Carbon dioxide capture equipment and processes linked to biogas quality improvement

Abstract

The present invention relates to a carbon dioxide capture device and process linked to biogas quality improvement, and provides a carbon dioxide capture device linked to biogas quality improvement that can not only simultaneously obtain high-purity methane and carbon dioxide, but also has excellent separation efficiency without an additional process by using the gas flow directly after the liquefaction process and recovering cold heat within the process.

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide capture device and process in conjunction with biogas upgrading. [Background technology]

[0002] Biogas is a gaseous fuel containing methane and carbon dioxide produced by the decomposition of organic waste resources such as sludge, food waste, and livestock manure by microorganisms. Methane gas from biogas, from which carbon dioxide and some other gases have been removed, is called biomethane, and it has recently been attracting attention as an energy source because it can be used as a clean fuel along with natural gas.

[0003] However, the methane content of biogas is about 50-70%, and the calorific value (5,000 kcal / m 3 The methane content of biogas is low (see below), making it difficult to use as transportation fuel or city gas, and in order to achieve a calorific value similar to that of natural gas, the methane content in biogas must be increased to over 95%. Therefore, only when a process is applied to separate the carbon dioxide / methane mixture that makes up the majority of biogas, making it high quality and enabling long-distance supply, can it be used as fuel for power generation, boilers, factories, and automobiles, or as city gas.

[0004] Membrane separation is a method of separating gases by selectively allowing specific components to permeate through a separation membrane. Gas separation using a separation membrane separates gases through a dissolution and diffusion process and does not involve a phase change, so it has the advantages of low energy consumption, small installation space, and easy maintenance and repair. Therefore, it has recently been attracting attention as a gas separation and purification technology.

[0005] In the past, carbon dioxide, a by-product of biogas, was released into the atmosphere, but carbon dioxide is a known cause of global warming and can cause other environmental problems. Therefore, there is a need to develop equipment and processes that can separate and recover high-purity methane and carbon dioxide. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Registration No. 10-2357385 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been devised to solve the above-mentioned problems, and an object of the present invention is to provide a carbon dioxide capture device and process linked to biogas quality improvement, which can not only simultaneously obtain high-purity methane and carbon dioxide, but also has excellent separation efficiency and recovery rate of methane and carbon dioxide without additional processes by using the gas flow after the liquefaction process as it is and recovering the cold energy of the low-temperature flow in the process. [Means for solving the problem]

[0008] One aspect of the present invention is a system including a first compressor that compresses a gas supplied to a first compressor, the gas including a biogas; a first separation membrane that separates a first separation membrane supply gas, including the gas compressed by the first compressor, into a first separation membrane permeate gas and a first separation membrane retentate gas; a second separation membrane that receives the first separation membrane retentate gas and separates it into a second separation membrane permeate gas and a second separation membrane retentate gas; a third separation membrane that receives the first separation membrane permeate gas and separates it into a third separation membrane permeate gas and a third separation membrane retentate gas; a second compressor that compresses a gas supplied to a second compressor, the third separation membrane permeate gas; Provided is a carbon dioxide capture device linked to improving the quality of biogas, which includes: a liquefaction heat exchanger that cools compressed gas; a separation tower that receives the gas cooled by the liquefaction heat exchanger; a carbon dioxide purification unit that includes an upper end where a carbon dioxide-containing gas is collected and a lower end where high-purity carbon dioxide liquid is collected; a first recovery separation membrane that receives the carbon dioxide-containing gas and separates it into a first recovery separation membrane permeate gas and a first recovery separation membrane retentate gas; and a first circulation unit that circulates the first recovery separation membrane permeate gas to the first separation membrane, the third separation membrane, or the second compressor.

[0009] Another aspect of the present invention is a biogas-containing gas-reducing system including a first compression step of compressing a first compressor-supplied gas containing biogas with a first compressor; a first separation step of supplying the gas compressed with the first compressor to a first separation membrane to separate it into a first separation membrane permeate gas and a first separation membrane retentate gas; a second separation step of supplying the first separation membrane retentate gas to a second separation membrane to separate it into a second separation membrane permeate gas and a second separation membrane retentate gas; a third separation step of supplying the first separation membrane permeate gas to a third separation membrane to separate it into a third separation membrane permeate gas and a third separation membrane retentate gas; and a second compression step of compressing a second compressor-supplied gas containing the third separation membrane permeate gas with a second compressor. a liquefaction step of cooling the gas compressed in the second compressor in a liquefaction heat exchanger; a separation and purification step of supplying the gas cooled in the liquefaction heat exchanger to a separation tower and obtaining a carbon dioxide-containing gas at the upper part of the separation tower through a separation and purification process and recovering a high-purity carbon dioxide liquid at the lower part; and a first recovery step of supplying the carbon dioxide-containing gas to a first recovery separation membrane to separate it into a first recovery separation membrane permeate gas and a first recovery separation membrane retentate gas, and circulating the first recovery separation membrane permeate gas to the first separation membrane, the third separation membrane, or the second compressor. [Effects of the Invention]

[0010] The carbon dioxide capture device and process linked to biogas quality improvement according to the present invention can not only simultaneously obtain high-purity methane and carbon dioxide, but also achieve excellent separation efficiency by directly using the gas flow after the liquefaction process in the capture separation membrane and recovering the cold energy of the low-temperature flow in the process. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a process diagram for carbon dioxide capture in conjunction with biogas quality improvement according to one embodiment of the present invention. [Figure 2] FIG. 1 is a process diagram for carbon dioxide capture in conjunction with biogas quality improvement including a dry ice generator and a heat exchange network according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will now be described in more detail with reference to the accompanying drawings and examples.

[0013] FIG. 1 is a process diagram for carbon dioxide capture in conjunction with biogas upgrading according to the present invention.

[0014] Referring to FIG. 1, a carbon dioxide capture device linked to biogas quality improvement according to one aspect of the present invention includes a first compressor 101, a first separation membrane 102, a second separation membrane 103, a third separation membrane 104, a second compressor 106, a liquefaction heat exchanger 108, a carbon dioxide purification section 109, and a first capture separation membrane 110.

[0015] In this specification, biogas refers to a gas produced by anaerobic digestion of organic waste resources such as sewage sludge, food and drink, and livestock manure by microorganisms, and refers to a gaseous fuel containing methane, carbon dioxide, etc.

[0016] The first compressor 101 compresses the first compressor supply gas 2 .

[0017] The first compressor supply gas 2 is a gas containing biogas 1, and may be biogas 1 or a mixture of biogas 1 and one or more gases selected from the second separation membrane permeate gas 7 and the third separation membrane retentate gas 10.

[0018] In particular, when the gas 2 supplied to the first compressor is a mixture of the biogas 1, the second separation membrane permeate gas 7, and the third separation membrane retentate gas 10, this is preferable because it results in significantly higher carbon dioxide and methane recovery rates.

[0019] The first compressor 101 may compress the first compressor supply gas 2 to achieve a pressure ratio for performing a separation process in the first separation membrane 102. More specifically, the first compressor 101 may compress the first compressor supply gas 2 to a pressure of 5 to 20 bar, preferably 6 to 11 bar. If the first compressor 101 compresses the first compressor supply gas 2 to a pressure less than 5 bar, the separation efficiency at the first separation membrane 102 may decrease. Conversely, if the first compressor 101 compresses the first compressor supply gas 2 to a pressure greater than 20 bar, more energy than necessary may be consumed, resulting in a decrease in process economy.

[0020] The first separation membrane 102 receives a first separation membrane supply gas 4 containing the gas 3 compressed by the first compressor, and allows the first separation membrane supply gas 4 to permeate through the first separation membrane 102, thereby separating the first separation membrane supply gas 4 into a first separation membrane permeate gas 5 that is relatively rich in carbon dioxide, and a first separation membrane retentate gas 6 that cannot permeate the first separation membrane 102 and is relatively rich in methane.

[0021] The first separation membrane supply gas 4 may be the gas 3 compressed by the first compressor or a mixture of the gas 3 and one or more of the first recovered separation membrane permeate gas 18 and the second recovered separation membrane permeate gas.

[0022] The first separation membrane permeate gas 5 is supplied to a third separation membrane 104 for concentration and recovery of carbon dioxide, and the first separation membrane retentate gas 6 is supplied to a second separation membrane 103 for concentration and recovery of methane.

[0023] The second separation membrane 103 receives the first separation membrane retentate gas 6 and allows the first separation membrane retentate gas 6 to permeate through the second separation membrane 103, thereby separating the first separation membrane retentate gas 6 into a second separation membrane permeate gas 7 that is relatively rich in carbon dioxide, and a second separation membrane retentate gas 8 that cannot permeate the second separation membrane 103 and contains high-purity methane.

[0024] The second separation membrane retentate gas 8 contains high-purity methane with a methane content of 97% or more. Here, the second separation membrane retentate gas 8 can be supplied to and stored in a methane storage tank, and the first recovered separation membrane retentate gas 19 can also be stored together with the second separation membrane retentate gas 8 because it is rich in methane.

[0025] In order to recover methane and carbon dioxide contained in the second separation membrane permeate gas 7, the gas can be circulated to the first compressor 101. Here, since it is preferable to also recover the third separation membrane residual gas 10, the gases can be mixed together and circulated to the first compressor 101.

[0026] The third separation membrane 104 receives the third separation membrane supply gas and allows it to permeate through the third separation membrane 104, separating it into a third separation membrane permeate gas 9 that is relatively rich in carbon dioxide, and a third separation membrane retentate gas 10 that cannot permeate the third separation membrane 104 and is relatively rich in methane.

[0027] The third separation membrane supply gas may be the first separation membrane permeate gas 5 or a mixture of the first separation membrane permeate gas 5 and at least one of the first recovered separation membrane permeate gas 18 and the second recovered separation membrane permeate gas.

[0028] In order to recover methane and carbon dioxide contained in the third separation membrane retentate gas 10, the third separation membrane retentate gas 10 may be circulated to the first compressor 101. Here, as described above, the third separation membrane retentate gas 10 may be mixed with the second separation membrane permeate gas 7 and circulated to the first compressor 101.

[0029] A vacuum pump 105 may be further installed in the line through which the third separation membrane permeated gas 9 is discharged, thereby improving separation efficiency.

[0030] The second compressor 106 compresses the second compressor supply gas 11. More specifically, the second compressor 106 compresses the second compressor supply gas 11 to a pressure of 20 to 50 bar, preferably 21 to 31 bar, which is the pressure required for the subsequent liquefaction step.

[0031] The second compressor supply gas 11 may be the second separation membrane permeate gas 9 or a mixture thereof with at least one of the first recovered separation membrane permeate gas 18 and the second recovered separation membrane permeate gas.

[0032] Typically, a compressor includes a cooler that removes moisture from the stream, but if trace amounts of moisture remain during the liquefaction process and freeze, this can cause damage or malfunction to instruments such as measuring devices. To prevent this, the carbon dioxide capture device linked to biogas quality improvement of the present invention can further include a dryer that removes moisture from the gas upstream of the liquefaction heat exchanger 108. The moisture content of the gas stream that has passed through the dryer can be, for example, about 50 ppm or less, preferably about 30 ppm or less, more preferably about 10 ppm or less, and most preferably substantially no moisture.

[0033] The liquefaction heat exchanger 108 performs separation and purification on the gas supplied to the liquefaction heat exchanger in a carbon dioxide purification section 109, and cools the gas to a temperature suitable for liquefying carbon dioxide, preferably −35 to −18° C. As a refrigerant for the liquefaction heat exchanger 108, Freon, nitrogen, propylene, etc. can be used.

[0034] The gas supplied to the liquefaction heat exchanger may be the gas 12 compressed by the second compressor or a gas stream obtained by removing moisture from the gas compressed by the second compressor in a dryer.

[0035] The carbon dioxide purification section 109 includes a separation tower that receives the gas 15 cooled by the liquefaction heat exchanger and separates and purifies it, an upper end that obtains carbon dioxide-containing gas 16 through the separation and purification, and a lower end that obtains high-purity carbon dioxide liquid 17.

[0036] The number of stages or trays in the separation tower may be 6 to 10, and may be changed in consideration of the purity of carbon dioxide and other process conditions, and may be changed by packing other than trays.

[0037] The carbon dioxide molar concentration of the high purity carbon dioxide liquid 17 recovered at the bottom of the separation tower may be 99% or more, and may be 99.9% or more depending on the use of carbon dioxide.

[0038] The first recovery separation membrane 110 receives the carbon dioxide-containing gas 16 and allows it to permeate through the first recovery separation membrane 110, separating it into a first recovery separation membrane permeate gas 18 that is relatively rich in carbon dioxide, and a first recovery separation membrane retentate gas 19 that cannot permeate the first recovery separation membrane 110 and contains high-purity methane.

[0039] Although high-purity carbon dioxide was recovered through the above-described separation membrane and separation tower process, there was a limit to maximizing the recovery rate of carbon dioxide and methane contained in biogas. Therefore, the present invention makes it possible to recover high-purity carbon dioxide liquid and methane by further introducing a recovery separation membrane that separates and recovers the residual carbon dioxide and methane from the carbon dioxide-containing gas 16 obtained at the top of the separation tower after passing through the separation tower.

[0040] The present invention is characterized in that the carbon dioxide-containing gas 16 obtained at the top of the separation tower after the carbon dioxide liquefaction process is supplied to the first recovery separation membrane 110 while still in a low temperature state, thereby significantly improving the separation efficiency of carbon dioxide and methane at the first recovery separation membrane 110. In addition, since there is no additional compression or cooling process to improve separation efficiency, separation efficiency is significantly improved while minimizing energy consumption.

[0041] More specifically, the temperature of the carbon dioxide-containing gas 16 supplied to the first recovery separation membrane 110 may be −40 to 0° C., preferably −35 to −18° C. In particular, when the temperature of the carbon dioxide-containing gas 16 satisfies the above preferred range, it is preferable in that the permeability is maintained at an excellent level, thereby significantly improving the selectivity and the separation efficiency without reducing the production amount.

[0042] In the present invention, the gas separation process using a separation membrane is carried out by a solution-diffusion mechanism, and therefore, the separation efficiency varies depending on the carbon dioxide / methane selectivity (e.g., CO2 / CH4) of the separation membrane.

[0043] The first recovery separation membrane 110 may be made of one or more materials selected from polysulfone (PSF) and polyimide (PI). As shown in Tables 1 and 2 below, polysulfone (PSF) and polyimide (PI) are preferred because they improve carbon dioxide / methane selectivity and separation efficiency at low temperatures. On the other hand, separation membranes made of other materials, such as polyamide or polyether, other than polysulfone (PSF) or polyimide (PI), may not be suitable for low-temperature processes because they only improve carbon dioxide selectivity at low temperatures.

[0044] [Table 1]

[0045] [Table 2]

[0046] The first separation membrane residual gas 19 is a high-purity methane gas having a high methane content, and can be stored in the methane storage tank together with the second separation membrane residual gas 8 .

[0047] The first recovery separation membrane permeate gas 18 can be circulated to the first separation membrane 102, the third separation membrane 104, or the second compressor 106 in order to increase the carbon dioxide recovery rate, and can preferably be circulated to the first separation membrane 102.

[0048] Although not shown in FIGS. 1 and 2 , the carbon dioxide capture device linked to biogas quality improvement according to an embodiment of the present invention may further include a second capture separation membrane that receives the first capture separation membrane retentate gas 19 and separates the first capture separation membrane retentate gas 19 into a second capture separation membrane permeate gas that is relatively rich in carbon dioxide and a second capture separation membrane retentate gas that is rich in methane. Here, the second capture separation membrane retentate gas contains high-purity methane and can be stored in the methane storage tank, and the second capture separation membrane permeate gas can be circulated to the first separation membrane 102, the third separation membrane 104, or the second compressor 106. By further including the second capture separation membrane when the carbon dioxide concentration supplied to the first capture separation membrane is low, the carbon dioxide content of the captured carbon dioxide stream and the methane content of the captured methane stream can be maintained at a high level.

[0049] FIG. 2 is a process diagram for carbon dioxide capture in conjunction with biogas quality improvement including a dry ice generator and a heat exchange network according to one embodiment of the present invention.

[0050] Referring to FIG. 2, a carbon dioxide capture device in conjunction with biogas quality improvement according to another aspect of the present invention may further include a heat exchange network 200.

[0051] The heat exchange network 200 exchanges heat with a low-temperature stream in the process to cool the gas 3 compressed by the first compressor before supplying it to the first separation membrane 102. This allows the separation process of the first separation membrane 102 to be performed at a low temperature. Furthermore, since the gas obtained after the separation process is performed by the first separation membrane 102 is also in a low-temperature state, the gas supplied to the second separation membrane 103 and the third separation membrane 104 is also in a low-temperature state, and the separation processes of the first separation membrane 102, the second separation membrane 103, and the third separation membrane 104 can all be performed at low temperatures.

[0052] That is, when the carbon dioxide capture device linked to biogas quality improvement of the present invention further includes a heat exchange network 200, heat exchange occurs between the low-temperature flow in the process and the gas supplied to the separation membranes, so that the gas supplied to the first separation membrane 102, the second separation membrane 103, and the third separation membrane 104 is in a low-temperature state. Therefore, it is more preferable that the separation membranes are made of one or more materials selected from polysulfone (PSF) and polyimide (PI), in order to significantly improve carbon dioxide separation efficiency. More specifically, the temperature of the gas supplied to the first separation membrane 102, the second separation membrane 103, and the third separation membrane 104 is -40 to 10°C, most preferably -25 to -15°C.

[0053] That is, it is preferable that the first separation membrane 102, the second separation membrane 103, and the third separation membrane 104 are made of at least one material selected from polysulfone (PSF) and polyimide (PI), since this significantly improves the separation efficiency of methane and carbon dioxide when the separation process is carried out at low temperatures.

[0054] The heat exchange network 200 can cool the gas 3 compressed by the first compressor by exchanging heat with any one or more of the second separation membrane permeate gas 7, the second separation membrane retentate gas 8, the third separation membrane permeate gas 9, the third separation membrane retentate gas 10, the carbon dioxide-containing gas 16, the first recovered separation membrane permeate gas 18, the first recovered separation membrane retentate gas 19, and the residual carbon dioxide gas 21 before supplying the gas 3 compressed by the first compressor to the first separation membrane 102. Preferably, the heat exchange network 200 can cool the gas 3 compressed by the first compressor by exchanging heat with all of the second separation membrane permeate gas 7, the second separation membrane retentate gas 8, the third separation membrane permeate gas 9, the third separation membrane retentate gas 10, the first recovered separation membrane retentate gas 19, and the residual carbon dioxide gas 21.

[0055] According to a preferred embodiment of the present invention, the heat exchange network 200 may include: a first heat exchanger 201 that exchanges heat between the gas 3 compressed by the first compressor and the third separation membrane permeate gas 9; a second heat exchanger 202 that exchanges heat between the gas 31 compressed by the first compressor and cooled in the first heat exchanger with a methane-rich gas 37 including at least one of the second separation membrane retentate gas 8 and the first recovery separation membrane retentate gas 19; a third heat exchanger 203 that exchanges heat between the gas 32 compressed by the first compressor and cooled in the second heat exchanger with a circulating gas 38 including at least one of the second separation membrane permeate gas 7 and the third separation membrane retentate gas 10; and a fourth heat exchanger 204 that exchanges heat between the gas 33 compressed by the first compressor and cooled in the third heat exchanger with the residual carbon dioxide gas 21. It has been confirmed that when the heat exchange network 200 includes the first to fourth heat exchangers, it is possible to minimize the required energy and cool to a temperature that can maximize the carbon dioxide separation efficiency without consuming additional energy.

[0056] The heat exchange network 200 may further include a cooling heat exchanger 205 that further cools the gas 3 compressed by the first compressor by exchanging heat with a refrigerant, thereby maximizing the carbon dioxide separation efficiency of the gas supplied to the first separation membrane 102.

[0057] Here, the cooling heat exchanger 205 may use a portion of the increased capacity by increasing the refrigerant capacity of the liquefaction heat exchanger 108, and the energy consumption due to increasing the capacity of the liquefaction heat exchanger 108 is very small compared to the effect of improving the carbon dioxide separation efficiency using the separation membrane.

[0058] The gas 3 may be supplied to the cooling heat exchanger 205 immediately after being compressed by the first compressor, or may be supplied after being partially cooled by heat exchange through the heat exchange network 200. Alternatively, a gas 35 obtained by mixing the gas 3 compressed by the first compressor and the first recovered separation membrane permeate gas 18 may be supplied.

[0059] When the carbon dioxide capture device linked to biogas quality improvement of the present invention further includes the heat exchange network 200 and the first recovered separation membrane permeate gas 18 circulates to the first separation membrane 102, the gas supplied to the first separation membrane 102 may be a gas obtained by mixing the first recovered separation membrane permeate gas 18 with the gas 3 compressed by the first compressor and cooling them together in the heat exchange network 200, a gas obtained by mixing the gas 3 compressed by the first compressor that has been partially cooled by the heat exchange network 200 with the first recovered separation membrane permeate gas 18 and then further cooling it through the heat exchange network 200, or a gas obtained by mixing the gas 3 compressed by the first compressor that has been cooled through the heat exchange network 200 with the first recovered separation membrane permeate gas 18.

[0060] When the carbon dioxide capture device linked to biogas quality improvement of the present invention further includes the heat exchange network 200, the separation efficiency of the first separation membrane 102 is improved, and therefore, even if the first compressor 101 compresses the gas to a low pressure, it can exhibit sufficiently excellent separation efficiency. More specifically, when the heat exchange network 200 is further included, the first compressor can compress the first compressor supply gas 2 to a pressure of 2 to 15 bar, preferably 3.5 to 7.5 bar.

[0061] When the carbon dioxide capture device linked to biogas quality improvement of the present invention further includes the heat exchange network 200, the second separation membrane permeate gas 7 and the second separation membrane retentate gas 8 are in a low temperature state, and at least one of the second separation membrane permeate gas 7 and the second separation membrane retentate gas 8 is supplied to the heat exchange network 200 to exchange heat with the gas 3 compressed by the first compressor, thereby cooling the gas 3 compressed by the first compressor.

[0062] When the carbon dioxide capture device linked to biogas quality improvement of the present invention further includes the heat exchange network 200, the third separation membrane permeate gas 9 and the third separation membrane retentate gas 10 are in a low temperature state, and at least one of the third separation membrane permeate gas 9 and the third separation membrane retentate gas 10 is supplied to the heat exchange network 200 and exchanges heat with the gas 3 compressed by the first compressor, thereby cooling the gas 3 compressed by the first compressor.

[0063] The carbon dioxide-containing gas 16 is cooled in the liquefaction heat exchanger 108 and is in a low temperature state, and is supplied to the heat exchange network 200, where it exchanges heat with the gas 3 compressed in the first compressor, thereby cooling the gas 3 compressed in the first compressor.

[0064] According to one embodiment of the present invention, the carbon dioxide capture device linked to biogas quality improvement of the present invention may further include an additional heat exchanger 107 that cools the gas 12 compressed by the second compressor by exchanging heat between the gas 12 compressed by the second compressor and the residual carbon dioxide gas 21.

[0065] Since the residual carbon dioxide gas 21 has a sufficiently low temperature of about -10 to 5°C even after being heated in the heat exchange network 200, the residual carbon dioxide gas 21 supplied to the additional heat exchanger 107 may be the gas heated in the heat exchange network 200.

[0066] When the carbon dioxide capture device linked to biogas quality improvement of the present invention further includes an additional heat exchanger 107, the gas supplied to the liquefaction heat exchanger may be gas 13 cooled by the additional heat exchanger.

[0067] Since the first recovered separation membrane permeate gas 18 and the first recovered separation membrane retentate gas 19 are cooled in the liquefaction heat exchanger 108 and are in a low temperature state, at least one of the first recovered separation membrane permeate gas 18 and the first recovered separation membrane retentate gas 19 is supplied to the heat exchange network 200 and exchanges heat with the gas 3 compressed by the first compressor, thereby cooling the gas 3 compressed by the first compressor.

[0068] When the present invention further includes a second recovery separation membrane, the second recovery separation membrane permeate gas and the second recovery separation membrane retentate gas are in a state in which they are maintained as low-temperature streams cooled in the liquefaction heat exchanger 108, and one or more of them can be supplied to the heat exchange network 200 and exchange heat with the gas 3 compressed in the first compressor.

[0069] Referring again to FIG. 2, the carbon dioxide capture device linked to biogas quality improvement according to another aspect of the present invention may further include a dry ice generator 111.

[0070] The dry ice generating unit 111 includes a chamber for receiving the high-purity carbon dioxide liquid 17 and converting it into dry ice 20, and an outlet for discharging the remaining carbon dioxide gas 21 that has not been converted into dry ice 20 from the high-purity carbon dioxide liquid 17. Here, the dry ice generating unit 111 may be supplied with all of the produced high-purity carbon dioxide liquid 17, or only a portion of it, if necessary.

[0071] The carbon dioxide capture device linked to biogas quality improvement according to the present invention further includes a dry ice production unit 111, thereby making more effective use of the carbon dioxide gas lost in the process of producing dry ice 20 from high-purity carbon dioxide liquid 17.

[0072] In the dry ice generating unit 111, the high purity carbon dioxide liquid 17 is not 100% converted into dry ice 20, and therefore residual carbon dioxide gas 21 is discharged. Here, since the temperature of the residual carbon dioxide gas 21 is in a very low state of -78 to -48°C, cold energy can be recovered through the heat exchange network 200 to improve the separation efficiency in the separation membrane.

[0073] The residual carbon dioxide gas 21 is in a very low temperature state, and has a sufficiently low temperature of about -10 to 5°C even after the cold energy is recovered through the heat exchange network 200, so that the gas 12 compressed by the second compressor can be cooled in the additional heat exchanger 107.

[0074] The remaining carbon dioxide gas 21 can be supplied to a carbon dioxide re-liquefaction facility after the cold energy is recovered.

[0075] Another aspect of the present invention is a biogas-containing gas-reducing system, comprising: a first compression step of compressing a gas supplied to a first compressor, the gas including biogas, with a first compressor; a first separation step of supplying the gas compressed by the first compressor to a first separation membrane to separate the gas into a first separation membrane permeate gas and a first separation membrane retentate gas; a second separation step of supplying the first separation membrane retentate gas to a second separation membrane to separate the gas into a second separation membrane permeate gas and a second separation membrane retentate gas; a third separation step of supplying the first separation membrane permeate gas to a third separation membrane to separate the gas into a third separation membrane permeate gas and a third separation membrane retentate gas; and a second compression step of compressing a gas supplied to a second compressor, the gas including the third separation membrane permeate gas, with a second compressor. a liquefaction step of cooling the gas compressed in the second compressor in a liquefaction heat exchanger; a separation and purification step of supplying the gas cooled in the liquefaction heat exchanger to a separation tower and obtaining a carbon dioxide-containing gas at an upper part of the separation tower through a separation and purification process and recovering a high-purity carbon dioxide liquid at a lower part; and a first recovery step of supplying the carbon dioxide-containing gas to a first recovery separation membrane to separate it into a first recovery separation membrane permeate gas and a first recovery separation membrane retentate gas, and circulating the first recovery separation membrane permeate gas to the first separation membrane, the third separation membrane, or the second compressor.

[0076] The carbon dioxide capture process linked to biogas quality improvement will be described in detail below. Here, detailed descriptions of parts that are considered to overlap with the description of the carbon dioxide capture device linked to biogas quality improvement will be partially omitted.

[0077] The first compression step is a step of compressing the first compressor supply gas 2 containing the biogas 1 by the first compressor 101, and more specifically, the first compressor supply gas 2 may be compressed to a pressure of 5 to 20 bar, preferably 6 to 11 bar.

[0078] The first compressor supply gas 2 is a gas containing biogas 1, and may be biogas 1 or a mixture of biogas 1 and one or more gases selected from the second separation membrane permeate gas 7 and the third separation membrane retentate gas 10.

[0079] The first separation step is a step of supplying the gas 3 compressed by the first compressor to a first separation membrane 102 and separating the gas 3 compressed by the first compressor into a first separation membrane permeate gas 5 that is relatively rich in carbon dioxide and a first separation membrane retentate gas 6 that is relatively rich in methane.

[0080] The first separation membrane supply gas 4 may be the gas 3 compressed by the first compressor or a mixture of the gas 3 and one or more of the first recovered separation membrane permeate gas 18 and the second recovered separation membrane permeate gas.

[0081] The second separation step is a step of supplying the first separation membrane retentate gas 6 to a second separation membrane 103 for concentrating and recovering methane, and separating the gas into a second separation membrane permeate gas 7 that is relatively rich in carbon dioxide and a second separation membrane retentate gas 8 that contains high-purity methane.

[0082] The second separation membrane retentate gas 8 contains high-purity methane with a methane content of 97% or more. Here, the second separation membrane retentate gas 8 can be supplied to and stored in a methane storage tank, and the first recovered separation membrane retentate gas 19 can also be stored together with the second separation membrane retentate gas 8 because it is rich in methane.

[0083] The second separation membrane permeate gas 7 can be circulated to the first compressor 101 to recover the contained methane and carbon dioxide. Here, it is preferable to also recover the third separation membrane retentate gas 10, so that the gases can be mixed together and circulated to the first compressor 101.

[0084] In the third separation step, the third separation membrane feed gas is supplied to a third separation membrane 104 and separated into a third separation membrane permeate gas 9 relatively rich in carbon dioxide and a third separation membrane retentate gas 10 relatively rich in methane.

[0085] The third separation membrane supply gas may be the first separation membrane permeated gas 5 or a mixture thereof with at least one of the first recovered separation membrane permeated gas 18 and the second recovered separation membrane permeated gas.

[0086] The third separation membrane retentate gas 10 can be circulated to the first compressor 101 to recover the contained methane and carbon dioxide.

[0087] The second compression step is a step of compressing the second compressor supply gas 11 in the second compressor 106 to a pressure required for the liquefaction process, specifically, 20 to 50 bar, preferably 21 to 31 bar.

[0088] The second compressor supply gas 11 may be the third separation membrane permeate gas 9 or a mixture thereof with at least one of the first recovered separation membrane permeate gas 18 and the second recovered separation membrane permeate gas.

[0089] In the liquefaction step, the gas supplied to the liquefaction heat exchanger is cooled to a temperature suitable for separation and purification in the separation column and liquefaction of carbon dioxide, preferably −35 to −18° C. The refrigerant used in the liquefaction heat exchanger 108 can be Freon, nitrogen, propylene, or the like.

[0090] The gas supplied to the liquefaction heat exchanger may be the gas 12 compressed by the second compressor or a gas stream obtained by removing moisture from the gas compressed by the second compressor in a dryer.

[0091] The separation and purification step is a step of supplying the gas 15 cooled in the liquefaction heat exchanger to a separation tower, and during the separation and purification process, obtaining a carbon dioxide-containing gas 16 at the top of the separation tower and recovering a high-purity carbon dioxide liquid 17 at the bottom of the separation tower.

[0092] The carbon dioxide molar concentration of the high purity carbon dioxide liquid 17 may be 99% or more, and may be 99.9% or more depending on the use of carbon dioxide.

[0093] The first recovery step is a step of supplying the carbon dioxide-containing gas 16 to a first recovery separation membrane 110 to separate it into a first recovery separation membrane permeate gas 18 and a first recovery separation membrane retentate gas 19, and circulating the first recovery separation membrane permeate gas 18 to the first separation membrane 102, the third separation membrane 104 or the second compressor 106, preferably the first separation membrane 102, to recover carbon dioxide and methane.

[0094] The first recovery separation membrane residual gas 19 is high-purity methane gas and can be stored in the methane storage tank.

[0095] The first recovery step is characterized by supplying the carbon dioxide-containing gas 16 at a low temperature to the first recovery separation membrane 110 for separation, thereby significantly improving the separation efficiency of carbon dioxide and methane at the first recovery separation membrane 110. In particular, since there is no additional compression or cooling process to improve separation efficiency, carbon dioxide selectivity is improved while minimizing energy consumption, and separation efficiency is significantly improved.

[0096] More specifically, the temperature of the carbon dioxide-containing gas 16 supplied to the first recovery / separation membrane 110 may be -40 to 0°C, preferably -35 to -18°C.

[0097] The first recovery separation membrane 110 may be made of at least one material selected from polysulfone (PSF) and polyimide (PI), which are preferred in that they improve carbon dioxide / methane selectivity and separation efficiency at low temperatures.

[0098] According to one embodiment of the present invention, the method may further include a second recovery step of supplying the first recovery separation membrane retentate gas 19 to a second recovery separation membrane to separate the first recovery separation membrane retentate gas 19 into a second recovery separation membrane permeate gas that is relatively rich in carbon dioxide and a second recovery separation membrane retentate gas that is relatively rich in methane. Here, the second recovery separation membrane retentate gas contains high-purity methane and may be stored in the methane storage tank, and the second recovery separation membrane permeate gas may be supplied to the first separation membrane 102, the third separation membrane 104, or the second compressor 106.

[0099] The carbon dioxide capture process linked to biogas quality improvement of the present invention may further include a heat exchange step of cooling the gas 3 compressed by the first compressor by exchanging heat with any one or more of the second separation membrane permeate gas 7, the second separation membrane retentate gas 8, the third separation membrane permeate gas 9, the third separation membrane retentate gas 10, the carbon dioxide-containing gas 16, the first recovered separation membrane permeate gas 18, the first recovered separation membrane retentate gas 19, and the residual carbon dioxide gas 21 in a heat exchange network 200 before supplying the gas 3 compressed by the first compressor to the first separation membrane.

[0100] When the carbon dioxide capture process linked to biogas quality improvement of the present invention further includes the heat exchange step, heat exchange occurs between a low-temperature stream in the process and a gas supplied to the separation membranes, so that the gas supplied to the first separation membrane 102, the second separation membrane 103, and the third separation membrane 104 is in a low-temperature state. More specifically, the temperature of the gas supplied to the first separation membrane 102, the second separation membrane 103, and the third separation membrane 104 may be −40 to 10° C., most preferably −25 to −15° C. Therefore, it is more preferable that the first separation membrane 102, the second separation membrane 103, and the third separation membrane 104 are made of one or more materials selected from polysulfone (PSF) and polyimide (PI), in order to significantly improve carbon dioxide separation efficiency.

[0101] The heat exchange step may be a step of cooling the gas 3 compressed by the first compressor by exchanging heat with at least one of the second separation membrane permeate gas 7, the second separation membrane retentate gas 8, the third separation membrane permeate gas 9, the third separation membrane retentate gas 10, the carbon dioxide-containing gas 16, the first recovered separation membrane permeate gas 18, the first recovered separation membrane retentate gas 19, and the residual carbon dioxide gas 21 in the heat exchange network 200 before supplying the gas 3 compressed by the first compressor to the first separation membrane 102, and is preferably a step of cooling the gas 3 compressed by the first compressor by exchanging heat with all of the second separation membrane permeate gas 7, the second separation membrane retentate gas 8, the third separation membrane permeate gas 9, the third separation membrane retentate gas 10, the first recovered separation membrane retentate gas 19, and the residual carbon dioxide gas 21.

[0102] More preferably, the heat exchange step may include the steps of: exchanging heat between the gas 3 compressed by the first compressor and the third separation membrane permeate gas 9 in a first heat exchanger 201; exchanging heat between the gas 31 compressed by the first compressor and cooled in the first heat exchanger with a methane-rich gas 37 containing at least one of the second separation membrane retentate gas 8 and the first recovery separation membrane retentate gas 19 in a second heat exchanger 202; exchanging heat between the gas 32 compressed by the first compressor and cooled in the second heat exchanger with a circulating gas 38 containing at least one of the second separation membrane permeate gas 7 and the third separation membrane retentate gas 10 in a third heat exchanger 203; and exchanging heat between the gas 33 compressed by the first compressor and cooled in the third heat exchanger with the residual carbon dioxide gas 21 in a fourth heat exchanger 204.

[0103] The heat exchanging step may further include a step of exchanging heat between the gas 3 compressed by the first compressor and a refrigerant in a cooling heat exchanger 205 to further cool the gas 3 .

[0104] The cooling heat exchanger 205 may be supplied with the gas 3 compressed by the first compressor, the gas 34 compressed by the first compressor that has been cooled in the fourth heat exchanger, or a heat exchanger supply gas 35 obtained by further mixing the gas 34 compressed by the first compressor that has been cooled in the fourth heat exchanger and the first recovered separation membrane permeate gas 18.

[0105] When the carbon dioxide capture process linked to biogas quality improvement of the present invention further includes the heat exchange step, the separation efficiency of the first separation membrane 102 is improved in the first separation step, so that even if the gas is compressed to a low pressure in the first compressor 101, sufficiently excellent separation efficiency can be exhibited. More specifically, when the heat exchange step is further included, the first compression step can compress the gas 2 supplied to the first compressor to a pressure of 2 to 15 bar, preferably 3.5 to 7.5 bar.

[0106] When the carbon dioxide capture process linked to biogas quality improvement of the present invention further includes the heat exchange step, the second separation membrane permeate gas 7 and the second separation membrane retentate gas 8 are in a low temperature state, and at least one of the second separation membrane permeate gas 7 and the second separation membrane retentate gas 8 is supplied to the heat exchange network 200 in the heat exchange step and exchanges heat with the gas 3 compressed by the first compressor to cool the gas 3 compressed by the first compressor.

[0107] When the carbon dioxide capture process linked to biogas quality improvement of the present invention further includes the heat exchange step, the third separation membrane permeate gas 9 and the third separation membrane retentate gas 10 are in a low temperature state, and at least one of the third separation membrane permeate gas 9 and the third separation membrane retentate gas 10 is supplied to the heat exchange network 200 in the heat exchange step and exchanges heat with the gas 3 compressed by the first compressor to cool the gas 3 compressed by the first compressor.

[0108] The carbon dioxide-containing gas 16 is cooled in the liquefaction heat exchanger 108 and is in a low temperature state, and is supplied to the heat exchange network 200 in the heat exchange step to exchange heat with the gas 3 compressed in the first compressor, thereby cooling the gas 3 compressed in the first compressor.

[0109] According to one embodiment of the present invention, an additional heat exchange step may be further included in which the gas 12 compressed by the second compressor is cooled by exchanging heat between the gas 12 compressed by the second compressor and the residual carbon dioxide gas 21 in an additional heat exchanger 107.

[0110] The residual carbon dioxide gas 21 has a sufficiently low temperature of about -10 to 5°C even after being heated by the heat exchange network 200. Therefore, the residual carbon dioxide gas 21 supplied to the additional heat exchanger 107 in the additional heat exchange step may be heated through the heat exchange network 200 in the heat exchange step.

[0111] When the carbon dioxide capture process linked to biogas quality improvement of the present invention further includes the additional heat exchange step, the gas supplied to the liquefaction heat exchanger may be gas 13 cooled in the additional heat exchanger.

[0112] Since the first recovered separation membrane permeate gas 18 and the first recovered separation membrane retentate gas 19 are maintained as low-temperature streams cooled in the liquefaction heat exchanger 108, at least one of them can be supplied to the heat exchange network 200 in the heat exchange step and exchange heat with the gas 3 compressed in the first compressor.

[0113] When the present invention further includes a second recovery step, the second recovered separation membrane permeate gas and the second recovered separation membrane retentate gas are in a state in which they are maintained as low-temperature streams cooled in the liquefaction heat exchanger 108, and at least one of them can be supplied to the heat exchange network 200 in the heat exchange step to exchange heat with the gas 3 compressed in the first compressor.

[0114] The carbon dioxide capture process linked to biogas quality improvement of the present invention may further include a dry ice production step of converting the high-purity carbon dioxide liquid 17 into dry ice 20 and obtaining the remaining carbon dioxide gas 21 that has not been converted into dry ice 20.

[0115] The dry ice production step is a step of converting the high purity carbon dioxide liquid 17 into dry ice 20 and collecting the remaining carbon dioxide gas 21 that has not been converted into dry ice.

[0116] Not 100% of the high-purity carbon dioxide liquid 17 is converted into dry ice 20, and residual carbon dioxide gas 21 is discharged. Here, since the temperature of the residual carbon dioxide gas 21 is very low, at -78 to -48°C, cold energy can be recovered through the heat exchange network 200 in the heat exchange step to improve the separation efficiency in the separation membrane.

[0117] The residual carbon dioxide gas 21 is in a very low temperature state, and therefore has a sufficiently low temperature of about -10 to 5°C even after the cold energy is recovered through the heat exchange network 200, and can cool the gas 12 compressed by the second compressor in the additional heat exchange step.

[0118] The present invention will be described in more detail below with reference to examples, etc. However, the following examples should not be construed as narrowing or limiting the scope and content of the present invention.

[0119] Example 1 The process was designed as shown in Figure 1, and the process was operated for each flow as shown in Table 3 below, and the process results are shown in Table 5 below. Here, the first separation membrane 102, the second separation membrane 103, the third separation membrane 104, and the first recovery separation membrane 110 were made of polysulfone (PSF) material.

[0120] [Table 3]

[0121] Example 2 The process was designed as shown in Figure 2, and the process was operated for each flow as shown in Table 4 below, and the process results are shown in Table 5 below. Here, the first separation membrane 102, the second separation membrane 103, the third separation membrane 104, and the first recovery separation membrane 110 were made of polysulfone (PSF) material.

[0122] [Table 4]

[0123] [Table 5]

[0124] As shown in Table 5, the carbon dioxide capture device and process linked to biogas quality improvement according to the present invention can have excellent separation efficiency and recovery rate of methane and carbon dioxide, and when a heat exchange network is further included, it can also significantly reduce electricity consumption. [Explanation of symbols]

[0125] 101 First compressor 102 First separation membrane 103 Second separation membrane 104 Third separation membrane 105 Vacuum Pump 106 Second compressor 107 Additional heat exchanger 108 Liquefaction heat exchanger 109 Carbon Dioxide Purification Department 110 First recovery separation membrane 111 Dry Ice Generator 201 1st heat exchanger 202 Second heat exchanger 203 Third heat exchanger 204 4th heat exchanger 205 Cooling heat exchanger 1. Biogas 2. First compressor supply gas 3 Gas compressed by the first compressor 4. First separation membrane supply gas 5. Gas permeating through the first separation membrane 6. Residual gas in the first separation membrane 7 Second separation membrane permeate gas 8 Second separation membrane residual gas 9 Third membrane permeate gas 10 Third separation membrane residual gas 11 Second compressor supply gas 12 Gas compressed by the second compressor 13 Gas cooled by additional heat exchanger 14. Gas dried in a dryer 15 Gas cooled by liquefaction heat exchanger 16 Carbon dioxide containing gas 17 High-purity carbon dioxide liquid 18 First recovery separation membrane permeate gas 19 First recovery separation membrane residual gas 20 dry ice 21 Residual carbon dioxide gas 31 Gas compressed by the first compressor cooled by the first heat exchanger 32 Gas compressed by the first compressor cooled by the second heat exchanger 33 Gas compressed by the first compressor cooled by the third heat exchanger 34 Gas compressed by the first compressor cooled by the fourth heat exchanger 35 Additional heat exchanger supply gas 36 Gas compressed by the first compressor cooled by the cooling heat exchanger 37 Methane-rich gas 38 Circulating Gas 39 Gas heated by the first heat exchanger 40 Gas heated by the second heat exchanger 41 Gas heated by the third heat exchanger 42 Gas heated by the fourth heat exchanger

Claims

1. a first compressor that compresses a first compressor supply gas containing biogas; a first separation membrane for separating a first separation membrane supply gas, including the gas compressed by the first compressor, into a first separation membrane permeate gas and a first separation membrane retentate gas; a second separation membrane that receives the first separation membrane retentate gas and separates it into a second separation membrane permeate gas and a second separation membrane retentate gas; a third separation membrane that receives the first separation membrane permeated gas and separates it into a third separation membrane permeated gas and a third separation membrane retentate gas; a second compressor that compresses a gas supplied to the second compressor, the gas including the third separation membrane permeated gas; a liquefaction heat exchanger that cools the gas compressed by the second compressor; a separation tower for receiving the gas cooled by the liquefaction heat exchanger, a carbon dioxide purification unit including an upper end for collecting carbon dioxide-containing gas and a lower end for collecting high-purity carbon dioxide liquid; a first recovery separation membrane that receives the carbon dioxide-containing gas and separates it into a first recovery separation membrane permeate gas and a first recovery separation membrane retentate gas; A carbon dioxide capture device linked to biogas quality improvement, including a first circulation unit that circulates the first recovery separation membrane permeated gas to the first separation membrane, the third separation membrane, or the second compressor, The dry ice generating unit further includes a chamber for receiving the high-purity carbon dioxide liquid and converting it into dry ice, and an outlet for discharging the remaining carbon dioxide gas that has not been converted into dry ice, a heat exchange network for cooling the gas compressed by the first compressor by heat exchanging heat with at least one of the second separation membrane permeate gas, the second separation membrane retentate gas, the third separation membrane permeate gas, the third separation membrane retentate gas, the carbon dioxide-containing gas, the first recovered separation membrane permeate gas, the first recovered separation membrane retentate gas, and the residual carbon dioxide gas before supplying the gas compressed by the first compressor to the first separation membrane; The heat exchange network comprises: a first heat exchanger for exchanging heat between the gas compressed by the first compressor and the gas permeated by the third separation membrane; a second heat exchanger for heat exchange of the gas compressed by the first compressor and cooled by the first heat exchanger with a methane-rich gas including at least one of the second separation membrane residue gas and the first recovery separation membrane residue gas; a third heat exchanger for heat exchange of the gas compressed by the first compressor and cooled by the second heat exchanger with a circulating gas containing at least one of the second separation membrane permeate gas and the third separation membrane retentate gas; A carbon dioxide capture device linked to biogas quality improvement, characterized by including a fourth heat exchanger that exchanges heat between the gas compressed by the first compressor and cooled by the third heat exchanger and the residual carbon dioxide gas.

2. The carbon dioxide capture device linked to biogas quality improvement according to claim 1, wherein the temperature of the gas supplied to the first separation membrane is −40 to 10° C.

3. The carbon dioxide capture device linked to biogas quality improvement according to claim 1, wherein the temperature of the gas supplied to the first capture / separation membrane is −40 to 0° C.

4. 2. The carbon dioxide capture device linked to biogas quality improvement according to claim 1, wherein the first separation membrane, the second separation membrane, the third separation membrane, and the first capture separation membrane are the same or different from one another and are made of at least one material selected from the group consisting of polysulfone (PSF) and polyimide (PI).

5. 2. The carbon dioxide capture device linked to biogas quality improvement according to claim 1, further comprising an additional heat exchanger that performs additional heat exchange between the gas compressed by the second compressor and the residual carbon dioxide gas to cool the gas compressed by the second compressor.

6. a first compression stage in which a first compressor feed gas containing biogas is compressed by the first compressor; a first separation step of supplying the gas compressed by the first compressor to a first separation membrane and separating the gas into a first separation membrane permeate gas and a first separation membrane retentate gas; a second separation step of supplying the first separation membrane retentate gas to a second separation membrane to separate the first separation membrane retentate gas into a second separation membrane permeate gas and a second separation membrane retentate gas; a third separation step of supplying the first separation membrane permeated gas to a third separation membrane and separating the first separation membrane permeated gas and the third separation membrane retentate gas; a second compression step of compressing a gas supplied to the second compressor, including the gas permeated through the third separation membrane, by the second compressor; a liquefaction step of cooling the gas compressed by the second compressor in a liquefaction heat exchanger; a separation and purification step of supplying the gas cooled in the liquefaction heat exchanger to a separation tower, and recovering a carbon dioxide-containing gas at the top of the separation tower through a separation and purification process, and recovering a high-purity carbon dioxide liquid at the bottom of the separation tower; a first recovery step of supplying the carbon dioxide-containing gas to a first recovery separation membrane to separate it into a first recovery separation membrane permeate gas and a first recovery separation membrane retentate gas, and circulating the first recovery separation membrane permeate gas to the first separation membrane, the third separation membrane, or the second compressor, The method further includes a dry ice producing step of converting the high-purity carbon dioxide liquid into dry ice and collecting the remaining carbon dioxide gas that has not been converted into dry ice, a heat exchange step of exchanging heat with at least one of the second separation membrane permeate gas, the second separation membrane retentate gas, the third separation membrane permeate gas, the third separation membrane retentate gas, the carbon dioxide-containing gas, the first recovered separation membrane permeate gas, the first recovered separation membrane retentate gas, and the residual carbon dioxide gas before supplying the gas compressed by the first compressor to the first separation membrane; The heat exchange step comprises: exchanging heat between the gas compressed by the first compressor and the gas permeated by the third separation membrane in a first heat exchanger; exchanging heat in a second heat exchanger between the gas compressed by the first compressor and cooled in the first heat exchanger and a methane-rich gas including at least one of the second separation membrane residue gas and the first recovery separation membrane residue gas; exchanging heat in a third heat exchanger between the gas compressed by the first compressor and cooled in the second heat exchanger and a circulating gas containing at least one of the second separation membrane permeate gas and the third separation membrane retentate gas; and exchanging heat in a fourth heat exchanger between the gas compressed by the first compressor and cooled in the third heat exchanger and the residual carbon dioxide gas.

7. The carbon dioxide capture process linked to biogas quality improvement according to claim 6, wherein the temperature of the gas supplied to the first separation membrane is −40 to 10° C.

8. The carbon dioxide capture process linked to biogas quality improvement according to claim 6, wherein the temperature of the gas supplied to the first capture and separation membrane is −40 to 0° C.

9. The carbon dioxide capture process linked to biogas quality improvement according to claim 6, wherein the first separation membrane, the second separation membrane, the third separation membrane, and the first capture separation membrane are the same or different from one another and are made of at least one material selected from the group consisting of polysulfone (PSF) and polyimide (PI).

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