JP2005288313A - System and method for recovering carbon dioxide in exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system for recovering carbon dioxide in an exhaust gas capable of trapping carbon dioxide in the exhaust gas as an insoluble compound and further regenerating an alkaline solution from the insoluble compound without using steam of a boiler for electric power generation, and a method for recovering. <P>SOLUTION: The alkaline solution 19 blown out from an alkaline solution blowout part 21 comes into gas-liquid contact with the exhaust gas 15 flowing from downward to upward in a filler 22 and absorbs carbon dioxide contained in the exhaust gas 15. The absorbed carbon dioxide is precipitated as the insoluble compound and the insoluble compound is recovered by a trap tank 11. The insoluble compound recovered by the trap tank 11 is mixed with an alkali substance in a mixing tank 12 to regenerate the alkaline solution 19. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a carbon dioxide recovery system that recovers carbon dioxide contained in exhaust gas discharged from a thermal power plant or a municipal waste incineration plant, and more particularly, in an exhaust gas that can recover carbon dioxide with an alkaline solution. The present invention relates to a carbon dioxide recovery system and a recovery method.

  In recent years, the problem of global warming due to the greenhouse effect of carbon dioxide, which is a combustion product of fossil fuel, has been increasing. In the Kyoto Protocol of the United Nations Framework Convention on Climate Change, Japan's goal to reduce greenhouse gas emissions is to achieve the 1990 ratio of minus 6% between 2008 and 2012.

  In such a background, for example, by using an aqueous solution of potassium carbonate, which is an alkaline substance, as an absorbent of carbon dioxide contained in exhaust gas discharged from a thermal power plant or municipal waste incineration plant, carbon dioxide is A recovery system has been proposed (see, for example, Patent Document 1).

  A conventional carbon dioxide recovery system 200 that recovers carbon dioxide using an aqueous potassium carbonate solution as an alkaline solution is shown in FIG.

  In the conventional carbon dioxide recovery system 200 shown in FIG. 2, exhaust gas 201 discharged by burning fossil fuel is guided to an absorption tower 203 by a gas blower 202. An alkaline solution 204 is supplied to the upper portion of the absorption tower 203, and the supplied alkaline solution 204 comes into contact with the introduced exhaust gas 201 and absorbs carbon dioxide in the exhaust gas 201.

  The alkaline solution 204 that has absorbed carbon dioxide is extracted from the lower part of the absorption tower 203, passes through a heat exchanger 206 by a pump 205, and is guided to a regeneration tower 207. On the other hand, the remaining exhaust gas 201 having carbon dioxide absorbed by the alkaline solution 204 is released from the upper part of the absorption tower 203 to the atmosphere.

  The alkaline solution 204 guided to the regeneration tower 207 is heated by the steam 209 of the heater 208, dissipates the absorbed carbon dioxide, and the alkaline solution 204 that can absorb carbon dioxide again is regenerated. The regenerated alkaline solution 204 is returned to the upper part of the absorption tower 203 by the circulation pump 210 through the heat exchanger 206 and the cooler 211. On the other hand, carbon dioxide released from the alkaline solution 204 is guided to the separator 213 through the cooler 212 and is collected after moisture is removed by the separator 213.

In the conventional carbon dioxide recovery system 200 configured as described above, an alkaline solution capable of absorbing carbon dioxide by instantaneously heating the alkaline solution 204 to about 120 ° C. using steam 209 of a power generation boiler in the regeneration tower 207. 204 was regenerated, and the regenerated alkaline solution 204 was returned to the absorption tower 203.
JP-A-4-346816

  In the above-described conventional carbon dioxide recovery system, since a large amount of heat is used from the steam of the power generation boiler to instantaneously heat the alkaline solution to a predetermined temperature in the regeneration tower, the thermal efficiency of the system can be improved. There was no problem.

  Accordingly, the present invention has been made to solve the above-described problems, and can capture carbon dioxide in exhaust gas as an insoluble compound. Further, the present invention can provide an alkali solution from the insoluble compound without using steam of a power generation boiler. An object of the present invention is to provide a system and a method for recovering carbon dioxide in exhaust gas that can regenerate a solution.

  In order to achieve the above object, a system for recovering carbon dioxide in exhaust gas of the present invention comprises an exhaust gas inlet, an alkali solution inlet, a remaining exhaust gas outlet and an alkaline solution outlet, and an exhaust gas introduced from the exhaust gas inlet and A carbon dioxide absorption tower that makes the alkali solution gas-liquid contact to absorb carbon dioxide in the exhaust gas; and an alkali solution discharged from the alkali solution outlet of the carbon dioxide absorption tower. The insoluble compound, which is a reaction product of the alkali solution and carbon dioxide, is connected to the alkali solution reflux line that is refluxed to the alkali solution reflux line and connected to a pipe branched from the alkali solution reflux line. A collection tank to be collected and an insoluble compound collected in the collection tank is introduced, and an alkaline substance is added to the insoluble compound. Mixed and characterized by comprising a mixing tank for reproducing an alkaline solution.

  According to the system for recovering carbon dioxide in the exhaust gas, carbon dioxide absorbed in the alkaline solution can be precipitated as an insoluble compound, and the precipitated insoluble compound can be collected in a collection tank. In addition, by mixing the insoluble compound and the alkaline substance in the mixing tank, the alkaline solution can be regenerated without using heat such as steam of the power generation boiler, thereby improving the thermal efficiency of the system. Can do.

  In addition, the system for recovering carbon dioxide in the exhaust gas of the present invention may further include a drying device in which a part of the insoluble compound collected in the collection tank is introduced and the insoluble compound is dried.

  The method for recovering carbon dioxide in exhaust gas according to the present invention includes an absorption step in which exhaust gas and an alkali solution are brought into gas-liquid contact, and the alkali solution absorbs carbon dioxide in the exhaust gas, and a reaction product of the alkali solution and carbon dioxide. And a regeneration step of regenerating an alkaline solution by mixing an alkali substance with the collected insoluble compound.

  According to the method for recovering carbon dioxide in the exhaust gas, the carbon dioxide absorbed in the alkaline solution in the absorption step can be precipitated as an insoluble compound, and the insoluble compound precipitated in the collection step can be collected. In addition, by mixing this insoluble compound and an alkaline substance in the regeneration process, the alkaline solution can be regenerated without using heat such as steam of a power generation boiler, thus improving the thermal efficiency of the system. Can do.

  The method for recovering carbon dioxide in the exhaust gas of the present invention may further include a drying step in which a part of the insoluble compound collected in the collecting step is introduced and the insoluble compound is dried.

  According to the system and method for recovering carbon dioxide in exhaust gas of the present invention, carbon dioxide in exhaust gas can be collected as an insoluble compound, and an alkaline solution can be obtained from the insoluble compound without using steam of a power generation boiler. Can be played.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an outline of a carbon dioxide recovery system 1 according to an embodiment of the present invention.
The carbon dioxide recovery system 1 according to an embodiment of the present invention collects an insoluble compound, which is a reaction product of an alkali solution and carbon dioxide, with an absorption tower 10 for bringing the introduced exhaust gas and the alkali solution into gas-liquid contact. Control for controlling the collection tank 11, a mixing tank 12 for mixing an insoluble compound with an alkali substance and regenerating an alkaline solution, a drying device 13 for drying a part of the insoluble compound, a pump, a valve, each device, etc. The unit 14 is mainly configured.

  1, the control unit 14 is electrically connected to each pump, each valve, a measuring instrument such as a pH meter, and each component device, which will be described later, but connection lines are omitted for the sake of clarity.

  At the lower part of the absorption tower 10, there is provided an exhaust gas inlet 16 for guiding the exhaust gas 15 containing carbon dioxide discharged from a thermal power plant or municipal waste incineration plant into the absorption tower 10. Is connected to a gas blower 17 for feeding the exhaust gas 15 into the absorption tower 10. An upper part of the absorption tower 10 is provided with an alkaline solution inlet 20 for introducing an alkaline solution 19 supplied from the collection tank 11 by a liquid feed pump 18. Further, the alkaline solution inlet 20 has an alkali solution inlet 20. An alkaline solution ejection part 21 for ejecting the solution 19 is provided. In addition, inside the absorption tower 10, a filler 22 is provided that mainly makes gas-liquid contact between the alkaline solution 19 ejected from the alkaline solution ejection section 21 and the exhaust gas 15 introduced into the absorption tower 10. Further, an exhaust port 23 is provided at the upper end of the absorption tower 10 for exhausting the exhaust gas 15 having absorbed carbon dioxide into the atmosphere by passing through the filler 22.

  In addition, an alkaline solution discharge port 24 for discharging the alkaline solution 19 that has absorbed carbon dioxide is provided at the bottom of the absorption tower 10. The alkaline solution discharge port 24 is connected to one end of a circulation pipe 26 that functions as an alkaline solution reflux line provided with a lead-out pump 25. The other end of the circulation pipe 26 branches corresponding to each divided collection tank 11, and each branch pipe is provided with a valve 27. The derivation pump 25 and the valve 27 are electrically connected to the control unit 14 and operate based on a signal from the control unit 14.

  Here, it is preferable that the alkaline solution 19 ejected from the alkaline solution ejection section 21 is ejected uniformly. For example, the alkaline solution ejection section 21 is provided with a spray nozzle or the like capable of obtaining a predetermined spray particle size and spray pattern. It may be used. In addition, when the alkali solution 19 can be dispersed almost uniformly in the absorption tower 10 by the configuration of the alkali solution introduction port 20, the alkali solution ejection part 21 may not be provided.

  In addition, the filler 22 may be formed of a material having a porous structure, a honeycomb structure, or the like, for example, as long as it has a function of disturbing the alkaline solution 19 passing through the filler 22. Further, the filler 22 may be configured without installing the filler 22 as long as the gas-liquid contact between the exhaust gas 15 and the alkaline solution 19 can be efficiently performed.

  The collection tank 11 includes divided tanks 11a and 11b divided into a plurality of parts. As described above, each of the dividing tanks 11a and 11b is provided with a branch pipe on the other end side of the circulation pipe 26 corresponding to each of the dividing tanks 11a and 11b. The supply of the alkaline solution 19 to each division tank 11a, 11b is switched by a valve 27 provided in each branch pipe.

  Furthermore, each division tank 11a, 11b is provided with a valve 28, and one end side is branched corresponding to each division tank 11a, 11b, and a circulation pipe 29 functioning as an alkaline solution reflux line is installed. One end of the branched circulation pipe 29 is immersed in a relatively upper position of the alkaline solution stored in each of the divided tanks 11a and 11b. As a result, when the alkaline solution 19 is circulated from each of the dividing tanks 11a and 11b, the alkaline solution 19 can be circulated without sucking up the insoluble compound precipitated at the bottom of each of the dividing tanks 11a and 11b. The other end of the circulation pipe 29 is connected to the alkaline solution inlet 20 of the absorption tower 10. Further, the circulation pipe 29 is provided with a liquid feeding pump 18, and this liquid feeding pump 18 is electrically connected to the control unit 14, and based on a signal from the control unit 14, the divided tanks 11 a and 11 b. The flow rate of the alkaline solution 19 supplied to the alkaline solution inlet 20 is adjusted.

  Further, each of the dividing tanks 11a and 11b is branched at one end corresponding to each of the dividing tanks 11a and 11b, and is provided with a liquid feed pump 30 for guiding the alkaline solution 19 supplied from the mixing tank 12. A pipe 31 is installed. The other end of the circulation pipe 31 is connected to the bottom of the mixing tank 12. Each branch pipe branched from the circulation pipe 31 is provided with a valve 32. Here, the liquid feed pump 30 and the valve 32 are electrically connected to the control unit 14, and adjust the flow rate of the alkaline solution 19 supplied to each of the divided tanks 11 a and 11 b based on a signal from the control unit 14. .

  Furthermore, each division tank 11a, 11b is provided with a measurement pipe 34 for guiding the alkaline solution 19 to a pH meter 33 for measuring the hydrogen ion exponent pH of the alkaline solution 19, and each measurement pipe 34 has a A valve 35 is provided. The pH meter 33 is electrically connected to the control unit 14 and outputs a signal based on the measurement result to the control unit 14.

  Further, a lead-out pipe 37 provided with a valve 36 for guiding insoluble compounds to the mixing tank 12 and the drying device 13 is connected to the bottom of each of the dividing tanks 11a and 11b. The outlet pipe 37 is provided with a slurry pump 38. The outlet pipe 37 is branched into the mixing tank 12 side and the drying apparatus 13 side on the downstream side of the slurry pump 38, respectively. 13 is connected. In addition, a valve 39 is provided in the outlet piping 37 on the downstream side of the branched slurry pump 38 to switch the flow path for guiding the insoluble compound to the mixing tank 12 or the drying device 13 and to adjust the flow rate of the insoluble compound. Do. Here, the slurry pump 38 and the valve 39 are electrically connected to the control unit 14 and controlled based on a signal from the control unit 14.

  In addition, although the number of the division tanks which comprise the collection tank 11 is not limited, if at least two, the collection system which can operate | move the system which collect | recovers a carbon dioxide continuously can be comprised. it can.

  The mixing tank 12 mixes an introduced insoluble compound (sodium hydrogen carbonate) with an alkali substance (sodium hydroxide) to regenerate an alkali solution (sodium carbonate solution) 19, and at least the inner wall surface thereof is, for example, FRP. It is made of an alkali-resistant material such as resin. In addition, an alkaline substance supply port 40 for supplying an alkaline substance (sodium hydroxide) is provided at the top of the mixing tank 12, and the circulation pipe 31 is connected to the bottom as described above. Furthermore, for example, a stirrer or the like for mixing the insoluble compound and the alkaline substance is provided inside the mixing tank 12. Since the reaction between sodium bicarbonate and sodium hydroxide generated in the mixing tank 12 is an exothermic reaction, the internal temperature of the mixing tank 12 increases. Sodium bicarbonate releases carbon dioxide when the temperature is higher than 75 ° C. Therefore, here, for example, a temperature adjusting means is provided so that the internal temperature of the mixing tank 12 does not rise above 75 ° C. It is preferable to adjust the temperature.

  The drying device 13 dries the introduced insoluble compound (sodium bicarbonate) to obtain dried sodium bicarbonate, and dries the insoluble compound by a vacuum drying method or a centrifugal dehydration method. Here, the purity of sodium hydrogen carbonate after drying is about 98%. In the carbon dioxide recovery system 1 according to the embodiment, an example in which the drying device 13 is provided is shown, but the carbon dioxide recovery system 1 may be configured without the drying device 13.

  Here, in the present invention, the alkaline solution 19 is regenerated in the mixing tank 12 after the system is operated, so there is no need to supply the alkaline solution 19, but the alkaline solution 19 is supplied to the collection tank 11 in advance at the initial operation of the system. It is necessary to keep it.

  Therefore, the alkaline solution 19 supplied to the collection tank 11 at the initial operation of the system is prepared by dissolving 10 to 28 g of sodium carbonate per 100 g of water and adjusting the weight concentration to 9 to 22%. . The sodium carbonate may be, for example, sodium carbonate containing impurities collected from coal ash, municipal waste incineration ash, sewage sludge incineration ash, biomass incineration ash, or the like. Further, the sodium carbonate may be, for example, sodium carbonate containing impurities collected from soil containing an alkaline component such as a desert. Further, the sodium carbonate may be, for example, sodium carbonate containing impurities collected from an alkaline lake by a salt salt method. However, the weight of impurities does not take into account the weight concentration of sodium carbonate (9 to 22%).

  Moreover, the temperature of the alkali solution 19 in the collection tank 11 and the absorption tower 10 is maintained at 40-75 degreeC. Here, the temperature of the alkaline solution 19 in the absorption tower 10 is set within this range because the absorption of carbon dioxide into the alkaline solution 19 is slow when the temperature is lower than 40 ° C., and the carbonic acid in the alkaline solution 19 is higher than 75 ° C. This is because sodium hydrogen begins to release carbon dioxide. Moreover, the temperature of the alkaline solution 19 in the collection tank 11 was set within this range because the sodium hydrogen carbonate in the alkaline solution 19 was deposited so as to stick to the wall of the collection tank 11 when cooled to less than 40 ° C. This is because when the temperature exceeds 75 ° C., sodium hydrogen carbonate in the alkaline solution 19 starts to release carbon dioxide.

  The alkali solution 19 can be heated by, for example, heating the circulation pipe 26 and the circulation pipe 29 using exhaust heat of exhaust gas from the power generation boiler. The heating method of the alkaline solution 19 is not limited to this. For example, a heat exchanger may be provided in the collection tank 11 and heated using exhaust heat of exhaust gas from a boiler for power generation. Good. In consideration of the thermal efficiency of the system as a heating source, it is preferable to use exhaust heat of exhaust gas from a boiler for power generation, but a heater or the like may be used as a heating source. Furthermore, a cooling means may be provided in the collection tank 11 in order to adjust the temperature to the optimum value.

  Next, the operation of the carbon dioxide recovery system 1 will be described.

  The exhaust gas 15 discharged from a thermal power plant or municipal waste incineration plant is supplied into the absorption tower 10 from the exhaust gas inlet 16 by the gas blower 17 without being subjected to desulfurization treatment. In addition, the temperature of the exhaust gas 15 supplied in the absorption tower 10 is 50-60 degreeC.

  When the exhaust gas 15 is supplied into the absorption tower 10, the alkaline solution 19 accommodated in the collection tank 11 is supplied from the alkaline solution inlet 20 via the circulation pipe 29 and is ejected from the alkaline solution ejection part 21. . The flow rate of the alkaline solution 19 ejected from the alkaline solution ejection unit 21 is adjusted by a liquid feed pump 18 that is controlled based on a signal from the control unit 14.

  The alkaline solution 19 ejected from the alkaline solution ejection part 21 is in gas-liquid contact with the exhaust gas 15 flowing upward from below through the filler 22 while flowing down through the filler 22, and carbon dioxide and sulfur contained in the exhaust gas 15. Absorbs oxides. Then, the alkaline solution 19 that has absorbed carbon dioxide and sulfur oxide flows down and is stored at the bottom of the absorption tower 10. On the other hand, part of the carbon dioxide is released from the exhaust port 23 to the atmosphere without being absorbed.

  The alkaline solution 19 stored at the bottom of the absorption tower 10 is guided to a circulation pipe 26 by a lead-out pump 25 and supplied to one divided tank 11 a constituting the collection tank 11. At this time, the valves 27 corresponding to the divided tanks 11b other than the valve 27 corresponding to the divided tank 11a to which the alkaline solution 19 is supplied are closed.

  Subsequently, the valve 35 of the measurement pipe 34 installed in the division tank 11 a is opened, and a part of the alkaline solution 19 is guided to the pH meter 33. The pH meter 33 detects the hydrogen ion exponent pH of the introduced alkaline solution 19 and outputs a signal corresponding to the detected value to the control unit 14.

  In the control part 14, based on the signal from the pH meter 33, it is determined whether the pH value of the alkaline solution 19 in the division tank 11a is in the range of 8-10. In addition, by absorbing the carbon dioxide contained in the exhaust gas 15, the alkaline solution 19 becomes an aqueous solution containing sodium hydrogen carbonate, and the pH value of 12 or more gradually decreases to about 11, and further rapidly decreases to 9 or less. To drop.

  When the controller 14 determines that the pH value of the alkaline solution 19 is greater than 8 to 10, the alkaline solution 19 guided to the dividing tank 11a is again supplied to the circulation pipe 29 and the alkaline solution inlet 20. Then, it is guided to the alkali solution jetting part 21 and jetted from the alkali solution jetting part 21, and the above-described operation is repeated.

  On the other hand, when the controller 14 determines that the pH value of the alkaline solution 19 is in the range of 8 to 10, the controller 14 controls the valve 27 provided in the circulation pipe 26 corresponding to the division tank 11a. Control to close. In the alkaline solution 19 having a pH value in the range of 8 to 10, an insoluble compound sodium hydrogen carbonate, which is a reaction product of the alkaline solution 19 and carbon dioxide, precipitates in the alkaline solution 19. The precipitated insoluble compound has a specific gravity larger than that of the alkaline solution, and is thus collected as a slurry 41 at the bottom of the dividing tank 11a.

  Subsequently, the control unit 14 performs control to open the valve 36 of the outlet pipe 37 corresponding to the division tank 11a. At the same time, control is performed to open the corresponding valve 39 for introduction into either the mixing tank 12 or the drying device 13. The slurry 41 may be guided to both the mixing tank 12 and the drying device 13 at the same time. Here, the derivation | leading-out to the mixing tank 12 and the drying apparatus 13 of the slurry 41 collected by the bottom part of the division tank 11a is started based on the elapsed time after the pH value reaches 8-10, for example, It is started after 30 minutes or more have passed since the pH value reached 8-10. The elapsed time after the pH value reaches 8 to 10 is not limited to 30 minutes or more after the pH value reaches 8 to 10, and the slurry 41 is sufficiently collected at the bottom of the dividing tank 11a. Any time can be used.

  When the slurry 41 is guided to the mixing tank 12, after the slurry 41 is introduced into the mixing tank 12, the control unit 14 performs control to open the valve 32 of the circulation pipe 31 corresponding to the division tank 11a. Then, an alkali substance (sodium hydroxide) is supplied to the mixing tank 12, and the slurry 41 and the alkali substance are mixed by a stirrer to regenerate an alkali solution (sodium carbonate solution). The regenerated alkaline solution is supplied to the dividing tank 11 a by the liquid feeding pump 30 via the circulation pipe 31.

  Here, about half of the slurry 41 guided from the dividing tank 11 a is introduced into the mixing tank 12. Further, the mass of sodium hydroxide added in the mixing tank 12 is added in the same molar mass as sodium hydrogen carbonate contained in the introduced slurry 41. The weight concentration of sodium carbonate contained in the regenerated sodium carbonate solution is adjusted to 9-22%. Here, the weight concentration of sodium carbonate contained in the sodium carbonate solution was set to 9 to 22%. When the weight concentration of sodium carbonate was less than 9%, the insoluble compound sodium bicarbonate was hardly precipitated. This is because when the ratio is larger than 22%, the filler 22 provided in the absorption tower 10 may be blocked. Therefore, by setting the upper limit value of the weight concentration of sodium carbonate contained in the sodium carbonate solution to 22%, it is provided in the absorption tower 10 generated when the weight concentration of sodium carbonate is high (for example, 23% or more). Problems such as blocking of the filled material 22 can be avoided.

  On the other hand, when the slurry 41 is guided to the drying device 13, the slurry 41 guided to the drying device 13 is dried to become dried sodium hydrogen carbonate. Here, about half of the slurry 41 guided from the dividing tank 11 a is introduced into the drying device 13.

  Here, the flow rate of each of the slurries 41 introduced into the mixing tank 12 and the drying device 13 is half the flow rate of the slurry 41 guided from the dividing tank 11a, but this ratio is the alkaline solution 19 to be regenerated. It can set suitably according to the required amount.

  Moreover, when the pH value of the alkaline solution 19 refluxed to the dividing tank 11a was lowered to about 8 to 10, the dividing tank for refluxing the alkaline solution 19 was switched to the dividing tank 11b, and the above-described dividing tank 11a was used. The same operation as in the case is performed.

  Here, in addition to absorbing carbon dioxide, the alkaline solution 19 also absorbs sulfur oxides contained in the exhaust gas 15, and sulfite ions accumulate in the alkaline solution 19 when the alkaline solution 19 is used for a long time. This accumulation of sulfite ions is not preferable from the viewpoint of reducing the carbon dioxide recovery rate. Therefore, for example, when the concentration of sulfite ions contained in the alkaline solution 19 of the dividing tank 11a reaches 0.5% by weight, calcium chloride is added to the dividing tank 11a to precipitate the sulfite ions as calcium sulfite. , Removed from the dividing tank 11a.

  The concentration of sulfite ions contained in the alkaline solution 19 when adding calcium chloride is not limited to 0.5% by weight, and even when it is in the range of 0.01 to 1.0%. Good. Here, the concentration range of sulfite ions contained in the alkaline solution 19 when adding calcium chloride is set to 0.01 to 1.0% because the concentration of sulfite ions is smaller than 0.01% by weight concentration. In this case, it is difficult to recover as calcium sulfate (gypsum), and when it is larger than 1.0%, the carbon dioxide recovery rate decreases. In addition, not only calcium sulfite but also calcium bicarbonate precipitates when calcium chloride is added.

  The concentration of sulfite ions is measured by an ion concentration measuring device such as ion chromatography (not shown) connected via a pipe branched from the measurement pipe 34 installed in each of the dividing tanks 11a and 11b. This ion concentration measuring apparatus is electrically connected to the control unit 14, and measurement information on the concentration of sulfite ions is output to the control unit 14.

  The calcium sulfite precipitated at the bottom of the dividing tank 11a is guided to the drying apparatus 13 in the same manner as the method for guiding the slurry 41 precipitated at the bottom of the dividing tank 11a to the drying apparatus 13. A new alkaline solution 19 is supplied to the dividing tank 11a from which sulfite ions have been removed as calcium sulfite.

  Here, when calcium sulfite is dried to form calcium sulfate in a short time, it is necessary to heat it together with air. In this case, the drying device 13 is a drying device having a configuration capable of such heating. Used. The atmospheric temperature when drying calcium sulfite together with air is preferably 150 to 200 ° C. The calcium sulfite (containing calcium carbonate) obtained here can be used for building materials, for example.

  In addition, when removing the insoluble compound (calcium sulfite), in order to reduce the amount of the insoluble compound (sodium hydrogen carbonate) mixed, the addition of calcium chloride to precipitate the insoluble compound (calcium sulfite) is performed in the dividing tank 11a. 30 minutes or more after the pH value of the alkaline solution 19 stored in the reactor reaches 8 to 10, that is, the insoluble compound (sodium hydrogen carbonate) is sufficiently precipitated in the dividing tank 11a, and the precipitated insoluble It is preferable to carry out after removing the compound (sodium hydrogen carbonate) from the dividing tank 11a.

  As described above, in the carbon dioxide recovery system 1 of the present invention, carbon dioxide can be recovered as an insoluble compound sodium bicarbonate, and the alkaline solution 19 is regenerated without heating from the insoluble compound sodium bicarbonate. Therefore, the thermal efficiency of the system can be improved. In the carbon dioxide recovery system 1, sulfur oxides that are air pollutants can also be recovered.

  Furthermore, since the carbon dioxide recovery system 1 of the present invention can recover a large amount of carbon dioxide emitted from a thermal power plant or a municipal waste incineration plant without using excessive energy, it can prevent global warming. Can contribute. Further, carbon dioxide can be fixed as sodium hydrogen carbonate, and this sodium hydrogen carbonate can be used as a pH adjuster or the like.

(Other embodiments)
With reference to FIG. 1, another embodiment of the present invention will be described.

  In the carbon dioxide recovery system 1 of the present invention, the absorption tower 10 and the collection tank 11 are separated separately, but the alkaline solution storage section and the collection tank 11 at the bottom of the absorption tower 10 may be configured integrally. Good. Also in this case, the same operation and effect as the carbon dioxide recovery system 1 can be obtained.

1 is a schematic diagram showing a carbon dioxide recovery system according to a first embodiment of the present invention. Schematic diagram showing a conventional carbon dioxide recovery system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Carbon dioxide recovery system, 10 ... Absorption tower, 11 ... Collection tank, 11a, 11b ... Dividing tank, 12 ... Mixing tank, 13 ... Drying device, 14 ... Control part, 15 ... Exhaust gas, 16 ... Exhaust gas inlet, DESCRIPTION OF SYMBOLS 17 ... Gas blower, 18, 30 ... Liquid feed pump, 19 ... Alkaline solution, 20 ... Alkaline solution inlet, 21 ... Alkaline solution ejection part, 22 ... Filler, 23 ... Exhaust port, 24 ... Alkaline solution discharge port, 25 ... Lead pump, 26, 29, 31 ... circulation piping, 27, 28, 32, 36, 39 ... valve, 33 ... pH meter, 34 ... measurement piping, 37 ... lead piping, 38 ... slurry pump, 40 ... alkali substance Supply port, 41 ... slurry.

Claims (7)

An exhaust gas inlet, an alkaline solution inlet, a remaining exhaust gas outlet and an alkaline solution outlet are provided. The exhaust gas introduced from the exhaust gas inlet and the alkaline solution are brought into gas-liquid contact, and the carbon dioxide in the exhaust gas is brought into contact with the alkaline solution. A carbon dioxide absorption tower to be absorbed,
An alkaline solution reflux line for refluxing the alkaline solution discharged from the alkaline solution outlet of the carbon dioxide absorption tower to the alkaline solution inlet;
A collection tank which is inserted into the alkali solution reflux line or connected by a pipe branched from the alkali solution reflux line and collects an insoluble compound which is a reaction product of the alkali solution and carbon dioxide;
A system for recovering carbon dioxide in exhaust gas, comprising: a mixing tank in which an insoluble compound collected in the collecting tank is introduced, and an alkali substance is mixed with the insoluble compound to regenerate an alkaline solution.   The system for recovering carbon dioxide in exhaust gas according to claim 1, further comprising a drying device for introducing a part of the insoluble compound collected in the collection tank and drying the insoluble compound.   The main solute of the alkaline solution is sodium carbonate, and the weight concentration of sodium carbonate contained in the alkaline solution is 9 to 22%. The carbon dioxide in exhaust gas according to claim 1 or 2, Collection system.   The system for recovering carbon dioxide in exhaust gas according to any one of claims 1 to 3, wherein the insoluble compound is sodium hydrogen carbonate.   The system for recovering carbon dioxide in exhaust gas according to any one of claims 1 to 4, wherein the alkaline substance mixed with the insoluble compound is sodium hydroxide. An absorption step in which the exhaust gas is brought into gas-liquid contact with the alkali solution, and the alkali solution absorbs carbon dioxide in the exhaust gas;
A collecting step of collecting an insoluble compound that is a reaction product of the alkaline solution and carbon dioxide;
And a regeneration step of regenerating an alkali solution by mixing an alkali substance with the collected insoluble compound.   The method for recovering carbon dioxide in exhaust gas according to claim 6, further comprising a drying step in which a part of the insoluble compound collected in the collecting step is introduced and the insoluble compound is dried.

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