Carbon dioxide capture systems, carbon dioxide capture methods

Abstract

This invention provides a carbon dioxide recovery system and method that solidifies carbon dioxide into dry ice and then smoothly liquefies and recovers the solidified dry ice without relying on a scraping mechanism. [Solution] The carbon dioxide recovery system 1 according to the present invention comprises a tube 10a through which a refrigerant passes, a shell 10b adjacent to the tube 10a via a heat transfer wall through which a carbon dioxide-containing gas passes, a carbon dioxide solidification device 10 for solidifying carbon dioxide inside the shell 10b, a carbon dioxide-containing gas supply line 75 for supplying carbon dioxide-containing gas to the shell 10b, a refrigerant supply line 71 for supplying refrigerant to the tube 10a, a liquefied carbon dioxide return line 85 and a liquefied carbon dioxide supply line 87 for circulating and supplying liquefied carbon dioxide to the shell 10b, and a liquefied carbon dioxide heater 40 disposed in the liquefied carbon dioxide supply line 87 for heating the liquefied carbon dioxide flowing through the liquefied carbon dioxide supply line 87.

Description

Technical Field

[0001] The present invention relates to a carbon dioxide recovery system and a carbon dioxide recovery method for solidifying carbon dioxide from a carbon dioxide-containing gas into dry ice and liquefying and recovering the dry ice-formed carbon dioxide.

Background Art

[0002] From the perspective of preventing global warming, technologies for separating and recovering carbon dioxide from the combustion exhaust gas of fossil fuels have been developed to prevent the emission of carbon dioxide into the atmosphere. As an example, there is an amine recovery method that uses an amine-based absorbent such as an aqueous alkanolamine solution. However, in the amine recovery method, the thermal energy input when desorbing carbon dioxide has been a problem, so there is a need for a technology that can separate and recover carbon dioxide with lower energy.

[0003] In this regard, Patent Document 1 discloses a technique for recovering carbon dioxide by flowing a refrigerant inside a plurality of cylindrical heat transfer tubes, flowing a carbon dioxide-containing gas outside, scraping dry ice formed on the outside of the heat transfer tubes, and ejecting a gas onto the scraped dry ice.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the Mohs hardness of dry ice is 2, and it is difficult to constantly scrape off the hard dry ice that has grown as crystals on the surface of the intricate heat transfer tubes with a mechanical mechanism. Furthermore, while the transport of liquefied carbon dioxide by tankers and other means has been proposed as a means of transporting large quantities of recovered carbon dioxide, there are currently no practical proposals for how to continuously transition between the low-pressure environment of dry ice production and the pressure environment of liquefied carbon dioxide at least 0.42 MPaG.

[0006] The present invention was made to solve the above problems, and aims to provide a carbon dioxide recovery system and method that solidifies carbon dioxide in a carbon dioxide-containing gas into dry ice, and then smoothly liquefies and recovers the solidified dry ice without relying on a scraping mechanism. [Means for solving the problem]

[0007] (1) The carbon dioxide recovery system according to the present invention comprises a refrigerant passage section through which a refrigerant at a temperature lower than the carbon dioxide solidification temperature passes, and a gas passage section adjacent to the refrigerant passage section via a heat transfer wall, through which a carbon dioxide-containing gas passes, and a carbon dioxide solidification device that uses the cold energy of the refrigerant to solidify the carbon dioxide contained in the carbon dioxide-containing gas within the gas passage section by heat exchange with the carbon dioxide-containing gas. A carbon dioxide-containing gas supply line is configured with a means for switching between supplying carbon dioxide-containing gas to the gas passage section and stopping the supply, The excess gas containing carbon dioxide supplied to the gas passage that did not solidify is discharged from the gas passage into an excess gas discharge line, which is configured with a switching mechanism for switching between a discharge state and a discharge stop state. A refrigerant supply line is configured with a means for switching between supplying refrigerant to the refrigerant passage and stopping the supply, A refrigerant discharge line is configured to include a means for switching between a refrigerant discharge state and a discharge stop state from the refrigerant passage section, A liquefied carbon dioxide circulation line is connected to the gas passage section and circulates and supplies liquefied carbon dioxide to the gas passage section, The invention is characterized by having a liquefied carbon dioxide heater installed in the liquefied carbon dioxide circulation line, which heats the liquefied carbon dioxide flowing through the liquefied carbon dioxide circulation line.

[0008] (2) The device described in (1) above is characterized by having a refrigerant drain line that communicates with the refrigerant passage section and discharges the refrigerant from the refrigerant passage section.

[0009] (3) In addition, in the device described in (2) above, a refrigerant gas circulation line that communicates with the refrigerant passage section and circulates and supplies a refrigerant in a gaseous or supercritical state to the refrigerant passage section, The invention is characterized by having a refrigerant gas circulation blower, which is disposed in the refrigerant gas circulation line and circulates the refrigerant flowing through the refrigerant gas circulation line in a gaseous or supercritical state.

[0010] (4) The present invention also has a plurality of carbon dioxide capture systems as described in any one of the above paragraphs (1) to (3), and is characterized by having a gas passage communication line configured with a means for switching between a connected state and a disconnected state between the gas passages of each carbon dioxide capture system.

[0011] (5) The carbon dioxide recovery method according to the present invention is a carbon dioxide solidification device comprising a refrigerant passage section through which a refrigerant at a temperature lower than the carbon dioxide solidification temperature passes, and a gas passage section arranged adjacent to the refrigerant passage section via a heat transfer wall, through which a carbon dioxide-containing gas passes, wherein the carbon dioxide contained in the carbon dioxide-containing gas is solidified in the gas passage section by utilizing the cold energy of the refrigerant through heat exchange with the carbon dioxide-containing gas. A carbon dioxide solidification step is performed by using the cold energy of the refrigerant to solidify the carbon dioxide contained in the carbon dioxide-containing gas within the gas passage section through heat exchange with the carbon dioxide-containing gas. The invention is characterized by having a dry ice melting step, in which liquefied carbon dioxide is circulated and supplied to the gas passage to melt the solidified carbon dioxide.

[0012] (6) Furthermore, the apparatus described in (5) above is characterized in that it has a refrigerant drain step for discharging the refrigerant in the refrigerant passage section after the carbon dioxide solidification step and before the dry ice melting step.

[0013] (7) The device described in (6) above is characterized in that, after the refrigerant draining process, it has a refrigerant gas circulation process in which a refrigerant in a gaseous or supercritical state is circulated and supplied to the refrigerant passage section.

[0014] (8) In addition, in any of the above (5) to (7), a plurality of carbon dioxide solidification devices are installed, and a carbon dioxide solidification chamber equalization step is provided between the carbon dioxide solidification step and the dry ice melting step in one carbon dioxide solidification device, which connects the gas passages of each carbon dioxide solidification device after the dry ice melting step in another carbon dioxide solidification device and before the next carbon dioxide solidification step. [Effects of the Invention]

[0015] According to the present invention, carbon dioxide in a carbon dioxide-containing gas can be solidified into dry ice, and the solidified dry ice can be smoothly liquefied and recovered without relying on a scraping mechanism. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram showing a carbon dioxide capture system according to Embodiment 1 of the present invention. [Figure 2] Figure 1 is an explanatory diagram of the operation of the carbon dioxide capture system (part 1). [Figure 3] Figure 1 is a diagram illustrating the operation of the carbon dioxide capture system (part 2). [Figure 4] Figure 1 is an explanatory diagram of the operation of the carbon dioxide capture system (part 3). [Figure 5] Figure 1 is an explanatory diagram of the operation of the carbon dioxide capture system (part 4). [Figure 6]In the carbon dioxide recovery system according to Embodiment 1, it is an explanatory diagram (Part 1) when equalizing pressure with another series of carbon dioxide recovery systems. [Figure 7] In the carbon dioxide recovery system according to Embodiment 1, it is an explanatory diagram (Part 2) when equalizing pressure with another series of carbon dioxide recovery systems. [Figure 8] It is a schematic diagram showing the carbon dioxide recovery system according to Embodiment 2 of the present invention. [Figure 9] It is a schematic diagram showing the carbon dioxide recovery system according to Embodiment 3 of the present invention. [Figure 10] It is a schematic diagram showing the carbon dioxide recovery system according to Embodiment 4 of the present invention.

Embodiments for Carrying out the Invention

[0017] [Embodiment 1] The carbon dioxide recovery system according to the present embodiment uses, as a carbon dioxide solidification device, a tube through which a refrigerant colder than the solidification temperature of carbon dioxide passes, and a shell that houses the tube and through which a carbon dioxide-containing gas passes. By passing LNG, which is a refrigerant, on the tube side and passing a carbon dioxide-containing gas on the shell side, carbon dioxide contained in the carbon dioxide-containing gas is solidified in the shell. An explanation will be given by taking a so-called shell & tube type heat exchanger as an example.

[0018] First, referring to FIG. 1, the configuration and function of Embodiment 1 of the present invention will be described. The carbon dioxide recovery system 1 according to Embodiment 1 of the present invention has, as main constituent devices, a carbon dioxide solidification device 10, a dry ice melting tank 20, a liquefied carbon dioxide circulation pump 30, and a liquefied carbon dioxide heater 40.

[0019] <Carbon Dioxide Solidification Device> The carbon dioxide solidification device 10 is a shell-and-tube type heat exchanger, having an upper channel chamber 10c and a lower channel chamber 10d where LNG, which is a refrigerant, is temporarily stored, and a shell 10b is provided between them as a gas passage through which carbon dioxide-containing gas passes. Multiple tubes 10a are provided between the upper channel chamber 10c and the lower channel chamber 10d, passing through the shell 10b. The upper channel chamber 10c, the lower channel chamber 10d, and the tubes 10a constitute the refrigerant passage section of the present invention.

[0020] A refrigerant supply line 71, which supplies LNG as a refrigerant, is connected to the lower channel chamber 10d, and a refrigerant supply valve 72 is provided in the refrigerant supply line 71 for supplying and stopping the refrigerant. Furthermore, a refrigerant discharge line 73 for discharging refrigerant is connected to the upper channel chamber 10c, and a refrigerant discharge valve 74 for discharging and stopping the refrigerant discharge is provided in the refrigerant discharge line 73.

[0021] A carbon dioxide-containing gas supply line 75 is connected to the lower part of the shell 10b for supplying carbon dioxide-containing gas, and a carbon dioxide-containing gas supply valve 76 is provided in the carbon dioxide-containing gas supply line 75 for supplying and stopping the carbon dioxide-containing gas. Furthermore, an excess gas discharge line 77 is provided at the top of the shell 10b to discharge excess gas that has not solidified inside the shell 10b, and an excess gas discharge valve 78 is provided in the excess gas discharge line 77 to discharge and stop the discharge of excess gas.

[0022] <Dry ice melting tank> The dry ice melting tank 20 is a metal container that temporarily stores liquefied carbon dioxide or a slurry of liquefied carbon dioxide containing dry ice, and melts the dry ice.

[0023] A liquefied carbon dioxide supply line 87 is connected to the bottom of the dry ice melting tank 20 to supply liquefied carbon dioxide to the bottom of the carbon dioxide solidification device shell 10b. Furthermore, a liquefied carbon dioxide discharge line 89 is provided, branching off from the liquefied carbon dioxide supply line 87, for discharging the liquefied carbon dioxide from the dry ice melting tank 20 to the outside.

[0024] The liquefied carbon dioxide supply line 87 is equipped with a liquefied carbon dioxide circulation pump 30 for pressurizing the liquefied carbon dioxide supplied from the dry ice melting tank 20, a liquefied carbon dioxide heater 40 for heating the liquefied carbon dioxide using the heat of a heat transfer medium supplied from an external source, and a liquefied carbon dioxide supply valve 88. Furthermore, a liquefied carbon dioxide drain line 90 is provided, with one end connected to a liquefied carbon dioxide supply line 87 and the other end connected to a dry ice melting tank 20, for returning the liquefied carbon dioxide in the shell 10b to the dry ice melting tank 20 as drain. A liquefied carbon dioxide drain valve 91 is provided in the liquefied carbon dioxide drain line 90. As described above, because it is necessary to return the liquefied carbon dioxide in the shell 10b to the dry ice melting tank 20 as drain, the dry ice melting tank 20 is installed such that its highest liquid level is lower than the lowest part of the shell 10b of the carbon dioxide solidification device 10.

[0025] A liquefied carbon dioxide return line 85 is provided at the top of the dry ice melting tank 20 to return the liquefied carbon dioxide that has passed through the shell 10b back to the dry ice melting tank 20, and a liquefied carbon dioxide discharge valve 86 is provided in the liquefied carbon dioxide return line 85. The liquefied carbon dioxide supply line 87 and the liquefied carbon dioxide return line 85 constitute the liquefied carbon dioxide circulation line of the present invention. Upstream of the liquefied carbon dioxide discharge valve 86 in the liquefied carbon dioxide return line 85, i.e., on the shell 10b side, a pressure equalization line 93 is connected to equalize the pressure inside the shell 10b, and a pressure equalization valve 92 is provided in the pressure equalization line 93.

[0026] <Liquefied carbon dioxide circulation pump> The liquefied carbon dioxide circulation pump 30 is a centrifugal pump that pressurizes the liquefied carbon dioxide supplied from the dry ice melting tank 20 and supplies it to the liquefied carbon dioxide heater 40.

[0027] <Liquefied carbon dioxide heater> The liquefied carbon dioxide heater 40 is a shell-and-tube type heat exchanger that uses the heat from an externally supplied heat transfer medium to heat the liquefied carbon dioxide supplied from the liquefied carbon dioxide circulation pump 30 and discharge it to the carbon dioxide solidification device 10.

[0028] Next, the operation of the carbon dioxide capture system 1 according to this embodiment will be explained based on Figures 2 to 5. In Figures 2 to 6, lines through which fluid is flowing are indicated by thick lines. Valves are shown in white when open and in black when closed.

[0029] <Carbon dioxide solidification process> As shown in Figure 2, LNG is supplied to the carbon dioxide solidification device 10 from the refrigerant supply line 71, and carbon dioxide-containing gas is supplied to the carbon dioxide solidification device 10 from the carbon dioxide-containing gas supply line 75. The LNG is assumed to be 100% methane, at a pressure of 1 MPaG, and at a temperature of -155°C. The carbon dioxide-containing gas is assumed to be 40% nitrogen, 10% oxygen, and 50% carbon dioxide, at a pressure of 30 kPaG, and at a temperature of 20°C.

[0030] The LNG supplied to the carbon dioxide solidification device 10 flows from the lower channel chamber 10d through the tube 10a towards the upper channel chamber 10c. In tube 10a, heat exchange takes place between the LNG and the carbon dioxide-containing gas flowing through shell 10b. The LNG evaporates, transferring sensible heat and latent heat of vaporization to the carbon dioxide-containing gas, and the carbon dioxide-containing gas is cooled to a temperature below -80°C. During this process, the carbon dioxide contained in the carbon dioxide-containing gas solidifies and grows as crystals on the outer surface of tube 10a.

[0031] Low-temperature gas (NG) is discharged to the outside through the refrigerant discharge line 73. In addition, the low-temperature excess gas containing carbon dioxide, which has decreased due to solidification, is discharged to the outside through the excess gas discharge line 77.

[0032] The carbon dioxide recovery system 1 stops the supply of LNG and carbon dioxide-containing gas to the carbon dioxide solidification device 10 by closing the refrigerant supply valve 72, the carbon dioxide-containing gas supply valve 76, and the excess gas discharge valve 78.

[0033] <Dry ice melting process> As shown in Figure 3, the carbon dioxide recovery system 1 opens the liquefied carbon dioxide supply valve 88 and the liquefied carbon dioxide discharge valve 86 and operates the liquefied carbon dioxide circulation pump 30 to increase the pressure of liquefied carbon dioxide stored in the dry ice melting tank 20, for example, at -50°C and 0.6 MPaG, to for example, 1.2 MPaG, and supplies it to the liquefied carbon dioxide heater 40.

[0034] The liquefied carbon dioxide supplied to the liquefied carbon dioxide heater 40 is heated to, for example, -40°C through heat exchange with a heat transfer medium supplied from the outside, and then supplied to the shell 10b of the carbon dioxide solidification device 10.

[0035] The liquefied carbon dioxide supplied to the shell 10b flows through the shell 10b, partially melting and detaching the dry ice adhering to the surface of the tube 10a, and is returned to the dry ice melting tank 20 via the liquefied carbon dioxide return line 85. At this time, the liquefied carbon dioxide is reduced in pressure at the liquefied carbon dioxide discharge valve 86 to the same pressure as that of the dry ice melting tank 20. The liquefied carbon dioxide is also cooled by the dry ice, tube 10a, and the LNG remaining in tube 10a, but a sufficient flow rate is selected to prevent the liquefied carbon dioxide from solidifying and causing blockage.

[0036] When liquefied carbon dioxide is supplied to the shell 10b at a sufficient flow rate, not only does the dry ice melt and detach, but the LNG remaining in the tube 10a is heated and evaporated.

[0037] The carbon dioxide recovery system 1 stops supplying liquefied carbon dioxide to the carbon dioxide solidification device 10 by stopping the operation of the liquefied carbon dioxide circulation pump 30.

[0038] <Liquefied carbon dioxide drain process> As shown in Figure 4, the carbon dioxide recovery system 1 opens the liquefied carbon dioxide drain valve 91 to extract the liquefied carbon dioxide filled in the shell 10b of the carbon dioxide solidification device 10 into the dry ice melting tank 20. At the same time, carbon dioxide gas from the gas layer of the dry ice melting tank 20 is supplied to the shell 10b of the carbon dioxide solidification device 10 from the liquefied carbon dioxide return line 85, thereby replacing the liquefied carbon dioxide inside the shell 10b with carbon dioxide gas.

[0039] At this point, the internal pressure of the shell 10b is equivalent to that of the dry ice melting tank 20, which is unnecessarily high for starting the supply of carbon dioxide-containing gas to the carbon dioxide solidification device 10. Therefore, it is preferable to perform a process to reduce the internal pressure of the shell 10b. This process may include, for example, reducing the pressure by connecting it to another container or by releasing it into the atmosphere.

[0040] <Carbon dioxide solidification chamber pressure equalization process> Furthermore, as another way to reduce the internal pressure of the shell 10b, as shown in Figure 5, a pressure equalization line 93 and a pressure equalization valve 92 are provided in communication with the shell 10b, and pressure equalization is performed between the shell 10b-1 in the low-pressure state of another carbon dioxide solidification device 10-1 system, as shown in Figure 6.

[0041] Specifically, as shown in Figure 6, the carbon dioxide recovery system 1 closes the liquefied carbon dioxide supply valve 88, the liquefied carbon dioxide discharge valve 86, and the liquefied carbon dioxide drain valve 91. Furthermore, the carbon dioxide recovery system 1 opens the pressure equalization valve 92, thereby equalizing the pressure inside the shell 10b-1, which is at a low pressure equivalent to that of the carbon dioxide-containing gas, just before the dry ice melting operation of the carbon dioxide solidification device 10-1 of the other system begins, and thereby lowering the pressure inside the shell 10b.

[0042] Subsequently, the carbon dioxide recovery system 1 closes the pressure equalization valve 92, opens the refrigerant supply valve 72 to resume the supply of LNG to the carbon dioxide solidification device 10, and opens the carbon dioxide-containing gas supply valve 76 and the excess gas discharge valve 78 to resume the supply of carbon dioxide-containing gas to the carbon dioxide solidification device 10.

[0043] According to the carbon dioxide recovery system 1 of this embodiment, after carbon dioxide solidifies inside the carbon dioxide solidification device 10, the dry ice is liquefied by the flow of liquefied carbon dioxide while melting and separating it. Therefore, solid carbon dioxide can be liquefied and recovered without relying on a mechanical mechanism.

[0044] Furthermore, according to the carbon dioxide capture system 1 of this embodiment, the cold energy of LNG can be effectively utilized for solidifying carbon dioxide, thus reducing the amount of cold energy of LNG that was previously discarded into the environment. For example, LNG vaporizers that use seawater as a heating medium discarded the cold energy of LNG into the ocean, but since the amount can be reduced, the impact on the ocean can be reduced.

[0045] Furthermore, according to the carbon dioxide recovery system 1 of this embodiment, the volume of the gas is drastically reduced by solidifying the carbon dioxide in the carbon dioxide solidification device 10, thereby allowing carbon dioxide to be drawn in from upstream. This also reduces the power required for a booster device, such as a blower, when one is installed upstream.

[0046] In this embodiment, the carbon dioxide solidification apparatus 10 was described as having a configuration in which carbon dioxide-containing gas or liquefied carbon dioxide flows on the shell side and LNG, which is the refrigerant, flows on the tube side. However, it may also be configured so that LNG flows on the shell side and carbon dioxide-containing gas or liquefied carbon dioxide flows on the tube side.

[0047] Furthermore, although this embodiment has been described as having a liquefied carbon dioxide heater 40 downstream of the dry ice melting tank 20, the dry ice melting tank 20 may also function as a heat exchanger.

[0048] Furthermore, although the types of heat transfer fluids and refrigerants, as well as the types of pumps, valves, heat exchangers, and containers, have been specified and described in this embodiment, the types can be appropriately selected within the scope of the design.

[0049] Furthermore, the above explanation states that the carbon dioxide solidification chamber pressure equalization process is performed between shell 10b after the liquefied carbon dioxide drain process and shell 10b-1 immediately before the dry ice melting operation in the other carbon dioxide solidification device 10-1 system begins. This is because the internal pressure of shell 10b after the liquefied carbon dioxide drain process is unnecessarily high, and although the pressure of shell 10b-1 is low just before the dry ice melting operation begins, it is not a problem if this pressure rises to the pressure inside the dry ice melting tank 20.

[0050] To summarize the process in the dry ice recovery method, excluding the carbon dioxide solidification chamber pressure equalization step, The process is as follows: carbon dioxide solidification process (Process A) → dry ice melting process (Process B) → liquefied carbon dioxide drain process (Process C) → carbon dioxide solidification process (Process A)... Furthermore, the pressure in the shell, which is the carbon dioxide solidification chamber, is low between process A and process B, and high between process C and process A. Therefore, the carbon dioxide solidification chamber pressure equalization process should be performed between the shell located between process A and process B, and between the shell located between process C and process A. In other words, within the series of steps of the dry ice recovery method, it is preferable to include a carbon dioxide solidification chamber pressure equalization step between the carbon dioxide solidification step (Step A) and the dry ice melting step (Step B), and between the liquefied carbon dioxide drain step (Step C) and the carbon dioxide solidification step (Step A).

[0051] Furthermore, by inserting a carbon dioxide solidification chamber pressure equalization process between the carbon dioxide solidification process (Process A) and the dry ice melting process (Process B), the pressure inside the shell can be increased in a short time. Therefore, the time required for the pressure inside the shell to rise due to heat input, etc., to reach the pressure necessary for circulating liquefied carbon dioxide in the next process can be minimized. Alternatively, by increasing the pressure inside the shell through pressure equalization, the risk of liquefied carbon dioxide flashing and solidifying, thereby hindering flow, can be minimized when circulating the liquefied carbon dioxide.

[0052] The above explanation assumes that a liquefied carbon dioxide draining process is performed. However, if the shell 10b of the carbon dioxide solidification device 10 is not filled with liquefied carbon dioxide, the liquefied carbon dioxide draining process is not necessary. In this case, the carbon dioxide solidification chamber pressure equalization process will be performed between the carbon dioxide solidification process (Process A) and the dry ice melting process (Process B), and between the dry ice melting process (Process B) and the carbon dioxide solidification process (Process A). When this is done in two series, as shown in Figure 7, the carbon dioxide solidification chamber equalization process is performed between shell 10b after the carbon dioxide solidification process of series 1 and shell 10b-1 after the dry ice melting process of series 2, and between shell 10b after the dry ice melting process of series 1 and shell 10b-1 after the carbon dioxide solidification process of series 2.

[0053] Furthermore, although the above description uses a shell-and-tube type heat exchanger as an example of a carbon dioxide solidification device, the carbon dioxide solidification device of the present invention is not limited to this. The carbon dioxide solidification apparatus according to the present invention comprises a refrigerant passage section and a gas passage section arranged adjacent to the refrigerant passage section via a heat transfer wall, through which a carbon dioxide-containing gas passes, and is capable of solidifying the carbon dioxide contained in the carbon dioxide-containing gas within the gas passage section by utilizing the cold energy of the refrigerant through heat exchange with the carbon dioxide-containing gas.

[0054] [Embodiment 2] Next, the configuration and function of Embodiment 2 will be described with reference to Figure 8. Components having the same configuration and function as Embodiment 1 are given the same number. The carbon dioxide recovery system 200 according to Embodiment 2 includes a refrigerant drain line 271 for extracting LNG, which is the refrigerant in the lower channel chamber 10d of the carbon dioxide solidification device 10, as drain; a refrigerant drain pot 210 for storing the drain extracted from the refrigerant drain line 271; a refrigerant delivery line 273 for sending the LNG in the refrigerant drain pot 210 to the refrigerant supply line 71; and a refrigerant drain pump 220 provided on the refrigerant delivery line 273. A refrigerant drain valve 272 is provided in the refrigerant drain line 271, and a refrigerant delivery valve 274 is provided in the refrigerant delivery line 273.

[0055] The refrigerant drain pot 210 is a metal container that temporarily stores the refrigerant when it is extracted from the carbon dioxide solidification device 10. Furthermore, the refrigerant drain pot 210 is installed such that its highest liquid level is lower than the lowest part of the lower channel chamber 10d of the carbon dioxide solidification device 10.

[0056] The refrigerant drain pump 220 is a centrifugal pump that pressurizes the LNG stored in the refrigerant drain pot 210 and discharges it to the refrigerant supply line 71 via the refrigerant delivery line 273.

[0057] Next, the operation of the carbon dioxide capture system 200 according to this embodiment will be described. The same operation as in Embodiment 1 will not be explained. In this embodiment, a refrigerant drain step is added between the carbon dioxide solidification step and the dry ice melting step.

[0058] <Refrigerant draining process> The carbon dioxide recovery system 200 stops the supply of LNG and carbon dioxide-containing gas to the carbon dioxide solidification device 10, and then recovers the LNG in the carbon dioxide solidification device 10 into the refrigerant drain pot 210 by opening the refrigerant drain valve 272. At this time, as the LNG liquid level drops, methane gas (including supercritical state) in the refrigerant discharge line 73 flows back into the upper channel chamber 10c, tube 10a, and lower channel chamber 10d, thereby replacing the LNG with methane gas. Subsequently, the carbon dioxide recovery system 200 closes the refrigerant drain valve 272.

[0059] The carbon dioxide recovery system 200 operates the refrigerant drain pump 220 at any time to pressurize the LNG recovered and stored in the refrigerant drain pot 210 and discharge it upstream of the refrigerant supply valve 72 in the refrigerant supply line 71. The discharged LNG is then supplied again to the carbon dioxide solidification device 10 or other carbon dioxide solidification devices.

[0060] According to the carbon dioxide recovery system 200 of this embodiment, when dry ice is melted, the LNG inside the carbon dioxide solidification device 10 is recovered before the liquefied carbon dioxide is circulated to the carbon dioxide solidification device 10. This eliminates the need for evaporation of the LNG in the tube 10a due to the circulation of liquefied carbon dioxide, and significantly reduces the time required for the dry ice melting operation.

[0061] [Embodiment 3] Next, the configuration and function of Embodiment 3 will be described with reference to Figure 9. Components having the same configuration and function as those in Embodiments 1 and 2 are given the same number. The carbon dioxide recovery system 300 according to Embodiment 3 includes a refrigerant gas recovery line 371 for recovering refrigerant gas in the refrigerant passage section of the carbon dioxide solidification device 10, and a refrigerant gas return line 373 for returning the recovered refrigerant gas to the refrigerant passage section of the carbon dioxide solidification device 10. The refrigerant gas recovery line 371 and the refrigerant gas return line 373 constitute the refrigerant gas circulation line of the present invention.

[0062] A refrigerant gas recovery valve 372 is provided in the refrigerant gas recovery line 371. Furthermore, a drain pot 310 for a refrigerant gas circulation blower is provided between the refrigerant gas recovery line 371 and the refrigerant gas return line 373, and a refrigerant gas return valve 374, a refrigerant gas circulation blower 320, and a refrigerant gas cooler 330 are provided in the refrigerant gas return line 373. Furthermore, the refrigerant gas drain discharge line 375 is equipped with a refrigerant gas drain pump 340 and a refrigerant gas drain discharge valve 376.

[0063] The drain pot 310 for the refrigerant gas circulation blower is a metal container provided to remove mist from the refrigerant gas recovered by the refrigerant gas recovery line 371 and supply it to the refrigerant gas circulation blower 320. The mist recovered in the drain pot 310 for the refrigerant gas circulation blower is temporarily stored and discharged by the refrigerant gas drain pump 340, which is a centrifugal pump, through the refrigerant gas drain discharge line 375 to, for example, the refrigerant delivery line 273.

[0064] The refrigerant gas circulation blower 320 is a centrifugal blower that pressurizes the refrigerant gas from which mist has been removed in the drain pot 310 for the refrigerant gas circulation blower and discharges it to the refrigerant gas cooler 330.

[0065] The refrigerant gas cooler 330 is a shell-and-tube type heat exchanger that cools the refrigerant gas by exchanging heat with an external refrigerant.

[0066] Next, the operation of the carbon dioxide capture system 300 according to this embodiment will be described. The same functions as in Embodiments 1 and 2 will not be explained. In this embodiment, a refrigerant gas circulation process is added after the refrigerant draining process, before the dry ice melting process, and during the dry ice melting process.

[0067] <Refrigerant gas circulation process> After recovering the refrigerant drain, the carbon dioxide recovery system 300 opens the refrigerant gas recovery valve 372 and the refrigerant gas return valve 374 before circulating the liquefied carbon dioxide to the carbon dioxide solidification device 10.

[0068] Then, by operating the refrigerant gas circulation blower 320, the refrigerant gas (actually in a supercritical state) contained in the carbon dioxide solidification device 10 is circulated while the liquefied carbon dioxide is circulated to the carbon dioxide solidification device 10. As a result, the temperature of the refrigerant gas rises due to the heat input of the refrigerant gas circulation blower 320, and by heating the tube 10a from the inside, the dry ice that has grown and solidified on the outside of the tube 10a is heated.

[0069] The carbon dioxide capture system 300 uses a refrigerant gas cooler 330 to regulate the temperature of the circulating refrigerant gas so that its temperature does not rise excessively. For example, the temperature of the refrigerant gas is maintained at around -50°C.

[0070] According to the carbon dioxide recovery system 300 of this embodiment, a refrigerant gas at approximately -50°C is circulated within the tube 10a. This allows the dry ice adhering to the outside of the tube 10a to be heated and easily melted and detached by the circulation of liquefied carbon dioxide. As a result, the risk of the liquefied carbon dioxide circulating around the outside of the tube 10a solidifying and causing blockage can be further reduced, and the time required to recover the dry ice by circulating liquefied carbon dioxide can be further shortened.

[0071] In this embodiment, the refrigerant discharge valve 74 was closed before starting the circulation of the refrigerant gas, but the refrigerant gas may be circulated with the refrigerant discharge valve 74 open.

[0072] Furthermore, in this embodiment, a separate drain pot 310 for the refrigerant gas circulation blower is installed in addition to the refrigerant drain pot 210. However, it is also possible to use the refrigerant drain pot 210 as the drain pot for the refrigerant gas circulation blower without providing the drain pot 310. In this case, the refrigerant gas recovery line 371 is not required, and the refrigerant gas return line 373 is connected to the refrigerant drain pot 210.

[0073] [Embodiment 4] Next, the configuration and function of Embodiment 4 will be described with reference to Figure 10. The carbon dioxide recovery system 400 according to Embodiment 4 includes, in addition to the configuration of Embodiment 2, a refrigerant drain pressure equalization line 471 and a refrigerant drain pressure equalization valve 472. Components having the same configuration and function as those in Embodiment 2 are given the same number.

[0074] In this embodiment, the carbon dioxide solidification device 10 uses the sensible heat of LNG to solidify the carbon dioxide contained in the carbon dioxide-containing gas. Therefore, liquid LNG is discharged from the refrigerant discharge line 73.

[0075] Next, the operation of the carbon dioxide capture system 400 according to this embodiment will be described. The effects similar to those of Embodiment 2 will not be explained. Between the carbon dioxide solidification process and the dry ice melting process, the carbon dioxide recovery system 400 stops the supply of LNG and carbon dioxide-containing gas to the carbon dioxide solidification device 10 by closing the refrigerant supply valve 72, the refrigerant discharge valve 74, the carbon dioxide-containing gas supply valve 76, and the excess gas discharge valve 78.

[0076] Next, the carbon dioxide recovery system 400 recovers the LNG in the carbon dioxide solidification device 10 into the refrigerant drain pot 210 by opening the refrigerant drain valve 272 and the refrigerant drain pressure equalization valve 472. At this time, as the LNG liquid level drops, the refrigerant gas in the gas layer of the refrigerant drain pot 210 flows into the upper channel chamber 10c, tube 10a, and lower channel chamber 10d. After that, the carbon dioxide recovery system 400 closes the refrigerant drain valve 272 and the refrigerant drain pressure equalization valve 472.

[0077] The carbon dioxide recovery system 400 then moves back to the carbon dioxide solidification process. By opening the refrigerant supply valve 72 while the refrigerant drain pressure equalization valve 472 is open, LNG is supplied to the carbon dioxide solidification device 10 and filled inside, while the pushed-out refrigerant gas is returned to the refrigerant drain pot 210. After that, the carbon dioxide recovery system 400 opens the refrigerant discharge valve 74 and starts the carbon dioxide solidification process.

[0078] According to the carbon dioxide recovery system 400 of this embodiment, even if the carbon dioxide solidification device 10 uses the sensible heat of LNG as a refrigerant, when melting dry ice, the LNG inside the carbon dioxide solidification device 10 is recovered before circulating the liquefied carbon dioxide back into the device 10. This eliminates the need for evaporation of the LNG in the tube 10a due to the circulation of liquefied carbon dioxide, and significantly reduces the time required for the dry ice melting operation. [Explanation of Symbols]

[0079] 1. Carbon dioxide capture system (Embodiment 1) 10. Carbon dioxide solidification device 10-1 Carbon dioxide solidification device 10a tubing 10a-1 Tube 10b shell 10b-1 Shell 10c Upper channel chamber 10c-1 Upper channel chamber 10d Lower channel chamber 10d-1 Lower channel chamber 20 Dry ice melting tank 30. Liquefied carbon dioxide circulation pump 40. Liquefied carbon dioxide heater 71 Refrigerant supply line 71-1 Refrigerant supply line 72 Refrigerant supply valve 72-1 Refrigerant supply valve 73 Refrigerant discharge line 73-1 Refrigerant discharge line 74 Refrigerant discharge valve 74-1 Refrigerant discharge valve 75. Carbon dioxide-containing gas supply line 75-1 Carbon Dioxide-Containing Gas Supply Line 76. Carbon dioxide-containing gas supply valve 76-1 Carbon dioxide-containing gas supply valve 77. Excess gas discharge line 77-1 Excess gas discharge line 78 Excess gas discharge valve 78-1 Excess gas discharge valve 85. Liquefied carbon dioxide return line 86 Liquefied carbon dioxide discharge valve 87 Liquefied carbon dioxide supply line 88. Liquefied carbon dioxide supply valve 89. Liquefied carbon dioxide discharge line 90 Liquefied carbon dioxide drain line 91 Liquefied carbon dioxide drain valve 92 Pressure equalization valve 93 Pressure Equalization Line 200 Carbon Dioxide Capture System (Embodiment 2) 210 Refrigerant Drain Pot 220 Refrigerant drain pump 271 Refrigerant drain line 272 Refrigerant drain valve 273 Refrigerant delivery line 274 Refrigerant delivery valve 300 Carbon Dioxide Capture System (Embodiment 3) 310 Drain pot for refrigerant gas circulation blower 320 Refrigerant Gas Circulation Blower 330 Refrigerant gas cooler 340 Refrigerant gas drain pump 371 Refrigerant gas recovery line 372 Refrigerant gas recovery valve 373 Refrigerant gas return line 374 Refrigerant gas return valve 375 Refrigerant gas drain discharge line 376 Refrigerant gas drain valve 400 Carbon Dioxide Capture System (Embodiment 4) 471 Refrigerant drain pressure equalization line 472 Refrigerant drain pressure equalization valve

Claims

1. A carbon dioxide solidification apparatus comprising a refrigerant passage section through which a refrigerant at a temperature lower than the carbon dioxide solidification temperature passes, and a gas passage section adjacent to the refrigerant passage section via a heat transfer wall, through which a carbon dioxide-containing gas passes, wherein the carbon dioxide contained in the carbon dioxide-containing gas is solidified within the gas passage section by utilizing the cold energy of the refrigerant through heat exchange with the carbon dioxide-containing gas. A carbon dioxide-containing gas supply line is configured with a means for switching between supplying carbon dioxide-containing gas to the gas passage section and stopping the supply, The excess gas containing carbon dioxide supplied to the gas passage that did not solidify is discharged from the gas passage into an excess gas discharge line, which is configured with a switching mechanism for switching between a discharge state and a discharge stop state. A refrigerant supply line is configured with a means for switching between supplying refrigerant to the refrigerant passage and stopping the supply, A refrigerant discharge line is configured to include a means for switching between a refrigerant discharge state and a discharge stop state from the refrigerant passage section, A liquefied carbon dioxide circulation line is connected to the gas passage section and circulates and supplies liquefied carbon dioxide to the gas passage section, A carbon dioxide recovery system characterized by comprising a liquefied carbon dioxide heater installed in the liquefied carbon dioxide circulation line and heating the liquefied carbon dioxide flowing through the liquefied carbon dioxide circulation line.

2. The carbon dioxide recovery system according to claim 1, characterized in that it has a refrigerant drain line that communicates with the refrigerant passage section and discharges the refrigerant from the refrigerant passage section.

3. A refrigerant gas circulation line that communicates with the refrigerant passage section and circulates and supplies a refrigerant in a gaseous or supercritical state to the refrigerant passage section, The carbon dioxide recovery system according to claim 2, further comprising a refrigerant gas circulation blower disposed in the refrigerant gas circulation line for circulating the refrigerant in a gaseous or supercritical state flowing through the refrigerant gas circulation line.

4. A carbon dioxide recovery system comprising a plurality of carbon dioxide recovery systems according to any one of claims 1 to 3, and having a gas passage communication line configured with a switching means for connecting and disconnecting the gas passage sections of each carbon dioxide recovery system.

5. A carbon dioxide recovery method using a carbon dioxide solidification apparatus comprising a refrigerant passage section through which a refrigerant at a temperature lower than the carbon dioxide solidification temperature passes, and a gas passage section adjacent to the refrigerant passage section via a heat transfer wall, through which a carbon dioxide-containing gas passes, wherein the carbon dioxide contained in the carbon dioxide-containing gas is solidified in the gas passage section by utilizing the cold energy of the refrigerant through heat exchange with the carbon dioxide-containing gas, A carbon dioxide solidification step is performed by using the cold energy of the refrigerant to solidify the carbon dioxide contained in the carbon dioxide-containing gas within the gas passage section through heat exchange with the carbon dioxide-containing gas. A method for recovering carbon dioxide, characterized by comprising a dry ice melting step of circulating and supplying liquefied carbon dioxide to the gas passage to melt solidified carbon dioxide.

6. The carbon dioxide recovery method according to claim 5, characterized in that, after the carbon dioxide solidification step and before the dry ice melting step, it includes a refrigerant drain step for discharging the refrigerant in the refrigerant passage section.

7. The carbon dioxide recovery method according to claim 6, further comprising a refrigerant gas circulation step of circulating and supplying a refrigerant in a gaseous or supercritical state to the refrigerant passage after the refrigerant drain step.

8. The carbon dioxide recovery method according to any one of claims 5 to 7, characterized in that a plurality of carbon dioxide solidification devices are installed, and a carbon dioxide solidification chamber equalization step is provided between the carbon dioxide solidification step and the dry ice melting step in one carbon dioxide solidification device, in which the gas passage sections of each carbon dioxide solidification device are connected after the dry ice melting step in another carbon dioxide solidification device and before the next carbon dioxide solidification step.

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