Boil-off gas treatment system for liquefied carbon dioxide and liquefied carbon dioxide storage apparatus including same

Abstract

Provided are: a boil-off gas treatment system for liquefied carbon dioxide in which combustible impurities in boil-off gas can be recycled by increasing the purity thereof by repeatedly performing a re-liquefaction process; and a liquefied carbon dioxide storage apparatus including same. The boil-off gas treatment system for liquefied carbon dioxide comprises: a first re-liquefaction apparatus which re-liquefies tank boil-off gas discharged from a storage tank for storing liquefied carbon dioxide and returns the re-liquefied tank boil-off gas to the storage tank; a first composition detection apparatus which measures a first concentration of combustible impurities included in a first boil-off gas remaining after the re-liquefaction by the first re-liquefaction apparatus; a second re-liquefaction apparatus which receives the first boil-off gas from the first composition detection apparatus when the first concentration is less than a predetermined threshold value, re-liquefies the first boil-off gas, and returns the reliquefied first boil-off gas to the storage tank; and a post-processing apparatus which receives the first boil-off gas from the first composition detection apparatus when the first concentration is equal to or greater than the predetermined threshold value, and performs post-processing for recycling the combustible impurities.

Description

Liquid carbon dioxide evaporation gas treatment system and liquid carbon dioxide storage device including the same

[0001] The present invention relates to a liquefied carbon dioxide vaporization gas treatment system and a liquefied carbon dioxide storage device including the same, and more particularly, to a liquefied carbon dioxide vaporization gas treatment system and a liquefied carbon dioxide storage device including the same, which can increase the purity of combustible impurities in vaporization gas by repeatedly performing a re-liquefaction process and recycle the vaporization gas.

[0002] Carbon dioxide, emitted in large quantities due to the increased use of fossil fuels, is designated as a greenhouse gas contributing to global warming. While its global warming potential is relatively low compared to other greenhouse gases, it accounts for approximately 80% of total greenhouse gas emissions, leading to an international consensus to regulate carbon dioxide emissions. Indeed, various international agreements regulate carbon dioxide emissions reductions. One emerging technology is carbon dioxide processing technology, which captures carbon dioxide generated from various industrial processes or power plants, liquefies it, and safely transports it to underground storage sites (e.g., exhausted oil or gas fields, salt domes, rock formations, etc.) for isolation and storage.

[0003] In this process, liquefied carbon dioxide carriers (LCCs) are a crucial device for transporting captured CO2 in a liquefied state. While LCCs are currently in the development stage and have not yet been implemented, they are known to be economically advantageous for long-distance transport of liquefied CO2.

[0004] Meanwhile, while there are systems that re-liquefy the boil-off gas of liquefied carbon dioxide, most of them were introduced in the manufacturing process of food and beverages such as carbonated drinks, and were designed assuming 100% carbon dioxide purity. Therefore, there are limitations in directly applying them to liquefied carbon dioxide carriers. Specifically, impurities are inevitably mixed in the process of capturing carbon dioxide in industrial processes or power plants. For example, if the liquefied carbon dioxide cargo contains 1 mol% hydrogen as an impurity, the hydrogen fraction in the boil-off gas increases rapidly, as the liquefaction temperature of hydrogen at atmospheric pressure is -252.7 degrees Celsius, and that of carbon dioxide is -78.5 degrees Celsius. Therefore, the hydrogen fraction remaining in the gaseous state after carbon dioxide re-liquefaction increases even more. If this boil-off gas is released into the atmosphere, there is a risk of explosion due to the large hydrogen content in the boil-off gas.

[0005] The problem to be solved by the present invention is to provide a system for processing liquefied carbon dioxide vapor gas, which can increase the purity of combustible impurities in vapor gas by repeatedly performing a re-liquefaction process and recycle the vapor gas.

[0006] Another problem to be solved by the present invention is to provide a liquefied carbon dioxide storage device including such an evaporation gas treatment system.

[0007] The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

[0008] According to one embodiment of the present invention for achieving the above object, a system for processing liquefied carbon dioxide boil-off gas includes: a first re-liquefaction device for re-liquefying tank boil-off gas discharged from a storage tank storing liquefied carbon dioxide and returning it to the storage tank; a first composition detection device for measuring a first concentration of combustible impurities contained in the first boil-off gas remaining after re-liquefaction by the first re-liquefaction device; a second re-liquefaction device for receiving the first boil-off gas from the first composition detection device, re-liquefying it, and returning it to the storage tank when the first concentration is lower than a predetermined threshold value; and a post-processing device for receiving the first boil-off gas from the first composition detection device and performing post-processing for recycling combustible impurities when the first concentration is higher than the predetermined threshold value.

[0009] The second concentration of combustible impurities contained in the second evaporation gas remaining after re-liquefaction by the second re-liquefaction device may be greater than the first concentration of combustible impurities contained in the first evaporation gas.

[0010] The above combustible impurity may be hydrogen, methane or a combination thereof.

[0011] The above threshold value may be 40 mol% as the concentration of combustible impurities in the first evaporated gas.

[0012] The first re-liquefaction device may include a first compressor that compresses the tank evaporation gas discharged from the storage tank; a first cooler that cools the compressed tank evaporation gas by heat exchange with a predetermined refrigerant; a first expansion valve that further cools the cooled tank evaporation gas by pressure drop; and a first gas-liquid separator that gas-liquid separates the further cooled tank evaporation gas into re-liquefied carbon dioxide and the first evaporation gas.

[0013] The second re-liquefaction device may include a second compressor that compresses the first evaporation gas supplied from the first composition detection device; a second cooler that cools the compressed first evaporation gas by heat exchange with a predetermined refrigerant; a second expansion valve that further cools the cooled first evaporation gas by pressure drop; and a second gas-liquid separator that gas-liquid separates the further cooled first evaporation gas into re-liquefied carbon dioxide and second evaporation gas.

[0014] The above post-processing device may be composed of a combustor that combusts the first evaporated gas, or a fuel cell that generates electric energy using the first evaporated gas as fuel.

[0015] According to one embodiment of the present invention for achieving the above-described other task, a liquefied carbon dioxide storage device includes a storage tank for storing liquefied carbon dioxide; and the evaporation gas treatment system for treating tank evaporation gas discharged from the storage tank.

[0016] At a given pressure, the liquefaction temperature of a combustible impurity may be lower than that of carbon dioxide.

[0017] A second composition detection device for measuring a second concentration of combustible impurities contained in the second evaporation gas remaining after re-liquefaction by the second re-liquefaction device; and a third re-liquefaction device for receiving the second evaporation gas from the second composition detection device, re-liquefying it, and returning it to the storage tank when the second concentration is below a predetermined threshold value. When the second concentration is above a predetermined threshold value, the post-processing device may receive the second evaporation gas from the second composition detection device and perform post-processing for recycling combustible impurities.

[0018] Specific details of other embodiments are included in the specific contents and drawings.

[0019] As described above, according to the liquefied carbon dioxide vaporization gas treatment system and the liquefied carbon dioxide storage device including the same, the vaporization gas of the liquefied carbon dioxide is not released into the atmosphere as is, but a re-liquefaction process is repeatedly performed on the vaporization gas to increase the concentration or purity of combustible impurities in the vaporization gas, so that it can be recycled in a post-treatment device.

[0020] For example, if the concentration of combustible impurities exceeds a threshold value after repeated re-liquefaction processes, the combustible impurities may be transferred to a combustor and combusted, and the waste heat may be recycled to surrounding facilities or equipment within the storage device (transport device or carrier), or the combustor may be configured as part of the engine of the storage device (transport device or carrier), and the combustible impurities may be used as propulsion fuel for the storage device (transport device or carrier).

[0021] Or, for example, if the concentration of combustible impurities exceeds a threshold value after repeated re-liquefaction processes, the combustible impurities can be transferred to the fuel cell, which can then use the fuel to generate electrical energy.

[0022] Figure 1 illustrates a configuration diagram of a liquefied carbon dioxide storage device according to one embodiment of the present invention.

[0023] Figure 2 shows a process flow diagram of the liquefied carbon dioxide storage device of Figure 1.

[0024] The advantages and features of the present invention, and the methods for achieving them, will become clearer with reference to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals designate like elements throughout the specification.

[0025]

[0026] In the present invention, the storage device includes any device having a liquefied carbon dioxide storage tank and capable of being transported via land or sea routes, or any onshore storage facility that stores liquefied carbon dioxide. Preferably, the storage device according to one embodiment of the present invention may be a transport device or a ship. In the present invention, the ship may include not only a ship with self-propulsion capability, but also a marine structure that floats on the sea but does not have propulsion capability. The ship according to one embodiment of the present invention may be, for example, a liquefied carbon dioxide carrier (LCO2carrier). However, the present invention is not limited thereto, and the embodiments described below may be equally applied to any ship having a liquefied carbon dioxide storage tank.

[0027]

[0028] Hereinafter, with reference to FIGS. 1 and 2, a liquefied carbon dioxide evaporation gas processing system and a liquefied carbon dioxide storage device including the same according to one embodiment of the present invention will be described. FIG. 1 illustrates a configuration diagram of a liquefied carbon dioxide storage device according to one embodiment of the present invention. FIG. 2 illustrates a process flow diagram of the liquefied carbon dioxide storage device of FIG. 1.

[0029] A liquefied carbon dioxide storage device (10) according to one embodiment of the present invention includes a storage tank (100) for storing liquefied carbon dioxide, a vaporization gas treatment system (20) for treating vaporization gas discharged from the storage tank (100), and an engine (not shown) including at least one of a propulsion engine and a power generation engine of the storage device.

[0030] The evaporation gas treatment system (20) includes a re-liquefaction device assembly (200) that re-liquefies the tank evaporation gas discharged from the storage tank (100) and returns it to the storage tank (100), a composition detection device assembly (300) that measures the concentration of combustible impurities contained in the evaporation gas remaining after the re-liquefaction treatment by the re-liquefaction device assembly (200) to determine whether additional re-liquefaction is required, and a post-treatment device (400) that receives the evaporation gas from the composition detection device assembly (300) and performs post-treatment when the concentration of combustible impurities in the evaporation gas is higher than a threshold value.

[0031] The re-liquefaction device assembly (200) includes one or more re-liquefaction devices (210, 220, 230, ...) that are sequentially connected in series from the storage tank (100). The composition detection device assembly (300) includes one or more composition detection devices (310, 320, ...) that connect two adjacent re-liquefaction devices (210, 220, 230, ...). For example, when the re-liquefaction device assembly (200) is composed of N re-liquefaction devices, the composition detection device assembly (300) may be composed of (N-1) composition detection devices (N is an integer greater than or equal to 2). In this embodiment, for the convenience of explanation, the re-liquefaction device assembly (200) is described as an example in which the re-liquefaction device assembly (200) is composed of three re-liquefaction devices (210, 220, 230) and the composition detection device assembly (300) is composed of two composition detection devices (310, 320), but the present invention is not limited thereto.

[0032] A vaporization gas treatment system (20) according to one embodiment of the present invention includes a first re-liquefaction device (210), a first composition detection device (310), a second re-liquefaction device (220), and a post-treatment device (400). Additionally, the vaporization gas treatment system (20) may further include a second composition detection device (320) and a third re-liquefaction device (230).

[0033] The first re-liquefaction device (210) re-liquefies the tank evaporation gas discharged from the storage tank (100) storing liquefied carbon dioxide and returns it to the storage tank (100). Specifically, the first re-liquefaction device (210) includes a first compressor (212), a first cooler (214), a first expansion valve (216), and a first gas-liquid separator (218) that are sequentially connected in series.

[0034] The first compressor (212) compresses the tank evaporation gas discharged from the storage tank (100). The first cooler (214) cools the tank evaporation gas compressed by the first compressor (212) through heat exchange with a predetermined refrigerant. The first expansion valve (216) further cools the tank evaporation gas cooled by the first cooler (214) through pressure drop. The first gas-liquid separator (218) gas-liquid separates the tank evaporation gas further cooled by the first expansion valve (216) into re-liquefied carbon dioxide and the first evaporation gas.

[0035] Accordingly, when liquefied carbon dioxide is stored in the storage tank (100) along the supply line (GL1), the tank boil-off gas discharged from the storage tank (100) flows along the first flow line (GL2), is compressed by the first compressor (212), and is cooled by the first cooler (214). Then, the tank boil-off gas expands while passing through the narrow valve hole of the first expansion valve (216), the pressure drops, and is further cooled. The further cooled tank boil-off gas is separated into liquid-state re-liquefied carbon dioxide and gas-state first boil-off gas by the first gas-liquid separator (218). The re-liquefied carbon dioxide is recovered to the storage tank (100) along the first recovery line (GL4), and the first boil-off gas is transferred to the first composition detection device (310) along the first inspection line (GL3).

[0036] The first composition detection device (310) measures the first concentration of combustible impurities contained in the first evaporated gas remaining after re-liquefaction by the first re-liquefaction device (210). Here, the combustible impurities may be composed of hydrogen, methane, or a combination thereof.

[0037] If the first concentration is below a predetermined threshold, the first evaporation gas is transferred to the second re-liquefaction device (220) along the second flow line (GL6) and an additional re-liquefaction process is performed. If the first concentration is above a predetermined threshold, the first evaporation gas is transferred to the post-processing device (400) along the first collection line (GL5) and a post-processing process for recycling is performed without an additional re-liquefaction process.

[0038] Here, the threshold value determining the transport path of the first evaporation gas may be 40 mol%, which is the concentration of combustible impurities in the first evaporation gas. If the threshold value is less than 40 mol%, the concentration or purity of combustible impurities may be low, making it difficult to recycle them. If the threshold value is greater than 40 mol%, the concentration or purity of combustible impurities may be high, posing a risk of explosion during the additional reliquefaction process.

[0039] The post-processing device (400) receives the first evaporation gas from the first composition detection device (310) when the first concentration is equal to or higher than a predetermined threshold value and performs post-processing for recycling combustible impurities. The post-processing device (400) may be composed of a combustor (410) that combusts the first evaporation gas or the combustible impurities contained therein. Alternatively, the post-processing device (400) may be composed of a fuel cell (420) that uses the first evaporation gas or the combustible impurities contained therein as fuel to generate electrical energy. In this embodiment, a combustor or a fuel cell is mentioned as an example of the post-processing device (400), but the present invention is not limited thereto. That is, the post-processing device (400) may be composed of a combustor front end for transporting combustible impurities to the combustor, or a fuel supply unit for supplying combustible impurities as fuel to the fuel cell.

[0040] The second re-liquefaction device (220) receives the first evaporated gas from the first composition detection device (310) when the first concentration is below a predetermined threshold value, re-liquefies it, and returns it to the storage tank. The second re-liquefaction device (220) may have substantially the same configuration as the first re-liquefaction device (210). Specifically, the second re-liquefaction device (220) includes a second compressor (222), a second cooler (224), a second expansion valve (226), and a second gas-liquid separator (228) that are sequentially connected in series.

[0041] The second compressor (222) compresses the first evaporation gas supplied from the first composition detection device (310). The second cooler (224) cools the first evaporation gas compressed by the second compressor (222) through heat exchange with a predetermined refrigerant. The second expansion valve (226) further cools the first evaporation gas cooled by the second cooler (224) through pressure drop. The second gas-liquid separator (228) gas-liquid separates the first evaporation gas further cooled by the second expansion valve (226) into re-liquefied carbon dioxide and the second evaporation gas.

[0042] Accordingly, the first evaporation gas transferred from the first composition detection device (310) flows along the second flow line (GL6), is compressed by the second compressor (222), and is cooled by the second cooler (224). Then, the first evaporation gas expands while passing through the narrow valve hole of the second expansion valve (226), the pressure drops, and is further cooled. The further cooled first evaporation gas is separated into liquid-state re-liquefied carbon dioxide and gas-state second evaporation gas by the second gas-liquid separator (228). The re-liquefied carbon dioxide is recovered to the storage tank (100) along the second recovery line (GL8), and the second evaporation gas is transferred to the second composition detection device (320) along the second inspection line (GL7).

[0043] The second concentration of combustible impurities contained in the second boil-off gas remaining after re-liquefaction by the second re-liquefaction device (220) may be greater than the first concentration of combustible impurities contained in the first boil-off gas remaining after re-liquefaction by the first re-liquefaction device (210). This is because the liquefaction temperature of combustible impurities (e.g., hydrogen = -252.7 degrees, methane = -162 degrees) is much lower than the liquefaction temperature of carbon dioxide (-78.5 degrees, atmospheric pressure), and thus the concentration or fraction of combustible impurities remaining in a gaseous state increases during repeated re-liquefaction. Therefore, it is preferable that the liquefaction temperature of combustible impurities be lower than the liquefaction temperature of carbon dioxide at a given pressure.

[0044] The second composition detection device (320) measures the second concentration of combustible impurities contained in the second evaporated gas remaining after re-liquefaction by the second re-liquefaction device (220). The second composition detection device (320) may have substantially the same configuration as the first composition detection device (310).

[0045] If the second concentration is less than a predetermined threshold, the second boil-off gas is transferred to the third re-liquefaction device (230) along the third flow line (GL10) and an additional re-liquefaction process is performed. The third re-liquefaction device (230) may have substantially the same configuration as the second re-liquefaction device (220). When the second concentration is less than a predetermined threshold, the third re-liquefaction device (230) receives the second boil-off gas from the second composition detection device (320), re-liquefies it, and returns it to the storage tank (100).

[0046] If the second concentration is higher than a predetermined threshold, the second evaporation gas is transferred to the post-processing device (400) along the second collection line (GL9), and the post-processing device (400) receives the second evaporation gas from the second composition detection device (320) and performs post-processing for recycling combustible impurities without an additional re-liquefaction process.

[0047]

[0048] Table 1 below shows the temperature, pressure, and component contents of the main lines in the process flow diagram of Fig. 2 using the Aspen HYSYS simulator from ApenTech (Bedford, MA, USA).

[0049] Temperature (℃)Pressure (bar)CO2 content (mole fraction)H2 content (mole fraction)Supply line (GL1) - 55.0080.99000.0100First flow line (GL2) - 52.3280.76780.2322First inspection line (GL3) - 55.7080.67080.3292First recovery line (GL4) - 55.7080.99820.0008Second inspection line (GL7) - 59.3380.57570.4243Second recovery line (GL8) - 59.3380.99900.0010Post-treatment device - 59.3380.57570.4243

[0050] As shown in Table 1, when 1 mol% of hydrogen, which is a combustible impurity, is present in the liquefied carbon dioxide stored in the storage tank (100) through the supply line (GL1), about 33 mol% of hydrogen is present in the first boil-off gas flowing along the first inspection line (GL3) after re-liquefaction through the first re-liquefaction device (210). In this case, since the hydrogen concentration in the first boil-off gas is less than the threshold value, about 42 mol% of hydrogen is present in the second boil-off gas flowing along the second inspection line (GL7) after re-liquefaction through the second re-liquefaction device (220). Therefore, since the hydrogen concentration in the second boil-off gas is greater than the threshold value, the second boil-off gas is transferred to the post-processing device (400).

[0051]

[0052] Although the embodiments of the present invention have been described with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

Claims

1. A first re-liquefaction device that re-liquefies tank evaporation gas discharged from a storage tank storing liquefied carbon dioxide and returns it to the storage tank; A first composition detection device that measures a first concentration of combustible impurities contained in the first evaporated gas remaining after re-liquefaction by the first re-liquefaction device; A second re-liquefaction device that receives the first evaporated gas from the first composition detection device, re-liquefies it, and returns it to the storage tank when the first concentration is below a predetermined threshold; and A liquefied carbon dioxide evaporation gas treatment system including a post-processing device that receives the first evaporation gas from the first composition detection device and performs post-processing for recycling combustible impurities when the first concentration is above a predetermined threshold value.

2. In paragraph 1, A liquefied carbon dioxide evaporation gas treatment system, characterized in that the second concentration of combustible impurities contained in the second evaporation gas remaining after re-liquefaction by the second re-liquefaction device is greater than the first concentration of combustible impurities contained in the first evaporation gas.

3. In paragraph 1, A liquefied carbon dioxide vaporization gas treatment system, characterized in that the above combustible impurities are hydrogen, methane or a combination thereof.

4. In paragraph 1, A liquefied carbon dioxide evaporation gas treatment system, characterized in that the threshold value is 40 mol% as the concentration of combustible impurities in the first evaporation gas.

5. In paragraph 1, The first re-liquefaction device includes a first compressor for compressing the tank evaporation gas discharged from the storage tank; a first cooler for cooling the compressed tank evaporation gas by heat exchange with a predetermined refrigerant; a first expansion valve for further cooling the cooled tank evaporation gas by pressure drop; and a first gas-liquid separator for gas-liquid separating the further cooled tank evaporation gas into re-liquefied carbon dioxide and the first evaporation gas. A liquefied carbon dioxide evaporation gas treatment system, wherein the second re-liquefaction device comprises: a second compressor for compressing the first evaporation gas supplied from the first composition detection device; a second cooler for cooling the compressed first evaporation gas by heat exchange with a predetermined refrigerant; a second expansion valve for further cooling the cooled first evaporation gas by pressure drop; and a second gas-liquid separator for gas-liquid separating the further cooled first evaporation gas into re-liquefied carbon dioxide and second evaporation gas.

6. In paragraph 1, A liquefied carbon dioxide evaporation gas treatment system, characterized in that the above post-processing device comprises a combustor that combusts the first evaporation gas or a fuel cell that generates electric energy using the first evaporation gas as fuel.

7. A storage tank for storing liquefied carbon dioxide; and A liquefied carbon dioxide storage device comprising an evaporation gas treatment system according to claim 1 for treating tank evaporation gas discharged from the storage tank.

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