WO2016133116A1 - Exhaust gas heat recovery system - Google Patents

Abstract

An exhaust gas heat recovery system is provided with: a furnace (11); a combustion device (12); a flue (13); a heat exchange unit (14); a heat recovery unit (71) that is provided further downstream than the heat exchanging unit (14) in the flue (13) and recovers heat from exhaust gas and for which the cross-sectional area of an outlet (73B) is smaller than the cross-sectional area of an inlet (72A); and a first heat exchanger (74) that heats air for combustion with the heat recovered from the heat recovery unit (71).

Description

Exhaust gas heat recovery system

The present invention relates to an exhaust gas heat recovery system that recovers heat of exhaust gas discharged from a boiler that generates steam by burning fuel and air.

For example, in a coal fired boiler, a plurality of combustion burners are arranged at the lower part of a furnace that is vertically formed and has a hollow shape, and a flue is connected to the upper part to recover the heat of exhaust gas in this flue. The heat exchanger is provided. And steam can be produced | generated by heating water with the waste gas generated by combustion in a furnace. The coal-fired boiler has a gas duct connected to the flue, and an air heater is provided in the gas duct. This air heater generates heated air by heating air with exhaust gas, and supplies this heated air as combustion air to a combustion burner.

This air heater performs heat exchange by rotating a heat element with respect to an exhaust gas passage and an air passage to alternately contact the exhaust gas and air, and heats the air with the exhaust gas to generate heated air. By the way, the exhaust gas discharged from the boiler contains a corrosive substance such as sulfurous acid (SO ₃ ), and the amount of heat recovered by the air heater is limited so that the sulfurous acid does not condense and become sulfuric acid. In addition, even if heat recovery is not performed to a temperature at which sulfurous acid is not condensed by the air heater, the air heater performs heat exchange by rotating the heat element, so that there is a region where the sulfurous acid decreases to the condensation temperature. End up. As a result, the heat element in the air heater may be corroded or blocked.

A coal fired boiler in which a heat recovery unit is provided instead of a rotary air heater is described in, for example, Patent Document 1 below. This heat recovery unit has a high-temperature loop and a low-temperature loop. A high-temperature heat medium circulates in the high-temperature loop, the combustion air is preheated by heat recovered from the exhaust gas, and a low-temperature heat medium circulates in the low-temperature loop. The combustion air is preheated by the heat recovered from the exhaust gas, the exhaust gas is reheated, and the boiler feed water is preheated.

JP 63-217103 A

The above-described heat recovery unit heats the heat medium using the heat of the exhaust gas, and heats the combustion air, the exhaust gas, and the boiler feed water with the heated heat medium. In this case, since the temperature of the exhaust gas at the inlet is 300 ° C. or higher and the temperature of the exhaust gas at the outlet is lowered to 100 ° C. or lower, the internal temperature change is 200 ° C. or higher. Therefore, in the heat recovery device, the volume of the exhaust gas passing through the inside greatly changes (decreases), and the flow velocity also changes (decreases). As a result, the heat recovery unit has a high exhaust gas flow rate at the inlet, which causes wear of the heat transfer tubes and a low exhaust gas flow rate at the outlet, which reduces heat exchange performance and accumulates dust and the like. End up.

The present invention solves the above-described problems, and an object thereof is to provide an exhaust gas heat recovery system that improves durability and improves heat recovery efficiency.

In order to achieve the above object, an exhaust gas heat recovery system according to the present invention comprises a furnace having a hollow shape and installed along a vertical direction, and a fuel gas mixed with fuel and combustion air directed toward the furnace. A combustion burner to be blown in, an exhaust gas passage connected to an upper portion of the furnace, a heat exchange portion provided in the exhaust gas passage for exchanging heat between the exhaust gas and water, and downstream of the heat exchange portion in the exhaust gas passage And a first heat exchanger that heats the combustion air by the heat recovered by the heat recovery unit, the heat recovery unit including the heat recovery unit The passage sectional area of the outlet portion is set smaller than the passage sectional area of the inlet portion.

Therefore, when the exhaust gas passes through the heat recovery section, the heat medium recovers the heat of the exhaust gas, so that the exhaust gas is reduced in volume and temperature. However, in the heat recovery section, the passage sectional area of the outlet portion is set smaller than the passage sectional area of the inlet portion. Therefore, when the exhaust gas having a large volume passes through the inlet portion, the flow rate of the exhaust gas does not increase, and when the exhaust gas having a small volume passes through the outlet portion, the flow rate of the exhaust gas decreases. Absent. That is, when the exhaust gas passes through the heat recovery section, even if the temperature decreases and the volume decreases, fluctuations in the flow rate are suppressed. As a result, wear of the heat transfer tubes constituting the heat recovery section is suppressed, and a decrease in heat exchange performance is suppressed, whereby durability can be improved and heat recovery efficiency can be improved.

In the exhaust gas heat recovery system of the present invention, the heat recovery part is characterized in that the inner dimension of the outlet part is set smaller than the inner dimension of the inlet part in the exhaust gas passage.

Therefore, even if the exhaust gas passes through the heat recovery unit with a simple configuration in which the inner size of the outlet unit is set smaller than the inner size of the inlet unit of the heat recovery unit, even if the temperature decreases and the volume decreases. , Fluctuations in flow velocity are suppressed. As a result, wear of the heat transfer tubes constituting the heat recovery section is suppressed, and heat can be efficiently recovered downstream from low-temperature exhaust gas heat-exchanged upstream.

In the exhaust gas heat recovery system of the present invention, the heat recovery unit is set to have a higher density of heat transfer tubes or heat transfer fins at the outlet than the density of heat transfer tubes or heat transfer fins at the inlet. It is characterized by.

Therefore, without changing the configuration of the exhaust gas passage, the exhaust gas is heat recovered with a simple configuration in which the arrangement, shape, number, etc. of the heat transfer tubes or heat transfer fins are changed at the inlet and outlet of the heat recovery unit. Even when the temperature decreases and the volume decreases when passing through the section, fluctuations in the flow velocity are suppressed. As a result, wear of the heat transfer tubes constituting the heat recovery section is suppressed, and heat can be efficiently recovered downstream from low-temperature exhaust gas heat-exchanged upstream.

In the exhaust gas heat recovery system of the present invention, the heat recovery part has an upstream high temperature part and a downstream low temperature part, and a passage sectional area of the low temperature part is smaller than a passage sectional area of the high temperature part. It is characterized by being set.

Therefore, when the exhaust gas passes through the heat recovery unit with a simple configuration in which the heat recovery unit is configured by the high temperature part and the low temperature part, and the passage cross sectional area of the low temperature part is set smaller than the passage cross sectional area of the high temperature part, Even if the temperature decreases and the volume decreases, fluctuations in the flow rate are suppressed. As a result, wear of the heat transfer tubes constituting the heat recovery section is suppressed, and heat can be efficiently recovered downstream from low-temperature exhaust gas heat-exchanged upstream.

In the exhaust gas heat recovery system of the present invention, the exhaust gas passage includes a vertical passage along a vertical direction and a horizontal passage connected to a lower portion of the vertical passage and along a horizontal direction, and the high temperature portion includes the vertical passage. The low temperature part is arranged in the horizontal passage.

Therefore, by arranging the high temperature part in the vertical passage and the low temperature part in the horizontal passage, the exhaust gas heat recovery system can be configured with a simple structure without changing the configuration of the existing exhaust gas passage such as the vertical passage and the horizontal passage. As a result, wear of the heat transfer tubes constituting the heat recovery section can be suppressed, and heat can be efficiently recovered on the downstream side even from low-temperature exhaust gas heat-exchanged on the upstream side.

In the exhaust gas heat recovery system of the present invention, a denitration device is provided, and the high temperature portion is disposed below the denitration device.

Therefore, by disposing the high-temperature part downstream of the exhaust gas flow in the denitration device, the exhaust gas flows into the high-temperature part after the harmful substances are removed by the denitration device, preventing the attachment of harmful substances to the heat recovery unit. can do.

The exhaust gas heat recovery system of the present invention is characterized in that a hopper is provided between the vertical passage and the horizontal passage and below the high temperature portion.

Therefore, by providing a hopper below the high temperature part, particles such as dust contained in the exhaust gas can be collected between the vertical passage and the horizontal passage.

In the exhaust gas heat recovery system of the present invention, a second heat exchanger is provided which is provided downstream from the heat recovery unit and reheats the exhaust gas before being discharged from the chimney by the heat recovered by the heat recovery unit. It is characterized by.

Therefore, the second heat exchanger can prevent white smoke by reheating the exhaust gas with the heat recovered by the heat recovery unit.

The exhaust gas heat recovery system of the present invention is characterized in that a third heat exchanger is provided for heating water supplied to the heat exchange unit by heat recovered by the heat recovery unit.

Therefore, the third heat exchanger can effectively use the recovered heat by heating the water supplied to the heat exchange part with the heat recovered by the heat recovery part.

In the exhaust gas heat recovery system of the present invention, there is provided a distribution amount adjusting device that adjusts a distribution amount of the heat medium supplied from the heat recovery unit to the first heat exchanger, the second heat exchanger, and the third heat exchanger. It is characterized by being provided.

Accordingly, the distribution amount adjusting device should use the heat recovered from the exhaust gas as an environmental measure by adjusting the distribution amount of the heat medium supplied from the heat recovery unit to each heat exchanger according to the operating state of the boiler. While maintaining the amount of heat, the remaining recovered heat can be used to improve power generation efficiency and the boiler can be operated properly.

According to the exhaust gas heat recovery system of the present invention, since the heat of the exhaust gas is recovered in the exhaust gas passage and the heat recovery section in which the passage sectional area of the outlet portion is set smaller than the passage sectional area of the inlet portion is provided, durability As well as improving heat recovery efficiency.

FIG. 1 is a schematic configuration diagram illustrating a boiler to which the exhaust gas heat recovery system of the first embodiment is applied. FIG. 2 is a schematic diagram showing the flow of water (steam) and the heat medium in the exhaust gas heat recovery system. FIG. 3 is a schematic diagram illustrating a heat recovery unit and a heat exchanger. FIG. 4 is a schematic diagram illustrating the configuration of the heat recovery unit. FIG. 5 is a schematic diagram illustrating a heat recovery unit and a heat exchanger in the exhaust gas heat recovery system of the second embodiment. FIG. 6 is a schematic diagram illustrating a heat recovery unit and a heat exchanger in the exhaust gas heat recovery system of the third embodiment. FIG. 7 is a schematic diagram illustrating a heat recovery unit and a heat exchanger in the exhaust gas heat recovery system of the fourth embodiment. FIG. 8 is a schematic configuration diagram illustrating a heat recovery unit in the exhaust gas heat recovery system of the fifth embodiment. FIG. 9 is a schematic diagram illustrating the fin tube of the heat recovery unit. FIG. 10 is a schematic diagram illustrating a heat recovery unit and a heat exchanger in the exhaust gas heat recovery system of the sixth embodiment.

Hereinafter, preferred embodiments of an exhaust gas heat recovery system according to the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this embodiment, and when there are two or more embodiments, what comprises combining each embodiment is also included.

[First Embodiment]
FIG. 1 is a schematic configuration diagram illustrating a boiler to which the exhaust gas heat recovery system of the first embodiment is applied.

The boiler provided with the exhaust gas heat recovery system of the first embodiment is a coal-fired boiler, in which pulverized coal obtained by pulverizing coal is used as pulverized fuel (fuel), and this pulverized fuel is burned by a combustion burner. The exhaust gas heat recovery system recovers heat generated by this combustion.

In the first embodiment, as shown in FIG. 1, the boiler 10 is a conventional boiler, and includes a furnace 11, a combustion device 12, a flue (exhaust gas passage) 13, and a heat exchange unit 14. Yes. First, the overall configuration of the boiler 10 will be described.

The furnace 11 has a rectangular hollow shape and is installed along the vertical direction. The furnace wall constituting the furnace 11 is constituted by a heat transfer tube.

The combustion device 12 is provided at the lower part of the furnace wall constituting the furnace 11. The combustion apparatus 12 has a plurality of stages of combustion burners 21, 22, 23, 24, 25 mounted on the furnace wall. In this embodiment, each of the combustion burners 21, 22, 23, 24, 25 is arranged as four sets at equal intervals along the circumferential direction, and 5 sets along the vertical direction, that is, Five stages are arranged. However, the shape of the furnace 11, the number of combustion burners in one stage, the number of stages of combustion burners, etc. are not limited to this embodiment, and may be set as appropriate.

Combustion burners 21, 22, 23, 24 and 25 use pulverized coal obtained by pulverizing coal as solid fuel. The combustion burners 21, 22, 23, 24, 25 are connected to pulverized coal machines (pulverizers, mills) 31, 32, 33, 34, 35 via pulverized coal supply pipes 26, 27, 28, 29, 30. ing. Although not shown, the pulverized coal machines 31, 32, 33, 34, and 35 are pulverized to a predetermined size when coal is introduced between a plurality of pulverization rollers and a pulverization table. The pulverized coal pulverized here is classified by the conveying air (primary air) and then supplied to the combustion burners 21, 22, 23, 24, 25 through the pulverized coal supply pipes 26, 27, 28, 29, 30. Is done.

The furnace 11 is provided with a wind box 36 at the mounting position of each combustion burner 21, 22, 23, 24, 25. Further, the furnace 11 is provided with an additional air nozzle 37 on the furnace wall above the mounting positions of the combustion burners 21, 22, 23, 24, 25. The air duct 38 is connected to a blower 39 at one end, and is connected to the additional air nozzle 37 while the other end is connected to the wind box 36. Therefore, the combustion air (secondary air) sent by the blower 39 is supplied to the wind box 36 by the air duct 38, and is supplied from the wind box 36 to the combustion burners 21, 22, 23, 24, 25. At the same time, the air is supplied to the additional air nozzle 37 by the air duct 38.

The furnace 11 has a flue 13 connected to an upper portion thereof, and the flue 13 is connected to an upper end portion of the furnace 11 and a first horizontal passage 41 connected to an end portion of the first horizontal passage 41. The vertical passage 42, the second horizontal passage 43 connected to the lower end of the first vertical passage 42, the second vertical passage 44 connected to the end of the second horizontal passage 43, and the end of the second vertical passage 45 It is comprised from the gas duct 45 connected with a part.

In the flue 13, a heat exchanging unit 14 that performs heat exchange between exhaust gas generated by combustion in the furnace 11 and water (steam) flowing in the heat transfer pipe is provided in the first horizontal passage 41 and the first vertical passage 42. Is provided. The heat exchanging unit 14 includes superheaters (super heaters) 46, 47, 48, reheaters (reheaters) 49, 50, and economizers 51, 52.

The flue 13 is provided with a denitration device (selective reduction catalyst) 61 in the second vertical passage 44. The denitration device 61 decomposes nitrogen oxide (NOx) in exhaust gas into harmless nitrogen and water vapor by the action of a catalyst with a reducing agent (for example, ammonia).

In the flue 13, an electric dust collector 62, an induction blower 63, a desulfurization device 64, and a chimney 65 are provided in the gas duct 45. The electric dust collector 62 collects dust by applying electric charges to various dust particles contained in the exhaust gas and drawing them to the dust collecting electrode. The desulfurization device 64 is a wet desulfurization device, and absorbs and removes sulfurous acid gas in the exhaust gas by injecting an absorbing liquid into contact with the exhaust gas flowing into the absorption tower.

The boiler 10 of this embodiment is provided with a heat recovery unit 71 that recovers the heat of exhaust gas downstream of the heat exchange unit 14 in the flue 13. The heat recovery unit 71 includes an upstream high temperature part 72 and a downstream low temperature part 73, and the high temperature part 72 and the low temperature part 73 are directly connected by a heat transfer tube. And the boiler 10 has the 1st heat exchanger 74 which heats combustion air with the heat | fever collect | recovered by this heat recovery part 71. FIG. That is, the heat recovery unit 71 and the first heat exchanger 74 are provided with a heat medium circulation passage 75 that circulates a heat medium (for example, water, steam) between them, and the heat medium circulation passage 75 is connected to the first heat exchanger 72 from the high temperature portion 72. A pump 76 for circulating a heat medium through the second circulation passage 75b, which includes a first circulation passage 75a leading to the first heat exchanger 74 and a second circulation passage 75b extending from the first heat exchanger 74 to the low temperature section 73. Is provided.

Further, the boiler 10 is provided with a second heat exchanger 77 that reheats the exhaust gas before being discharged from the chimney 65 by the heat recovered by the heat recovery unit 71. Furthermore, the boiler 10 is provided with a third heat exchanger 78 (see FIG. 2) described later that heats the feed water supplied to the economizers 51 and 52 of the heat exchange unit 14 by the heat recovered by the heat recovery unit 71. It has been.

Therefore, when the pulverized coal machines 31, 32, 33, 34, and 35 are driven, the coal is pulverized to generate pulverized coal, and the combustion burner 21 is supplied from the pulverized coal supply pipes 26, 27, 28, 29, and 30 by the conveying air. , 22, 23, 24, 25. The combustion air heated by the first heat exchanger 74 is supplied from the air duct 38 to the combustion burners 21, 22, 23, 24, 25 through the wind box 36 and to the additional air nozzle 37. Supplied. Then, the combustion burners 21, 22, 23, 24, and 25 blow a pulverized coal mixture, which is a mixture of pulverized coal and carrier air, into the furnace 11 and blow combustion air into the furnace 11 and ignite at this time. To form a flame. Further, the additional air nozzle 37 blows additional air into the furnace 11 to perform combustion control, thereby reducing NOx generated by the combustion of pulverized coal. Thereafter, NOx is removed from the exhaust gas that has passed through the heat exchanger 14 of the flue 13 by the denitration device 61, particulate matter is removed by the electrostatic precipitator 62, SOx is removed by the desulfurization device 64, and then from the chimney 65. Released into the atmosphere.

Next, the flow of water (steam) and heat medium in the exhaust gas heat recovery system will be described. FIG. 2 is a schematic diagram illustrating flows of water and a heat medium in the exhaust gas heat recovery system, and FIG. 3 is a schematic diagram illustrating a heat recovery unit and a heat exchanger.

As shown in FIGS. 2 and 3, the heat recovery unit 71 includes a high-temperature unit 72 and a low-temperature unit 73, and the high-temperature unit 72 and the low-temperature unit 73 have heat transfer tubes 72 a and 73 a disposed therein, and one end portions thereof Are connected. The first heat exchanger 74 has a heat transfer tube 74a disposed therein, the other end of the heat transfer tube 72a and one end of the heat transfer tube 74a are connected by a first circulation passage 75a, and the other end of the heat transfer tube 73a is transferred to the first heat exchanger 74a. The other end of the heat pipe 74a is connected by a second circulation passage 75b, and a pump 76 is provided in the second circulation passage 75b.

The second heat exchanger 77 has a heat transfer tube 77a disposed therein, a first branch passage 81a branched from the first circulation passage 75a is connected to one end of the heat transfer tube 77a, and a second branch branched from the second circulation passage 75b. A two-branch passage 81b is connected to the other end of the heat transfer tube 77a. The third heat exchanger 78 has a heat transfer tube 78a disposed therein, a third branch passage 82a branched from the first branch passage 81a is connected to one end of the heat transfer tube 78a, and a second branch passage 81b branched from the second branch passage 81b. A four branch passage 82b is connected to the other end of the heat transfer tube 78a.

Further, the steam turbine 91 operated by steam generated by the boiler has a high pressure turbine 92 and a low pressure turbine 93. A water / steam circulation passage 94 for circulating water and steam is provided between the heat exchange unit 14 (see FIG. 1) of the boiler 10 and the steam turbine 91. The water / steam circulation passage 94 includes superheaters 46, 47, 48, a high pressure turbine 92, reheaters 49, 50, a low pressure turbine 93, a condenser 95, a third heat exchanger 78, a deaerator 96, and water supply. The pump 97 and the economizers 51 and 52 are provided in this order.

Therefore, when the exhaust gas flows through the flue 13, the exhaust gas (300 ° C. to 400 ° C.) sequentially flows through the high temperature portion 72 and the low temperature portion 73 of the heat recovery unit 71, and the heat recovery unit 71 transfers the heat of the exhaust gas to the heat medium. To collect. That is, the heat medium (65 ° C. to 100 ° C.) is circulated through the heat medium circulation passage 75 by the pump 76, whereby the heat medium is heated by the heat of the exhaust gas. A part of the high-temperature heat medium (100 ° C. to 350 ° C.) is supplied to the first heat exchanger 74, so that the heat medium circulating in the heat medium circulation passage 75 and the air flowing through the air duct 38 are separated. Heat exchange is performed, and the air is heated by a heat medium to form high-temperature air, and this high-temperature air is sent to the combustion device 12 (see FIG. 1) as combustion air (200 ° C. to 330 ° C.).

Further, a part of the high-temperature heat medium generated in the heat recovery unit 71 is supplied to the second heat exchanger 77, so that the high-temperature heat medium and the exhaust gas discharged from the desulfurization apparatus 64 (40 ° C. to 70 ° C.). Exhaust gas (80 ° C. to 100 ° C.) reheated by the heat medium is sent to the chimney 65. Furthermore, a part of the high-temperature heat medium generated in the heat recovery unit 71 is supplied to the third heat exchanger 78, so that the high-temperature heat medium and water flowing through the water / steam circulation passage 94 (30 ° C. to 30 ° C.) The water is heated by a heat medium to become high-temperature water (60 ° C. to 100 ° C.), and this high-temperature water is sent to the economizers 51 and 52.

On the other hand, the water supplied from the water supply pump 97 is preheated by the economizers 51 and 52, then supplied to a steam drum (not shown), and heated to become saturated steam while being supplied to each heat transfer tube on the furnace wall. , Sent to the steam drum. The saturated steam of the steam drum is introduced into the superheaters 46, 47 and 48 and is superheated by the exhaust gas. The superheated steam generated by the superheaters 46, 47 and 48 is supplied to the high pressure turbine 92 and drives the high pressure turbine 92. The steam discharged from the high-pressure turbine 92 is introduced into the reheaters 49 and 50 and superheated again, and then supplied to the low-pressure turbine 93 to drive the low-pressure turbine 93. The steam discharged from the low-pressure turbine 93 is cooled by the condenser 95 to become condensed water, and after being heated by the third heat exchanger 78, the remaining oxygen is removed by the deaerator 96, Returned to economizers 51 and 52.

In the above description, the third heat exchanger 78 is assumed to heat the water supplied to the economizers 51 and 52 of the heat exchanging unit 14 by the heat recovered by the heat recovering unit 71, and the heat transfer tube 78a. However, the present invention is not limited to this configuration. As shown in FIG. 3, the third heat exchanger 79 is configured to heat the feed water supplied to the economizers 51 and 52 of the heat exchange unit 14 by the heat recovered by the heat recovery unit 71. The water / steam circulation passage 94 may be connected to the 82a and the fourth branch passage 82b.

Here, the heat recovery unit 71 will be described in detail. FIG. 4 is a schematic diagram illustrating the configuration of the heat recovery unit.

As shown in FIG. 4, the heat recovery part 71 has a high temperature part 72 and a low temperature part 73, the high temperature part 72 is disposed in the second vertical passage (vertical passage) 44, and the low temperature part 73 is a gas duct. (Horizontal passage) 45 is arranged. A denitration device 61 is disposed in the second vertical passage 44, and a high temperature portion 72 is disposed below the denitration device 61 by a predetermined distance. The second vertical passage 44 is connected to the base end portion of the gas duct 45 so that the lower portion is bent at a right angle, and a hopper 66 is provided at the connecting portion (bending portion) between the second vertical passage 44 and the gas duct 45. . The hopper 66 is disposed below the denitration device 61 and the high temperature part 72 and on the side of the low temperature part 73.

In the heat recovery unit 71, the passage sectional area of the outlet part is set smaller than the passage sectional area of the inlet part. That is, the high temperature part 72 located in the second vertical passage 44 is provided with an inlet part 72A at the upper part and an outlet part 72B at the lower part. The low temperature part 73 is provided with an inlet 73A at one end and an outlet 73B at the other end. That is, since the heat recovery unit 71 includes the high temperature part 72 and the low temperature part 73, the inlet part of the heat recovery part 71 is the inlet part 72A of the high temperature part 72 and the outlet part of the heat recovery part 71. Is the exit part 73 </ b> B of the low temperature part 73.

Here, the passage cross-sectional area is an area where the exhaust gas can flow in a cross section obtained by cutting the second vertical passage 44 or the gas duct 45 in the flue 13 perpendicular to the flow direction of the exhaust gas. Specifically, the cross section is obtained by cutting the second vertical passage 44 or the gas duct 45 perpendicularly to the flow direction of the exhaust gas and excluding the portion blocked by the heat transfer tubes or fins.

Specifically, in the heat recovery part 71, the inner dimension of the outlet part 73B is set smaller than the inner dimension of the inlet part 72A in the flue 13. The second vertical passage 44 and the gas duct 45 are formed by a box-shaped casing having a rectangular cross section. The high temperature portion 72 includes a heat transfer tube 72a therein, and the low temperature portion 73 includes a heat transfer tube 73a therein. Is arranged. The inner dimension of the gas duct 45 is set smaller than the inner dimension of the second vertical passage 44. Here, in the high temperature part 72 and the low temperature part 73, the heat transfer tubes 72a and 73a are set to have the same density. That is, the heat transfer tubes 72a and 73a are bent so that a plurality of pipes are curved, and are arranged adjacent to each other with a predetermined interval, and the intervals between the pipes are the same.

Here, the inner dimension is an inner area of the second vertical passage 44 or the gas duct 45 in the flue 13. If the cross-sectional shape of the second vertical passage 44 or the gas duct 45 is rectangular, the cross-sectional shape of the second vertical passage 44 or the gas duct 45 is a circular area. For example, the area is calculated by diameter × circumferential ratio. That is, it is an area that does not consider a portion blocked by a heat transfer tube or a fin disposed inside the second vertical passage 44 or the gas duct 45.

Therefore, the exhaust gas that has passed through the denitration device 61 in the second vertical passage 44 is a high-temperature exhaust gas of 300 ° C. to 400 ° C., and when the high-temperature exhaust gas passes through the high-temperature portion 72 of the heat recovery unit 71, the heat flowing through the heat transfer tube 72a By heating the medium, the temperature decreases and the volume decreases. In addition, when the exhaust gas that has passed through the high temperature section 72 passes through the low temperature section 73, the volume is reduced while the temperature is decreased by heating the heat medium flowing through the heat transfer tube 73a. The exhaust gas that has passed through the heat recovery section 71 (low temperature section 73) in the gas duct 45 becomes low temperature exhaust gas of 80 ° C. to 120 ° C. On the other hand, the heat medium introduced into the high temperature part 72 of the heat recovery part 71 at 65 ° C. to 100 ° C. is heated to 100 ° C. to 300 ° C. and discharged from the low temperature part 73.

At this time, in the second vertical passage 44, the high-temperature exhaust gas having a large volume passes through the high-temperature section 72 having a large passage cross-sectional area, and in the gas duct 45, the low-temperature exhaust gas having a small volume has a low passage cross-sectional area. It will pass through part 73. Therefore, when the high-temperature exhaust gas having a large volume passes through the high-temperature part 72, the flow rate of the exhaust gas does not increase, and when the low-temperature exhaust gas having a small volume passes through the low-temperature part 73, the exhaust gas The flow rate does not decrease. That is, when the exhaust gas passes through the heat recovery unit 71, even if the temperature gradually decreases and the volume decreases, fluctuations in the flow rate are suppressed, and the flow rate is maintained substantially constant.

As described above, in the exhaust gas heat recovery system of the first embodiment, the furnace 11, the combustion device 12, the flue 13, and the heat exchange unit 14 are provided, and the downstream side of the heat exchange unit 14 in the flue 13. The heat recovery part 71 is provided on the side to recover the heat of the exhaust gas, and the passage sectional area of the outlet part 73B is set smaller than the passage sectional area of the inlet part 72A, and combustion is performed by the heat recovered by the heat recovery part 71 And a first heat exchanger 74 for heating the working air.

Therefore, when the exhaust gas passes through the heat recovery unit 71, even if the temperature decreases and the volume decreases, fluctuations in the flow rate of the exhaust gas are suppressed at the high temperature part 72 and the low temperature part 73. As a result, wear of the heat transfer tubes 72a and 73a constituting the heat recovery unit 71 is suppressed because the flow velocity is not particularly increased.

In the exhaust gas heat recovery system of the first embodiment, the inner dimension of the outlet part 73B is set smaller than the inner dimension of the inlet part 72A of the heat recovery part 71 in the flue 13. Therefore, when the exhaust gas passes through the heat recovery unit 71 with a simple configuration, even if the temperature decreases and the volume decreases, fluctuations in the flow velocity are suppressed. As a result, wear of the heat transfer tubes constituting the heat recovery unit 71 is suppressed, and heat can be efficiently recovered from the low-temperature exhaust gas heat-exchanged on the upstream side.

In the exhaust gas heat recovery system of the first embodiment, as the heat recovery part 71, an upstream high temperature part 72 and a downstream low temperature part 73 are provided, and the passage of the low temperature part 73 with respect to the passage cross-sectional area of the high temperature part 72 is cut off. The area is set small. Therefore, the heat recovery unit 71 is configured by the high temperature unit 72 and the low temperature unit 73, and the gas is recovered from the heat recovery unit 71 with a simple configuration in which the passage sectional area of the low temperature unit 73 is set smaller than the passage sectional area of the high temperature unit 72. Even when the temperature decreases and the volume decreases, the flow rate fluctuations are suppressed. As a result, wear of the heat transfer tubes constituting the heat recovery unit 71 is suppressed, and heat can be efficiently recovered from the low-temperature exhaust gas heat-exchanged on the upstream side.

In the exhaust gas heat recovery system of the first embodiment, as the flue 13, a second vertical passage 44 along the vertical direction and a horizontal gas duct 45 connected to the lower portion of the second vertical passage 44 along the horizontal direction are provided. The high temperature part 72 is arranged in the second vertical passage 44, and the low temperature part 73 is arranged in the gas duct 45. Therefore, in the heat exchanger inlet portion 72A into which the high-temperature exhaust gas easily flows without changing the configuration of the existing flue 13, the low-temperature exhaust gas that suppresses wear of the heat transfer tube and is heat-exchanged on the upstream side. Therefore, it is possible to set the cross-sectional area of the passage so that the exhaust gas flow rate enables efficient heat recovery.

In the exhaust gas heat recovery system of the first embodiment, a denitration device 61 is provided in the second vertical passage 44, and a high temperature section 72 is disposed below the denitration device 61. Accordingly, the exhaust gas flows into the high temperature part 72 after the harmful substances are removed by the denitration device 61, and adhesion of the harmful substances to the heat recovery part 71 can be prevented.

In the exhaust gas heat recovery system of the first embodiment, a hopper 66 is provided between the second vertical passage 44 and the gas duct 45 and below the high temperature portion 72. Therefore, by providing the hopper 66 below the high temperature part 72, particles such as dust contained in the exhaust gas can be collected between the second vertical passage 44 and the gas duct 45.

In the exhaust gas heat recovery system of the first embodiment, a second heat exchanger 77 is provided that reheats the exhaust gas before being discharged from the chimney 65 by the heat recovered by the heat recovery unit 71. Therefore, the 2nd heat exchanger 77 can prevent white smoke by reheating exhaust gas with the heat which heat recovery part 71 collected.

In the exhaust gas heat recovery system of the first embodiment, a third heat exchanger 78 (79) that heats water supplied to the heat exchange unit 14 by heat recovered by the heat recovery unit 71 is provided. Therefore, the third heat exchanger 78 (79) can effectively use the recovered heat by heating the water supplied to the heat exchanging unit 14 with the heat recovered by the heat recovery unit 71.

[Second Embodiment]
FIG. 5 is a schematic diagram illustrating a heat recovery unit and a heat exchanger in the exhaust gas heat recovery system of the second embodiment. In addition, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above, and detailed description is abbreviate | omitted.

As shown in FIG. 5, the exhaust gas heat recovery system of the second embodiment distributes the heat medium supplied from the heat recovery unit 71 to the first heat exchanger 74, the second heat exchanger 77, and the third heat exchanger 78. A distribution amount adjusting device for adjusting the amount is provided.

The heat recovery part 71 has a high temperature part 72 and a low temperature part 73, heat transfer tubes 72a and 73a are arranged inside, and one end parts are connected to each other. A first circulation passage 75a and a second circulation passage 75b are connected to the other end, respectively. The first circulation passage 75a and the second circulation passage 75b are connected by the bypass passage 101, the flow rate adjusting valve 102 is provided in the bypass passage 101, and the low temperature portion 73 side from the connection portion of the bypass passage 101 in the second circulation passage 75b. A flow rate adjustment valve 103 is provided.

The first heat exchanger 74 has a heat transfer tube 74a disposed therein, a first circulation passage 75a is connected to an end of the heat transfer tube 72a, and a flow rate adjustment valve on the first heat exchanger 74 side in the first circulation passage 75a. 104 is provided. The second heat exchanger 77 has a heat transfer tube 77a disposed therein, a first branch passage 81a is connected to an end of the heat transfer tube 77a, and a flow rate adjusting valve on the second heat exchanger 77 side in the first branch passage 81a. 105 is provided. The third heat exchanger 78 has a heat transfer tube 78a disposed therein, a third branch passage 82a is connected to the end of the heat transfer tube 78a, and a flow rate adjustment valve on the third heat exchanger 78 side in the third branch passage 82a. 106 is provided.

Also, a temperature sensor 107 that measures the temperature of the exhaust gas on the outlet portion 73B side of the low temperature portion 73 of the heat recovery portion 71 is provided. A temperature sensor 108 for measuring the temperature of combustion air on the outlet side of the first heat exchanger 74 is provided. A temperature sensor 109 that measures the temperature of the exhaust gas on the outlet side of the second heat exchanger 77 is provided. A temperature sensor 110 that measures the temperature of the heat medium on the outlet side of the second heat exchanger 77 is provided. A temperature sensor 111 that measures the temperature of the feed water on the outlet side of the third heat exchanger 78 is provided.

The control device 100 adjusts the opening degree of the flow rate adjusting valves 102, 103, 104, 105, 106 based on the measurement results of the temperature sensors 107, 108, 109, 110, 111, thereby The distribution amount of the heat medium supplied to the exchangers 74, 77, 78 is adjusted. Basically, the opening degree of the flow rate adjusting valves 102 and 103 is adjusted so that the temperature of the exhaust gas on the outlet 73B side of the heat recovery unit 71 becomes a predetermined temperature (85 ° C. to 120 ° C.), and each heat exchanger 74, The supply amount of the heat medium to 77 and 78 is increased or decreased. In addition, the opening of the flow rate adjustment valve 104 is adjusted so that the temperature of the combustion air on the outlet side of the first heat exchanger 74 becomes a predetermined temperature (200 ° C. to 330 ° C.), Increase or decrease the supply amount of the heat medium. Further, the temperature of the exhaust gas on the outlet side of the second heat exchanger 77 becomes a predetermined temperature (80 ° C. to 100 ° C.), and the temperature of the heat medium on the outlet side of the second heat exchanger 77 becomes a predetermined temperature (80 ° C. to 80 ° C.). The opening degree of the flow rate adjustment valve 105 is adjusted to 95 ° C., and the supply amount of the heat medium to the second heat exchanger 77 is increased or decreased. Supply the heat medium to the third heat exchanger 78 by adjusting the opening of the flow rate adjustment valve 106 so that the temperature of the feed water on the outlet side of the third heat exchanger 78 becomes a predetermined temperature (60 ° C. to 100 ° C.). Increase or decrease the amount.

Thus, in the exhaust gas heat recovery system of the second embodiment, the heat medium supplied from the heat recovery unit 71 to the first heat exchanger 74, the second heat exchanger 77, and the third heat exchanger 78 (79). As the distribution amount adjusting device for adjusting the distribution amount, flow rate adjusting valves 102, 103, 104, 105, and 106, and a control device 100 for controlling the same are provided.

Therefore, the distribution amount adjusting device adjusts the distribution amount of the heat medium supplied from the heat recovery unit 71 to each of the heat exchangers 74, 77, 78 (79) according to the operating state of the boiler 10, thereby reducing the amount of exhaust gas from the exhaust gas. The remaining recovered heat can be used to improve power generation efficiency while maintaining the amount of heat that should be used as an environmental measure.

[Third Embodiment]
FIG. 6 is a schematic diagram illustrating a heat recovery unit and a heat exchanger in the exhaust gas heat recovery system of the third embodiment. In addition, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above, and detailed description is abbreviate | omitted.

As shown in FIG. 6, the exhaust gas heat recovery system of the third embodiment distributes the heat medium supplied from the heat recovery unit 71 to the first heat exchanger 74, the second heat exchanger 77, and the third heat exchanger 78. A distribution amount adjusting device for adjusting the amount is provided.

The first heat exchanger 74 is provided with a bypass passage 121 that connects each end of the heat transfer tube 74a, that is, an inlet portion and an outlet portion, and the bypass passage 121 is provided with a flow rate adjusting valve 122. The second heat exchanger 77 is provided with a bypass passage 123 that connects each end of the heat transfer tube 77 a, that is, an inlet portion and an outlet portion, and a flow rate adjusting valve 124 is provided in the bypass passage 123. The third heat exchanger 78 is provided with a bypass passage 125 that connects each end of the heat transfer tube 78 a, that is, an inlet portion and an outlet portion, and a flow rate adjustment valve 126 is provided in the bypass passage 125.

The control device 100 adjusts the opening degree of the flow rate adjusting valves 122, 124, 126 based on the measurement results of the temperature sensors 107, 108, 109, 110, 111, so that each heat exchanger 74, The distribution amount of the heat medium supplied to 77 and 78 is adjusted. That is, by adjusting the opening degree of the flow rate adjusting valves 122, 124, 126, the flow rate of the heat medium that bypasses the heat exchangers 74, 77, 78 can be adjusted. The adjustment control of the distribution amount of the other heat medium by the control device 100 is the same as in the second embodiment.

Thus, in the exhaust gas heat recovery system of the third embodiment, the distribution amount of the heat medium supplied from the heat recovery unit 71 to the first heat exchanger 74, the second heat exchanger 77, and the third heat exchanger 78. As a distribution amount adjusting device for adjusting the flow rate, there are provided flow rate adjusting valves 102, 103, 104, 105, 106, 122, 124, 126 and a control device 100 for controlling them.

Therefore, the distribution amount adjusting device adjusts the distribution amount of the heat medium supplied from the heat recovery unit 71 to the heat exchangers 74, 77, 78 in accordance with the operating state of the boiler 10, thereby recovering the heat recovered from the exhaust gas. The boiler 10 can be appropriately operated by appropriately using the.

In the exhaust gas heat recovery system of the third embodiment, the heat transfer tubes 74a in the first heat exchanger 74 and the heat transfer tubes in the second heat exchanger 77 are controlled by controlling the opening degree of the flow rate adjusting valves 122, 124, 126. 77a, the flow rate of the heat medium that bypasses the heat transfer tube 78a in the third heat exchanger 78 can be adjusted, and the distribution of the heat medium according to the amount of heat required by each heat exchanger 74, 77, 78 is efficient. Can be implemented.

[Fourth Embodiment]
FIG. 7 is a schematic diagram illustrating a heat recovery unit and a heat exchanger in the exhaust gas heat recovery system of the fourth embodiment. In addition, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above, and detailed description is abbreviate | omitted.

As shown in FIG. 7, the exhaust gas heat recovery system of the fourth embodiment distributes the heat medium supplied from the heat recovery unit 71 to the first heat exchanger 74, the second heat exchanger 77, and the third heat exchanger 78. A distribution amount adjusting device for adjusting the amount is provided.

The first heat exchanger 74 has heat transfer tubes 74a and 74b, the first circulation passage 75a is connected to the end of the heat transfer tube 74a, and the bypass passage 131 branched from the first circulation passage 75a is the heat transfer tubes 74a and 74b. It is connected between. A flow rate adjustment valve 104 is provided in the first circulation passage 75a, and a flow rate adjustment valve 132 is provided in the bypass passage 131. The second heat exchanger 77 has heat transfer tubes 77a and 77b, the first branch passage 81a is connected to the end of the heat transfer tube 77a, and the bypass passage 133 branched from the first branch passage 81a is the heat transfer tubes 77a and 77b. It is connected between. A flow rate adjustment valve 105 is provided in the first branch passage 81a, and a flow rate adjustment valve 134 is provided in the bypass passage 133. The third heat exchanger 78 has heat transfer tubes 78a and 78b, the third branch passage 82a is connected to the end of the heat transfer tube 78a, and the bypass passage 135 branched from the third branch passage 82a is the heat transfer tubes 78a and 78b. It is connected between. A flow rate adjustment valve 106 is provided in the third branch passage 82a, and a flow rate adjustment valve 136 is provided in the bypass passage 135.

The control device 100 adjusts the opening degree of the flow rate adjustment valves 132, 134, and 136 based on the measurement results of the temperature sensors 107, 108, 109, 110, and 111, so that each heat exchanger 74, The distribution amount of the heat medium supplied to 77 and 78 is adjusted. That is, the flow rate of the heat medium that bypasses the heat exchangers 74, 77, 78 can be adjusted by adjusting the opening degree of the flow rate adjustment valves 132, 134, 136. The adjustment control of the distribution amount of the other heat medium by the control device 100 is the same as that in the third embodiment.

Thus, in the exhaust gas heat recovery system of the fourth embodiment, the distribution amount of the heat medium supplied from the heat recovery unit 71 to the first heat exchanger 74, the second heat exchanger 77, and the third heat exchanger 78. As a distribution amount adjusting device for adjusting the flow rate, there are provided flow rate adjusting valves 102, 103, 104, 105, 106, 122, 124, 126, 132, 134, 136 and a control device 100 for controlling the same.

Therefore, the distribution amount adjusting device adjusts the distribution amount of the heat medium supplied from the heat recovery unit 71 to the heat exchangers 74, 77, 78 in accordance with the operating state of the boiler 10, thereby recovering the heat recovered from the exhaust gas. The boiler 10 can be appropriately operated by appropriately using the.

In the exhaust gas heat recovery system of the fourth embodiment, each heat exchanger 74, 77, 78 is made up of two heat transfer tubes 74a, 74b, 77a, 77b, 78a, 78b, and flow rate adjusting valves 132, 134 provided therebetween. , 136 by controlling the opening degree of the heat transfer tubes 74a and 74b in the first heat exchanger 74, the heat transfer tubes 77a and 77b in the second heat exchanger 77, and the heat transfer tubes 78a and 78b in the third heat exchanger 78. The heat medium can be selectively used to adjust the flow rate of the heat medium, and the heat medium can be efficiently distributed according to the amount of heat required by the heat exchangers 74, 77, and 78.

[Fifth Embodiment]
FIG. 8 is a schematic configuration diagram illustrating a heat recovery unit in the exhaust gas heat recovery system of the fifth embodiment, and FIG. 9 is a schematic diagram illustrating a fin tube of the heat recovery unit. In addition, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above, and detailed description is abbreviate | omitted.

In the exhaust gas heat recovery system of the fifth embodiment, as shown in FIG. 8, in the heat recovery unit 140, the passage sectional area of the outlet part 140B is set smaller than the passage sectional area of the inlet part 140A. Specifically, the heat recovery unit 140 is provided in the gas duct 45 in the flue 13, and the heat transfer tube 140 a or the heat transfer in the outlet unit 140 B with respect to the density of the heat transfer tubes 140 a or the heat transfer fins 140 b in the inlet unit 140 A The degree of density of the fins 140b is set high.

For example, as shown in FIG. 9, in the heat recovery unit 140, the heat transfer fins 140b are set to have a high density from the inlet 140A to the outlet 140B. Here, the heat transfer tubes 140a are bent so that a plurality of pipes are bent, and are arranged adjacent to each other with a predetermined interval, and the intervals between the pipes are the same. On the other hand, the heat transfer fins 140b are fixed to the outer peripheral portion of the heat transfer tube 140a, and the distance between the heat transfer fins 140b decreases from the inlet portion 140A toward the outlet portion 140B, and the number thereof increases. Yes. Then, the heat transfer fin 140b partially closes the gas duct 45, so that the heat recovery unit 140 has a reduced exhaust gas passage cross-sectional area from the inlet 140A to the outlet 140B.

Therefore, when the high-temperature exhaust gas passes through the heat recovery unit 140, by heating the heat medium flowing through the heat transfer tube 140a, the temperature decreases and the volume decreases, and the exhaust gas that has passed through the heat recovery unit 140 becomes low-temperature exhaust gas. Become. At this time, the exhaust gas having a large volume at a high temperature passes through a large passage cross-sectional area on the inlet portion 140A side, and the exhaust gas having a small volume at a low temperature passes through a small passage sectional area on the outlet portion 140B side. Therefore, when the high-temperature exhaust gas having a large volume passes through the inlet portion 140A side, the flow rate of the exhaust gas does not increase, and when the low-temperature exhaust gas having a small volume passes through the outlet portion 140B side, The flow rate of the exhaust gas does not decrease. That is, when the exhaust gas passes through the heat recovery unit 140, even if the temperature gradually decreases and the volume decreases, fluctuations in the flow velocity are suppressed.

Thus, in the exhaust gas heat recovery system of the fifth embodiment, in the heat recovery unit 140, the heat transfer tube 140a in the outlet portion 140B is compared with the degree of density of the heat transfer tubes 140a or the heat transfer fins 140b in the inlet portion 140A. Alternatively, the density of the heat transfer fins 140b is set high.

Therefore, a simple configuration in which the arrangement, shape, number, etc., of the heat transfer tubes 140a or the heat transfer fins 140b are changed at the inlet portion 140A and the outlet portion 140B of the heat recovery unit 140 without changing the configuration of the flue 13. Thus, when the exhaust gas passes through the heat recovery unit 140, even if the temperature decreases and the volume decreases, fluctuations in the flow rate are suppressed. As a result, wear of the heat transfer tube 140a constituting the heat recovery unit 140 is suppressed, and heat can be efficiently recovered downstream from low-temperature exhaust gas heat-exchanged upstream.

[Sixth Embodiment]
FIG. 10 is a schematic diagram illustrating a heat recovery unit and a heat exchanger in the exhaust gas heat recovery system of the sixth embodiment. In addition, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above, and detailed description is abbreviate | omitted.

As shown in FIG. 10, the exhaust gas heat recovery system of the sixth embodiment includes a heat recovery unit 71 that has a high temperature part 72 and a low temperature part 73 to recover the heat of exhaust gas, and heat recovered by the heat recovery part 71. The first heat exchanger 74 that heats the combustion air, the second heat exchanger 77 that reheats the exhaust gas discharged from the chimney 65 by the heat recovered by the heat recovery unit 71, and the heat recovered by the heat recovery unit 71 And a third heat exchanger 78 that heats the feed water supplied to the economizers 51 and 52 of the heat exchanging unit 14.

As shown in FIG. 10, in the heat recovery unit 71, the end of the heat transfer tube 72a is connected to one end of the heat transfer tube 74a of the first heat exchanger 74 by the first circulation passage 75a. In the first heat exchanger 74, the other end of the heat transfer tube 74 a is connected to one end of the heat transfer tube 77 a of the second heat exchanger 77 through the first connection passage 151. In the second heat exchanger 77, the other end of the heat transfer tube 77 a is connected to one end of the heat transfer tube 78 a of the third heat exchanger 78 through the second connection passage 152. In the third heat exchanger 78, the other end of the heat transfer tube 78a is connected to the end of the heat transfer tube 73a of the heat recovery unit 71 by the second circulation passage 75b.

Therefore, the heat medium having a high temperature in the heat recovery unit 71 is supplied to the first heat exchanger 74 to heat the air flowing through the air duct 38 to generate high-temperature combustion air. The high-temperature heat medium discharged from the first heat exchanger 74 is supplied to the second heat exchanger 77 to reheat the exhaust gas. The high-temperature heat medium discharged from the second heat exchanger 77 is supplied to the third heat exchanger 78 to heat the feed water.

Thus, in the exhaust gas heat recovery system of the sixth embodiment, the first heat exchanger 74 that heats the combustion air by the heat recovered by the heat recovery unit 71, and the chimney by the heat recovered by the heat recovery unit 71 A second heat exchanger 77 for reheating the exhaust gas discharged from 65 and a third heat exchanger 78 for heating the feed water supplied to the heat exchange unit 14 by the heat recovered by the heat recovery unit 71 are arranged in series. is doing.

Therefore, by sending the heat medium in order according to the required temperatures for combustion air, exhaust gas, and feed water, the heat medium can be supplied and heated appropriately, and the structure of the heat medium supply piping can be simplified. The apparatus can be reduced in size.

In the first to third embodiments described above, the high temperature part 72 and the low temperature part 73 are provided as the heat recovery part 71, but the number is not limited to two, and three or more may be provided. The high temperature portion 72 is disposed in the second vertical passage 44 and the low temperature portion 73 is disposed in the horizontal gas duct 45. However, both the high temperature portion 72 and the low temperature portion 73 are disposed in the second vertical passage 44 or the gas duct 45. Also good. At this time, the inner dimension of the flue may be gradually reduced, or the degree of density of the heat transfer tubes or heat transfer fins may be gradually increased.

In the above-described embodiment, the three heat exchangers 74, 77, and 78 are arranged with respect to the heat recovery unit 71, but it is not necessary to provide all of them, and only the first heat exchanger 74 may be provided. .

DESCRIPTION OF SYMBOLS 10 Boiler 11 Furnace 12 Combustion device 13 Flue 14 Heat exchange part 21, 22, 23, 24, 25 Combustion burner 36 Wind box 37 Additional air nozzle 38 Air duct 39 Blower 41 First horizontal passage 42 First vertical passage 43 Second Horizontal passage 44 Second vertical passage 45 Gas duct 46, 47, 48 Superheater 49, 50 Reheater 51, 52 Carbon-saving device 61 Denitration device 62 Electric dust collector 64 Desulfurization device 65 Chimney 66 Hopper 71, 140 Heat recovery unit 72 High temperature unit 72A, 73A, 140A Inlet part 72B, 73B, 140B Outlet part 73 Low temperature part 74 First heat exchanger 76 Pump 77 Second heat exchanger 78, 79 Third heat exchanger 100 Controller 102, 103, 104, 105, 106, 122, 124, 126, 132, 134, 136 Flow rate adjusting valve (distribution amount adjusting device)
107, 108, 109, 110, 111 Temperature sensor

Claims (10)

A furnace that is hollow and installed along the vertical direction;
A combustion burner for blowing a fuel gas mixed with fuel and combustion air into the furnace;
An exhaust gas passage connected to an upper portion of the furnace;
A heat exchanging unit that is provided in the exhaust gas passage and performs heat exchange between the exhaust gas and water;
A heat recovery unit that is provided downstream of the heat exchange unit in the exhaust gas passage and recovers heat of the exhaust gas;
A first heat exchanger that heats the combustion air with the heat recovered by the heat recovery unit,
The exhaust gas heat recovery system is characterized in that the heat recovery part has a passage cross-sectional area of an outlet part smaller than a passage cross-sectional area of an inlet part of the heat recovery part. 2. The exhaust gas heat recovery system according to claim 1, wherein the heat recovery part is set such that an inner dimension of the outlet part is set smaller than an inner dimension of the inlet part in the exhaust gas passage. The heat recovery unit is set such that a heat transfer tube or a heat transfer fin at the outlet portion has a higher density than a heat transfer tube or a heat transfer fin at the inlet portion. Item 3. An exhaust gas heat recovery system according to Item 2. The heat recovery unit includes an upstream high-temperature part and a downstream low-temperature part, and a passage cross-sectional area of the low-temperature part is set smaller than a passage cross-sectional area of the high-temperature part. The exhaust gas heat recovery system according to any one of claims 1 to 3. The exhaust gas passage includes a vertical passage along a vertical direction, and a horizontal passage connected to a lower portion of the vertical passage along a horizontal direction, the high temperature portion is disposed in the vertical passage, and the low temperature portion is The exhaust gas heat recovery system according to claim 4, wherein the exhaust gas heat recovery system is disposed in the horizontal passage. 6. The exhaust gas heat recovery system according to claim 5, wherein a denitration device is provided in the vertical passage, and the high temperature portion is disposed downstream of the exhaust gas flow in the denitration device. The exhaust gas heat recovery system according to claim 5 or 6, wherein a hopper is provided between the vertical passage and the horizontal passage and below the high temperature portion. The second heat exchanger is provided downstream of the heat recovery unit and reheats the exhaust gas before being discharged from the chimney by the heat recovered by the heat recovery unit. Item 8. The exhaust gas heat recovery system according to any one of Items 7. The exhaust gas heat recovery system according to claim 8, further comprising a third heat exchanger that heats water supplied to the heat exchange unit by heat recovered by the heat recovery unit. The distribution amount adjusting device for adjusting a distribution amount of a heat medium supplied from the heat recovery unit to the first heat exchanger, the second heat exchanger, and the third heat exchanger is provided. The exhaust gas heat recovery system according to claim 9.

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