Carbon dioxide separation system and carbon dioxide separation method

Abstract

To provide a carbon dioxide separation system and a carbon dioxide separation method, each stabilizing operation of a dehumidifier and ensuring energy saving.SOLUTION: A carbon dioxide separation system 1 is provided in which a membrane separator 3 performs primary separation of carbon dioxide in combustion exhaust gas, and after a temperature swing type dehumidifier 5 dehumidifies the primary separation gas, a pressure swing type adsorption device 7 performs secondary separation. The carbon dioxide separation system comprises a first one-stage dry screw type vacuum pump 9 sucking gas with concentrated carbon dioxide from the membrane separator 3, and an exhaust heat recovery heat-exchanger 11 exchanging heat between gas sucked by the first vacuum pump 9 to have its temperature raised and gas supplied to the temperature swing type dehumidifier 5 as regenerated gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a carbon dioxide separation system and a carbon dioxide separation method in which carbon dioxide in a combustion exhaust gas is primarily separated using a membrane separation device, the primarily separated gas is dehumidified using a temperature swing dehumidifier, and then secondarily separated using a pressure swing adsorption device. [Background technology]

[0002] The largest source of carbon dioxide, a greenhouse gas, is the flue gas from thermal power plants. In order to prevent global warming, there is a need to separate and capture carbon dioxide from this flue gas. The most widely used carbon dioxide separation technology is the chemical absorption method, which uses alkaline absorbing solutions such as amine aqueous solutions. This method has high absorption efficiency and extremely high selectivity for nitrogen and oxygen, but on the other hand, it is necessary to heat the absorbing solution to a high temperature when regenerating it, and when the absorbing solution is an aqueous solution, it is heated under pressure to above the boiling point at normal pressure to prevent water evaporation, so the heat required for this is large and the energy required for carbon dioxide separation is large.

[0003] For example, in the case of a coal-fired thermal power plant, even a high-performance facility has an output per unit of carbon dioxide emissions of 4.5 GJ / t-CO according to the reference value published by the Ministry of the Environment. 2 The energy consumption when applying the chemical absorption method to combustion exhaust gas is about 2.5GJ / t-CO 2 This means that more than half of the energy generated by the electricity would be consumed in separating carbon dioxide, making this approach unrealistic.

[0004] Among the technologies for separating carbon dioxide from combustion exhaust gas discharged at atmospheric pressure, a membrane separation device using a gas separation membrane is known to consume little energy. However, a membrane separation device alone has the disadvantage that it cannot increase the purity of the separated carbon dioxide. As a technology to compensate for this, for example, Patent Document 1 discloses a method in which a pressure swing adsorption device is installed downstream of the membrane separation device to increase the purity of the carbon dioxide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-327936 Summary of the Invention [Problem to be solved by the invention]

[0006] Pressure swing adsorption equipment also consumes little energy, but when zeolite is used as the adsorbent, moisture must be removed as a pretreatment, and a dehumidifier must be installed. Temperature swing adsorption dehumidifiers are widely used for this purpose, but heat is required to regenerate the adsorbent, which increases the overall energy consumption.

[0007] In the technology disclosed in Patent Document 1, a portion of the combustion exhaust gas is extracted and used as a heat source required for regenerating the adsorbent, thereby eliminating the need for a new heat source for the system. However, since the heat of the combustion exhaust gas is generally recovered by a waste heat recovery facility, there are cases where the temperature of the combustion exhaust gas does not reach the temperature required for regeneration of the adsorbent. Also, although the combustion exhaust gas supplies the heat required for regeneration through heat exchange, the deterioration of heat transfer due to dust in the combustion exhaust gas may result in insufficient heat exchange and insufficient heat required for regeneration. Therefore, when the combustion exhaust gas is used as a heat source required for regenerating the dehumidifier, there is a problem that the operation of the dehumidifier becomes unstable.

[0008] Chemical absorption carbon dioxide separation equipment, which has been used for natural gas pretreatment and off-gas treatment in chemical manufacturing, has the appearance of a chemical plant with a row of tall absorption towers and the regeneration towers are classified as Class 1 pressure vessels because the absorption liquid is regenerated under pressure. In comparison, membrane separation equipment and pressure swing adsorption equipment are easy to operate and maintain and are not subject to special legal regulations, so they have the important advantage of being easily accepted by businesses that emit combustion exhaust gas. However, since using heat from the combustion exhaust gas to regenerate the dehumidifier to protect the expensive zeolite adsorbent would result in this advantage being lost if operation became unstable, there is a need to utilize heat that is steadily generated within the system. The present invention has been made to solve such problems, and has an object to provide a carbon dioxide separation system and a carbon dioxide separation method that stabilize the operation of a dehumidifier and achieves energy savings. [Means for solving the problem]

[0009] Since the large amount of energy consumed in carbon dioxide separation technology from combustion exhaust gas is a fatal flaw, a system that is specialized in this field and pursues energy conservation is required. From this perspective, the inventors have conducted a detailed study on the heat balance of a carbon dioxide separation system equipped with a membrane separation device and a pressure swing adsorption device.

[0010] Generally, the carbon dioxide concentration in combustion exhaust gas is around 10%, and it is difficult to obtain high-purity carbon dioxide using a membrane separation device. However, it is possible to increase the concentration of carbon dioxide separated by creating a higher vacuum in the membrane separation device. For example, if a high-performance separation membrane with a ratio of the carbon dioxide to nitrogen permeability coefficient, which indicates separation performance, exceeds 200 is used and a vacuum of about 2 kPa is created, it is not impossible to obtain carbon dioxide at about 95%.

[0011] However, achieving such a high vacuum requires a large amount of power for the vacuum pump, and the advantage of low energy consumption is lost. However, 95% is still insufficient purity, so in the end a separate high-purity device is required in the downstream stage. To achieve low energy consumption, it is important to reduce the power required by the vacuum pump of the membrane separation unit. The degree of vacuum should be set at about 10 kPa, and the operating conditions should be optimized using the type of vacuum pump that requires the least amount of power.

[0012] Of the vacuum pumps used industrially, the dry screw vacuum pump consumes the least amount of energy. If the degree of vacuum is about 10 kPa, compression in one stage is possible, and a single-stage dry screw vacuum pump is one of the pumps that consumes the least amount of energy, so it is an option. Each vacuum pump manufacturer has its own unique screw shape, and the suction pressure at which it is efficient varies. In other words, choosing a single-stage dry screw vacuum pump from a manufacturer that is designed to be efficient at a suction pressure of about 10 kPa is likely to result in the lowest energy consumption. However, when using a single-stage dry screw vacuum pump, the compression ratio is 10 times even with a suction pressure of 10 kPa, and even if the suction temperature is close to room temperature, the discharge temperature will rise to around 200°C due to the heat of compression, so it is often avoided.

[0013] In this regard, the inventors aimed to further reduce energy consumption and considered making positive use of this compression heat. In other words, it was thought that by supplying the heat for regenerating the adsorbent in the temperature swing dehumidifier, which serves as a pretreatment for the pressure swing adsorption unit, from the high-temperature gas on the discharge side of the vacuum pump of the membrane separation unit, it would be possible to create a system that consumes the least amount of energy in all respects. As a result, it became possible to stably regenerate the adsorbent in the temperature swing dehumidifier, and it was discovered that it was possible to realize a carbon dioxide separation system that consumes low energy and is easy to operate and maintain. The present invention is based on such findings and specifically has the following configuration.

[0014] (1) The carbon dioxide separation system according to the present invention primarily separates carbon dioxide in a combustion exhaust gas using a membrane separation device, dehumidifies the primarily separated gas using a temperature swing dehumidifier, and then performs secondary separation using a pressure swing adsorption device, The dehumidifier is characterized by comprising a single-stage dry screw vacuum pump that draws in gas in which carbon dioxide is concentrated from the membrane separation device, and a waste heat recovery heat exchanger that exchanges heat between the gas drawn in and heated by the vacuum pump and the gas to be supplied to the temperature swing dehumidifier as regeneration gas.

[0015] (2) The carbon dioxide separation method according to the present invention is a method for primarily separating carbon dioxide in a combustion exhaust gas using a membrane separation device, dehumidifying the primarily separated gas using a temperature swing dehumidifier, and then secondarily separating the gas using a pressure swing adsorption device, The gas in which carbon dioxide is concentrated from the membrane separation device is sucked in and heated by a single-stage dry screw vacuum pump, and the heated gas is heated by heat exchange with a gas to be supplied to the temperature swing dehumidifier as a regeneration gas. Effect of the Invention

[0016] In this embodiment, in a carbon dioxide separation system for combustion exhaust gas in which a pressure swing adsorption device is installed downstream of a membrane separation device, a single-stage dry screw vacuum pump, which is highly effective in reducing the energy consumption of the membrane separation device, is adopted as the first vacuum pump, and by taking advantage of the high discharge temperature of this first vacuum pump and providing a waste heat recovery heat exchanger that can exchange heat between the discharge gas of the first vacuum pump and the regeneration gas of the temperature swing dehumidifier, it is possible to omit the electric heater for regenerating the adsorbent in the temperature swing dehumidifier and obtain a carbon dioxide separation system that consumes significantly less energy overall. [Brief description of the drawings]

[0017] [Figure 1] 1 is a diagram showing a device configuration and a flow of a carbon dioxide separation system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing the device configuration and flow of a carbon dioxide separation system according to Comparative Examples 1 and 2 in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] As shown in FIG. 1, the carbon dioxide separation system 1 according to this embodiment primarily separates carbon dioxide in a combustion exhaust gas using a membrane separation device 3, and the primarily separated gas is dehumidified using a temperature swing dehumidifier 5, and then secondary separation is performed using a pressure swing adsorption device 7. The system is equipped with a one-stage dry screw vacuum pump as a first vacuum pump 9 that sucks in gas enriched in carbon dioxide from the membrane separation device 3, and a waste heat recovery heat exchanger 11 that exchanges heat between the gas sucked and heated by the first vacuum pump 9 and the gas to be supplied to the temperature swing dehumidifier 5 as regeneration gas. Each component and additional components will be described in detail below.

[0019] <Combustion exhaust gas> The combustion exhaust gas is, for example, exhaust gas from an existing boiler or generator, and the combustion exhaust gas introduced into the carbon dioxide separation system 1 is assumed to have had NOx, SOx, soot, and other contaminants treated in accordance with emission regulations. A part of the combustion exhaust gas is introduced into the carbon dioxide separation system 1, and the rest is released into the atmosphere as exhaust gas from a chimney. However, all of the combustion exhaust gas may be introduced into the carbon dioxide separation system 1.

[0020] <Scrubber> In this embodiment, in order to further reduce adverse effects on the carbon dioxide separation system 1, a scrubber 13 is installed at the inlet of the system. The scrubber 13 serves the purpose of preventing deterioration of the equipment in the system by removing impurities and dust from the exhaust gas, as well as cooling the high-temperature exhaust gas of around 150°C to around 40°C. Most gas separation membranes are polymer membranes with a heat resistance of about 60°C, but all gas separation membranes can be used if they are cooled to 40°C. If the temperature of the combustion exhaust gas is higher, it is advisable to consider separate waste heat recovery.

[0021] <Fan> A fan 15 is installed downstream of the scrubber 13 to offset the pressure loss caused by the scrubber 13 and membrane separation. It is desirable to install this fan 15 at this position because the temperature is sufficiently lowered in the scrubber 13, improving the efficiency of the fan 15, and for the purpose of increasing the high-pressure side pressure of the membrane separation device 3 as much as possible. However, the fan 15 can also be installed anywhere in the flow of the combustion exhaust gas, such as upstream of the scrubber 13 or downstream of the membrane separation.

[0022] <Membrane separation equipment> The membrane separation device 3 is configured to obtain a gas with a high carbon dioxide concentration on the low pressure side by creating a pressure difference on both sides of a separation membrane, and the separation membrane may be either a ceramic membrane or a polymer membrane. When combustion exhaust gas at nearly atmospheric pressure is introduced into the high-pressure side of the separation membrane of the membrane separation device 3, the residual gas that has not permeated the separation membrane is discharged from the outlet. This residual gas contains some carbon dioxide, but by leaving a certain amount of it, it is possible to maintain the carbon dioxide partial pressure on the high-pressure side and increase the efficiency of membrane separation, which is an important point for reducing energy consumption. The remaining gas that does not permeate the separation membrane is treated as exhaust gas.

[0023] The low pressure side of the separation membrane is connected to the suction side of a first vacuum pump 9 and is maintained at a predetermined vacuum level. The selectivity of a separation membrane is the ratio of the permeation rate of carbon dioxide to that of nitrogen, and is often around 30 to 50. Using a separation membrane with good selectivity increases the carbon dioxide concentration on the low-pressure side, resulting in greater energy savings. On the other hand, there are many separation membranes that have a higher water vapor permeation rate than carbon dioxide, and when a large amount of water vapor permeates to the low pressure side, the load on the first vacuum pump 9 increases, and energy consumption increases. In such a case, it may be possible to reduce the total energy consumption by installing a cooler using a refrigerator in front of the separation membrane to cool the temperature to about 20°C and thereby reduce the water vapor in the combustion exhaust gas.

[0024] In order to obtain a carbon dioxide purity of 99.5% using a method with low energy consumption, a pressure swing adsorption device 7 is installed, and zeolite is often used as an adsorbent for adsorbing carbon dioxide. Zeolite is vulnerable to water vapor, so it is necessary to dehumidify the treated gas to a dew point of about -30°C in pretreatment. In this embodiment, a temperature swing dehumidifier 5 is used as the dehumidifier, but the temperature swing dehumidifier 5 requires a heat source to regenerate the adsorbent by circulating heated gas. Normally, an electric heater 21 (see FIG. 2) is installed as a heat source for regeneration, but in this embodiment, this heat source also uses the heat of the gas sucked by the first vacuum pump 9 as waste heat inside the system, thereby reducing energy consumption.

[0025] <First vacuum pump> The first vacuum pump 9 used for membrane separation has an appropriate suction pressure of about 10 kPa because high vacuum increases energy consumption. A dry vacuum pump is effective as a low energy consumption type vacuum pump, and in this embodiment, a one-stage dry screw type vacuum pump, which is one of the models with the lowest energy consumption, is used. It is known that dry vacuum pumps cannot directly remove heat using liquids or the like, resulting in a high discharge temperature. In the case of single-stage compression in particular, the discharge temperature can reach around 200°C, and is usually quickly cooled by an aftercooler. However, in this embodiment, waste heat recovery heat exchanger 11 is installed to effectively utilize the heat of the discharged high-temperature gas as a heat source for producing heated gas for regenerating the adsorbent in temperature swing dehumidifier 5. This eliminates the need for electricity for regenerating the adsorbent in temperature swing dehumidifier 5 and also reduces the amount of cooling water used.

[0026] <Waste heat recovery heat exchanger> Waste heat recovery heat exchanger 11 exchanges heat between the high-temperature (around 200°C) gas in which carbon dioxide is concentrated and discharged from first vacuum pump 9 and the gas for adsorbent regeneration in temperature swing dehumidifier 5, thereby heating the gas for adsorbent regeneration. The gas for regenerating the adsorbent in temperature swing dehumidifier 5 is not particularly limited, but in this embodiment, the unadsorbed residual gas in pressure swing adsorption apparatus 7 is used. The reason for using this unadsorbed residual gas as the gas for regenerating the adsorbent will be described later.

[0027] <Temperature swing dehumidifier> Temperature swing dehumidifier 5 is used to remove moisture from the gas in which carbon dioxide has been concentrated by membrane separation before the gas is further concentrated in pressure swing adsorption apparatus 7 . For regeneration of the adsorption tower of temperature swing dehumidifier 5, as described above, the unadsorbed residual gas in pressure swing adsorber 7 is heated in waste heat recovery heat exchanger 11 and used.

[0028] After the regeneration process is completed, the adsorption tower of temperature swing dehumidifier 5 needs to be cooled before being returned online. In this embodiment, the unadsorbed gas discharged from pressure swing adsorption device 7 is bypassed without passing through waste heat recovery heat exchanger 11 and circulated through the adsorption tower after regeneration is completed to cool it. During and after regeneration, the dehumidifier off-gas that has passed through the adsorption tower is released into the atmosphere from the stack together with the retentate gas from the membrane separation device 3 and the untreated combustion exhaust gas.

[0029] <Pressure swing type adsorption device> Pressure swing adsorption apparatus 7 is normally an apparatus that alternately uses two adsorption towers to repeat adsorption and regeneration. In the adsorption operation, concentrated carbon dioxide gas from which moisture has been removed by temperature swing dehumidifier 5 is circulated at atmospheric pressure to selectively adsorb only carbon dioxide onto the adsorbent, and in the regeneration operation, the adsorption tower in which carbon dioxide has been adsorbed is depressurized by second vacuum pump 19 to desorb and extract the carbon dioxide.

[0030] When the purity of the product carbon dioxide is to be 99.5%, the level normally used, carbon dioxide of intermediate purity generated when switching from adsorption to desorption is not made into product gas, but is recycled back to the inlet of the membrane separation device 3. In this case, the amount of product gas decreases, and the energy consumption of the membrane separation device 3 relative to the amount of product carbon dioxide increases. Therefore, in order to prevent this, it is preferable to use a three-tower pressure swing adsorption device 7 and perform a pressure equalization operation between the adsorption operation and the desorption operation so that the carbon dioxide gas of the intermediate concentration is not recycled but can be used as product gas in the next desorption operation.

[0031] If carbon dioxide breaks through without being adsorbed by pressure swing adsorption device 7, this also increases the energy consumption of membrane separation device 3 relative to the amount of carbon dioxide, so it is necessary to make the adsorption tower filled with a sufficient amount of adsorbent that does not break through. As a result, the unadsorbed gas that is not adsorbed by pressure swing adsorption device 7 has a low carbon dioxide concentration, and there is no need to recycle it to the inlet of membrane separation device 3. On the other hand, since moisture in this unadsorbed gas has been sufficiently removed by temperature swing dehumidifier 5, if heated, it is optimal as a gas for regenerating the adsorbent of temperature swing dehumidifier 5. Therefore, as described above, this unadsorbed gas is introduced into waste heat recovery heat exchanger 11, heated to a sufficient temperature, and then allowed to flow through the adsorption tower during regeneration of temperature swing dehumidifier 5.

[0032] <Second vacuum pump> It is also preferable to select the second vacuum pump 19 of a type requiring a small amount of power, for example a three-stage dry roots type.

[0033] In the present embodiment, in carbon dioxide separation system 1 for combustion exhaust gas in which pressure swing adsorption device 7 is installed downstream of membrane separation device 3, the moisture content of the off-gas from pressure swing adsorption device 7 is almost zero, and the discharge temperature of the one-stage dry screw vacuum pump, which is highly effective in reducing the energy consumption of membrane separation device 3, is taken into consideration, and by utilizing this, waste heat recovery heat exchanger 11 is provided that can exchange heat between the discharge gas from first vacuum pump 9 and the off-gas from pressure swing adsorption device 7, thereby omitting electric heater 21 (see Figure 2) for regenerating the adsorbent in temperature swing dehumidifier 5, resulting in carbon dioxide separation system 1 with significantly less energy consumption overall. EXAMPLES

[0034] [Example] Examples of the present invention will be described below together with comparative examples. The device configuration and flow of the embodiment are as shown in FIG. 6,000 Nm3 of combustion exhaust gas with a carbon dioxide concentration of 12% 3 / h was extracted and treated in the carbon dioxide separation system 1 according to the present invention. The operating temperature of the membrane separation device 3 was kept at 40°C at the outlet of the scrubber 13, and the gas with a carbon dioxide concentration of 39% was heated to 1,870 Nm 3 This concentrated gas was obtained by reducing the pressure on the low pressure side of the membrane separation device 3 to an absolute pressure of about 10 kPa by a first vacuum pump 9, and the first vacuum pump 9 was a one-stage dry screw type with low power requirements.

[0035] As a result, the temperature on the discharge side of the first vacuum pump 9 rose to about 200° C. At this time, the power required by the first vacuum pump 9 was about 225 kW on average. The gas in which carbon dioxide is concentrated is further concentrated in pressure swing adsorption device 7, but before that it needs to be cooled and then moisture removed in temperature swing dehumidifier 5. Normally, cooling is performed with cooling water in a vacuum pump aftercooler, but in this embodiment, waste heat recovery heat exchanger 11 is installed before the aftercooler and heat is used to heat the unadsorbed residual gas in pressure swing adsorption device 7. The unadsorbed residual gas temperature was about 65°C on average, and it was possible to heat it up to 180°C by waste heat recovery heat exchanger 11. As a result, it could be used as a high-temperature gas for regenerating the adsorbent in temperature swing dehumidifier 5, and good regeneration was achieved.

[0036] On the other hand, the discharge gas from first vacuum pump 9 is cooled from 200°C to 171°C, and then cooled to 30°C in a water-cooled aftercooler before entering temperature swing dehumidifier 5. In summer, when the temperature of the cooling water is high, it is thought that the cooling water chiller will require a maximum of about 16 kW of power. The unadsorbed residual gas that has passed through temperature swing dehumidifier 5 and pressure swing adsorption device 7 warms up, to about 65°C on average, as mentioned above. Meanwhile, pressure swing adsorption device 7 is a three-tower type that switches at regular intervals to repeat the adsorption process, pressure equalization and reduced pressure regeneration process, and pressurization process. Of these, in the reduced pressure regeneration process, the adsorption tower containing the adsorbent that has already adsorbed carbon dioxide is depressurized by second vacuum pump 19, promoting the desorption of carbon dioxide and discharging the desorbed carbon dioxide gas. The discharged carbon dioxide gas contains trace amounts of other gases, mainly nitrogen, that remained in the dead space in the adsorption tower, but has an average purity of 99.5% and a concentration of 430 Nm 3 / h was obtained stably.

[0037] It is preferable to select a model requiring less power for this second vacuum pump 19 as well, so a three-stage dry roots type was used. However, the second vacuum pump 19 did not utilize waste heat because the suction pressure repeatedly changed in a sawtooth wave and the compression ratio fluctuated, resulting in an unstable discharge temperature.

[0038] Table 1 shows the temperature and power consumption of each part in this embodiment. [Table 1]

[0039] In this example, the carbon dioxide yield was 840 kg / h, while the power consumed by the entire system, including the cooling water system, was 354 kW. This is 1.52 GJ / t-CO 2 equivalent to 2.5 GJ / t-CO by chemical absorption 2 This achieved overwhelming energy savings compared to conventional methods.

[0040] [Comparative Example 1] The device configuration and flow of Comparative Example 1 are shown in FIG. In Comparative Example 1, a general-purpose water ring pump was used as the first vacuum pump 9 . In addition, in Comparative Example 1, a waste heat recovery heat exchanger 11 that utilizes the discharge temperature of first vacuum pump 9 in the embodiment is installed in the exhaust gas line before being discharged to carbon dioxide separation system 1, and the waste heat of the combustion exhaust gas is used as a heat source for regenerating the adsorbent in temperature swing dehumidifier 5.

[0041] However, a waste heat recovery boiler was already installed in the exhaust gas line, and because the combustion exhaust gas temperature was low at 150°C on average, the temperature of the regeneration gas was insufficient with just the waste heat recovery heat exchanger 11, and the temperature was further raised to 180°C by the electric heater 21. This electric heater 21 required an average of 5 kW of power. Furthermore, in this case, the waste heat recovery heat exchanger 11 was located far from the carbon dioxide separation system 1, and a fan 15 for the regeneration gas was required to compensate for the pressure loss in the piping and the pressure loss in the two heat exchangers, and this fan 15 consumed 6 kW of power.

[0042] Table 2 shows the temperatures and power consumption of each part in Comparative Example 1. [Table 2]

[0043] In Comparative Example 1, a general-purpose water-sealed pump was used as the first vacuum pump 9, and it was found that the power required was 490 kW on average, which ruined the advantage of the low energy consumption of membrane separation. As a result, the power used by the entire system was 631 kW, which was 2.70 GJ / t-CO 2 This means that the advantages of membrane separation device 3 and pressure swing adsorption device 7 could not be utilized.

[0044] [Comparative Example 2] The apparatus configuration and flow of Comparative Example 2 are as shown in FIG. In Comparative Example 2, in order to improve the power consumption of the first vacuum pump 9, which was a problem in Comparative Example 1, the type of the first vacuum pump was changed to the same single-stage dry screw type as in the Example. As a result, the power consumption of the first vacuum pump 9 was significantly improved. However, since the temperature of the discharge line was 200°C on average, it was necessary to double the amount of cooling water in the aftercooler to lower the inlet temperature of the temperature swing type dehumidifier 5 to 30°C. Therefore, contrary to expectations, the amount of cooling water used in large quantities by the water ring vacuum pump could not be reduced.

[0045] Also, at this time, outside the carbon dioxide separation system, the combustion exhaust gas temperature had dropped to an average of 130°C because it had just been after the cleaning of the waste heat recovery boiler for the combustion exhaust gas, reducing the amount of heat that the waste heat recovery heat exchanger 11 could receive. This increased the load on the electric heater 21, resulting in an average power consumption of 8kW. If the waste heat recovery heat exchanger 11 becomes contaminated with soot from this state and the amount of heat it can receive further decreases, there is a risk that the additional heating by the installed electric heater 21 will not be able to reach the required 180°C, and the danger of using the waste heat of the combustion exhaust gas containing soot before it passes through the scrubber 13 became clear.

[0046] Table 3 shows the temperatures and power consumption of each part in Comparative Example 2. [Table 3]

[0047] As shown in Table 3, the total power required in Comparative Example 2 was 375 kW and the total power consumption was 1.61 GJ / t-CO 2 is equivalent to. [Explanation of symbols]

[0048] 1 Carbon Dioxide Separation System 3 Membrane separation equipment 5. Temperature swing dehumidifier 7. Pressure Swing Adsorption Unit 9. First Vacuum Pump 11 Waste heat recovery heat exchanger 13 Scrubber 15 Fan 17 Second Vacuum Pump 19 Electric heater

Claims

1. A carbon dioxide separation system in which carbon dioxide in a combustion exhaust gas is primarily separated by a membrane separation device, the primarily separated gas is dehumidified by a temperature swing dehumidifier, and then secondary separation is performed by a pressure swing adsorption device, a single-stage dry screw vacuum pump that draws in gas in which carbon dioxide is concentrated from the membrane separation device, and a waste heat recovery heat exchanger that exchanges heat between the gas drawn in and heated by the vacuum pump and gas to be supplied to the temperature swing dehumidifier as regeneration gas.

2. A carbon dioxide separation method comprising the steps of: primarily separating carbon dioxide in a combustion exhaust gas using a membrane separation device; dehumidifying the primarily separated gas using a temperature swing dehumidifier; and then secondarily separating the gas using a pressure swing adsorption device, A carbon dioxide separation method comprising the steps of: sucking the gas in which carbon dioxide is concentrated from the membrane separation device using a single-stage dry screw vacuum pump while heating it; and heating the heated gas by heat exchange between the gas to be supplied to the temperature swing dehumidifier as a regeneration gas.

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