Carbon dioxide capture device and carbon dioxide capture method

Abstract

The present invention provides a carbon dioxide capture device and a carbon dioxide capture method that can efficiently capture carbon dioxide while suppressing the energy required for carbon dioxide capture. [Solution] A carbon dioxide recovery device 10 circulates an absorbent liquid between an absorption tower 11 and a regeneration tower 12 via a rich liquid supply pipe 13 and a lean liquid supply pipe 14, allowing carbon dioxide to be absorbed by the absorbent liquid in the absorption tower 11 and recovered in the regeneration tower 12. The device includes a heating means (heat pump) 33 that heats the absorbent liquid, which is supplied to the regeneration tower 12 via the rich liquid supply pipe 13 after absorbing carbon dioxide in the absorption tower 11, through heat exchange with a heat transfer medium. The heating means 33 is set to processing conditions that cause carbon dioxide to be released from the absorbent liquid.

Description

Technical Field

[0001] The present invention relates to a carbon dioxide recovery apparatus and a carbon dioxide recovery method, in which an absorption liquid is circulated through a supply line between an absorption tower and a regeneration tower, carbon dioxide is absorbed by the absorption liquid in the absorption tower, and carbon dioxide is recovered in the regeneration tower.

Background Art

[0002] Conventionally, as a carbon dioxide recovery method, a chemical absorption method using a carbon dioxide absorption liquid such as an amine solution (hereinafter simply referred to as "absorption liquid") is known. In this method, a treatment target gas containing carbon dioxide is brought into contact with an absorption liquid to once absorb carbon dioxide in the treatment target gas into the absorption liquid, and then the absorption liquid is heated to desorb and recover carbon dioxide.

[0003] In this carbon dioxide recovery method, a large amount of energy is required for heating the absorption liquid, increasing the carbon dioxide recovery cost. Therefore, for example, in Patent Document 1 (see paragraphs

[0036] to

[0041] and FIG. 1), a carbon dioxide recovery apparatus applying a heat pump as a heating means for heating the absorption liquid has been proposed.

[0004] The carbon dioxide recovery apparatus of Patent Document 1 is provided with a heat pump that moves the heat generated by the exothermic reaction when the absorption liquid absorbs carbon dioxide gas in the absorption tower through a heat medium and uses the heat as a heat source for the endothermic reaction when carbon dioxide gas is separated from the absorption liquid in the regeneration tower. On the absorption tower side, the absorption liquid of the intercooler system is cooled by the heat medium of the heat pump. The heat medium heated by heat exchange with the absorption liquid during this cooling is heated by a heat medium heater and a heat medium compressor and supplied to the piping of the reboiler system. In the piping of the reboiler system, the absorption liquid after passing through the reboiler body is further heated using a heat medium heating type heat exchanger. The heat medium cooled by heat exchange with the absorption liquid during this heating is further cooled by a heat medium cooler and a heat medium expansion valve and supplied again to the intercooler system to cool the absorption liquid.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2015-131735 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In Patent Document 1, the object heated by the heat pump (heat transfer medium heating type heat exchanger) is the absorbent liquid, which has been further heated in the reboiler body after a certain amount of carbon dioxide desorption has been completed in the regeneration tower, and before it is removed from the regeneration tower and returned to the regeneration tower. For this reason, it cannot be said that the energy required to heat the absorbent liquid by the heat pump is effectively used for carbon dioxide desorption, and furthermore, since the heating efficiency of a heat pump generally decreases as the temperature of the object being heated increases, the power consumption of the heat pump increases, and there was room for improvement in terms of energy efficiency and other aspects.

[0007] This invention has been made in view of the above-mentioned problems, and aims to provide a carbon dioxide capture device and a carbon dioxide capture method that can efficiently capture carbon dioxide while suppressing the energy required for carbon dioxide capture. [Means for solving the problem]

[0008] The characteristic configuration of the carbon dioxide capture device according to the present invention, which solves the above problems, is as follows: A carbon dioxide recovery apparatus that circulates an absorbent liquid between an absorption tower and a regeneration tower via a supply path, allows carbon dioxide to be absorbed by the absorbent liquid in the absorption tower, and recovers carbon dioxide in the regeneration tower, The absorption tower, after absorbing carbon dioxide, is supplied to the regeneration tower via the supply path, and the absorption liquid is heated by heat exchange with a heat transfer medium, The heating means is set to processing conditions that cause carbon dioxide to be released from the absorbent liquid.

[0009] In this carbon dioxide recovery system, the heating means promotes the desorption of carbon dioxide from the absorbent by heating the absorbent through heat exchange with a heat transfer medium. The target of heating by the heating means is the absorbent that has absorbed carbon dioxide in the absorption tower and is then supplied to the regeneration tower via the supply path; that is, the relatively low-temperature absorbent before carbon dioxide is desorbed by the endothermic reaction in the regeneration tower. Thus, since the target of heating is the absorbent that has absorbed carbon dioxide in the absorption tower, the energy invested in heating is effectively utilized for the desorption of carbon dioxide. Furthermore, since the target of heating is the relatively low-temperature absorbent before it is introduced into the regeneration tower, the decrease in heating efficiency is suppressed. In addition, since the operating conditions of the heating means are set to processing conditions that allow carbon dioxide to be desorbed from the absorbent, the absorbent that is introduced into the regeneration tower is one in which carbon dioxide has been largely desorbed, and carbon dioxide is efficiently recovered in the regeneration tower. In this way, carbon dioxide can be efficiently recovered while suppressing the energy required for carbon dioxide recovery.

[0010] In the carbon dioxide recovery device according to the present invention, Preferably, the processing conditions involve setting the temperature of the heat transfer medium in the heating means to a temperature higher than the temperature at which carbon dioxide is desorbed from the absorbent liquid.

[0011] Several conditions are necessary for carbon dioxide to be released from the absorbent. One of these is temperature. The amount of carbon dioxide absorbed by the absorbent depends on the temperature, and the release of carbon dioxide begins when the temperature rises above a predetermined level. Therefore, in this carbon dioxide recovery system, the temperature of the heat transfer medium in the heating means is set higher than the temperature at which carbon dioxide is released from the absorbent. This allows the release of carbon dioxide to begin before it is introduced into the regeneration tower, thereby suppressing the energy required for the endothermic reaction inside the regeneration tower.

[0012] In the carbon dioxide recovery device according to the present invention, Preferably, the processing conditions involve setting the pressure of the absorbent liquid in the heating means to a pressure at which carbon dioxide is released from the absorbent liquid.

[0013] The amount of carbon dioxide absorbed by the absorbent liquid changes depending on the pressure acting on the absorbent liquid. Therefore, in this carbon dioxide recovery system, the pressure of the absorbent liquid in the heating means is set to the pressure at which carbon dioxide is desorbed from the absorbent liquid. This allows the desorption of carbon dioxide to begin before it is introduced into the regeneration tower, thereby suppressing the energy required for the endothermic reaction inside the regeneration tower.

[0014] In the carbon dioxide recovery device according to the present invention, It is preferable to include a pressure adjustment means for adjusting the pressure to a level at which carbon dioxide can be released from the absorbent liquid.

[0015] This carbon dioxide recovery apparatus includes a pressure adjustment means that adjusts the pressure of the absorbent liquid to a pressure at which carbon dioxide can be released, making it easy to adjust the pressure of the absorbent liquid in the heating means to a pressure at which carbon dioxide is released.

[0016] In the carbon dioxide recovery device according to the present invention, The aforementioned supply line is A first supply path for supplying the absorbent liquid from the absorption tower to the regeneration tower, A second supply path for supplying the absorbent liquid from the regeneration tower to the absorption tower, Includes, The heating means is a heat pump equipped with a condenser and an evaporator. The system further comprises an absorbent liquid heat exchanger interposed between the first and second supply channels, which is capable of heat exchange between the absorbent liquid flowing through the first supply channel and the absorbent liquid flowing through the second supply channel. The condenser is interposed between the heat exchanger and the regeneration tower in the first transmission line. It is preferable that the evaporator is interposed between the heat exchanger and the absorption tower in the second supply line.

[0017] According to the carbon dioxide recovery device of this configuration, the absorption liquid from the absorption tower flowing through the first supply path is heated by heat exchange with the absorption liquid from the regeneration tower in the absorption liquid heat exchanger, and then further heated by heat exchange with the heat medium in the condenser. Thereby, the carbon dioxide recovery efficiency can be further improved. On the other hand, the absorption liquid from the regeneration tower flowing through the second supply path is cooled by heat exchange with the absorption liquid from the absorption tower in the absorption liquid heat exchanger, and then further cooled by heat exchange with the heat medium in the evaporator. Thereby, an absorption liquid that is more likely to absorb carbon dioxide can be obtained.

[0018] In the carbon dioxide recovery device according to the present invention, It is preferable to include a reboiler that further heats the absorption liquid heated by the heating means.

[0019] According to the carbon dioxide recovery device of this configuration, since the absorption liquid heated by the heating means is further heated by the reboiler, it is possible to reliably recover the carbon dioxide that remains without being desorbed by the heating of the heating means.

[0020] Next, the characteristic configuration of the carbon dioxide recovery method according to the present invention for solving the above problems is A carbon dioxide recovery method in which an absorption liquid is circulated through a supply path between an absorption tower and a regeneration tower, carbon dioxide is absorbed by the absorption liquid in the absorption tower, and carbon dioxide is recovered in the regeneration tower, including a heating step of heating the absorption liquid fed to the regeneration tower through the supply path after absorbing carbon dioxide in the absorption tower by heat exchange with a heat medium, The heating step is performed under processing conditions in which carbon dioxide is desorbed from the absorption liquid.

[0021] According to the carbon dioxide recovery method of this configuration, since the absorption liquid that has absorbed carbon dioxide in the absorption tower is the object to be heated in the heating step, the energy input by heating is effectively used for the desorption of carbon dioxide. In addition, since the relatively low-temperature absorption liquid before being introduced into the regeneration tower is the object to be heated in the heating step, a decrease in heating efficiency is suppressed. Furthermore, since the heating step is performed under the treatment conditions in which carbon dioxide is desorbed from the absorption liquid, the absorption liquid in a state where the desorption of carbon dioxide from the absorption liquid has progressed is introduced into the regeneration tower, and carbon dioxide is efficiently recovered in the regeneration tower. Thus, carbon dioxide can be efficiently recovered while suppressing the energy required for carbon dioxide recovery.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a carbon dioxide recovery apparatus according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, the present invention will be described with reference to the drawings. However, the present invention is not intended to be limited to the configurations described in the embodiments and drawings below.

[0024] <Schematic Configuration of Carbon Dioxide Recovery Apparatus> FIG. 1 is a schematic diagram showing a schematic configuration of a carbon dioxide recovery apparatus 10 according to an embodiment (this embodiment) of the present invention. The carbon dioxide recovery apparatus 10 shown in FIG. 1 recovers carbon dioxide from a carbon dioxide-containing gas (hereinafter referred to as "treatment gas G"), such as biogas or combustion exhaust gas, through an absorption liquid. The carbon dioxide recovery apparatus 10 employs a chemical absorption method in which carbon dioxide is absorbed into the absorption liquid by reacting an alkaline compound in the absorption liquid with carbon dioxide. In the following description, if necessary, an absorption liquid with a high carbon dioxide content that has absorbed carbon dioxide is referred to as a "rich liquid", and an absorption liquid with a low carbon dioxide content from which the absorbed carbon dioxide has been desorbed is referred to as a "lean liquid".

[0025] <Absorbent liquid> The absorbent liquid used in the present invention is one that can desorb absorbed carbon dioxide at a relatively low temperature of about 90°C. For example, a non-aqueous carbon dioxide absorbent liquid (amine solution) disclosed in Japanese Patent Application Publication No. 2021-154237 can be used. This carbon dioxide absorbent liquid contains a carbon dioxide chemically absorbing amine having nitrogen-hydrogen bonds and a tertiary polydentate amine that does not have nitrogen-hydrogen bonds, and further contains a diluent. The carbon dioxide chemically absorbing amine, the tertiary polydentate amine, and the diluent are usually liquids at room temperature, and the carbon dioxide absorbent liquid is obtained by mixing the carbon dioxide chemically absorbing amine and the tertiary polydentate amine and adding the diluent. As an absorbent liquid other than the amine solution, for example, an alkaline solution, more preferably a caustic soda solution, can be used.

[0026] The combination of carbon dioxide chemically absorbing amine, tertiary polydentate amine, and diluent is not particularly limited, but for example, a combination of one or more of the following as the carbon dioxide chemically absorbing amine: diethanolamine, dipropanolamine, dibutanolamine, N-methylethanolamine, N-ethylethanolamine, 3-methylamino-1-propanol, N-butylethanolamine, or N-propylethanolamine; one or more of the following as the tertiary polydentate amine: N-methyldiethanolamine, N-ethyldiethanolamine, or N-butyldiethanolamine; and a combination of dimethyl sulfoxide, hexamethyl phosphate triamide, 1,3-dimethyl-2-imidazolidinone, N,N'-dimethylpropylene urea, or tetramethylurea as the diluent is preferred.

[0027] <Overall configuration of the carbon dioxide capture system> The carbon dioxide recovery device 10 comprises an absorption tower 11, a regeneration tower 12, a rich liquid supply pipe 13, a lean liquid supply pipe 14, an absorption liquid heat exchanger 15, and heating means 16a and 16b. In the carbon dioxide recovery device 10, the absorption liquid is circulated between the absorption tower 11 and the regeneration tower 12 via supply lines (rich liquid supply pipe 13, lean liquid supply pipe 14). The rich liquid supply pipe 13 corresponds to the "first supply line" of the present invention. The lean liquid supply pipe 14 corresponds to the "second supply line" of the present invention.

[0028] <Fusion Tower> The absorption tower 11 brings a lean liquid capable of absorbing carbon dioxide into contact with the treatment gas G, allowing the carbon dioxide in the treatment gas G to be absorbed by the lean liquid to produce a rich liquid, which is then contained and stored. A treatment gas introduction pipe 20 is connected to the lower part of the absorption tower 11 for introducing the treatment gas G into the tower. A decarbonated gas discharge pipe 21 is connected to the top of the absorption tower 11 for discharging the decarbonated gas after carbon dioxide has been recovered from the treatment gas G. A lean liquid sprayer 22 is installed in the upper part of the absorption tower 11 for spraying the lean liquid, and an absorption tower packing material 23 is installed in the intermediate section between the lean liquid sprayer 22 and the lower part of the absorption tower 11. The absorption tower packing material 23 is provided to improve the efficiency of gas-liquid contact.

[0029] The absorption tower packing material 23 may be made of metal or resin, and in order to increase the gas-liquid contact area, irregular packing materials such as Raschig rings, Berl saddles, and pole rings may be used, and other materials such as porous structures or honeycomb structures may also be used. The absorption tower 11 may be a structure such as a scrubber that absorbs carbon dioxide from the treated gas G while circulating a large amount of absorbent liquid, and it is also applicable to structures that do not have absorption tower packing material 23, such as spray towers and plate towers.

[0030] <Regeneration Tower> The regeneration tower 12 removes carbon dioxide from the rich liquid supplied from the absorption tower 11, regenerating the rich liquid into a lean liquid. A recovered gas discharge pipe 24 is connected to the top of the regeneration tower 12 for discharging the gas containing the recovered carbon dioxide. A rich liquid sprayer 25 for spraying the rich liquid is installed inside the upper part of the regeneration tower 12, and a regeneration tower packing material 26 is installed in the intermediate section between the rich liquid sprayer 25 and the lower part of the regeneration tower 12. The regeneration tower packing material 26 is the same as the absorption tower packing material 23 described above.

[0031] A gas-liquid separator 27 is installed in the middle section of the recovery gas discharge pipe 24 to separate the condensate, which is generated when the recovered gas containing carbon dioxide is cooled by a cooling means (not shown), from the carbon dioxide-based gas. The condensate separated by the gas-liquid separator 27 is recovered to the regeneration tower 12 via a return pipe 41. The uncondensed carbon dioxide-based gas separated by the gas-liquid separator 27 is recovered via the recovery gas discharge pipe 24 and temporarily stored, for example, in a gas holder (not shown), before being put to effective use.

[0032] <Rich liquid supply pipe> The rich liquid supply pipe 13 connects the bottom of the absorption tower 11 to the rich liquid sprayer 25 of the regeneration tower 12. A rich liquid supply pump 28 is installed near the absorption tower 11, and the rich liquid that has absorbed carbon dioxide in the absorption tower 11 is supplied to the regeneration tower 12 through the rich liquid supply pipe 13. A pressure regulating valve 29, such as a pressure reducing valve, is installed downstream of the rich liquid supply pump 28, allowing the liquid pressure of the rich liquid to be set to a predetermined level. In this example, the rich liquid supply pump 28 and the pressure regulating valve 29 are interposed between the bottom of the absorption tower 11 and the absorption liquid heat exchanger 15 in the rich liquid supply pipe 13.

[0033] <Lean liquid supply pipe> The lean liquid supply pipe 14 connects the bottom of the regeneration tower 12 to the lean liquid sprayer 22. In addition, similar to the rich liquid supply pipe 13, a lean liquid supply pump and a pressure regulating valve (neither of which are shown) are interposed in the lean liquid supply pipe 14 so as to be positioned appropriately between the bottom of the regeneration tower 12 and the absorption liquid heat exchanger 15. The lean liquid that has been regenerated in the regeneration tower 12 and from which carbon dioxide has been removed is supplied to the absorption tower 11 through the lean liquid supply pipe 14.

[0034] <Heat exchanger> The rich liquid supply pipe 13 and the lean liquid supply pipe 14 are arranged in such a way that they intersect via an absorbent liquid heat exchanger 15. The absorbent liquid heat exchanger 15 is designed to exchange heat between the rich liquid flowing through the rich liquid supply pipe 13 and the lean liquid flowing through the lean liquid supply pipe 14. In some cases, heat exchange (heating, cooling) between the rich liquid and the lean liquid is not performed, in which case the absorbent liquid heat exchanger 15 is omitted.

[0035] <Heating means> The carbon dioxide recovery device 10 includes a first heating means 16a, which includes a heat pump 33 and heats the rich liquid, and a second heating means 16b, which includes a reboiler 34 and further heats the rich liquid heated by the first heating means 16a. As will be described later, the absorbent liquid heated by the second heating means 16b has already had most of the carbon dioxide removed by the first heating means 16a, and the amount of remaining carbon dioxide has decreased, but since it is an absorbent liquid that still contains unrecovered carbon dioxide, this absorbent liquid is also referred to as the "rich liquid".

[0036] <Heat pump> The heat pump 33 is installed in the supply passage (rich liquid supply pipe 13, lean liquid supply pipe 14) for circulating the absorbent liquid between the absorption tower 11 and the regeneration tower 12, and includes a compressor 35, a condenser 36, an expansion valve 37, an evaporator 38, a heat transfer medium supply pipe 39, and a heat transfer medium return pipe 40. In the heat pump 33, the condenser 36 and the evaporator 38 are connected by the heat transfer medium supply pipe 39 and the heat transfer medium return pipe 40. A compressor 35 is installed in the middle of the heat transfer medium supply pipe 39 to increase the temperature by compressing the heat transfer medium, and an expansion valve 37 is installed in the middle of the heat transfer medium return pipe 40 to decrease the temperature by expanding the compressed heat transfer medium. In the heat pump 33, the heat transfer medium repeatedly passes through the compressor 35, condenser 36, expansion valve 37, and evaporator 38 in sequence to form a heat transfer medium circulation circuit 42.

[0037] In the carbon dioxide recovery system 10, the condenser 36 is located between the absorbent liquid heat exchanger 15 and the rich liquid sprayer 25 (regeneration tower 12) in the rich liquid supply pipe 13, and the rich liquid whose temperature has risen in the absorbent liquid heat exchanger 15 flows into it. In the condenser 36, heat exchange takes place between the heat transfer medium, which has been compressed and whose temperature has risen in the compressor 35, and the rich liquid, further increasing the temperature of the rich liquid flowing through the rich liquid supply pipe 13. This can further improve the carbon dioxide recovery efficiency.

[0038] Furthermore, the evaporator 38 is located between the absorption liquid heat exchanger 15 and the lean liquid sprayer 22 (absorption tower 11) in the lean liquid supply pipe 14, and the lean liquid whose temperature has been lowered in the absorption liquid heat exchanger 15 flows into it. In the evaporator 38, heat exchange takes place between the heat transfer medium, which has been expanded by the expansion valve 37 and whose temperature has been lowered, and the lean liquid, further lowering the temperature of the lean liquid flowing through the lean liquid supply pipe 14.

[0039] As shown in Figure 1, the heat pump 33 in this configuration has a distinctive feature in its installation location. Specifically, it is installed downstream of the absorbent liquid heat exchanger 15 in order to minimize the temperature difference of the heat transfer medium circulating inside the heat pump 33. The rich liquid flows into the absorbent liquid heat exchanger 15 after leaving the absorption tower 11, while the lean liquid flows into the same absorbent liquid heat exchanger 15 after leaving the regeneration tower 12. At this time, the rich liquid is heated to about 87°C by the heat of the lean liquid at about 92°C, and the lean liquid is cooled to about 48°C.

[0040] In this configuration, before the heat pump 33 heats and cools the absorbent liquid, the rich liquid at approximately 40°C that has flowed out of the absorption tower 11 and the lean liquid at approximately 92°C that has returned from the regeneration tower 12 are circulated through the absorbent liquid heat exchanger 15, thereby setting the temperature difference between the two to a small amount of approximately 40°C (rich liquid at approximately 87°C and lean liquid at approximately 48°C). The main purpose of the heat pump 33 in this embodiment is to raise the temperature of the rich liquid to near the desorption start temperature of carbon dioxide, and in this process, the smaller the temperature difference between the lean liquid and the rich liquid, the less energy is required to heat the heat transfer medium. Therefore, a carbon dioxide recovery device 10 with low overall energy consumption can be obtained.

[0041] The temperature changes of the heat transfer medium flowing through the heat transfer medium circulation circuit 42 will be explained starting from the expansion valve 37. At the expansion valve 37, the heat transfer medium expands, the pressure decreases, and the temperature drops. The heat transfer medium, now at a lower temperature, flows through the heat transfer medium return pipe 40 into the evaporator 38 in a mixture of liquid and gas. In the evaporator 38, the heat transfer medium is heated and evaporates by heat exchange with the lean liquid flowing through the lean liquid supply pipe 14, and then vaporizes. Subsequently, the heat transfer medium is compressed by the compressor 35, its temperature rises, and it flows through the heat transfer medium supply pipe 39 into the condenser 36. In the condenser 36, heat exchange takes place with the rich liquid flowing through the rich liquid supply pipe 13. The heat transfer medium loses heat to the rich liquid, its temperature drops, and it condenses, and the liquefied heat transfer medium returns to the expansion valve 37. Through the above path, the heat transfer medium circulates within the heat transfer medium circulation circuit 42.

[0042] <Heating medium> As mentioned above, in this example, an amine solution from which carbon dioxide is removed at around 90°C is used as the absorbent. Therefore, in order to remove and recover carbon dioxide from the absorbent, it is necessary to heat the absorbent to a temperature of 90°C or higher. Accordingly, the critical temperature of the heat transfer medium used in the heat pump 33 must be sufficiently higher than the temperature at which carbon dioxide removal from the absorbent begins (hereinafter referred to as the carbon dioxide removal temperature), preferably 110°C or higher. If the critical temperature of the heat transfer medium is lower than the carbon dioxide removal temperature, when removing carbon dioxide from the absorbent, the temperature of the heat transfer medium in the condenser 36 may exceed the critical temperature, preventing condensation of the heat transfer medium and potentially reducing the heating efficiency of the heat pump 33.

[0043] Furthermore, it is preferable that the heat transfer medium used in the heat pump 33 is one that does not contain hydrocarbons. This is because if hydrocarbons are present, there is a risk of them easily igniting if they leak to the outside. Specifically, it is preferable that the heat transfer medium be at least one selected from the group consisting of R1224yd(Z), R1233zd(E), R1234ze(Z), R1336mzz(Z), R245fa, ammonia, and water.

[0044] <Revoiler> The second heating means 16b will now be described. The second heating means 16b, the reboiler 34, is a device that extracts a portion of the absorbent liquid stored in the regeneration tower 12, heats it, and recirculates it back into the regeneration tower 12. The reboiler 34 is connected to a reflux pipe 45 connected to the lower part of the regeneration tower 12, and the absorbent liquid stored in the regeneration tower 12 is extracted through the reflux pipe 45. The reflux pipe 45 may be installed in a form that branches off from the lean liquid supply pipe 14.

[0045] The heating of the absorbent liquid by the reboiler 34 can be achieved, for example, by using a boiler attached to a waste incinerator. The boiler generates steam by utilizing heat recovered from the combustion exhaust gas. By introducing and releasing this steam, the absorbent liquid can be heated using the steam as a heat source. The absorbent liquid inside the regeneration tower 12 is heated by absorbing the heat from the steam through heat exchange between the absorbent liquid introduced into the reboiler 34 via the reflux pipe 45 and the steam introduced into the reboiler 34.

[0046] Furthermore, the heat source for heating the absorbent liquid is not limited to steam as described above. For example, the exhaust gas, after being treated to remove dust, sent from an exhaust gas treatment facility (not shown) that processes combustion exhaust gas, may be connected to the reboiler 34 in a way that allows for introduction and exit, and the heat from the exhaust gas may be used to heat the absorbent liquid.

[0047] (Activation of carbon dioxide capture device) The operation of the carbon dioxide capture device 10 with the configuration described above will now be explained. Note that the absorbent liquid temperatures described below are examples to illustrate the operating conditions, and the operating conditions are not limited to these values.

[0048] First, the treatment gas G is introduced into the lower part of the absorption tower 11 via the treatment gas introduction pipe 20 installed in the absorption tower 11. The treatment gas G rises inside the absorption tower 11, and at the same time, lean liquid is sprayed downward from the lean liquid sprayer 22 installed above the absorption tower 11. The lean liquid flows down along the absorption tower packing material 23 and comes into gas-liquid contact with the treatment gas G. Since the absorption tower packing material 23 is configured to have a large surface area and a large gas-liquid contact area, the contact efficiency between the rising treatment gas G and the descending lean liquid is improved, and the absorption of carbon dioxide by the lean liquid is promoted.

[0049] In the absorption tower 11, the lean liquid absorbs carbon dioxide from the treatment gas G, becoming a rich liquid with a high carbon dioxide content, which is stored at the bottom of the tower. Since the reaction when the lean liquid absorbs carbon dioxide is exothermic, the temperature of the rich liquid rises. In this embodiment, the temperature of the rich liquid stored at the bottom of the tower is about 40°C. The decarbonized gas, after carbon dioxide has been removed from the treatment gas G, is discharged to the outside through the decarbonized gas discharge pipe 21 installed at the top of the absorption tower 11.

[0050] The rich liquid stored in the absorption tower 11 is taken out through the rich liquid supply pipe 13 and sent to the absorption liquid heat exchanger 15 by the rich liquid supply pump 28. In the absorption liquid heat exchanger 15, the rich liquid exchanges heat with the lean liquid sent from the regeneration tower 12. The lean liquid is heated in the reboiler 34, and its temperature is approximately 92°C when it reaches the absorption liquid heat exchanger 15. The rich liquid's temperature rises through heat exchange with the lean liquid, and it is set so that its temperature when it reaches the condenser 36 is approximately 87°C, which is slightly lower than the carbon dioxide desorption temperature (90°C).

[0051] In this embodiment, an amine solution from which carbon dioxide is removed at approximately 90°C is used as the absorbent. The temperature of the rich liquid that reaches the condenser 36 is slightly lower than the carbon dioxide removal temperature, and the removal of carbon dioxide from the rich liquid has not yet begun.

[0052] <Heating process> Subsequently, the rich liquid is further heated inside the condenser 36 by heat exchange with the heat transfer medium of the heat pump 33, which is the first heating means 16a. The temperature of the heat transfer medium in the condenser 36 does not need to be excessively high, as long as it is sufficient to desorb carbon dioxide from the absorbent liquid. Also, the thermal efficiency of the heat pump improves as the temperature of the heat transfer medium in the condenser 36 decreases. Therefore, it is preferable to set the temperature of the heat transfer medium in the condenser 36 to be about 1°C to 5°C higher than the carbon dioxide desorption temperature, and in this embodiment, it is set to about 95°C.

[0053] As a result, the temperature of the rich liquid rises above the carbon dioxide desorption temperature, causing the carbon dioxide absorbed in the rich liquid to be desorbed. In this way, the carbon dioxide gas desorbed from the absorbent liquid is sent together with the liquid absorbent liquid through the rich liquid supply pipe 13 to the rich liquid sprayer 25 of the regeneration tower 12.

[0054] In the carbon dioxide recovery device 10 of this embodiment, by incorporating a heat pump 33, the absorbent liquid can be heated using internal energy (thermal energy from the exothermic reaction when the absorbent liquid absorbs carbon dioxide). Therefore, the amount of thermal energy supplied from an external source when heating the absorbent liquid for carbon dioxide recovery can be reduced.

[0055] Furthermore, since the reaction when the absorbent liquid desorbs carbon dioxide is an endothermic reaction, the energy used for desorption of carbon dioxide is utilized and contributes little to the temperature rise of the absorbent liquid. In particular, in the carbon dioxide recovery device 10 of this embodiment, carbon dioxide is desorbed by heating the absorbent liquid inside the condenser 36. Therefore, the supply of thermal energy to heat the absorbent liquid and the absorption of thermal energy by desorbing carbon dioxide occur simultaneously, so despite supplying thermal energy to heat the absorbent liquid, the temperature rise of the absorbent liquid is small. In this way, in the carbon dioxide recovery device 10 of this embodiment, the temperature rise of the absorbent liquid is suppressed, and the temperature of the heat transfer medium is maintained at an appropriate temperature without becoming too high, making it less likely for the heat conversion efficiency to deteriorate when reheating by the heat pump 33. Therefore, the power consumption of the heat pump 33 can be reduced, and the cost of carbon dioxide recovery can be reduced.

[0056] Furthermore, the carbon dioxide recovery device 10 is set to a condition in which carbon dioxide is desorbed in the condenser 36, and the heat transfer medium of the heat pump 33 inside the condenser 36 is set to a temperature only about 1 to 5 degrees Celsius higher than the carbon dioxide desorption temperature (90 degrees Celsius). As a result, the temperature difference between the high-temperature side (the side where the condenser 36 is installed) and the low-temperature side (the side where the evaporator 38 is installed) is reduced, which allows for a higher heat conversion efficiency of the heat pump 33.

[0057] <Pressure adjustment process> As explained above, in this embodiment, the desorption of carbon dioxide absorbed in the rich liquid is initiated by heating the rich liquid temperature inside the condenser 36 to a temperature above the carbon dioxide desorption temperature. However, since the lower the pressure of the absorbent liquid, the more absorbed carbon dioxide can be recovered, the pressure of the rich liquid may be set to a condition in which carbon dioxide is desorbed in order to desorb carbon dioxide. For example, by adjusting the pressure on the discharge side of the rich liquid supply pump 28, specifically by adjusting the pressure using a pressure regulating valve 29 installed downstream of the rich liquid supply pump 28, the pressure of the rich liquid supplied to the condenser 36 can be set to a condition in which carbon dioxide is desorbed. In this way, by lowering the pressure of the rich liquid inside the condenser 36, carbon dioxide is desorbed and an endothermic reaction occurs. As a result, the temperature rise of the absorbent liquid and the heat transfer medium is suppressed, and the heat exchange efficiency of the heat pump 33 can be increased.

[0058] Furthermore, as a means of reducing the pressure of the rich liquid, for example, a vacuum pump (not shown) may be connected to the inside of the regeneration tower 12 via the recovered gas discharge pipe 24 to reduce the pressure inside the rich liquid supply pipe 13. In this case, the pressure of the rich liquid inside the condenser 36 can be set to a pressure lower than atmospheric pressure, so the carbon dioxide desorption temperature can be lowered. Therefore, since carbon dioxide is desorbed at an even lower temperature, the temperature rise of the absorbent liquid and the heat transfer medium can be suppressed, and the heat exchange efficiency of the heat pump 33 can be further increased. Furthermore, as a means of reducing the pressure of the rich liquid, the pressure inside the condenser 36 may be reduced by adjusting the size of the outlet diameter of the spray nozzle of the rich liquid sprayer 25. It is also possible to appropriately combine and apply several of the above-listed methods: pressure adjustment by the pressure regulating valve 29, pressure reduction by a vacuum pump, and pressure reduction by adjusting the outlet diameter of the spray nozzle of the rich liquid sprayer 25.

[0059] The absorbent liquid heated in the condenser 36, while decarbonizing, is supplied to the regeneration tower 12 through the rich liquid supply pipe 13 in a gas-liquid two-phase flow, i.e., a flow in which gas and liquid coexist, with gaseous carbon dioxide gas and liquid absorbent liquid being released. In the regeneration tower 12, the absorbent liquid is sprayed downward from the rich liquid sprayer 25 and stored at the bottom of the tower.

[0060] A portion of the absorbent liquid extracted from the bottom of the regeneration tower 12 is withdrawn via the lean liquid supply pipe 14 and the reflux pipe 45 and introduced into the reboiler 34. After being heated in the reboiler 34, it is introduced back into the regeneration tower 12. Heating in the reboiler 34 raises the temperature of the absorbent liquid, causing any remaining carbon dioxide in the absorbent liquid to be released. The carbon dioxide rises inside the regeneration tower 12 and is recovered from the top of the regeneration tower 12 via the recovery gas discharge pipe 24.

[0061] When carbon dioxide is recovered in the regeneration tower 12, thermal energy is supplied from the reboiler 34 in proportion to the amount of carbon dioxide remaining. The absorbent liquid sent from the condenser 36 to the regeneration tower 12 has already had some of the absorbed carbon dioxide removed in the condenser 36, so the amount of carbon dioxide remaining in the absorbent liquid is small. Therefore, the thermal energy supplied by the reboiler 34 is significantly reduced compared to the thermal energy required if it were assumed that the absorbent liquid stored in the regeneration tower 12 had absorbed the maximum amount of carbon dioxide.

[0062] Therefore, in the carbon dioxide recovery device 10 of this embodiment, the total amount of thermal energy required to heat the heat transfer medium in the heat pump 33 and the thermal energy required to desorb carbon dioxide in the regeneration tower 12 can be reduced, thereby lowering the cost of carbon dioxide recovery.

[0063] The absorbent liquid stored in the regeneration tower 12 is supplied as lean liquid to the lean liquid sprayer 22 in the absorption tower 11 via the lean liquid supply pipe 14. The lean liquid supply pipe 14 has an absorbent liquid heat exchanger 15 and an evaporator 38 installed in sequence from the upstream side to the downstream side of the lean liquid flow. The lean liquid is cooled in the absorbent liquid heat exchanger 15 by heat exchange with the rich liquid from the absorption tower 11. Subsequently, it is further cooled in the evaporator 38 by heat exchange with a heat transfer medium, so the temperature of the absorbent liquid when it flows into the absorption tower 11 has decreased to about 40°C. This makes it possible to regenerate an absorbent liquid that is more efficient at absorbing carbon dioxide.

[0064] The desorption of carbon dioxide from the absorbent is an endothermic reaction. In the carbon dioxide recovery device 10, the conditions are set so that carbon dioxide is desorbed inside the condenser 36, and thus the desorption of carbon dioxide begins. This desorption reaction is an endothermic reaction, and this desorption cools the heat transfer medium of the heat pump 33.

[0065] Therefore, the absorbent liquid is maintained at a moderately high temperature, and after being supplied to the regeneration tower 12, it is only slightly heated to remove carbon dioxide. On the other hand, the heat transfer medium of the heat pump 33 is cooled to a moderate temperature, and excessive energy consumption occurs in the heat pump 33 when the heat transfer medium is subsequently heated.

[0066] In this way, by installing the condenser 36 of the heat pump 33 upstream of the regeneration tower 12, the heating energy required for the heat transfer medium inside the condenser 36 is reduced, thereby lowering the power consumption of the heat pump 33. This reduces energy costs and carbon dioxide capture costs.

[0067] As described above, the carbon dioxide recovery device 10 of this embodiment installs the condenser 36 of the heat pump 33 upstream of the regeneration tower 12 to supply thermal energy to the absorbent liquid while releasing carbon dioxide from the absorbent liquid, thereby suppressing the temperature rise of the heat pump 33. This improves the heat exchange efficiency of the heat pump 33 and reduces the power consumption of the heat pump 33. As a result, carbon dioxide recovery costs can be reduced. The embodiments described above are illustrative examples, and various modifications are possible without departing from the spirit of the present invention. [Industrial applicability]

[0068] The carbon dioxide recovery apparatus and carbon dioxide recovery method of the present invention can be used, for example, to separate and recover carbon dioxide contained in exhaust gas generated by the combustion of fossil fuels in thermal power plants, steel mills, petroleum refineries, etc.; carbon dioxide contained in exhaust gas generated by the combustion of off-gas in hydrogen production facilities; carbon dioxide contained in exhaust gas generated by the combustion of waste in general waste incineration facilities; and carbon dioxide contained in exhaust gas generated by the combustion of biomass fuel in biomass power generation facilities. [Explanation of symbols]

[0069] 10. Carbon dioxide capture device 11 Absorption Tower 12 Regeneration Tower 13. Rich liquid supply pipe (first supply line) 14 Lean liquid feed pipe (second feed path) 15 Absorbent liquid heat exchanger 29. Pressure regulating valve (pressure regulating means) 33. Heat pump (heating means) 34 Reboiler

Claims

1. A carbon dioxide recovery apparatus that circulates an absorbent liquid between an absorption tower and a regeneration tower via a supply path, allows carbon dioxide to be absorbed by the absorbent liquid in the absorption tower, and recovers carbon dioxide in the regeneration tower, The absorption tower, after absorbing carbon dioxide, is supplied to the regeneration tower via the supply path, and the absorption liquid is heated by heat exchange with a heat transfer medium, The heating means is a carbon dioxide recovery device set to processing conditions that cause carbon dioxide to be released from the absorbent liquid.

2. The carbon dioxide recovery apparatus according to claim 1, wherein the processing conditions are such that the temperature of the heat transfer medium in the heating means is higher than the temperature at which carbon dioxide is desorbed from the absorbent liquid.

3. The carbon dioxide recovery apparatus according to claim 1, wherein the processing conditions are such that the pressure of the absorbent liquid in the heating means is set to the pressure at which carbon dioxide is released from the absorbent liquid.

4. The carbon dioxide recovery apparatus according to claim 3, further comprising a pressure adjustment means for adjusting the pressure to a level at which carbon dioxide can be released from the absorbent liquid.

5. The aforementioned supply line is A first supply path for supplying the absorbent liquid from the absorption tower to the regeneration tower, A second supply path for supplying the absorbent liquid from the regeneration tower to the absorption tower, Includes, The heating means is a heat pump equipped with a condenser and an evaporator. The system further comprises an absorbent liquid heat exchanger interposed between the first and second supply channels, which is capable of heat exchange between the absorbent liquid flowing through the first supply channel and the absorbent liquid flowing through the second supply channel. The condenser is interposed between the heat exchanger and the regeneration tower in the first transmission line. The carbon dioxide recovery apparatus according to any one of claims 1 to 4, wherein the evaporator is interposed between the heat exchanger and the absorption tower in the second supply line.

6. A carbon dioxide recovery apparatus according to any one of claims 1 to 4, further comprising a reboiler for heating the absorbent liquid heated by the heating means.

7. A carbon dioxide recovery method comprising circulating an absorbent liquid between an absorption tower and a regeneration tower via a supply path, allowing carbon dioxide to be absorbed by the absorbent liquid in the absorption tower, and recovering carbon dioxide in the regeneration tower, The absorption liquid, which has absorbed carbon dioxide in the absorption tower and is then supplied to the regeneration tower via the supply path, is heated by heat exchange with a heat transfer medium, including a heating step. The aforementioned heating step is a carbon dioxide recovery method performed under processing conditions in which carbon dioxide is detached from the absorbent liquid.

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