Recovery device and recovery method of carbon dioxide

Abstract

To provide a recovery device of carbon dioxide capable of efficiently utilizing heat, and reducing a heat energy charge amount to a regeneration tower.SOLUTION: A recovery device of carbon dioxide includes an absorption tower which brings gas containing carbon dioxide into contact with an absorption liquid, and produces rich liquid absorbing carbon dioxide, a heat exchanger for preheating the rich liquid, and a regeneration tower which heats the rich liquid and discharges the carbon dioxide, produces the lean liquid, and discharges the discharged carbon dioxide, and has a first heat exchanger for using gas containing carbon dioxide as a heat source before contacting the absorption liquid, and preheating the rich liquid, and a second heat exchanger for using the lean liquid discharged from the regeneration tower as a heat source, and preheating the rich liquid discharged from the first heat exchanger, as heat exchangers.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a carbon dioxide recovery apparatus and a recovery method.

Background Art

[0002] In recent years, as an effective countermeasure against the global warming problem that is a concern on a global scale, efforts have been made toward the practical application of carbon dioxide recovery technology. As carbon dioxide recovery technologies, a physical absorption method, a chemical absorption method, a membrane separation method, a cryogenic separation method, etc. are known. Among them, the chemical absorption method is a method suitable for recovering carbon dioxide contained in exhaust gas discharged in large quantities at thermal power plants, plants, etc.

[0003] Conventionally, as a carbon dioxide recovery apparatus using the chemical absorption method, for example, before supplying combustion exhaust gas to an absorption tower, it is purified by a dust collector and a desulfurization apparatus, and the purified combustion exhaust gas is brought into contact with an absorption liquid using an alkanolamine aqueous solution in a regeneration tower to absorb carbon dioxide, and the absorption liquid that has absorbed carbon dioxide is heated in the regeneration tower to expel carbon dioxide and recover carbon dioxide. A combustion exhaust gas purification apparatus is known (Patent Document 1). Further, as a carbon dioxide recovery apparatus that effectively utilizes the heat of exhaust gas, heat is recovered from the exhaust gas of a boiler by a heat recovery apparatus, and the recovered heat is given to the absorption liquid sent from the regeneration tower to the reboiler by a heat exchange means, and an exhaust gas treatment system that supplies the heated absorption liquid to the regeneration tower has been proposed (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The chemical absorption method is a technology for recovering carbon dioxide by utilizing the property that the absorption liquid absorbs carbon dioxide at a low temperature (for example, 30 to 40 °C) and releases it at a high temperature (for example, 120 °C). However, in order to release carbon dioxide from the absorption liquid (rich liquid) that has absorbed carbon dioxide in the regeneration tower, it is necessary to raise the temperature of the rich liquid to a predetermined temperature, which requires a huge amount of thermal energy. Therefore, reduction of the thermal energy input to the regeneration tower is demanded. Accordingly, an object of the present invention is to provide a carbon dioxide recovery apparatus and a recovery method capable of efficiently utilizing heat and reducing the amount of thermal energy input to a regeneration tower.

Means for Solving the Problems

[0006] The inventors of the present invention have conducted various studies to further reduce the amount of thermal energy input to the regeneration tower. As a result, in Patent Document 2, it is described that when the rich liquid discharged from the absorption tower is heated using the heat of the exhaust gas and the temperature rises too much, the rich liquid does not fall to the lower tank in the regeneration tower, making it difficult to circulate the liquid. Therefore, it is necessary to provide a limit to the preheating of the rich liquid. However, the inventors of the present invention have provided a second heat exchange means that utilizes the heat of the lean liquid in addition to the first heat exchange means that utilizes the heat of the exhaust gas to preheat the rich liquid in two stages. Surprisingly, it has been found that the amount of thermal energy input to the regeneration tower can be significantly reduced without causing the above-described problems. Here, in the present specification, the “rich liquid” refers to an absorption liquid that has absorbed carbon dioxide, and the “lean liquid” refers to an absorption liquid that has been regenerated by removing carbon dioxide from the rich liquid.

[0007] That is, the present invention provides the following [1] to [3]. [1] An absorption tower that brings a gas containing carbon dioxide into contact with an absorption liquid to generate a rich liquid that has absorbed carbon dioxide, A heat exchanger that preheats the rich liquid, A regeneration tower that heats the rich liquid to release carbon dioxide, generates a lean liquid, and discharges the released carbon dioxide and is provided with As a heat exchanger, it has a first heat exchanger that uses the gas containing carbon dioxide before contacting the absorption liquid as a heat source to preheat the rich liquid, and a second heat exchanger that uses the lean liquid discharged from the regeneration tower as a heat source to preheat the rich liquid discharged from the first heat exchanger. Carbon dioxide recovery device. 〔2〕The carbon dioxide recovery device according to 〔1〕, wherein the gas containing carbon dioxide is combustion exhaust gas or calcination exhaust gas. 〔3〕A first step of bringing the gas containing carbon dioxide into contact with the absorption liquid to generate a rich liquid that has absorbed carbon dioxide, A second step of preheating the rich liquid, A third step of heating the rich liquid to release carbon dioxide, generating a lean liquid, and recovering the released carbon dioxide including, The second step has a first heat exchange step that uses the gas containing carbon dioxide before the first step as a heat source to preheat the rich liquid, and a second heat exchange step that uses the lean liquid as a heat source to preheat the rich liquid after the first heat exchange step. Carbon dioxide recovery method.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a carbon dioxide recovery device and a recovery method that can efficiently utilize heat and reduce the amount of heat energy input to the regeneration tower.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. Note that the following embodiments are examples for explaining the present invention, and are not intended to limit the present invention to the following content. Also, for the sake of illustration, the dimensional ratios in the drawings do not necessarily match those in the description.

[0011] FIG. 1 is a diagram schematically showing a carbon dioxide recovery apparatus according to the present embodiment. Hereinafter, the recovery apparatus and a method for recovering carbon dioxide using the recovery apparatus will be described.

[0012] The carbon dioxide recovery apparatus shown in FIG. 1 includes an absorption tower that brings a gas containing carbon dioxide into contact with an absorption liquid to generate a rich liquid that has absorbed carbon dioxide, and a regeneration tower that heats the rich liquid to release carbon dioxide to generate a lean liquid and discharges the released carbon dioxide. That is, in the absorption tower and the regeneration tower, carbon dioxide is absorbed and separated by a chemical absorption method. Then, the absorption liquid (lean liquid) regenerated by releasing carbon dioxide from the rich liquid in the regeneration tower is supplied to the absorption tower and circulates between the absorption tower and the regeneration tower. In addition, two heat exchangers are provided between the absorption tower and the regeneration tower. That is, the first heat exchanger is provided between the absorption tower and the second heat exchanger, uses the gas containing carbon dioxide before contacting the absorption liquid as a heat source, and preheats the rich liquid. The second heat exchanger is provided between the first heat exchanger and the regeneration tower, uses the lean liquid discharged from the regeneration tower as a heat source, and preheats the rich liquid discharged from the first heat exchanger.

[0013] The gas containing carbon dioxide is not particularly limited as long as it contains carbon dioxide, and examples thereof include exhaust gases such as combustion exhaust gas and firing exhaust gas. Examples of the combustion exhaust gas include exhaust gases generated by fuel combustion in a thermal power plant, a boiler, etc., and exhaust gases generated by incineration of garbage in a cleaning factory. Examples of the firing exhaust gas include cement kiln exhaust gas generated by firing clinker raw materials in a cement kiln. Other examples include biomass exhaust gas generated by methane fermentation of biomass.

[0014] The gas containing carbon dioxide flows through the flow path and is supplied to the absorption tower. The absorption tower brings the gas containing carbon dioxide into contact with an absorption liquid that absorbs carbon dioxide, and causes the carbon dioxide contained in the gas to be absorbed by the absorption liquid to generate a rich liquid.

[0015] The absorption liquid is not particularly limited as long as it can come into contact with the gas containing carbon dioxide and absorb carbon dioxide. For example, organic amines can be mentioned. The organic amine can be a primary amine, a secondary amine, or a tertiary amine. For example, alkanolamine, TMDAH (tetramethyldiaminohexane), piperazine (PZ / PIPA) can be mentioned. Among them, alkanolamine is preferred from the viewpoints of carbon dioxide absorption / separation efficiency and cost. Specific examples include, for example, monoethanolamine (MEA), EAE (ethylaminoethanol), IPAE (isopropaanolaminoethanol), methyldiethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP). The organic amine can be used as it is or in the form of an aqueous solution, but the form of an aqueous solution is preferred from the viewpoint of preventing corrosion of the device. The concentration of the aqueous solution of the organic amine can be appropriately selected, but is usually 10 to 45% by mass.

[0016] In the absorption tower, the absorption liquid descends while the gas containing carbon dioxide ascends. As a result, the absorption liquid and the gas containing carbon dioxide are in countercurrent contact, and the carbon dioxide contained in the gas is absorbed by the absorption liquid. The amount of carbon dioxide absorbed by the absorption liquid depends on the temperature. Therefore, by controlling the temperature inside the absorption tower, the amount of carbon dioxide absorbed by the absorption liquid can be adjusted. Also, in order to increase the contact efficiency between the gas containing carbon dioxide and the absorption liquid, one or more packing layers may be provided from above to below inside the absorption tower.

[0017] Inside the absorption tower, the absorption liquid descends while making gas-liquid contact with the gas containing carbon dioxide, and absorbs the carbon dioxide contained in the gas to generate a rich liquid (the first step). The gas from which carbon dioxide has been removed (carbon dioxide-removed gas) rises inside the absorption tower and is discharged outside the absorption tower through a flow path connected to the top of the absorption tower.

[0018] The temperature inside the absorption tower can be appropriately set according to, for example, the type of absorption liquid. For example, it is 30 to 40°C. The pressure inside the absorption tower is, for example, 0 to 1.0 MPa.

[0019] The rich liquid that has absorbed carbon dioxide in the absorption tower is accumulated at the bottom of the absorption tower and is discharged from the absorption tower at, for example, 30 to 50°C through a flow path connected to the bottom of the tower. The rich liquid discharged from the absorption tower is supplied to the first heat exchanger via a pump.

[0020] When using exhaust gas as the gas containing carbon dioxide, for example, the exhaust gas from a cement kiln is at a high temperature of 100 to 120°C. Therefore, in order to effectively utilize the thermal energy of the exhaust gas, a first heat exchanger is provided. And in the first heat exchanger, the rich liquid is preheated with the heat recovered from the exhaust gas. As a result, the rich liquid is preheated to, for example, 50 to 80°C and discharged from the first heat exchanger.

[0021] Note that the exhaust gas discharged from the first heat exchanger is cooled to an appropriate temperature (for example, 30 to 40°C) with a cooler or the like before being supplied to the absorption tower. Also, since the exhaust gas contains sulfur oxides, nitrogen oxides, etc. in addition to carbon dioxide, the cooled exhaust gas may be supplied to the absorption tower after removing sulfur oxides and nitrogen oxides with a desulfurization device or a denitration device.

[0022] The rich liquid discharged from the first heat exchanger flows through a flow path and is supplied to the second heat exchanger. The lean liquid discharged from the regeneration tower is, for example, at a high temperature of around 120°C. Therefore, in order to effectively utilize the thermal energy of the lean liquid, a second heat exchanger is provided. And in the second heat exchanger, the rich liquid discharged from the first heat exchanger is preheated with the heat recovered from the lean liquid. As a result, the rich liquid is preheated to, for example, 90 to 110°C and discharged from the second heat exchanger.

[0023] Examples of the first heat exchanger and the second heat exchanger include plate heat exchangers, multi-tube heat exchangers, and tube-type heat exchangers. The first heat exchanger and the second heat exchanger may be of the same type or different types.

[0024] In this way, the rich liquid is preheated in two stages, namely the first heat exchange step and the second heat exchange step (the second step), before being supplied to the regeneration tower. As a result, the rich liquid can be supplied to the regeneration tower in a state where it is heated to a certain temperature or higher, so that the amount of heat energy required for the release of carbon dioxide in the regeneration tower can be significantly reduced.

[0025] Note that the lean liquid discharged from the second heat exchanger is cooled to an appropriate temperature (for example, 30 to 40 °C) by a cooler or the like before being supplied to the absorption tower. Also, before cooling the lean liquid by a cooler or the like, for example, the carbon dioxide-removed gas discharged from the absorption tower is at 30 to 40 °C and is likely to condense in the flow path. Therefore, as a countermeasure against condensation, a third heat exchanger may be provided to preheat the carbon dioxide-removed gas using the lean liquid discharged from the second heat exchanger as a heat source. The third heat exchanger can also be of the same type as described above. And the lean liquid discharged from the third heat exchanger may be cooled to an appropriate temperature by a cooler or the like.

[0026] The rich liquid discharged from the second heat exchanger flows through the flow path and is supplied to the regeneration tower. The regeneration tower releases carbon dioxide from the rich liquid generated in the absorption tower to regenerate the absorption liquid. In the regeneration tower, one or more packing layers may be provided from top to bottom in order to efficiently separate the liquid and the gas.

[0027] The rich liquid introduced into the regeneration tower flows down inside the regeneration tower and stays on a tray provided at or near the bottom of the regeneration tower. Outside the regeneration tower, a heat exchanger A for heating the absorption liquid staying at or near the bottom of the regeneration tower is provided. The absorption liquid flows through a flow path and is introduced into the heat exchanger A, where it exchanges heat with steam, which is the heat medium, and is heated. The absorption liquid is heated by the heat exchanger A to, for example, 110 to 130°C, preferably 120°C. The heated absorption liquid flows through a flow path and returns to the inside of the regeneration tower.

[0028] The heat exchanger A heats the absorption liquid by exchanging heat with steam, which is the heat medium. The steam flows through a flow path from the boiler section and is supplied to the heat exchanger A.

[0029] The carbon dioxide released from the absorption liquid rises inside the regeneration tower. Then, the carbon dioxide is discharged outside the regeneration tower through a flow path connected to the top of the regeneration tower. In this way, the carbon dioxide in the gas containing carbon dioxide is separated from the absorption liquid, and the absorption liquid is regenerated (the third step). The concentration of the carbon dioxide discharged from the flow path connected to the top of the regeneration tower is, for example, 99% by volume or more, preferably 99.9% by volume or more.

[0030] At the bottom of the regeneration tower, a flow path for discharging the absorption liquid (lean liquid) from which carbon dioxide has been removed from the regeneration tower is connected. The lean liquid flows through a flow path and is introduced into the second heat exchanger, where it is cooled by exchanging heat with the rich liquid from the absorption tower. Then, the lean liquid cooled by the second heat exchanger flows through a flow path and is introduced into a cooler, where it is cooled to, for example, 30 to 40°C. Then, the absorption liquid (lean liquid) flows through a flow path and is supplied to the upper part of the absorption tower. In this way, the absorption liquid is used while circulating between the absorption tower and the regeneration tower.

Example

[0031] Hereinafter, the embodiments of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[0032] Example 1 and Comparative Examples 1 and 2 Using cement kiln exhaust gas and a 30% aqueous monoethanolamine solution as the organic amine liquid, carbon dioxide separation and recovery were carried out under the following conditions. In Example 1, the carbon dioxide recovery apparatus according to the present invention shown in FIG. 1 was used. First, the low-temperature rich liquid was preheated by a first heat exchanger that contacts it with the high-temperature exhaust gas, and then two-stage heat exchange was performed, where the rich liquid was preheated by a second heat exchanger that contacts it with the lean liquid. In Comparative Example 1, the carbon dioxide recovery apparatus shown in FIG. 2 was used, and one-stage heat exchange was performed, where the rich liquid was preheated only by the second heat exchanger that contacts it with the lean liquid. In Comparative Example 2, the carbon dioxide recovery apparatus shown in FIG. 3 was used, and the arrangement of the heat exchangers in the carbon dioxide recovery apparatus shown in FIG. 1 was interchanged. Two-stage heat exchange was performed, where first the low-temperature rich liquid was preheated by the second heat exchanger that contacts it with the lean liquid, and then the rich liquid was preheated by the first heat exchanger that contacts it with the high-temperature exhaust gas.

[0033] (Operating conditions) · Amine liquid flow rate: 6000 L / h · Exhaust gas flow rate: 4000 Nm 3 / h · Exhaust gas temperature: 120 °C · Exhaust gas specific heat: 1.4 kJ / (K·Nm 3 ) · Amine liquid specific heat: 4.2 kJ / (K·kg) · Amine liquid specific gravity: 1.0 · Absorption tower temperature: 40 °C · Desorption tower temperature: 120 °C · CO2 recovery amount: 500 kg-CO2 / h

[0034] (Heat exchange conditions between the exhaust gas and the rich liquid) The temperature of the rich liquid discharged from the heat exchanger was set to be 1 °C higher than the temperature of the rich liquid supplied to the heat exchanger, as shown in the following formula.

[0035] X (°C) = Y (°C) + 1 °C [In the formula, X represents the temperature of the rich liquid discharged from the heat exchanger, and Y represents the temperature (°C) of the rich liquid supplied to the low heat exchanger.]

[0036] (Heat exchange conditions between rich liquid and lean liquid) The temperature efficiency of the rich liquid supplied to the heat exchanger was set to 80% as calculated by the following formula.

[0037] Temperature efficiency (%) = [(A - B) / (C - B)] × 100 [In the formula, A represents the temperature (°C) of the rich liquid discharged from the heat exchanger, B represents the temperature (°C) of the rich liquid supplied to the heat exchanger, and C represents the temperature (°C) of the lean liquid supplied to the heat exchanger.]

[0038] Then, it was calculated by comparing with the amount of heat energy input to the regeneration tower of Comparative Example 1 how much the amount of heat energy input to the regeneration tower of the carbon dioxide recovery apparatuses of Example 1 and Comparative Example 2 could be reduced. The results are shown in Table 1.

[0039] (Calculation of heat energy reduction amount) Based on the respective temperatures of the rich liquid supplied to the regeneration towers of Comparative Example 1, Example 1, and Comparative Example 2, the reduction amount of heat energy input to the regeneration tower was calculated by comparing with Comparative Example 1. The temperature of the rich liquid supplied to the regeneration tower was 104°C for Comparative Example 1, 108°C for Example 1, and 107°C for Comparative Example 2.

[0040] (Comparison between Example 1 and Comparative Example 1) The reduction amount of heat energy compared with Comparative Example 1 was calculated by the following formula.

[0041] Specific heat of amine liquid [kJ / (K·kg)] × amine liquid flow rate (L / h) × specific gravity × [(temperature (°C) of the rich liquid supplied to the regeneration tower of Example 1) - (temperature (°C) of the rich liquid supplied to the regeneration tower of Comparative Example 1)]

[0042] The reduction amount of heat energy compared with Comparative Example 1 is as follows. 4.2 × 6000 × 1 × (108 - 104) = 101 MJ / h

[0043] (Comparison between Comparative Example 2 and Comparative Example 1) The amount of heat energy reduction compared with Comparative Example 1 was calculated by the following formula.

[0044] Specific heat of amine solution [kJ / (K·kg)] × Amine solution flow rate (L / h) × Specific gravity × [(Rich solution temperature (°C) supplied to the regeneration column in Comparative Example 2) - (Rich solution temperature (°C) supplied to the regeneration column in Comparative Example 1)]

[0045] The amount of heat energy reduction compared with Comparative Example 1 is as follows in the following formula. 4.2×6000×1×(107 - 104) = 76 MJ / h

[0046]

Table 1

[0047] As shown in Table 1, in Comparative Example 2, the temperature of the rich solution supplied to the regeneration column was 3°C higher than that in Comparative Example 1, and the heat energy could be reduced by 76 MJ per hour. On the other hand, in Example 1, the temperature of the rich solution supplied to the regeneration column was 4°C higher than that in Comparative Example 1, and the heat energy could be reduced by 101 MJ per hour. From this result, it can be seen that Example 1 can not only significantly reduce the amount of heat energy input to the regeneration column compared with Comparative Example 1, but also reduce the amount of heat energy input to the regeneration column by about 30% compared with Comparative Example 2. Therefore, the carbon dioxide recovery device of the present invention first preheats the low-temperature rich solution by a first heat exchanger that brings it into contact with high-temperature exhaust gas, and then preheats this rich solution by a second heat exchanger that brings it into contact with the lean solution. By performing two-stage heat exchange, it is possible to significantly improve the heat exchange efficiency without causing the conventional problem of poor circulation in the regeneration column due to excessive temperature rise of the rich solution.

Claims

1. An absorption tower that brings a gas containing carbon dioxide into contact with an absorption liquid to produce a rich liquid that has absorbed carbon dioxide, a heat exchanger that preheats the rich liquid, a regeneration tower that heats the rich liquid to release carbon dioxide to produce a lean liquid and discharges the released carbon dioxide and is provided with, as the heat exchanger, a first heat exchanger that uses the gas containing carbon dioxide before contacting the absorption liquid as a heat source to preheat the rich liquid, and a second heat exchanger that uses the lean liquid discharged from the regeneration tower as a heat source to preheat the rich liquid discharged from the first heat exchanger, a carbon dioxide recovery device.

2. The carbon dioxide recovery device according to Claim 1, wherein the gas containing carbon dioxide is combustion exhaust gas or calcination exhaust gas.

3. A first step of bringing a gas containing carbon dioxide into contact with an absorption liquid to produce a rich liquid that has absorbed carbon dioxide, a second step of preheating the rich liquid, and a third step of heating the rich liquid to release carbon dioxide to produce a lean liquid and recovering the released carbon dioxide are included, wherein the second step has a first heat exchange step of using the gas containing carbon dioxide before the first step as a heat source to preheat the rich liquid, and a second heat exchange step of using the lean liquid as a heat source to preheat the rich liquid after the first heat exchange step, a method for recovering carbon dioxide.

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