CN115773629A - Carbon dioxide preparation process and cold box - Google Patents
Carbon dioxide preparation process and cold box Download PDFInfo
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- CN115773629A CN115773629A CN202211505893.6A CN202211505893A CN115773629A CN 115773629 A CN115773629 A CN 115773629A CN 202211505893 A CN202211505893 A CN 202211505893A CN 115773629 A CN115773629 A CN 115773629A
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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
- F25J3/0228—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 characterised by the separated product stream
- F25J3/0266—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 characterised by the separated product stream separation of carbon dioxide
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- 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
- F25J2200/02—Processes or apparatus using separation by rectification in a single pressure main column system
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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
- 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
- F25J2205/04—Processes or apparatus using other separation and/or other processing means using simple phase separation in a vessel or drum in the feed line, i.e. upstream of the fractionation step
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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
- F25J2215/00—Processes characterised by the type or other details of the product stream
- F25J2215/04—Recovery of liquid products
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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
- F25J2220/00—Processes or apparatus involving steps for the removal of impurities
- F25J2220/80—Separating impurities from carbon dioxide, e.g. H2O or water-soluble contaminants
- F25J2220/82—Separating low boiling, i.e. more volatile components, e.g. He, H2, CO, Air gases, CH4
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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
- F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
- F25J2230/30—Compression of the feed stream
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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
- F25J2270/00—Refrigeration techniques used
- F25J2270/02—Internal refrigeration with liquid vaporising loop
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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
- F25J2270/00—Refrigeration techniques used
- F25J2270/04—Internal refrigeration with work-producing gas expansion loop
- F25J2270/06—Internal refrigeration with work-producing gas expansion loop with multiple gas expansion loops
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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
- F25J2270/00—Refrigeration techniques used
- F25J2270/80—Quasi-closed internal or closed external carbon dioxide refrigeration cycle
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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
- F25J2270/00—Refrigeration techniques used
- F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
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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
- F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
- F25J2290/34—Details about subcooling of liquids
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Abstract
The invention belongs to the technical field of gas recovery. The invention provides a process for preparing carbon dioxide in a cold box, which comprises the following steps: sequentially compressing, drying and condensing the raw material gas, and then carrying out gas-liquid separation to obtain liquid carbon dioxide and gaseous carbon dioxide; introducing the liquid carbon dioxide into a carbon dioxide rectifying tower to obtain tail gas and rectified carbon dioxide; discharging gaseous carbon dioxide out of the device after multistage expansion; the rectified carbon dioxide is compressed after being supercooled and reheated in sequence to obtain compressed carbon dioxide; the tail gas is exhausted out of the device after being expanded; partially compressed carbon dioxide is sequentially cooled, compressed by auxiliary refrigerant, condensed by auxiliary refrigerant and supercooled by auxiliary refrigerant to obtain a supercooled product; the remaining compressed carbon dioxide is sent to downstream equipment. The process for preparing the carbon dioxide in the cold box can recover the carbon dioxide in the mixed gas with the molar content of 40-85 percent, and the recovery rate of the carbon dioxide is high and can reach more than 55 percent.
Description
Technical Field
The invention relates to the technical field of gas recovery, in particular to a carbon dioxide preparation process and a cold box.
Background
Carbon dioxide emission reduction has become a focus of common attention all over the world, and liquid carbon dioxide products are prepared through a reasonable process flow, so that carbon dioxide emission reduction is realized while carbon dioxide tail gas is recycled.
At present, most of carbon dioxide recycling processes are used for recycling carbon dioxide with the content of more than 85%, and the process for recycling carbon dioxide with the content of 40-85% is less, however, carbon dioxide tail gas with the concentration is more common, and the lower the temperature is, the higher the recovery rate of carbon dioxide is. The carbon dioxide triple point is near 56.6 ℃ below zero, so that the risk of carbon dioxide freezing and blocking pipelines and equipment exists at the temperature near the temperature, and the temperature of 55 ℃ below zero is almost the cooling limit of the mixed gas, so that the carbon dioxide can be prevented from freezing and blocking, and the recovery rate of the carbon dioxide can be improved. However, the cold energy used by the traditional carbon dioxide liquefaction process can only be cooled to-30 ℃, and a large amount of carbon dioxide in tail gas cannot be recycled.
Therefore, it is a hot spot of current research to provide a method capable of recovering carbon dioxide from a carbon dioxide gas mixture with a carbon dioxide content of 40 to 85% and a high recovery rate.
Disclosure of Invention
The invention aims to provide a carbon dioxide preparation process and a cold box aiming at the defects of the prior art.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a process for preparing carbon dioxide in a cold box, which comprises the following steps:
1) Sequentially compressing, drying and condensing the raw material gas, and then carrying out gas-liquid separation to obtain liquid carbon dioxide and gaseous carbon dioxide;
2) Introducing liquid carbon dioxide into a carbon dioxide rectifying tower to obtain tail gas and rectified carbon dioxide; discharging gaseous carbon dioxide out of the device after multistage expansion;
3) The rectified carbon dioxide is compressed after being supercooled and reheated in sequence to obtain compressed carbon dioxide; the tail gas is exhausted out of the device after being expanded;
4) Partially compressed carbon dioxide is sequentially cooled, compressed by auxiliary refrigerant, condensed by auxiliary refrigerant and supercooled by auxiliary refrigerant to obtain a supercooled product; the remaining compressed carbon dioxide is sent to downstream equipment.
Preferably, the molar content of the carbon dioxide in the raw material gas in the step 1) is 40-85%.
Preferably, the pressure of the compressed feed gas in the step 1) is 3-4.5 MPa; the drying temperature is 10-40 ℃; the temperature of the condensed feed gas is-55 to-40 ℃.
Preferably, the temperature of the gaseous carbon dioxide in the step 2) is-20 to 5 ℃.
Preferably, the multistage expansion of step 2) comprises a first stage expansion and a second stage expansion; wherein, the pressure intensity of the first-stage expansion is reduced from 3.5-4.5 MPa to 1.4-1.8 MPa, and the pressure intensity of the second-stage expansion is reduced from 1.4-1.8 MPa to 0.2-0.6 MPa; the temperature of the first-stage expansion and the second-stage expansion is independently reduced from minus 2 to 2 ℃ to minus 55 to minus 50 ℃.
Preferably, the supercooling in the step 3) is at a temperature of-20 to-15 ℃; the temperature after rewarming is 25-35 ℃; the re-incubation and the condensation of step 1) are independently carried out in a main heat exchanger.
Preferably, the pressure of the compressed carbon dioxide in the step 3) is 1.5-4 MPa; the temperature of the tail gas is-20 to 5 ℃; the pressure of the gas expansion is reduced from 3.5-4.5 MPa to 0.2-0.6 MPa.
Preferably, the cooling mode in the step 4) is circulating water or air cooler cooling; the supercooled product enters a spherical tank for storage or serves as a supplementary refrigerant of a low-temperature area.
Preferably, the pressure intensity of the compressed auxiliary refrigerant in the step 4) is 1.5-2 MPa; the auxiliary refrigerant is liquid ammonia, freon, propane or propylene.
The beneficial effects of the invention include the following:
1) The process for preparing the carbon dioxide in the cold box can recover the carbon dioxide in the mixed gas with the molar content of 40-85 percent, and the recovery rate of the carbon dioxide is high and can reach more than 55 percent.
2) When the carbon dioxide is prepared in the cold box, the temperature of the carbon dioxide mixed gas can be reduced to be close to-55 ℃, and the carbon dioxide can be recovered as much as possible while the carbon dioxide is ensured not to be frozen.
Drawings
FIG. 1 is a flow diagram of a process for producing carbon dioxide in a cold box according to the present invention.
Detailed Description
The technological process of the present invention for producing carbon dioxide in a cold box is shown in figure 1.
The invention provides a process for preparing carbon dioxide in a cold box, which comprises the following steps:
1) The method comprises the following steps of sequentially compressing (raw gas compression in figure 1), drying (raw gas drying in figure 1), condensing (performed in a main heat exchanger in figure 1) and then performing gas-liquid separation (gas-liquid separation in figure 1) on raw gas to obtain liquid carbon dioxide and gaseous carbon dioxide;
2) Introducing liquid carbon dioxide into a carbon dioxide rectification column (CO of figure 1) 2 A rectification column) to obtain tail gas and rectified carbon dioxide; the gaseous carbon dioxide is discharged out of the device (tail gas outlet device 1 of figure 1) after being subjected to multi-stage expansion (first-stage expansion and second-stage expansion of figure 1);
3) The rectified carbon dioxide is successively subcooled (liquid phase CO of FIG. 1) 2 Subcooling), rewarming (in the main heat exchanger of fig. 1) and compression (CO of fig. 1) 2 Compression) to obtain compressed carbon dioxide; the tail gas is discharged out of the device (the tail gas outlet device 2 in the figure 1) after being expanded by the gas (the gas in the figure 1 is expanded);
4) The partially compressed carbon dioxide is sequentially cooled (liquid phase CO of FIG. 1) 2 Product cooling), auxiliary refrigerant compression (auxiliary refrigerant compression of fig. 1), auxiliary refrigerant condensation (auxiliary refrigerant condensation of fig. 1), auxiliary coolingAgent subcooling (auxiliary refrigerant subcooling of fig. 1) to obtain a subcooled product; the remaining compressed carbon dioxide is sent to downstream units (high pressure gas phase CO of FIG. 1) 2 Product to downstream equipment).
In the present invention, the molar content of carbon dioxide in the raw material gas in step 1) is preferably 40 to 85%, more preferably 50 to 75%, and still more preferably 55 to 70%.
In the invention, the pressure of the compressed feed gas in the step 1) is preferably 3-4.5 MPa, and more preferably 3.5-4 MPa; the drying temperature is preferably 10-40 ℃, more preferably 15-35 ℃, and more preferably 20-30 ℃; the temperature of the condensed feed gas is preferably-55 to-40 ℃, more preferably-50 to-45 ℃, and more preferably-48 to-46 ℃.
In the invention, the dew point of the dried feed gas in the step 1) is preferably-60 to-40 ℃, more preferably-55 to-45 ℃, and even more preferably-50 ℃.
In the present invention, the temperature of the gaseous carbon dioxide in step 2) is preferably-20 to 5 ℃, more preferably-15 to 0 ℃, and still more preferably-10 to-5 ℃.
In the present invention, the multistage expansion of step 2) preferably includes a primary expansion and a secondary expansion; wherein, the pressure intensity of the first-stage expansion is preferably reduced from 3.5-4.5 MPa to 1.4-1.8 MPa, more preferably from 3.8-4.2 MPa to 1.5-1.7 MPa, and more preferably from 4MPa to 1.6MPa; the pressure intensity of the secondary expansion is preferably reduced from 1.4-1.8 MPa to 0.2-0.6 MPa, more preferably from 1.5-1.7 MPa to 0.3-0.5 MPa, and even more preferably from 1.6MPa to 0.4MPa; the temperature of the primary expansion and the secondary expansion is independently reduced to-55 to-50 ℃ from-2 to 2 ℃, more preferably to-52 to-50 ℃ from 0 to 2 ℃, and even more preferably to-52 ℃ from 0 ℃.
In the present invention, the supercooling in step 3) is preferably-20 to-15 ℃, more preferably-18 to-16 ℃, and still more preferably-16 ℃; the temperature after rewarming is preferably 25-35 ℃, more preferably 28-32 ℃, and more preferably 30 ℃; the reheating and the condensation of step 1) are preferably carried out independently in a main heat exchanger.
In the invention, the pressure of the compressed carbon dioxide in the step 3) is preferably 1.5-4 MPa, more preferably 2-3.5 MPa, and more preferably 2.5-3 MPa; the temperature of the tail gas is preferably-20-5 ℃, more preferably-15-0 ℃, and more preferably-10-5 ℃; the pressure of the gas expansion is preferably reduced from 3.5 to 4.5MPa to 0.2 to 0.6MPa, more preferably from 3.8 to 4.2MPa to 0.3 to 0.5MPa, and even more preferably from 4MPa to 0.4MPa.
In the invention, the cooling mode in the step 4) is preferably circulating water or air cooler cooling; the subcooled product is preferably stored in a spherical tank (liquid phase CO of FIG. 1) 2 Product goes to the spherical tank) or as a supplementary refrigerant in the low-temperature area.
In the invention, the pressure intensity of the compressed auxiliary refrigerant in the step 4) is preferably 1.5-2 MPa, more preferably 1.6-1.8 MPa, and even more preferably 1.7MPa; the auxiliary refrigerant is preferably liquid ammonia, freon, propane or propylene.
In the present invention, the volume ratio of the partially compressed carbon dioxide to the remaining compressed carbon dioxide in the step 4) is preferably 1; more preferably 1:1 to 1.8, and still more preferably 1.2 to 1.5.
In the invention, the auxiliary refrigerant can be completely liquefied by circulating water or an air cooler when the pressure is less than or equal to 2MPa, and the refrigeration temperature is preferably-35 to-15 ℃, and more preferably-25 to-20 ℃.
The technical solutions provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
Example 1
Compressing a feed gas (the molar content of carbon dioxide is 60%) to a pressure of 3MPa, drying at a temperature of 10 ℃ (the dew point of the dried feed gas is-60 ℃), condensing the feed gas in a main heat exchanger to-55 ℃, and then carrying out gas-liquid separation to obtain liquid carbon dioxide and gaseous carbon dioxide; introducing the liquid carbon dioxide into a carbon dioxide rectifying tower to obtain tail gas and rectified carbon dioxide; after the gaseous carbon dioxide is reheated to-20 ℃, the gaseous carbon dioxide is discharged out of the device after primary expansion (the pressure is reduced from 3.5MPa to 1.4MPa, the temperature is reduced from-2 ℃ to-55 ℃) and secondary expansion (the pressure is reduced from 1.4MPa to 0.2MPa, and the temperature is reduced from-2 ℃ to-55 ℃) in sequence.
Supercooling the rectified carbon dioxide at the temperature of-20 ℃, then reheating to 25 ℃ in a main heat exchanger, and then compressing to the pressure of 1.5MPa to obtain compressed carbon dioxide; after the tail gas is reheated to-20 ℃, gas expansion (the pressure is reduced from 3.5MPa to 0.6 MPa) is carried out and then the tail gas is discharged out of the device; cooling part of compressed carbon dioxide by circulating water, then compressing the carbon dioxide under the condition of liquid ammonia in sequence (the pressure of the compressed carbon dioxide is 1.5 MPa), condensing and supercooling to obtain a supercooling product, and then storing the supercooling product in a spherical tank; the remaining compressed carbon dioxide is sent to a downstream unit (the volume ratio of partially compressed carbon dioxide to the remaining compressed carbon dioxide is 1:2).
The yield of carbon dioxide in this example was 67%.
Example 2
Compressing a feed gas (the molar content of carbon dioxide is 40%) to a pressure of 4.5MPa, drying at 40 ℃ (the dew point of the dried feed gas is-40 ℃), condensing the feed gas in a main heat exchanger to-40 ℃, and performing gas-liquid separation to obtain liquid carbon dioxide and gaseous carbon dioxide; introducing the liquid carbon dioxide into a carbon dioxide rectifying tower to obtain tail gas and rectified carbon dioxide; after the gaseous carbon dioxide is reheated to 5 ℃, the gaseous carbon dioxide is discharged out of the device after primary expansion (the pressure is reduced from 4.5MPa to 1.8MPa, the temperature is reduced from 2 ℃ to-50 ℃) and secondary expansion (the pressure is reduced from 1.8MPa to 0.6MPa, and the temperature is reduced from 2 ℃ to-50 ℃) in sequence.
Supercooling the rectified carbon dioxide at-15 ℃, then reheating to 35 ℃ in a main heat exchanger, and then compressing to the pressure of 4MPa to obtain compressed carbon dioxide; after the tail gas is reheated to 5 ℃, gas expansion (the pressure is reduced from 4.5MPa to 0.4 MPa) is carried out and then the tail gas is discharged out of the device; cooling part of the compressed carbon dioxide by an air cooler, and then sequentially compressing the carbon dioxide under the condition of Freon (the pressure of the compressed carbon dioxide is 2 MPa), condensing and supercooling to obtain a supercooling product, wherein the supercooling product is used as a supplementary refrigerant of a low-temperature area; the remaining compressed carbon dioxide is sent to a downstream unit (the volume ratio of partially compressed carbon dioxide to the remaining compressed carbon dioxide is 2:1).
The yield of carbon dioxide in this example was 58%.
Example 3
Compressing a feed gas (the molar content of carbon dioxide is 70%) to a pressure of 4MPa, drying at a temperature of 20 ℃ (the dew point of the dried feed gas is-50 ℃), condensing the feed gas in a main heat exchanger to-50 ℃, and then carrying out gas-liquid separation to obtain liquid carbon dioxide and gaseous carbon dioxide; introducing the liquid carbon dioxide into a carbon dioxide rectifying tower to obtain tail gas and rectified carbon dioxide; after the gaseous carbon dioxide is reheated to 0 ℃, the gaseous carbon dioxide is discharged out of the device after primary expansion (the pressure is reduced from 4MPa to 1.6MPa, the temperature is reduced from 0 ℃ to-52 ℃) and secondary expansion (the pressure is reduced from 1.6MPa to 0.5MPa, and the temperature is reduced from 0 ℃ to-52 ℃) in sequence.
Supercooling the rectified carbon dioxide at-18 ℃, reheating to 30 ℃ in a main heat exchanger, and then compressing to the pressure of 2.5MPa to obtain compressed carbon dioxide; after the tail gas is reheated to 0 ℃, gas expansion (the pressure is reduced from 4MPa to 0.5 MPa) is carried out and then the tail gas is discharged out of the device; cooling part of compressed carbon dioxide by circulating water, then sequentially compressing the carbon dioxide under the propane condition (the pressure of the compressed carbon dioxide is 1.8 MPa), condensing and supercooling to obtain a supercooling product, and then storing the supercooling product in a spherical tank; the remaining compressed carbon dioxide is sent to downstream equipment (the volume ratio of the partially compressed carbon dioxide to the remaining compressed carbon dioxide is 10.
The yield of carbon dioxide in this example was 79%.
Example 4
Compressing raw material gas (the molar content of carbon dioxide is 85%) to a pressure of 3.5MPa, drying at 35 ℃ (the dew point of the dried raw material gas is-45 ℃), condensing the raw material gas in a main heat exchanger to-45 ℃, and performing gas-liquid separation to obtain liquid carbon dioxide and gaseous carbon dioxide; introducing the liquid carbon dioxide into a carbon dioxide rectifying tower to obtain tail gas and rectified carbon dioxide; after the gaseous carbon dioxide is reheated to 10 ℃, the gaseous carbon dioxide is discharged out of the device after primary expansion (the pressure is reduced from 3.8MPa to 1.5MPa, the temperature is reduced from-1 ℃ to-52 ℃) and secondary expansion (the pressure is reduced from 1.5MPa to 0.4MPa, and the temperature is reduced from-1 ℃ to-52 ℃) in sequence.
Supercooling the rectified carbon dioxide at-16 ℃, then reheating to 30 ℃ in a main heat exchanger, and then compressing to the pressure of 3MPa to obtain compressed carbon dioxide; after the tail gas is reheated to 10 ℃, gas expansion (the pressure is reduced from 3.8MPa to 0.4 MPa) is carried out and then the tail gas is discharged out of the device; cooling part of compressed carbon dioxide by circulating water, then compressing the carbon dioxide under the condition of propylene in sequence (the pressure of the compressed carbon dioxide is 1.6 MPa), condensing and supercooling to obtain a supercooling product, wherein the supercooling product is used as a low-temperature region supplementary refrigerant; the remaining compressed carbon dioxide is sent to a downstream unit (the volume ratio of partially compressed carbon dioxide to the remaining compressed carbon dioxide is 5:2).
The yield of carbon dioxide in this example was 86%.
From examples 1 to 4, it can be seen that: the recovery method can recover the carbon dioxide in the mixed gas with the carbon dioxide molar content of 40-85%, and the recovery rate of the carbon dioxide is high and can reach more than 55%.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and amendments can be made without departing from the principle of the present invention, and these modifications and amendments should also be considered as the protection scope of the present invention.
Claims (9)
1. A process for producing carbon dioxide in a cold box, comprising the steps of:
1) Sequentially compressing, drying and condensing the raw material gas, and then carrying out gas-liquid separation to obtain liquid carbon dioxide and gaseous carbon dioxide;
2) Introducing the liquid carbon dioxide into a carbon dioxide rectifying tower to obtain tail gas and rectified carbon dioxide; discharging gaseous carbon dioxide out of the device after multistage expansion;
3) The rectified carbon dioxide is compressed after being supercooled and reheated in sequence to obtain compressed carbon dioxide; the tail gas is exhausted out of the device after being expanded;
4) Partially compressed carbon dioxide is sequentially cooled, compressed by auxiliary refrigerant, condensed by auxiliary refrigerant and supercooled by auxiliary refrigerant to obtain a supercooled product; the remaining compressed carbon dioxide is sent to downstream equipment.
2. The process for producing carbon dioxide in a cold box according to claim 1, wherein the molar content of carbon dioxide in the feed gas in step 1) is 40 to 85%.
3. The process for preparing carbon dioxide in the cold box according to claim 1 or 2, wherein the pressure of the compressed feed gas in the step 1) is 3-4.5 MPa; the drying temperature is 10-40 ℃; the temperature of the condensed feed gas is-55 to-40 ℃.
4. The process for producing carbon dioxide in a cold box according to claim 1, wherein the temperature of the gaseous carbon dioxide of step 2) is-20 to 5 ℃.
5. The process for producing carbon dioxide in a cold box according to claim 4, wherein the multi-stage expansion of step 2) comprises a first stage expansion and a second stage expansion; wherein, the pressure intensity of the first-stage expansion is reduced from 3.5-4.5 MPa to 1.4-1.8 MPa, and the pressure intensity of the second-stage expansion is reduced from 1.4-1.8 MPa to 0.2-0.6 MPa; the temperature of the first-stage expansion and the second-stage expansion is independently reduced from minus 2 to 2 ℃ to minus 55 to minus 50 ℃.
6. The process for producing carbon dioxide in a cold box according to claim 4 or 5, wherein the temperature of the supercooling in step 3) is-20 to-15 ℃; the temperature after rewarming is 25-35 ℃; the re-incubation and the condensation of step 1) are independently carried out in a main heat exchanger.
7. The process for preparing carbon dioxide in a cold box according to claim 6, wherein the pressure of the compressed carbon dioxide of step 3) is 1.5 to 4MPa; the temperature of the tail gas is-20 to 5 ℃; the pressure of the gas expansion is reduced from 3.5-4.5 MPa to 0.2-0.6 MPa.
8. The process for preparing carbon dioxide in a cold box according to claim 7, wherein the cooling in the step 4) is performed by circulating water or air cooling; the supercooled product enters a spherical tank for storage or serves as a supplementary refrigerant of a low-temperature area.
9. The process for preparing carbon dioxide in the cold box according to claim 8, wherein the pressure of the compressed auxiliary refrigerant in the step 4) is 1.5-2 MPa; the auxiliary refrigerant is liquid ammonia, freon, propane or propylene.
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