WO2012132003A1

WO2012132003A1 - Exhaust gas treatment system and exhaust gas treatment method

Info

Publication number: WO2012132003A1
Application number: PCT/JP2011/058313
Authority: WO
Inventors: 亮太落合; 考司村本; 片川　篤; 隆行斉藤; 中本　隆則; 石坂　浩; みさき隅倉; 康二原田
Original assignee: バブコック日立株式会社; 株式会社ササクラ
Priority date: 2011-03-31
Filing date: 2011-03-31
Publication date: 2012-10-04
Also published as: AU2011364094B2; AU2011364094A1

Abstract

[Problem] The purpose of the present invention is to provide an exhaust gas treatment system and exhaust gas treatment method that can reduce the amount of make-up water to a desulfurization means and make a reduction in the heat source required for a desalination means. [Solution] This exhaust gas treatment system (10) is characterized by comprising a wet type desulfurization means (40) that eliminates sulfur oxides in the exhaust gas, a desalination means (80) that produces fresh water from seawater and supplies the same to the wet type desulfurization means (40), a heat exchanger (20) that heats a heating medium by means of the exhaust gas in a stage prior to the wet type desulfurization means (40), a seawater heater (22) for the desalination means (80), and a circulation line (24) that connects the heat exchanger (20) to the seawater heater and circulates the heating medium.

Description

Exhaust gas treatment system and exhaust gas treatment method

The present invention particularly relates to an exhaust gas treatment system and an exhaust gas treatment method provided with wet desulfurization means for removing sulfur oxides and the like in the exhaust gas.

Exhaust gas discharged from boilers installed in thermal power plants and factories contains acidic gases such as sulfur oxides, hydrogen chloride, and hydrogen fluoride. There is a wet desulfurization apparatus as means for removing the acid gas. The wet desulfurization apparatus has advantages such as higher desulfurization performance than the dry desulfurization apparatus and less pollution of waste water discharged from the apparatus.

Exhaust gas from boilers installed in conventional thermal power plants and factories is introduced into wet desulfurization equipment at a relatively high temperature of 120 ° C. to 160 ° C. Therefore, in the absorption tower of the wet desulfurization apparatus, the high temperature exhaust gas and the slurry come into contact with each other and are vaporized to increase the amount of steam water. The generated large amount of mist (steam) cannot be captured by the mist eliminator and is discharged outside the absorption tower. For this reason, in order to supplement the amount of water for the steam discharged to the outside, make-up water has to be added, and a large amount of make-up water has been required.

Thus, the conventional wet desulfurization apparatus requires a large amount of makeup water. In areas where it is difficult to secure fresh water (industrial water), fresh water is produced by a desalinator that converts seawater into fresh water and used as make-up water for wet desulfurization equipment.

As a conventional desalination apparatus, there is a method using an evaporation method such as a multistage flash method or a multi-effect method. In the desalination apparatus using the evaporation method, it is necessary to supply heat from the outside by supplying steam or hot water to the seawater heater in the process of producing fresh water. Therefore, there has been a problem that power generation efficiency is reduced in a plant such as a thermal power plant. As an example, in order to produce about 160 Ton / h of fresh water, the desalination apparatus requires heat of about 1-2 Ton / h of steam and 110 ° C. and about 1000 Ton / h of hot water.

On the other hand, there is a wet desulfurization apparatus that uses seawater as a desulfurization absorbent. In this method, seawater is directly supplied to the absorption tower, and after removing sulfur oxides and dust in the exhaust gas, the seawater is discharged to the sea. However, when seawater is used, the amount of seawater supplied to the absorption tower and discharged becomes large. Therefore, when wastewater treatment is performed, the facility becomes large in order to treat a large amount of wastewater. Moreover, in the simple waste water treatment which only adjusts the dissolved oxygen concentration in waste water, the heavy metal etc. in waste water are not processed, and waste water temperature is also high. For this reason, the problem of secondary pollution of contaminated wastewater such as an increase in seawater temperature has occurred.

Patent Documents 1 and 2 are examples of techniques for desalinating seawater using exhaust heat from a boiler or the like. In Patent Document 1, seawater is desalinated using the exhaust heat of the power generation apparatus, and the efficiency of the power generation facility is increased, and the exhaust heat from the gas turbine is directly supplied to the seawater heater of the evaporative seawater desalination apparatus. However, facilities for heating seawater are disclosed.
Patent Document 2 discloses a facility that heats seawater by using exhaust heat from a plurality of power plants such as a waste heat boiler and directly supplying it to a seawater heater of a seawater desalination apparatus.

Further, Patent Documents 3 and 4 can be cited as technologies including a desulfurization apparatus and a desalination apparatus. Patent Document 3 is a system that cools exhaust gas and seawater in indirect contact with each other in a heat exchanger on the desulfurization processing side of an indirect heat exchange device. Patent Document 3 discloses a system in which moisture in exhaust gas is condensed and recovered by cooling, and heated seawater is supplied to an electrodialysis apparatus.

Patent Document 4 is a system in which exhaust gas from a thermal power generation boiler is processed by a dry-type flue gas desulfurization apparatus, and sensible heat of the exhaust gas is used as a heat source of a seawater desalination apparatus. The seawater desalination apparatus of patent document 4 is a multistage flash, and supplies the obtained fresh water to a boiler.

JP 2006-70889 A Japanese Patent Laid-Open No. 61-15003 JP 62-30530 A JP 59-107105 A

However, the use of exhaust heat disclosed in Patent Documents 1 and 2 is a configuration in which heat of exhaust gas discharged from a power plant is directly exchanged as a heat source of a seawater desalination apparatus. This type of direct heat exchange between the exhaust gas and seawater, and when a malfunction occurs in the heat exchanger during plant operation, the exhaust gas treatment process and the desalination process are linked, resulting in a malfunction. Only the installed equipment could not be stopped, and the entire system had to be stopped.

In Patent Document 3, heat exchange is performed after the desulfurization apparatus. For this reason, there is a problem that the temperature difference between the exhaust gas temperature and the seawater is small, and efficient heat exchange cannot be performed unless the capacity of the heat exchanger is increased, and the entire apparatus becomes large.
In Patent Document 4, since a dry method is used as a desulfurization method, expensive active coke is required, and there is a problem that the desulfurization performance is low as compared with the wet method.

In order to solve the above-described problems of the prior art, an object of the present invention is to provide an exhaust gas treatment system and an exhaust gas treatment method that can reduce the amount of makeup water in the desulfurization means.
Another object of the present invention is to provide an exhaust gas treatment system and an exhaust gas treatment method capable of reducing the heat source required for the desalination means.
Another object of the present invention is to provide an exhaust gas treatment system and an exhaust gas treatment method that improve the efficiency of fresh water production by the desalination means.
Another object of the present invention is to provide an exhaust gas treatment system and an exhaust gas treatment method in which the dust collection efficiency of the electric dust collection means is improved.

The exhaust gas treatment system of the present invention includes a wet desulfurization means for removing sulfur oxides in the exhaust gas, a desalination means for producing fresh water from seawater and supplying the fresh water to the wet desulfurization means, and the exhaust gas before the wet desulfurization means. A heat exchanger for heating the heat medium, a seawater heater for the desalination means, and a circulation line for the heat medium by connecting the heat exchanger to the seawater heater. .

According to the above configuration, the amount of makeup water supplied to the desulfurization means can be reduced. Further, a heat source of exhaust gas can be used for the desalination means. Therefore, it is possible to reduce the cost of the entire system and save energy.

In this case, connected to the bypass line connecting the feed pipe and the return pipe of the circulation line, the flow control valve provided in the circulation line and the bypass line to adjust the flow rate of the heating medium, and the flow control valve. And a control means for controlling the supply amount of the heat medium to the seawater heater.
According to the said structure, the heating temperature of seawater can be controlled and manufacture of fresh water can be performed efficiently.

In this case, seawater temperature measuring means for detecting the outlet temperature of the seawater heater is provided, and the control means sets the measured value of the temperature measuring means so that the outlet temperature of the seawater heater becomes a predetermined temperature. Based on this, the supply amount of the heat medium to the seawater heater may be controlled.
According to the said structure, the heating temperature of seawater can be controlled to the preset setting value, and manufacture of fresh water can be performed efficiently.

In this case, it is preferable that an electric dust collecting means is provided in the previous stage of the heat exchanger.
According to the above configuration, heat exchange between the heat medium of the heat exchanger and the exhaust gas can be performed without lowering the exhaust gas temperature of the electric dust collecting means.

In this case, an electric dust collecting means may be provided between the heat exchanger and the wet desulfurization means.
According to the said structure, the gas temperature of the hot exhaust gas introduce | transduced into an electrical dust collection means can be lowered | hung and dust removal efficiency can be performed efficiently.

In this case, the control means may be connected to the flow rate control valve to control the supply amount of the heat medium to the heat exchanger.
According to the said structure, exhaust gas temperature can be controlled and it can remove efficiently with an electrical dust collection means.

In this case, gas temperature measuring means for detecting the temperature of the exhaust gas to be introduced into the electric dust collecting means is provided, and the control means has a predetermined temperature for the exhaust gas to be introduced into the electric dust collecting means. Thus, it is preferable to control the supply amount of the heat medium to the heat exchanger based on the measured value of the gas temperature measuring means.
According to the said structure, exhaust gas temperature can be controlled to the preset value of gas temperature, and it can remove efficiently with an electrical dust collection means.

In this case, when a second heat exchanger is provided in the liquid distillation section of the wet desulfurization means and connected to the circulation line, the heat medium circulates between the heat exchanger and the second heat exchanger. Good.
According to the above configuration, the heat medium can be heated by exchanging heat between the heat medium and the absorbing liquid without reducing the dust removal efficiency of the electric dust collecting means. Therefore, even when the exhaust gas temperature is low, the heating medium can be heated, the amount of steam used in the desalination means can be reduced, and the cost of the entire system and energy saving can be achieved.

The exhaust gas treatment system of the present invention includes a wet desulfurization means for removing sulfur oxides in the exhaust gas, a desalination means for producing fresh water from seawater and supplying the fresh water to the wet desulfurization means, and the exhaust gas after the wet desulfurization means. A heat exchanger for heating the heat medium, a seawater heater for the desalination means, a heat medium circulation line for connecting the heat exchanger to the seawater heater and circulating the heat medium, and in the exhaust gas. And a mist eliminator for removing mist contained therein.

According to the above configuration, the exhaust gas that has been saturated with water after the desulfurization treatment can be condensed and recovered by reducing the gas temperature by heat exchange with the heat medium of the heat exchanger. Further, by using the heat of the exhaust gas for heating the seawater of the desalination means, the amount of steam used can be reduced, and the overall cost of the system can be reduced and the energy can be saved.

The exhaust gas treatment method of the present invention is the exhaust gas treatment method for removing sulfur oxides contained in the exhaust gas, wherein the exhaust gas before the desulfurization treatment and the heat medium are heat-exchanged to lower the gas temperature of the exhaust gas to reduce the heat. A step of heating the medium, a step of desulfurizing the exhaust gas whose gas temperature has decreased, a step of circulating the heated heating medium to a seawater heater, a step of exchanging heat between the heated heating medium and seawater, It comprises a step of producing fresh water from the heated seawater, and a step of measuring the heated seawater temperature and controlling the circulation amount of the heating medium.

According to the above configuration, the amount of makeup water supplied to the desulfurization means can be reduced. Further, a heat source of exhaust gas can be used for the desalination means. Therefore, it is possible to reduce the cost of the entire system and save energy. Moreover, the heating temperature of seawater can be controlled and the manufacture of fresh water can be performed efficiently.

A heat exchanger can be installed on the upstream side (front stage) of the wet desulfurization means to lower the exhaust gas temperature at the inlet of the wet desulfurization means. Thereby, a large amount of water in the absorption tower is not vaporized and discharged to the outside. Therefore, the amount of water supplied to the absorption tower can be reduced.

In addition, by using the heat exchanger as an indirect type and reusing the heat obtained by heat exchange with the exhaust gas as a heat source for the desalination means, it is no longer necessary to supply steam necessary for the water purification means, thus reducing the energy consumption of the entire system. Can be planned.

1 is a schematic configuration diagram of an exhaust gas treatment system according to a first embodiment. 1 is a schematic configuration diagram of an exhaust gas treatment system using a multiple effect method for desalination means. 1 is a schematic configuration diagram of an exhaust gas treatment system using a multistage flash method as a desalination means. It is a graph which shows the correlation of absorption tower inlet gas temperature and absorption tower evaporation water amount. It is a composition schematic diagram of an exhaust gas treatment system concerning a 2nd embodiment. It is a block schematic diagram of the waste gas treatment system concerning a 3rd embodiment. It is a block schematic diagram of the exhaust gas treatment system concerning a 4th embodiment. It is a block schematic diagram of the exhaust gas treatment system concerning a 5th embodiment.

Embodiments of an exhaust gas treatment system and an exhaust gas treatment method of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an exhaust gas treatment system according to the first embodiment. As shown in the figure, the exhaust gas treatment system 10 according to the first embodiment removes sulfur components from the exhaust gas disposed in the subsequent stage of the electrostatic dust collection means 12 for removing soot and dust from the exhaust gas. The desulfurization means 40 for this purpose, the desalination means 80 for producing fresh water from seawater, and the heat exchanger 20 that uses the heat of the exhaust gas for the seawater heating of the desalination means are the main basic components.

The electric dust collecting means 12 is mainly composed of a discharge electrode and a dust collecting plate. The electric dust collecting means 12 having such a configuration charges and removes dust in the exhaust gas discharged from the boiler by corona discharge generated between the discharge electrode and the dust collecting plate.
An exhaust gas fan 14 is provided after the electric dust collecting means 12. The exhaust gas fan 14 pressurizes the exhaust gas.

The heat exchanger 20 is a multi-tube type, and is disposed in the outlet path of the electric dust collecting means 12 and has a structure in which exhaust gas flows on the outer surface of the heat transfer tube and heat medium flows on the inner surface of the heat transfer tube. The heat exchanger 20 is connected to a seawater heater 22 provided in the desalination means 80 via a heat medium circulation line 24. The circulation line 24 is a heat medium circulation path including a circulation pump 26. Through the circulation line 24, heat exchange between the exhaust gas and the heat medium is performed by the heat exchanger 20, heat exchange between the heat medium and the sea water is performed by the seawater heater 22, and the desalination means 80 is utilized using the heat of the exhaust gas. The supplied seawater is heated. As an example, the temperature of exhaust gas discharged from a boiler installed in a thermal power plant, a plant or the like is a relatively high temperature of 120 ° C. to 160 ° C. in the case of a coal fired boiler. In the heat exchanger 20 having such a configuration, the heat medium is heated by high-temperature exhaust gas. The heated heat medium is sent to the seawater heater 22, heat exchange is performed between the seawater and the heat medium, and the seawater is heated. On the other hand, the exhaust gas temperature is lowered by heat exchange with the heat medium flowing on the inner surface of the pipe. Note that fresh water (industrial water) is preferably used as the heat medium. Thereby, an inexpensive carbon steel material can be used for the heat exchanger and the circulation line. Further, by circulating the heat medium in a closed system such as the circulation line 24, it is not necessary to supply the heat medium from outside the system. Furthermore, by making the heat exchanger 20 on the exhaust gas side and the seawater side indirect, even if a failure occurs in the heat exchanger 20 in the operation of the plant, the exhaust gas treatment process and the fresh water treatment process are processed independently. It does not have a big influence on both operations. Therefore, a highly reliable system can be constructed for plant operation.

The desulfurization means 40 basically has a configuration in which an absorption tower 42 is provided with a liquid reservoir 44 disposed in the lower portion thereof, an absorption portion 46 disposed in an exhaust gas rising path, and a mist eliminator 48 disposed in an outlet portion. Yes.

The absorption tower 42 is provided with a gas inflow portion 41 on the upstream side where the exhaust gas pressurized by the exhaust gas fan 14 is introduced.
The liquid reservoir 44 is provided in the lower part of the absorption tower 42 and can temporarily store an absorbent slurry for reacting with a sulfur component in the exhaust gas. An absorbent slurry (limestone slurry) supply unit 50 is connected to the liquid reservoir 44. Necessary absorbent slurry (limestone slurry) is supplied from the supply unit 50 to the liquid reservoir 44 in accordance with the amount of sulfur oxide contained in the exhaust gas from the boiler or the like.

The liquid reservoir 44 is connected to the absorber 46 through the absorbent circulation pipe 52. The absorption liquid circulation pipe 52 is provided with an absorption liquid circulation pump 54. With this configuration, the slurry-like absorption liquid in the liquid reservoir 44 is circulated and supplied to the absorption section 46 via the absorption liquid circulation pipe 52 by the absorption liquid circulation pump 54.

The absorber 46 is provided above the liquid reservoir 44 in the absorption tower 42. The absorber 46 is provided with spray headers 56 in multiple stages in the gas flow direction, and an absorbent is supplied to the spray headers 56. Each spray header 56 is provided with a plurality of spray nozzles 58. Due to the supply pressure of the absorption liquid circulation pump 54, the absorption liquid is sprayed from the spray nozzle 58 toward the upward flow of the exhaust gas. With such a configuration, the absorption unit 46 absorbs an acidic gas such as sulfur oxide, hydrogen chloride, or hydrogen fluoride contained in the exhaust gas by gas-liquid contact between the absorption liquid sprayed from the spray nozzle 58 and the exhaust gas. It is absorbed by the droplet surface of the absorbing liquid circulating in the tower 42. At this time, the absorption liquid partially evaporates depending on the temperature of the exhaust gas to be mist.

The mist eliminator 48 is provided at the desulfurization means gas outlet 59 (after the absorber 46) in the absorption tower 42. The mist eliminator 48 can remove mist contained in the exhaust gas. With such a configuration, the exhaust gas containing mist is finally discharged from a chimney (not shown) after the mist is removed by the mist eliminator 48.

On the other hand, the sulfur oxide contained in the exhaust gas reacts with the calcium compound in the absorption liquid to become calcium sulfite as an intermediate product and flows down to the liquid reservoir 44.
The liquid reservoir 44 is provided with an oxidizing air blower 60 and an oxidizing stirrer 62. Air is forcibly supplied to the liquid reservoir 44 by the oxidation air blower 60, and an oxidation reaction between the air and calcium sulfite is performed to generate gypsum slurry as a reaction product. At this time, the oxidized air supplied to the liquid reservoir 44 is refined by an oxidizing stirrer 62 that stirs the absorbing liquid in the liquid reservoir 44. Thereby, the use efficiency of oxidized air can be improved.

The liquid reservoir 44 is connected to the gypsum dewatering means 64. On the pipe connected to the gypsum dewatering means 64, an absorbing liquid extraction pump 66 is provided. In the liquid reservoir 44 having such a configuration, the absorbent slurry is extracted from the liquid reservoir 44 to the gypsum dewatering means 64 by the absorption liquid extraction pump 66 according to the amount of gypsum produced.

The gypsum dewatering means 64 is dehydrated and collected as powder gypsum 65. On the other hand, the treated water is temporarily stored in the filtrate collection tank 67 and discharged to the outside by the filtrate pump 68 as makeup water or drainage.
The desalination means 80 is a seawater desalination apparatus that produces fresh water from seawater. The desalination means of this embodiment employs an evaporation method such as a multi-effect method or a multistage flash method.

FIG. 2 is a schematic diagram of the configuration of an exhaust gas treatment system using a multi-effect method as a desalination means. The configuration other than the desalination means is the same as the configuration shown in FIG. 1, and the same reference numerals are given and detailed description is omitted.

The multi-effect desalination means 80a depressurizes the inside of the system, a pre-heater 82 that heats the sea water with warm water before the sea water heater 22, a sea water sprayer and a steam heat exchanger. An ejector 86 and a condenser 88 that heats the taken-in seawater and condenses fresh water at the most concentrated stage of the effect cans 84 have a main basic configuration.

The taken seawater is heated by supplying it to the condenser 88 and sent to the seawater return line, and a part of the seawater is supplied to the preheater 82 heated by the hot water. The seawater heated by the pre-heater 82 is sprayed from the sprayers of the effect cans 84 and condensed in the steam supplied to the heat exchangers of the effect cans 84, and is further heated and decompressed by the ejector 86. It becomes steam. The seawater from the preheater 82 is further heated by the seawater heater 22 by the heat medium of the circulation line 24 or the heat of steam from the outside. And it is supplied to the 1st effect can 84a, and becomes a partial vapor | steam by the pressure_reduction | reduced_pressure by the ejector 86 and the heat | fever water of the back | latter stage of the preheater 82. FIG. The heat of the steam generated here can be used for the evaporation of seawater in the second effect can 84b. The steam generated in the first effect can 84a is supplied to the second effect can 84b in the subsequent stage. In the second effect can 84b, the sea water on the rear stage side of the preheater 82 is heated, and the steam is condensed to become fresh water. This operation is repeated with utility cans 84 arranged in multiple stages. The fresh water condensed in the final stage condenser 88 is discharged out of the system by the fresh water pump 90 and used as industrial water. On the other hand, the concentrated water is discharged out of the system by the concentrated water pump 92.
As described above, the heat quantity of the steam and hot water necessary for heating the seawater is performed by the exhaust gas heat upstream of the absorption tower 42 of the wet desulfurization means 40, thereby enabling more efficient heat exchange.

FIG. 3 is a schematic configuration diagram of an exhaust gas treatment system using a multistage flash method as a desalination means. The configuration other than the desalination means is the same as the configuration shown in FIG. 1, and the same reference numerals are given and detailed description is omitted.
The desalination means 80b using the multi-stage flash method is composed of an exhaust heat section 94 and a heat recovery section 95 in which evaporation chambers 93 are formed in multiple stages, and each evaporation chamber 93 is provided with a condenser 96 and a concentrated water reservoir 97. ing.

Such desalination means 80b is configured such that the drawn seawater passes through the condenser 96 of the exhaust heat section 94 and condenses the flash vapor in the evaporation chamber 93, and then is sent to the seawater return line, and part of the exhaust heat section. 94 is supplied to the concentrated water reservoir 97. The seawater in the concentrated water reservoir 97 of the exhaust heat unit 94 is supplied to the condenser 96 of the heat recovery unit 95 via the supply pump 98 and condensed by the flash vapor of each evaporation chamber 93 and then heated by the seawater heater 22. . The heated seawater is supplied to the first-stage concentrated water reservoir 97a of the heat recovery unit 95, and sequentially moves from the first-stage concentrated water reservoir 97a to the subsequent-stage concentrated water reservoir 97. It is condensed with. The condensed water generated in each evaporation chamber sequentially moves to the subsequent stage, and is discharged out of the system by the fresh water pump 90 from the final-stage evaporation chamber 93b and used as industrial water. On the other hand, the concentrated water is discharged out of the system by the concentrated water pump 92. The seawater heated by the seawater heater 22 generates steam by the decompression of the ejector 86 at each stage. Seawater is used before this steam is generated. Seawater used for condensation passes through the condenser 96 and is supplied to the seawater heater 22 while being heated at each stage. By supplementing the amount of heat of the steam necessary for heating the seawater with the heat of the exhaust gas upstream of the absorption tower 42 of the wet desulfurization means 40, more efficient heat exchange is possible.
A part of the fresh water produced by the desalination means 80 is used as makeup water for the absorption liquid in the absorption tower 42. It is also used as cleaning water for the inlet of the absorption tower 42.

Further, the absorbing liquid circulating in the absorption tower 42 is scattered on the mist eliminator 48 installed at the outlet of the absorption tower 42 and adheres to the elements of the mist eliminator 48. For this reason, fresh water is used as washing water, and the element is washed with water.
Further, the absorption liquid in the liquid reservoir 44 is approximately 50 ° C. The outlet temperature of the oxidizing air blower 60 is normally 120 ° C. to 150 ° C. If it is supplied to the liquid reservoir 44 as it is, a dry state and a wet state are alternately repeated at the end of the pipe inserted into the absorbing liquid in the liquid reservoir 44, and the slurry adheres. Therefore, fresh water is sprayed on the air at the outlet of the oxidizing air blower 17 to lower the air temperature and then introduced into the liquid reservoir 44.
In the exhaust gas treatment system 10 of the present invention having the above-described configuration, the exhaust gas discharged from the boiler or the like is introduced into the electric dust collecting means 12, and dust in the exhaust gas is removed.

Next, the exhaust gas is pressurized by the exhaust gas fan 14 and introduced into the heat exchanger 20. The temperature of the exhaust gas decreases due to heat exchange with the heat medium flowing on the inner surface of the tube of the heat exchanger 20.
The heat medium heated by the heat exchanger 20 is subjected to heat exchange between the seawater and the heat medium in the seawater heater 22 via the circulation line 24. In the desalination means 80, fresh water can be manufactured from the heated seawater.

Next, the exhaust gas whose gas temperature has decreased is introduced into the wet desulfurization means 40, and gas-liquid contact occurs between the absorption liquid sprayed from the spray nozzle 58 and the exhaust gas in the absorption section 46. Then, an acidic gas such as sulfur oxide, hydrogen chloride, or hydrogen fluoride contained in the exhaust gas is absorbed by the surface of the droplet of the absorbing liquid circulating in the absorption tower 42.
A part of the absorbing solution is misted in the absorption tower 42, and the exhaust gas containing the mist is finally discharged from the chimney (not shown) after the mist is removed by the mist eliminator 48.

FIG. 4 is a graph showing the correlation between absorption tower inlet gas temperature and absorption tower evaporation water amount. The horizontal axis of the graph represents the absorption tower inlet gas temperature (° C.), and the vertical axis represents the absorption tower evaporation water amount (t / h). As shown in the figure, the absorption tower inlet gas temperature and the absorption tower evaporation water amount are in a proportional relationship. Therefore, if the absorption tower inlet gas temperature is reduced, the absorption tower evaporation water amount can also be reduced.

According to such an exhaust gas treatment system of the present invention, the exhaust gas temperature introduced into the wet desulfurization means is lowered by the heat exchanger, so that the steam generated in the absorption tower of the wet desulfurization means can be reduced. Therefore, steam is not discharged to the outside of the wet desulfurization means and the absorption liquid is not reduced, and the amount of makeup water can be greatly reduced. Further, by using the heat of the exhaust gas for heating the seawater of the desalination means, the amount of steam used can be reduced, and the overall cost of the system can be reduced and the energy can be saved. In this embodiment, the heat exchanger and the desalination unit are connected by a circulation line to perform heat exchange. In addition, the desalination unit is installed on the top of the heat exchanger to save space. You may comprise so that.

FIG. 5 is a schematic configuration diagram of an exhaust gas treatment system according to the second embodiment. The amount of heat recovered by the heat exchanger 20 varies depending on the amount of exhaust gas from the boiler, the exhaust gas temperature, and the like. The exhaust gas treatment system 100 according to the second embodiment includes a seawater temperature measuring means 102 that measures the outlet temperature of seawater heated by the seawater heater 22, and a first flow rate control valve 104 that can adjust the flow rate of the circulation line 24. A bypass line 106 that connects the feed pipe and return pipe of the circulation line, a second flow rate control valve 108 that adjusts the flow rate of the bypass line 106, and a control means 110 are provided.
The seawater temperature measuring means 102 is a temperature sensor that can be attached to the outlet side of the seawater heater 22 in the circulation line 24 and measure the heated seawater temperature.

The first flow rate control valve 104 is a valve that is attached to the circulation line 24 and can adjust the flow rate of the heat medium flowing in the piping.
The bypass line 106 is a pipe that connects the feed pipe and the return pipe of the circulation line 24.

The second flow rate control valve 108 is a valve that is attached to the bypass line 106 and can adjust the flow rate of the heat medium flowing in the pipe.
The control means 110 is electrically connected to the seawater temperature measurement means 102 and the first and second flow

rate control valves

104 and 108. The control means 110 controls the flow rate of the heating medium in the circulation line 24 based on the detected value of the outlet temperature (heated seawater temperature) of the seawater heater 22 by the seawater temperature measuring means 102, and the seawater temperature is determined in advance. The set value can be controlled.

As an example, when the heating temperature is 120 ° C. or higher, the control target value of the seawater outlet side temperature of the seawater heater 22 in the circulation line 24 is 105 ° C. When the seawater temperature becomes higher than the target value, there is a scaling problem in which the salt content in the seawater adheres to the seawater heater 22, so the bypass line 106 is opened to increase the amount of heat medium bypassing the seawater. It is necessary to control the circulating amount of the heat medium to the heater 22 to be small. Or the opening degree of the 1st flow control valve 104 can be made small, and the circulation amount of a heat medium can also be controlled small.

On the other hand, when the seawater temperature is lower than the target value, the differential pressure of each stage of the evaporator of the desalination means 80 becomes small and it is difficult to evaporate. For this reason, it is necessary to control the seawater flow rate by reducing the seawater flow rate. Further, when the seawater heater outlet temperature is low, it is necessary to heat the seawater separately from the heat exchanger 20 by introducing steam from the outside.

According to the exhaust gas treatment system 100 of the second embodiment as described above, the seawater temperature to be heated can be controlled to a preset value of the seawater temperature, and freshwater can be efficiently produced by the desalination means.

FIG. 6 is a schematic configuration diagram of an exhaust gas treatment system according to the third embodiment.
As shown in the figure, the exhaust gas treatment system 200 according to the third embodiment has a heat exchanger 20 a disposed on the upstream side of the electric dust collection means 12. In place of the seawater temperature measuring means, a gas temperature measuring means 102a for the exhaust gas is provided between the heat exchanger 20a and the electrostatic dust collecting means 12. The control means 110 is electrically connected to the gas temperature measuring means 102a. Other configurations are the same as those of the exhaust gas treatment system 100 according to the second embodiment, and detailed description thereof is omitted.

Exhaust gas discharged from boilers has a relatively high gas temperature of 120 ° C to 160 ° C. By disposing the heat exchanger 20a on the upstream side of the electric dust collecting means 12, the exhaust gas temperature introduced into the electric dust collecting means 12 can be lowered by heat exchange between the exhaust gas and the heat medium.

Here, the removal performance of the dust contained in the exhaust gas by the electrostatic dust collecting means 12 is determined by a plurality of factors such as dust particle size, dust composition, dust electric resistance value, charge amount in the electrostatic dust collecting means 12 and the like. . In general, the electrical resistance value of dust is lowered due to a decrease in gas temperature, and the dust removal performance is improved. However, when the inlet gas temperature of the electrostatic precipitator 12 drops below a certain value, it is difficult to fix the dust inside the electrostatic precipitator 12 and transport the dust collected by the electrostatic precipitator 12. There are problems such as becoming.

Therefore, in the exhaust gas treatment system 200 according to the third embodiment, the gas temperature measuring means 102a is installed at the outlet of the heat exchanger 20a. The control means 110 controls the flow rate of the heat medium in the circulation line 24 based on the detected value of the outlet temperature (exhaust gas temperature) of the heat exchanger 20a by the gas temperature measuring means 102a, and sets the exhaust gas temperature to a predetermined value. Can be controlled.

As an example, when the boiler is in a low-load operation state, the exhaust gas / exhaust gas temperature at the boiler outlet decreases, and the inlet temperature of the electrostatic dust collecting means 12 also decreases. If the inlet temperature of the electrostatic precipitator 12 is too low, ash sticks to the internal electrode plate, ash is clogged at the hopper of the precipitator 12, and stable operation becomes difficult. For this reason, in the case of a low boiler load, the opening amount of the first flow control valve 104 is reduced to reduce the circulation amount of the heat medium so that the outlet temperature of the heat exchanger 20a does not decrease too much. The inlet temperature of the means 12 can be maintained at a preset value (for example, 80 ° C.) or higher.

According to the exhaust gas treatment system 200 of the third embodiment, the exhaust gas temperature can be controlled to a preset value of the gas temperature, and can be efficiently removed by the electric dust collection means 12.

FIG. 7 is a schematic configuration diagram of an exhaust gas treatment system according to the fourth embodiment.
As shown in the figure, an exhaust gas treatment system 300 according to the fourth embodiment has a basic configuration of the exhaust gas treatment system 200 of the third embodiment. In the exhaust gas treatment system 200 according to the third embodiment, the heat exchange between the exhaust gas and the heat medium is performed before the electric dust collecting means 12, and therefore the exhaust gas temperature is too low when the initial temperature of the exhaust gas is low. The dust removal efficiency of the electrostatic precipitator 12 is reduced. Therefore, there is a limit to the temperature for cooling the exhaust gas.

Therefore, in the exhaust gas treatment system 300 of the fourth embodiment, the second heat exchanger 21 is provided in the absorption tower 42 of the wet desulfurization means 40 to heat the heat medium. The second heat exchanger 21 is connected to the second circulation line 25 branched to the circulation line 24. Specifically, the second heat exchanger 21 is disposed in the liquid reservoir 44. The oxidation reaction of absorbed SO ₂ occurring inside the absorption tower 42 is an exothermic reaction. For this reason, the second heat exchanger 21 can heat the heat medium by exchanging heat between the heat medium and the absorbing liquid. Then, this heat medium is introduced into the circulation line 24 via the second circulation line 25, and heat exchange with the seawater can be performed by the seawater heater 22.

According to the exhaust gas treatment system 300 according to the fourth embodiment having such a configuration, heat is exchanged between the heat medium and the absorbing liquid without reducing the dust removal efficiency of the electrostatic precipitator 12. The medium can be heated. Therefore, even when the exhaust gas temperature is low, the heating medium can be heated, the amount of steam used in the desalination means can be reduced, and the cost of the entire system and energy saving can be achieved.

FIG. 8 is a schematic configuration diagram of an exhaust gas treatment system according to the fifth embodiment.
As shown in the figure, the exhaust gas treatment system 400 according to the fifth embodiment is provided with the heat exchanger 20 according to the first embodiment in the subsequent stage of the first mist eliminator 48a. And the 2nd mist eliminator 48b is arrange | positioned in the back | latter stage of the heat exchanger 20b. The second mist eliminator 48b is connected to a makeup water supply line of the wet desulfurization means 40. Other configurations are the same as those of the first embodiment, and detailed description thereof is omitted.

According to the exhaust gas treatment system 400 according to the fifth embodiment having the above-described configuration, the first mist eliminator 48a is introduced with exhaust gas from which components such as sulfur oxide have been removed and mist vaporized by high-temperature exhaust gas. The The exhaust gas containing the mist that has passed through the first mist eliminator 48a is heat-exchanged with the heat medium of the heat exchanger 20b. The heat medium exchanges heat with the seawater by the seawater heater 22 via the circulation line 24. The exhaust gas that has become a water saturated state in which the gas temperature has decreased due to heat exchange with the heat medium in the heat exchanger 20b can be recovered by condensing the water in the second mist eliminator 48b. The recovered moisture can be used as makeup water for the absorption liquid in the absorption tower 42.

According to such an exhaust gas treatment system according to the fifth embodiment, the exhaust gas that has been saturated with water through the desulfurization process is cooled to the gas temperature in the saturated state by heat exchange with the heat medium of the heat exchanger. Water can be condensed and recovered. Further, by using the heat of the exhaust gas for heating the seawater of the desalination means, the amount of steam used can be reduced, and the overall cost of the system can be reduced and the energy can be saved.

In addition, the heat exchanger may be installed on the inlet side or the outlet side of the absorption tower liquid circulation pump 54 of the absorption liquid circulation pipe 52. The seawater heater 22 may be installed on the seawater inlet side of the desalination means 80.

The exhaust gas treatment system and exhaust gas treatment method of the present invention can be applied to exhaust gas treatment of various plants such as thermal power plants that contain sulfur oxide in the exhaust gas.

10, 100, 200, 300, 400 ......... Exhaust gas treatment system, 12 ......... Electric dust collecting means, 14 ......... Exhaust gas fan, 20, 20a, 20b ......... Heat exchanger, 21 ......... Second Heat exchanger, 22 ......... Seawater heater, 24 ......... Circulation line, 25 ......... Second circulation line, 26 ......... Circulation pump, 40 ......... Desulfurization means, 41 ......... Gas inlet, 42 ......... Absorption tower, 44 ......... Liquid reservoir, 46 ......... Absorber, 48 ......... Mist eliminator, 50 ......... Supply section, 52 ......... Absorbing liquid circulation piping, 54 ......... Absorption Liquid circulation pump 56 ... Spray header 58 ... Spray nozzle 59 ... Desulfurization means gas outlet, 60 ... Air blower for oxidation, 62 ... Stirrer for oxidation, 64 ... Gypsum dehydration Means, 65 ... gypsum, 66 ... absorption pump, 67 ... ... Filtrate recovery tank, 68 ... ... Filtrate pump, 80 ... ... Desalination means, 82 ... ... Preheater, 84 ... ... Effect can, 86 ... ... Ejector, 88 ... ... Condenser, 90 ... ...... Fresh water pump, 92 ......... Concentrated water pump, 93 ......... Evaporation chamber, 94 ......... Exhaust heat section, 95 ...... Heat recovery section, 96 ......... Condenser, 97 ......... Concentrated water reservoir, 98 ......... Supply pump, 102 ......... Seawater temperature measuring means, 102a ......... Gas temperature measuring means, 104 ......... First flow control valve, 106 ......... Bypass line, 108 ......... Second flow control Valve, 110... Control means.

Claims

Wet desulfurization means for removing sulfur oxides in exhaust gas;
Desalination means for producing fresh water from seawater and supplying the wet desulfurization means;
A heat exchanger that heats the heat medium with the exhaust gas before the wet desulfurization means;
A seawater heater of the desalination means;
A heating medium circulation line for connecting the heat exchanger to the seawater heater and circulating the heating medium;
An exhaust gas treatment system characterized by comprising:
A bypass line connecting the feed pipe and return pipe of the circulation line;
A flow rate control valve for adjusting the flow rate of the heat medium provided in the circulation line and the bypass line;
Control means for controlling the supply amount of the heat medium to the seawater heater connected to the flow rate control valve,
The exhaust gas treatment system according to claim 1, comprising:
Sea water temperature measuring means for detecting the outlet temperature of the sea water heater,
The said control means controls the supply amount of the heat medium to the said seawater heater based on the measured value of the said temperature measurement means so that the exit temperature of the said seawater heater may become predetermined temperature. Item 3. The exhaust gas treatment system according to Item 2.
The exhaust gas treatment system according to any one of claims 1 to 3, wherein an electrostatic precipitator is provided in front of the heat exchanger.
The exhaust gas treatment system according to claim 2, wherein an electrostatic dust collecting means is provided between the heat exchanger and the wet desulfurization means.
The exhaust gas treatment system according to claim 5, wherein the control means is connected to the flow rate control valve to control a supply amount of the heat medium to the heat exchanger.
Comprising gas temperature measuring means for detecting the temperature of the exhaust gas introduced into the electric dust collecting means,
The control means controls the heat medium supply amount to the heat exchanger based on the measured value of the gas temperature measuring means so that the temperature of the exhaust gas introduced into the electric dust collecting means becomes a predetermined temperature. The exhaust gas treatment system according to claim 6.
A second heat exchanger is provided in the liquid distillation part of the wet desulfurization means and connected to the circulation line,
The exhaust gas treatment system according to any one of claims 5 to 7, wherein the heat medium circulates between the heat exchanger and the second heat exchanger.
Wet desulfurization means for removing sulfur oxides in exhaust gas;
Desalination means for producing fresh water from seawater and supplying the wet desulfurization means;
A heat exchanger that heats the heat medium with the exhaust gas after the wet desulfurization means;
A seawater heater of the desalination means;
A heating medium circulation line for connecting the heat exchanger to the seawater heater and circulating the heating medium;
A mist eliminator for removing mist contained in the exhaust gas;
An exhaust gas treatment system characterized by comprising:
In the exhaust gas treatment method for removing sulfur oxides contained in the exhaust gas,
Heat exchange of the exhaust gas and the heat medium before desulfurization treatment to lower the gas temperature of the exhaust gas and heating the heat medium;
A step of desulfurizing the exhaust gas whose gas temperature has decreased;
Circulating the heated heating medium to a seawater heater;
Heat exchange between the heated heating medium and seawater;
Producing fresh water from the heated seawater;
Measuring the heated seawater temperature to control the circulation amount of the heating medium;
An exhaust gas treatment method comprising: