JP2015085235A - Exhaust gas treatment system and exhaust gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas treatment system and an exhaust gas treatment method capable of ensuring excellent durability, reducing treatment cost, ensuring high desulfurization and denitration efficiency, and recovering carbon dioxide at high purity.SOLUTION: An exhaust gas treatment system includes: a desulfurization unit removing sulfur oxide; a denitration unit removing nitrogen oxide; and a carbon dioxide recovery unit recovering carbon dioxide, the desulfurization unit including a desulfurization device removing the sulfur oxide from exhaust gas using an absorbent containing a calcium compound; and a washing device washing the exhaust gas discharged from the desulfurization device using wash water so as to remove calcium-based particles contained in the exhaust gas. In the denitration unit, the exhaust gas is pressurized to accelerate an oxidation reaction, and nitrogen dioxide is removed from the exhaust gas using an aqueous absorbent.

Description

  The present invention relates to an exhaust gas treatment system and a treatment method for removing sulfur oxides, nitrogen oxides and the like from exhaust gas containing carbon dioxide such as combustion gas, and separating and recovering carbon dioxide.

  Facilities such as thermal power plants, steelworks, and boilers use large amounts of fuel such as coal, heavy oil, and super heavy oil. Sulfur oxides, nitrogen oxides, and carbon dioxide emitted by the combustion of fuel are There is a need for quantitative and concentration restrictions on emissions from the perspective of air pollution prevention and global environmental protection. In recent years, carbon dioxide has been seen as a major cause of global warming, and movements to suppress emissions have become active worldwide. For this reason, various researches are energetically advanced to enable recovery and storage of carbon dioxide from combustion exhaust gas and process exhaust gas without releasing them into the atmosphere. Combustion exhaust gas contains nitrogen oxides, sulfur oxides, mercury, hydrogen chloride, dust (particulate matter), etc. as trace components in addition to carbon dioxide and moisture. It is important for environmental conservation to increase the purity by reducing the amount of impurities contained.

  Of the nitrogen oxides contained in combustion exhaust gas, nitrogen dioxide can be removed by a wet absorption process using an alkaline agent, but nitric oxide is hardly soluble in water, so denitration is generally performed. The technology is often based on a dry ammonia catalytic reduction method, and a nitrogen source is reduced by a catalytic reaction by supplying a hydrogen source such as ammonia. If a desulfurization denitration apparatus is configured based on this, in the desulfurization part, the sulfur oxide in the exhaust gas is treated in the form of ammonium salt.

  On the other hand, as for the desulfurization method, various dry or wet treatment techniques for removing sulfur oxides using an alkaline desulfurization agent have been studied. For example, Patent Document 1 below describes a wet exhaust gas treatment method in which a slurry containing a desulfurization agent and exhaust gas are in gas-liquid contact, and carbon dioxide is recovered by desulfurization of the exhaust gas. Examples of alkali agents that can be used in such a desulfurization method include sodium hydroxide (or sodium carbonate), limestone (or slaked lime, dolomite), magnesium hydroxide, and the like. Sodium hydroxide has a very high removal efficiency of sulfur oxides. However, it is expensive and processing cost is high. For this reason, in large plants such as thermal power plants, a limestone / gypsum method using inexpensive limestone (calcium carbonate) or slaked lime (calcium hydroxide) is generally applied.

  In addition, as a method for treating exhaust gas without using a hydrogen source or a desulfurizing agent as described above, a method of condensing moisture in the exhaust gas by pressurizing the exhaust gas and cooling it has been proposed (see Patent Document 2 below). In this method, sulfur oxides and nitrogen oxides contained in the pressurized exhaust gas are dissolved in the condensed water, and the exhaust gas is denitrated and desulfurized by separating the condensed water from the exhaust gas.

JP 2012-106163 A International publication pamphlet WO2012-107953

  In the desulfurization method using the limestone / gypsum method, sulfite ions are generated by capturing sulfur oxides in exhaust gas using a slurry in which an absorbent is dispersed in water as an absorbing solution, and this is oxidized to form gypsum (calcium sulfate). Precipitates from the water, so the sulfur oxides are recovered as gypsum. Since the solubility of limestone in water is not high, the absorption liquid is handled in the form of a slurry in which solid particles are dispersed. Therefore, when it comes into contact with high-temperature exhaust gas introduced from the combustion system, moisture is deprived from the absorption liquid, resulting in fine solids. Particles are scattered and easily accompany the exhaust gas. In particular, when the desulfurization device is configured by a spraying device for spraying the absorbing liquid, the liquid droplets of the absorbing liquid are easily dried to become solid particles. Such scattered particles are liable to cause troubles such as wear and failure in subsequent mechanical devices, but if a filter medium such as a filter bag is used to separate the scattered particles from the exhaust gas, the exhaust resistance of the exhaust gas is very large. Thus, energy and a power unit for energizing the air supply are required. On the other hand, if drying is suppressed by precooling the exhaust gas before the desulfurization treatment, the scattering of particles is reduced, but a considerable amount of water is required for cooling, so the installation conditions of the exhaust gas treatment system may be limited. There is.

  On the other hand, the technique of Patent Document 2 that removes sulfur oxides and nitrogen oxides together with condensed water by pressurization and cooling of exhaust gas does not require a chemical agent such as a desulfurization agent. , Sulfurous acid) easily damages equipment such as compressors. Therefore, if desulfurization and denitration are performed using this technology alone, the burden on the apparatus is large, and it is difficult to achieve desulfurization and denitration with high removal efficiency.

  The object of the present invention is to solve the above-mentioned problems, prevent damage and failure of equipment when processing exhaust gas, and efficiently perform exhaust gas desulfurization and denitration while reducing energy required for processing as much as possible. Thus, an exhaust gas processing system and a processing method capable of recovering carbon dioxide with high purity are provided.

  Another object of the present invention is to provide an exhaust gas treatment system and a treatment method in which the installation conditions and the installation environment are not limited, the operation cost can be reduced, and the maintenance management is easy.

  In order to solve the above-mentioned problems, the present inventors have conducted extensive research and as a result, can solve the problem of scattered particles in the limestone / gypsum method with a simple configuration, and can be combined with a configuration by pressurization and cooling to save energy. The present invention has been completed by finding that it is possible to effectively treat exhaust gas while efficiently using.

  According to an aspect of the present invention, an exhaust gas treatment system includes a desulfurization unit that removes sulfur oxide from exhaust gas, a denitration unit that is disposed downstream of the desulfurization unit and removes nitrogen oxide from exhaust gas, and the desulfurization unit And a carbon dioxide recovery system disposed downstream of the denitration unit and recovering carbon dioxide from the exhaust gas, wherein the desulfurization unit uses the absorption liquid containing a calcium compound to form the exhaust gas. The present invention includes a desulfurization apparatus that removes sulfur oxides from the waste water, and a cleaning apparatus that removes calcium-containing particles contained in the exhaust gas by cleaning exhaust gas discharged from the desulfurization apparatus using cleaning water.

  Further, according to one aspect of the present invention, the exhaust gas treatment method includes desulfurization treatment for removing sulfur oxide from exhaust gas, denitration treatment for removing nitrogen oxide from exhaust gas, and carbon dioxide for recovering carbon dioxide from the exhaust gas. An exhaust gas treatment method having a recovery process, wherein the desulfurization treatment includes a desulfurization step of removing sulfur oxides from the exhaust gas using an absorption liquid containing a calcium compound, and cleaning water from the exhaust gas after the desulfurization step. And a washing step of removing calcium-containing particles contained in the exhaust gas by washing with the use.

  In the treatment system, the desulfurization apparatus includes a spraying unit that sprays the absorption liquid onto the exhaust gas, and the gas-liquid contact phase that causes the exhaust gas to contact the absorption liquid is formed by spraying the absorption liquid. It is good to. In addition, the desulfurization device has a mist removal member disposed so that the exhaust gas that has passed through the gas-liquid contact phase passes before being discharged from the desulfurization device, and the mist removal member It is good to comprise by the several swash plate which inclines with respect to the passage direction and provides a gap | interval. The denitration unit can be configured to include a reaction device that causes an oxidation reaction to generate nitrogen dioxide from nitric oxide, and a denitration device that removes nitrogen dioxide from exhaust gas using an aqueous absorbent. The reactor has at least one compressor for compressing exhaust gas discharged from the desulfurization unit, and the denitration unit further cools at least one exhaust gas compressed by the at least one compressor. It may be configured to have two coolers. As one form, the reaction apparatus includes a plurality of compressors for compressing exhaust gas, the denitration unit further includes a plurality of coolers, and the plurality of compressors and the plurality of coolers include: They can be arranged alternately so that compression and cooling are repeated alternately. Alternatively, as another form, the desulfurization unit further includes a first reaction unit that is arranged in a preceding stage of the desulfurization apparatus to cause an oxidation reaction to generate sulfur trioxide from sulfur dioxide, and the denitration unit includes A second reaction unit disposed downstream from the desulfurization unit to cause an oxidation reaction to generate nitrogen dioxide from nitric oxide, and a denitration device to remove nitrogen dioxide from the exhaust gas using an aqueous absorbent. It can be configured as follows. The desulfurization unit further includes a gypsum separator for separating and removing gypsum generated from the sulfur oxide of the exhaust gas and the calcium compound of the absorption liquid in the desulfurization apparatus, and the desulfurization apparatus includes: Furthermore, if it comprises so that it may have the washing | cleaning nozzle for wash | cleaning the said mist removal member using the absorption liquid from which the gypsum was removed by the said gypsum separator, the effect of a mist removal member is maintained suitably. It is preferable that the cleaning device is disposed downstream of the desulfurization device, and the cleaning water contains a sodium compound as an alkaline agent. Furthermore, high purity carbon dioxide can be efficiently recovered by having a drying section for removing moisture from the exhaust gas and a mercury removal section for removing mercury from the exhaust gas.

  According to the present invention, it is not necessary to cool the exhaust gas in advance, and the problem of particle scattering in the exhaust gas treatment by the limestone / gypsum method can be solved by a simple method, so the installation conditions of the system are not restricted unnecessarily, and the processing cost It is possible to efficiently perform desulfurization and denitration of exhaust gas without increasing the amount of carbon dioxide, and it is possible to increase the recovery purity of carbon dioxide. Therefore, it contributes to the reduction of the operating cost of the exhaust gas treatment system, it is possible to develop the use of recovered carbon dioxide, contribute to the installation of the treatment system of exhaust gas containing carbon dioxide and the spread of the treatment method, and to improve environmental problems Useful for. In particular, for oxyfuel combustion apparatuses in which most of the exhaust gas is moisture and carbon dioxide, the spread of exhaust gas treatment can be promoted by developing applications based on the recovery of high-purity carbon dioxide. It is economically advantageous because it can be carried out easily using general equipment without requiring special equipment or expensive equipment.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows one Embodiment of the waste gas processing system which concerns on this invention. The schematic block diagram which shows other embodiment of the processing system of the waste gas which concerns on this invention.

  The main components of the exhaust gas such as combustion gas are water and carbon dioxide, and further contain small amounts of sulfur oxide, nitrogen oxide, hydrogen chloride, oxygen, mercury, dust (particulate matter) and the like as impurities. Sulfur oxides are generally derived from fuel, and nitrogen oxides are mainly derived from nitrogen in the air. The amount of oxygen remaining in the exhaust gas varies depending on the combustion conditions. In the oxygen combustion exhaust gas in which the combustion efficiency is increased using oxygen, the oxygen amount is about 5%, the remainder is about 20% moisture, and carbon dioxide is Although it becomes about 75%, the point which contains the above-mentioned impurity is the same. Sulfur oxides (SOx) include sulfur dioxide, sulfur trioxide, etc., which are mainly present in the exhaust gas as sulfur dioxide, but all of them are dissolved in water to become sulfurous acid or sulfuric acid. Nitrogen oxide (NOx) includes several types including nitrogen monoxide and nitrogen dioxide, and exists mainly as nitrogen monoxide or nitrogen dioxide. Nitrogen dioxide dissolves in water, but nitric oxide is insoluble in water. Therefore, in order to perform denitration using water, it is necessary to oxidize nitrogen oxides. In this regard, when pressure is applied to the exhaust gas, an oxidation reaction in which nitrogen monoxide is converted into nitrogen dioxide by oxygen remaining in the exhaust gas proceeds, so that removal treatment using water becomes possible. However, as for sulfur oxides, sulfuric acid is generated from sulfur trioxide and water vapor generated by the oxidation reaction, so this is likely to corrode metals and damage compressors, etc., but in the case of exhaust gas that has been subjected to desulfurization treatment in advance, Corrosion due to sulfuric acid can be avoided even when pressure is applied. Therefore, desulfurization and denitration can be performed cheaply and safely by sequentially performing desulfurization treatment by the limestone-gypsum method, oxidation reaction by pressurization, and wet denitration treatment on the exhaust gas, and the removal performance of impurities is also high. Become. However, in the desulfurization treatment by the limestone-gypsum method, there is a problem that the scattered particles generated when contacting the high-temperature exhaust gas cause a failure in the subsequent equipment. Therefore, the configuration in which the exhaust gas after desulfurization is pressurized as it is is not preferable. In the present invention, in order to solve this problem, an exhaust gas treatment system is configured by interposing a washing device for removing scattered particles by water washing. As a result, it is possible to prevent a failure due to scattered particles from occurring in a pressurizing facility such as a subsequent compressor. Since the cleaning device has a simple structure and can collect scattered particles without increasing the ventilation resistance of the exhaust gas, it is possible to suppress power consumption.

That is, the exhaust gas treatment system according to the present invention includes a desulfurization unit that removes sulfur oxide from the exhaust gas, a denitration unit that removes nitrogen oxide from the exhaust gas, and a carbon dioxide recovery unit that recovers carbon dioxide from the exhaust gas. An exhaust gas treatment system, in which the desulfurization section has a desulfurization device based on a limestone / gypsum method, removes sulfur oxide from the exhaust gas using an absorption liquid containing a calcium compound, and further disperses calcium from the desulfurization device In order to collect the contained particles, a cleaning device for cleaning the exhaust gas discharged from the desulfurization device using cleaning water is provided, and the calcium-containing particles contained in the exhaust gas are removed. The denitration part is placed downstream from the desulfurization part, but the scattered particles from the desulfurization unit do not affect the denitration part, and the nitrogen dioxide recovery part is placed downstream from the desulfurization part and the denitration part. Carbon dioxide can be recovered from exhaust gas with high purity. Since a wet denitration method can be used efficiently, a hydrogen source such as ammonia is not required unlike a denitration treatment in which a reduction method is applied in conventional exhaust gas treatment.
Embodiments of an exhaust gas treatment system of the present invention will be described below with reference to the drawings.

  FIG. 1 describes a first embodiment of an exhaust gas treatment system according to the present invention. The treatment system 1 includes a desulfurization unit 2 that removes sulfur oxide from the exhaust gas G, a denitration unit 3 that is disposed downstream of the desulfurization unit 2 and removes nitrogen oxide from the exhaust gas G, and a desulfurization unit 2 and a denitration unit 3. And a carbon dioxide recovery unit 4 that is disposed in the rear stage and recovers carbon dioxide from the exhaust gas G. Further, the processing system 1 includes a drying unit 5 that removes moisture from the exhaust gas and a mercury removal unit 6 that removes mercury from the exhaust gas between the denitration unit 3 and the carbon dioxide recovery unit 4.

  The desulfurization unit 2 includes a desulfurization device 10 that removes sulfur oxides from the exhaust gas G using the absorption liquid A1, and a cleaning device 20 that cleans the exhaust gas discharged from the desulfurization device 10 using the cleaning water W. . The desulfurization apparatus 10 is an apparatus that performs a desulfurization process using a limestone / gypsum method, and uses an aqueous dispersion containing a calcium compound such as limestone as an alkaline absorbent for absorbing sulfur oxides as the absorbent A1. To do. In the desulfurization apparatus 10, there is a spraying means for spraying the absorbing liquid A1 to the exhaust gas G. Specifically, a spray nozzle 11 for spraying the absorbing liquid A1 is provided at the upper part in the desulfurization apparatus 10, and a circulation path 12 for connecting the bottom part and the upper part is provided outside the apparatus. The absorbing liquid A1 sprayed from the spray nozzle 11 and stored in the bottom of the desulfurization apparatus 10 is returned to the spray nozzle 11 by driving the pump 13 on the circulation path 12, and the absorbing liquid A1 is repeatedly sprayed. An exhaust gas G is introduced from the gas introduction part 14 below the spray nozzle 11, and a gas-liquid contact phase for bringing the exhaust gas G into contact with the absorption liquid A <b> 1 by spraying the absorption liquid A <b> 1 is between the spray nozzle 11 and the gas introduction part 14. It is formed. In order to measure the nitrogen oxide concentration and the sulfur dioxide concentration of the exhaust gas G introduced into the desulfurization apparatus 10, an analyzer S1 is provided. Due to the contact between the exhaust gas G and the absorption liquid A1, sulfur oxides contained in the exhaust gas G are absorbed by the absorption liquid A1 to form calcium salts. At this time, sulfur dioxide dissolves as sulfite ions in the absorption liquid A1, whereas sulfur trioxide forms calcium and gypsum (calcium sulfate) when it is absorbed in the absorption liquid A1, and is dispersed. In addition, acidic halides such as hydrogen chloride contained in the exhaust gas G are also absorbed by the absorbing liquid A1, and further, there is an effect of cleaning and removing dust. A water-cooled cooler 15 is provided in the circulation path 12, and the absorption liquid A <b> 1 of the desulfurization apparatus 10 is cooled by the cooler 15 while flowing through the circulation path 12, thereby preventing an increase in liquid temperature.

  The exhaust gas G is cooled by the sprayed absorption liquid A1, but when the temperature of the exhaust gas G to be introduced is high, the sprayed absorption liquid vaporizes moisture due to the temperature rise, and the components contained in the absorption liquid are fine solids. It is scattered as particles (mist) and is accompanied by the exhaust gas G. The components of the scattered particles are calcium-containing solids such as limestone, gypsum, and calcium sulfite. In order to suppress to some extent such solid particles accompanying the exhaust gas G and discharged outside, a mist removing member 16 is disposed above the spray nozzle 11 and rises through the gas-liquid contact phase. G passes through the mist removing member 16 before being discharged from the desulfurization apparatus 10. The mist removing member 16 is configured in a horizontal layer by a plurality of swash plates arranged in parallel with a gap. Since the plurality of swash plates are inclined with respect to the passage direction (vertical direction) of the exhaust gas G, the solid particles contained in the exhaust gas G easily collide with the swash plate. When the height (vertical direction) of the mist removing member 16 is about 150 to 250 mm and the gap (aeration width) of the swash plate is about 50 to 100 mm, the particles are effective while suppressing an increase in the ventilation resistance of the exhaust gas. It is preferable to remove the particles efficiently, and when the inclination angle of the swash plate (with respect to the vertical direction) is about 20 to 45 degrees, it is preferable for efficiently removing the particles. Since the impinging solid particles may be blocked when deposited on the swash plate, cleaning nozzles 17 and 17 ′ for cleaning the solid particles are provided above the mist removing member 16.

  A cleaning device 20 is disposed downstream of the desulfurization device 10, and the exhaust gas G discharged from the desulfurization device 10 is supplied to the cleaning device 20 through the pipe 18. The pipe 18 is provided with an analyzer S2 for measuring the sulfur dioxide concentration of the exhaust gas G. The cleaning device 20 is provided to sufficiently remove the scattered particles that cannot be removed by the mist removing member 16 of the desulfurization device 10 from the exhaust gas G, and the exhaust gas G discharged from the desulfurization device 10 is cleaned using the cleaning water W. The calcium-containing particles contained in the exhaust gas G are removed. Further, hydrogen chloride and dust contained in the exhaust gas G are also taken into the cleaning water, and the exhaust gas G is cooled by cleaning.

  The cleaning device 20 is configured as follows. A spray nozzle 21 for spraying the cleaning water W is provided in the upper part of the cleaning device 20, and a circulation path 22 that connects the bottom and the upper part is provided outside the device. Water is preferably used as the washing water W. However, when an aqueous solution of a highly water-soluble alkaline agent is used as the washing water W, the ability to capture scattered particles (calcium compounds) is improved, and a desulfurization / denitration effect is also exhibited. . A pump 23 is provided on the circulation path 22, and by this driving, the cleaning water W is sprayed from the spray nozzle 21 and stored at the bottom of the cleaning device 20, and is returned to the spray nozzle 21 through the circulation path 22 to be supplied to the cleaning water W. Spraying is repeated. Below the spray nozzle 21, a filler 24 is loaded to promote contact between the exhaust gas G and the cleaning water W. By spraying the cleaning water W from the spray nozzle 21 and introducing the exhaust gas G from the bottom of the cleaning device 20, the exhaust gas G and the absorbing liquid A 2 come into contact with each other in the gap between the fillers 24, and the scattered particles contained in the exhaust gas G Is captured and washed in the washing water W. Further, acidic halides such as hydrogen chloride, residual sulfur oxides, and nitrogen dioxide contained in the exhaust gas G are also absorbed by the cleaning water W. A water-cooled cooler 25 is provided on the circulation path 22, and by cooling the washing water W flowing through the circulation path 22, the temperature of the washing water W in the washing apparatus 20 is prevented from rising and maintained at an appropriate temperature. Is done. A mist removing member 26 is disposed above the spray nozzle 21 to prevent fine droplets or the like of the cleaning water W from being accompanied by the exhaust gas G and discharged to the outside. Like the mist removing member 16 of the desulfurization apparatus 10, the mist removing member 56 may be configured as a horizontal layer by a plurality of swash plates arranged in parallel with a gap, but may be in other forms, For example, you may comprise using a net-like member, a porous thin plate, etc. The exhaust gas G that has passed through the mist removing member 26 is discharged from the cleaning device 20 through the pipe 27. As the cleaning process proceeds, the cleaning water W contains a calcium compound, and the alkaline agent is consumed by neutralizing the absorbed acidic substance. Accordingly, a tank 28 for storing replenishing cleaning water or a high-concentration alkaline agent aqueous solution is attached, and if necessary, the used cleaning water is discharged from the drain via the circulation path 22 to obtain new cleaning water or The alkaline agent is replenished from the tank 28 to the cleaning device 20 via the circulation path 22.

  As the washing water W used in the washing apparatus 20, a substantially neutral or basic aqueous solution adjusted to about pH 5 to 9 is preferably used. When an aqueous solution containing an alkaline agent is used as the washing water W, the desulfurization function of the desulfurization apparatus 10 can be supplemented, and desulfurization and removal of acidic substances can be performed with higher accuracy. As the alkali agent, for example, an alkali metal hydroxide such as sodium hydroxide is preferable. An analyzer S3 for measuring the pH of the cleaning water W is installed at the bottom of the cleaning device 20.

In the desulfurization apparatus 10, sulfur dioxide absorbed from the exhaust gas G is dissolved as sulfite ions in the absorbing liquid A1. In order to treat this, an oxidation tank 30 is provided, a part of the absorbing liquid A1 flowing through the circulation path 12 is supplied to the oxidation tank 30 through the branch path 31, and an on-off valve 32 for controlling the supply is provided in the branch path 31 Provided. The oxidation tank 30 is provided with an introduction portion 33 for introducing a gas containing oxygen such as air, whereby the sulfurous acid in the absorbing liquid A1 is oxidized to sulfuric acid. The absorbent in the oxidation tank 30 is supplied to the desulfurization apparatus 10 through the reflux path 36 by driving the pump 35. The air in which oxygen is consumed is released from the oxidation tank 30 to the outside. Calcium sulfate generated by oxidation in the oxidation tank 30 is precipitated from the absorbing liquid A1. Therefore, sulfites, sulfates, and the like formed by the sulfur oxides absorbed from the exhaust gas G and the calcium ions eluted from the absorbent in the desulfurization apparatus 10 are finally obtained from the absorbing liquid A1 as gypsum (calcium sulfate). It precipitates and is collected through solid-liquid separation in the gypsum separator 38. The liquid separated from the gypsum can be returned to the desulfurization apparatus 10 as appropriate, or may be supplied as cleaning water to the cleaning nozzle 17 or 17 ′. In the embodiment of FIG. 1, a flow path connecting the gypsum separator 38 and the washing nozzles 17, 17 ′ is provided, and the gypsum generated from the sulfur oxide of the exhaust gas G and the calcium compound of the absorption liquid A 1 in the desulfurization apparatus 10. The absorption liquid A1 containing is supplied to the gypsum separator 38, and the gypsum is separated and removed from the absorption liquid A1, and the absorption liquid from which the gypsum is removed by the gypsum separator 38 is supplied to the cleaning nozzles 17 and 17 '. It is used as cleaning water for cleaning the mist removing member 16. The supply of the cleaning water to the cleaning nozzles 17 and 17 ′ is configured to be switchable by an on-off valve, and during the desulfurization process, the cleaning water is sprayed upward from the cleaning nozzle 17 ′ below the mist removing member 16 and stopped. In the state, spraying from the upper cleaning nozzle 17 to the mist removing member 16 prevents the cleaning water droplets from being discharged together with the exhaust gas G, which is advantageous in terms of cleaning efficiency. In the state where the supply of the exhaust gas G and the desulfurization treatment are stopped, the supernatant of the absorbing liquid A1 stored in the bottom of the desulfurization apparatus 10 is supplied to the cleaning nozzle 17 and used as cleaning water to clean the mist removing member 16. Is also possible. In this case, for example, the circulation path 12 can be branched and connected to the cleaning nozzle 17.
The oxidation tank 30 is provided with a stirrer 34 for stirring the absorption liquid, and the oxidation reaction proceeds uniformly in the absorption liquid by uniformly stirring and mixing the absorption liquid. Since the absorbent in the absorbent is consumed as the desulfurization process proceeds, a tank 37 for storing slurry in which the absorbent is dispersed in a high content is attached, and the absorbent is appropriately replenished from the tank 37 to the desulfurizer 10. The The absorbent supplied to the desulfurization apparatus 10 is uniformly mixed with the absorbent A1 by the stirrer 19 provided at the bottom of the desulfurization apparatus 10. An analyzer S4 for measuring the pH of the absorbing liquid A1 is installed at the bottom of the desulfurization apparatus 10.

  The gypsum precipitated from the absorbing solution supplied with oxygen can be modified so as to be separated and recovered in the oxidation tank 30. In this case, the stirring of the oxidation tank 30 is interrupted, and the supernatant liquid of the absorption liquid is refluxed to the desulfurization apparatus 10 to collect gypsum. Since the supernatant liquid of the absorbing liquid is suitable for use as washing water for washing the mist removing member 16 of the desulfurization apparatus 10, the washing nozzle is installed above and below the mist removing member 16 by branching the reflux path 36. 17 and 17 ', and it is good to comprise so that a part of supernatant liquid of the oxidation tank 30 may be supplied to washing nozzle 17' during a desulfurization process, and to washing nozzle 17 in a stop state. Alternatively, the absorbent in the oxidation tank 30 may be appropriately sent to the gypsum separator 38 to collect the gypsum.

  A denitration unit 3 that removes nitrogen oxides from the exhaust gas G is disposed downstream of the desulfurization unit 2. The denitration unit 3 includes a reaction device 40 that causes an oxidation reaction to generate nitrogen dioxide from nitric oxide, and a denitration device 50 that removes nitrogen dioxide from the exhaust gas using an aqueous absorbent, and is included in the exhaust gas. By converting nitric oxide, which is not soluble in water, into nitrogen dioxide, the denitration efficiency by the denitration device 50 is increased. As the reactor 40, a means capable of pressurizing exhaust gas is used. Specifically, at least one compressor for compressing the exhaust gas G discharged from the desulfurization unit 2 is used, and in the processing system 1 of FIG. 1, the reaction device 40 includes a first compressor 41 and a second compressor. 42. The exhaust gas G discharged from the desulfurization section 2 is pressurized in stages by the first compressor 41 and the second compressor 42, and oxygen and nitrogen oxides contained in the exhaust gas G act by pressurization in the compressor. As a result, a reaction in which nitric oxide is oxidized to nitrogen dioxide proceeds. Accordingly, the concentration of nitrogen monoxide in the pressurized exhaust gas G decreases and the concentration of nitrogen dioxide increases. Further, when sulfur oxides remain in the exhaust gas G, the oxidation of the sulfur oxides proceeds, and nitrogen dioxide is oxidized to nitrogen trioxide. Although the temperature of the compressed exhaust gas G becomes high, the denitration unit 3 of the present invention further has at least one cooler for cooling the compressed exhaust gas, and cools the exhaust gas G to an appropriate temperature. Specifically, the 1st cooler 43 and the 2nd cooler 44 are arranged in the latter part of each of the 1st compressor 41 and the 2nd compressor 42, and compression and cooling are repeated alternately. The cooling method of the first cooler 43 and the second cooler 44 may be either a water cooling method or a cooling method using other refrigerants, and has a drain function for separating and discharging the condensate generated by cooling by gas-liquid separation. Anything can be used. For example, a general cooler or heat exchanger and a gas-liquid separator may be connected and used as the first cooler 43 and the second cooler 44. When the compressed exhaust gas G is cooled by the first cooler 43 and the second cooler 44, the water vapor contained in the exhaust gas G is condensed and the water is separated, and the water-soluble component contained in the exhaust gas G is dissolved in the water. That is, nitrogen dioxide in the exhaust gas moves to condensed water, and even when sulfur oxides or the like remain, they are dissolved in the condensed water, and the concentrations of nitrogen oxides and other water-soluble impurities in the exhaust gas G are lowered. . Therefore, by separating and removing the condensed water generated by the cooling of the first cooler 43 and the second cooler 44 from the exhaust gas G, the exhaust gas G in which the concentrations of nitrogen oxides and other impurities are reduced is recovered. Thus, by alternately arranging a plurality of compressors and the plurality of coolers and alternately repeating the compression and cooling of the exhaust gas, the progress of the oxidation reaction and the dissolution / removal of the oxidation product are repeated, and the exhaust gas is exhausted. The concentration of nitrogen oxides, sulfur oxides and other water-soluble impurities of G is gradually reduced. An analyzer S5 for measuring the nitrogen oxide concentration of the exhaust gas G is installed at the rear stage of the reactor 40.

  In the processing system 1 of FIG. 1, a drain function is provided in the same manner as the first and second coolers 43 and 44 for the purpose of adjusting the temperature of the exhaust gas G to a temperature suitable for the processing temperature in the denitration device 50. The 3rd cooler 45 which has is provided in the front | former stage of the denitration apparatus 50, and waste gas G is fully cooled to appropriate temperature. Since the cooling temperature in the third cooler 45 is lower than that of the first and second coolers 43 and 44, it is preferable to use a cooling system that can cool to a lower temperature, even if a heat pump using a refrigerant is used. Good.

  The denitration apparatus 50 in the processing system 1 of the present invention is an apparatus that performs a wet process, and uses a substantially neutral or basic aqueous solution having a pH of about 5 to 9 as the absorbing liquid A2. The absorbent A2 contains an alkali metal compound such as sodium hydroxide as a strong alkaline absorbent that absorbs nitrogen oxides (nitrogen dioxide). The denitration device 50 has spraying means for spraying the absorbing liquid A2 into the exhaust gas G in the form of droplets. Specifically, a spray nozzle 51 for spraying the absorbing liquid A2 is provided at the upper part in the denitration apparatus 50, and a circulation path 52 for connecting the bottom part and the upper part is provided outside the apparatus. The absorbing liquid A2 sprayed from the spray nozzle 51 and stored in the bottom of the denitration apparatus 50 is returned to the spray nozzle 51 by driving the pump 53 on the circulation path 52, and the absorbing liquid A2 is repeatedly sprayed. A filler 54 is loaded below the spray nozzle 51 to form a gas-liquid contact phase for contacting the exhaust gas G with the absorbing liquid A2. By spraying the absorbing liquid A2 from the spray nozzle 51 and introducing the exhaust gas G from the bottom of the denitration device 50, the exhaust gas G and the absorbing liquid A2 come into contact with each other in the gap between the fillers 54, and the nitrogen dioxide contained in the exhaust gas G Is absorbed in the absorbent A2 and dissolved as nitrate. Further, acidic halides such as hydrogen chloride and residual sulfur oxides contained in the exhaust gas G are also absorbed by the absorbing liquid A2. A water-cooled cooler 55 is provided on the circulation path 52, and by cooling the absorption liquid A2 flowing through the circulation path 52, the temperature rise of the absorption liquid A2 in the denitration device 50 is prevented and maintained at an appropriate temperature. Is done.

A mist removing member 56 is disposed above the spray nozzle 51 and passes through the filler 54 in order to prevent fine droplets or the like caused by the absorbing liquid A2 from being accompanied by the exhaust gas G and discharged to the outside. The rising exhaust gas G passes through the mist removing member 56 and is then discharged from the denitration device 50 through the pipe 57. Like the mist removing member 16 of the desulfurization apparatus 10, the mist removing member 56 may be configured as a horizontal layer by a plurality of swash plates arranged in parallel with a gap, but may be in other forms, For example, you may comprise using a net-like member, a porous thin plate, etc. Since the absorbent in the absorbent A2 is consumed as the denitration process proceeds, a tank 58 for storing an aqueous solution containing the absorbent at a high concentration is attached, and the absorbent in the tank 58 passes through the circulation path 52. The denitration device 50 is appropriately replenished. The pH of the absorbing liquid A2 in the denitration apparatus 40 is monitored by the analyzer S6 at the bottom.
In addition, regarding the first to third coolers 43 to 45 described above, a cooler without a drain function can also be used, but in that case, condensed water is introduced into the denitration device 50 together with the compressed exhaust gas G. The absorbent of the absorbing liquid A2 is consumed by the acidic component dissolved in the condensed water.

  The treatment system 1 of the present invention includes a drying unit 5 that removes moisture from the exhaust gas and a mercury removal unit 6 that removes mercury from the exhaust gas at the subsequent stage of the denitration unit 3, and is discharged from the denitration device 50 through a pipe 57. Before the denitration exhaust gas G is supplied to the carbon dioxide recovery unit 4, moisture and mercury are removed. An analyzer S7 for measuring the nitrogen oxide concentration of the exhaust gas is provided in the pipe 57.

  The drying unit 5 is configured using a desiccant D that adsorbs moisture, and loads the pair of columns 61a and 61b with the desiccant D so that drying of the exhaust gas G and regeneration of the desiccant D can be alternately repeated. And use it. Specifically, the end of the pipe 57 is branched and connected to each of the columns 61a and 61b, and a three-way switching valve 62a for controlling the supply of the exhaust gas G to the columns 61a and 61b is provided. The exhaust gas G dried in the columns 61a and 61b is supplied to the mercury removing unit 6 through the pipe 63 and the three-way switching valve 62b. Further, a three-way switching valve 64a for controlling the gas supply to the columns 61a and 61b is connected to each of the columns 61a and 61b by branching the end of the pipe 65 for refluxing the gas G ′ discharged from the carbon dioxide recovery unit 4. Is provided. In order to discharge the gas G 'supplied to the columns 61a and 61b, a pipe 66 and a three-way switching valve 64b are provided. By controlling the connection switching of the three-way switching valves 62a, 62b, 64a, 64b, it is possible to supply the exhaust gas G to only one of the columns 61a, 61b and supply the gas G 'to the other. That is, when the three-way switching valves 62 a and 62 b are communicated with the column 61 a and the three-way switching valves 64 a and 64 b are communicated with the column 61 b, the exhaust gas G is supplied from the pipe 57 to the column 61 a and is recirculated from the carbon dioxide recovery unit 4. When G ′ is supplied from the pipe 65 to the column 61b and the three-way switching valve is communicated in the opposite direction, the gas supply is reversed. The desiccant D can be appropriately selected from those generally used as a desiccant, and examples thereof include molecular sieves and silica gel.

  The mercury removing unit 6 can be configured by filling a column with a material capable of adsorbing mercury as an adsorbent, and examples of the adsorbent include activated carbon. The dried exhaust gas G discharged from the columns 61a and 61b is supplied to the mercury removing unit 6 through the pipe 63 and passes through the adsorbent, whereby mercury is adsorbed and removed from the exhaust gas G.

  The exhaust gas G from which sulfur oxides, nitrogen oxides, water and mercury have been removed through the desulfurization unit 2, the denitration unit 3, the drying unit 5 and the mercury removal unit 6 contains carbon dioxide at a high concentration and is contained as an impurity. Substantially becomes oxygen, nitrogen and argon. The exhaust gas G is supplied to a carbon dioxide recovery unit 4 including a heat exchanger for cooling the gas and a low-temperature distillation tower. Carbon dioxide can be liquefied when compressed at a pressure above the boiling line in the temperature range from the triple point to the critical point, but the exhaust gas G supplied to the carbon dioxide recovery unit 4 can be liquefied in the denitration unit 3. Since the pressure is increased, the carbon dioxide in the exhaust gas G is liquefied when it is cooled below the boiling line temperature in the heat exchanger of the carbon dioxide recovery unit 4. Since liquefied carbon dioxide contains impurities such as oxygen, it is distilled at a distillation temperature of about −30 ° C. in a low-temperature distillation tower, and impurities such as oxygen are released from the liquefied carbon dioxide as a gas. Therefore, the gas G ′ discharged from the carbon dioxide recovery unit 4 through the pipe 65 is carbon dioxide gas having a higher ratio of impurities such as oxygen than the exhaust gas G supplied to the carbon dioxide recovery unit 4. This gas G ′ is refluxed to the columns 61 a and 61 b and used as a regeneration gas for drying the desiccant D. The purified liquefied carbon dioxide C is recovered from the carbon dioxide recovery unit 4.

  The gas G ′ discharged from the pipe 65 is heated to about 100 ° C. or higher by the heating device 67 in order to regenerate the desiccant D. The carbon dioxide recovery unit 4 uses a heat pump (refrigeration cycle) device to supply a cooling refrigerant to the heat exchanger, and the exhaust heat released in the heat pump device can be used as a heat source for heating. The exhaust gas can be used in the heating device 67 to heat the gas G ′ discharged from the pipe 65. The heated regeneration gas G ′ is refluxed to the columns 61a and 61b of the drying unit 5 through the pipe 65, and as described above, the exhaust gas G is not supplied by the control of the three-way switching valves 62a, 62b, 64a, and 64b. The desiccant D is heated by being supplied to the other column, and moisture is released from the desiccant D. Thereby, the gas G ′ containing water vapor is discharged from the columns 61 a and 61 b. In addition, since the desiccant D is heated by regeneration, it is desirable to cool the regenerated desiccant D before using it for drying. For this purpose, when the regeneration of the desiccant D is completed, the heating of the gas G ′ by exhaust heat is stopped, the unheated gas G ′ is supplied to cool the desiccant D, and then the exhaust gas G is dried. It is better to switch the three-way switching valve so as to change the column to be used.

  In the configuration of the processing system 1 described above, the cleaning device 20 can capture solid particles scattered from the desulfurization device 10 by the limestone / gypsum method without increasing the flow resistance of the exhaust gas introduced from the combustion system. Since the compressor 41 can be suitably prevented from being worn, damaged, etc., it is suitable for improving the durability of the system. In addition, the first compressor 41 and the second compressor 42 need to utilize a wet denitration process by advancing an oxidation reaction and utilize a reducing denitration process using ammonia, a catalyst, or the like. Disappear. Moreover, it not only functions as a reactor 40 that advances the oxidation reaction, but also acts as a means for applying a pressure necessary for liquefying carbon dioxide. That is, the pressure required to liquefy carbon dioxide is used for the denitration process. Since the desulfurization treatment by the limestone / gypsum method and the wet denitration treatment are advantageous options in terms of treatment costs, the combination of these treatments is realized by incorporating a reaction using a compressor. A treatment system is economically preferred.

One embodiment of the exhaust gas treatment method implemented in the treatment system 1 will be described below.
The treatment method of the present invention includes a desulfurization process for removing sulfur oxide from the exhaust gas G, a denitration process for removing nitrogen oxide from the exhaust gas G, and a carbon dioxide recovery process for recovering carbon dioxide from the exhaust gas G. Furthermore, by performing a drying process and a mercury removal process between the denitration process and the carbon dioxide recovery process, the aluminum parts of the heat exchanger used in the liquefaction of carbon dioxide are prevented from being damaged by mercury. Liquefied carbon dioxide can be efficiently recovered. The desulfurization treatment includes a desulfurization process that removes sulfur oxide from the exhaust gas using an absorbing solution, and a cleaning process that removes calcium-containing particles contained in the exhaust gas that has undergone the desulfurization process. The cleaning process is performed in the cleaning device 20.

  As the absorbing liquid A1, an aqueous dispersion containing an absorbent is prepared and accommodated in the desulfurization apparatus 10. As the absorbent, calcium compounds such as limestone (calcium carbonate), quick lime (calcium oxide), slaked lime (calcium hydroxide) can be used, and limestone is preferably used from the viewpoint of cost. Since the calcium compound is not highly water-soluble, it is preferably pulverized into a powder and mixed with water to prepare a dispersion liquid in which fine particles are dispersed and used as the absorbent A1. The desulfurization process proceeds by spraying the absorbing liquid A1 from the spray nozzle 11 by driving the pump 13 and introducing the exhaust gas G from the gas introduction part 14 to bring it into gas-liquid contact. From the viewpoint of gas-liquid contact efficiency, when the spray nozzle 11 having a diameter of about 30 to 120A is used, the absorbing liquid A1 is sprayed as droplets of a suitable size. The absorbing liquid A1 sprayed from the spray nozzle 11 is cooled by the cooler 15 in the circulation path 12, and an increase in the liquid temperature is prevented. The introduction rate of the exhaust gas G is appropriately adjusted according to the sulfur oxide concentration of the exhaust gas G so that the residence time during which the sulfur oxide in the exhaust gas G is sufficiently absorbed by the absorbent A can be obtained. Sulfur oxide contained in the exhaust gas G is absorbed by the absorption liquid A1 to form a calcium salt. Sulfur dioxide dissolves as calcium and calcium sulfite in the absorption liquid A1, and sulfur trioxide forms and precipitates calcium sulfate (gypsum). Therefore, the dispersion in the absorption liquid A1 includes limestone and gypsum. Acid halides such as hydrogen chloride contained in the exhaust gas G are also absorbed and dissolved in the absorbing liquid A1, and dust is also captured.

  The temperature of the exhaust gas G supplied from the combustion system is generally about 100 to 200 ° C. When the exhaust gas G is introduced, the temperature after gas-liquid contact in the desulfurization apparatus 10 is about 50 to 100 ° C. For this reason, the moisture of the droplets of the absorbing liquid A1 is vaporized, and the solid component contained in the absorbing liquid is scattered as particles (mist) and is accompanied by the exhaust gas G, but while passing through the mist removing member 16 In addition, since the solid particles easily collide with the swash plate, the solid particles can be removed to some extent, and can be sufficiently removed by the subsequent cleaning device 20. Therefore, in the treatment system of FIG. 1, the introduction temperature of the exhaust gas G is allowed to about 200 ° C.

  In the absorbing liquid A1 in which the sulfur oxide is absorbed from the exhaust gas G by the desulfurization apparatus 10, calcium sulfite generated from sulfur dioxide is dissolved. A part of the absorbing liquid A1 is supplied from the circulation path 12 to the oxidation tank 30 through the branch path 31, and here, a gas containing oxygen such as air is supplied. Thereby, the sulfurous acid in the absorption liquid A1 is oxidized into sulfuric acid and precipitates from the absorption liquid A1 as gypsum (calcium sulfate), so that the sulfur oxide in the exhaust gas G finally precipitates from the absorption liquid A1 as gypsum. . The gas supplied to the oxidation tank 30 may be any gas that can supply oxygen such as air, and supplies an amount capable of sufficiently oxidizing sulfurous acid. The absorbing liquid A1 that has undergone oxidation in the oxidation tank 30 is returned to the bottom of the desulfurization apparatus 10 by driving the pump 35. The stirring speed of the stirrer 34 is adjusted so that the oxidation reaction proceeds uniformly in the absorbing solution. Since the absorbent is consumed as the desulfurization process proceeds, an aqueous slurry in which the absorbent is dispersed in a high content is appropriately supplied from the tank 37 to the desulfurization apparatus 10 to replenish the absorbent, and the agitator 19 mixes uniformly. To do. The concentration of the aqueous slurry supplied from the tank 37 may be adjusted in consideration of the water content of gypsum recovered from the desulfurization apparatus 10. The gypsum deposited from the absorbing liquid A1 is separated and collected by the gypsum separator 38. The absorbent from which the gypsum has been removed is supplied as cleaning water to the cleaning nozzle 17 ′ and used for cleaning the mist removing member 16, but may be reused in the desulfurization apparatus 10 as necessary. The mist removing member 16 can be washed while the supply of the exhaust gas G and the desulfurization process are stopped. In this case, washing water is supplied from the gypsum separator 38 to the washing nozzle 17. Alternatively, it is possible to use the supernatant of the absorbent A1 stored at the bottom of the desulfurization apparatus 10 as washing water.

  In addition, when changing so that sedimentation separation of gypsum is performed in the oxidation tank 30, the sedimentation separation of gypsum can be optimized by stopping the stirring in the oxidation tank 30 as necessary. The on-off valve 32 and the pump 35 may be controlled so that the gypsum sedimentation process, the supernatant liquid reflux process, the gypsum discharge process, and the absorption liquid A1 uptake process may be performed sequentially. The supernatant liquid in which the concentration of the sulfur oxide-derived component and calcium is reduced is suitable for use as washing water for the mist removing member 16, and is supplied to the washing nozzle 17 ′ during the desulfurization process and to the washing nozzle 17 in the stopped state. Can be deformed. By cleaning the mist removing member, the limestone and gypsum particles absorb water and fall, and drop onto the bottom of the desulfurization apparatus 10. In the meantime, since sulfur oxides can be absorbed from the exhaust gas G, cleaning may be performed in parallel with the spraying of the absorbing liquid A1.

  The exhaust gas G discharged from the desulfurization apparatus 10 through the desulfurization process is supplied to the cleaning apparatus 20 through the pipe 18, and the cleaning process of cleaning the exhaust gas G using the cleaning water W is performed. Thereby, scattered particles that cannot be removed by the mist removing member 16 are sufficiently removed from the exhaust gas G. At this time, dust and hydrogen chloride contained in the exhaust gas G are also washed away. The temperature of the exhaust gas G is cooled to about 40 to 80 ° C.

  In the cleaning process, the cleaning water W is sprayed from the spray nozzle 21 by driving the pump 23 and the exhaust gas G is introduced from the bottom of the cleaning device 20, so that the exhaust gas G and the cleaning water W come into contact with each other in the gap of the filler 24. Thus, the scattered particles contained in the exhaust gas G are captured and washed by the washing water W. Water is preferably used as the washing water W. However, when an aqueous solution of a highly water-soluble alkaline agent is used as the washing water W, the ability to capture scattered particles (calcium compounds) is improved, and a desulfurization / denitration effect is also exhibited. . Examples of the alkali agent include alkali metal compounds such as sodium compounds and potassium compounds, and preferably alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The washing water W is preferably adjusted to a basicity of about pH 7-9. In order to prevent the fine droplets of the cleaning water W from being accompanied by the exhaust gas G, it is preferable that the temperature of the cleaning water W is maintained at about 40 to 80 ° C. As the cleaning process proceeds, the cleaning water W contains a calcium compound, and the pH decreases due to the absorption of the acidic substance. When the washing water W shows acidity, replenishment washing water is supplied from the tank 28, and when the washing water W is contaminated or acidified, the washing water is discharged from the drain and the inside of the tank 28 is washed. Refill with water W.

The exhaust gas G discharged from the cleaning apparatus 20 through the cleaning process is subjected to a reaction process, a cooling process, and a denitration process as a denitration process. First, in a reaction process, it supplies to the 1st compressor 41 of the denitration part 3, is compressed to about 1.0-2.0 MPa, and temperature rises to about 100-200 degreeC with compression heat. As the pressure increases, the oxidation reaction proceeds in the exhaust gas G, nitrogen dioxide is generated from nitric oxide, and the oxygen content decreases. In the desulfurization section 2, the sulfur oxides in the exhaust gas are almost removed, but the oxidation reaction also proceeds in the remaining sulfur oxides, and sulfur trioxide is generated from the sulfur dioxide. Mercury is also oxidized to Hg ²⁺ and easily dissolved in water. In the cooling step, the exhaust gas G compressed by the first compressor 41 is supplied to the first cooler 43 and cooled to a temperature of about 40 ° C., and water vapor contained in the exhaust gas G is condensed. In the water-cooling type cooling, the cooling is generally performed at about 40 ° C. Thereby, since nitrogen dioxide, sulfur oxide, and mercury contained in the exhaust gas G are dissolved in the condensed water, the amount of these contained in the exhaust gas G is reduced. The condensed water is separated from the exhaust gas G and discharged by the drain. The exhaust gas G is further supplied to the second compressor 42 and the reaction process is repeated. At this time, the carbon dioxide is compressed at a pressure capable of liquefying carbon dioxide. Specifically, it is compressed to about 2.0 to 4.0 MPa, and the temperature rises again to about 100 to 200 ° C. As the pressure increases, the oxidation reaction proceeds again to produce nitrogen dioxide from the remaining nitric oxide, further reducing the oxygen content. The oxidation reaction also proceeds in the remaining sulfur oxide, and sulfur trioxide is generated from sulfur dioxide. Mercury oxidation proceeds as well. The exhaust gas G compressed by the second compressor 42 is cooled again to a temperature of about 40 ° C. in the second cooler 44 as a cooling process, and water vapor contained in the exhaust gas G is condensed. In the water-cooling type cooling, the cooling is generally about 40 ° C. Nitrogen dioxide, sulfur oxides and mercury contained in the exhaust gas G are dissolved in the condensed water, and these amounts contained in the exhaust gas G are further reduced. The condensed water is separated from the exhaust gas G and discharged by the drain. The exhaust gas G cooled by the second cooler 44 is further cooled by the third cooler 45 and adjusted to a temperature of about 0 to 10 ° C. suitable for the treatment temperature in the denitration device 50. Condensed water is likewise discharged by the drain. As a result, impurities (nitrogen dioxide, sulfur oxide, Hg ²⁺ ) for dissolving the condensed water generated in the cooler are removed from the exhaust gas G.

  The exhaust gas G that has passed through the third cooler 45 is supplied to the denitration device 50, and a denitration process is performed. That is, while the exhaust gas G rises between the fillers 54, it comes into gas-liquid contact with the absorbing liquid A2 sprayed from the spray nozzle 51 by driving the pump 53, and the nitrogen dioxide contained in the exhaust gas G is absorbed by the absorbing liquid A2. It dissolves as nitrate. Acid halides such as hydrogen chloride and residual sulfur oxides contained in the exhaust gas G are also absorbed by the absorbent A2. As the absorbing liquid A2, a substantially neutral or basic aqueous liquid containing an absorbent for absorbing nitrogen oxide is used, and the pH is adjusted to about 5 to 9 and used as the absorbing liquid A2. As the absorbent, an alkali metal compound, preferably, a strongly basic alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is used, and an aqueous solution in which the absorbent is dissolved in water is prepared and used. preferable. The cooler 55 prevents the temperature of the sprayed absorbing liquid A2 from rising. In order to supplement the absorbent consumed as the denitration process proceeds, the absorbent is appropriately supplied from the tank 58.

  The exhaust gas G discharged from the denitration device 50 is subjected to a drying process in the drying unit 5. That is, the exhaust gas G is supplied to one of the columns 61a and 61b and moisture is removed by the desiccant D. During this time, the regeneration gas supplied from the carbon dioxide recovery unit 4 in the other column is used to remove the desiccant D. Playback is performed. Since the treatment capacity of the exhaust gas G can be set in advance based on the hygroscopic capacity of the desiccant D accommodated in the column, the three-way switching valves 62a and 62b are required before the supply amount of the exhaust gas G reaches the maximum processable amount. The column for supplying the exhaust gas G is changed and at the same time the column for regenerating the desiccant D is changed by switching the three-way switching valves 64a and 64b. This switching may be performed every certain processing time. The desiccant D can be appropriately selected from those generally used as a desiccant. For example, it absorbs or adsorbs moisture physically or chemically such as molecular sieve, silica gel, alumina, zeolite, etc. Possible ones. The temperature in the drying process is preferably about 100 ° C. or higher, and the exhaust gas G is supplied to the columns 61a and 61b at such a temperature. The regeneration gas G ′ supplied from the carbon dioxide recovery unit 4 is dry carbon dioxide having a high concentration of oxygen, nitrogen, and argon, and is heated to a temperature suitable for regeneration, preferably about 100 ° C. or more. Supplied and regenerated by releasing moisture from the desiccant D.

  The dried exhaust gas G discharged from the columns 61a and 61b is supplied to the mercury removing unit 6, and mercury is adsorbed and removed by the adsorbent. Examples of the adsorbent for the mercury removing unit 6 include activated carbon, activated carbon supporting potassium iodide, ion exchange resin, and the like. Since the exhaust gas G discharged from the mercury removing unit 6 has sulfur oxides, nitrogen oxides, water, and mercury removed, it contains carbon dioxide at a very high concentration, and the components contained as impurities are substantially Oxygen, nitrogen and argon.

  The temperature of the exhaust gas G in the denitration unit 3, the drying unit 5, and the mercury removal unit 6 substantially depends on the temperature in the denitration device 50, and the pressure of the exhaust gas G depends on the degree of compression in the second compressor 42. In the compression in the second compressor 42, as described above, the pressure at which carbon dioxide can be liquefied, that is, the pressure G is compressed to about 2.0 to 4.0 MPa, and the exhaust gas G maintained at this pressure is oxidized. It is supplied to the carbon recovery unit 4. Accordingly, when the exhaust gas G is cooled to the boiling line temperature or lower, preferably about −20 to −50 ° C. in the heat exchanger of the carbon dioxide recovery unit 4, the carbon dioxide in the exhaust gas G is liquefied. The liquefied carbon dioxide is distilled at a temperature of about −20 to −50 ° C. in a low-temperature distillation tower, and impurities such as oxygen, nitrogen, and argon are removed from the liquefied carbon dioxide. Since the carbon dioxide gas in which the ratio of these impurities is increased is released from the low-temperature distillation tower, the gas G ′ is heated to 100 ° C. or more, preferably about 100 to 200 ° C., and then the pipe 65 is connected to the columns 61a and 61b. It is refluxed to the desiccant D and used as a regeneration gas. For heating the regeneration gas, exhaust heat from a heat pump (refrigeration cycle) device that supplies refrigerant to the heat exchanger of the carbon dioxide recovery unit 4 can be used. By regenerating the desiccant D by heating, the gas G 'containing water vapor is discharged from the columns 61a and 61b. The purified liquefied carbon dioxide C is recovered from the carbon dioxide recovery unit 4. In the drying unit 5, the desiccant D heated for regeneration is desirably cooled before being used for drying. For this purpose, when regeneration of the desiccant D is completed, heating of the regeneration gas is stopped, the gas G ′ that is not heated is supplied to cool the desiccant D, and then the three-way switching valve is switched, It is preferable to switch between a column for drying and a column for regeneration.

  In the processing system 1, the first cooler 43 can be omitted, but the amount of water vapor in the exhaust gas in the subsequent stage compressor is removed by cooling each time it is compressed as shown in FIG. 1 to remove condensed water. Decreases and the load decreases. Moreover, although the reaction apparatus 40 of the processing system 1 is constituted by two compressors, it may be constituted by a single or three or more compressors, and the number of compressors constituting the reaction apparatus 40 is increased. As a result, the amount of compression for increasing the pressure required to liquefy carbon dioxide is dispersed in each compressor, and the load on each compressor is reduced. When the pressure of the exhaust gas G that has passed through the reactor 40 does not increase to a pressure at which carbon dioxide can be liquefied, it is necessary to change the configuration so as to pressurize the exhaust gas G in the carbon dioxide recovery unit 4 or in the preceding stage. For example, a compressor and a cooler are attached upstream of the carbon dioxide recovery unit 4.

  The exhaust gas treatment system 1 shown in FIG. 1 is an embodiment configured to cope with the introduction of high-temperature exhaust gas G. However, when the temperature of the exhaust gas G is a low temperature less than 100 ° C., the corresponding capability Based on the above, it is possible to make a change that improves the processing efficiency. Such an embodiment is shown in FIG.

  The exhaust gas processing system 1 ′ shown in FIG. 2 is configured by using the same components as the processing system 1 of FIG. 1, but the arrangement of the first compressor 41 is changed and the first cooler 43 is omitted. Is different. That is, in the processing system 1 ′, the reactor 40 in FIG. 1 is divided into a first reaction unit and a second reaction unit, and the first compressor 41 ′ constituting the first reaction unit is desulfurized in the desulfurization unit 2 ′. Arranged in the front stage of the apparatus 10, the second reactor is constituted only by the second compressor 42 'in the denitration part 3' subsequent to the desulfurization part 2 '. Therefore, in both the desulfurization part 2 'and the denitration part 3', the oxidation reaction proceeds by pressurization in the exhaust gas G before treatment.

Specifically, when the exhaust gas G of about 100 to 200 ° C. is supplied to the treatment system 1 ′, it is first compressed to about 1.0 to 2.0 MPa in the first compressor 41 ′, and the temperature is increased by the compression heat. It rises within a range of about 100 to 200 ° C. As the pressure increases, the oxidation reaction proceeds in the exhaust gas G, and sulfur trioxide is generated from sulfur dioxide. Further, nitrogen dioxide is generated from nitric oxide, mercury is also oxidized to Hg ²⁺ and is easily dissolved in water, and the oxygen content is reduced. Since the temperature of the compressed exhaust gas G conforms to the initial temperature condition of the exhaust gas G supplied to the treatment system 1 in FIG. 1, the desulfurization apparatus 10 and the cleaning apparatus 20 can suitably perform the desulfurization process. The temperature of the exhaust gas G after coming into gas-liquid contact with the absorbing liquid A1 is about 40 to 80 ° C. as in the case of FIG. That is, the absorption liquid spraying of the desulfurization apparatus 10 also plays the role of the first cooler 43 in FIG. Particles scattered from the absorbing liquid A1 are removed to some extent while passing through the mist removing member 16, and the rest are accompanied by the exhaust gas G discharged from the desulfurization apparatus 10 and are sufficiently removed by the cleaning apparatus 20.

Compared with the embodiment of FIG. 1, the component absorbed by the absorbent A <b> 1 of the desulfurization apparatus 10 has a decrease in sulfur dioxide and an increase in sulfur trioxide. At 30, the amount of oxygen required for the oxidation of sulfur dioxide is reduced. Further, the amount of nitrogen dioxide and Hg ²⁺ absorbed by the absorbing liquid A1 also increases. Therefore, the contents of nitrogen monoxide and mercury in the exhaust gas G discharged from the cleaning device 20 of the desulfurization section 2 ′ are reduced as compared with the case of FIG.

  The exhaust gas G discharged from the cleaning device 20 is supplied to the second compressor 42 ', and is compressed to a pressure at which carbon dioxide can be liquefied, similarly to the second compressor 42 of FIG. 1, and the temperature rises. . As the pressure increases, the oxidation reaction proceeds again, nitrogen dioxide is generated from the remaining nitric oxide, and the oxygen content is further reduced. The oxidation reaction also proceeds in the remaining sulfur oxide, and sulfur trioxide is generated from sulfur dioxide. Mercury oxidation proceeds as well. The exhaust gas G compressed by the second compressor 42 is cooled in the second cooler 44, and water vapor contained in the exhaust gas G is condensed. Nitrogen dioxide, sulfur oxides and mercury contained in the exhaust gas G are dissolved in the condensed water, and these amounts contained in the exhaust gas G are further reduced. The condensed water is separated from the exhaust gas G and discharged by the drain.

  After that, the exhaust gas G cooled by the second cooler 44 is cooled by the third cooler 45, denitrated by the denitration device 50, dried by the drying unit 5, and adsorbed and removed by mercury by the mercury removing unit 6. However, these are the same as the processing system 1 of FIG.

When the compressor is arranged in the front stage of the desulfurization apparatus 10 as in the processing system 1 ′ of FIG. 2, the amount of oxygen in the exhaust gas G consumed by the oxidation reaction accompanying pressurization increases. Therefore, the oxygen content of the exhaust gas G supplied to the carbon dioxide recovery unit 4 is smaller than in the case of the processing system 1 of FIG. In addition, since the components solubilized in water by oxidation (nitrogen dioxide, Hg ²⁺ ) increase in contact with the aqueous liquid, they are advantageous in terms of improving the removal efficiency and the service life of the mercury adsorbent. In the processing system 1 ′ of FIG. 2, the second reactor of the denitration unit 3 ′ can be configured using a plurality of compressors, which are compressed before the desulfurization device 10 of the processing system 1 of FIG. Equivalent to the form of adding a vessel. When increasing the number of compressors, the compression rate of each compressor may be set so that the pressure of the exhaust gas G discharged from the final compressor becomes a pressure at which carbon dioxide can be liquefied.

  The present invention can recover high-purity carbon dioxide in the treatment of exhaust gas discharged from facilities such as thermal power plants, steelworks, and boilers, and can use the treatment of exhaust gas to provide liquefied carbon dioxide. is there. It is useful for reducing the amount of carbon dioxide released and its impact on the environment when used for the treatment of carbon dioxide-containing gas. The processing cost can be reduced while ensuring the durability of the apparatus, and an exhaust gas processing system that can perform system management without any trouble can be provided, thereby contributing to environmental protection.

1,1 'treatment system, 2,2' desulfurization section, 3,3 'denitration section,
4 carbon dioxide recovery section, 5 drying section, 6 mercury removal section,
10 Desulfurization equipment, 11, 21, 51 spray nozzle,
12, 22, 52 circuit, 13, 23, 35, 53 pump,
14 gas introduction part, 15, 25, 55 cooler,
16, 26, 56 Mist removing member, 17, 17 'cleaning nozzle,
18, 27, 57, 63, 65, 66 piping, 19, 34 stirrer,
20 cleaning device, 24,54 filler,
28, 37, 58 tanks,
30 oxidation tank, 31 branch path, 32 on-off valve,
33 introduction part, 36 reflux path, 38 gypsum separator,
40 reactor, 41, 41 ′ first compressor, 42, 42 ′ second compressor,
43 1st cooler, 44 2nd cooler, 45 3rd cooler,
50 Denitration equipment, 61a, 61b column,
62a, 62b, 64a, 64b three-way switching valve,
67 heating device,
S1, S2, S3, S4, S5, S6, S7 analyzer,
A1, A2 absorption liquid, C liquefied carbon dioxide, D desiccant,
G exhaust gas, G 'gas, W wash water.

Claims (11)

A desulfurization section for removing sulfur oxide from the exhaust gas; a denitration section for removing nitrogen oxide from the exhaust gas disposed downstream from the desulfurization section; and a carbon dioxide from the exhaust gas disposed after the desulfurization section and the denitration section. An exhaust gas processing system having a carbon dioxide recovery unit for recovering
A desulfurization apparatus that removes sulfur oxides from the exhaust gas using an absorbent containing a calcium compound;
An exhaust gas treatment system comprising: a cleaning device that cleans exhaust gas discharged from the desulfurization device using cleaning water and removes calcium-containing particles contained in the exhaust gas.   2. The exhaust gas according to claim 1, wherein the desulfurization apparatus includes a spraying unit that sprays the absorption liquid onto the exhaust gas, and a gas-liquid contact phase that contacts the exhaust gas with the absorption liquid is formed by spraying the absorption liquid. Processing system.   The denitration unit includes a reaction device that generates an oxidation reaction to generate nitrogen dioxide from nitric oxide, and a denitration device that removes nitrogen dioxide from exhaust gas using an aqueous absorbent. Exhaust gas treatment system.   The reactor has at least one compressor for compressing exhaust gas discharged from the desulfurization unit, and the denitration unit further cools at least one exhaust gas compressed by the at least one compressor. The exhaust gas treatment system according to claim 3, comprising two coolers.   The reactor includes a plurality of compressors for compressing exhaust gas, the denitration unit further includes a plurality of coolers, and the plurality of compressors and the plurality of coolers are capable of compressing and cooling. The exhaust gas treatment system according to claim 3 or 4, which is alternately arranged so as to be repeated alternately.   The desulfurization device has a mist removal member that is disposed so that the exhaust gas that has passed through the gas-liquid contact phase passes before being discharged from the desulfurization device, and the mist removal member is arranged in a direction in which the exhaust gas passes. The exhaust gas treatment system according to claim 2, wherein the exhaust gas treatment system is configured by a plurality of swash plates that are arranged in parallel with a gap therebetween.   The desulfurization unit further includes a gypsum separator for separating and removing gypsum generated from the sulfur oxide of the exhaust gas and the calcium compound of the absorption liquid in the desulfurization apparatus, and the desulfurization apparatus includes: The exhaust gas treatment system according to claim 6, further comprising a cleaning nozzle for cleaning the mist removing member using an absorbent from which gypsum has been removed by the gypsum separator.   The exhaust gas treatment system according to any one of claims 1 to 7, wherein the cleaning device is disposed downstream of the desulfurization device, and the cleaning water contains a sodium compound as an alkaline agent. The desulfurization unit further includes a first reaction unit that is arranged in a preceding stage of the desulfurization apparatus to cause an oxidation reaction to generate sulfur trioxide from sulfur dioxide,
The denitration unit is disposed downstream of the desulfurization unit and proceeds with an oxidation reaction to generate nitrogen dioxide from nitrogen monoxide, and a denitration unit that removes nitrogen dioxide from exhaust gas using an aqueous absorbent. The exhaust gas treatment system according to any one of claims 1 to 4 and 6 to 7, comprising an apparatus.   The exhaust gas treatment system according to any one of claims 1 to 9, further comprising a drying unit that removes moisture from the exhaust gas and a mercury removal unit that removes mercury from the exhaust gas. An exhaust gas treatment method comprising: a desulfurization process for removing sulfur oxides from exhaust gas; a denitration process for removing nitrogen oxides from exhaust gas; and a carbon dioxide recovery process for recovering carbon dioxide from exhaust gas, wherein the desulfurization process comprises: ,
A desulfurization step of removing sulfur oxides from the exhaust gas using an absorbent containing a calcium compound;
And a cleaning step of removing the calcium-containing particles contained in the exhaust gas by cleaning the exhaust gas that has passed through the desulfurization step with cleaning water.

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