The present invention relates to an exhaust gas treatment system that removes carbon dioxide (CO2) in a combustion exhaust gas by a chemical absorption method, and particularly to an exhaust gas treatment system comprising an equipment for removing CO2 from a combustion exhaust gas using an amine compound aqueous solution as a CO2 absorbent.
Recently, large amounts of fossil fuel, heavy oil, and the like are used as fuel in thermal power equipments and boiler equipments. In terms of preventing air pollution and global warming, studies on the reduction of CO2 emission into the atmosphere have been globally advanced. As a technique for separating and recovering CO2 from exhaust gases of thermal power equipments, chemical plants, and the like, which are large sources of CO2, a chemical absorption method that uses an aqueous solution of amine, such as alkanolamine, as a CO2 absorbing solution is widely known.
In the absorption column 18, CO2 is absorbed by an amine absorbing solution by means of a packed bed 19 in which the reaction of absorption of CO2 in the exhaust gas by the amine absorbing solution occurs, and an absorbing solution spray portion 20 for spraying the absorbing solution. In this case, in order to cool and water-wash the eliminated CO2 exhaust gas 21, whose temperature is raised by the exoergic reaction of absorbing CO2, a water washing portion 22 and a water washing spray portion 23 for washing and removing the amine absorbing solution accompanying the eliminated CO2 exhaust gas 21, a wash water storing portion 24 for storing the wash water, a cooler 25 for cooling the circulating wash water, and a water washing pump 26 for circulating the wash water are provided. Further, a demister 27 is provided in the top of the water washing portion so as to remove mist of the absorbing solution passing through the water washing portion. The treated gas 28 discharged from the absorption column outlet is heated to 80 deg C. to 90 deg C. by a GGH reheater 9 and discharged from a chimney 10. Moreover, the amine solution that absorbed CO2 is transferred to a regeneration column 31 from the solution storage in the bottom of the absorption column 18 by an absorption column extract pump 29 while passing through a regeneration column solution feed piping 30. Then, in the top of a packed bed 32 disposed in the middle of the regeneration column 31, the absorbing solution sprayed from a spray portion 33 is brought into gas-liquid contact with steam rising from the bottom, and thereby CO2 contained in the absorbing solution is degassed. Subsequently, the degassed CO2 gas is washed by a water washing portion 34 and a water washing spray 35, and mist passing through the water washing portion along with the gas is collected by a demister 36 and discharged as a CO2 gas 37 from the top of the regeneration column. The CO2 gas 37 is cooled to 40 deg C. by a cooler 38, and then separated into a gas and condensed water by a CO2 separator 39. The separated CO2 gas is introduced into a CO2 liquefaction equipment, which is not shown. Further, the condensed water is fed to the water washing spray 35 by a drain pump 40. On the other hand, the CO2-degassed amine solution is stored in a regeneration column solution storing portion 41, and then transferred to a reboiler 43 passing through a reboiler solution feed piping 42. The reboiler 43 is provided with a heat transfer tube or the like therein. The amine solution is indirectly heated by steam 44 fed by a steam feed piping, and thereby a vapor from the reboiler passes through a vapor feed piping 45 and is fed to a regeneration column. In addition, from the solution storage in the bottom of the regeneration column, the amine absorbing solution passes through a regeneration column solution extract piping 46, is cooled by a heat exchanger 47, and is introduced into an absorption column.
In the conventional technique, the outlet gas temperature of the wet-type desulfurization device 6 was 50 deg C. In order to maintain CO2 removal performance, it was necessary to reduce the gas temperature of the inlet of the CO2 absorption column to about 40 deg C. in the above-mentioned prescrubber 7, for which a cooler for the absorbent was required. Furthermore, in order to perform desulfurization with high efficiency, it was necessary to use high-cost basic agents, such as sodium hydroxide (NaOH). Challenge was to reduce utility costs, including installation of a cooling system for cooling the exhaust gas and the accompanying increase in the amount of desulfurization effluent to be treated, as well as the cost of the prescrubber.
In the above conventional technique, it was necessary to use a basic agent (for example, sodium hydroxide) as the desulfurization absorbent in the prescrubber of the CO2 removal equipment, and the increased cost was problematic. Moreover, since the amount of desulfurization effluent was increased by the prescrubber, there was a problem of increased utility costs associated with effluent treatment. Furthermore, in order to maintain the efficiency of the CO2 removal equipment, it was necessary to cool the exhaust gas (for example, from 50 deg. C. to 40 deg. C. or lower) in the prescrubber; however, this cooling system required the use of a large amount of cooling water.
An object of the present invention is to provide a CO2 removal treatment system for removing CO2 in a combustion exhaust gas, which can reduce environmental burdens during operation of the CO2 removal equipment, and which can minimize the installation cost of a prescrubber and utility costs.
The above object can be achieved by using seawater as the desulfurization absorbent in the prescrubber of the CO2 removal equipment for absorbing and removing CO2 in a combustion exhaust gas. That is, inventions to be claimed in the present application are as follows.
(1) An exhaust gas treatment system with a CO2 removal equipment for absorbing and removing carbon dioxide (CO2) in a combustion exhaust gas using an absorbing solution of an amine compound, the system comprising a prescrubber for bringing the exhaust gas into contact with seawater, the prescrubber being disposed on the upstream side of the CO2 removal equipment.
(2) The exhaust gas treatment system according to (1), wherein the exhaust gas treatment system comprises a wet-type exhaust gas desulfurization device, and the prescrubber is disposed downstream the wet-type exhaust gas desulfurization device and has a function of cooling an outlet exhaust gas of the wet-type exhaust gas desulfurization device.
In the present invention, since the use of seawater as the SO2 absorbent in the prescrubber disposed upstream the CO2 removal equipment eliminates the need for conventional absorbents, such as NaOH, cost reduction can be achieved. In general seawater desulfurization, the discharge of hazardous substances, such as mercury (Hg), contained in the exhaust gas causes problems; however, in the present invention (claim 2), such hazardous substances are removed by the desulfurization device using a limestone-gypsum process disposed upstream the prescrubber, and secondary pollution is therefore less likely to occur.
Furthermore, the use of a cooling system in the prescrubber can be saved by feeding seawater having the temperature of usually 20 deg C. to 30 deg C., to the prescrubber, and installation costs, the amount of cooling water, and utility costs associated therewith can be reduced.
As described above, according to the present invention, seawater is used in place of the desulfurization absorbent in the prescrubber to pre-treat an exhaust gas to be introduced into the CO2 removal equipment, thereby saving the use of a cooler and reducing the load of treating the desulfurization effluent, and thus reducing installation costs and utility costs. In addition, since the desulfurization device disposed upstream the prescrubber removes most of the hazardous substances, including mercury, the discharge of the used seawater is less likely to cause secondary pollution.
An embodiment of the present invention is described with reference to
1: Boiler
2: Denitration device
3: Air heater
4: GGH (heat recovery device)
5: Electric precipitator
6: Wet-type desulfurization device
7: Prescrubber
8: CO2 removal equipment
9: GGH (reheater)
10: Chimney
11: Boiler steam
18: Absorption column
29: Absorption column extract pump
30: Regeneration column solution feed piping
31: Regeneration column
32: Packed bed
33: Spray portion
36: Demister
38: Cooler
39: CO2 separator
42: Reboiler solution feed piping
43: Reboiler
47: Heat exchanger
Number | Date | Country | Kind |
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2010-167051 | Jul 2010 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2011/066813 | 7/25/2011 | WO | 00 | 2/26/2013 |