Carbon dioxide cyclic purification method and system

Abstract

The invention discloses a carbon dioxide cyclic purification method and system, and belongs to the technical field of substance separation devices or systems. The invention solves the problem of how to further reduce the purification cost. According to the method, raw material liquid CO2 is pressurized, then gas-liquid separation is performed to obtain liquid CO2 and first non-condensable gas, the liquid CO2 is heated and converted into gaseous CO2 through cooperation of a gasification heat exchanger and a gasification heater, then the gaseous CO2 is fed into a purifier, and then the refined gaseous CO2 is conveyed into the gasification heat exchanger for heat exchange to serve as a heat supply source of the gasification heat exchanger; and then the refined CO2 is subjected to heat exchange until the temperature is lower than the increased boiling point, then gas-liquid separation is conducted again, finished liquid CO2 and second non-condensable gas are obtained, and the non-condensable gas serves as a cold supply source of the supercooling heat exchanger. According to the invention, the energy of liquid and gas at different temperatures in each stage in the purification process is utilized, the energy consumption of the whole purification process is reduced, and the whole purification process does not need expensive purification equipment, so that the purification cost is extremely low.

Description

Technical Field

[0001] The present invention belongs to the technical field of material separation devices or systems, and in particular relates to a carbon dioxide circulation purification method and system. Background Art

[0002] Carbon dioxide is one of the main greenhouse gases. Its large-scale emission will lead to global warming, exacerbating climate anomalies and extreme weather events. By recycling and utilizing carbon dioxide in flue gas, greenhouse gas emissions can be effectively reduced, the trend of global warming can be slowed down, and the ecological environment can be protected. Recycled and purified carbon dioxide can be used to produce various chemicals, fuels, and building materials, etc., to improve resource utilization and reduce dependence on fossil fuels. By recycling carbon dioxide, companies can reduce waste gas treatment costs, and at the same time, using purified carbon dioxide to produce other products can also bring additional economic benefits.

[0003] The flue gas generated in industrial activities contains a large amount of carbon dioxide. Therefore, extracting carbon dioxide from the flue gas can not only convert it into valuable chemicals, but also reduce the resulting environmental pollution.

[0004] Various carbon dioxide purification systems in the prior art either require high equipment investment or high energy consumption. How to reduce the cost of processing the largest byproduct in human history is a difficult problem that needs to be explored in this field. Summary of the invention

[0005] In order to solve the problem of how to further reduce the purification cost in the prior art, the present invention provides a carbon dioxide circulation purification method and system.

[0006] The technical solution adopted by the present invention is as follows: A carbon dioxide circulation purification method comprises the following steps: S1: pressurize the raw liquid CO2 to increase the pressure of CO2 to the storage pressure range (2-2.5MPa) specified by the carbon dioxide storage tank; S2: The pressurized raw liquid CO2 is subjected to gas-liquid separation in the first gas-liquid separator to obtain preliminarily purified liquid CO2 and a first non-condensable gas, and the first non-condensable gas is transported to the subcooling heat exchanger as a cooling source for the subcooling heat exchanger; S3: The initially purified liquid CO2 is heated by heat exchange in the gasification heat exchanger. If the liquid CO2 has been converted into gaseous CO2 after heat exchange in the gasification heat exchanger, the gaseous CO2 is directly sent to the purifier for purification to obtain refined gaseous CO2; if the liquid CO2 has not been converted into gaseous CO2 after heat exchange in the gasification heat exchanger, the liquid CO2 is heated by a gasification heater to convert it into gaseous CO2, and then the gaseous CO2 is sent to the purifier for purification to obtain refined gaseous CO2; S4: The refined gaseous CO2 discharged from the purifier is converted into refined liquid CO2 after heat exchange and temperature reduction in the gasification heat exchanger and the subcooling heat exchanger; S5: The refined liquid CO2 is transported to the second gas-liquid separator for gas-liquid separation again to obtain product liquid CO2 and a second non-condensable gas. The second non-condensable gas is transported to the subcooling heat exchanger as a cooling source for the subcooling heat exchanger.

[0007] Preferably, the pressure of the raw liquid CO2 in the storage tank is 0.8 MPa and the temperature is -50 to -60°C; the pressure after pressurization in S1 is 2.5 MPa.

[0008] Preferably, the purification process of the purifier in S3 includes: desulfurization, denitrification, dehydration and dust removal.

[0009] A carbon dioxide circulation purification system, used to implement the carbon dioxide circulation purification method, comprising: Liquid booster pump, used to compress the raw liquid CO2 to increase the pressure of the raw liquid CO2 to the storage pressure range (2-2.5MPa) specified by the carbon dioxide storage tank; A first gas-liquid separator is used to perform gas-liquid separation on the pressurized raw liquid CO2 to obtain a first non-condensable gas and liquid CO2; The gasification heat exchanger, the liquid outlet of the first gas-liquid separator is connected to the low-temperature circuit inlet of the gasification heat exchanger, for increasing the temperature of the liquid CO2; A gasification heater, wherein the outlet of the low-temperature circuit of the gasification heat exchanger is connected to the inlet of the gasification heater, and is used to convert liquid CO2 into gaseous CO2; The purifier, the outlet of the gasification heater is connected to the inlet of the purifier, which is used to purify the gaseous CO2 to obtain refined gaseous CO2. The outlet of the purifier is connected to the inlet of the high-temperature circuit of the gasification heater to preliminarily cool the gaseous CO2. The outlet of the low-temperature circuit of the gasification heat exchanger is provided with a branch directly connected to the purifier without passing through the gasification heater; The subcooling heat exchanger, the high temperature circuit outlet of the gasification heater is connected to the high temperature circuit inlet of the subcooling heat exchanger, and is used to convert the refined gaseous CO2 into liquid CO2; A second gas-liquid separator, wherein the outlet of the high-temperature circuit of the subcooling heat exchanger is connected to the inlet of the second gas-liquid separator, and is used for performing gas-liquid separation to obtain refined liquid CO2 and a second non-condensable gas; The gas outlet of the first gas-liquid separator and the gas outlet of the second gas-liquid separator are both connected to the low-temperature circuit inlet of the subcooling heat exchanger, and the low-temperature circuit outlet of the subcooling heat exchanger is connected to the outside; The second gas-liquid separator liquid outlet is connected to an external carbon dioxide liquid storage tank; The gas outlets of the first gas-liquid separator and the second gas-liquid separator are connected, and then connected to the low-temperature inlet of the subcooling heat exchanger. The low-temperature circuit outlet of the subcooling heat exchanger is connected to the atmosphere.

[0010] Preferably, a first throttle valve for throttling and cooling is arranged on the pipeline connecting the second gas-liquid separator and the low-temperature circuit of the subcooling heat exchanger, and a second throttle valve for throttling and cooling is arranged on the pipeline connecting the first gas-liquid separator and the low-temperature circuit of the subcooling heat exchanger.

[0011] Preferably, the liquid outlet of the second gas-liquid separator is connected to a carbon dioxide liquid storage tank.

[0012] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: The present invention first pressurizes the raw liquid CO2 to reach the storage pressure range specified by the carbon dioxide storage tank. The first gas-liquid separator and the second gas-liquid separator both operate in a low-temperature state. However, since it is impossible to completely keep warm, external heat will inevitably enter the gas-liquid separator through the gas-liquid separator shell for slight heating. This will cause internal gas-liquid separation in the first gas-liquid separator and the second gas-liquid separator, thereby achieving a preliminary purification effect. In order to further purify the liquid CO2, it is necessary to convert it into gaseous carbon dioxide. In order to reduce the energy consumption of the process, a gasification heat exchanger is also provided in the present application. During the initial operation, the liquid CO2 is heated by a gasification heater until it is converted into gaseous CO2, and then the gaseous CO2 is sent to a purifier for further purification. The gas obtained after purification The gaseous CO2 can be transported to the gasification heat exchanger for heat exchange with the low-temperature liquid CO2 introduced later. At this time, it can be directly introduced into the purifier for purification without the gasification heater, which greatly reduces energy consumption. The heat exchange reduces the temperature of the normal temperature gaseous CO2, reducing the energy consumption required for converting it into liquid carbon dioxide later. After being discharged from the gasification heat exchanger, the gaseous CO2 enters the supercooling heat exchanger to further reduce the temperature until its temperature drops below the boiling point and becomes liquid, thereby obtaining the finished liquid CO2 after separation by the second gas-liquid separator. In this process, the supercooling heat exchanger uses the low-temperature non-condensable gas separated by the first gas-liquid separator and the second gas-liquid separator as a cold source. In order to reduce the temperature of the non-condensable gas, a throttle valve can also be set to reduce the pressure and temperature, so no additional energy consumption is required. In the present invention, the liquid and gas energy of different temperatures in each stage of the purification process is fully utilized, which reduces the energy consumption of the entire purification process. The entire purification process does not require expensive purification equipment, so the purification cost is extremely low. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of the present invention; Among them, 1-the first gas-liquid separator, 2-the second throttle valve, 3-the subcooling heat exchanger, 4-the first throttle valve, 5-the second gas-liquid separator, 6-the purifier, 7-the gasification heater, 8-the gasification heat exchanger, and 9-the liquid pressure pump. DETAILED DESCRIPTION

[0014] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0015] In the description of the embodiments of the present application, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or are the positions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0016] It should be noted that the non-condensable gas described in the present invention refers to a gas that will not condense into a liquid state under a specific pressure and temperature, and all devices and corresponding pipelines in the system whose material temperature is not the same as the ambient temperature are provided with insulation measures, and the insulation measures required for the first gas-liquid separator 1 and the second gas-liquid separator 5 need to control the daily heat exchange amount with the outside world to about 1%, so as to achieve the purpose of micro-heating in the first gas-liquid separator 1 and the second gas-liquid separator 5.

[0017] like Figure 1 As shown, a carbon dioxide circulation purification system comprises: The liquid booster pump 9 is used to compress the raw liquid CO2 to increase the pressure of the raw liquid CO2 to the storage pressure range specified by the carbon dioxide storage tank, that is, from 0.8 MPa to 2.5 MPa; A first gas-liquid separator 1, wherein the first gas-liquid separator 1 is connected to a liquid pressure pump 9, and the raw liquid CO2 compressed by the liquid pressure pump 9 enters the first gas-liquid separator 1 for gas-liquid separation to obtain liquid CO2 and a first non-condensable gas, and the gas outlet of the first gas-liquid separator 1 is connected to the low-temperature circuit inlet of the subcooling heat exchanger 3; The gasification heat exchanger 8 includes a low-temperature circuit and a high-temperature circuit. The liquid outlet of the first gas-liquid separator 1 is connected to the low-temperature circuit. The raw liquid CO2 is heated in the gasification heat exchanger 8. The gasification heater 7 is connected with the low-temperature circuit outlet of the gasification heat exchanger 8. The gasification heater 7 is used to heat the liquid CO2 to convert it into gaseous CO2. The low-temperature circuit outlet of the gasification heat exchanger 8 is provided with a branch directly connected to the purifier 6 without passing through the gasification heater 7. A temperature sensor can be provided at the low-temperature circuit outlet of the gasification heat exchanger 8 to detect the temperature of the material discharged from the gasification heat exchanger 8. Valves are provided on the pipeline provided with the gasification heater 7 and on the pipeline directly connected to the gasification heat exchanger 8 and the purifier 6. One of the valves on the two pipelines can be closed according to the monitored temperature to achieve the effect of changing the processing path according to the state of the liquid CO2; A purifier 6, which is used to purify the gaseous CO2 again to obtain refined gaseous CO2. The purifier 6 is connected to the high-temperature circuit. In this embodiment, the purifier 6 includes desulfurization, denitrification, dehydration and dust removal, so it includes an activated carbon fluidized bed adsorber, an adsorber and a filter connected in sequence. The activated carbon fluidized bed adsorber removes sulfur and nitrate from the gaseous CO2; a subcooling heat exchanger 3, wherein the subcooling heat exchanger 3 includes a high-temperature circuit and a low-temperature circuit. The high-temperature circuit inlet of the subcooling heat exchanger 3 is connected to the high-temperature circuit outlet of the gasification heat exchanger 8, and the gas outlet of the first gas-liquid separator 1 is connected to the low-temperature circuit of the subcooling heat exchanger 3; The second gas-liquid separator 5, the feed port of the second gas-liquid separator 5 is connected to the high-temperature circuit outlet of the subcooling heat exchanger 3, and is used for performing gas-liquid separation again on the refined liquid CO2 discharged from the high-temperature circuit of the subcooling heat exchanger 3 to obtain finished liquid CO2 and the second non-condensable gas. The gas outlet of the second gas-liquid separator 5 is connected to the low-temperature circuit of the subcooling heat exchanger 3.

[0018] A carbon dioxide circulation purification method, the specific steps are as follows: S1: The raw liquid CO2 is transported to the liquid booster pump 9 for pressurization. The initial temperature of the raw liquid CO2 entering the liquid booster pump 9 is -55°C and the pressure is 0.8MPa. After being compressed by the liquid booster pump 9, the temperature is -54°C and the pressure is 2.5MPa. S2: The raw liquid CO2 with a temperature of -54°C and a pressure of 2.5MPa enters the first gas-liquid separator 1 for gas-liquid separation to obtain preliminarily purified liquid CO2 and a first non-condensable gas. The first non-condensable gas is transported from the gas outlet at the top of the first gas-liquid separator 1 to the low-temperature circuit of the subcooling heat exchanger 3 to perform heat exchange with the heat exchange medium of the subcooling heat exchanger 3 as a cooling source for the subcooling heat exchanger 3; S3: The initially purified liquid CO2 enters the low-temperature circuit of the gasification heat exchanger 8 for heat exchange and temperature increase. If the liquid CO2 has been converted into gaseous CO2 after heat exchange in the gasification heat exchanger 8, the gaseous CO2 is directly sent to the purifier 6 for desulfurization, denitrification, dehydration and dust removal, and further purified to obtain refined gaseous CO2; if the liquid CO2 has not been converted into gaseous CO2 after heat exchange in the gasification heat exchanger 8, the liquid CO2 will be heated by the gasification heater 7 to convert it into gaseous CO2, and then the gaseous CO2 will be sent to the purifier 6 for desulfurization, denitrification, dehydration and dust removal for further purification to obtain refined gaseous CO2; S4: The refined gaseous CO2 is transported to the high-temperature circuit of the gasification heat exchanger 8 for heat exchange as the heat source of the gasification heat exchanger 8, and then the refined CO2 with a lowered temperature after heat exchange is transported to the high-temperature circuit of the subcooling heat exchanger 3 for heat exchange to a temperature of -55°C. In this process, the first non-condensable gas discharged from the first gas-liquid separator 1 and the second non-condensable gas discharged from the second gas-liquid separator 5 are used as the cooling source of the subcooling heat exchanger 3; in other embodiments, a first throttle valve 4 may be provided on the pipeline connecting the second gas-liquid separator 5 with the low-temperature circuit, and a second throttle valve 2 may be provided on the pipeline connecting the first gas-liquid separator 1 with the low-temperature circuit. The non-condensable gas is throttled and cooled by the first throttle valve 4 and the second throttle valve 2, thereby further reducing the temperature of the heat exchange medium in the subcooling heat exchanger 3.

[0019] S5: The carbon dioxide after heat exchange in the subcooling heat exchanger 3 is input to the second gas-liquid separator 5 for further gas-liquid separation to obtain finished liquid CO2, which can be transported to the carbon dioxide liquid storage tank for storage; and the non-condensable gas separated by the second gas-liquid separator 5 can be discharged.

[0020] The existing technology consumes 90 to 100 kWh of energy to purify one ton of carbon dioxide. After calculation, the equipment cost of this embodiment is: since there is no distillation tower and no gas compressor, the equipment cost is only 25% of similar equipment; the unit energy consumption of purified carbon dioxide is 1000 watt-hours per ton; the purity of the refined carbon dioxide obtained is 99.99%; 1000 (carbon dioxide processing volume, kilograms) ÷ 3600 (time, seconds) × (25 (pressure 2.5 MPa after treatment converted to mass, kilograms) - 8 (pressure 0.8 MPa before treatment converted to mass, kilograms)) ÷ 9.8 (gravitational acceleration) = 0.368, so considering the efficiency, one kWh is taken, that is, the energy consumption of the present invention is about 1% of the prior art.

[0021] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A carbon dioxide circulation purification method, characterized in that: The following steps are involved: S1: pressurizing the raw liquid CO2 to increase the pressure of CO2 to the storage pressure range specified by the carbon dioxide storage tank; S2: The pressurized raw liquid CO2 is subjected to gas-liquid separation in the first gas-liquid separator to obtain preliminarily purified liquid CO2 and a first non-condensable gas, and the first non-condensable gas is transported to the subcooling heat exchanger as a cooling source for the subcooling heat exchanger; S3: The initially purified liquid CO2 is heated by heat exchange in the gasification heat exchanger. If the liquid CO2 has been converted into gaseous CO2 after heat exchange in the gasification heat exchanger, the gaseous CO2 is directly sent to the purifier for purification to obtain refined gaseous CO2; if the liquid CO2 has not been converted into gaseous CO2 after heat exchange in the gasification heat exchanger, the liquid CO2 is heated by a gasification heater to convert it into gaseous CO2, and then the gaseous CO2 is sent to the purifier for purification to obtain refined gaseous CO2; S4: The refined gaseous CO2 discharged from the purifier is converted into refined liquid CO2 after heat exchange and temperature reduction in the gasification heat exchanger and the subcooling heat exchanger; S5: The refined liquid CO2 is transported to the second gas-liquid separator for gas-liquid separation again to obtain finished liquid CO2 and a second non-condensable gas. The second non-condensable gas is transported to the subcooling heat exchanger as a cooling source for the subcooling heat exchanger.

2. A carbon dioxide circulation purification method according to claim 1, characterized in that: The pressure of the raw liquid CO2 in the raw material storage tank is 0.8MPa and the temperature is -50 to -60°C; the pressure after pressurization in S1 is 2-2.5MPa.

3. A carbon dioxide circulation purification method according to claim 1, characterized in that: The purification process of the purifier in S3 includes: desulfurization, denitrification, dehydration and dust removal.

4. A carbon dioxide circulation purification system, characterized in that: The method for realizing the carbon dioxide circulation purification method according to any one of claims 1 to 3 comprises: Liquid booster pump, used to compress the raw liquid CO2 to increase the pressure of the raw liquid CO2 to the storage pressure range specified by the carbon dioxide storage tank; A first gas-liquid separator is used to perform gas-liquid separation on the pressurized raw liquid CO2 to obtain a first non-condensable gas and liquid CO2; The gasification heat exchanger, the liquid outlet of the first gas-liquid separator is connected to the low-temperature circuit inlet of the gasification heat exchanger, for increasing the temperature of the liquid CO2; A gasification heater, wherein the outlet of the low-temperature circuit of the gasification heat exchanger is connected to the inlet of the gasification heater, and is used to convert liquid CO2 into gaseous CO2; The purifier, the outlet of the gasification heater is connected to the inlet of the purifier, which is used to purify the gaseous CO2 to obtain refined gaseous CO2. The outlet of the purifier is connected to the inlet of the high-temperature circuit of the gasification heater to preliminarily cool the gaseous CO2. The outlet of the low-temperature circuit of the gasification heat exchanger is provided with a branch directly connected to the purifier without passing through the gasification heater; The subcooling heat exchanger, the high temperature circuit outlet of the gasification heater is connected to the high temperature circuit inlet of the subcooling heat exchanger, and is used to convert the refined gaseous CO2 into liquid CO2; The second gas-liquid separator, the outlet of the high-temperature circuit of the subcooling heat exchanger is connected to the inlet of the second gas-liquid separator, for performing gas-liquid separation to obtain finished liquid CO2 and the second non-condensable gas; The gas outlet of the first gas-liquid separator and the gas outlet of the second gas-liquid separator are both connected to the low-temperature circuit inlet of the subcooling heat exchanger, and the low-temperature circuit outlet of the subcooling heat exchanger is connected to the outside; The liquid outlet of the second gas-liquid separator is connected to an external carbon dioxide liquid storage tank; The gas outlets of the first gas-liquid separator and the second gas-liquid separator are connected, and then connected to the low-temperature inlet of the subcooling heat exchanger. The low-temperature circuit outlet of the subcooling heat exchanger is connected to the atmosphere.

5. A carbon dioxide circulation purification system according to claim 4, characterized in that: A first throttle valve for throttling and cooling is arranged on the pipeline connecting the second gas-liquid separator and the low-temperature circuit of the subcooling heat exchanger, and a second throttle valve for throttling and cooling is arranged on the pipeline connecting the first gas-liquid separator and the low-temperature circuit of the subcooling heat exchanger.

6. A carbon dioxide circulation purification system according to claim 4, characterized in that: The liquid outlet of the second gas-liquid separator is connected to a carbon dioxide liquid storage tank.

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