JP2013078742A - Exhaust gas treatment apparatus and exhaust gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas treatment apparatus capable of reducing makeup water supplied to a wet desulfurization apparatus with a simple structure.SOLUTION: In an exhaust gas treatment apparatus including a wet desulfurization apparatus 5 removing sulfur oxide by spraying absorption liquid to exhaust gas from a boiler 1, a heat recovery heat exchanger 45 is provided at an upstream side of the wet desulfurization apparatus 5, a reheating heat exchanger 46 heating the exhaust gas by a heat medium from the heat recovery heat exchanger 45 is provided at a downstream side of the wet desulfurization apparatus 5, and circulation piping 52 communicating with a heat transfer pipe between the heat recovery heat exchanger 45 and the reheating heat exchanger 46 is provided to circulate the heat medium therein. A heat removal heat exchanger 48 is provided at a heat medium flow passage of the circulation piping 52 from the reheating heat exchanger 46 to the heat recovery heat exchanger 45. By supplying drain water from a drain water recovery part 49 at a lower part of a gas duct of the heat recovery heat exchanger 45 to the wet desulfurization apparatus 5, exhaust gas temperature introduced to the wet desulfurization apparatus 5 is lowered to reduce makeup water, and the drain water is efficiently used as the makeup water of the wet desulfurization apparatus.

Description

  The present invention relates to an exhaust gas treatment apparatus and a waste gas treatment method provided with a wet desulfurization apparatus for removing sulfur oxides contained in exhaust gas generated from a coal fired boiler, and more particularly to a technique for reducing the amount of water supplied to the wet desulfurization apparatus. Is.

In a coal-fired thermal power plant, sulfur components contained in coal exist as sulfur dioxide (SO ₂ ) in the exhaust gas, and when it is released into the atmosphere, it causes acid rain and the like. Therefore, generally, a method of removing SO ₂ in exhaust gas with a wet desulfurization apparatus or the like is used. The structure of the conventional coal slag exhaust gas treatment apparatus is shown in FIG.

  Coal is supplied to the boiler 1 from the coal supply line 21 and air is supplied from the combustion air supply line 36, and high-pressure steam is generated in the boiler heat exchanger 11 by heat generated by the combustion reaction of coal. Then, the turbine 12 is rotated by the high-pressure steam to generate power by the generator 13 connected to the turbine 12. The steam that has exited the turbine 12 is cooled by the condenser 14, is pressurized again by the booster pump 15, and is sent to the boiler heat exchanger 11.

On the other hand, the combustion exhaust gas discharged from the boiler 1 exchanges heat with combustion air in an air preheater 3 (hereinafter also referred to as A / H, air heater. For example, a regenerative heat exchanger is used), and then a dust collector 4. The dust in the exhaust gas is removed. Generally, the gas temperature at the outlet of the dust collector 4 is about 130 to 200 ° C. The exhaust gas that has exited the dust collector 4 is supplied to the wet desulfurization device 5, and after SO _{2 in} the exhaust gas is removed, it is discharged from the chimney 7.

In the wet desulfurization apparatus 5, dust particles in the exhaust gas are brought into gas-liquid contact with absorbent droplets such as slurry containing limestone or lime sprayed as fine droplets from the spray nozzle 27 and the exhaust gas rising in the apparatus. In addition to acidic gas such as hydrogen chloride (HCl) and hydrogen fluoride (HF), SO _{2 in} the exhaust gas is chemically absorbed and removed on the surface of the desulfurization absorbing droplets of the spray nozzle 27.

The desulfurization absorption liquid 28 that has absorbed SO ₂ is stored in a tank 30 below the wet desulfurization apparatus 5, is pressurized by a circulation pump 26, and sprayed from the spray nozzle 27 again via the absorption liquid circulation pipe 25. Further, SO ₂ absorbed in the desulfurization absorbing liquid 28 reacts with calcium carbonate supplied from the calcium carbonate solution supply device 44 and is released out of the system as gypsum.

  Further, since the desulfurization absorbing liquid 28 is sprayed inside the wet desulfurization apparatus 5, the temperature of the exhaust gas is reduced to the water saturation temperature. Generally, the moisture concentration in the exhaust gas during coal combustion is about 10% (mass%, the same applies hereinafter), so the exhaust gas temperature at the outlet of the wet desulfurization apparatus 5 is about 46 ° C. For this reason, when low-temperature exhaust gas is discharged from the chimney 7 as it is, white smoke is generated.

  Therefore, in order to prevent the white smoke, a method of increasing the exhaust gas temperature at the outlet of the wet desulfurization apparatus 5 by the reheating heat exchanger 46 is used. As a heat source of the reheating heat exchanger 46, heat is used. A heat recovery heat exchanger 45 having a heat transfer tube through which a medium flows is used. That is, the heat of the exhaust gas is recovered by the heat recovery heat exchanger 45 installed at the outlet of the dust collector 4, and the recovered heat is used as the heat source of the reheating heat exchanger 46. Heat the exhaust gas. The reheating heat exchanger 46 is a heat exchanger provided with a heat transfer tube through which a heat medium flows, similarly to the heat recovery heat exchanger 45.

The exhaust gas temperature at the outlet of the heat recovery heat exchanger 45 is reduced to 106 ° C. and supplied to the wet desulfurization apparatus 5 by heat exchange between the exhaust gas and the heat medium flowing in the heat transfer pipe. The heat transfer tubes of the heat recovery heat exchanger 45 and the reheating heat exchanger 46 are communicated with each other by a heat medium circulation pipe 52, and the heat recovery heat exchanger 45 and the reheating heat exchange are performed by a heat medium circulation pump 47. A heat medium is circulated between the container 46 and the container 46.
FIG. 5 shows an example of exhaust gas temperature at the inlet and outlet of each device. When the exhaust gas temperature at the outlet of the dust collector 4 is 130 ° C., the exhaust gas temperature is reduced to 106 ° C. by the heat recovery heat exchanger 45. And supplied to the wet desulfurization apparatus 5.

  After the desulfurization absorbing liquid 28 is sprayed inside the wet desulfurization apparatus 5, the exhaust gas temperature is reduced to a water dew point of 46 ° C., and then the exhaust gas is supplied to the reheating heat exchanger 46. In the reheating heat exchanger 46, the exhaust gas is heated to 70 ° C. by the heat medium heated by the heat recovery heat exchanger 45. At this time, the temperature of the heat medium is 80 ° C. at the inlet of the heat recovery heat exchanger 45, and is heated to 93 ° C. by exchanging heat with the exhaust gas at the outlet of the dust collector 4. By heating the exhaust gas at the outlet of the wet desulfurization apparatus 5, the temperature decreases to 80 ° C.

In such a conventional exhaust gas treatment apparatus, water evaporates inside the wet desulfurization apparatus, and therefore it is necessary to continuously supply water to the wet desulfurization apparatus.
There are the following patent documents as techniques for reducing the makeup water.

  In Patent Document 1 below, a heat exchanger (first gas gas heater) is provided upstream of the exhaust gas duct of the wet desulfurization apparatus, and the heat exchange tube is a carbon tube, so that the exhaust gas temperature at the inlet of the wet desulfurization apparatus is about 50 ° C. However, a configuration that can prevent corrosion and reduce makeup water is disclosed. In addition, the heat flow other than the heat necessary for heating the gas after the desulfurization treatment is collected in the flow path of water, which is the heat exchange medium of the heat exchanger and the reheater (second gas gas heater), and the replenishment water is reduced. A third heat exchanger that warms up to 70 ° C. is provided. The make-up water is used for recovery of gypsum and then supplied to a wet desulfurization apparatus.

  Further, Patent Document 2 below discloses a wastewater treatment apparatus that extracts an absorbent slurry in a wet desulfurization apparatus, evaporates and concentrates it in an evaporator, and a heat recovery device provided upstream of an exhaust gas duct of the wet desulfurization apparatus. In the exhaust gas treatment facility having a reheater provided downstream of the exhaust gas duct of the desulfurization device, heat that is being sent from the reheater to the heat recovery device as a heater for heating the desulfurization wastewater for evaporation in the evaporator A configuration provided with a heat exchanger for recovering heat from the medium is disclosed. By using the heat exchanger as a heater for evaporation and concentration in the evaporator, the amount of steam used is reduced, and the exhaust gas temperature at the outlet side of the heat recovery unit, that is, at the inlet side of the wet desulfurization apparatus is reduced from 110 ° C to 105 ° C. By reducing the amount, make-up water in the wet desulfurization apparatus is reduced.

  Further, in Patent Document 3 below, a second heat exchanger is further provided between the first heat exchanger provided upstream of the exhaust gas duct of the wet desulfurization apparatus and the wet desulfurization apparatus, and the second heat exchanger is provided. The structure which aimed at reduction of make-up water by making exhaust gas temperature into 40-45 degreeC by this and introduce | transducing the exhaust gas cooled to 40-45 degreeC into a wet desulfurization apparatus is disclosed.

JP-A-8-21618 Japanese Patent Laid-Open No. 11-76750 JP 2008-212891 A

In the prior art, since water evaporates inside the wet desulfurization apparatus, it is necessary to continuously supply water to the wet desulfurization apparatus. Especially in areas where it is difficult to secure a large amount of industrial water, it is necessary to install a separate facility such as a seawater desalination unit to secure the water to be supplied to the wet desulfurization unit. Requires a lot of energy and cost.
According to the configurations described in Patent Documents 1 to 3, the makeup water is reduced by lowering the exhaust gas temperature introduced into the wet desulfurization apparatus.

  In Patent Document 1, the water content of gypsum is lowered by heating the makeup water to about 70 ° C. and washing the gypsum with a third heat exchanger provided between the heat exchanger and the reheater. However, in the heat medium flowing from the heat exchanger to the reheater, the amount necessary for heating by the reheater is ensured, and the other heat is used for heating the makeup water. Therefore, the temperature of the heat medium flowing from the reheater to the heat exchanger is kept relatively high, and the supply of make-up water is always necessary, so it is not a very effective method. .

In Patent Document 2, the exhaust gas temperature at the inlet side of the wet desulfurization apparatus is lowered from about 110 ° C. to about 105 ° C., but the purpose of providing the heat exchanger is to reduce the amount of steam used in the first place. If it drops, the effect of reducing makeup water is not expected.
Furthermore, in Patent Document 3, a first heat exchanger and a second heat exchanger are provided upstream of the exhaust gas duct of the wet desulfurization apparatus, and a reheater is further provided downstream of the exhaust gas duct of the wet desulfurization apparatus. Problems such as the installation cost and installation space of the second heat exchanger, and the installation (cost and space) of the cooler for cooling the heat medium between the boiler and the second heat exchanger. There is also.

  An object of the present invention is to provide an exhaust gas treatment device and an exhaust gas treatment method capable of reducing the makeup water supplied to the wet desulfurization device with a simple configuration.

  The above problem is that a heat recovery heat exchanger is installed upstream of the exhaust gas duct of the wet desulfurization device, and a reheating heat exchanger is installed downstream of the exhaust gas duct of the wet desulfurization device, and is heated by the heat recovery heat exchanger. The heat recovery heat exchanger and the heat transfer pipe of the reheating heat exchanger are connected by a heat medium circulation pipe so that the heat medium is cooled by the reheating heat exchanger, and heat is removed in the middle of the heat medium circulation pipe. This can be solved by installing a heat exchanger and supplying drain water in the lower part of the exhaust gas duct of the heat recovery heat exchanger to the wet desulfurization apparatus. Moreover, it is good to use the feed water or seawater supplied to a boiler for the heat medium of the heat exchanger for heat removal.

Specifically, the problems of the present invention can be solved by the following means.
The invention according to claim 1 is an exhaust gas treatment apparatus including a wet desulfurization apparatus that removes sulfur oxides in exhaust gas by spraying an absorption liquid on exhaust gas generated from a coal-fired boiler. A heat recovery heat exchanger provided with a heat transfer tube for recovering heat of exhaust gas to a heat medium is provided in the exhaust gas duct on the upstream side, and the exhaust gas is exchanged in the exhaust gas duct on the downstream side of the wet desulfurization apparatus A heat exchanger for reheating provided with a heat transfer tube for heating with a heat medium supplied from the heater, and further communicating with the heat transfer tubes respectively provided for the heat exchanger for heat recovery and the heat exchanger for reheating, A heat medium circulation pipe that circulates the heat medium is provided inside, and a heat medium is removed from the heat medium in the heat medium flow path from the reheating heat exchanger to the heat recovery heat exchanger of the heat medium circulation pipe. A heat exchanger for heat is provided, and the heat recovery heat exchanger exhaust The drain water recovery section provided in the lower portion of the duct, an exhaust gas treatment apparatus of the drain water provided drain water supply unit for supplying to the wet desulfurization system in the drain water recovery unit.

  According to a second aspect of the present invention, the wet desulfurization apparatus includes a tank that stores an absorbing liquid that has absorbed sulfur oxide, and a spray nozzle that is provided above the tank and sprays the absorbing liquid on the exhaust gas in a plurality of stages in the exhaust gas flow direction. An installed spray section, an absorption liquid circulation pipe for sending an absorption liquid provided with a circulation pump for sucking up the absorption liquid in the tank to the spray nozzle, and a carbonic acid for converting the sulfur dioxide in the absorption liquid in the tank into gypsum. 2. The exhaust gas treatment apparatus according to claim 1, further comprising a calcium carbonate supply device that supplies a calcium solution, wherein the drain water supply unit supplies drain water in a drain water recovery unit to the tank.

  According to a third aspect of the present invention, the wet desulfurization apparatus includes a tank that stores an absorbing liquid that has absorbed sulfur oxide, and a spray nozzle that is provided above the tank and sprays the absorbing liquid on the exhaust gas in a plurality of stages in the exhaust gas flow direction. An installed spray section, an absorption liquid circulation pipe for sending an absorption liquid provided with a circulation pump for sucking up the absorption liquid in the tank to the spray nozzle, and a carbonic acid for converting the sulfur dioxide in the absorption liquid in the tank into gypsum. 2. The exhaust gas treatment device according to claim 1, further comprising a calcium carbonate supply device that supplies a calcium solution, wherein the drain water supply unit supplies drain water in a drain water recovery unit to the calcium carbonate supply device. .

According to a fourth aspect of the present invention, there is provided the exhaust gas treatment apparatus according to any one of the first to third aspects, wherein the surface of the heat transfer tube of the heat recovery heat exchanger is coated with a corrosion-resistant material containing a fluororesin. It is.
According to a fifth aspect of the present invention, a heat recovery heat exchanger is provided by supplying a refrigerant to the heat removal heat exchanger and cooling a heat medium flowing from the reheating heat exchanger into the heat recovery heat exchanger. The exhaust gas treatment apparatus according to any one of claims 1 to 3, further comprising a refrigerant supply unit configured to set an exhaust gas temperature at an outlet to a temperature equal to or higher than the temperature of the refrigerant and equal to or lower than a water saturation temperature of the exhaust gas.

A sixth aspect of the present invention is the exhaust gas processing apparatus according to the fifth aspect, wherein a boiler water supply section for supplying water to the boiler is provided, and the water supply of the boiler water supply section is used as the refrigerant of the refrigerant supply section.
The invention according to claim 7 is the exhaust gas treatment apparatus according to claim 5, wherein seawater is used as a refrigerant of the refrigerant supply unit.
The invention according to claim 8 is the exhaust gas treatment apparatus according to claim 5, further comprising an absorption liquid supply section for supplying the absorption liquid in the tank of the wet desulfurization apparatus to the heat recovery heat exchanger.

  The invention according to claim 9 is an exhaust gas treatment method in which sulfur oxides in exhaust gas are removed by a wet desulfurization device having a configuration in which an absorbing liquid is sprayed on exhaust gas generated from a boiler using coal as a fuel. In order to heat the exhaust gas after the desulfurization treatment by the wet desulfurization equipment, by recovering the heat of the exhaust gas by the heat recovery heat exchanger equipped with a heat transfer tube having a heat medium for recovering heat from the exhaust gas before the desulfurization by The heat medium is circulated and supplied from the heat recovery heat exchanger to a reheating heat exchanger having a heat transfer tube having a heat transfer tube therein, and the reheating heat exchanger is transferred to the heat recovery heat exchanger. It is an exhaust gas treatment method for removing heat from a supplied heat medium and supplying drain water accumulated in a lower portion of the heat recovery heat exchanger to the wet desulfurization apparatus.

  The invention according to claim 10 is a tank that stores an absorbing liquid that has absorbed sulfur oxides, and a spray part that is provided above the tank and has a plurality of spray nozzles that spray the absorbing liquid on the exhaust gas in the exhaust gas flow direction, An absorption liquid circulation pipe for supplying an absorption liquid provided with a circulation pump for sucking the absorption liquid in the tank to the spray nozzle, and a carbonic acid solution for supplying a calcium carbonate solution for converting the sulfur dioxide in the absorption liquid in the tank into gypsum. 10. An exhaust gas treatment method for removing sulfur oxides in exhaust gas by a wet desulfurization device including a calcium supply device, wherein drain water accumulated in a lower portion of the heat recovery heat exchanger is supplied to the tank. This is an exhaust gas treatment method.

  The invention according to claim 11 is a tank that stores an absorbing liquid that has absorbed sulfur oxides, and a spray part that is provided above the tank and has a plurality of spray nozzles that spray the absorbing liquid on the exhaust gas in the exhaust gas flow direction. An absorption liquid circulation pipe for supplying an absorption liquid provided with a circulation pump for sucking the absorption liquid in the tank to the spray nozzle, and a carbonic acid solution for supplying a calcium carbonate solution for converting the sulfur dioxide in the absorption liquid in the tank into gypsum. An exhaust gas treatment method for removing sulfur oxides in exhaust gas by a wet desulfurization device including a calcium supply device, wherein drain water accumulated in a lower portion of the heat recovery heat exchanger is supplied to the calcium carbonate supply device. Item 10. The exhaust gas treatment method according to Item 9.

The invention described in claim 12 is the heat transfer tube of the heat recovery heat exchanger, wherein a heat transfer tube whose surface is coated with a corrosion-resistant material containing a fluororesin is used. The exhaust gas treatment method described.
The invention according to claim 13 removes heat by cooling the heat medium flowing into the heat recovery heat exchanger from the reheating heat exchanger with the refrigerant, and sets the exhaust gas temperature at the heat recovery outlet to the refrigerant. The exhaust gas treatment method according to any one of claims 9 to 11, wherein the exhaust gas treatment temperature is set to a temperature equal to or higher than a water saturation temperature of the exhaust gas.

The invention described in claim 14 is the exhaust gas treatment method according to claim 13, wherein boiler supply water for supplying water to the boiler is used as the refrigerant.
The invention according to claim 15 is the exhaust gas treatment method according to claim 13, wherein seawater is used as the refrigerant.
A sixteenth aspect of the present invention is the exhaust gas treatment method according to the thirteenth aspect of the present invention, wherein the absorption liquid in the tank of the wet desulfurization apparatus is supplied to the heat recovery heat exchanger.

(Function)
A heat removal heat exchanger is provided in the heat medium flow path from the reheating heat exchanger to the heat recovery heat exchanger in the heat medium circulation piping, and boiler feed water or seawater is supplied as a refrigerant to the heat removal heat exchanger. By doing so, it becomes possible to reduce the temperature of the heat medium supplied to the heat recovery heat exchanger to about the temperature of the refrigerant. And the exhaust gas temperature discharged | emitted from a dust collector can be reduced below to the moisture saturation temperature of waste gas by supplying the heat medium about the temperature of a refrigerant | coolant to the heat exchanger for heat recovery. By setting the exhaust gas temperature to a water saturation temperature (for example, 46 ° C. when the water concentration is 10%) or less, the water in the exhaust gas can be recovered as drain water. By collecting this drain water and supplying it to the wet desulfurization apparatus, the makeup water of the wet desulfurization apparatus can be greatly reduced.

  Specifically, according to the first or ninth aspect of the invention, the temperature of the heat medium is reduced by removing heat from the heat medium flowing from the reheating heat exchanger to the heat recovery heat exchanger. This low temperature heat medium improves the efficiency of heat recovery of the exhaust gas and can reduce the temperature of the exhaust gas introduced into the heat recovery heat exchanger. Can be reduced. And by supplying the drain water of the heat exchanger for heat recovery to the wet desulfurization apparatus, the drain water can be effectively used as the makeup water for the wet desulfurization apparatus.

  According to the invention of claim 2 or claim 10, in addition to the action of the invention of claim 1 or claim 9, the drain water of the heat exchanger for heat recovery is supplied to the tank of the wet desulfurization apparatus. By supplying, drain water can be stored in a tank, and drain water can be easily effectively used as makeup water for a wet desulfurization apparatus.

And according to invention of Claim 3 or Claim 11, in addition to the effect | action of the invention of the said Claim 1 or Claim 9, the drain water of the heat exchanger for heat recovery is supplied to a calcium carbonate supply apparatus. By doing so, the drain water can be stored in the calcium carbonate supply device, and the drain water can be easily effectively used as makeup water for the wet desulfurization device. The drain water of the heat exchanger for heat recovery is strongly acidic because it contains SO _{2 in} the exhaust gas, but the acid is neutralized by supplying the drain water to the calcium carbonate supply device. . And surplus calcium carbonate can use drain water effectively without wasting by being supplied to a wet desulfurization apparatus.

According to the invention of claim 4 or claim 12, in addition to the action of the invention of any one of claims 1 to 3, or claims 9 to 11, Even if the drain water of the heat exchanger for heat recovery is strongly acidic due to SO _{2 in} the exhaust gas, the heat transfer tube surface of the heat recovery heat exchanger is coated with a corrosion-resistant material such as fluororesin, Corrosion can be prevented.

  According to the invention of claim 5 or claim 13, in addition to the action of the invention of any one of claims 1 to 3 and claims 9 to 11, By setting the temperature of the exhaust gas at the outlet of the heat recovery heat exchanger to be equal to or higher than the temperature of the refrigerant removing heat from the heat medium flowing into the heat recovery heat exchanger from the reheating heat exchanger to the moisture saturation temperature of the exhaust gas, Since the exhaust gas temperature at the inlet of the wet desulfurization apparatus is about the same and the evaporation of water inside the wet desulfurization apparatus is almost eliminated, the loss of moisture can be greatly reduced. In addition, by setting the temperature of the exhaust gas at the outlet of the heat recovery heat exchanger to be equal to or lower than the moisture saturation temperature of the exhaust gas, a portion of the water contained in the exhaust gas becomes easy to accumulate as drain water. By supplying it to a tank of a wet desulfurization device or a calcium carbonate supply device, it becomes possible to significantly reduce makeup water.

  According to the invention described in claim 6 or claim 14, in addition to the operation of the invention described in claim 5 or claim 13, replenishment is achieved by using boiler feed water as the refrigerant of the heat exchanger for heat removal. Can prevent increase of water. In addition, since it is not necessary to provide a separate facility for water used for the refrigerant of the heat removal heat exchanger, the heat removal heat exchanger can be installed with a simple configuration.

  According to invention of Claim 7 or Claim 15, in addition to the effect | action of the invention of Claim 5 or Claim 13, by using seawater for the refrigerant | coolant of the heat exchanger for heat removal, industrial water The use of can be suppressed.

  According to the invention described in claim 8 or claim 16, in addition to the action of the invention described in claim 5 or claim 13, the absorption liquid in the tank of the wet desulfurization apparatus is supplied to the heat recovery heat exchanger. By doing so, since the absorption liquid in the tank contains calcium carbonate, the strongly acidic drain water is neutralized.

  According to the present invention, it becomes possible to use the moisture in the exhaust gas as an absorbing solution for the exhaust gas, and greatly reduce the makeup water to the wet desulfurization apparatus. Accordingly, it is possible to greatly reduce the facility costs and costs for water production used in areas where water is insufficient.

Specifically, according to the invention described in claim 1 or claim 9, since the exhaust gas temperature introduced into the wet desulfurization apparatus is lowered by reducing the temperature of the exhaust gas introduced into the heat recovery heat exchanger, replenishment It becomes possible to reduce water. Further, the drain water of the heat exchanger for heat recovery can be effectively used as make-up water for the wet desulfurization apparatus and is economical. According to the invention of claim 2 or claim 10, the invention of claim 1 or claim In addition to the effects of the invention described in 9, the drain water of the heat recovery heat exchanger is stored in the tank of the wet desulfurization device, so that the drain water can be easily effectively used as make-up water for the wet desulfurization device. It is.

  And according to invention of Claim 3 or Claim 11, in addition to the effect of the invention of Claim 1 or Claim 9, the drain water of the heat exchanger for heat recovery is stored in the calcium carbonate supply device. By doing so, drain water can be easily effectively used as make-up water for the wet desulfurization apparatus, which is economical. Moreover, since strongly acidic drain water is neutralized with calcium carbonate, corrosion of the heat transfer tube of the heat exchanger for heat recovery can be prevented. Further, excess calcium carbonate can be effectively used without waste by supplying it to the wet desulfurization apparatus.

  According to the invention of claim 4 or claim 12, in addition to the effect of the invention of any one of claims 1 to 3 and claims 9 to 11, By coating the surface of the heat exchanger for heat recovery with a corrosion resistant material, corrosion of the heat transfer tube surface can be prevented.

  According to the invention of claim 5 or claim 13, in addition to the effect of the invention of any one of claims 1 to 3 and claims 9 to 11, Since the exhaust gas temperature at the inlet of the wet desulfurization device is not less than the temperature of the refrigerant that removes heat from the heat medium flowing into the heat recovery heat exchanger from the reheating heat exchanger and below the moisture saturation temperature of the exhaust gas, Water evaporation is almost eliminated and water loss can be greatly reduced. In addition, since some of the water contained in the exhaust gas tends to accumulate as drain water, drastic reduction of makeup water can be achieved by supplying drain water to a tank of a wet desulfurization unit or a calcium carbonate supply unit. Can be achieved.

  According to the invention of claim 6 or claim 14, in addition to the effect of the invention of claim 5 or claim 13, replenishment is achieved by using boiler feed water as the refrigerant of the heat exchanger for heat removal. An increase in water can be prevented, and a heat exchanger for heat removal can be installed with a simple configuration without requiring large-scale equipment.

  According to the invention of claim 7 or claim 15, in addition to the effect of the invention of claim 5 or claim 13, by using seawater as the refrigerant of the heat exchanger for heat removal, industrial water It will be a water-saving facility that uses less water.

  According to the invention described in claim 8 or claim 16, in addition to the effect of the invention described in claim 5 or claim 13, the absorption liquid in the tank of the wet desulfurization apparatus is supplied to the heat recovery heat exchanger. By doing so, since strongly acidic drain water is neutralized, corrosion of the heat exchanger tube of the heat exchanger for heat recovery can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram of the waste gas processing apparatus of Example 1 of this invention. It is a whole block diagram of the exhaust gas processing apparatus of Example 2 of this invention. It is a whole block diagram of the exhaust gas processing apparatus of Example 3 of this invention. It is a whole block diagram of the exhaust gas processing apparatus of Example 4 of this invention. It is a whole block diagram of the exhaust gas processing apparatus of a prior art.

  An embodiment of the exhaust gas treatment apparatus of the present invention will be described with reference to the drawings.

FIG. 1 shows an overall configuration diagram of an exhaust gas treatment apparatus according to Embodiment 1 of the present invention.
This exhaust gas treatment device differs from the prior art exhaust gas treatment device shown in FIG. 5 in that a heat removal heat exchanger is provided in the heat medium circulation pipe 52 between the heat recovery heat exchanger 45 and the reheating heat exchanger 46. 48 is provided, and a part of boiler feed water is supplied to the heat removal heat exchanger 48. The temperature of the heat medium supplied to the heat recovery heat exchanger 45 is reduced to about 20 to 30 ° C. by supplying boiler feed water at room temperature (20 to 30 ° C.) as a refrigerant to the heat removal heat exchanger 48. Is possible.

  And the exhaust gas temperature discharged | emitted from the dust collector 4 can be reduced to about 30 degreeC by supplying a heat medium of 20-30 degreeC to the heat exchanger 45 for heat recovery. By setting the exhaust gas temperature to a water saturation temperature (for example, 46 ° C. when the water concentration is 10%) or less, the water in the exhaust gas can be recovered as drain water. That is, since 10% of moisture is contained in the exhaust gas of the coal fired boiler, a part of the moisture in the exhaust gas becomes drain water by lowering the exhaust gas temperature to 30 ° C. In particular, if the temperature is set to 30 ° C., which is 10 ° C. or more lower than 46 ° C., the drain water can be more reliably obtained. Then, the drain water is recovered and supplied to the wet desulfurization apparatus, so that the makeup water in the wet desulfurization apparatus can be greatly reduced.

A heat transfer tube coated with a fluororesin such as polytetrafluoroethylene (PTFE) is used in the heat recovery heat exchanger 45. This is to prevent corrosion of the heat transfer tube surface caused by the absorption of SO ₂ in the exhaust gas by the moisture condensed on the surface of the heat recovery heat exchanger 45. Various fluororesins include tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / ethylene copolymer (ETFE), and polyvinylidene fluoride. Ride (PVDF), polychlorotrifluoroethylene (PCTFE), and the like. In order to prevent corrosion of the surface of the heat transfer tube, coating with a corrosion resistant material such as enamel paint, silicone resin (silicon resin), and epoxy resin can be considered, but all have the same effect.

An operation example of this embodiment is shown below.
Coal is supplied to the boiler 1 from the coal supply line 21 and air is supplied from the combustion air supply line 36, and high-pressure steam is generated in the boiler heat exchanger 11 by heat generated by the combustion reaction of coal. Then, the turbine 12 is rotated by the high-pressure steam to generate power by the generator 13 connected to the turbine 12. The steam that has exited the turbine 12 is cooled by the condenser 14, is pressurized again by the booster pump 15, and is sent to the boiler heat exchanger 11.

  On the other hand, the combustion exhaust gas discharged from the boiler 1 exchanges heat with combustion air at A / H 3, and then dust in the exhaust gas is removed by the dust collector 4. Thereafter, the exhaust gas temperature is cooled to 30 ° C. by the heat exchanger 45 for heat recovery based on the present embodiment, and then supplied to the wet desulfurization apparatus 5.

In the wet desulfurization apparatus 5, dust particles in the exhaust gas are brought into gas-liquid contact with absorbent droplets such as limestone or slurry containing lime sprayed as fine droplets from the spray nozzle 27 and exhaust gas rising in the apparatus. SO _{2 in} the exhaust gas is chemically absorbed and removed on the surface of the desulfurization absorbing droplets of the spray nozzle 27 together with acidic gas such as hydrogen chloride, hydrogen chloride and hydrogen fluoride.

The absorbing solution that has absorbed SO ₂ is stored in a tank 30 below the wet desulfurization device 5, is pressurized by the circulation pump 26, and sprayed from the nozzle 27 again via the absorbing solution circulation pipe 25. Further, SO ₂ absorbed in the desulfurization absorbing liquid 28 reacts with calcium carbonate supplied from the calcium carbonate solution supply device 44 and is released out of the system as gypsum.

  The exhaust gas after the treatment in the wet desulfurization apparatus 5 is heated to 70 ° C. by the heat exchanger 46 for reheating and discharged from the chimney 7. The heat transfer pipes of the heat recovery heat exchanger 45 and the reheating heat exchanger 46 are communicated with each other by a heat medium circulation pipe 52, and the heat recovery heat exchanger 45 and the reheating heat exchanger 46 are heated by a heat medium circulation pump 47. The heat medium is circulated between the two.

Here, the part which reduces the inlet exhaust gas temperature of the wet desulfurization apparatus 5 based on a present Example to 30 degreeC is described in detail.
First, the heat medium circulation pump 47 supplies a heat medium of about 20 ° C. to the heat recovery heat exchanger 45 installed upstream of the exhaust gas duct of the wet desulfurization apparatus 5 to reduce the temperature of the exhaust gas to about 30 ° C. At this time, the heat medium receives the heat of the exhaust gas and is heated to 93 ° C. Next, the heated heat medium is supplied to a reheating heat exchanger 46 installed downstream of the exhaust gas duct of the wet desulfurization device 5, and the temperature of the exhaust gas discharged from the wet desulfurization device 5 is raised to 70 ° C. To do. At this time, the temperature of the heat medium decreases to 72 ° C.

  The heat medium exiting the reheating heat exchanger 46 is supplied to a heat removal heat exchanger 48. A part of boiler feed water supplied to the boiler is supplied to the heat removal heat exchanger 48 as a refrigerant from the boiler feed water line 16, and the temperature of the heat medium is reduced to 20 ° C. by this refrigerant. By using boiler feed water as the refrigerant to be supplied to the heat removal heat exchanger 48, it is possible to prevent an increase in makeup water, and it is not necessary to provide a separate water facility for the refrigerant of the heat removal heat exchanger 48. The heat exchanger 48 for heat removal can be installed with a simple configuration without requiring large-scale equipment.

The heat removal heat exchanger 48 may be, for example, a compact and highly heat efficient plate type heat exchanger that exchanges heat between the heat medium (liquid) and the refrigerant (liquid).
If the heat removal heat exchanger 48 is installed in the low-temperature exhaust gas duct, heat is exchanged between the exhaust gas and the heat medium (liquid), and a large-scale heat exchanger needs to be installed. According to this embodiment, since the heat removal heat exchanger 48 is installed in the heat medium circulation pipe 52, there is an advantage that a compact device can be manufactured at low cost.

Next, the behavior of water in the wet desulfurization apparatus 5 will be described.
When the exhaust gas temperature is reduced to 30 ° C. by the heat recovery heat exchanger 45 installed upstream of the exhaust gas duct of the wet desulfurization apparatus 5, a part of the water contained in the exhaust gas becomes drain water, It is collected in a drain water recovery unit 49 installed at the bottom of the recovery heat exchanger 45. By supplying this drain water to the tank 30 through the drain water supply pipe 50, the amount of the desulfurization absorbing liquid 28 increases, and it becomes possible to reduce the replenishment of moisture.

  Moreover, since the temperature of the exhaust gas introduced into the wet desulfurization apparatus 5 is reduced to 30 ° C., the evaporation of water in the wet desulfurization apparatus 5 is almost eliminated, and the loss of moisture can be greatly reduced. Therefore, the amount of water supplied to the wet desulfurization apparatus 5 can be significantly reduced.

FIG. 2 shows an overall configuration diagram of an exhaust gas treatment apparatus according to Embodiment 2 of the present invention.
In this embodiment, the drain water recovered by the drain water recovery unit 49 installed in the lower part of the heat recovery heat exchanger 45 is connected to the supply device 44 of the calcium carbonate solution as the deflowing agent. Other than this, the configuration is the same as that of FIG.

By supplying the drain water of the heat exchanger 45 for heat recovery to the calcium carbonate supply device 44, the drain water can be effectively used as make-up water for the wet desulfurization device 5, and the same effect as in the first embodiment can be obtained. .
Further, the drain water of the heat recovery heat exchanger 45 is strongly acidic because SO _{2 in} the exhaust gas is contained, but the acid is neutralized by supplying the drain water to the calcium carbonate supply device 44. Is done. Excess calcium carbonate can be effectively used without waste by supplying it to the wet desulfurization apparatus 5.

The whole block diagram of the exhaust gas treatment apparatus of Example 3 of the present invention is shown in FIG.
In the heat removal heat exchanger 48 of the exhaust gas treatment apparatus shown in the first and second embodiments, a part of boiler feed water is supplied as a refrigerant from the boiler feed water line 16 to the heat removal heat exchanger 48. In this embodiment, seawater supply line 38 is provided, and seawater is used as a refrigerant to be supplied to heat removal heat exchanger 48. Therefore, since the refrigerant supplied to the heat removal heat exchanger 48 is the same as that of the first embodiment except that it is seawater, the description thereof is omitted.

  It is possible to reduce the temperature of the heat medium supplied to the heat recovery heat exchanger 45 to about 20 to 30 ° C. by supplying normal temperature (20 to 30 ° C.) seawater as a refrigerant to the heat removal heat exchanger 48. It becomes possible. And by supplying a heat medium of 20-30 degreeC to the heat exchanger 45 for heat recovery, the exhaust gas temperature discharged | emitted from the dust collector 4 can be reduced to about 30 degreeC, and also in a present Example, said Example 1 and It is possible to obtain an equivalent effect.

Further, by using seawater as the refrigerant of the heat removal heat exchanger 48, the use of industrial water can be suppressed, and further water saving can be realized.
In this embodiment, the drain water of the heat recovery heat exchanger 45 may be supplied to the calcium carbonate supply device 44 as in the second embodiment.

The whole block diagram of the exhaust gas treatment apparatus of Example 4 of the present invention is shown in FIG.
In this embodiment, the desulfurization absorption liquid 28 in the tank 30 of the wet desulfurization apparatus 5 is supplied to the drain water recovery unit 49 installed in the lower part of the heat exchanger 45 for heat recovery. Since this is the same as the configuration of, the description is omitted.

When there are many sulfur components contained in coal which is a fuel, the concentration of SO ₂ in the exhaust gas generated from the boiler 1 becomes high. Depending on the coal production area, 2 to 3% of sulfur may be contained, and the SO ₂ concentration in the exhaust gas is as high as 1500 to 2500 ppm.
In the heat recovery heat exchanger 45 provided upstream of the exhaust gas duct of the wet desulfurization apparatus 5, a large amount of SO ₂ in the exhaust gas is absorbed by the generated drain water and becomes strongly acidic, and the exhaust gas duct and piping are corroded. It may be a cause.

In particular, in this embodiment in which the exhaust gas temperature is reduced to 30 ° C., which is approximately 70 to 80 ° C. lower than that in the case of FIG.
As a countermeasure in such a case, as shown in FIG. 4, the desulfurization absorption liquid 28 in the tank 30 of the wet desulfurization apparatus 5 is absorbed into the heat transfer tube surface of the heat recovery heat exchanger 45 and the drain water recovery unit 49. It is effective to provide an absorption liquid supply pipe 53 (supply system) via the liquid pump 51.

Since the desulfurization absorption liquid 28 contains calcium carbonate, it is possible to neutralize the strongly acidic drain water generated on the heat transfer tube surface of the heat recovery heat exchanger 45. Therefore, corrosion of the heat transfer tube of the heat recovery heat exchanger 45 can be prevented.
Moreover, since excess calcium carbonate is supplied to the wet desulfurization apparatus 5 with drain water through the drain water supply piping 50, it is effectively used without waste.

In this embodiment, the drain water of the heat recovery heat exchanger 45 may be supplied to the calcium carbonate supply device 44 as in the second embodiment, or the heat removal heat exchange as in the third embodiment. Seawater may be used as the refrigerant of the vessel 48.
This example is suitable when the SO ₂ concentration in the exhaust gas is high.

  According to the present invention, not only in a coal fired boiler, but also in an exhaust gas treatment device and an exhaust gas treatment method provided with a wet desulfurization device that removes sulfur oxides contained in exhaust gas generated from other combustion devices, the wet desulfurization device As a technique for reducing the amount of water supplied to the water, it can be used.

1 Boiler 3 Air preheater (A / H; Air heater)
DESCRIPTION OF SYMBOLS 4 Dust collector 5 Desulfurization device 7 Chimney 11 Boiler heat exchanger 12 Turbine 13 Generator 14 Condenser 15 Booster pump 16 Boiler feed line 21 Coal supply line 25 Absorption liquid circulation piping 26 Absorption liquid circulation pump 27 Spray nozzle 28 Desulfurization absorption liquid 30 Tank 36 Combustion Air Supply Line 38 Seawater Supply Line 44 Calcium Carbonate Solution Supply Device 45 Heat Recovery Heat Exchanger 46 Reheating Heat Exchanger 47 Heat Medium Circulation Pump 48 Heat Removal Heat Exchanger 49 Drain Water Recovery Unit 50 Drain Water Supply piping 51 Absorption liquid pump 52 Heat medium circulation piping 53 Absorption liquid supply piping

Claims (16)

In an exhaust gas treatment apparatus equipped with a wet desulfurization apparatus that removes sulfur oxides in exhaust gas by spraying an absorbing liquid on exhaust gas generated from a coal-fired boiler,
The exhaust gas duct on the upstream side of the wet desulfurization apparatus is provided with a heat recovery heat exchanger provided with a heat transfer tube that recovers the heat of the exhaust gas into a heat medium,
In the exhaust gas duct on the downstream side of the wet desulfurization apparatus, a reheating heat exchanger provided with a heat transfer tube for heating the exhaust gas with a heat medium supplied from the heat recovery heat exchanger is provided,
Further, the heat transfer pipes provided in the heat exchanger for heat recovery and the heat exchanger for reheating are connected to each other, and a heat medium circulation pipe for circulating the heat medium is provided therein,
A heat exchanger for removing heat from the heat medium is provided in a flow path of the heat medium from the heat exchanger for reheating to the heat exchanger for heat recovery of the heat medium circulation pipe;
An exhaust gas treatment characterized in that a drain water recovery unit is provided at a lower part of an exhaust gas duct of the heat recovery heat exchanger, and a drain water supply unit for supplying drain water in the drain water recovery unit to the wet desulfurization apparatus is provided. apparatus. The wet desulfurization apparatus includes a tank that stores an absorbing liquid that has absorbed sulfur oxides, a spray unit that is provided above the tank and has spray nozzles that spray the absorbing liquid on the exhaust gas in a plurality of stages in the exhaust gas flow direction, and the tank. An absorption liquid circulation pipe for sending an absorption liquid provided with a circulation pump for sucking up the absorption liquid in the spray nozzle, and a calcium carbonate supply for supplying a calcium carbonate solution for making the sulfur dioxide in the absorption liquid in the tank into gypsum With the device,
2. The exhaust gas treatment apparatus according to claim 1, wherein the drain water supply unit is configured to supply drain water in a drain water recovery unit to the tank. The wet desulfurization apparatus includes a tank that stores an absorbing liquid that has absorbed sulfur oxides, a spray unit that is provided above the tank and has spray nozzles that spray the absorbing liquid on the exhaust gas in a plurality of stages in the exhaust gas flow direction, and the tank. An absorption liquid circulation pipe for sending an absorption liquid provided with a circulation pump for sucking up the absorption liquid in the spray nozzle, and a calcium carbonate supply for supplying a calcium carbonate solution for making the sulfur dioxide in the absorption liquid in the tank into gypsum With the device,
Furthermore, the said drain water supply part is the structure which supplies the drain water in a drain water collection | recovery part to the said calcium carbonate supply apparatus, The exhaust gas processing apparatus of Claim 1 characterized by the above-mentioned.   The exhaust gas treatment apparatus according to any one of claims 1 to 3, wherein a surface of a heat transfer tube of the heat recovery heat exchanger is coated with a corrosion-resistant material containing a fluororesin.   The refrigerant is supplied to the heat removal heat exchanger, and the heat medium flowing into the heat recovery heat exchanger from the reheating heat exchanger is cooled, whereby the exhaust gas temperature at the heat recovery heat exchanger outlet is reduced. The exhaust gas treatment apparatus according to any one of claims 1 to 3, further comprising a refrigerant supply unit configured to set the temperature to a temperature equal to or lower than a water saturation temperature of the exhaust gas. A boiler water supply unit for supplying water to the boiler is provided,
6. The exhaust gas treatment apparatus according to claim 5, wherein water supplied from the boiler water supply unit is used as a refrigerant in the refrigerant supply unit.   6. The exhaust gas treatment apparatus according to claim 5, wherein seawater is used as a refrigerant of the refrigerant supply unit.   6. The exhaust gas treatment apparatus according to claim 5, further comprising an absorption liquid supply unit that supplies an absorption liquid in a tank of the wet desulfurization apparatus to the heat recovery heat exchanger. In the exhaust gas treatment method of removing sulfur oxides in the exhaust gas by a wet desulfurization apparatus having a configuration in which an absorption liquid is sprayed on the exhaust gas generated from a coal-fired boiler,
The heat of the exhaust gas is recovered by a heat recovery heat exchanger having a heat transfer tube having a heat medium for recovering heat from the exhaust gas before desulfurization by the wet desulfurization apparatus, and the exhaust gas after desulfurization treatment by the wet desulfurization apparatus Circulating the heat medium from the heat recovery heat exchanger to a reheating heat exchanger having a heat transfer tube having a heat medium for heating
Removing heat from the heat medium supplied from the reheating heat exchanger to the heat recovery heat exchanger and supplying drain water accumulated in a lower portion of the heat recovery heat exchanger to the wet desulfurization apparatus, Exhaust gas treatment method. A tank for storing an absorbing solution that has absorbed sulfur oxide, a spray unit that is provided above the tank and that sprays the absorbing solution on the exhaust gas in a plurality of stages in the exhaust gas flow direction, and the absorbing solution in the tank is spray nozzle A wet type equipped with an absorption liquid circulation pipe for sending an absorption liquid provided with a circulation pump for sucking up and a calcium carbonate supply device for supplying a calcium carbonate solution for making sulfur dioxide in the absorption liquid in the tank into gypsum An exhaust gas treatment method for removing sulfur oxides in exhaust gas by a desulfurization device,
The exhaust gas treatment method according to claim 9, wherein drain water accumulated in a lower portion of the heat recovery heat exchanger is supplied to the tank. A tank for storing an absorbing solution that has absorbed sulfur oxide, a spray unit that is provided above the tank and that sprays the absorbing solution on the exhaust gas in a plurality of stages in the exhaust gas flow direction, and the absorbing solution in the tank is spray nozzle A wet type equipped with an absorption liquid circulation pipe for sending an absorption liquid provided with a circulation pump for sucking up and a calcium carbonate supply device for supplying a calcium carbonate solution for making sulfur dioxide in the absorption liquid in the tank into gypsum An exhaust gas treatment method for removing sulfur oxides in exhaust gas by a desulfurization device,
The exhaust gas treatment method according to claim 9, wherein drain water accumulated in a lower portion of the heat recovery heat exchanger is supplied to the calcium carbonate supply device.   The exhaust gas according to any one of claims 9 to 11, wherein a heat transfer tube whose surface is coated with a corrosion-resistant material containing a fluororesin is used as the heat transfer tube of the heat recovery heat exchanger. Processing method.   The heat medium flowing into the heat recovery heat exchanger from the reheating heat exchanger is cooled by the refrigerant to remove heat, and the exhaust gas temperature at the outlet of the heat recovery heat exchanger is equal to or higher than the refrigerant temperature and the moisture saturation temperature of the exhaust gas. The exhaust gas treatment method according to any one of claims 9 to 11, wherein:   14. The exhaust gas treatment method according to claim 13, wherein boiler supply water for supplying water to the boiler is used as the refrigerant.   The exhaust gas treatment method according to claim 13, wherein seawater is used as the refrigerant.   The exhaust gas treatment method according to claim 13, wherein the absorption liquid in the tank of the wet desulfurization apparatus is supplied to the heat recovery heat exchanger.

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