CN114034160B - Novel two-stage rectification self-cascade natural gas liquefaction system and control method thereof - Google Patents

Novel two-stage rectification self-cascade natural gas liquefaction system and control method thereof Download PDF

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CN114034160B
CN114034160B CN202111523782.3A CN202111523782A CN114034160B CN 114034160 B CN114034160 B CN 114034160B CN 202111523782 A CN202111523782 A CN 202111523782A CN 114034160 B CN114034160 B CN 114034160B
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outlet
channel
inlet
target value
throttling mechanism
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CN114034160A (en
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谢肥东
侯翠红
牛柏林
陈佳恒
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Zhengzhou University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/0002—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the fluid to be liquefied
    • F25J1/0022—Hydrocarbons, e.g. natural gas
    • 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
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0225—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using other external refrigeration means not provided before, e.g. heat driven absorption chillers
    • F25J1/0227—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process using other external refrigeration means not provided before, e.g. heat driven absorption chillers within a refrigeration cascade
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B1/00—Compression machines, plants or systems with non-reversible cycle
    • F25B1/10—Compression machines, plants or systems with non-reversible cycle with multi-stage compression
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B39/00—Evaporators; Condensers
    • F25B39/04—Condensers
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B40/00—Subcoolers, desuperheaters or superheaters
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B40/00—Subcoolers, desuperheaters or superheaters
    • F25B40/06—Superheaters
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B41/00—Fluid-circulation arrangements
    • F25B41/30—Expansion means; Dispositions thereof
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B41/00—Fluid-circulation arrangements
    • F25B41/30—Expansion means; Dispositions thereof
    • F25B41/39—Dispositions with two or more expansion means arranged in series, i.e. multi-stage expansion, on a refrigerant line leading to the same evaporator
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B5/00—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity
    • F25B5/04—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity arranged in series
    • 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
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
    • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
    • F25J1/0052—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream
    • F25J1/0055—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by vaporising a liquid refrigerant stream originating from an incorporated cascade
    • 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
    • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
    • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
    • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
    • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
    • F25J1/0262—Details of the cold heat exchange system
    • F25J1/0264—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams
    • F25J1/0265—Arrangement of heat exchanger cores in parallel with different functions, e.g. different cooling streams comprising cores associated exclusively with the cooling of a refrigerant stream, e.g. for auto-refrigeration or economizer
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/05—Compression system with heat exchange between particular parts of the system
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/05—Compression system with heat exchange between particular parts of the system
    • F25B2400/054—Compression system with heat exchange between particular parts of the system between the suction tube of the compressor and another part of the 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/13—Economisers
    • 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
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
    • F25B2400/23—Separators
    • 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
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/34—Details about subcooling of liquids

Abstract

The invention discloses a two-stage rectification self-cascade natural gas liquefaction system, which adopts two-stage rectification to realize two-stage separation of mixed refrigerant components, increases the proportion of low-boiling point components in the mixed refrigerant entering an evaporator, improves the evaporation pressure of the system, reduces the working pressure ratio of a compressor, and improves the performance of the system. Meanwhile, the novel system introduces an intermediate air supplement technology, and the high-pressure refrigerant of a part of flow paths only needs to be throttled to intermediate pressure, so that the throttling loss of the system is greatly reduced, and the system performance is further improved.

Description

Novel two-stage rectification self-cascade natural gas liquefaction system and control method thereof
Technical Field
The invention belongs to the field of chemical equipment, and particularly relates to a two-stage rectification self-cascade natural gas liquefaction system and a control method thereof.
Background
At present, the self-cascade natural gas liquefaction system has been widely applied and developed due to the advantages of low cost, simple mechanism, small control difficulty and the like. For a self-cascade system, how to improve the separation efficiency of high and low boiling point components of a non-azeotropic refrigerant is a key factor for improving the performance of the system, and the more sufficient the separation of the components of the refrigerant is, the better the performance of the system is. The traditional self-cascade refrigeration system generally adopts a gas-liquid separator to separate components of a mixed refrigerant, has poor component separation effect, and is difficult to meet the separation purity requirement required by the high-efficiency operation of the ultralow-temperature self-cascade refrigeration system, so that the working pressure of a compressor is overlarge, and the energy efficiency of the system is low. On the other hand, because the working pressure ratio of the self-cascade refrigeration system is relatively large, the working medium has relatively large throttling loss in the process of reducing the pressure of the high-pressure fluid and throttling to the low-pressure fluid, so that how to reduce the throttling loss of the system becomes the key for improving the performance of the self-cascade refrigeration system.
Chinese patent No. CN02110664.9, published 2004 as 6.2.2004, entitled deep refrigeration device, discloses that a rectification device is used to replace a gas-liquid separator in a conventional self-cascade refrigeration system, and the separation effect of refrigerant components is improved, thereby improving the system efficiency. However, the system essentially only realizes one-time refrigerant component separation, the component separation effect of the multi-component mixed refrigerant commonly used in the field of natural gas liquefaction is not sufficient, all high-pressure refrigerants need to be throttled to the lowest pressure, the throttling loss is large, and great performance improvement potential exists.
Disclosure of Invention
In order to solve the defects of the prior art, the invention aims to provide a two-stage rectification self-cascade natural gas liquefaction system, and the system improves the evaporation pressure of the system, reduces the working pressure ratio of a compressor and the throttling loss of the system by introducing two-stage rectification and intermediate gas supplementing technologies, thereby greatly improving the performance of the self-cascade natural gas liquefaction system.
In order to achieve the purpose, the invention adopts the technical scheme that:
a two-stage rectification self-cascade natural gas liquefaction system comprises a first compressor, wherein the inlet of the first compressor is connected with the outlet of a second channel of a heat regenerator, the inlet of a second compressor is connected with the outlet of the first compressor and the outlet of a tower top heat exchanger of a first rectification device, the outlet of the second compressor is connected with the inlet of the first rectification device through a condenser, and the kettle bottom liquid phase outlet of the first rectification device is connected with the inlet of the second channel of a first evaporative condenser through a first throttling mechanism; the outlet of the second channel of the first evaporative condenser is connected with the inlet of the tower top heat exchanger of the first rectifying device, the tower top gas phase outlet of the first rectifying device is connected with the inlet of the first channel of the first evaporative condenser, and the outlet of the first channel of the first evaporative condenser is connected with the inlet of the first channel of the heat regenerator;
a first channel outlet of the heat regenerator is connected with an inlet of the second rectifying device through a second throttling mechanism, a kettle bottom liquid phase outlet of the second rectifying device is connected with a second channel inlet of the second evaporative condenser through a third throttling mechanism, and a second channel outlet of the second evaporative condenser and an outlet of a tower top heat exchanger of the second rectifying device are connected with a second channel inlet of the heat regenerator after being converged; the tower top gas phase outlet of the second rectifying device is connected with the first channel inlet of the second evaporative condenser, the first channel outlet of the second evaporative condenser is connected with the refrigerant inlet of the evaporator through the fourth throttling mechanism, the refrigerant outlet of the evaporator is connected with the tower top heat exchanger inlet of the second rectifying device, and the evaporator is provided with a liquefied gas outlet and a raw material inlet.
Preferably, both rectification devices comprise a bottom tower kettle, a tower body, a tower top and a heat exchanger inside the tower top.
Preferably, the working medium used by the system is a binary and above non-azeotropic mixed working medium.
Preferably, the four throttling mechanisms are adjustable throttling mechanisms.
Preferably, the heat regenerator and the two evaporative condensers adopt a double-pipe heat exchanger or a plate heat exchanger, and a first channel and a second channel for flowing of working media are arranged inside the heat regenerator and the two evaporative condensers.
Correspondingly, the invention also provides a control method based on the two-stage rectification self-cascade natural gas liquefaction system, which comprises the following steps:
1) The rotating speeds of the first compressor and the second compressor are adjusted and controlled based on the supercooling degree of the liquefied natural gas at the liquefied gas outlet of the evaporator; if the supercooling degree is less than the set target value, increasing the rotating speed of the compressor, and if the supercooling degree is greater than the target value, reducing the rotating speed of the compressor;
2) The fan rotating speed of the condenser is controlled based on the minimum heat exchange temperature difference between the condenser and the environment; if the minimum heat exchange temperature difference is smaller than a set target value, the fan rotating speed of the condenser is reduced, and if the minimum heat exchange temperature difference is larger than the target value, the fan rotating speed of the condenser is increased;
3) The opening degree of the first throttling mechanism is adjusted and controlled based on the superheat degree of a refrigerant at the outlet of the tower top heat exchanger of the first rectifying device; if the superheat degree is less than a set target value, reducing the opening degree of the first throttling mechanism, and if the superheat degree is greater than the target value, increasing the opening degree of the first throttling mechanism;
4) The opening degree of the second throttling mechanism is adjusted and controlled based on the supercooling degree of the refrigerant at the outlet of the first channel of the second evaporative condenser; if the supercooling degree is greater than the set target value, reducing the opening degree of the second throttling mechanism, and if the supercooling degree is less than the set target value, increasing the opening degree of the second throttling mechanism;
5) The opening degree of the third throttling structure is adjusted and controlled based on the superheat degree of the refrigerant at the outlet of the second channel of the second evaporative condenser; if the superheat degree is larger than the set target value, the opening degree of the third throttling mechanism is increased, and if the superheat degree is smaller than the set target value, the opening degree of the third throttling mechanism is decreased;
6) The opening degree of the fourth throttling mechanism is adjusted and controlled based on the temperature of the throttled refrigerant; if the temperature is higher than the set target value, the opening degree of the fourth throttling mechanism is decreased, and if the temperature is lower than the target value, the opening degree of the fourth throttling mechanism is increased.
The invention has the following beneficial effects:
the system provided by the invention adopts two-stage rectification to improve the component separation effect of the mixed refrigerant, and increases the proportion of low-boiling-point components in the mixed refrigerant entering the evaporator, thereby improving the evaporation pressure of the system, reducing the working pressure ratio of the compressor and improving the system performance. Meanwhile, the novel system introduces an intermediate air supplement technology, the refrigerant of part of flow paths only needs to be throttled to intermediate pressure, all flow path working media are not required to be throttled to the lowest working pressure like a conventional self-cascade system, the throttling loss of the system is greatly reduced, and the system performance is further improved.
Drawings
FIG. 1 is a schematic diagram of a system cycle of the present invention.
Detailed Description
As shown in FIG. 1, the invention provides a two-stage rectification self-cascade natural gas liquefaction system and a control method thereof. Two working medium circulation channels are arranged in the first evaporative condenser 105, the heat regenerator 107 and the second evaporative condenser 110. An inlet of the first compressor 101 is connected with a second channel outlet 107c of the heat regenerator 107, an inlet of the second compressor is connected with an outlet of the first compressor 101 and an outlet 104d of the tower top heat exchanger of the first rectifying device 104, an outlet of the second compressor 102 is connected with an inlet 104c of the first rectifying device 104 through the condenser 103, a kettle bottom liquid phase outlet 104a of the first rectifying device 104 is connected with an inlet of the first throttling mechanism 106, and an outlet of the first throttling mechanism 106 is connected with a second channel inlet 105d of the first evaporative condenser 105. A second channel outlet 105c of the first evaporative condenser 105 is connected with an inlet 104e of the top heat exchanger of the first rectifying device 104, an overhead gas phase outlet 104b of the first rectifying device 104 is connected with a first channel inlet 105a of the first evaporative condenser 105, a first channel outlet 105b of the first evaporative condenser 105 is connected with a first channel inlet 107a of the heat regenerator 107, a first channel outlet 107b of the heat regenerator 107 is connected with an inlet of the second throttling mechanism 109, an outlet of the second throttling mechanism 109 is connected with an inlet 108c of the second rectifying device 108, a kettle bottom liquid phase outlet 108a of the second rectifying device 108 is connected with an inlet of the third throttling mechanism 111, an outlet of the third throttling mechanism 111 is connected with a second channel inlet 110d of the second evaporative condenser 110, and a second channel outlet 110c of the second evaporative condenser 110 and an overhead heat exchanger outlet 108e of the second rectifying device 108 are merged and then connected with a second channel inlet 107d of the heat regenerator 107; the top gas phase outlet 108b of the second rectifying device 108 is connected with the first channel inlet 110a of the second evaporative condenser 110, the first channel outlet 110b of the second evaporative condenser 110 is connected with the inlet of the fourth throttling mechanism 112, the outlet of the fourth throttling mechanism 112 is connected with the refrigerant inlet 113a of the evaporator 113, the refrigerant outlet 113b of the evaporator 113 is connected with the top heat exchanger inlet 108d of the second rectifying device 108, and the evaporator is provided with a liquefied gas outlet 103c and a raw material inlet 103d.
The first evaporative condenser 105, the heat regenerator 107 and the second evaporative condenser 110 are provided with a first channel and a second channel for the working medium to flow. The first evaporative condenser 105, the regenerator 107, and the second evaporative subcooler 110 are double pipe heat exchangers or plate heat exchangers. The working medium used by the system is a binary and above non-azeotropic mixed working medium.
The four throttling mechanisms adopt adjustable throttling mechanisms.
The two rectifying devices comprise a bottom tower kettle, a tower body, a tower top and a heat exchanger inside the tower top.
The working flow of the system is as follows:
the high-temperature high-pressure refrigerant leaves the outlet of the first compressor 101, is condensed into two-phase fluid by the condenser 103, and then enters the first rectifying device 104 to realize the first-stage separation of high-boiling point components and low-boiling point components. After leaving the top gas-phase outlet 104b of the first rectifying device 104, the gaseous mixed refrigerant rich in the low-boiling point component sequentially passes through the first channel of the first evaporative condenser 105 and the first channel of the heat regenerator 107 to be condensed into a supercooled refrigerant liquid; after leaving the still bottom liquid phase outlet 104a of the first rectification apparatus 104, the liquid refrigerant rich in the high boiling point component is throttled in the first throttling mechanism 106 into a medium-pressure two-phase fluid, and then is subjected to heat absorption evaporation in the second passage of the first evaporation condenser 105, and condenses the gaseous refrigerant rich in the low boiling point component from the overhead gas phase outlet 104b of the first rectification apparatus 104, and then flows out from the overhead heat exchanger outlet 104d after further absorbing heat in the overhead heat exchanger of the first rectification apparatus 104, and is merged with the refrigerant at the outlet of the first compressor 101 and then returns to the inlet of the second compressor 102.
The refrigerant liquid rich in low-boiling point components from the outlet 107b of the first channel of the regenerator 107 is throttled in the second throttling mechanism 109 to become two-phase refrigerant, and then enters the second rectifying device 108 to realize the two-stage separation of high-boiling point components and low-boiling point components. The gaseous mixed refrigerant rich in more low-boiling point components leaves the top gas phase outlet 108b of the second rectification device 108, is completely condensed in the first passage of the second evaporative condenser 110, is throttled into a low-pressure two-phase refrigerant by the fourth throttling mechanism 112, and then flows into the top heat exchanger of the second rectification device 108 after being evaporated in the evaporator 113 to further absorb heat. The liquid refrigerant separated by the second rectification device 108 and rich in high boiling point components leaves the still bottom liquid phase outlet 108a and then is throttled in the third throttling mechanism 111 to become a low-pressure two-phase refrigerant, and then is subjected to heat absorption and evaporation in the second channel of the second evaporative condenser 110, and the gaseous refrigerant from the gas phase outlet 108b at the top of the second rectification device 108 is condensed, then is merged with the refrigerant from the heat exchanger outlet 108e at the top of the second rectification device 108, and finally is heated and warmed through the second channel of the heat regenerator 107 and returns to the inlet of the compressor 101.
Correspondingly, the invention also provides a control method based on the system, and the control process comprises the following contents:
1) The rotation speeds of the first compressor 101 and the second compressor 102 are adjusted and controlled based on the degree of supercooling of the liquefied natural gas at the liquefied gas outlet 113c of the evaporator 113. If the supercooling degree is less than the set target value, increasing the rotating speed of the compressor; and if the supercooling degree is larger than the set target value, reducing the rotating speed of the compressor.
2) The fan speed of the condenser 103 is controlled based on the minimum heat exchange temperature difference between the condenser and the environment (i.e., the difference between the condenser outlet refrigerant temperature and the ambient temperature). If the minimum heat exchange temperature difference is smaller than the set target value, the fan rotating speed of the condenser 103 is reduced; if the minimum heat exchange temperature difference is greater than the set target value, the fan rotation speed of the condenser 103 is increased.
3) The opening degree of the first throttling mechanism 106 is adjusted and controlled based on the superheat degree of the refrigerant at the outlet of the tower top heat exchanger 104d of the first rectifying device 104. If the degree of superheat is less than the set target value, the opening degree of the first throttling mechanism 106 is decreased; if the degree of superheat is greater than the set target value, the opening degree of the first throttle mechanism 106 is increased.
4) The opening degree of the second throttling mechanism 109 is adjustably controlled based on the degree of supercooling of the refrigerant at the first passage outlet 110b of the second evaporative condenser 110. If the supercooling degree is greater than the set target value, the opening degree of the second throttling mechanism 109 is decreased; if the degree of subcooling is less than the set target value, the opening degree of the second throttling structure 109 is increased.
5) The opening degree of the third throttling structure 111 is adjusted and controlled based on the degree of superheat of the refrigerant at the second passage outlet 110c of the second evaporative condenser 110. If the degree of superheat is greater than the set target value, the opening degree of the third throttling mechanism 111 is increased; if the degree of superheat is less than the set target value, the opening degree of the third throttling means 111 is decreased.
6) The opening degree of the fourth throttling mechanism 112 is adjusted and controlled based on the throttled refrigerant temperature. If the temperature is greater than the set target value, the opening degree of the fourth throttling mechanism 112 is reduced; if the temperature is less than the set target value, the opening degree of the fourth throttle mechanism 112 is increased.
Compared with the prior art that single-stage refrigerant component separation is carried out only under the same pressure, the invention adopts two-stage rectification, reduces the pressure and throttles the refrigerant liquid rich in the low-boiling-point component after the first rectification and the condensation, carries out the second-stage rectification, further improves the concentration of the low-boiling-point component entering the evaporator, achieves better component separation effect, increases the proportion of the low-boiling-point component in the mixed refrigerant entering the evaporator, thereby improving the evaporation pressure of a system, reducing the working pressure ratio of a compressor and improving the system performance. Meanwhile, the novel system introduces an intermediate air supply technology, the refrigerant of part of flow paths only needs to be throttled to intermediate pressure, all flow path working media do not need to be throttled to the lowest working pressure like a conventional self-cascade system, the throttling loss of the system is greatly reduced, and the system performance is further improved.

Claims (5)

1. A control method of a two-stage rectification self-cascade natural gas liquefaction system is characterized by comprising the following steps: the two-stage rectification self-cascade natural gas liquefaction system comprises a first compressor, wherein the inlet of the first compressor is connected with the outlet of a second channel of a heat regenerator, the inlet of a second compressor is connected with the outlet of the first compressor and the outlet of a tower top heat exchanger of a first rectification device, the outlet of the second compressor is connected with the inlet of the first rectification device through a condenser, and a kettle bottom liquid phase outlet of the first rectification device is connected with the inlet of the second channel of a first evaporative condenser through a first throttling mechanism; the outlet of the second channel of the first evaporative condenser is connected with the inlet of the tower top heat exchanger of the first rectifying device, the gas phase outlet at the tower top of the first rectifying device is connected with the inlet of the first channel of the first evaporative condenser, and the outlet of the first channel of the first evaporative condenser is connected with the inlet of the first channel of the heat regenerator;
a first channel outlet of the heat regenerator is connected with an inlet of the second rectifying device through a second throttling mechanism, a kettle bottom liquid phase outlet of the second rectifying device is connected with a second channel inlet of the second evaporative condenser through a third throttling mechanism, and a second channel outlet of the second evaporative condenser and an outlet of a tower top heat exchanger of the second rectifying device are connected with a second channel inlet of the heat regenerator after being converged; the tower top gas phase outlet of the second rectifying device is connected with the first channel inlet of the second evaporative condenser, the first channel outlet of the second evaporative condenser is connected with the refrigerant inlet of the evaporator through a fourth throttling mechanism, the refrigerant outlet of the evaporator is connected with the tower top heat exchanger inlet of the second rectifying device, and the evaporator is provided with a liquefied gas outlet and a raw material inlet;
the control method for the liquefaction system specifically comprises the following processes:
1) The rotating speeds of the first compressor and the second compressor are adjusted and controlled based on the supercooling degree of the liquefied natural gas at the liquefied gas outlet of the evaporator; if the supercooling degree is smaller than the set target value, increasing the rotating speed of the compressor, and if the supercooling degree is larger than the target value, reducing the rotating speed of the compressor;
2) The fan rotating speed of the condenser is controlled based on the minimum heat exchange temperature difference between the condenser and the environment; if the minimum heat exchange temperature difference is smaller than a set target value, the fan rotating speed of the condenser is reduced, and if the minimum heat exchange temperature difference is larger than the target value, the fan rotating speed of the condenser is increased;
3) The opening degree of the first throttling mechanism is adjusted and controlled based on the superheat degree of a refrigerant at the outlet of the tower top heat exchanger of the first rectifying device; if the superheat degree is less than a set target value, reducing the opening degree of the first throttling mechanism, and if the superheat degree is greater than the target value, increasing the opening degree of the first throttling mechanism;
4) The opening degree of the second throttling mechanism is adjusted and controlled based on the supercooling degree of the refrigerant at the outlet of the first channel of the second evaporative condenser; if the supercooling degree is greater than the set target value, reducing the opening degree of the second throttling mechanism, and if the supercooling degree is less than the set target value, increasing the opening degree of the second throttling mechanism;
5) The opening degree of the third throttling structure is adjusted and controlled based on the superheat degree of the refrigerant at the outlet of the second channel of the second evaporative condenser; if the superheat degree is larger than the set target value, the opening degree of the third throttling mechanism is increased, and if the superheat degree is smaller than the set target value, the opening degree of the third throttling mechanism is decreased;
6) The opening degree of the fourth throttling mechanism is adjusted and controlled based on the temperature of the throttled refrigerant; if the temperature is higher than the set target value, the opening degree of the fourth throttling mechanism is decreased, and if the temperature is lower than the target value, the opening degree of the fourth throttling mechanism is increased.
2. The method of controlling a two-stage distillation self-cascade natural gas liquefaction system of claim 1, wherein: the two rectifying devices comprise a bottom tower kettle, a tower body, a tower top and a heat exchanger inside the tower top.
3. The method of controlling a two-stage distillation auto-cascade natural gas liquefaction system according to claim 1, wherein: the working medium used by the system is a binary and above non-azeotropic mixed working medium.
4. The method of controlling a two-stage distillation self-cascade natural gas liquefaction system of claim 1, wherein: the four throttling mechanisms are all adjustable throttling mechanisms.
5. The method of controlling a two-stage distillation self-cascade natural gas liquefaction system of claim 1, wherein: the heat regenerator and the two evaporative condensers adopt a double-pipe heat exchanger or a plate heat exchanger, and a first channel and a second channel for flowing of working media are arranged in the heat regenerator and the two evaporative condensers.
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US5746066A (en) * 1996-09-17 1998-05-05 Manley; David B. Pre-fractionation of cracked gas or olefins fractionation by one or two mixed refrigerant loops and cooling water
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CN105546864B (en) * 2016-01-13 2018-05-18 西安交通大学 A kind of Auto-cascade cycle steam compressed refrigerating circulating system of band evaporation subcooler
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CN207438936U (en) * 2017-07-20 2018-06-01 南京天源冷冻设备有限公司 A kind of two-way bypasses three-level auto-cascading refrigeration system
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