JP2009247932A - Method for removing carbon dioxide using exhaust gas heat source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for removing carbon dioxide of combustion exhaust gas coming out of a coal-burning boiler, while suppressing the undermining of power generation output. <P>SOLUTION: This method for removing carbon dioxide is to remove carbon dioxide of at least, a part of combustion exhaust gas by chemically absorbing the carbon dioxide with the help of an absorption liquid through the contact between at least, a part of the wet-treated combustion exhaust gas and the absorption liquid. In the method, the absorption liquid which has chemically absorbed the carbon dioxide, is regenerated using the heat of the combustion exhaust gas before wet treatment, and at the same time, the combustion exhaust gas after wet treatment is reheated using the heat of the regenerated absorption liquid. Besides, it is possible to use the heat of the combustion exhaust gas before wet treatment for the purpose of heating up the absorption liquid through the chemical absorption of the carbon dioxide, or possible to use the heat for generating stripping steam for regenerating the absorption liquid through the chemical absorption of the carbon dioxide. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for removing carbon dioxide contained in exhaust gas from a combustion apparatus such as a coal fired boiler.

  In recent years, global warming due to greenhouse gases such as carbon dioxide has become a major problem. In thermal power plants, since a large amount of carbon dioxide is emitted from combustion processes such as boilers, the need to switch fuel from coal to natural gas, which produces less carbon dioxide, has been called out. However, coal is still used in large quantities because it has abundant recoverable reserves and can be procured at low cost, and the current situation is that carbon dioxide emissions have not been sufficiently reduced.

  Therefore, a method for reducing carbon dioxide emission from the power plant by selectively removing carbon dioxide generated in the combustion process has been studied. For example, Patent Document 1 proposes a method of removing carbon dioxide by bringing a chemical absorption liquid such as an aqueous amine solution into contact with combustion exhaust gas. This method has been put into practical use for a long time in the field of gas treatment such as natural gas and petroleum refining, and is expected to be put to practical use in the treatment of flue gas from thermal power plants.

  Non-Patent Document 1 proposes a method for removing carbon dioxide in combustion exhaust gas using an amino acid-based chemical absorption solution. This method uses an amino acid-based chemical absorbing solution that is less corrosive than an aqueous amine solution, and is expected as a method that can remove carbon dioxide at a lower cost.

JP 2007-325996 A Jacco van Holst, et al., “CO2 capture from flue gas using amino acid salt solutions,” 8th International Conference on Greenhouse Gas Control Technologies (GHGT-8), 19-22 June 2006, Trondheim, Norway

In general, a large amount of heat is required to regenerate the absorbing solution by releasing carbon dioxide from the absorbing solution in which carbon dioxide is chemically absorbed. For example, in the case of a 28 wt% monoethanolamine (MEA) aqueous solution, The amount of heat of 1200 kcal / kg-CO ₂ , that is, the amount of heat of about 1200 kcal is required to dissipate 1 kg of carbon dioxide absorbed in the absorption liquid. For this reason, even if carbon dioxide in the combustion exhaust gas discharged from the boiler can be removed to a predetermined level by absorbing it in the absorption liquid, a large amount of steam generated in the boiler is consumed to regenerate the absorption liquid. As a result, there is a problem that the power generation output is significantly reduced.

  In view of such circumstances, an object of the present invention is to provide a method of removing carbon dioxide in combustion exhaust gas discharged from a boiler while suppressing a decrease in power generation output.

  In order to achieve the above object, a method for removing carbon dioxide provided by the present invention comprises bringing at least a part of wet-treated combustion exhaust gas into contact with an absorbent, thereby removing carbon dioxide in the at least part of the combustion exhaust gas. This is a method of removing the chemical by absorbing it in the absorption liquid, regenerating the absorption liquid that chemically absorbed carbon dioxide using the heat of the combustion exhaust gas before the wet treatment, and using the heat of the regenerated absorption liquid. It is characterized by reheating the combustion exhaust gas after wet processing.

  In the method for removing carbon dioxide provided by the present invention, the heat of the combustion exhaust gas before the wet treatment may be used for raising the temperature of the chemically absorbed absorbent. Furthermore, in the method for removing carbon dioxide provided by the present invention, the heat of the combustion exhaust gas before the wet treatment may be used to generate stripping steam for regeneration of the chemically absorbed absorbent. In the method for removing carbon dioxide provided by the present invention, it is preferable that the amount of carbon dioxide removed from the combustion exhaust gas is determined according to the amount of heat of the combustion exhaust gas before the wet treatment.

  According to the present invention, the absorption liquid that has chemically absorbed carbon dioxide is regenerated using the heat of the flue gas before wet treatment, and the flue gas after wet treatment is regenerated using the heat of the regenerated absorption liquid. Since heating is performed, it is possible to remove carbon dioxide in the combustion exhaust gas while suppressing a decrease in power generation output while performing good gas gas heat exchange of the combustion exhaust gas before and after the wet treatment.

  Hereinafter, a specific example of the carbon dioxide removing apparatus according to the present invention will be described with reference to FIG. As shown in FIG. 1, high-temperature combustion exhaust gas discharged from a boiler 2 that uses fossil fuel such as coal is led to an exhaust gas cooler 12 through a flue and cooled to a predetermined temperature. The cooled combustion exhaust gas is guided to the wet processing apparatus 3, where sulfurous acid gas and soot are removed by the wet processing. The combustion exhaust gas wet-processed by the wet processing apparatus 3 is guided to the exhaust gas reheater 16 through the flue, where it is overheated to prevent white smoke, and then discharged from the chimney 4.

  A bypass is provided in the flue from the wet treatment device 3 to the exhaust gas reheater 16, and at least a part of the combustion exhaust gas treated by the wet treatment device 3 is extracted here as a bypass gas and removed. 1 is supplied to the bottom of the absorption tower 10. The bypass gas that has entered the tower from the bottom of the absorption tower 10 rises in the tower in countercurrent contact with an absorption liquid (hereinafter also referred to as a lean solution) supplied from the top of the absorption tower 10. . The tower is provided with packings and shelves, where gas-liquid contact is efficiently performed, and carbon dioxide in the bypass gas is chemically absorbed by the lean solution.

  The type of the absorbing solution is not particularly limited, but an aqueous solution of an amine such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), etc. Alternatively, it is preferable to use a chemical absorption solution such as a mixture thereof or an amino acid-based aqueous solution.

  The amount of gas extracted from the flue combustion exhaust gas as a bypass gas is proportional to the amount of carbon dioxide removed from the combustion exhaust gas when the carbon dioxide removal rate in the absorption tower 10 is constant. The amount of extracted gas may be arbitrarily determined, but is preferably determined as appropriate based on the amount of heat of the high-temperature combustion exhaust gas. This is because the amount of lean solution supplied to the absorption tower 10 is determined according to the amount of gas extracted, so that if the amount of gas extracted is too large, the amount of heat required to regenerate the absorbing solution increases significantly, and the absorption described later. This is because the amount of heat that the high-temperature combustion exhaust gas used for liquid regeneration has is limited, so that the amount of steam consumed by the reboiler increases and the power generation output is greatly reduced.

  The bypass gas from which carbon dioxide has been removed to a predetermined level in the absorption tower 10 exits the top of the absorption tower 10 and then returns to the flue to join other gases that have not been taken out as bypass gas. Note that a water washing treatment device for recovering the absorbent accompanying the bypass gas from which carbon dioxide has been removed may be provided at the top of the absorption tower 10 or the position from the top of the tower to the flue. good.

  The lean solution descending the absorption tower 10 gradually rises in temperature by absorption heat as the carbon dioxide in the bypass gas is chemically absorbed, and is several tens compared with the temperature when supplied to the top of the tower. The temperature rises to ℃ and is extracted from the bottom of the tower. The absorbing liquid extracted from the bottom of the column (hereinafter also referred to as rich solution) is sequentially sent to the lean / rich heat exchanger 11 and the exhaust gas cooler 12 to be heated.

  The rich solution exiting the exhaust gas cooler 12 is sent to the upper part of the regeneration tower 13. The rich solution that has entered the tower from the top of the regeneration tower 13 descends in countercurrent contact with stripping steam that rises from the bottom of the tower. The tower is provided with packings and shelves, where the rich solution and stripping steam are efficiently brought into gas-liquid contact, and carbon dioxide is gradually released from the rich solution.

  The absorbing solution that has been almost completely regenerated is extracted from the bottom of the regeneration tower 13 and sent to the reboiler 14. In the reboiler 14, the absorption liquid is heated by a heating medium such as steam, a part thereof is stripped steam, led to the bottom of the regeneration tower 13, and the rest is extracted as a lean solution from the reboiler 14.

  On the other hand, the carbon dioxide released from the rich liquid is sent to the condenser 15 provided at the top of the regeneration tower 13 together with the stripping steam. Here, the stripping steam is condensed to be a reflux liquid, while carbon dioxide is cooled but exits the condenser 15 in a gas phase without being condensed. The reflux liquid merges with the rich solution described above at the top of the regeneration tower 13 and descends in the tower of the regeneration tower 13.

  The carbon dioxide that exits the condenser 15 is fixed by a liquefaction facility (not shown), enhanced oil recovery (EOR), or the like. In FIG. 1, the condenser 15 is provided at the top of the regeneration tower 13, but the condenser 15 may be provided at a position that exits the top of the regeneration tower 13. Further, a reflux drum or a reflux pump may be provided at the rear stage of the condenser 15.

  The lean solution exiting the reboiler 14 is sequentially sent to the exhaust gas reheater 16 and the lean rich heat exchanger 11 to be cooled, and further cooled to a predetermined temperature by a refrigerant such as cooling water in the lean cooler 17. , And sent to the top of the absorption tower 10. In the above specific example, the lean / rich heat exchanger 11 is provided to perform heat exchange between the rich solution and the lean solution, but the inlet / outlet temperatures of the exhaust gas cooler 12 and the exhaust gas reheater 16 are appropriately set. Accordingly, the lean / rich heat exchanger 11 can be omitted.

  Thus, in one specific example of the removal apparatus 1 of the present invention, by heating the rich solution before being supplied to the regeneration tower 13 by heat exchange with the high-temperature combustion exhaust gas exiting the boiler 2, The amount of heat required for regenerating the rich solution can be reduced. Thereby, it becomes possible to reduce the steam consumption of the reboiler 14, and can suppress the output fall of a power plant.

  That is, since the steam extracted from the steam turbine steam generated in the boiler 2 is used as the heat source of the reboiler 14, the reduction in the output of the power plant is suppressed by reducing the required steam volume in the reboiler 14. be able to. Further, since the amount of extraction from the steam for the steam turbine is reduced, the influence on the operation of the steam turbine can be reduced.

  By the way, as described above, the wet treatment facility for combustion exhaust gas is provided with a gas gas heat exchanger that exchanges heat between the combustion exhaust gas before the wet treatment and the combustion exhaust gas after the wet treatment. In this gas gas heat exchanger, There are cases where direct heat exchange is performed between gases and heat exchange is performed via a heat exchange medium such as water.

  Among these, when applying the carbon dioxide removal device of the present invention to an existing thermal power plant having a gas gas heat exchanger via a heat exchange medium such as water, a gas gas is provided after providing a bypass in a part of the flue. It is only necessary to install the removing device 1 along the heat exchanger and change the heat exchange medium of the gas gas heat exchanger from water to an absorbing liquid. As a result, it is possible to remove carbon dioxide in the combustion exhaust gas while suppressing a decrease in output of the power plant while maintaining the function of the existing gas gas heat exchanger, which is extremely advantageous in terms of construction period and cost.

  Next, another specific example of the carbon dioxide removing apparatus according to the present invention will be described with reference to FIG. In FIG. 2, the same components as those shown in FIG. As can be seen from FIG. 2, also in this specific example, as in FIG. 1, carbon dioxide contained in at least a part of the combustion exhaust gas discharged from the wet treatment apparatus 3 is absorbed and removed by the absorption tower 10, and carbon dioxide is removed. The absorption liquid that has absorbed carbon is regenerated in the regeneration tower 13, but in this specific example, the position where the absorption liquid heated by the exhaust gas cooler 12 is taken out is different from that in FIG.

  Specifically, in this specific example, the rich solution exiting the bottom of the absorption tower 10 is sent to the lean rich heat exchanger 11 for heat exchange, and then the exhaust gas cooler, unlike the removal apparatus of FIG. Without passing through 12, it is sent to the regeneration tower 13 as it is.

  The almost completely regenerated absorption liquid is extracted from the bottom of the regeneration tower 13 and sent to the gas-liquid separation drum 14a. The absorption liquid sent to the gas-liquid separation drum 14a is further guided to the exhaust gas cooler 12, where it is heated by the high-temperature combustion exhaust gas and partly evaporates into a two-phase flow. This two-phase flow is returned to the gas-liquid separation drum 14a for gas-liquid separation, and the gas phase side becomes stripping steam and is led to the bottom of the regeneration tower 13. On the other hand, the liquid phase side after the gas-liquid separation is merged with the absorption liquid in the gas-liquid separation drum 14 a that has not been led to the exhaust gas cooler 12 to become a lean solution and is extracted from the gas-liquid separation drum 14 a.

  Thus, in another specific example of the removal apparatus 1 of the present invention, since the high-temperature combustion exhaust gas discharged from the boiler 2 is used as the heat source for the reboiler 14, the reboiler is extracted from the steam for the steam turbine. 14 need not be supplied. Therefore, it is possible to suppress a decrease in the output of the power plant and further stabilize the operation of the steam turbine.

  As in the removal device shown in FIG. 1, the amount of gas extracted from the flue combustion exhaust gas is preferably determined as appropriate based on the amount of heat of the high-temperature combustion exhaust gas. Because the supply amount of the lean solution supplied to the absorption tower 10 is determined according to the gas extraction amount, if the gas extraction amount increases too much, the high-temperature combustion exhaust gas has the amount of heat necessary for generating stripping steam. This is because the amount of heat is exceeded and it is necessary to extract and use steam from steam for the steam turbine.

[Example]
A process design for removing a part of carbon dioxide in combustion exhaust gas discharged from a coal-fired boiler in a thermal power plant with an output of 1000 MW by the carbon dioxide removal apparatus shown in FIG. 1 was performed. The absorbing solution was 30 wt% MEA, and the amount of heat required for the regeneration was 1100 kcal / kg-CO ₂ . Of the amount of heat required for regeneration, 50% of the amount of heat of the combustion exhaust gas before wet processing is used to raise the rich solution, and steam generated by a coal-fired boiler is used to generate stripping steam in the reboiler. . In the absorption tower, it was decided to remove 90% of the carbon dioxide contained in the bypass gas extracted from the flue.

  Under these conditions, first, the temperature of the rich solution in the exhaust gas cooler is set to 35 ° C., the amount of circulation of the absorption liquid is obtained, and the bypass gas flow rate (from flue combustion exhaust gas that can be treated with this circulation amount of absorption liquid is obtained. Gas extraction amount). Based on these circulation amounts and bypass gas flow rates, the heat balance and mass balance calculation of other streams were performed.

  The results calculated in this way are shown in Tables 1 and 2 below. Table 1 summarizes the heat balance and material balance of the combustion exhaust gas, and Table 2 summarizes the heat balance and material balance of the absorbent. The stream number corresponds to the code shown in FIG.

  From this result, it was found that 8.0% of carbon dioxide in the combustion exhaust gas after the wet treatment could be removed while performing gas gas heat exchange of the combustion exhaust gas before and after the wet treatment using the absorbing liquid as a heat exchange medium. Moreover, it turned out that the output fall of the electric power at this time is 1.1%. This reduction in output corresponds to a power sales loss of about 1.1 billion yen per year (7000 hours) when the unit price of electricity is 15 yen / kW.

[Comparative example]
The power output reduction was calculated in the same manner as in the example except that the amount of heat of the high-temperature combustion exhaust gas discharged from the boiler was not used for regeneration of the absorbent. In addition, the conventional system which uses water as the heat exchange medium was adopted for the gas gas heat exchange of the combustion exhaust gas before and after the wet treatment.

  As a result, in order to remove 8.0% of the carbon dioxide in the combustion exhaust gas after the wet treatment as in the example, it was found that the output decrease was 2.1%, which is about twice that of the example. . This reduction in output is equivalent to a loss in power sales of approximately 2.2 billion yen per year (7000 hours) when the unit price of electricity is 15 yen / kW, and it was found that the loss was increased by approximately 1.1 billion yen compared to the example. .

It is a schematic diagram which shows one specific example of the carbon dioxide removal apparatus by this invention. It is a schematic diagram which shows the other specific example of the carbon dioxide removal apparatus by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Removal apparatus 2 Coal-fired boiler 3 Flue gas desulfurization apparatus 4 Chimney 10 Absorption tower 11 Lean rich heat exchanger 12 Exhaust gas cooler 13 Regeneration tower 14 Reboiler 14a Gas-liquid separation drum 15 Condenser 16 Exhaust gas reheater 17 Lean cooler

Claims (4)

  A method for removing carbon dioxide in at least a part of the combustion exhaust gas by absorbing it into the absorption liquid by contacting at least part of the combustion exhaust gas that has been wet-treated with the absorption liquid. Removal of carbon dioxide, characterized by regenerating the absorption liquid that chemically absorbed carbon dioxide using the heat of exhaust gas and reheating the combustion exhaust gas after wet treatment using the heat of the regenerated absorption liquid Method.   The method for removing carbon dioxide according to claim 1, wherein the heat of the combustion exhaust gas before the wet treatment is used for raising the temperature of the chemically absorbed absorbent.   The method for removing carbon dioxide according to claim 1, wherein heat of the combustion exhaust gas before the wet treatment is used to generate stripping steam for regeneration of the chemically absorbed absorbent.   The method for removing carbon dioxide according to any one of claims 1 to 3, wherein an amount of carbon dioxide removed from the combustion exhaust gas is determined according to a heat amount of the combustion exhaust gas before the wet treatment.

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