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CN109140903B - Air separation system and air separation method utilizing cold energy of liquefied natural gas - Google Patents

Air separation system and air separation method utilizing cold energy of liquefied natural gas Download PDF

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Publication number
CN109140903B
CN109140903B CN201810973812.2A CN201810973812A CN109140903B CN 109140903 B CN109140903 B CN 109140903B CN 201810973812 A CN201810973812 A CN 201810973812A CN 109140903 B CN109140903 B CN 109140903B
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nitrogen
heat exchanger
lng
liquid
gas
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CN109140903A (en
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邢仁钊
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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
    • F25J3/04006—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
    • F25J3/04018—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 main feed air
    • 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
    • F25J3/04006—Providing pressurised feed air or process streams within or from the air fractionation unit
    • F25J3/04078—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression
    • F25J3/04084—Providing pressurised feed air or process streams within or from the air fractionation unit providing pressurized products by liquid compression and vaporisation with cold recovery, i.e. so-called internal compression 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
    • F25J3/04193—Division of the main heat exchange line in consecutive sections having different functions
    • 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
    • F25J3/04254—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using the cold stored in external cryogenic fluids
    • F25J3/0426—The cryogenic component does not participate in the fractionation
    • F25J3/04266—The cryogenic component does not participate in the fractionation and being liquefied hydrocarbons
    • F25J3/04272—The cryogenic component does not participate in the fractionation and being liquefied hydrocarbons and comprising means for reducing the risk of pollution of hydrocarbons into the air fractionation
    • 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
    • F25J3/04357—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 and comprising a gas work expansion loop
    • 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
    • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
    • F25J5/002—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger
    • F25J5/007—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger combined with mass exchange, i.e. in a so-called dephlegmator
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/20—Boiler-condenser with multiple exchanger cores in parallel or with multiple re-boiling or condensing streams
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/30—External or auxiliary boiler-condenser in general, e.g. without a specified fluid or one fluid is not a primary air component or an intermediate fluid
    • F25J2250/40—One fluid being air
    • 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
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/30—External or auxiliary boiler-condenser in general, e.g. without a specified fluid or one fluid is not a primary air component or an intermediate fluid
    • F25J2250/42—One fluid 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

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

Abstract

The invention discloses an air separation system and an air separation method utilizing cold energy of liquefied natural gas. The system comprises an air separation unit, an LNG cold energy utilization unit and an ethylene glycol solution circulating and cooling unit; the new flow organization form of replacing the low-temperature circulating nitrogen compressor by using the circulating liquid nitrogen pump greatly reduces the production energy consumption of the LNG cold energy air separation system, has high oxygen and argon extraction rate, ensures that the nitrogen liquefaction rate of the product reaches 100 percent, and has high added value; the LNG cold change can be matched in a liquid nitrogen reflux cold supplementing mode, so that the technical requirements on the LNG receiving station are low, and the universality is high; compared with the prior LNG cold energy space division technology, the method has the advantages that the comprehensive energy consumption is reduced by more than 40%, the unit energy consumption is reduced by more than 60%, the unit energy consumption under the extreme production reduction working condition is still lower than that of the prior art, and the cost advantage is quite obvious.

Description

Air separation system and air separation method utilizing cold energy of liquefied natural gas
Technical Field
The invention relates to an air separation method, in particular to an air separation method utilizing liquefied natural gas cold energy.
Background
Natural gas is used as one of chemical energy sources, and is gradually promoted into main energy support columns after coal and petroleum due to huge storage capacity and low pollution, so that the natural gas has wide application prospect. The trade forms of natural gas mainly include pipeline transportation and LNG (liquefied natural gas) transportation, and before the LNG enters a natural gas user pipe network, the LNG needs to be gasified from a liquefied state to normal temperature, and huge cold energy is released in the gasification process. The air separation device can obviously reduce power consumption and increase the production of liquid by fully utilizing the gasification cold energy of LNG, and improves the competitiveness of the product in the market sales, and the economic benefit is obvious. However, since the air separation system is an oxygen-enriched zone, natural gas is a very sensitive hazardous substance as a hydrocarbon. Therefore, the utilization of LNG cold energy generally adopts an intermediate medium to transfer the cold energy, and the direct contact of LNG and an air separation system is avoided. In the longitudinal and domestic LNG cold energy air separation device, the phenomena of excessively complex flow organization, high energy consumption, difficult implementation, inconvenient operation control or poor safety and reliability generally exist. For example, a plurality of compressors, a plurality of expanders, separation tanks and the like are adopted, so that the heat exchanger channels are more, especially LNG is high pressure, and the heat exchanger channels are more, so that the cost is increased sharply. In addition, the process organization is complex, and areas with more electric elements such as valves, measuring points and the like need to be explosion-proof, so that hidden danger is brought to the safety of the device.
Chinese patent application specification CN 101571340a discloses an air separation system utilizing cold energy of liquefied natural gas, and this patent adopts a circulating nitrogen compressor with three sections of low-temperature air intake, adopts an ethylene glycol cooling system, but the liquid oxygen product is mainly obtained by means of throttling high-pressure supercooled liquid nitrogen in a low-pressure oxygen and LNG-nitrogen heat exchanger to low pressure for heat exchange, and one of cold sources of supercooled circulating high-pressure liquid nitrogen is throttled low-pressure liquid nitrogen, namely, the inlet flow of one section of circulating low-temperature nitrogen compressor is larger, resulting in higher shaft power of the low-temperature nitrogen compressor.
Chinese patent application specification CN 101532768A discloses an air separation system that uses lng cold energy efficiently, and some embodiments of the patent use a liquid expander instead of a throttle valve to expand high-pressure liquid nitrogen, but the cold energy transfer medium circulates nitrogen driven by a low-temperature circulating nitrogen compressor to compress the circulating nitrogen to supercritical pressure, and the energy consumption is several tens times higher than that of liquid nitrogen pumped by a liquid pump. And a large amount of high-purity nitrogen is diffused due to the fact that the nitrogen cannot be liquefied, so that the comprehensive unit energy consumption of the system is further increased.
For this reason, it is required to develop a space division system using lng cold energy which can eliminate the above-mentioned drawbacks.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an air separation system with strong universality and utilizing the cold energy of liquefied natural gas, wherein the system organically combines the low-temperature cold energy pressurized to the LNG with the specified pressure with an air separation unit, and fully utilizes the cold energy of the LNG.
The invention also provides an air separation method by utilizing the air separation system of the liquefied natural gas cold energy, namely the low-temperature cold energy of the LNG is used for producing a liquid air separation product and an internal compressed gas product so as to reduce the unit power consumption of the liquid air separation product and the internal compressed gas product, and simultaneously, the LNG is gasified and heated in the air separation system to reach the required pipe transportation temperature.
The technical scheme adopted by the invention for achieving the purpose is as follows:
an air separation system utilizing liquefied natural gas cold energy, which is characterized in that: comprises an air separation unit, an LNG cold energy utilization unit and an ethylene glycol solution circulating and cooling unit;
the glycol solution circulation cooling unit comprises an LNG-glycol heat exchanger 12 and a glycol solution circulation pump 15;
the LNG cold energy utilization unit comprises a circulating liquid nitrogen pump 9, an LNG-nitrogen heat exchanger 11, a gas-liquid separator 10, a liquid booster expander 13 and a vent silencer 17;
the air separation unit comprises a self-cleaning air filter 1, an air compressor 2, a molecular sieve 3, a regenerated gas heater 14, a main heat exchanger 4, a liquefying heat exchanger 5, a rectifying tower and a venting silencer 16, wherein the rectifying tower comprises a lower tower 6, a main condensing evaporator 7 and an upper tower 8.
In the air separation unit, the outlet of the self-cleaning air filter 1 is connected with the inlet of the air compressor 2; the inlet of the molecular sieve 3 is respectively connected with the outlet of the air compressor 2 and the air vent silencer 16; the outlet of the molecular sieve 3 is respectively connected with the main heat exchanger 4 and the regenerated gas heater 14;
the hot end and the cold end of the main heat exchanger 4 are respectively provided with three strands, and the hot end is respectively connected with the outlet of the molecular sieve 3, the hot end of the LNG-nitrogen heat exchanger 11 and the regenerated gas heater 14; the cold end is respectively connected with one hot end of the liquefaction heat exchanger 5 and one cold end and the outlet of the circulating liquid nitrogen pump 9;
six strands of heat are respectively arranged at the hot end and the cold end of the liquefaction heat exchanger 5; the cold end is respectively connected with one cold end of the main heat exchanger 4, the upper part and the top of the upper tower 8, the top of the lower tower 6 and the upper part and the top of the gas-liquid separator 10; the hot end is respectively connected with the bottom and the top of the lower tower 6, one cold end of the main heat exchanger 4, one hot end of the LNG-nitrogen heat exchanger 11 and a pressurizing end inlet of the liquid pressurizing expander 13;
the top of the lower tower 6 is provided with two groups of outlets and inlets, one group is respectively connected with the hot end and the cold end of the main condensing evaporator 7, and the other group is respectively connected with the hot end and the cold end of the liquefaction heat exchanger 5; the bottom inlet is connected with the hot end of the liquefaction heat exchanger 5, and the bottom outlet is connected with the upper part of the upper tower 8 through a throttle valve;
the inlet of the main condensation evaporator 7 is connected with the top of the lower tower 6, the outlet is divided into three parts, and the three parts are respectively connected with the top of the lower tower 6, a product liquid oxygen storage tank and the top of the upper tower 8 through a throttle valve;
the outlet of the upper tower 8 is divided into three strands, namely a first outlet at the top is connected with a product liquid nitrogen storage tank, and a second outlet at the top and an outlet at the upper part are connected with two cold ends of the liquefaction heat exchanger 5 respectively; the top and upper two inlets are connected to the main condensing evaporator 7 and the bottom of the lower column 6, respectively.
For continuous and uninterrupted use, the molecular sieve 3 is divided into two parts, alternately used, purified and regenerated. The inlet of the purifying end is connected with the outlet of the air compressor 2, and the outlet of the purifying end is connected with the hot end of the main heat exchanger 4; the inlet of the regeneration end is connected to the outlet of the regeneration gas heater 14 and the outlet of the regeneration end is connected to the purge muffler 16.
In the glycol solution circulation cooling unit, two strands are respectively arranged at the hot end and the cold end of the LNG-glycol heat exchanger 12, the two strands at the cold end are respectively connected with the inlets of the low-temperature natural gas pipeline, the interstage cooler of the air compressor 2 and the final-stage cooler, and the hot end is respectively connected with the outlets of the natural gas pipeline and the glycol solution circulation pump 15;
the inlet of the glycol solution circulating pump 15 is connected with the outlets of the air compressor 2 interstage cooler and the final-stage cooler, and the outlet is connected with the hot end of the LNG-glycol heat exchanger 12; the effects of reducing the energy consumption of the air compressor and the adsorption resistance of the molecular sieve are achieved by reducing the two-stage and three-stage suction temperature of the air compressor 2 and the molecular sieve suction temperature.
In the LNG cold energy utilization unit, an inlet of the circulating liquid nitrogen pump 9 is connected with the bottom of the gas-liquid separator 10, and an outlet of the circulating liquid nitrogen pump is connected with the cold end of the main heat exchanger 4; the compressed liquid is used for replacing compressed gas, namely a liquid nitrogen pump is used for replacing a low-temperature nitrogen compressor on equipment, so that the effect of greatly reducing energy consumption is achieved.
The top outlet and the upper inlet of the gas-liquid separator 10 are respectively connected with two cold ends of the liquefaction heat exchanger 5, the other inlet of the upper part is connected with a liquid nitrogen product storage tank, and the bottom outlet is respectively connected with the inlet of the circulating liquid nitrogen pump 9, the product liquid nitrogen storage tank and the LNG-nitrogen heat exchanger 11; the middle inlet is connected with the outlet of the expansion end of the liquid booster expander 13;
in order to improve the nitrogen liquefaction rate and reduce the waste of the air separation nitrogen product, a liquid booster expander of liquid nitrogen is used for replacing a liquid nitrogen throttle valve, so that the system has the capability of liquefying all the product nitrogen. The liquid booster expander 13 is divided into a booster end and an expansion end, the inlet of the booster end is connected with two hot ends of the liquefaction heat exchanger 5, and the outlet of the booster end is connected with the hot ends of the LNG-nitrogen heat exchanger 11; the inlet of the expansion end is connected with the cold end of the LNG-nitrogen heat exchanger 11, and the outlet of the expansion end is connected with the gas-liquid separator 10;
five cold ends and four hot ends of the LNG-nitrogen heat exchanger 11 are respectively connected with an LNG pipeline, the hot end of the liquefaction heat exchanger 5, an expansion end inlet of the liquid booster expander 13, the LNG-glycol heat exchanger (12) and the bottom of the gas-liquid separator 10; the hot end is respectively connected with a natural gas pipeline, a supercharging end outlet of the liquid supercharging expander 13, the hot end of the main heat exchanger 4 and the emptying silencer 17.
In order to improve the adaptability of the LNG cold energy air separation system to the cold source LNG cold energy change, the LNG-nitrogen heat exchanger 11 is provided with a heat exchange channel, and two ends of the LNG-nitrogen heat exchanger are respectively connected with the gas-liquid separator 10 and the emptying silencer 17, so that the LNG cold energy air separation system is started to be used when the LNG cold energy is insufficient; a stream 604 is withdrawn in the middle of the natural gas heat exchange path to adjust the refrigeration to the LNG-ethylene glycol heat exchanger 12.
In order to facilitate the start-up of the whole system, the gas-liquid separator 10 is provided with a pipeline 216 connected with a liquid nitrogen tank of the product, and is used when the air separation system is started up.
In order to prevent the heat exchange efficiency from being affected by the phase change of the multiple streams, the main heat exchanger 4, the liquefaction heat exchanger 5 and the LNG-nitrogen heat exchanger 11 are all composed of a single heat exchanger or multiple heat-separating heat exchangers, so that temperature crossing in the heat exchangers is avoided.
The invention also provides a method for air separation by using the air separation system of liquefied natural gas cold energy, which comprises the following steps:
a) Raw material air is subjected to the self-cleaning filter 1 to remove most of solid impurities, then enters the air compressor 2 to be compressed, and the impurities such as water, hydrocarbon and the like are removed through the molecular sieve system 3 to obtain purified air 103;
b) The purified air 103 is cooled and liquefied in the main heat exchanger 4 by exchanging heat with the dirty nitrogen 402 and the high-pressure circulating liquid nitrogen 501 which are withdrawn from the upper part of the upper tower 8 and provided with cold energy in the liquefaction heat exchanger 5 and preliminarily reheated; the polluted nitrogen 403 which is completely reheated in the main heat exchanger is connected with the purification system 3 to be used as regenerated gas and cold blowing gas;
c) The liquefied air 104 provides cold energy for liquefied pressure nitrogen 205 and 208 in the liquefying heat exchanger 5, and is reheated to be gas-liquid mixed air 105, and enters the rectifying tower system to be separated into an exhaust stream, wherein the exhaust stream comprises pure nitrogen 202 and liquid nitrogen product 218 obtained from the top of the upper tower 7, polluted nitrogen 401 obtained from the upper part of the upper tower 7 and liquid oxygen 301 obtained from the bottom of the upper tower;
d) After the raw material air 105 is subjected to preliminary separation in the lower tower 6, an oxygen-enriched liquid air 106 is obtained at the bottom of the lower tower 6, medium-pressure nitrogen is obtained at the top of the lower tower 6, the medium-pressure nitrogen enters the main condensing evaporator 7 and is condensed into liquid nitrogen by liquid oxygen at the bottom of the upper tower 8, part of the liquid nitrogen is sent back to the lower tower 6 to maintain the rectification working condition of the lower tower 6, and the other part of the liquid nitrogen 201 is throttled and sent to the top of the upper tower 8 to participate in rectification; in addition, a stream of pressure nitrogen 208 is pumped out to enter the liquefaction heat exchanger 5, and is liquefied and then returned to the lower tower 6 to be used as reflux liquid; the oxygen-enriched liquid space 106 is throttled and then sent into the middle part of the upper tower 8 to participate in the rectification of the upper tower 8;
e) The liquid nitrogen 201, the oxygen-enriched liquid air 106 and the gas oxygen evaporated by the main condensation evaporator 7 which are fed into the upper tower are rectified again, low-pressure nitrogen 202 and liquid nitrogen 218 are obtained from the top of the upper tower 8, dirty nitrogen 401 is obtained from the upper part of the upper tower 8, the upper part of the main condensation evaporator 7 is communicated with the bottom of the upper tower 8, liquid oxygen is obtained from the bottom of the upper tower 8, unvaporized liquid oxygen 301 is extracted from the main condensation evaporator 7, and the unvaporized liquid oxygen is sent out as product liquid oxygen; the polluted nitrogen 401 obtained from the upper part of the upper tower 8 is reheated in the liquefaction heat exchanger 5 and the main heat exchanger 4 and heated up to be separated into two paths after an air separation unit, one path of polluted nitrogen is treated by the regenerated gas heater 16 to the air purifier 3 to be used as regeneration gas, and the other path of polluted nitrogen is treated by the air purification silencer to be discharged; if the space division is provided with an argon system, an argon fraction is obtained from the middle part of the upper tower, and the argon fraction is sent to an argon making system for preparing liquid argon, wherein the argon making system is well known to the person skilled in the art and is not further described herein;
f) Part of liquid nitrogen 213 obtained in the gas-liquid separator 10 enters a circulating liquid nitrogen pump 9 to be pressurized into supercritical pressure liquid nitrogen 501, enters a main heat exchanger 4 to be reheated to normal temperature, enters an LNG-nitrogen heat exchanger 11 to be cooled into supercritical liquid nitrogen 503 by high-pressure LNG602, and LNG cold energy is obtained; after liquefaction, the mixture enters an expansion end of the liquid booster expander 13 to be expanded into low-pressure gas-liquid mixed nitrogen 210, and the low-pressure gas-liquid mixed nitrogen enters the gas-liquid separator 10 to be separated into nitrogen 211 and liquid nitrogen. Pure nitrogen 202 and nitrogen 211 extracted from the top of the upper tower 8 enter the liquefaction heat exchanger 5 to provide cold energy, are mixed into nitrogen 203 after reheating and enter the pressurizing end of the liquid pressurizing expander 13 to be compressed into low-pressure nitrogen 204, enter the LNG-nitrogen heat exchanger 11 to be cooled, enter the liquefaction heat exchanger 5 to be further cooled and liquefied into liquid nitrogen 206, enter the gas-liquid separator 10 after throttling, and are mixed with the liquid nitrogen separated after expansion into liquid nitrogen 212;
g) Liquid nitrogen 212 in the gas-liquid separator 10 is divided into three paths, namely circulating liquid nitrogen 213, product liquid nitrogen 217 and cooling liquid nitrogen 214; the flow rate of the circulating liquid nitrogen 213 is fixed, when the LNG601 meets the design requirement of the system, the flow rate of the cold supplementing liquid nitrogen 214 is 0, and when the flow rate of the LNG601 is lower than the design flow rate or the temperature is higher than the design temperature or both the two conditions occur simultaneously, the flow rate of the product liquid nitrogen 217 is reduced according to the actual condition, and the flow rate of the cold supplementing liquid nitrogen 214 is increased so as to maintain the stable operation of the system; in extreme cases, liquid nitrogen in the storage tank can also be used for supplementing cooling;
h) LNG601 is gasified into natural gas 604 and 605 which are discharged from an LNG-nitrogen heat exchanger 11 after heat exchange, the temperature of the medium-drawn natural gas 604 is still lower than 0 ℃, mixed LNG603 and glycol aqueous solution 701 are subjected to heat exchange in an ethylene glycol heat exchanger 12, glycol aqueous solution 703 of cold energy of LNG603 and natural gas 604 is obtained and used as cooling mediums of an air compressor 2 inter-stage cooler and a final-stage cooler, the heat-exchanged glycol aqueous solution 702 is pressurized by a glycol solution circulating pump 15, and the mixture of LNG603 and natural gas 604 is heated to normal temperature and natural gas 606 and is mixed with natural gas 605 and sent into a natural gas pipe network 607 after the circulation heat exchange of the glycol solution is carried out in the ethylene glycol heat exchanger 12.
In order to prevent natural gas from leaking into the air separation unit to threaten production safety, the pressure of the supercritical circulating nitrogen 502 is higher than that of the LNG601, and the possibility that the LNG601 leaks to the nitrogen 502 is low; an alarm-linked hydrocarbon detector is arranged on the nitrogen 205 pipeline. If contamination occurs, the liquid nitrogen 217 may be cut off in an emergency to prevent contamination of the liquid nitrogen in the tank.
The invention has the beneficial effects that:
in the invention, the circulating liquid nitrogen pump is used for compressing liquid nitrogen, and the method is used for driving a cold energy transfer medium between the air separation unit and the LNG cold energy utilization unit, and compared with a low-temperature circulating nitrogen compressor in the prior art, the energy consumption and equipment investment of the liquid nitrogen pump can be reduced by more than 90 percent; in addition, the low-temperature circulating nitrogen compressor has more irreversible loss than the circulating liquid nitrogen pump in acting, and can greatly raise the dosage of LNG; meanwhile, the low-temperature circulating nitrogen compressor belongs to a special compressor, and has higher operation difficulty and maintenance cost; the invention solves a series of problems of high energy consumption, large investment, complex operation, expensive maintenance and the like of equipment for driving the circulating nitrogen in the prior art by using the circulating liquid nitrogen pump to replace a new flow organization form of a low-temperature circulating nitrogen compressor, and has strong practicability.
According to the invention, the supercritical pressure liquid nitrogen cooled by LNG is expanded by the liquid expander, meanwhile, the non-liquefied nitrogen in the work compression system is output to the pressurizing end, so that conditions are provided for further cooling, throttling and liquefying, and the liquid pressurizing expander can fully utilize the pressure energy of the high-pressure liquid nitrogen, and meanwhile, the liquefying rate of the product nitrogen is greatly improved; compared with a liquid throttle valve, the liquid booster expander has the disadvantages of high equipment investment, large occupied area and the like, but the liquid throttle valve is used for achieving the same liquid yield under the same conditions, a low-temperature nitrogen compressor is additionally arranged, and the energy consumption of the system is increased by about 14% while the investment is increased; according to the invention, the liquid booster expander is used for replacing the liquid throttle valve, so that the problem of waste of the expansion pressure energy of the ultrahigh-pressure liquid nitrogen in the prior art is solved, and the production energy consumption is further reduced.
According to the invention, a heat exchange channel is arranged, so that the product liquid nitrogen can flow through the LNG-nitrogen heat exchanger to release cold energy to replace part of LNG cold energy, and the resistance of the system to LNG cold energy fluctuation is greatly improved. The external gas transmission capacity of the LNG receiving station generally fluctuates greatly, the flow fluctuation also affects the LNG temperature, and the LNG flow and temperature change can seriously affect the normal operation production of cold energy air separation; the invention has low production cost, and when the LNG cold source is not ideal, a method of replacing LNG with product liquid nitrogen can be adopted to ensure the stable operation of the air separation system; under the working condition that liquid nitrogen products extracted by the LNG cold energy utilization unit are gasified through the LNG-nitrogen heat exchanger, the average production cost of the liquid products is still lower than that of the prior art, and the liquid products have strong competitiveness. According to the invention, by using the liquid nitrogen reflux LNG cold energy utilization unit, the problem of extremely high dependence of cold energy air separation on the quality of the LNG cold energy externally transmitted by the LNG receiving station in the prior art is solved, the adaptability is stronger, and the production is more stable.
The technical scheme of the invention is in detail with the main performance of domestic LNG cold energy space division, and the performance of the invention is superior to the domestic advanced level and the energy-saving effect is very remarkable as can be seen from the attached table.
And (3) comparing and analyzing technical indexes:
note that: the standard working condition is the working condition that the flow of 214 pipeline cold supplementing liquid nitrogen is zero;
the minimum working condition is the working condition that the liquid nitrogen flow of the 217 pipeline product is zero;
the condition of using liquid nitrogen in the storage tank for supplementing cooling is extreme and is not listed here.
Drawings
Fig. 1 is a schematic diagram of the operation of the present invention.
In the figure: the device comprises a 1-self-cleaning air filter, a 2-air compressor, a 3-molecular sieve, a 4-main heat exchanger, a 5-liquefaction heat exchanger, a 6-lower tower, a 7-main condensation evaporator, an 8-upper tower, a 9-circulating liquid nitrogen pump, a 10-gas-liquid separator, a 11-LNG-nitrogen heat exchanger, a 12-LNG-glycol heat exchanger, a 13-liquid booster expander, a 14-regenerated gas heater, a 15-glycol solution circulating pump, a 16-emptying silencer and a 17-emptying silencer.
101-preliminary filtration air, 102-compressed air, 103-pure compressed air, 104-liquid compressed air, 105-gas-liquid mixed compressed air, 106-oxygen-enriched liquid air, 201-main cold liquid nitrogen, 202/203-nitrogen, 204/205-medium pressure nitrogen, 206-medium pressure liquid nitrogen, 207-liquid nitrogen, 208-lower column nitrogen, 209-auxiliary cold liquid nitrogen, 210-gas-liquid mixed nitrogen, 211-nitrogen, 212/213-liquid nitrogen, 214-supplementary cold liquid nitrogen, 215-liquid nitrogen, 216-start liquid nitrogen, 217/218-product liquid nitrogen, 301-product liquid oxygen, 401/402-dirty nitrogen, 403-normal temperature dirty nitrogen, 501-supercritical liquid nitrogen, 502-supercritical normal temperature nitrogen, 503-supercritical liquid nitrogen, 601/602/603-LNG, 604-low temperature NG, 605/606/607-normal temperature NG, 701/702-high temperature ethylene glycol aqueous solution, 703-low temperature ethylene glycol aqueous solution.
Detailed Description
In order to clearly illustrate the technical characteristics of the scheme, the invention is further described below through specific embodiments and with reference to the accompanying drawings.
Embodiment one:
an air separation system utilizing liquefied natural gas cold energy comprises an air separation unit, an LNG cold energy utilization unit and an ethylene glycol solution circulating cooling unit;
the glycol solution circulation cooling unit comprises an LNG-glycol heat exchanger 12 and a glycol solution circulation pump 15;
the LNG cold energy utilization unit comprises a circulating liquid nitrogen pump 9, an LNG-nitrogen heat exchanger 11, a gas-liquid separator 10, a liquid booster expander 13 and a vent silencer 17;
the air separation unit comprises a self-cleaning air filter 1, an air compressor 2, a molecular sieve 3, a regenerated gas heater 14, a main heat exchanger 4, a liquefying heat exchanger 5, a rectifying tower and a venting silencer 16, wherein the rectifying tower comprises a lower tower 6, a main condensing evaporator 7 and an upper tower 8.
In the air separation unit:
the outlet of the self-cleaning air filter 1 is connected with the inlet of the air compressor 2; the inlet of the molecular sieve 3 is connected with the outlet of the air compressor 2 and the vent silencer 16; the outlet of the molecular sieve 3 is connected with the main heat exchanger 4 and the regenerated gas heater 14;
the hot end and the cold end of the main heat exchanger 4 are respectively provided with three strands, and the hot end is respectively connected with the outlet of the molecular sieve 3, the hot end of the LNG-nitrogen heat exchanger 11 and the regenerated gas heater 14; the cold end is respectively connected with one hot end of the liquefaction heat exchanger 5 and one cold end and the outlet of the circulating liquid nitrogen pump 9;
six strands of heat are respectively arranged at the hot end and the cold end of the liquefaction heat exchanger 5; the cold end is respectively connected with one cold end of the main heat exchanger 4, the upper part and the top of the upper tower 8, the top of the lower tower 6 and the upper part and the top of the gas-liquid separator 10; the hot end is respectively connected with the bottom and the top of the lower tower 6, one cold end of the main heat exchanger 4, one hot end of the LNG-nitrogen heat exchanger 11 and a pressurizing end inlet of the liquid pressurizing expander 13;
the top of the lower tower 6 is provided with two groups of outlets and inlets, one group is respectively connected with the hot end and the cold end of the main condensing evaporator 7, and the other group is respectively connected with the hot end and the cold end of the liquefaction heat exchanger 5; the bottom inlet is connected with the hot end of the liquefaction heat exchanger 5, and the bottom outlet is connected with the upper part of the upper tower 8 through a throttle valve;
the inlet of the main condensation evaporator 7 is connected with the top of the lower tower 6, the outlet is divided into three parts, and the three parts are respectively connected with the top of the lower tower 6, a product liquid oxygen storage tank and the top of the upper tower 8 through a throttle valve;
the outlet of the upper tower 8 is divided into three strands, namely a first outlet at the top is connected with a product liquid nitrogen storage tank, and a second outlet at the top and an outlet at the upper part are connected with two cold ends of the liquefaction heat exchanger 5 respectively; the top and upper two inlets are connected to the main condensing evaporator 7 and the bottom of the lower column 6, respectively.
The molecular sieve 3 is divided into two parts, which are alternately used, one part is purified and the other part is regenerated; the inlet of the purifying end is connected with the outlet of the air compressor 2, and the outlet of the purifying end is connected with the hot end of the main heat exchanger 4; the inlet of the regeneration end is connected to the outlet of the regeneration gas heater 14 and the outlet of the regeneration end is connected to the purge muffler 16.
The glycol solution circulation cooling unit comprises:
two hot ends and cold ends of the LNG-glycol heat exchanger 12 are respectively connected with a low-temperature natural gas pipeline and inlets of two interstage coolers and a final-stage cooler of the air compressor 2, and two hot ends of the LNG-glycol heat exchanger are respectively connected with outlets of the natural gas pipeline and an ethylene glycol solution circulating pump 15;
and the inlet of the glycol solution circulating pump 15 is connected with the outlets of the interstage cooler and the final-stage cooler of the air compressor 2, and the outlet is connected with the hot end of the LNG-glycol heat exchanger 12.
The LNG cold energy utilization unit comprises:
an inlet of the circulating liquid nitrogen pump 9 is connected with the bottom of the gas-liquid separator 10, and an outlet of the circulating liquid nitrogen pump is connected with the cold end of the main heat exchanger 4;
the top outlet and the upper inlet of the gas-liquid separator 10 are respectively connected with two cold ends of the liquefaction heat exchanger 5, the other inlet of the upper part is connected with a liquid nitrogen product storage tank, and the bottom outlet is respectively connected with the inlet of the circulating liquid nitrogen pump 9, the product liquid nitrogen storage tank and the LNG-nitrogen heat exchanger 11; the middle inlet is connected with the outlet of the expansion end of the liquid booster expander 13;
the liquid booster expander 13 is divided into a booster end and an expansion end, the inlet of the booster end is connected with two hot ends of the liquefaction heat exchanger 5, and the outlet of the booster end is connected with the hot ends of the LNG-nitrogen heat exchanger 11; the inlet of the expansion end is connected with the cold end of the LNG-nitrogen heat exchanger 11, and the outlet of the expansion end is connected with the gas-liquid separator 10;
five cold ends and four hot ends of the LNG-nitrogen heat exchanger 11 are respectively connected with an LNG pipeline, the hot end of the liquefaction heat exchanger 5, an expansion end inlet of the liquid booster expander 13, the LNG-glycol heat exchanger 12 and the bottom of the gas-liquid separator 10; the hot end is respectively connected with a natural gas pipeline, a supercharging end outlet of the liquid supercharging expander 13, the hot end of the main heat exchanger 4 and the emptying silencer 17.
The LNG-nitrogen heat exchanger 11 is provided with a heat exchange channel, and two ends of the heat exchange channel are respectively connected with the gas-liquid separator 10 and the emptying silencer 17, so that the heat exchange channel is started to be used when LNG cold energy is insufficient; a stream 604 is withdrawn in the middle of the natural gas heat exchange path to adjust the refrigeration to the LNG-ethylene glycol heat exchanger 12.
The gas-liquid separator 10 is provided with a pipeline 216 connected with a liquid nitrogen tank of a product, and is used when the air separation system is started, liquid nitrogen in the liquid nitrogen tank is extracted to enter the air separation system of liquefied natural gas cold energy, and a key equipment circulating liquid nitrogen pump 9 is conveniently started.
The main heat exchanger 4, the liquefaction heat exchanger 5 and the LNG-nitrogen heat exchanger 11 are all plate heat exchangers, and are composed of a single heat exchanger or a plurality of heat-separating heat exchangers, so that temperature crossing in the heat exchangers is avoided.
Embodiment two:
an air separation method by using an air separation system of liquefied natural gas cold energy comprises the following steps:
a) Raw material air is subjected to the self-cleaning filter 1 to remove most of solid impurities, then enters the air compressor 2 to be compressed, and the impurities such as water, hydrocarbon and the like are removed through the molecular sieve system 3 to obtain purified air 103;
b) The purified air 103 is cooled and liquefied in the main heat exchanger 4 by exchanging heat with the dirty nitrogen 402, which is withdrawn from the upper part of the upper column 8 and supplied with cold and primarily reheated in the liquefaction heat exchanger 5, and the high-pressure circulating liquid nitrogen 501. The polluted nitrogen 403 which is completely reheated in the main heat exchanger is connected with the purification system 3 to be used as regenerated gas and cold blowing gas;
c) The liquefied air 104 provides cold energy for liquefied pressure nitrogen 205 and 208 in the liquefying heat exchanger 5, and is reheated to be gas-liquid mixed air 105, and enters the rectifying tower system to be separated into an exhaust stream, wherein the exhaust stream comprises pure nitrogen 202 and liquid nitrogen product 218 obtained from the top of the upper tower 7, polluted nitrogen 401 obtained from the upper part of the upper tower 7 and liquid oxygen 301 obtained from the bottom of the upper tower;
d) After the raw material air 105 is subjected to preliminary separation in the lower tower 6, an oxygen-enriched liquid air 106 is obtained at the bottom of the lower tower 6, medium-pressure nitrogen is obtained at the top of the lower tower 6, the medium-pressure nitrogen enters the main condensing evaporator 7 and is condensed into liquid nitrogen by liquid oxygen at the bottom of the upper tower 8, part of the liquid nitrogen is sent back to the lower tower 6 to maintain the rectification working condition of the lower tower 6, and the other part of the liquid nitrogen 201 is throttled and sent to the top of the upper tower 8 to participate in rectification; in addition, a stream of pressure nitrogen 208 is pumped out to enter the liquefaction heat exchanger 5, and is liquefied and then returned to the lower tower 6 to be used as reflux liquid; the oxygen-enriched liquid space 106 is throttled and then sent into the middle part of the upper tower 8 to participate in the rectification of the upper tower 8;
e) The liquid nitrogen 201, the oxygen-enriched liquid air 106 and the gas oxygen evaporated by the main condensation evaporator 7 which are fed into the upper tower are rectified again, low-pressure nitrogen 202 and liquid nitrogen 218 are obtained from the top of the upper tower 8, dirty nitrogen 401 is obtained from the upper part of the upper tower 8, the upper part of the main condensation evaporator 7 is communicated with the bottom of the upper tower 8, liquid oxygen is obtained from the bottom of the upper tower 8, the gasified liquid oxygen 301 is extracted from the main condensation evaporator 7, and the liquid oxygen is sent out as product liquid oxygen; the polluted nitrogen 401 obtained from the upper part of the upper tower 8 is reheated in the liquefaction heat exchanger 5 and the main heat exchanger 4 and heated up to be separated into two paths after an air separation unit, one path of polluted nitrogen is treated by the regenerated gas heater 16 to the air purifier 3 to be used as regeneration gas, and the other path of polluted nitrogen is treated by the air purification silencer to be discharged; if the space division is provided with an argon system, an argon fraction is obtained from the middle part of the upper tower, and the argon fraction is sent to a full-rectification hydrogen-free argon preparation system to prepare liquid argon, wherein the argon preparation system is well known to the person skilled in the art and is not described again here;
f) Part of liquid nitrogen 213 obtained in the gas-liquid separator 10 enters a circulating liquid nitrogen pump 9 to be pressurized into supercritical pressure liquid nitrogen 501, enters a main heat exchanger 4 to be reheated to normal temperature, enters an LNG-nitrogen heat exchanger 11 to be cooled into supercritical liquid nitrogen 503 by high-pressure LNG602, and LNG cold energy is obtained; after liquefaction, the mixture enters an expansion end of a liquid booster expander 13 to be expanded into low-pressure gas-liquid mixed nitrogen 210, and the low-pressure gas-liquid mixed nitrogen enters a gas-liquid separator 10 to be separated into nitrogen 211 and liquid nitrogen; pure nitrogen 202 and nitrogen 211 extracted from the top of the upper tower 8 enter the liquefaction heat exchanger 5 to provide cold energy, are mixed into nitrogen 203 after reheating and enter the pressurizing end of the liquid pressurizing expander 13 to be compressed into low-pressure nitrogen 204, enter the LNG-nitrogen heat exchanger 11 to be cooled, enter the liquefaction heat exchanger 5 to be further cooled and liquefied into liquid nitrogen 206, enter the gas-liquid separator 10 after throttling, and are mixed with the liquid nitrogen separated after expansion into liquid nitrogen 212;
g) Liquid nitrogen 212 in the gas-liquid separator 10 is divided into three paths, namely circulating liquid nitrogen 213, product liquid nitrogen 217 and cooling liquid nitrogen 214; the flow rate of the circulating liquid nitrogen 213 is fixed, when the LNG601 meets the design requirement of the system, the flow rate of the cold supplementing liquid nitrogen 214 is 0, and when the flow rate of the LNG601 is lower than the design flow rate or the temperature is higher than the design temperature or both the two conditions occur simultaneously, the flow rate of the product liquid nitrogen 217 is reduced according to the actual condition, and the flow rate of the cold supplementing liquid nitrogen 214 is increased so as to maintain the stable operation of the system; in the extreme case, the liquid nitrogen in the tank can also be used for replenishing cold by starting the pipeline of liquid nitrogen 216;
h) LNG601 is gasified into natural gas 604 and 605 which are discharged from an LNG-nitrogen heat exchanger 11 after heat exchange, the temperature of the medium-drawn natural gas 604 is still lower than 0 ℃, mixed LNG603 and glycol aqueous solution 701 are subjected to heat exchange in an ethylene glycol heat exchanger 12, glycol aqueous solution 703 of cold energy of LNG603 and natural gas 604 is obtained and used as cooling mediums of an air compressor 2 inter-stage cooler and a final-stage cooler, the heat-exchanged glycol aqueous solution 702 is pressurized by a glycol solution circulating pump 15, and the mixture of LNG603 and natural gas 604 is heated to normal temperature and natural gas 606 and is mixed with natural gas 605 and sent into a natural gas pipe network 607 after the circulation heat exchange of the glycol solution is carried out in the ethylene glycol heat exchanger 12.
Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are merely illustrative, not restrictive, and many forms may be made by those having ordinary skill in the art without departing from the spirit of the present invention and the scope of the appended claims, which are within the scope of the present invention.

Claims (9)

1. An air separation system utilizing liquefied natural gas cold energy, which is characterized in that: comprises an air separation unit, an LNG cold energy utilization unit and an ethylene glycol solution circulating and cooling unit;
the glycol solution circulating and cooling unit comprises an LNG-glycol heat exchanger (12) and a glycol solution circulating pump (15);
the LNG cold energy utilization unit comprises a circulating liquid nitrogen pump (9), an LNG-nitrogen heat exchanger (11), a gas-liquid separator (10), a liquid booster expander (13) and a first emptying silencer (17);
the air separation unit comprises a self-cleaning air filter (1), an air compressor (2), a molecular sieve (3), a regenerated gas heater (14), a main heat exchanger (4), a liquefying heat exchanger (5), a rectifying tower and a second emptying silencer (16), wherein the rectifying tower comprises a lower tower (6), a main condensing evaporator (7) and an upper tower (8); the air separation unit comprises:
the outlet of the self-cleaning air filter (1) is connected with the inlet of the air compressor (2); the inlet of the molecular sieve (3) is connected with the outlet of the air compressor (2) and the second emptying silencer (16); the outlet of the molecular sieve (3) is connected with the main heat exchanger (4) and the regenerated gas heater (14);
three hot ends and three cold ends of the main heat exchanger (4) are respectively connected with an outlet of the molecular sieve (3), the hot end of the LNG-nitrogen heat exchanger (11) and the regenerated gas heater (14); the cold end is respectively connected with one hot end of the liquefaction heat exchanger (5) and one cold end and the outlet of the circulating liquid nitrogen pump (9);
six strands of heat are respectively arranged at the hot end and the cold end of the liquefaction heat exchanger (5); the cold end is respectively connected with one cold end of the main heat exchanger (4), the upper part and the top of the upper tower (8), the top of the lower tower (6) and the upper part and the top of the gas-liquid separator (10); the hot end is respectively connected with the bottom and the top of the lower tower (6), one cold end of the main heat exchanger (4), one hot end of the LNG-nitrogen heat exchanger (11) and a pressurizing end inlet of the liquid pressurizing expander (13);
two groups of outlets and inlets are arranged at the top of the lower tower (6), one group is respectively connected with the hot end and the cold end of the main condensing evaporator (7), and the other group is respectively connected with the hot end and the cold end of the liquefying heat exchanger (5); the bottom inlet is connected with the hot end of the liquefaction heat exchanger (5), and the bottom outlet is connected with the upper part of the upper tower (8) through a throttle valve;
the inlet of the main condensation evaporator (7) is connected with the top of the lower tower (6), the outlet is divided into three strands, and the three strands of the main condensation evaporator are respectively connected with the top of the lower tower (6), the product liquid oxygen storage tank and the top of the upper tower (8) through a throttle valve;
the outlet of the upper tower (8) is divided into three strands, namely a first outlet at the top is connected with a liquid nitrogen storage tank of the product, and a second outlet at the top and an outlet at the upper part are connected with two cold ends of the liquefaction heat exchanger (5) respectively; the top and the upper inlet are respectively connected with the main condensing evaporator (7) and the bottom of the lower tower (6); the LNG cold energy utilization unit comprises:
an inlet of the circulating liquid nitrogen pump (9) is connected with the bottom of the gas-liquid separator (10), and an outlet of the circulating liquid nitrogen pump is connected with the cold end of the main heat exchanger (4);
the top outlet and the upper inlet of the gas-liquid separator (10) are respectively connected with two cold ends of the liquefaction heat exchanger (5), the other inlet of the upper part is connected with a liquid nitrogen product storage tank, and the bottom outlet is respectively connected with an inlet of the circulating liquid nitrogen pump (9), the product liquid nitrogen storage tank and the LNG-nitrogen heat exchanger (11); the middle inlet is connected with an outlet of an expansion end of the liquid booster expander (13);
the liquid booster expander (13) is divided into a booster end and an expansion end, the inlet of the booster end is connected with two hot ends of the liquefaction heat exchanger (5), and the outlet of the booster end is connected with the hot ends of the LNG-nitrogen heat exchanger (11); the inlet of the expansion end is connected with the cold end of the LNG-nitrogen heat exchanger (11), and the outlet of the expansion end is connected with the gas-liquid separator (10);
five cold ends and four hot ends of the LNG-nitrogen heat exchanger (11) are respectively connected with an LNG pipeline, the hot end of the liquefaction heat exchanger (5), an expansion end inlet of the liquid booster expander (13), the LNG-glycol heat exchanger (12) and the bottom of the gas-liquid separator (10); the hot end is respectively connected with a natural gas pipeline, a supercharging end outlet of the liquid supercharging expander (13), the hot end of the main heat exchanger (4) and the first emptying silencer (17).
2. An air separation system utilizing lng cold energy as defined in claim 1, wherein: the molecular sieve (3) is divided into two parts, which are alternately used, one part is purified and the other part is regenerated; the inlet of the purifying end is connected with the outlet of the air compressor (2), and the outlet of the purifying end is connected with the hot end of the main heat exchanger (4); the inlet of the regeneration end is connected with the outlet of the regeneration gas heater (14), and the outlet of the regeneration end is connected with the second emptying silencer (16).
3. An air separation system utilizing lng cold energy according to claim 1, wherein in the glycol solution circulation cooling unit:
two hot ends and cold ends of the LNG-glycol heat exchanger (12) are respectively connected with a low-temperature natural gas pipeline and an inlet of an interstage cooler and a final-stage cooler of an air compressor (2), and two hot ends of the LNG-glycol heat exchanger are respectively connected with an outlet of a natural gas pipeline and an outlet of a glycol solution circulating pump (15);
and the inlet of the glycol solution circulating pump (15) is connected with the outlets of the interstage cooler and the final-stage cooler of the air compressor (2), and the outlet is connected with the hot end of the LNG-glycol heat exchanger (12).
4. An air separation system utilizing lng cold energy as defined in claim 1, wherein: the LNG-nitrogen heat exchanger (11) is provided with a heat exchange channel, two ends of the heat exchange channel are respectively connected with the gas-liquid separator (10) and the first emptying silencer (17), and the heat exchange channel is opened for use when LNG cold energy is insufficient; a natural gas (604) is pumped out from the middle of the natural gas heat exchange channel to adjust the cold energy input into the LNG-glycol heat exchanger (12).
5. An air separation system utilizing lng cold energy as defined in claim 1, wherein: the gas-liquid separator (10) is provided with a pipeline (216) connected with a liquid nitrogen tank of a product, and is used when the air separation system is started.
6. An air separation system utilizing lng cold energy as defined in claim 1, wherein: the main heat exchanger (4), the liquefaction heat exchanger (5) and the LNG-nitrogen heat exchanger (11) are respectively composed of a single heat exchanger or a plurality of sub-heat exchangers, so that temperature crossing in the heat exchangers is avoided.
7. A method for air separation using an air separation system using liquefied natural gas cold energy according to any one of claims 1 to 6, characterized in that: the method comprises the following steps:
a) Raw material air is compressed by an air compressor (2) after most solid impurities are removed by a self-cleaning air filter (1), and pure air (103) is obtained after impurities are removed by a molecular sieve (3) system;
b) The pure air (103) is cooled and liquefied in the main heat exchanger (4) by exchanging heat with the dirty nitrogen (402) and the supercritical pressure liquid nitrogen (501) which are pumped out from the upper part of the upper tower (8) and provide cold energy and are preliminarily reheated in the liquefying heat exchanger (5); the polluted nitrogen (403) which is completely reheated in the main heat exchanger is connected with a molecular sieve (3) system to be used as regenerated gas and cold blowing gas;
c) The liquefied air (104) provides cold energy for nitrogen (205) from the LNG-nitrogen heat exchanger (11) and pressure nitrogen (208) from the top of the lower tower (6) in the liquefaction heat exchanger (5), and is reheated to be gas-liquid mixed air (105) and enters the rectifying tower system to be separated into an effluent stream, wherein the effluent stream comprises pure nitrogen (202) and liquid nitrogen products (218) obtained from the top of the upper tower (8), dirty nitrogen (401) obtained from the upper part of the upper tower (8) and liquid oxygen (301) obtained from the bottom of the upper tower;
d) After the raw material air (105) is subjected to preliminary separation in the lower tower (6), an oxygen-enriched liquid air (106) is obtained at the bottom of the lower tower (6), medium-pressure nitrogen is obtained at the top of the lower tower (6), the medium-pressure nitrogen enters the main condensing evaporator (7) and is condensed into liquid nitrogen by liquid oxygen at the bottom of the upper tower (8), part of the liquid nitrogen is returned to the lower tower (6) to maintain the rectifying working condition of the lower tower (6), and the other part of the liquid nitrogen (201) is throttled and sent to the top of the upper tower (8) to participate in rectification; in addition, a stream of pressure nitrogen (208) is pumped out to enter a liquefaction heat exchanger (5), and is liquefied and then returned to the lower tower (6) to be used as reflux liquid; the oxygen-enriched liquid air (106) is throttled and then sent into the middle part of the upper tower (8) to participate in the rectification of the upper tower (8);
e) Rectifying the liquid nitrogen (201), the oxygen-enriched liquid air (106) and the gas oxygen evaporated by the main condensation evaporator (7) fed into the upper tower again, obtaining pure nitrogen (202) and a liquid nitrogen product (218) from the top of the upper tower (8), obtaining polluted nitrogen (401) from the upper part of the upper tower (8), communicating the upper part of the main condensation evaporator (7) with the bottom of the upper tower (8), obtaining liquid oxygen at the bottom of the upper tower (8), extracting unvaporized liquid oxygen (301) from the bottom of the upper tower (8), and sending out the liquid oxygen as a product; the polluted nitrogen (401) obtained from the upper part of the upper tower (8) is reheated in the liquefaction heat exchanger (5) and the main heat exchanger (4) and heated up to an air separation unit and then is divided into two paths, one path of polluted nitrogen is treated as regeneration gas by a molecular sieve (3) system through a regenerated gas heater (14), and the other path of polluted nitrogen is treated as emptying polluted nitrogen to a second emptying silencer (16);
f) Part of liquid nitrogen (213) obtained in the gas-liquid separator (10) enters a circulating liquid nitrogen pump (9) to be pressurized into supercritical pressure liquid nitrogen (501) and enters a main heat exchanger (4) to be reheated to normal temperature, and then enters an LNG-nitrogen heat exchanger (11) to be cooled into supercritical liquid nitrogen (503) by high-pressure LNG (602) to obtain LNG cold energy; after liquefaction, the mixture enters an expansion end of a liquid booster expander (13) to be expanded into low-pressure gas-liquid mixed nitrogen (210), and the low-pressure gas-liquid mixed nitrogen enters a gas-liquid separator (10) to be separated into nitrogen (211) and liquid nitrogen; pure nitrogen (202) pumped out from the top of the upper tower (8) and nitrogen (211) from the gas-liquid separator (10) enter the liquefaction heat exchanger (5) to provide cold energy, are reheated and mixed into nitrogen (203) and enter the pressurizing end of the liquid pressurizing expander (13) to be compressed into low-pressure nitrogen (204), enter the LNG-nitrogen heat exchanger (11) to be cooled and then enter the liquefaction heat exchanger (5) to be further cooled and liquefied into liquid nitrogen (206), enter the gas-liquid separator (10) after throttling, and are mixed with the liquid nitrogen separated after being expanded by the expanding end of the liquid pressurizing expander (13);
g) The liquid nitrogen (212) in the gas-liquid separator (10) is divided into three paths, namely circulating liquid nitrogen (213), product liquid nitrogen (217) and cooling liquid nitrogen (214); the flow of the circulating liquid nitrogen (213) is fixed, when the flow and the temperature of the LNG (601) meet the design requirement of the system, the flow of the cold supplementing liquid nitrogen (214) is 0, and when the flow of the LNG (601) is lower than the design flow or the temperature is higher than the design temperature or the two conditions occur simultaneously, the flow of the product liquid nitrogen (217) is reduced according to the actual conditions, and the flow of the cold supplementing liquid nitrogen (214) is increased so as to maintain the stable operation of the system; in extreme cases, liquid nitrogen in the storage tank is also used for supplementing cooling;
h) And (3) gasifying a part of LNG (602) after heat exchange into natural gas (604) extracted from the middle part of the LNG-nitrogen heat exchanger (11) and natural gas (605) flowing out of the end part of the LNG-nitrogen heat exchanger (11), wherein the temperature of the natural gas (604) extracted from the middle part is still lower than 0 ℃, mixing another part of LNG (603) and then exchanging heat with an ethylene glycol aqueous solution (701) in the LNG-ethylene glycol heat exchanger (12), obtaining an ethylene glycol aqueous solution (703) of cold energy of the natural gas (604) extracted from the middle part and the other part of LNG (603) as cooling media of an air compressor (2) cooler and a final-stage cooler, pressurizing the heat-exchanged ethylene glycol aqueous solution (702) by an ethylene glycol solution circulating pump (15), returning the LNG-ethylene glycol heat exchanger (12) for circulating heat exchange, and heating the other part of LNG (603) and the natural gas (604) extracted from the middle part into normal-temperature natural gas (606) and mixing the natural gas (605) flowing out of the end part of the LNG-nitrogen heat exchanger (11) into a natural gas pipe network (607).
8. A method for air separation using lng cold energy air separation system according to claim 7, wherein: the pressure of the supercritical nitrogen (502) flowing out of the main heat exchanger (4) is higher than that of the LNG (601); an alarm-linked hydrocarbon detector is arranged on a nitrogen (205) pipeline between the LNG-nitrogen heat exchanger (11) and the liquefaction heat exchanger (5).
9. A method for air separation using lng cold energy air separation system according to claim 7, wherein: the space division system is provided with an argon production system, an argon fraction is obtained from the middle part of the upper tower, and the argon fraction is sent into the argon production system to produce liquid argon.
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