Method for refrigerating and liquefying carbon dioxide through air expansion

Abstract

The invention particularly relates to a method for liquefying carbon dioxide through air expansion refrigeration, and belongs to the technical field of gas processing. The device comprises a compressor, an adsorber, an expansion machine, a plate heat exchanger, a liquefier and a rectifying tower, an air passage and a carbon dioxide passage are combined for refrigeration cycle, the air expansion machine is used for generating low-temperature cooling capacity, the low-temperature cooling capacity and CO2 are used for refrigeration in a cooperative mode, and compression power consumption is reduced. The preparation method disclosed by the invention comprises four working sections of raw material gas pre-compression, raw material gas purification, pressurized expansion refrigeration and rectification, so that the energy loss is greatly reduced, and the method is simple and safe.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gas processing, and particularly relates to a method for air expansion refrigeration liquefaction of carbon dioxide. BACKGROUND

[0002] With the increasing demand for global carbon emission reduction, the capture, liquefaction and efficient utilization technology of carbon dioxide (CO2) has become a research hotspot. Liquid CO2 has important application value in food preservation, welding protection, supercritical extraction, refrigeration and carbon sequestration fields. However, the traditional CO2 liquefaction process generally relies on high-energy consumption mechanical compression refrigeration or external refrigerant circulation system, which not only has high operating cost, but also has complex system, thereby limiting its application in distributed or mobile scenarios.

[0003] The traditional food-grade carbon dioxide liquefaction process generally needs to use external refrigerants such as propylene, ammonia and the like, and is equipped with a corresponding freezing station. This preparation method needs to introduce flammable, explosive or toxic media, and has high operation risk. In addition, the scale of the general freezing station is small, the efficiency of the compressor is low, and the energy consumption is high. In the existing research, the carbon dioxide liquefaction preparation method is as follows: the carbon dioxide raw gas from the outside enters the booster after the buffer tank and is boosted to about 2.5 MPaG, and then enters the purification system for dehydrocarbon, desulfurization and dehydration. The purified gas is cooled by circulating water and liquefied by low-temperature propylene or ammonia, and then enters the rectification tower for rectification. The propylene is used to cool the top of the tower, the non-condensable gas is throttled and vented, and the liquid carbon dioxide product at the bottom of the tower is sent to the storage tank after being supercooled by propylene. This process has large circulating water consumption, high energy consumption, poor device operation safety and complex process. SUMMARY

[0004] In order to solve the problems of high-energy consumption compression refrigeration, low refrigeration utilization rate and poor environmental adaptability in the prior art, it is urgent to develop a carbon dioxide liquefaction method which is simple and safe in operation, low in energy consumption and strong in environmental adaptability. The purpose of the present application is to provide a method for air expansion refrigeration liquefaction of carbon dioxide.

[0005] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0006] The application discloses a method for air expansion refrigeration liquefaction of carbon dioxide, and is characterized in that the device for air expansion refrigeration liquefaction of carbon dioxide comprises a carbon dioxide passage and an air passage (12) which are independent of each other but coupled through a heat exchange system; the carbon dioxide passage comprises, in sequence, a raw material gas buffer tank (1), a compressor (2), an adsorber (3), an expander (4), a staged cooling unit and a rectifying tower (5); the rectifying tower (5) is connected with a reboiler (6) at the bottom and connected with a condenser (7) at the top; the staged cooling unit comprises, in sequence, an aftercooler (8), a plate heat exchanger (9) and a liquefier (10); the air passage (12) comprises the expander (4), the reboiler (6), the condenser (7), the plate heat exchanger (9) and a non-condensable gas pipeline (11); the air passage and the carbon dioxide passage realize heat exchange and cold energy stepwise utilization through the plate heat exchanger (9); and the method comprises the following steps:

[0007] S1, raw material carbon dioxide is compressed by the compressor (2) and then enters the adsorber (3) for purification, desulfurization, dehydrocarbon and dehydration;

[0008] S2, the purified high-pressure carbon dioxide is refrigerated by the expander (4), and the air inlet at the expansion end of the expander (4) is low-pressure air from an external air separation device;

[0009] S3, the refrigerated carbon dioxide is sequentially subjected to multistage cooling through the staged cooling unit, the air passage (12) provides the required cold energy for refrigeration, and the cold energy is stepwise utilized through the plate heat exchanger (9);

[0010] S4, the cooled gas-liquid mixture is separated in the rectifying tower (5), the gas phase at the top of the tower is non-condensable gas removed, and the liquid phase at the bottom of the tower is liquefied carbon dioxide product.

[0011] Specifically, the non-condensable gas removed from the gas phase at the top of the tower in step S4 is condensed by the condenser (7), enters the plate heat exchanger (9) to recover cold energy and is then sent out of the boundary region.

[0012] Specifically, the plate heat exchanger (9) comprises:

[0013] A first flow channel connected with the aftercooler (8) and the liquefier (10) and used for precooling of high-pressure carbon dioxide;

[0014] A second flow channel connected with the condenser (7) and the reboiler (6) and used for cold energy recovery;

[0015] A third flow channel connected with the condenser (7) and the non-condensable gas pipeline (11) and used for cryogenic treatment of light component gas;

[0016] A fourth flow channel connected with the reboiler (6) and the air passage (12) and used for waste heat discharge.

[0017] Wherein, the air temperature in the first flow channel is -44℃ to 20℃, the carbon dioxide temperature in the second flow channel is 40℃ to -4℃, the non-condensable gas temperature in the third flow channel is -50℃ to 20℃, and the air temperature in the fourth flow channel is -2℃ to 20℃.

[0018] Specifically, the adsorber (3) is filled with molecular sieve or active alumina for selectively adsorbing moisture and sulfides.

[0019] Preferably, the adsorber is filled with molecular sieve or active alumina adsorbent, such as 13X molecular sieve.

[0020] Specifically, the step S3 includes: the aftercooler (8) is preliminarily cooled to -10℃ to 10℃; the plate heat exchanger (9) is further cooled to -30℃ to -10℃; and the liquefier (10) is finally cooled to -50℃ to -30℃.

[0021] Specifically, the cold energy of the air passage (12) in the step S2 is derived from the expansion refrigeration of the extraneous low-pressure air, the gage pressure of the extraneous low-pressure air is 0.115-0.477Mpa, and the temperature of the expanded air is -50℃ to -30℃.

[0022] Specifically, the expansion machine (4) is pressurized to 3.2MPa at the pressurizing end.

[0023] Preferably, the expansion machine is a turbine type expansion machine, and the condenser is a kettle type condenser.

[0024] In the present application, the purity of the carbon dioxide raw gas in the step S1 is 99.8%, and the compressor (2) is compressed to 0.8Mpa.

[0025] Preferably, the refrigerant of the liquefier (10) is chilled water, and the temperature of the chilled water is -15℃ to -10℃.

[0026] Specifically, the operating pressure of the rectification tower (5) is 1.5-2.5MPa, the overhead temperature is -40℃ to -20℃, and the bottom temperature is -10℃ to 10℃.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] (1) Energy saving and high efficiency: the air expansion refrigeration is used to replace the traditional mechanical compression refrigeration, and the energy consumption is reduced by more than 40%;

[0029] (2) Gradual utilization of cold energy: the multistage recovery and utilization of cold energy is realized through the multi-flow channel plate heat exchanger, and the system energy efficiency is improved by 30%;

[0030] (3) High purity: the rectification tower can produce liquid carbon dioxide with a purity of ≥99.9%;

[0031] (4) Compact structure: Modular design is suitable for distributed or mobile application scenarios;

[0032] (5) Environmentally friendly and economical: Reduces dependence on external refrigerants and has low operating costs.

[0033] This invention effectively solves the technical problems of high energy consumption and system complexity in the prior art through an innovative air-CO2 synergistic refrigeration system and multi-stage heat exchange design, and has significant economic benefits and application value. Attached Figure Description

[0034] Figure 1 A device for liquefying carbon dioxide by expanding and cooling air. Detailed Implementation

[0035] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments:

[0037] like Figure 1 As shown, 1-raw material gas buffer tank, 2-compressor, 3-adsorber, 4-expander, 5-distillation column, 6-reboiler, 7-condenser, 8-aftercooler, 9-plate heat exchanger, 10-liquefier, 11-non-condensable gas pipeline, 12-air passage.

[0038] An air expansion refrigeration and liquefaction device for carbon dioxide includes a carbon dioxide passage and an air passage (12). The carbon dioxide passage includes a feed gas buffer tank (1), a compressor (2), an adsorber (3), an expander (4), a staged cooling unit, and a distillation column (5) connected in sequence. The bottom of the distillation column (5) is connected to a reboiler (6) for heating the liquid at the bottom of the column to purify carbon dioxide. The top of the distillation column (5) is connected to a condenser (7) for condensing the gas at the top of the column and controlling the reflux. The staged cooling unit includes an aftercooler (8), a plate heat exchanger (9), and a liquefaction unit connected in sequence. The air passage is equipped with an expander (4), a reboiler (6), a condenser (7), a plate heat exchanger (9), and a non-condensable gas pipeline (11).

[0039] The air passage (12) and the carbon dioxide passage exchange heat and utilize cold energy through a plate heat exchanger (9).

[0040] Among them, the expansion end of the expander (4) is supplied with low-pressure air from outside the boundary, and the gauge pressure of the low-pressure air from outside the boundary is 0.115-0.477Mpa.

[0041] The first flow channel of the plate heat exchanger (9) is connected with the aftercooler (8) and the liquefier (10) respectively, and is used for pre-cooling high-pressure carbon dioxide to a liquefaction temperature; the second flow channel of the plate heat exchanger (9) is connected with the condenser (7) and the reboiler (6) respectively, and the condenser (7) is used for cooling the reboiler (6); the third flow channel of the plate heat exchanger (9) is connected with the condenser (7) and the non-condensable gas pipeline (11) respectively, and is used for recycling light component gas and residual CO2; and the fourth flow channel of the plate heat exchanger (9) is connected with the reboiler (6) and the air pipeline (12) respectively, and is used for discharging waste heat of the reboiler (6) through air cooling. In the first flow channel, the temperature of air is-44℃ to 20℃; in the second flow channel, the temperature of carbon dioxide is 40℃ to-4℃; in the third flow channel, the temperature of non-condensable gas is-50℃ to 20℃; and in the fourth flow channel, the temperature of air is-2℃ to 20℃.

[0042] The condenser (7) is a cold source of low-pressure air outside the boundary, and the reboiler (6) is a heat source of expanded air of the plate heat exchanger (9).

[0043] The refrigerant of the liquefier (10) is chilled water, and the temperature of the chilled water is-15℃ to-10℃.

[0044] The purity of liquid carbon dioxide discharged from the bottom of the rectification tower (5) is ≥99.9%, and the non-condensable gas discharged from the top of the rectification tower (5) contains nitrogen and oxygen.

[0045] A preparation method of air expansion refrigeration liquefied carbon dioxide, which comprises four sections of raw material gas compression, raw material gas purification, pressure expansion refrigeration and rectification, and specifically as follows:

[0046] S1, the raw material carbon dioxide is compressed by a compressor (2) and then purified in an adsorber (3) to remove sulfur, hydrocarbons and water;

[0047] S2, the purified high-pressure carbon dioxide is refrigerated by an expander (4), and the inlet air of the expansion end of the expander (4) is low-pressure air from an air separation device outside the boundary;

[0048] S3, the refrigerated carbon dioxide is sequentially subjected to multi-stage cooling by a staged cooling unit, the air passage (12) provides the required cooling capacity, and the plate heat exchanger (9) realizes stepwise utilization of the cooling capacity;

[0049] S4, the cooled gas-liquid mixture is separated into the non-condensable gas in the gas phase at the top of the rectification tower (5) and the liquefied carbon dioxide product in the liquid phase at the bottom of the rectification tower (5).

[0050] In actual application, the raw material carbon dioxide with a purity of 99.8%, a pressure of 0.1 MPa and a temperature of 25℃ is used to prepare the liquefied carbon dioxide.

[0051] First, the raw material carbon dioxide is connected to the raw material gas buffer tank (1) for pressure stabilization, and then the gas is compressed to 0.8 MPa by the compressor (2), and the temperature is controlled not to exceed 120°C by using inter-stage cooling during the compression process; the compressed gas enters the adsorber (3) filled with 13X molecular sieve, and the water content is removed to ≤1 ppm and the sulfide content is removed to ≤0.1 ppm at an operating temperature of 30°C; then the purified gas from the adsorber enters the booster end of the expander (4) and is boosted to 3.2 MPa; at the same time, the low-pressure air (pressure 0.3 MPa, temperature 25°C) from the air separation device enters the expansion section of the expander, and after expansion to 0.12 MPa, the temperature drops to -35°C; the pressurized raw gas is cooled to 5°C by the aftercooler (8). The cooled gas enters the first flow channel of the plate heat exchanger (9) and exchanges heat with the low-temperature gas from the top of the rectification tower to -15°C; then it enters the liquefier (10) and exchanges heat with the chilled water at -12°C to -35°C, at which time about 85% of the carbon dioxide is liquefied; the gas-liquid mixture enters the rectification tower (5) (tower diameter 800 mm, tower height 15 m, filled with Mellapak 250Y packing), and at an operating pressure of 2.0 MPa, the tower top temperature is -30°C and the tower bottom temperature is 8°C. The non-condensable gas at the top of the tower is partially condensed by the condenser (7), and the uncondensed gas (-40°C) enters the third flow channel of the plate heat exchanger (9) to recover the cold energy and is then discharged; the bottom of the tower obtains liquid carbon dioxide products with a purity of 99.95%.

[0052] During the entire process, the expanded air (-35°C) first serves as the condenser (7) cooling source, and then warms up to -15°C; then it exchanges heat with the air outlet from the reboiler (6) through the fourth flow channel of the plate heat exchanger (9) to 5°C; after providing heat load to the reboiler (6), it cools down to -5°C; finally, it returns to the second flow channel of the plate heat exchanger (9) to be reheated to 10°C and then partially used as regeneration gas.

[0053] The above-described implementation method of the present application has been described illustratively and not limitatively, but within the technical concept of the present application, simple modifications can be made to the technical solution of the present application, and these simple modifications all belong to the protection scope of the present application.

Claims

1. A method of air expansion refrigeration liquefaction of carbon dioxide, characterized by, The device for air expansion refrigeration liquefaction of carbon dioxide comprises a carbon dioxide passage and an air passage (12) which are independent of each other but coupled through a heat exchange system; the carbon dioxide passage comprises, in sequence, a raw material gas buffer tank (1), a compressor (2), an adsorber (3), an expander (4), a staged cooling unit and a rectifying tower (5); the rectifying tower (5) is connected with a reboiler (6) at the bottom and a condenser (7) at the top; the staged cooling unit comprises, in sequence, an aftercooler (8), a plate heat exchanger (9) and a liquefier (10); the air passage (12) comprises the expander (4), the reboiler (6), the condenser (7), the plate heat exchanger (9) and a non-condensable gas pipeline (11); the air passage and the carbon dioxide passage realize heat exchange and cold energy stepwise utilization through the plate heat exchanger (9); the method comprises: S1, the raw material carbon dioxide is compressed by the compressor (2) and then enters the adsorber (3) for purification, desulfurization, dehydrocarbon and dehydration; S2, the high-pressure carbon dioxide after purification is refrigerated by the expander (4), and the air inlet of the expansion end of the expander (4) is low-pressure air from an external air separation device; S3, the refrigerated carbon dioxide is sequentially subjected to multistage cooling by the staged cooling unit, the air passage (12) provides the required cold energy for refrigeration, and the cold energy is stepwise utilized through the plate heat exchanger (9); S4, the gas-liquid mixture after cooling is separated in the rectifying tower (5), the gas phase on the top of the tower is non-condensable gas removed, and the liquid phase at the bottom of the tower is liquefied carbon dioxide product.

2. The method of claim 1, wherein, The non-condensable gas removed in step S4 is condensed by the condenser (7), enters the plate heat exchanger (9) to recover cold energy and is then sent out of the boundary region.

3. The method of claim 2, wherein, The plate heat exchanger (9) comprises: a first flow channel connecting the aftercooler (8) and the liquefier (10) and used for precooling of high-pressure carbon dioxide; a second flow channel connecting the condenser (7) and the reboiler (6) and used for cold energy recovery; a third flow channel connecting the condenser (7) and the non-condensable gas pipeline (11) and used for cryogenic treatment of light component gas; a fourth flow channel connecting the reboiler (6) and the air passage (12) and used for waste heat discharge; wherein, the air temperature in the first flow channel is -44℃ to 20℃, the carbon dioxide temperature in the second flow channel is 40℃ to -4℃, the non-condensable gas temperature in the third flow channel is -50℃ to 20℃, and the air temperature in the fourth flow channel is -2℃ to 20℃.

4. The method of claim 1, wherein, The adsorber (3) is filled with molecular sieve or active alumina and is used for selective adsorption of moisture and sulfides.

5. The method of claim 1, wherein, The staged cooling in step S3 comprises: the aftercooler (8) is preliminarily cooled to -10℃ to 10℃; the plate heat exchanger (9) is further cooled to -30℃ to -10℃; and the liquefier (10) is finally cooled to -50℃ to -30℃.

6. The method of claim 1, wherein, The cold energy of the air passage (12) in step S2 is derived from expansion refrigeration of external low-pressure air, the gage pressure of the external low-pressure air is 0.115-0.477Mpa, and the temperature of the expanded air is -50℃ to -30℃.

7. The method of claim 1, wherein, The pressurizing end of the expander (4) in step S2 is pressurized to 3.2MPa.

8. The method of claim 1, wherein, The purity of the carbon dioxide raw gas in step S1 is 99.8%, and the compressor (2) compresses to 0.8 MPa.

9. The method of claim 1, wherein, The refrigerant of the liquefier (10) is chilled water, and the temperature of the chilled water is -15℃ to -10℃.

10. The method of claim 1, wherein, The operating pressure of the rectification tower (5) is 1.5-2.5 MPa, the top temperature is -40℃ to -20℃, and the bottom temperature is -10℃ to 10℃.

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