exchanges heat with the liquid component output from the bottom of the tower at the heat exchanger C, one output port of the heat exchanger C is connected with the input end of the flow divider B in sequence, one output port of the flow divider B is connected with the rectification section of the high-pressure rectification tower, and the other output port of the flow divider B is connected with a main cooler; the other output port of the heat exchanger C is connected with a heat exchanger E between the flash tank B, a gas phase outlet of the flash tank B is connected with a stripping section of the high-pressure rectifying tower, and an input end of a liquid phase outlet secondary heat pump rectifying system of the flash tank B is connected.
4. An open heat pump air separation and efficient ammonia synthesis system based on LNG cold energy as claimed in claim 3, wherein: the secondary heat pump rectification system comprises a low-pressure rectification tower, a compressor C, a heat exchanger F, a throttle valve C, a throttle valve D, a heat exchanger G, a flow divider C, a heat exchanger H and a flash tank C, wherein the interior of the low-pressure rectification tower is divided into a rectification section and a stripping section which are distributed up and down through a feeding tower plate, the throttle valve C is connected between the input end of the low-pressure rectification tower and the liquid phase outlet of the flash tank B, a vapor component output from the top of the low-pressure rectification tower is compressed by the compressor C and exchanges heat with a liquid phase component output from the bottom of the tower in the heat exchanger F, one output port of the heat exchanger F is connected with the input end of the flow divider C in sequence, one output port of the flow divider C is connected with the rectification section of the low-pressure rectification tower, and the other output port of the flow divider C is connected with the ammonia synthesis system; the heat exchanger H is connected between the other output port of the heat exchanger F and the flash tank C, and the liquid phase output port of the flash tank C is connected with the stripping section of the low-pressure rectifying tower.
5. An open heat pump air separation and efficient ammonia synthesis system based on LNG cold energy as claimed in claim 3, wherein: the gas treatment assembly comprises a compressor D, a heat exchanger I and a main cooler which are sequentially connected along the air conveying direction, and an output port of the main cooler is connected with an input end of the high-pressure rectifying tower; and a heat exchanger V and a heat exchanger B are arranged between the heat exchanger I and the LNG cooling system, and the LNG cooling system is directly used as a cold source of the heat exchanger I after being cooled by a circulation loop taking R23 as an intermediate secondary refrigerant and the heat exchanger B.
6. An open heat pump air separation and efficient synthesis ammonia system based on LNG cold energy as claimed in claim 1, wherein: the methane steam reforming hydrogen production system comprises a mixer A, a heat exchange component A, a mixer B, a preheating component, a steam reforming reactor, a heat exchange component B, a shift reactor, a gas-liquid separator and a separation component which are sequentially connected, wherein water input from the mixer A is heated into steam through the heat exchange component A and then mixed with methane gas in the mixer B, the mixture output by the mixer B is sent into the steam reforming reactor for reforming reaction after being preheated by the preheating component, then is sent into the shift reactor for shift reaction after being cooled by the heat exchange component B, liquid water component is separated by the gas-liquid separator, liquid water component flows back into the mixer A, residual gaseous component is separated by the separation component, and the obtained hydrogen component flows into the ammonia synthesis system as ammonia synthesis raw material gas.
7. The open heat pump air separation and high efficiency ammonia synthesis system based on LNG cold energy of claim 6, wherein: the heat exchange assembly A comprises a heat exchanger L, a heat exchanger M and a heat exchanger N which are sequentially arranged; the preheating component comprises a preheater A, a preheater B and a preheater C which are sequentially arranged; the heat exchange assembly B comprises a heat exchanger O and a heat exchanger P which are sequentially arranged; a heat exchanger Q for cooling reaction products is connected between the gas-liquid separator and the shift reactor; the separation assembly comprises a separator A and a separator B.
8. An open heat pump air separation and efficient synthesis ammonia system based on LNG cold energy as claimed in claim 1, wherein: the synthesis ammonia system comprises a raw material mixer, a first-stage synthesis ammonia reactor, a second-stage synthesis ammonia reactor, a third-stage synthesis ammonia reactor, a cooler, a flash tank D and a mixer C which are sequentially connected, wherein gas output by the third-stage synthesis ammonia reactor is cooled by the cooler and then enters the flash tank D to separate out liquid ammonia, and one output port of the mixer C is connected with the input end of the raw material mixer.
9. The open heat pump air separation and high efficiency ammonia synthesis system based on LNG cold energy of claim 8, wherein: the device comprises a raw material mixer, a first section of synthetic ammonia reactor, a second section of synthetic ammonia reactor, a heat exchanger U, a heat exchanger R, a compressor E and a heat exchanger S, wherein the raw material mixer is sequentially connected with the first section of synthetic ammonia reactor, the heat exchanger T is connected between the first section of synthetic ammonia reactor and the second section of synthetic ammonia reactor, and the heat exchanger U is connected between the second section of synthetic ammonia reactor and the third section of synthetic ammonia reactor.
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