JP2012149792A - Exhausts gas treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent ash from adhering to the surface of a heat transfer tube of a heat exchanger arranged on the inlet side of a dust collector.SOLUTION: This system includes: a steam circulation line 17 for supplying steam generated in a steam generating heat exchanger 13 of a boiler 11 to a steam turbine 15, cooling exhaust gas from the steam turbine and returning the cooled gas to the steam generating heat exchanger; an exhaust gas treatment line 19 for treating the gas from the boiler; an exhaust gas circulation duct 21 for returning a part of the exhaust gas to the boiler; a first heat exchanger 29 for exchanging heat between water discharged from a condenser in the steam circulation line and a heating medium (a); a second heat exchanger 63 for compressing exhaust gas flowing in the downstream side of a dust collector 37 in the exhaust gas treatment line and exchanging heat between heated exhaust gas and the heating medium (a); and a third heat exchanger 35 for exchanging heat between exhaust gas flowing in the inlet side of the dust collector in the exhaust gas treatment line and the heating medium (a). The heating medium cooled by the first heat exchanger is heated by the second heat exchanger and further heated by the third heat exchanger and the heated heating medium is returned to the first heat exchanger.

Description

  The present invention relates to an exhaust gas treatment system including a boiler that burns fuel using a combustion gas in which oxygen-rich gas and circulating exhaust gas are mixed.

In recent years, oxyfuel boilers (hereinafter abbreviated as “boilers”) have attracted attention as a technique for reducing carbon dioxide (CO ₂ ) emissions, which are one of the causes of global warming. Since this boiler uses high-concentration oxygen gas (hereinafter abbreviated as oxygen) instead of air as an oxidizing agent, the main components of exhaust gas discharged from the boiler are water and carbon dioxide. For this reason, carbon dioxide (CO ₂ ) can be easily separated from the exhaust gas by compressing the exhaust gas.

An oxyfuel combustion system equipped with this type of boiler includes a boiler, a heat exchanger (hereinafter referred to as A / H) that recovers the heat of the exhaust gas of the boiler, a dust collector that removes ash in the exhaust gas, It comprises a desulfurizer that removes SOx and a CO ₂ separation means that removes carbon dioxide in the exhaust gas. In such a configuration, the exhaust gas discharged from the boiler is reduced in temperature by A / H and then guided to a dust collector to remove ash. The exhaust gas from which the ash has been removed is guided to a desulfurization apparatus, and after SOx in the exhaust gas is absorbed and separated by the absorption liquid, it is guided to a CO ₂ separation means. The exhaust gas introduced into the CO ₂ separation means is compressed by a compressor, and heat generated at that time is removed by a heat exchanger, whereby liquid water is separated from the exhaust gas. Further, after the exhaust gas is compressed by the compressor, the heat is removed by the heat exchanger, whereby liquid carbon dioxide is separated from the exhaust gas.

  By the way, since oxygen is introduced into this type of boiler as an oxidizer, the combustion temperature is higher than that of an air combustion boiler using air as an oxidizer. For this reason, one end of the exhaust gas circulation duct is connected to the flue between the dust collector and the desulfurizer, and the other end of the exhaust gas circulation duct is connected to the boiler so that a part of the exhaust gas that has passed through the dust collector is It goes back to the boiler via the way to lower the combustion temperature.

However, when a part of the exhaust gas is extracted from the upstream side of the desulfurization apparatus in this way, the exhaust gas circulation duct passes through the exhaust gas circulation duct that has not been desulfurized. There is a risk of corrosion. Here, when the exhaust gas circulation duct is branched from the flue on the downstream side of the desulfurization device, the exhaust gas after the desulfurization treatment flows through the exhaust gas circulation duct, thereby suppressing the corrosion of the exhaust gas circulation duct. However, since the amount of exhaust gas treated by the desulfurizer increases, it is not preferable in terms of economy and the like. In addition, when the exhaust gas contains mercury, the compressor provided in the CO ₂ separation means may corrode.

In contrast, in the oxyfuel combustion system of Japanese Patent Application No. 2009-267914, the applicant of the present application provides a heat exchanger in the flue between the A / H and the dust collector, and the exhaust gas passing through this heat exchanger. Has been proposed to reduce the temperature of the exhaust gas at the inlet of the dust collector to a temperature below the acid dew point of SO ₃ and above the water dew point. That is, by reducing the exhaust gas temperature to a temperature below the acid dew point, SO _{3 in} the exhaust gas is condensed and adheres to the ash. For this reason, by collecting this ash with a dust collector, it is possible to reduce the SO ₃ concentration in the exhaust gas and suppress corrosion. Also, mercury in the exhaust gas can be recovered with a dust collector by lowering the exhaust gas temperature in the same manner.

  In addition, in the exhaust gas treatment plant of Patent Document 1, a condensate discharged from a steam supply path for supplying steam generated by a steam generating heat exchanger installed in a boiler to a steam turbine and a condenser for condensing the exhaust of the steam turbine. Is heated by exchanging heat with the heat medium in the condensate reheater, and then returned to the steam generating heat exchanger, a heat exchanger installed in the flue between the A / H and the dust collector, and this heat The structure provided with the circulation path which circulates a heat medium between an exchanger and the reheater for condensates is disclosed.

In this way, in the condensate reheater, the exhaust gas temperature is lowered to a predetermined temperature by supplying the heat medium heat-exchanged with the condensate and reduced in temperature to the heat exchanger to exchange heat with the exhaust gas. Therefore, SO ₃ , mercury, and the like can be removed by collecting ash with a downstream dust collector. Moreover, since the heat which the heat medium collect | recovered from waste gas with the heat exchanger can be utilized for the heating of condensate, thermal efficiency can be improved.

JP 2006-308269 A

  Here, the structure of the heat exchanger (excluding A / H) installed on the upstream side of the dust collector will be described with reference to FIG. For example, the temperature of the exhaust gas that has passed through A / H has been reduced to about 160 to 200 ° C. In order to obtain highly efficient heat exchange performance in such a low temperature field, the heat transfer tube 1 as shown in FIG. It is common to use a fin tube 5 having a plurality of fins 3 attached to the outer periphery thereof.

  In addition, a soot blower 7 in which a large number of holes are formed is usually provided on the upstream side of the fin tube 5. A part of the steam generated by the heat of the boiler is guided to the soot blower 7, and steam 9 is temporarily ejected from many holes toward the fin tube 5. Thus, the ash adhering to the fin tube 5 can be removed by spraying the vapor | steam ejected from the soot blower 7 to the fin 3 of the fin tube 5 or the heat exchanger tube 1.

  By the way, when the heat exchanger having such a structure is used for the heat exchanger described in Japanese Patent Application No. 2009-267914, that is, the heat exchanger installed in the flue between the A / H and the dust collector, A large amount of ash adheres to the tube 5, and the ash may not be completely removed simply by spraying steam from the soot blower 7. In particular, it has been found that this phenomenon is prominent when coal containing a large amount of sulfur used in the United States and China is used. This is considered to be caused by moisture and SOx contained in a large amount in the exhaust gas of the oxyfuel combustion system.

Table 1 shows a comparison of exhaust gas compositions when air having a sulfur content of 2.7% is subjected to air combustion or oxygen combustion. It can be seen that the SO ₂ concentration and the SO ₃ concentration are 4 to 5 times higher than that in air combustion, and the water concentration is increased to 30%, which is 3 times higher. Thus, when the moisture concentration increases from 10% to 30%, the water dew point of the exhaust gas increases from 50 ° C. to 70 ° C., and moisture tends to condense on the surface of the heat transfer tube. Moreover, since SO ₂ and SO ₃ in the exhaust gas are easily dissolved in water, the SO ₂ and SO ₃ are dissolved in water generated on the surface of the heat transfer tube to become an acidic solution. When an acidic liquid is generated on the surface of the heat transfer tube in this way, a large amount of ash in the exhaust gas adheres, the heat transfer performance decreases, and ash removal becomes difficult.

  On the other hand, in the case of Patent Document 1, the heat transfer tube of the heat exchanger is supplied with a heat medium that has been cooled to room temperature by exchanging heat with the condensate in the condensate reheater. The surface temperature is about 30 ° C to 50 ° C. For this reason, the water | moisture content in the waste gas which passes a heat exchanger may condense on the surface of a heat exchanger tube, and there exists a possibility that the problem of ash adhesion may arise.

  This invention is made | formed in view of such a situation, and makes it a subject to suppress the ash adhesion to the surface of the heat exchanger tube of the heat exchanger arrange | positioned at the inlet side of a dust collector.

  In order to solve the above problems, an exhaust gas treatment system of the present invention is generated by a boiler that burns fuel using a combustion gas in which oxygen-rich gas and circulating exhaust gas are mixed, and a steam generation heat exchanger provided in the boiler. A steam circulation line for supplying steam to the steam turbine to generate electricity, cooling the steam discharged from the steam turbine and returning it to the heat exchanger for steam generation, an exhaust gas treatment line for treating the exhaust gas generated from the boiler, and exhaust gas An exhaust gas treatment system comprising an exhaust gas circulation line that extracts a part of exhaust gas flowing downstream of a dust collector provided in the treatment line and guides the exhaust gas to a boiler, and a condenser that cools steam discharged from a steam turbine of the steam circulation line; A first heat exchanger provided between the heat exchanger for generating steam and exchanging heat between the water discharged from the condenser and the heat medium; and a dust collector in the exhaust gas treatment line A second heat exchanger for exchanging heat between the exhaust gas generated by compressing the exhaust gas flowing on the downstream side and the heat medium; and an exhaust gas and heat medium flowing on the inlet side of the dust collector in the exhaust gas treatment line. A heat exchanger cooled with the first heat exchanger, the heat medium cooled by the first heat exchanger is led to the second heat exchanger and heated, and the heated heat medium is led to the third heat exchanger. Further heating is performed, and the heated heat medium is returned to the first heat exchanger.

  According to this, a heat medium is introduced into a 2nd heat exchanger, after heat-exchanging with the water which came out of the condenser with the 1st heat exchanger, and cooling to normal temperature. The heat medium introduced into the second heat exchanger is heated to, for example, 50 to 70 ° C. by exchanging heat with the exhaust gas that has been compressed and generated heat (for example, 130 ° C.). Since the heat medium heated in this way is introduced into the third heat exchanger into which the higher temperature exhaust gas flows, the surface temperature of the heat transfer tube of the third heat exchanger becomes higher than 70 ° C. Therefore, since the surface temperature of the heat transfer tube does not fall below 70 ° C., which is the water dew point temperature when the moisture concentration in the exhaust gas is 30%, for example, moisture in the exhaust gas is not condensed on the surface of the heat transfer tube, The adhesion of ash to the surface of the heat transfer tube can be suppressed.

  In this case, the temperature of the heat medium introduced into the third heat exchanger is set to be 70 ° C. or higher, preferably 80 ° C. or higher. In order to set the temperature of the heat medium in this way, the heat exchange amount and the like may be adjusted by a known method for heat exchangers other than the third heat exchanger.

  Further, in place of such an exhaust gas treatment system, the water discharged from the condenser is provided between a condenser for cooling the steam discharged from the steam turbine of the steam circulation line and the heat exchanger for generating steam. First heat exchanger that exchanges heat with the heat medium, and second heat exchange that exchanges heat between the desulfurization liquid stored in the bottom of the wet desulfurization apparatus provided on the downstream side of the dust collector of the exhaust gas treatment line and the heat medium And a third heat exchanger provided on the inlet side of the dust collector of the exhaust gas treatment line for exchanging heat between the exhaust gas flowing through the inlet side and the heat medium, and the heat medium cooled by the first heat exchanger It is led to the second heat exchanger and heated, the heated heat medium is led to the third heat exchanger and further heated, and the heated heat medium is returned to the first heat exchanger. It is good.

  That is, in the oxyfuel combustion system, since the exhaust gas contains a large amount of moisture, the temperature in the wet denitration apparatus rises to about 70 ° C. For this reason, the heat medium at normal temperature can be heated up to about 50-70 degreeC by carrying out heat exchange of the heat medium with the desulfurization liquid stored in the bottom part of the wet desulfurization apparatus. Thus, for example, a second heat exchanger is installed in the desulfurization liquid stored in the bottom of the wet desulfurization apparatus, and the heat medium heated by exchanging heat with the desulfurization liquid in the second heat exchanger is converted into the third heat. By guiding to the exchanger, the surface temperature of the heat transfer tube becomes about 70 to 90 ° C., so that moisture in the exhaust gas does not condense on the surface of the heat transfer tube and suppresses the adhesion of ash to the surface of the heat transfer tube. be able to.

  Further, in place of these exhaust gas treatment systems, water provided between the condenser for cooling the steam discharged from the steam turbine in the steam circulation line and the heat exchanger for steam generation, A first heat exchanger for exchanging heat with the heat medium; a second heat exchanger for exchanging heat between the exhaust gas flowing between the dust collector of the exhaust gas treatment line and a wet desulfurization device provided downstream thereof; A third heat exchanger provided on the inlet side of the dust collector of the exhaust gas treatment line and exchanging heat between the exhaust gas flowing through the inlet side and the heat medium, and the second heat medium cooled by the first heat exchanger The heat exchanger is led to heat, the heated heat medium is led to a third heat exchanger and further heated, and the heated heat medium is returned to the first heat exchanger. Good.

  That is, since the exhaust gas temperature at the dust collector outlet in the oxyfuel combustion system is about 90 to 110 ° C., heat exchange between the exhaust gas flowing between the dust collector and the wet-type desulfurization apparatus on the downstream side and the heat medium causes heat at normal temperature. The medium can be heated to about 50-70 ° C. Therefore, a second heat exchanger is installed between the dust collector of the exhaust gas treatment line and the wet desulfurization device provided downstream thereof, and the heat medium heated by exchanging heat with the exhaust gas in the second heat exchanger. Since the surface temperature of the heat transfer tube is about 70 to 90 ° C. by introducing the water to the third heat exchanger, moisture in the exhaust gas does not condense on the surface of the heat transfer tube, and ash adheres to the surface of the heat transfer tube. Can be suppressed.

  According to the exhaust gas treatment system of the present invention, it is possible to suppress ash adhesion to the heat transfer tube of the heat exchanger disposed on the inlet side of the dust collector.

1 is a schematic system diagram in a first embodiment of an exhaust gas treatment system to which the present invention is applied. It is a schematic system diagram in a second embodiment of an exhaust gas treatment system to which the present invention is applied. It is a schematic system diagram in a third embodiment of an exhaust gas treatment system to which the present invention is applied. It is a figure which shows the structure of the heat exchanger arrange | positioned at the entrance side of a dust collector.

(First embodiment)
Hereinafter, a first embodiment of an exhaust gas treatment system to which the present invention is applied will be described with reference to FIG. In the present embodiment, an example in which an oxyfuel boiler is used and pulverized coal fuel is used as fossil fuel burned in the boiler will be described. However, the fossil fuel is not limited to pulverized coal fuel. In this embodiment, oxygen-rich gas (hereinafter abbreviated as oxygen) separated from air is used as the oxidant supplied to the boiler.

  The exhaust gas treatment system of this embodiment supplies a steam generated from a boiler 11 that burns pulverized coal fuel using oxygen as an oxidizer and a steam generation heat exchanger 13 provided in the boiler 11 to a steam turbine 15 to generate power. The steam discharged from the steam turbine 15 is liquefied and heated and then returned to the heat exchanger 13 for steam generation, the exhaust gas treatment line 19 for treating the exhaust gas generated from the boiler 11, and the exhaust gas treatment An exhaust gas circulation duct 21 that extracts a part of the exhaust gas flowing through the flue of the line 19 and guides it to the boiler is provided.

  The steam circulation line 17 includes a steam generating heat exchanger 13 that generates steam using the combustion heat of the boiler 11, a steam turbine 15 that drives the generator 23 using the steam, A condenser 25 that cools and condenses the exhaust, a booster pump 27 that boosts the condensate discharged from the condenser 25, and heats the condensate discharged from the booster pump 27 by exchanging heat with the heat medium a. And a first heat exchanger 29. The first heat exchanger 29 is configured by accommodating a heat transfer tube through which a heat medium flows in a container through which condensate is guided. As a result, the steam exiting the steam generating heat exchanger 13 becomes condensate through the steam turbine 15 and the condenser 25 in this order, and this condensate passes through the booster pump 27 and the first heat exchanger 29 in order. The steam generation heat exchanger 13 is then returned.

The exhaust gas treatment line 19 includes a denitration device 31 that removes NOx in the exhaust gas discharged from the boiler 11, an A / H 33 that heat-exchanges the exhaust gas and the circulating exhaust gas (described later) to reduce the temperature of the exhaust gas, and heats the exhaust gas. A third heat exchanger 35 that reduces the temperature by exchanging heat with the medium a, a dust collector 37 that collects ash in the exhaust gas, a wet desulfurization device 39 that removes SOx in the exhaust gas, and carbon dioxide in the exhaust gas. The CO ₂ separation means 41 that is liquefied and separated is connected by a flue 43 in this order. The third heat exchanger 35 is configured to accommodate a heat transfer tube through which a heat medium flows, that is, a fin tube (FIG. 4), in a container into which exhaust gas is introduced, and a soot blower is provided on the upstream side thereof.

  The boiler 11 is provided with a burner (not shown), and a fuel supply path 45 for supplying pulverized coal fuel into the furnace is connected to the burner. A distributor 47 is provided in the flue portion connecting the dust collector 37 and the desulfurization device 39, and one end of the exhaust gas circulation duct 21 for extracting a part of the exhaust gas flowing through the flue 43 is connected to the distributor 47. Has been. The other end of the exhaust gas circulation duct 21 extending via the A / H 33 is connected to an exhaust gas mixer 49 provided in the fuel supply path 45.

  Between the distributor 47 of the exhaust gas circulation duct 21 and the A / H 33, a circulation fan 51 for adjusting the flow rate of the circulating exhaust gas flowing through the exhaust gas circulation duct 21 is provided. The combustion temperature of the boiler 11 is adjusted to the same level as in the air combustion operation by adjusting the fan rotation speed of the circulation fan 51 so that the circulation amount of the circulation exhaust gas is, for example, 70 to 80% of the entire exhaust gas amount. Can do. In addition, the exhaust gas circulation duct 21 may be configured such that the flue 43 on the downstream side of the desulfurization device 39 is branched and connected at one end to extract and circulate the exhaust gas after the desulfurization treatment.

  The fuel supply path 45 is supplied with pulverized coal fuel pulverized to a predetermined particle size by a coal pulverization mill (not shown) along with the carrier gas. An oxygen mixer 53 to which an oxygen supply path is connected is provided on the upstream side of the exhaust gas mixer 49 in the fuel supply path 45. The oxygen mixer 53 is supplied with oxygen to provide pulverized coal fuel and oxygen. Are to be mixed. The exhaust gas mixer 49 is supplied with the circulating exhaust gas flowing through the exhaust gas circulation duct 21, where the pulverized coal fuel, oxygen and the circulating exhaust gas are mixed.

  The desulfurization device 39 flows the exhaust gas introduced from the lower inlet of the absorption tower 55 toward the upper outlet, and sprays the desulfurization liquid from the spray nozzle 57 to the exhaust gas flowing in the tower. At a position lower than the exhaust gas inlet, that is, at the bottom of the absorption tower 55, a bottom 59 is formed for collecting and storing the absorbent discharged from the spray nozzle 57.

In the CO ₂ separation means 41, the first compressor 61, the second heat exchanger 63, and the second compressor 65 are sequentially connected by piping, and water and carbon dioxide are liquefied in the process of compressing the exhaust gas. Each is separated from the exhaust gas.

  The second heat exchanger 63 is configured by accommodating a heat transfer tube through which a heat medium flows in a container into which exhaust gas is introduced, and in this container, drainage supply for extracting moisture separated from the exhaust gas from the container One end of the duct 67 is connected, and the other end is connected to a wastewater treatment facility (not shown). As a result, the exhaust gas that has been compressed and heated by the first compressor 61 is heat-exchanged with the heat medium by the second heat exchanger 63 to remove heat, and after the water is separated, the second compressor is further removed. After being compressed at 65, the carbon dioxide liquefied by heat removal is separated.

  Here, in this embodiment, the flow path of the heat medium a flowing through the heat transfer tube of the first heat exchanger 29, the flow path of the heat medium a flowing through the heat transfer tube of the second heat exchanger 63, and the third heat exchange. A heat medium circulation line 71 through which the heat medium a circulates is formed by communicating the flow path of the heat medium a flowing through the heat transfer tube of the vessel 35 via a pipe 69. That is, the heat medium a flowing through the heat transfer tube of the first heat exchanger 29 flows into the heat transfer tube of the second heat exchanger 63, and the heat medium a flowing through the heat transfer tube of the second heat exchanger 63 is the third heat. The heat medium a flowing into the heat transfer tube of the exchanger 35 and flowing through the heat transfer tube of the third heat exchanger 35 is returned to the heat transfer tube of the first heat exchanger 29. Here, a circulation pump 73 is provided in a pipe 69 in which the heat medium a that has flowed through the heat transfer tube of the first heat exchanger 29 flows toward the heat transfer tube of the second heat exchanger 63, and the circulation pump 73. Is driven, the heat medium a circulates through the heat medium circulation line 71.

  Next, the operation of the exhaust gas treatment system configured as described above will be described.

  In the steam circulation line 17, high-temperature and high-pressure steam is generated from the steam-generating heat exchanger 13 by heat generated by the combustion reaction in the boiler 11, and this steam is introduced into the steam turbine 15 to rotate the steam turbine 15. As a result, the generator 23 generates power. The low-pressure steam discharged from the steam turbine 15 is gradually cooled and liquefied in the condenser 25 and is sucked into the booster pump 27 as condensate. The condensed water boosted by the booster pump 27 is guided into the container of the first heat exchanger 29, heated by exchanging heat with the heat medium a flowing through the heat transfer tube, and then returned to the steam generating heat exchanger 13. It is.

  In the exhaust gas treatment line 19, pulverized coal fuel is combusted by supplying pulverized coal fuel, oxygen, and circulating exhaust gas to the boiler 11 through the fuel supply path 45. As a result of this combustion, the exhaust gas discharged from the boiler 11 passes through the flue 43 and is guided to the denitration device 31, and NOx in the exhaust gas is removed by contacting with the denitration catalyst. Subsequently, after the exhaust gas exiting the denitration device 31 is led to the A / H 33 and heat-exchanged with the circulating exhaust gas, the temperature is reduced to about 160 ° C. to 200 ° C. Led. In the third heat exchanger 35, the exhaust gas is heat-exchanged with the heat medium a flowing through the heat transfer tube, so that the temperature is reduced to, for example, 110 ° C. to 160 ° C. and is discharged after being at or above the water dew point. The exhaust gas leaving the third heat exchanger 35 is guided to the dust collector 37 to remove ash contained in the exhaust gas.

  A part of the exhaust gas exiting the dust collector 37 is extracted from the flue 43 by driving the circulation fan 51 and guided to the exhaust gas circulation duct 21. The circulating exhaust gas flowing through the exhaust gas circulation duct 21 is guided to the A / H 33 via the circulation fan 51 and heated by exchanging heat with the exhaust gas exiting the denitration device 31, and then via the fuel supply path 45. Guided into the boiler 11.

On the other hand, the exhaust gas exiting the dust collector 37 is introduced into the absorption tower 55 of the desulfurization device 39. The exhaust gas rising in the absorption tower 55 comes into contact with the desulfurization liquid sprayed from the spray nozzle 57, and SO ₂ contained in the exhaust gas is absorbed by the desulfurization liquid. The desulfurization liquid that has absorbed SO ₂ is stored in the bottom 59 of the absorption tower 55, where, for example, SO _{2 that} has reacted with the components of the desulfurization liquid becomes a salt and is separated from the desulfurization liquid at the bottom 59. Although not shown, the desulfurization liquid stored in the bottom 59 is pumped up by the pump, supplied to the spray nozzle 57, and sprayed again into the absorption tower 55.

Subsequently, the exhaust gas at about 50 ° C. exiting the desulfurization apparatus 7 is guided to the CO ₂ separation means 41. Here, first, the exhaust gas is compressed by the first compressor 61. The exhaust gas that has generated heat up to about 130 ° C. by this compression is guided into the container of the second heat exchanger 63 and is cooled to room temperature by exchanging heat with the heat medium a flowing through the heat transfer tube. As a result, most of the moisture in the exhaust gas becomes liquid and drains from the waste water supply duct 67 as drain water. On the other hand, the exhaust gas emitted from the second heat exchanger 63 is further compressed by the second compressor 65, and then cooled to separate the liquefied carbon dioxide. The carbon dioxide separated here is stored in a reservoir (not shown). The exhaust gas exiting the CO ₂ separation means 41 is released into the atmosphere from a chimney (not shown).

  Here, the operation of the heat medium a flowing through the heat medium circulation line 71 which is a characteristic configuration of the present invention will be described.

  First, the heat medium a flowing into the heat transfer tube of the first heat exchanger 29 exchanges heat with the water flowing into the container of the first heat exchanger 29, that is, the condensate discharged from the condenser 25. It is cooled to about 20-40 ° C. at room temperature. Subsequently, the heat medium a is supplied to the second heat exchanger 63 via the circulation pump 73. The heat medium a flowing into the heat transfer tube of the second heat exchanger 63 is compressed by the exhaust gas introduced into the container of the second heat exchanger 63, that is, the first compressor 61, and generates heat (about 130 ° C.). It is heated to about 50 to 70 ° C. by exchanging heat with the exhaust gas.

  The heat medium a heated in the second heat exchanger 63 in this way flows into the heat transfer tube of the third heat exchanger 35, and is exhaust gas introduced into the container of the second heat exchanger 63, that is, A / Heat exchange is performed with the exhaust gas that has come out of H33 and has reached about 160 to 200 ° C, so that it is heated to about 90 to 110 ° C. And the heat medium heated with the 3rd heat exchanger 35 is returned to the heat exchanger tube of the 1st heat exchanger 29, and is cooled to normal temperature again.

  Here, the heat transfer pipe of the third heat exchanger 35 is supplied with the heat medium a that has been heated to about 50 to 70 ° C. by the second heat exchanger 63, and further, in the container of the third heat exchanger 35. Since an exhaust gas of about 160 ° C. to 200 ° C. flows into the heat transfer tube, the temperature of the heat transfer tube surface of the third heat exchanger 35 is maintained at 70 ° C. or higher (for example, 70 to 90 ° C.). Therefore, the temperature of the heat transfer tube surface of the third heat exchanger 35 does not become lower than the water dew point of 70 ° C. of the exhaust gas (moisture concentration 30%) discharged from the oxyfuel boiler 11. Moisture does not condense on the surface of the heat transfer tube, and ash adhering to the surface of the heat transfer tube can be easily removed with a soot blower, so that stable operation can be realized.

  Further, according to the present embodiment, the heat recovered by the heat medium a from the exhaust gas in the second heat exchanger 63 and the third heat exchanger 35 can be used for heating the condensate, thereby improving the thermal efficiency. Can be made.

(Second Embodiment)
Hereinafter, a second embodiment of the exhaust gas treatment system to which the present invention is applied will be described with reference to FIG. In the present embodiment, differences from the first embodiment will be described, and the same components as those in the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

  In the present embodiment, the fourth heat exchanger 75 is installed in the desulfurization liquid stored in the bottom 59 of the absorption tower 55 of the desulfurization apparatus 39, and the heat transfer tube of the first heat exchanger 29 is installed in the heat medium circulation line 71. In the first embodiment, the heat medium a that has passed through the second heat exchanger 75 is guided to the heat transfer tube of the fourth heat exchanger 75 to exchange heat with the desulfurization liquid, and is then guided to the heat transfer tube of the third heat exchanger 35. Different from form. In the present embodiment, another heat medium different from the heat medium a is used as the heat medium flowing through the heat transfer tubes of the second heat exchanger 63.

  That is, the exhaust gas discharged from the oxyfuel boiler has a high moisture concentration of 30%, and the temperature in the absorption tower 55 of the desulfurization apparatus 39 rises to about 70 ° C. Therefore, the fourth heat exchanger 75 Is placed in a desulfurization liquid at about 70 ° C. stored in the bottom 59 in the absorption tower 55, and the normal temperature heat medium a that has passed through the first heat exchanger 29 is guided to the fourth heat exchanger 75, thereby generating heat. The temperature of the medium a can be raised to about 50 to 70 ° C. And the surface temperature of the heat exchanger tube of the 3rd heat exchanger 35 is 70 degreeC or more (for example, 70-90) by guide | inducing the heat medium a heated with this 4th heat exchanger 75 to the 3rd heat exchanger 35. ° C). Therefore, even when configured as in the present embodiment, moisture in the exhaust gas does not condense on the surface of the heat transfer tube of the third heat exchanger 35, so ash adhering to the surface of the heat transfer tube can be easily removed with a soot blower. Therefore, stable operation can be realized.

  Further, the desulfurization performance of the desulfurization apparatus 39 generally tends to decrease as the temperature in the absorption tower increases. However, according to the present embodiment, the temperature of the desulfurization apparatus 39 is recovered by the heat medium a and lowered. Therefore, a decrease in desulfurization performance can be suppressed.

(Third embodiment)
Hereinafter, a third embodiment of the exhaust gas treatment system to which the present invention is applied will be described with reference to FIG. In the present embodiment, differences from the first and second embodiments will be described, and the same configurations as those of the embodiments will be denoted by the same reference numerals and description thereof will be omitted.

  In the present embodiment, the fifth heat exchanger 77 is installed in the flue 43 between the dust collector 37 and the desulfurization device 39, and the heat medium a that has passed through the heat transfer tube of the first heat exchanger 29 in the heat medium circulation line 71. Is guided to the heat transfer tube of the fifth heat exchanger 77 to exchange heat with the exhaust gas, and then is guided to the heat transfer tube of the third heat exchanger 35, which is different from the first embodiment.

  That is, since the temperature of the exhaust gas exiting the dust collector 37 is about 90 to 110 ° C., the fifth heat exchanger 77 is installed in the flue through which the exhaust gas flows, and the normal temperature after passing through the first heat exchanger 29 is reached. By introducing the heat medium a to the fifth heat exchanger 77, the temperature of the heat medium a can be raised to about 50 to 70 ° C. And the heat transfer tube surface temperature of the 3rd heat exchanger 35 is 70 degreeC or more (for example, 70-90 degreeC) by guide | inducing the heat medium a heated with this 5th heat exchanger 77 to the 3rd heat exchanger 35. ). Therefore, even when configured as in the present embodiment, moisture in the exhaust gas does not condense on the surface of the heat transfer tube of the third heat exchanger 35, so ash adhering to the surface of the heat transfer tube can be easily removed with a soot blower. Therefore, stable operation can be realized.

  Moreover, according to this embodiment, since the temperature of the exhaust gas introduced into the desulfurization apparatus 39 can be further lowered, it is possible to suppress a decrease in desulfurization performance. In addition, according to the present embodiment, the heat recovered by the heat medium a from the exhaust gas in the fifth heat exchanger 77 and the third heat exchanger 35 can be used for heating the condensate, so that the thermal efficiency is improved. Can be improved.

As described above, according to the above-described embodiment, the exhaust gas flowing from the inlet side of the dust collector 37 and the heat medium a even in the exhaust gas discharged from the oxyfuel boiler, that is, the exhaust gas having a high moisture concentration or SO ₂ concentration. Since the heat transfer tube surface temperature of the third heat exchanger 35 for exchanging heat with the water can be maintained at 70 ° C. or higher at which water does not condense, adhesion of ash to the heat transfer tube surface can be greatly reduced, and the exhaust gas treatment plant Stable operation becomes possible.

  In addition, said embodiment is only an illustration of this invention, and this invention is not limited only to the structure of these embodiment. For example, with respect to the heat exchangers other than the first heat exchanger 29 and the third heat exchanger 35 in the heat medium circulation line 71, the above-described implementation is performed within a range in which condensation does not occur on the heat transfer tube surface of the third heat exchanger 35. You may make it comprise combining the structure of the heat exchanger of a form suitably.

  In order to more reliably prevent the occurrence of condensation on the surface of the heat transfer tube without being affected by the temperature change of the exhaust gas flowing through the third heat exchanger 35, the heat introduced into the heat transfer tube of the third heat exchanger 35 is It is effective to set the temperature of the medium a to be 70 ° C. or higher, more preferably 80 ° C. or higher. In order to set the temperature of the heat medium a in this way, the heat exchange amount and the like may be adjusted by a known method for heat exchangers other than the third heat exchanger 35.

DESCRIPTION OF SYMBOLS 11 Boiler 13 Heat exchanger for steam generation 15 Steam turbine 17 Steam circulation line 19 Exhaust gas treatment line 21 Exhaust gas circulation duct 25 Condenser 27 Booster pump 29 1st heat exchanger 35 3rd heat exchanger 37 Dust collector 39 Desulfurizer 41 CO ₂ Separation means 59 Bottom 63 Second heat exchanger 71 Heat medium circulation line 75 Fourth heat exchanger 77 Fifth heat exchanger

Claims (4)

A boiler that burns fuel with a combustion gas in which oxygen-rich gas and circulating exhaust gas are mixed, and steam that is generated by a steam generation heat exchanger provided in the boiler is supplied to the steam turbine to generate power, and the steam turbine A steam circulation line that cools the steam discharged from the steam and returns it to the heat exchanger for steam generation, an exhaust gas treatment line that treats exhaust gas generated from the boiler, and a downstream of a dust collector provided in the exhaust gas treatment line In an exhaust gas treatment system comprising an exhaust gas circulation line for extracting a part of the exhaust gas and leading it to the boiler,
Provided between a condenser for cooling the steam discharged from the steam turbine in the steam circulation line and the heat generating heat exchanger, and heat exchange between the water exiting the condenser and the heat medium. A first heat exchanger;
A second heat exchanger for exchanging heat between the exhaust gas generated by compressing the exhaust gas flowing downstream of the dust collector of the exhaust gas treatment line and the heat medium;
A third heat exchanger provided on the inlet side of the dust collector of the exhaust gas treatment line, for exchanging heat between the exhaust gas flowing through the inlet side and the heat medium;
The heat medium cooled by the first heat exchanger is led to the second heat exchanger and heated, the heated heat medium is led to the third heat exchanger and further heated, and this heated An exhaust gas treatment system, wherein the heat medium is returned to the first heat exchanger.   The exhaust gas treatment system according to claim 1, wherein the temperature of the heat medium introduced into the third heat exchanger is set to be 70 ° C or higher. A boiler that burns fuel with a combustion gas in which oxygen-rich gas and circulating exhaust gas are mixed, and steam that is generated by a steam generation heat exchanger provided in the boiler is supplied to the steam turbine to generate power, and the steam turbine A steam circulation line that cools the steam discharged from the steam and returns it to the heat exchanger for steam generation, an exhaust gas treatment line that treats exhaust gas generated from the boiler, and a downstream of a dust collector provided in the exhaust gas treatment line In an exhaust gas treatment system comprising an exhaust gas circulation line for extracting a part of the exhaust gas and leading it to the boiler,
Provided between a condenser for cooling the steam discharged from the steam turbine in the steam circulation line and the heat generating heat exchanger, and heat exchange between the water exiting the condenser and the heat medium. A first heat exchanger;
A second heat exchanger for exchanging heat between the desulfurization liquid stored in the bottom of a wet desulfurization device provided on the downstream side of the dust collector in the exhaust gas treatment line, and the heat medium;
A third heat exchanger provided on the inlet side of the dust collector of the exhaust gas treatment line, for exchanging heat between the exhaust gas flowing through the inlet side and the heat medium;
The heat medium cooled by the first heat exchanger is led to the second heat exchanger and heated, the heated heat medium is led to the third heat exchanger and further heated, and this heated An exhaust gas treatment system, wherein the heat medium is returned to the first heat exchanger. A boiler that burns fuel with a combustion gas in which oxygen-rich gas and circulating exhaust gas are mixed, and steam that is generated by a steam generation heat exchanger provided in the boiler is supplied to the steam turbine to generate power, and the steam turbine A steam circulation line that cools the steam discharged from the steam and returns it to the heat exchanger for steam generation, an exhaust gas treatment line that treats exhaust gas generated from the boiler, and a downstream of a dust collector provided in the exhaust gas treatment line In an exhaust gas treatment system comprising an exhaust gas circulation line for extracting a part of the exhaust gas and leading it to the boiler,
Provided between a condenser for cooling the steam discharged from the steam turbine in the steam circulation line and the heat generating heat exchanger, and heat exchange between the water exiting the condenser and the heat medium. A first heat exchanger;
A second heat exchanger for exchanging heat between the exhaust gas flowing between the dust collector of the exhaust gas treatment line and a wet desulfurization device provided downstream thereof, and the heat medium;
A third heat exchanger provided on the inlet side of the dust collector of the exhaust gas treatment line, for exchanging heat between the exhaust gas flowing through the inlet side and the heat medium;
The heat medium cooled by the first heat exchanger is led to the second heat exchanger and heated, the heated heat medium is led to the third heat exchanger and further heated, and this heated An exhaust gas treatment system, wherein the heat medium is returned to the first heat exchanger.

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