CN108007068B - Heat integration rectification air separation system for LNG cold energy utilization - Google Patents

Heat integration rectification air separation system for LNG cold energy utilization Download PDF

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CN108007068B
CN108007068B CN201810013441.3A CN201810013441A CN108007068B CN 108007068 B CN108007068 B CN 108007068B CN 201810013441 A CN201810013441 A CN 201810013441A CN 108007068 B CN108007068 B CN 108007068B
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air
nitrogen
pressure tower
passage
tower
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CN108007068A (en
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董学智
许剑
刘锡阳
陈仕卿
高庆
张华良
谭春青
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Institute of Engineering Thermophysics of CAS
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Institute of Engineering Thermophysics of CAS
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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
    • F25J3/04624—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 integrated mass and heat exchange, so-called non-adiabatic rectification, e.g. dephlegmator, reflux exchanger
    • F25J3/0463—Simultaneously between rectifying and stripping sections, i.e. double 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
    • 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
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
    • F25J3/04781—Pressure changing devices, e.g. for compression, expansion, liquid pumping
    • 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
    • F25J3/04054—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 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
    • F25J3/04151—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
    • F25J3/04248—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
    • 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
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
    • F25J3/04793—Rectification, e.g. columns; Reboiler-condenser
    • 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
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04866—Construction and layout of air fractionation equipments, e.g. valves, machines
    • F25J3/04872—Vertical layout of cold equipments within in the cold box, e.g. columns, heat exchangers etc.
    • 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
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04866—Construction and layout of air fractionation equipments, e.g. valves, machines
    • F25J3/04896—Details of columns, e.g. internals, inlet/outlet devices
    • F25J3/04933—Partitioning walls or sheets
    • F25J3/04939—Vertical, e.g. dividing wall 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
    • F25J2200/00—Processes or apparatus using separation by rectification
    • F25J2200/04—Processes or apparatus using separation by rectification in a dual pressure main column system
    • F25J2200/06—Processes or apparatus using separation by rectification in a dual pressure main column system in a classical double column flow-sheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column

Abstract

The invention discloses a heat integration rectification air separation system for utilizing LNG cold energy, which adopts LNG cold energy to cool raw material low-pressure air and utilizes a heat integration rectification tower to perform air separation, and compared with the traditional air separation system, the heat integration rectification system can reduce the pressure of raw material air from 0.6MPa to 0.4MPa, thereby reducing the total pressure ratio and the power consumption of an air compressor; the LNG is adopted to cool the raw material air, so that the power consumption of the air compressor is further reduced, and the liquid oxygen yield is improved, thereby reducing the energy consumption of unit liquid products; the heat integration rectification can also reduce fire loss in the rectification process of the high-pressure tower and the rectification process of the low-pressure tower, and improve the separation purity of oxygen and nitrogen; in addition, LNG is adopted to cool raw material air, so that the starting time of the air separation system can be greatly reduced.

Description

Heat integration rectification air separation system for LNG cold energy utilization
Technical Field
The invention belongs to the field of air separation, and relates to a heat integration rectification air separation system, in particular to a heat integration rectification air separation system for utilizing LNG cold energy.
Background
Air separation systems have important roles in the fields of steel, chemical, semiconductor, food processing, and medical. The low-temperature rectification air separation system is a main scheme for realizing large-scale preparation of high-purity nitrogen, oxygen and argon. The low temperature rectification air separation system consumes a great deal of energy, especially in the process of preparing products of liquid oxygen and liquid nitrogen. Liquefied Natural Gas (LNG) is a low-temperature (about 111K) mixed liquid obtained by liquefying natural gas by cryogenic process, and its main component is methane (CH) 4 ) Has the advantages of high combustion heat value, small pollution of emissions, low storage and transportation cost, and the like. LNG cold energy is huge in quantity and high in energy level, and common application mainly comprises direct power generation and air liquefaction separationSeparating, preparing liquefied dry ice, deep cooling, pulverizing, and low-temperature cooling warehouse. Considering that the process temperature of the air separation system is about 78-100K and lower than the temperature of LNG, the condition of low-temperature cold energy high-temperature use can be avoided, and the efficient utilization principle of 'temperature opposite port and cascade utilization' energy is met, so that the cold energy utilization scheme is considered as the most reasonable utilization mode in the prior art.
The energy-saving effect of the existing LNG cold energy utilization air separation system can be mainly classified into the following two factors: (1) The temperature of the working medium at the inlet of the LNG cold energy cooling air compressor or the nitrogen compressor can reduce the requirement of an air system on electric power energy consumption; (2) LNG cold energy can replace the high-purity liquid oxygen/liquid nitrogen cold energy released by the main heat exchanger to reduce the temperature of raw material air, and the power energy consumption required by extra low-temperature liquid product cold energy preparation is reduced. Compared with a conventional air separation system, the air separation system adopting LNG cold energy can reduce the energy consumption for preparing unit liquid products by about 50 percent through the calculation of related documents and patents.
However, the operation pressure of the rectifying tower of the prior air separation system scheme for utilizing LNG cold energy is close to 0.6MPa, and the addition of cold energy only reduces the energy consumption for producing liquid products without any beneficial influence on the separation work of the air separation system. There are 2 main reasons for this: (1) The rectification units of the traditional air separation system all adopt double-stage rectification towers, the reflux gas-liquid of the upper tower and the lower tower is realized through the heat exchange of low-pressure liquid oxygen and high-pressure nitrogen, and the boiling point of the nitrogen is far lower than that of oxygen under the same pressure, so that the lower rectification tower needs to operate at high pressure; (2) The working temperature of the two-stage rectifying tower is 78-100K, the storage temperature of LNG is 112K, if LNG cold energy acts on the rectifying process, raw material air still needs to be pressurized, and lower working temperature is generated through expansion or throttling. The method for adjusting the two reasons only reduces the pressure of the rectifying tower by changing the traditional two-stage rectifying cold-hot coupling mode, converts partial LNG cold energy into separation work, and further reduces the energy consumption of the air separation system for utilizing the LNG cold energy.
Disclosure of Invention
Aiming at the defects and shortcomings of the prior art, the invention aims to provide a heat integration rectification air separation system for utilizing LNG cold energy, which adopts LNG cold energy to cool raw material low-pressure air and utilizes a heat integration rectification tower to perform air separation, and compared with the traditional air separation system, the heat integration rectification system can reduce the pressure of raw material air from 0.6MPa to 0.4MPa, reduce the total pressure ratio and reduce the power consumption of an air compressor; the LNG is adopted to cool the raw material air, so that the power consumption of the air compressor is further reduced, and the liquid oxygen yield is improved, thereby reducing the energy consumption of unit liquid products; the heat integration rectification can also reduce fire loss in the rectification process of the high-pressure tower and the rectification process of the low-pressure tower, and improve the separation purity of oxygen and nitrogen; in addition, LNG is adopted to cool raw material air, so that the starting time of the air separation system can be greatly reduced.
The invention adopts the technical proposal for solving the technical problems that:
the heat integration rectification air separation system for LNG cold energy utilization comprises a fan, a water cooling tower, a molecular sieve, a precooler, an air compressor, a main heat exchanger, a subcooler I, a high-pressure tower, a heat integration unit, a low-pressure tower, a subcooler II, an LNG storage device and a low-temperature pump, and is characterized in that,
the precooler comprises an air passage and a natural gas passage;
the main heat exchanger comprises an air passage, an LNG passage, a nitrogen passage and a polluted nitrogen passage;
the subcooler I comprises an air passage, a polluted nitrogen passage and a nitrogen passage;
the high-pressure tower is provided with tower plates in a staggered manner in the height direction, the bottom of the high-pressure tower is provided with a low-temperature air inlet and a liquid air outlet, and the top of the high-pressure tower is provided with a liquid nitrogen outlet;
the low-pressure tower is provided with tower plates in a staggered manner in the height direction, the bottom is provided with a liquid oxygen outlet, and the upper part is provided with a liquid air inlet, a liquid nitrogen inlet, a pure nitrogen outlet and a polluted nitrogen outlet;
the subcooler II comprises a liquid air passage, a nitrogen passage, a polluted nitrogen passage and a liquid nitrogen passage,
wherein,
an outlet of the LNG storage device is communicated with an inlet of a natural gas passage of the precooler through an LNG passage of the cryogenic pump and the main heat exchanger in sequence through a pipeline;
the air inlet of the fan is communicated with the outside air, and the air outlet of the fan is communicated with the air inlet at the bottom of the high-pressure tower through a pipeline sequentially through the water cooling tower, the molecular sieve, the air passage of the precooler, the air passage of the main heat exchanger and the air passage of the subcooler I;
the liquid air outlet at the bottom of the high-pressure tower is communicated with the liquid air inlet arranged at the upper part of the low-pressure tower through a liquid air passage of the subcooler II by a pipeline, and the liquid nitrogen outlet at the top of the high-pressure tower is communicated with the liquid nitrogen inlet arranged at the upper part of the low-pressure tower through a liquid nitrogen passage of the subcooler II by a pipeline;
the rectifying section of the high-pressure tower and the stripping section of the low-pressure tower are positioned at the same height, and heat exchange is carried out by direct contact or through a heat exchanger;
the pure nitrogen outlet at the upper part of the low-pressure tower is communicated with the inlet of the nitrogen passage of the subcooler II, the nitrogen passage I of the subcooler I and the nitrogen passage of the main heat exchanger in sequence through pipelines,
the dirty nitrogen outlet at the upper part of the low-pressure tower is communicated with the inlet of the dirty nitrogen passage of the main heat exchanger through a pipeline sequentially passing through the dirty nitrogen passage of the subcooler II, the dirty nitrogen passage of the subcooler I and the dirty nitrogen passage of the main heat exchanger.
Preferably, the natural gas passage outlet of the precooler is communicated with a natural gas storage or utilization device through a pipeline.
Further, a heat exchange integrated unit formed by a plurality of heat exchangers which are arranged in parallel is arranged between the rectifying section of the high-pressure tower and the stripping section of the low-pressure tower, and heat of the rectifying section of the high-pressure tower is transferred to the stripping section of the low-pressure tower through the heat exchange integrated unit.
Further, the stripping section of the low-pressure tower is nested in the rectifying section of the high-pressure tower, and the heat of the rectifying section of the high-pressure tower is directly transferred to the stripping section of the low-pressure tower.
Preferably, the liquid oxygen outlet at the bottom of the low pressure column is in communication with the inlet of a liquid oxygen storage or utilization device via a conduit.
Preferably, the outlet of the nitrogen passage of the main heat exchanger is in communication with the inlet of a nitrogen storage or utilization device.
Preferably, the outlet of the dirty nitrogen passage of the main heat exchanger is in communication with an air cooling system of the molecular sieve.
Preferably, the liquid air inlet and the liquid nitrogen inlet at the upper part of the low-pressure tower are respectively provided with a control valve.
Preferably, the outlet pressure of the air compressor is about 0.4 MPa.
Preferably, the air cooled by the precooler, the main heat exchanger and the subcooler I in sequence is cooled to a temperature close to the bubble point and fed to the bottom of the high-pressure tower.
The invention relates to a heat integration rectification air separation system for utilizing LNG cold energy, which mainly utilizes the LNG cold energy to cool raw material high-pressure air and adopts a heat integration rectification tower to perform air separation, and the specific working process is as follows:
the air is boosted by a fan and cooled by a water cooling tower, the boosted pressure is used for compensating the pressure loss when the molecular sieve removes impurities such as water, carbon dioxide and the like, the air after the molecular sieve removes the impurities enters a precooler and an LNG heat exchange absorption part to absorb cold energy, the air is continuously boosted to the pressure of the pressure to be equal to the MPa in an air compressor, and the temperature of the air at the outlet of the air compressor is close to the ambient temperature; the air under pressure enters a main heat exchanger, the subcooler I is cooled to a temperature close to the bubble point by LNG, reflux nitrogen and dirty nitrogen, and the air is sent to the bottom of a high-pressure tower, and rising air and reflux liquid nitrogen are repeatedly condensed and evaporated on a tower plate in the high-pressure tower, so that oxygen-enriched liquid air with higher oxygen concentration is concentrated at the bottom of the high-pressure tower, and high-purity liquid nitrogen is concentrated at the top of the high-pressure tower; liquid nitrogen and oxygen-enriched liquid air pumped from the top and the bottom of the high-pressure tower pass through a cooler II and then enter the low-pressure tower to participate in the rectification process; the heat of the rectifying section of the high-pressure tower is transferred to the stripping section of the low-pressure tower through a heat exchange integrated unit formed by a plurality of heat exchangers which are arranged in parallel, so that each tower plate of the high-pressure tower is promoted to generate more condensed liquid, and each tower plate of the low-pressure tower generates more evaporation gas; the liquid oxygen at the bottom of the low-pressure tower is directly output as a product (stored in a liquid oxygen storage device), pure nitrogen at the top is output as a nitrogen product after being rewuped by a subcooler II, a subcooler I and a main heat exchanger, and polluted nitrogen is sent to an air cooling system of a molecular sieve after being rewuped by the subcooler II, the subcooler I and the main heat exchanger.
Compared with the traditional air separation system in the prior art, the heat integration rectification air separation system for LNG cold energy utilization can reduce the pressure of raw material air from 0.6MPa to 0.4MPa by adopting the heat integration rectification system, thereby reducing the total pressure ratio and the power consumption of an air compressor; the LNG is adopted to cool the raw material air, so that the power consumption of the air compressor is further reduced, and the liquid oxygen yield is improved, thereby reducing the energy consumption of unit liquid products; the heat integration rectification can reduce the fire loss in the rectification process of the high-pressure tower and the rectification process of the low-pressure tower, and improve the separation purity of oxygen and nitrogen. In addition, the LNG is adopted to cool the raw material air, so that the starting time of the air separation system can be greatly reduced.
Drawings
FIG. 1 is a schematic diagram of a heat integrated rectifying air separation system for LNG cold energy utilization of the present invention;
FIG. 2 shows a tube-in-tube type rectifying apparatus used in example 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail below by referring to the accompanying drawings and examples. It should be noted that the following description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited thereby.
Example 1
As shown in fig. 1, the heat integration rectification air separation system for LNG cold energy utilization of the present invention includes a fan 1, a water cooling tower 2, a molecular sieve 3, a precooler 4, an air compressor 5, a main heat exchanger 6, a subcooler i 7, a high-pressure tower 8, a heat exchange integration unit 9, a low-pressure tower 10, a subcooler ii 11, a liquid oxygen storage or utilization device 12, an LNG storage device 13, and a cryogenic pump 14. Wherein the precooler 4 comprises an air passage and a natural gas passage; the main heat exchanger 6 includes an air passage, an LNG passage, a nitrogen passage, and a dirty nitrogen passage; the subcooler I7 comprises an air passage, a polluted nitrogen passage and a nitrogen passage; the high-pressure tower 8 is provided with tower plates in a staggered manner in the height direction, the bottom is provided with a low-temperature air inlet and a liquid air outlet, and the top is provided with a liquid nitrogen outlet; the low-pressure tower 10 is provided with tower plates in a staggered manner in the height direction, the bottom is provided with a liquid oxygen outlet, and the upper part is provided with a liquid air inlet, a liquid nitrogen inlet, a pure nitrogen outlet and a polluted nitrogen outlet; the subcooler II 11 includes a liquid air passage, a nitrogen passage, a dirty nitrogen passage and a liquid nitrogen passage.
The outlet of the LNG storage device 13 is sequentially connected with the natural gas channel inlet of the precooler 4 through a pipeline via the cryopump 14 and the LNG channel of the main heat exchanger 6, and the natural gas channel outlet of the precooler 4 is connected with a natural gas storage or utilization device (not shown in the figure) through a pipeline. The air inlet of the fan 1 is communicated with the outside air, and the air outlet of the fan 1 is communicated with the air inlet at the bottom of the high-pressure tower 8 through a pipeline sequentially through the water cooling tower 2, the molecular sieve 3, the air passage of the precooler 4, the air passage of the main heat exchanger 6 and the air passage of the subcooler I7; the liquid air outlet at the bottom of the high-pressure tower 8 is communicated with the liquid air inlet arranged at the upper part of the low-pressure tower 10 through a liquid air passage of the cooler II 11 by a pipeline, and the liquid nitrogen outlet at the top of the high-pressure tower 8 is communicated with the liquid nitrogen inlet arranged at the upper part of the low-pressure tower 10 through a liquid nitrogen passage of the cooler II 11 by a pipeline; the rectifying section of the high-pressure tower 8 and the stripping section of the low-pressure tower 10 are positioned at the same height, a heat exchange integrated unit 9 consisting of a plurality of heat exchangers which are arranged in parallel is arranged between the rectifying section of the high-pressure tower 8 and the stripping section of the low-pressure tower 10, and heat of the rectifying section of the high-pressure tower 8 is transferred to the stripping section of the low-pressure tower 10 through the heat exchange integrated unit 9; the liquid oxygen outlet at the bottom of the low-pressure tower 10 is communicated with the inlet of the liquid oxygen storage device 12 through a pipeline; the pure nitrogen outlet at the upper part of the low-pressure tower 10 is communicated with the inlet of a nitrogen storage or utilization device (not shown in the figure) through a pipeline sequentially passing through the nitrogen passage of the subcooler II 11, the nitrogen passage I of the subcooler I7 and the nitrogen passage of the main heat exchanger 6, and the dirty nitrogen outlet at the upper part of the low-pressure tower 10 is communicated with the air cooling system of the molecular sieve 3 through a pipeline sequentially passing through the dirty nitrogen passage of the subcooler II 11, the dirty nitrogen passage of the subcooler I7 and the dirty nitrogen passage of the main heat exchanger 6.
The invention relates to a heat integration rectification air separation system for utilizing LNG cold energy, which mainly utilizes the LNG cold energy to cool raw material high-pressure air and adopts a heat integration rectification tower to perform air separation, and the specific working process is as follows:
firstly, air is boosted by a fan 1 and cooled by a water cooling tower 3, the boosted pressure is used for compensating pressure loss when the molecular sieve 3 removes impurities such as moisture, carbon dioxide and the like, the air after the impurities are removed by the molecular sieve 3 enters a precooler 4 to exchange heat with LNG to absorb part of cold energy, the air is continuously boosted to 0.4MPa in an air compressor 5, and at the moment, the temperature of the outlet air of the air compressor 5 is close to the ambient temperature; the air with pressure enters the main heat exchanger 6, the subcooler I7 is cooled to be close to the bubble point temperature by LNG, reflux nitrogen and dirty nitrogen, and is sent to the bottom of the high-pressure tower 8, and in the high-pressure tower 8, rising air and reflux liquid nitrogen are repeatedly condensed and evaporated on a tower plate, so that oxygen-enriched liquid air with higher oxygen concentration is concentrated at the bottom of the high-pressure tower 8, and high-purity liquid nitrogen is concentrated at the top of the high-pressure tower 8; liquid nitrogen and oxygen-enriched liquid air pumped from the top and the bottom of the high-pressure tower 8 pass through the cooler II 11 and then enter the low-pressure tower 10 to participate in the rectification process; the heat of the rectifying section of the high-pressure tower 8 is transferred to the stripping section of the low-pressure tower 10 through the heat exchange integrated unit 9 consisting of a plurality of heat exchangers which are arranged in parallel, so that each tower plate of the high-pressure tower 8 is promoted to generate more condensed liquid, and each tower plate of the low-pressure tower 10 generates more evaporation gas; the liquid oxygen at the bottom of the low-pressure tower 10 is directly output as a product (stored in a liquid oxygen storage device 12), pure nitrogen at the top is output as a nitrogen product after being rewuped by a cooler II 11, a subcooler I7 and a main heat exchanger 6, and polluted nitrogen is sent to an air cooling system of the molecular sieve 3 after being rewuped by the cooler II 11, the subcooler I7 and the main heat exchanger 6.
Example 2
The difference from example 1 is that, as shown in fig. 2, the higher pressure column 8 and the lower pressure column 10 in example 2 are integrated together to form a double pipe rectifying device, and the stripping section of the lower pressure column 10 is nested in the rectifying section of the higher pressure column 8, and heat exchange is directly carried out between the two. Except for this, the connection relationship between the other components in embodiment 2 is the same as that in embodiment 1.
Compared with the traditional air separation system in the prior art, the heat integration rectification air separation system for LNG cold energy utilization can reduce the pressure of raw material air from 0.6MPa to 0.4MPa by adopting the heat integration rectification system, thereby reducing the total pressure ratio and the power consumption of an air compressor; the LNG is adopted to cool the raw material air, so that the power consumption of the air compressor is further reduced, and the liquid oxygen yield is improved, thereby reducing the energy consumption of unit liquid products; the heat integration rectification can reduce the fire loss in the rectification process of the high-pressure tower and the rectification process of the low-pressure tower, and improve the separation purity of oxygen and nitrogen. In addition, the LNG is adopted to cool the raw material air, so that the starting time of the air separation system can be greatly reduced.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (6)

1. The heat integration rectification air separation system for LNG cold energy utilization comprises a fan, a water cooling tower, a molecular sieve, a precooler, an air compressor, a main heat exchanger, a subcooler I, a high-pressure tower, a heat exchange integrated unit, a low-pressure tower, a subcooler II, an LNG storage device and a low-temperature pump, and is characterized in that,
the precooler comprises an air passage and a natural gas passage;
the main heat exchanger comprises an air passage, an LNG passage, a nitrogen passage and a polluted nitrogen passage;
the subcooler I comprises an air passage, a polluted nitrogen passage and a nitrogen passage;
the high-pressure tower is provided with tower plates in a staggered manner in the height direction, the bottom of the high-pressure tower is provided with a low-temperature air inlet and a liquid air outlet, and the top of the high-pressure tower is provided with a liquid nitrogen outlet;
the low-pressure tower is provided with tower plates in a staggered manner in the height direction, the bottom is provided with a liquid oxygen outlet, and the upper part is provided with a liquid air inlet, a liquid nitrogen inlet, a pure nitrogen outlet and a polluted nitrogen outlet;
the subcooler II comprises a liquid air passage, a nitrogen passage, a polluted nitrogen passage and a liquid nitrogen passage,
wherein,
an outlet of the LNG storage device is communicated with an inlet of a natural gas passage of the precooler through an LNG passage of the cryogenic pump and the main heat exchanger in sequence through a pipeline;
the air inlet of the fan is communicated with the outside air, the air outlet of the fan is communicated with the air inlet at the bottom of the high-pressure tower through a pipeline sequentially through the water cooling tower, the molecular sieve, the air passage of the precooler, the air compressor, the air passage of the main heat exchanger and the air passage of the subcooler I, the outlet air pressure of the air compressor is about 0.4MPa, the temperature of the outlet air is close to the ambient temperature, and the air after being cooled sequentially is cooled to be close to the bubble point temperature and is sent to the bottom of the high-pressure tower;
the liquid air outlet at the bottom of the high-pressure tower is communicated with the liquid air inlet arranged at the upper part of the low-pressure tower through a liquid air passage of the subcooler II by a pipeline, and the liquid nitrogen outlet at the top of the high-pressure tower is communicated with the liquid nitrogen inlet arranged at the upper part of the low-pressure tower through a liquid nitrogen passage of the subcooler II by a pipeline;
the rectifying section of the high-pressure tower and the stripping section of the low-pressure tower are positioned at the same height, the heat exchange integrated unit formed by a plurality of heat exchangers arranged in parallel is arranged between the rectifying section of the high-pressure tower and the stripping section of the low-pressure tower, and heat exchange is carried out between the rectifying section of the high-pressure tower and the stripping section of the low-pressure tower through the heat exchange integrated unit;
the pure nitrogen outlet at the upper part of the low-pressure tower is communicated with the inlet of the nitrogen passage of the subcooler II, the nitrogen passage I of the subcooler I and the nitrogen passage of the main heat exchanger in sequence through pipelines,
the sewage nitrogen outlet at the upper part of the low-pressure tower is communicated with the sewage nitrogen passage of the subcooler II, the sewage nitrogen passage of the subcooler I and the inlet of the sewage nitrogen passage of the main heat exchanger in sequence through pipelines, and the outlet of the sewage nitrogen passage of the main heat exchanger is communicated with the air cooling system of the molecular sieve;
and, the heat integration rectification space division system has the following concrete working processes:
firstly, after being boosted by the fan, outside air is led into the water cooling tower for cooling, then enters the precooler after being subjected to impurity removal by the molecular sieve and exchanges heat with LNG in the precooler to absorb part of cold energy, and then is led into the air compressor for continuously boosting to 0.4Mpa, and the temperature of the outlet air of the air compressor is close to the ambient temperature;
then, the pressurized air sequentially enters the main heat exchanger and the subcooler I, is cooled to be close to the bubble point temperature by LNG, reflux nitrogen and dirty nitrogen, and is sent to the bottom of the high-pressure tower;
in the high-pressure tower, rising air and reflux liquid nitrogen are repeatedly condensed and evaporated on a tower plate, so that oxygen-enriched liquid air with higher oxygen concentration is concentrated at the bottom of the high-pressure tower, and high-purity liquid nitrogen is concentrated at the top of the high-pressure tower;
liquid nitrogen and oxygen-enriched liquid air which are pumped out from the top and the bottom of the high-pressure tower enter the low-pressure tower after passing through the subcooler II so as to participate in the rectification process;
the heat of the rectifying section of the high-pressure tower is transferred to the stripping section of the low-pressure tower through the heat exchange integrated unit consisting of a plurality of heat exchangers which are arranged in parallel, so that each tower plate of the high-pressure tower is promoted to generate more condensed liquid, and each tower plate of the low-pressure tower generates more evaporated gas;
the liquid oxygen at the bottom of the low-pressure tower is directly used as a product to be output, pure nitrogen at the top of the low-pressure tower is sequentially subjected to rewarming by the subcooler II, the subcooler I and the main heat exchanger and then is used as a nitrogen product to be output, and polluted nitrogen at the top of the low-pressure tower is sequentially subjected to rewarming by the subcooler II, the subcooler I and the main heat exchanger and then is sent to an air cooling system of the molecular sieve.
2. The LNG cold energy utilizing heat integrated rectifying space division system of claim 1, wherein the natural gas passage outlet of the precooler is in communication with a natural gas storage or utilization device through a pipeline.
3. The LNG cold energy utilizing heat integrated rectifying space division system of claim 1, wherein the stripping section of the low pressure column is nested within the rectifying section of the high pressure column, and heat from the rectifying section of the high pressure column is transferred directly to the stripping section of the low pressure column.
4. The LNG cold energy utilizing heat integrated rectifying space division system according to claim 1, wherein the liquid oxygen outlet at the bottom of the low pressure column is in communication with the inlet of the liquid oxygen storage or utilizing device through a pipeline.
5. The LNG cold energy utilizing heat integrated rectifying space division system according to claim 1, wherein an outlet of the nitrogen passage of the main heat exchanger is communicated with an inlet of a nitrogen storage or utilizing device.
6. The LNG cold energy utilizing heat integrated rectifying air separation system according to claim 1, wherein the liquid air inlet and the liquid nitrogen inlet at the upper part of the low pressure tower are both provided with control valves.
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