JP2019069417A - Method and installation for recovering carbon dioxide from exhaust gas - Google Patents

Abstract

To solve such a problem that, when CO2 solid adsorbent is used as a system for separating and recovering CO2 from an exhaust gas, purity of recovered CO2 decreases due to influence from an exhaust gas remaining in a clearance in an adsorption tower after CO2 is absorbed.SOLUTION: A method for recovering carbon dioxide from an exhaust gas includes a purge step that is provided between CO2 adsorption step and a desorption step as CO2 separation recovery step using CO2 solid adsorbent. A purge gas used for the purge step is supplied from CO2 storage step for storing CO2 that is condensed in the desorption step.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a carbon dioxide recovery method and equipment.

  The Paris Agreement, a new international framework to combat global warming after 2020, came into force on November 4, 2016. Prior to the conclusion of the agreement on December 12, 2015, a draft of Japan's commitment on July 17 of the same year was secured by the reduction and absorption of CO2 emissions, which are global warming gases. It is submitted to the UN Framework Convention on Climate Change (UNFCCC) to achieve a level (about 1,042 million t-CO2) compared to the FY 2005 level. Based on the above, it is considered that the movement for reducing carbon dioxide emissions will be increasingly developed on a global scale.

The sources of carbon dioxide (CO2) emissions are diverse, such as thermal power generation, steel, natural gas mining, various chemical industries, etc. CO2 recovery technology from these sources has been developed since the late 20th century. As methods that have been put into practical use as CO2 recovery technologies up to the present, in addition to chemical absorption and physical absorption methods using an absorbing solution, a membrane separation method that selectively allows CO2 permeation and liquefaction temperature difference of mixed gas are used. There is a cryogenic separation method etc. CO ₂ separation and recovery technology has technical and cost advantages respectively, but as a CO ₂ separation and recovery technology from a large-scale plant, it is considered that the chemical absorption method or physical absorption method using CO2 absorbent is suitable There is.

  However, in the CO2 separation and recovery technology using the CO2 absorbing solution, a large amount of energy is required to regenerate the absorbing solution that has absorbed CO2, and the energy required for the regeneration is the main cause of the increase in CO2 recovery cost. To solve this problem, for example, as shown in Patent Document 1, a method of recovering low temperature waste heat by utilizing a heat pump for heat recovery, and as shown in Patent Document 2, waste heat suppression of condensation latent heat using vapor compression. The reduction of external energy input required for CO2 regeneration is being considered by However, these are significant methods in terms of the improvement of the regeneration efficiency of the absorbing solution, but they cause the system complexity and the initial cost increase due to the increase in the number of components.

  On the other hand, there is a CO2 recovery method using a solid CO2 adsorbent as a CO2 capture material. Since the solid adsorbent has a smaller heat capacity than the above-described absorbent, it is considered to be a technology capable of reducing the regenerated energy, and has recently attracted attention. Patent Document 3 describes an example of a CO 2 separation and recovery method using a solid adsorbent. A gas containing CO 2 (CO 2 -containing gas) is introduced into a container filled with a solid adsorbent, and the adsorbent is brought into contact with the CO 2 -containing gas to capture and remove CO 2 in the adsorbent. Thereafter, the adsorbed CO2 is released by heating the adsorbent and recovered. This patent document adopts a fixed bed system, and the CO2 separation recovery comprises a CO2 adsorption process, a CO2 desorption process from the CO2 adsorbent, and a cooling process of the adsorbent after regeneration. Further, Patent Document 4 describes an example of a CO 2 separation and recovery method using a drum system as another system. In the technology described in Patent Document 4, the adsorption step, the desorption step, and the cooling step are sequentially performed by rotating a drum-shaped adsorbent made of zeolite as a raw material. In this system, at the time of desorption, the adsorbent is heated by circulating high temperature CO 2 to desorb CO 2.

Patent No. 5468562 gazette Patent No. 5725992 Unexamined-Japanese-Patent No. 2010-69398 Unexamined-Japanese-Patent No. 2004-344703

  In the patent documents 3 and 4 mentioned above, the CO2 separation and recovery process is made into three processes of CO2 adsorption, desorption, and cooling. However, when the CO 2 adsorption to the adsorbent is saturated in the CO 2 adsorption step, the exhaust gas containing CO 2 remains in the voids in the adsorption tower filled with the adsorbent. When the adsorbent is regenerated in the desorption process in the presence of the residual gas, the regenerated gas contains not only CO2 desorbed from the adsorbent but also exhaust gas components remaining in the adsorption process. As a result, it is considered that the CO2 purity in the regeneration gas is reduced. This is a problem common to the system using a solid adsorbent, and the same applies to the fixed bed system and the drum system. The main purpose of attaching CO2 separation and recovery equipment in various industrial fields, which are CO2 emission sources, is presumed to be to reduce CO2 emissions from plants, but in cases where recycled CO2 is to be reused for other applications , Purity of recovered CO2 is important.

  The present invention for solving the above means is an adsorption tower packed with a CO2 adsorbent that selectively adsorbs CO2, a CO2 adsorption process for adsorbing and separating CO2 contained in exhaust gas, and an exhaust gas present in voids in the CO2 adsorption tower A carbon dioxide recovery method comprising a purge step of discharging the carbon dioxide, a CO2 desorption step of desorbing CO2 adsorbed on the CO2 adsorbent from the adsorbent by thermal energy, and a cooling step of cooling the CO2 adsorption tower after CO2 desorption; The carbon dioxide recovery method further includes a CO 2 storage step of temporarily storing CO 2 concentrated and separated in the CO 2 desorption step, and the purge gas in the purge step uses CO 2 supplied from the CO 2 storage step.

  In the CO2 desorption step, the CO2 adsorbent packed in the adsorption tower is heated beforehand by internal or external heating, water vapor is supplied from the inlet of the adsorption tower, and CO2 desorbed from the CO2 adsorbent is discharged from the adsorption tower A carbon dioxide recovery method characterized by:

  Furthermore, the outlet of the adsorption column is provided with a CO2 concentration measurement step, and when the CO2 concentration in the exhaust gas discharged during the CO2 adsorption step and the purge step reaches a predetermined value or more, the gas from the previous exhaust gas introduction line and the CO2 supply line It is a carbon dioxide recovery method characterized by stopping supply.

  According to the present invention, the CO2 purity in the regeneration gas from the CO2 adsorbent can be improved.

1 is a process flow of the present invention shown in Example 1; It is an example of the system block diagram of this invention shown in Example 2. FIG. FIG. 16 is an example of a system configuration diagram of the present invention shown in the third embodiment.

  Hereinafter, although an embodiment is given and described about an embodiment of the present invention, the present invention is not limited to the following embodiments.

  In the present example, the CO 2 separation and recovery method of the present invention will be described. FIG. 1 shows a conceptual diagram of the CO2 separation and recovery method according to the present invention. Here, the gas species to be supplied to the adsorption tower in the four steps of adsorption, purge, desorption, and cooling will be described for one adsorption tower packed with a CO 2 solid adsorbent, and the state in the adsorption tower at that time.

  First, the exhaust gas 1 containing CO 2 is supplied to the adsorption tower as the first step. When CO2 in the exhaust gas 1 is captured by the adsorbent, the exhaust gas 2 containing no CO2 is discharged from the outlet of the adsorption tower. The temperature of the exhaust gas 1 supplied to the adsorbent depends on the type of adsorbent to be charged. The appropriate temperature is also considered to be different depending on whether the adsorbent captures CO 2 by physical adsorption or chemical adsorption. However, when CO2 is captured not by absorption but by adsorption, it is desirable to select an adsorbent that can be adsorbed at a low temperature as much as possible considering the energy required for regeneration. As a standard, it is 100 ° C. or less, preferably 50 ° C. or less. The supply of the exhaust gas 1 is stopped when the CO2 adsorption to the adsorbent reaches saturation in the adsorption step. At that time, the exhaust gas 1 containing CO 2 remains in the air gap in the adsorption tower.

  Next, CO2 is supplied to the adsorption tower in a purge step in order to discharge the exhaust gas 1 remaining in the void. The CO2 to be supplied here is supplied from the CO2 storage step storing the high concentration of CO2 discharged in the next step, the desorption step. The purpose of the purge step is to discharge the exhaust gas 1 remaining in the void from the adsorption tower, and the exhaust gas 1 discharged from the adsorption tower is exhausted out of the system. Therefore, if the amount of CO2 supplied in the purge step is excessive, the amount of CO2 in the exhaust gas increases, and the CO2 recovery rate of the plant decreases. Therefore, it is desirable that the amount of CO2 supplied in the purge step 空隙 void amount. Also, in order to suppress mixing of the supplied CO 2 and the exhaust gas 1 in the air gap in the adsorption tower, a flow straightening plate such as a mesh plate is installed above the adsorbent in the adsorption tower to make the flow uniform In addition, it is desirable to control the flow rate such that the flow is laminar. After the end of the purge step, the adsorbent is CO 2 saturated and adsorbed, and a high concentration of CO 2 remains in the air gap.

  Next, CO2 in the adsorbent is desorbed in the desorption step to regenerate the adsorbent. There are temperature swing method (TSA: Thermal Swing Adsorption) using thermal energy, and pressure swing method (PSA: Pressure Swing Adsorption) that uses gas compression and expansion as driving force as CO 2 desorption method from adsorbent. The present invention is directed to TSA. Further, in the present invention, steam is used as a medium gas for discharging from the adsorption column the CO2 desorbed from the adsorbent by the thermal energy and the CO2 retained in the pores. The reason for using water vapor is that separation from CO2 is easy. That is, the regenerated gas containing CO2 and steam discharged from the adsorption column can be easily separated into high concentration CO2 and water by the cooler and the gas-liquid separator. The adsorption and purge steps are operated at low temperatures below 100 ° C. Therefore, when steam as a medium gas is supplied to the adsorption tower immediately after the purge step, the steam is condensed on the adsorbent. Therefore, it is necessary to heat the adsorbent before supplying the water vapor. The preheating method may be either external / internal heating. The heating temperature depends on the characteristics of the adsorbent to be packed into the adsorption column, but the temperature from 100 ° C to 250 ° C, the CO2 desorption characteristic, the regeneration temperature of the chemical absorption method using the aforementioned absorbent, the adsorbent in the next step 100 ° C. to 200 ° C. is desirable in consideration of the time required for cooling, etc. When the adsorbent is sufficiently heated by preheating, water vapor is supplied to discharge CO2 which is desorbed from the adsorbent and CO2 in the air gap to the outside of the adsorption tower. The regenerated gas discharged from the adsorption tower is cooled and subjected to gas-liquid separation, and CO2 is sent to the CO2 storage step.

  Finally, the adsorbent (tower) heated in the desorption step is cooled. Preferred as the cooling gas is the exhaust gas 2 not containing CO 2 exhausted after CO 2 adsorption in the adsorption step. Specifically, a step of storing the exhaust gas from which CO 2 has been removed is provided in the exhaust gas line of the exhaust gas, and the cooling gas used in the cooling step is supplied therefrom. That is, the exhaust gas is circulated and supplied as the cooling gas in the CO 2 separation and recovery mechanism. By using the exhaust gas as the cooling gas, the cooling cost can be reduced. If a surplus utility such as nitrogen or oxygen can be used in a plant where a CO2 separation and recovery facility is installed, these gases may be used. Here, it is assumed that there is no surplus utility. The cooling gas should be a dry gas, and a gas free of CO2 is preferred. For example, in the case of cooling using exhaust gas 1 containing CO 2, not only CO 2 is discharged as exhaust gas under the assumption of cooling but also CO 2 is adsorbed to the adsorbent, and the CO 2 adsorption amount decreases in the subsequent adsorption step. is there. In the cooling step, the exhaust gas 2 is used to cool the adsorbent (column) to 100 ° C. or less, which is the adsorption temperature in the adsorption step. After being cooled to the use temperature in the adsorption step, the same operation as described above is repeated from the adsorption step again.

  In addition, in the cooling step, the CO 2 lean gas from the adsorption step may be used and circulated and supplied in the CO 2 separation and recovery mechanism. By using the CO2 lean gas in the cooling step, the adsorption of CO2 on the adsorbent can be suppressed, and the CO2 removal rate can be improved by cooling the adsorbent.

  The present embodiment shows an example of a system according to the present invention. An example of a system configuration diagram is shown in FIG. The system of FIG. 2 comprises an adsorption tower 1 filled with an adsorbent 2, an electric heater 3 for external heating, a CO 2 storage tank 4, an exhaust gas storage tank 5, a pump 6, a cooler 7, and a knockout drum 8. In the present embodiment, the fixed bed adsorption tower has four columns. Here, an example of CO 2 adsorption operation in the exhaust gas is shown for the first adsorption tower 1a.

  First, the exhaust gas 101 is supplied to the adsorption tower 1a. At that time, the valve V1a installed in the exhaust gas supply pipe 21 and the valve V3a installed in the exhaust gas discharge pipe 24 are opened. During the adsorption operation, part of the exhaust gas discharged from the adsorption tower is supplied to the exhaust gas storage tank 5 and stored. After the CO2 adsorption to the adsorbent 2a reaches saturation, the valve V1a is closed, the exhaust gas to the adsorption tower 1a is stopped, and at the same time the valve V1b is opened to shift to the adsorption operation of the adsorption tower 1b. Any adsorbent may be used as the adsorbent to be packed in the adsorption column, as long as it is a solid that adsorbs CO2 such as activated carbon, zeolite, cerium oxide, etc. If water is contained in the exhaust gas, CO2 is absorbed by the adsorption of water onto the adsorbent. Since there is a concern about adsorption inhibition, adsorbents of, for example, cerium oxide type, which are less affected by moisture, are preferred. Also, the filling method may be any form as long as it can be filled in a fixed layer such as granular, honeycomb or plate-like. However, when the volume of the processing gas is large, in consideration of pressure loss, it is preferable to use a honeycomb-like or plate-like form in which the adsorptive material is coated on the surface.

  Next, in the adsorption tower 1a, the valve 4a installed in the CO2 supply pipe 22 is opened, CO2 stored in the CO2 storage tank 4 is supplied via the pump 6a, and the inside of the adsorption tower is purged with CO2. During the purge operation, the amount of voids in the adsorption tower is measured in advance, and control is performed to supply the minimum amount of CO 2 for discharging the exhaust gas remaining in the voids to the outside of the adsorption tower. After the purge operation is completed, the valve 4a and the valve 3a are closed.

  Next, the detachment operation is performed. In the present embodiment, an external heating electric heater 3 was installed in each adsorption tower. As long as it can heat the adsorption tower and the packed adsorbent, any heating method may be used either external / internal heating type, and the heating method may be any medium having heat such as water vapor other than electric heaters, for example. It may be a method. In the desorption operation, first, the valve V5a installed in the desorption gas discharge pipe 25 is opened, and then the adsorption tower is heated to the desorption temperature by an electric heater. The amount of gas expansion in the process of heating and CO 2 desorbed from the adsorbent are discharged from the CO 2 discharge pipe and sent to the CO 2 storage tank 4. After the temperature of the adsorption tower 1a is raised to a predetermined temperature, the valve V6a installed in the steam supply pipe 23 is opened, steam is introduced into the adsorption tower 1a, and the CO2 retained in the void is discharged out of the adsorption tower At the same time, the CO2 desorbed from the adsorbent 2a is discharged to the outside of the column as the CO2 partial pressure decreases. The desorbed gas containing water vapor is separated into CO2 and water by the cooler 7a and the knockout drum 8a, and a part of the CO2 is stored in the CO2 storage tank. After completion of the detachment operation, the valves 5a and 6a are closed, and the electric heater 3a is stopped.

  Finally, the cooling operation is performed. The cooling operation is performed using a gas which is discharged from the adsorption tower at the time of the adsorption operation and contains almost no CO 2 stored in the exhaust gas storage tank. First, among the valves installed in the exhaust gas supply pipe 21, V1a and V2a are opened. Further, the valve V3a installed in the exhaust gas discharge pipe is opened. Thereafter, the exhaust gas stored in the exhaust gas storage tank 5 is supplied to the adsorption tower 1a via the pump 6b. At the initial stage of the cooling operation, the water vapor remaining in the adsorption tower is exhausted together with the exhaust gas, so after gas-liquid separation is performed by the cooler 7b and the knockout drum 8b, the exhaust gas is returned to the adsorption tower again via the exhaust gas storage tank 5 and the pump 6b. To supply When the inside of the adsorption tower drops to a predetermined temperature, the valve V2a is closed to stop the supply of the circulating gas.

  In this embodiment, another example of the CO2 separation and recovery system and an example of an operation control method are shown. An example of a system configuration different from that of the second embodiment is shown in FIG. The main components of this system are the same as in the second embodiment. One of the differences from Example 2 is that an internal heating system in which a water vapor pipe is installed in the adsorption column is adopted as a heating system of the adsorption column. For example, when a CO2 separation and recovery facility is installed in a coal-fired power plant, extracted steam for steam turbine supply can be used. The steam 102 is a low pressure extraction steam from the steam turbine, and is also used to heat the adsorption tower simultaneously with the adsorption tower supply in the desorption step. The steam used for the adsorption tower heating is condensed and returned to the feed water heater.

  The second difference from Example 2 is that the CO 2 analyzer 9 is installed in the exhaust gas discharge pipe of each adsorption tower. The CO2 analyzer 9 is used during the adsorption operation and the purge operation. In the adsorption operation, CO2 is adsorbed on the adsorbent, and when the adsorption on the adsorbent reaches saturation, the concentration of CO2 contained in the outlet exhaust gas gradually increases. The CO 2 analyzer 9 measures the exhaust gas concentration at the adsorber outlet at the time of adsorption operation, and when CO 2 of a predetermined concentration is detected from the exhaust gas, the valve V 3 is closed to shut off the supply of the exhaust gas. By this control, the CO 2 concentration in the exhaust gas from the adsorption tower can be kept constant even when the time of the adsorption operation fluctuates due to the influence of the fluctuation of the CO 2 concentration contained in the exhaust gas or the deterioration of the adsorbent. In addition, when the CO2 concentration in the exhaust gas increases during the purge operation, it can be confirmed that CO2 supplied as a purge gas is discharged from the outlet in addition to the CO2 in the exhaust gas remaining in the void. When the concentration becomes higher than a predetermined concentration, the valve V3 is closed to stop the supply of CO2 for purge. By this operation, it is possible to suppress an increase in the concentration of CO2 in the exhaust gas and to prevent a decrease in the CO2 recovery rate of the plant.

DESCRIPTION OF SYMBOLS 1 ... Adsorption tower, 2 ... Adsorbent, 3 ... Electric heater, 4 ... CO2 storage tank, 5 ... Exhaust gas storage tank, 6 ... Pump, 7 ... Cooler, 8 ... Knockout drum, 9 ... CO2 analyzer, 21 ... Exhaust gas Supply pipe, 22: CO2 supply pipe, 23: water vapor supply pipe, 24: exhaust gas exhaust pipe, 25: desorption gas exhaust pipe, V1-7: valve, 101: exhaust gas, 102: water vapor

Claims (14)

  In an adsorption tower packed with a CO 2 adsorbent that selectively adsorbs carbon dioxide (CO 2), a CO 2 adsorption step of adsorbing and separating CO 2 contained in exhaust gas, and a purge step of discharging exhaust gas present in voids in the CO 2 adsorption tower And a CO2 recovery method comprising a CO2 desorption step of desorbing CO2 adsorbed on the CO2 adsorbent from the adsorbent by thermal energy and a cooling step of cooling the CO2 adsorption tower after CO2 desorption, the CO2 desorption step A carbon dioxide recovery method comprising: a CO 2 storage step of temporarily storing CO 2 concentrated and separated, and using as the purge gas in the purge step CO 2 supplied from the CO 2 storage step.   The carbon dioxide recovery method according to claim 1, wherein the CO2 adsorption tower has a fixed bed type multi-column configuration, and CO2 adsorption, purge, CO2 desorption, and cooling steps are repeatedly performed in each adsorption tower. Carbon recovery method.   The carbon dioxide recovery method according to claim 1 or 2, wherein the inlet of the CO2 adsorption column is provided with an exhaust gas introduction line, a CO2 supply line, and a steam supply line, and the outlet of the CO2 adsorption column is an exhaust gas discharge line, A carbon dioxide recovery method comprising an outgassing line.   In the carbon dioxide recovery method according to any one of claims 1 to 3, in the CO2 desorption step, the CO2 adsorbent filled in the adsorption tower is heated in advance by internal or external heating, and then steam is supplied from the steam supply line. A carbon dioxide recovery method characterized in that the CO2 desorbed from the CO2 adsorbent is discharged from the adsorption tower.   The carbon dioxide recovery method according to any one of claims 1 to 4, wherein the exhaust gas discharge line comprises an exhaust gas storage step for storing the exhaust gas from which CO2 has been removed in the CO2 adsorption step, and the cooling gas used in the cooling step is from the exhaust gas storage step. A carbon dioxide recovery method characterized by supplying and circulating supply.   The carbon dioxide recovery method according to any one of claims 1 and 5, further comprising a gas cooling step and a gas-liquid separation step upstream of the CO2 storage step and the exhaust gas storage step.   The carbon dioxide recovery method according to any one of claims 1 to 6, wherein the exhaust gas discharge line is provided with a CO2 concentration measuring step, and the CO2 concentration in the exhaust gas discharged during the CO2 adsorption step and the purge step becomes equal to or higher than a predetermined value. A carbon dioxide recovery method characterized by stopping the gas supply from the exhaust gas introduction line and the CO2 supply line.   The carbon dioxide recovery method according to claim 1, wherein the CO 2 adsorbent is an oxide containing Ce.   In the adsorption tower packed with a CO 2 adsorbent that selectively adsorbs carbon dioxide (CO 2), after adsorbing CO 2 contained in the exhaust gas, the exhaust gas present in the void in the CO 2 adsorption tower is discharged to purge the inside of the adsorption tower Regarding CO2 recovery equipment that repeats the operation of desorbing CO2 adsorbed on CO2 adsorbent from the adsorbent by thermal energy and cooling the CO2 adsorption tower after CO2 desorption, temporarily storing concentrated CO2 discharged from the adsorption tower A carbon dioxide recovery facility comprising a CO 2 storage tank, wherein the purge gas used for the purge in the adsorption tower uses CO 2 supplied from the CO 2 storage tank.   In the carbon dioxide recovery facility according to claim 9, the CO2 adsorption tower is a fixed bed multi-column configuration, and an exhaust gas feed pipe, a CO2 feed pipe, and a steam feed pipe are provided at the inlet of each CO2 adsorption tower. An exhaust gas discharge pipe and a desorption gas discharge pipe are provided at an outlet, and a carbon dioxide recovery facility is characterized.   11. The carbon dioxide recovery facility according to claim 9, wherein the adsorption tower is equipped with a heating facility capable of internal or external heating.   The carbon dioxide recovery facility according to any one of claims 9 to 11, wherein the exhaust gas discharge pipe is provided with an exhaust gas storage tank and a circulation pump for storing the exhaust gas from which CO2 has been removed in the CO2 adsorption step, and the cooling gas used for cooling the adsorption tower is A carbon dioxide recovery facility characterized by supplying from an exhaust gas storage tank and circulating supply.   The carbon dioxide recovery facility according to claim 9, wherein a gas cooler and a gas-liquid separator are provided upstream of the CO2 storage tank and the exhaust gas storage tank.   The carbon dioxide recovery facility according to any one of claims 9 to 13, wherein the exhaust gas discharge pipe is provided with a CO2 concentration meter, and the CO2 concentration in the exhaust gas discharged at the time of CO2 adsorption and adsorption tower purge becomes a predetermined value or more A carbon dioxide recovery facility characterized by stopping gas supply from an exhaust gas introduction pipe and a CO 2 supply pipe.

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