JP5345873B2 - Waste heat recovery method and waste heat recovery system - Google Patents

Description

  The present invention relates to an exhaust heat recovery method and an exhaust heat recovery system that perform heat recovery and cooling on a high-temperature exhaust gas generated when a waste is burned.

  When waste is burned, high-temperature exhaust gas is generated. However, some exhaust gas is guided to a boiler for heat recovery. A conventional garbage gasification and melting system will be described with reference to FIG.

  The garbage 111a accommodated in the garbage pit 111 is thrown in from the top of the melting furnace 101 by the garbage crane 110, and the gas generated by the thermal decomposition of the garbage 111a in the melting furnace 101 passes through the gas pipe 102 to the combustion chamber. Combusted at 103. Air necessary for combustion in the combustion chamber 103 is supplied from the combustion air blower 108 to the combustion chamber 103. The temperature of the combustion gas becomes a high temperature of 850 to 1050 ° C., and heat is recovered by the boiler 104 at the subsequent stage.

  The boiler 104 is constituted by a water-cooled wall, and the exhaust gas from the combustion chamber 103 is cooled by the radiation cooling unit 104e, and further cooled and recovered by the superheater 104d, the evaporator 104c, and the economizer 104b.

  Boiler water is supplied to the boiler 104 from the boiler feed pump 109, and the supplied water is guided to the steam / water separation drum 104a via the economizer 104b. The water in the steam-water separation drum 104a is supplied to the water cooling wall and the evaporator 104c and returns to the steam-water separation drum as steam. The steam from the steam-water separation drum is sent to the superheater 104d to be superheated steam and taken out from the boiler 104. This steam is usually sent to a steam turbine and used for power generation.

  The temperature of the exhaust gas that has passed through the boiler 104 is about 200 ° C., and is cooled to about 150 to 170 ° C. by the evaporative cooling method using the water spray nozzle 105 a in the temperature reducing tower 105. The exhaust gas moved from the temperature reducing tower 105 to the bag filter (dust collector) 106 is removed by the bag filter 106 and then sent from the induction blower 107 to the chimney. Here, the purpose of cooling the exhaust gas in the temperature reducing tower 105 is to prevent the temperature of the exhaust gas supplied to the bag filter 106 from exceeding the heat resistance temperature of the filter cloth used in the bag filter 106. This is to improve the efficiency of removing hydrogen chloride contained in the exhaust gas in the bag filter 106.

JP-A 61-157333 JP 2002-228139 A

  In the configuration shown in FIG. 5, since the exhaust gas is cooled by spraying water in the temperature reducing tower 105, energy is lost from the viewpoint of heat recovery.

  Here, in order to omit the cooling process in the temperature reducing tower 105, it is desirable to cool the exhaust gas in the boiler 104 to the temperature range (reference temperature range, for example, 150 to 170 ° C.) in the temperature reducing tower 105. . However, for example, in the economizer 104b located on the most downstream side of the boiler 104, the temperature of the exhaust gas after passing through the economizer 104b is controlled even if the temperature of the exhaust gas is reduced to a predetermined temperature. I can't. This is because the amount of boiler water supplied to the economizer 104b is determined based on the water level of the steam separator 104a and the amount of steam generated.

  The temperature of the water supplied to the economizer 104b is normally set to about 110 to 140 ° C. in order to prevent the heat transfer tube of the economizer 104b from undergoing low temperature corrosion or the like. The temperature of the water subjected to heat exchange in the charcoal unit 104b is about 160 ° C. In such a configuration, it is difficult to reduce the temperature of the exhaust gas to the reference temperature range described above in the economizer 104b.

  A main object of the present invention is to provide an exhaust heat recovery method and an exhaust heat recovery system capable of efficiently recovering heat from high-temperature exhaust gas.

The first invention of the present application is an exhaust heat recovery method for recovering sensible heat of exhaust gas generated by combustion and incineration of waste, and recovers the heat of exhaust gas by a boiler, and is 90 ° C. or higher. And the 2nd temperature state from which the cooling water of the 1st temperature state lower than 100 degreeC becomes substantially 100 degreeC of the air-water mixing state partially vaporized by heat exchange with the waste gas which passed the boiler that converts to.

Here, the present application in the first invention, by using cooling water in the second temperature state (air-water mixing water), and warm the combustion air used in the combustion process. The cooling water after was the combustion air heated in order to return to the first temperature state, it can be used again to heat exchange with the exhaust gas. That is, the cooling water can be circulated and used. Further, the cooling water in the second temperature state can be used for heating the combustion air, and a part of the cooling water can be used for maintaining the cooling water used for heat exchange with the exhaust gas in the first temperature state. .

  A second invention of the present application is an exhaust heat recovery system that recovers sensible heat of exhaust gas that has been generated by gasification and melting or incineration of waste and that has been subjected to combustion processing. A boiler that performs recovery, an exhaust gas heat exchanger that performs heat exchange using the cooling water on the exhaust gas that has passed through the boiler, and an exhaust gas heat exchanger that has a cooling water of 90 ° C. or higher and 100 ° C. And a supply mechanism for supplying at a lower first temperature state. The exhaust gas heat exchanger converts the cooling water supplied from the supply mechanism into a second temperature state, which is an air-water mixture state of approximately 100 ° C., by heat exchange with the exhaust gas.

Here, the present application in the second aspect of the present invention, by using the cooling water of the second temperature condition is provided a heat exchanger for the combustion air to warm the combustion air used in the combustion process. Moreover, it is arrange | positioned in the position adjacent to the heat exchanger for waste gas, and can provide the channel | path which allows the waste gas from a boiler to pass through without exchanging heat, and the damper for adjusting the movement amount of the waste gas in a channel | path. .

  On the other hand, a cooling water after heating the combustion air is guided, and a water supply tank for storing the cooling water supplied to the exhaust gas heat exchanger can be provided. The second temperature state cooling water is branched from a duct that leads to the combustion air heat exchanger, and the second temperature state cooling water is led to the feed water tank, and the second temperature state coolant is led to the feed water tank via the branch duct. There can be provided a valve for adjusting the amount of cooling water to be discharged, a water temperature sensor for detecting the water temperature in the water supply tank, and a controller for controlling the drive of the valve based on the temperature detected by the water temperature sensor. . Here, the controller controls the open / close state of the valve so that the detected temperature is 90 ° C. or higher and lower than 100 ° C., and adjusts the amount of cooling water in the second temperature state guided to the water supply tank. Can do.

In the second invention of the present application , it is possible to provide a controller that controls the driving of the damper, and a temperature sensor for detecting the temperature of the exhaust gas that has passed through the heat exchanger for exhaust gas and the passage. Here, the controller increases the passage amount of the exhaust gas in the passage if the temperature detected by the temperature sensor is lower than the lower limit value of the reference temperature range, and the exhaust gas in the passage if the detected temperature is higher than the upper limit value of the reference temperature range. Can be reduced. The exhaust gas heat exchanger can be constituted by a heat transfer tube that moves cooling water.

  According to the first and second inventions of the present application, heat exchange can be performed on the exhaust gas heat-exchanged by the boiler using the cooling water in the first temperature state. Thereby, the thermal energy which cannot be recovered by the boiler can be recovered using the cooling water. The cooling water converted from the first temperature state to the second temperature state can be used, for example, for warming combustion air used in the combustion process, and heat energy can be used efficiently.

It is a figure which shows the structure of the gasification melting system which is Example 1 of this invention. It is a figure which shows the one part structure in the boiler exit side of Example 1. FIG. It is AA sectional drawing of FIG. It is a flowchart which shows the temperature control process of the exhaust gas in an exhaust gas bypass control valve. It is a figure which shows the structure of the conventional gasification melting system.

  Examples of the present invention will be described below.

  A gasification and melting system equipped with an exhaust heat recovery system that is Embodiment 1 of the present invention will be described with reference to FIG.

  The garbage 11a accommodated in the garbage pit 11 is transported by the garbage crane 10 and put into the melting furnace 1 from the top. The garbage 11a is thermally decomposed in the melting furnace 1 under a high temperature atmosphere, and the exhaust gas generated by the thermal decomposition passes through the gas pipe 2 and is guided to the combustion chamber 3. In the fuel chamber 3, exhaust gas is burned using combustion air.

  Here, a combustion air blower 8 is connected to the combustion chamber 3, and air is supplied from the combustion air blower 8 into the combustion chamber 3. Although the temperature of the air sent out from the combustion air blower 8 is a normal temperature, the air from the combustion air blower 8 is heated by receiving heat from the air heat exchanger 14 as will be described later. Yes.

  By the combustion treatment in the combustion chamber 3, the exhaust gas becomes a high temperature state of, for example, 850 to 1050 ° C. and is led to the boiler 4. The boiler 4 is constituted by a water-cooled wall, and the exhaust gas from the combustion chamber 3 contacts the radiation cooling unit 4e, the superheater 4d, the evaporator 4c, the economizer 4b, and the exhaust gas heat exchanger 12 in this order. By doing so, heat exchange is performed.

  The boiler feed pump 9 supplies water to the boiler 4, and the water supplied from the boiler feed pump 9 passes through the economizer 4b and is guided to the steam-water separation drum 4a. The water from the boiler feed pump 9 receives heat from the exhaust gas passing through the economizer 4b when moving through the heat transfer tube of the economizer 4b. For example, the water temperature supplied to the economizer 4b is 110 to 140 ° C, and the water temperature after heat exchange in the economizer 4b is about 160 ° C to 180 ° C. The water in the steam-water separation drum 4a is led to the water cooling wall and the evaporator 4c, receives the heat from the exhaust gas moving through the evaporator 4c and the like, and becomes steam.

  The steam generated by the evaporator 4c is guided to the superheater 4d through the steam separator. In the superheater 4d, superheated steam is generated by the exhaust gas passing through the superheater 4d and is taken out from the boiler 4. The superheated steam taken out from the boiler 4 is supplied to a steam turbine, and electric power is generated by a generator by driving the steam turbine. The specific configuration and operation of the exhaust gas heat exchanger 12 will be described later.

  As described above, the high-temperature exhaust gas generated in the combustion chamber 3 is cooled by passing through the boiler 4 and heat recovery is performed. And the exhaust gas which passed the boiler 4 is guide | induced to the bag filter (dust collector) 6, and the dust (hydrogen chloride, sulfur oxide, fly ash, etc.) contained in exhaust gas is removed. Specifically, a plurality of filter cloths 6a are provided in the bag filter 6, and dust collection processing is performed by passing the exhaust gas from the boiler 4 through the filter cloth 6a.

  The exhaust gas that has passed through the bag filter 6 is supplied to the chimney via the induction blower 7 and discharged from the chimney to the atmosphere. Here, in the conventional configuration shown in FIG. 5, the temperature reducing tower 105 is arranged between the boiler 104 and the bag filter 106, but in this embodiment, the temperature reducing tower 105 is omitted, and the boiler 4 The exhaust gas from is directly introduced into the bag filter 6.

  Moreover, in the boiler 4 of a present Example, the waste gas heat exchanger 12 is arrange | positioned with respect to the economizer 4b in the downstream in the movement direction of waste gas. The exhaust gas heat exchanger 12 contacts the exhaust gas that has passed through the economizer 4b and absorbs the heat of the exhaust gas. In the present embodiment, the exhaust gas heat exchanger 12 is provided in the boiler 4, but is not limited thereto, and can be disposed on the exhaust gas movement path between the boiler 4 and the bag filter 6. . That is, before the exhaust gas enters the bag filter 6, the exhaust gas heat exchanger 12 may be used to lower the temperature of the exhaust gas.

  A specific configuration of the exhaust gas heat exchanger 12 will be described with reference to FIGS. 2 and 3. Here, FIG. 2 is an enlarged view showing a peripheral structure of the exhaust gas heat exchanger 12. 3 is a cross-sectional view taken along the line AA of FIG. 2 and is a top view showing the configuration of the exhaust gas heat exchanger 12.

  The exhaust gas heat exchanger 12 has a heat transfer tube 12a formed of a bare tube. In the boiler 4, the region where the exhaust gas heat exchanger 12 is located is divided into three regions C1 to C3, and the heat transfer tubes 12a are arranged in the regions C2 and C3. Further, the exhaust gas bypass control valve 15 is arranged in a region C1 located between the regions C2 and C3. The configuration of the exhaust gas bypass control valve 15 will be described later.

  Water is supplied to the heat transfer tube 12a from the circulation pump 13 (see FIG. 1), and the exhaust gas that has contacted the outer surface of the heat transfer tube 12a is cooled by the water moving in the heat transfer tube 12a. The circulation pump 13 supplies the water accommodated in the water supply tank 17 to the heat transfer pipe 12a. The temperature of the water supplied to the heat transfer tube 12a is 90 ° C. or higher and is lower than 100 ° C. By supplying water at 90 ° C. or higher to the heat transfer tube 12a, the temperature of the heat transfer tube 12a can be maintained at 90 ° C. or higher (lower than 100 ° C.) and the low temperature corrosion of the heat transfer tube 12a is suppressed. Can do.

  The water in the heat transfer tube 12a receives the heat from the exhaust gas passing through the heat transfer tube 12a, and becomes gas-liquid mixed water (mixed of steam and water) at approximately 100 ° C. The temperature of the exhaust gas that has passed through the economizer 4b, in other words, the temperature of the exhaust gas that enters the exhaust gas heat exchanger 12 is about 200 ° C. on average, and water of 90 ° C. or more supplied to the heat transfer tube 12a The temperature of exhaust gas can be reduced efficiently. That is, the exhaust gas can be cooled in the exhaust gas heat exchanger 12 without increasing the heat transfer area of the heat transfer tube 12a.

  The gas-liquid mixed water generated in the heat transfer tube 12 a is taken out from the exhaust gas heat exchanger 12 and guided to the combustion air heat exchanger 14 through the circulation duct 25. The combustion air heat exchanger 14 is provided in a duct 26 that connects the combustion air blower 8 and the combustion chamber 3, and moves the heat of the gas-liquid mixed water led from the exhaust gas heat exchanger 12 through the duct 26. Transmit to air. Thereby, the air sent out from the combustion air blower 8 is supplied to the combustion chamber 3 in a heated state. Further, the gas-liquid mixed water is liquefied by heat exchange in the combustion air heat exchanger 14, and this water is guided to the water supply tank 17.

  By supplying the air heated by the combustion air heat exchanger 14 to the combustion chamber 3, the combustion efficiency in the combustion chamber 3 can be improved. Further, the amount of heat of the exhaust gas guided to the boiler 4 can be increased, and the amount of steam generated in the boiler 4 can be increased. Furthermore, since the air supplied to the combustion chamber 3 is heated using the thermal energy discarded in the temperature reducing tower 105 in the conventional configuration (FIG. 5), the thermal energy generated in the combustion chamber 3 is efficiently used. Can be used well.

  In addition, since there is no dust in the air which moves the heat exchanger tube of the combustion air heat exchanger 14, a fin tube can be used as the heat exchanger tube of the combustion air heat exchanger 14, for example.

  A heater 24 is arranged in the water supply tank 17 for start-up, and the water temperature in the water supply tank 17 is 90 ° C. or higher and lower than 100 ° C. by the heat generated by the heater 24. As the heat source of the heater 24, for example, steam can be used.

  Further, if the water temperature in the water supply tank 17 is raised in advance before starting the gasification melting system of the present embodiment, low temperature corrosion of the heat transfer tube 12a in the exhaust gas heat exchanger 12 can be suppressed, or the bag filter 6 It is possible to make it easier to raise the inlet temperature. The water supply tank 17 is provided with a vent pipe 18 for allowing movement of air between the outside (atmosphere). And by providing the vent pipe 18, the water temperature in the water supply tank 17 is prevented from exceeding 100 ° C.

  In this embodiment, a branch duct 27 is connected to the circulation duct 25, and the branch duct 27 guides a part of the gas-liquid mixed water from the heat transfer pipe 12 a into the water supply tank 17. Here, the branch duct 27 is provided with a water amount adjusting valve 22 to adjust the amount of the gas-liquid mixed water guided to the water supply tank 17.

  The operation of the water amount adjustment valve 22 is controlled by the water temperature control device 21. Specifically, the water temperature control device 21 detects the water temperature in the water supply tank 17 based on the output of the water temperature sensor 23, and controls the driving of the water amount adjustment valve 22 based on the detection result.

  Here, if the temperature detected by the water temperature sensor 23 is lower than 90 ° C., the amount of the gas-liquid mixed water heading from the heat transfer pipe 12 a toward the water supply tank 17 is increased by operating the water amount adjusting valve 22 in the opening direction. Thereby, hot gas-liquid mixed water mixes in the water supply tank 17, and the water temperature in the water supply tank 17 can be raised. In a normal state, the water temperature in the water supply tank 17 is 90 ° C. or higher, and the water amount adjustment valve 22 is closed.

  By performing such control, the water temperature in the water supply tank 17 can be maintained at 90 ° C. or higher and lower than 100 ° C.

  Next, the configuration of the exhaust gas bypass control valve 15 will be described. In this embodiment, one exhaust gas bypass control valve 15 is used, but a plurality of exhaust gas bypass control valves 15 may be used.

  The exhaust gas bypass control valve 15 includes a casing 15a, a rotary shaft 15b rotatably supported by the casing 15a, and a valve plate (damper) 15c formed on the outer periphery of the rotary shaft 15b. The rotating shaft 15b is connected to the actuator 16 and is rotated by receiving a driving force from the actuator 16.

  The rotating shaft 15b rotates in the direction indicated by the arrow R, and generally closes the exhaust gas movement passage in the casing 15a or allows the movement of the exhaust gas in the casing 15a. Further, the amount of exhaust gas passing through the casing 15a can be adjusted by adjusting the rotation angle of the rotary shaft 15b. If the valve plate 15c is positioned so as to be substantially parallel to the wall surface of the casing 15a, the amount of exhaust gas passing through the exhaust gas bypass control valve 15 can be maximized.

A gas temperature sensor 20 is provided in the duct 28 connecting the boiler 4 and the bag filter 6. The gas temperature sensor 20 is provided for detecting the temperature of the exhaust gas passing through the duct 28. In addition, the gas temperature sensor 20 should just be located between the boiler 4 (exhaust gas heat exchanger 12) and the bag filter 6, and the arrangement position of the gas temperature sensor 20 can be set suitably in this range. .

  The exhaust gas temperature control device 19 detects the temperature of the exhaust gas based on the output signal of the gas temperature sensor 20. Further, the exhaust gas temperature control device 19 controls the driving of the actuator 16 based on the temperature detected by the gas temperature sensor 20.

  Here, a specific processing operation in the exhaust gas temperature control device 19 will be described with reference to a flowchart shown in FIG.

  In step S <b> 10, the exhaust gas temperature control device 19 detects the temperature of the exhaust gas based on the output of the gas temperature sensor 20. In step S11, it is determined whether or not the temperature of the exhaust gas detected in step S10 is lower than the lower limit value of the reference temperature range. The reference temperature range is a temperature range of exhaust gas that can be guided to the bag filter 6 and is set in advance. For example, the reference temperature range can be set to 150 (lower limit value) to 170 (upper limit value) ° C.

  Here, if the temperature of the exhaust gas is lower than 150 ° C., the casing of the bag filter 6 may be corroded at low temperature. Moreover, when the temperature of exhaust gas exceeds 170 degreeC, there exists a possibility that the collection effect of the hydrogen chloride in the filter cloth 6a surface of the bag filter 6 by the slaked lime sprayed on the entrance flue of the bag filter 6 may fall. is there. Furthermore, when the temperature of the exhaust gas exceeds 170 ° C., the heat-resistant filter cloth 6a must be used as the filter cloth 6a of the bag filter 6, resulting in an increase in cost. And if the temperature of exhaust gas exceeds 200 degreeC, it will also become impossible to use the heat-resistant filter cloth 6a.

  In step S11, when the detected temperature is lower than the lower limit value, the process proceeds to step S12. Otherwise, the process proceeds to step S13.

  In step S <b> 12, the exhaust gas temperature control device 19 drives the actuator 16 to increase the amount of exhaust gas passing through the exhaust gas bypass control valve 15. As shown in FIG. 2, the exhaust gas from the economizer 4 b is divided into a component that passes through the heat transfer pipe 12 a and a component that passes through the exhaust gas bypass control valve 15. Here, as described above, the exhaust gas passing through the heat transfer tube 12a is cooled by heat exchange with water (90 to 100 ° C.) moving in the heat transfer tube 12a. On the other hand, the exhaust gas that has entered the exhaust gas bypass control valve 15 passes through the exhaust gas bypass control valve 15 without being cooled.

  For this reason, if the amount of exhaust gas passing through the exhaust gas bypass control valve 15 is increased, the temperature of the exhaust gas detected by the gas temperature sensor 20 can be increased.

  In step S13, the exhaust gas temperature control device 19 determines whether or not the temperature of the exhaust gas detected in step S10 is higher than the upper limit value of the reference temperature range. If the detected temperature is higher than the upper limit value, the process proceeds to step S14. If not, the process ends.

  In step S <b> 14, the exhaust gas temperature control device 19 drives the actuator 16 to reduce the amount of exhaust gas passing through the exhaust gas bypass control valve 15. If the passage amount of the exhaust gas is decreased, the temperature of the exhaust gas detected by the gas temperature sensor 20 can be lowered.

  By performing the control described above, the temperature of the exhaust gas detected by the gas temperature sensor 20, in other words, the temperature of the exhaust gas guided to the bag filter 6 can be maintained within the reference temperature range. Thereby, it can suppress that an excessive thermal load is applied with respect to the filter cloth 6a in the bag filter 6, or can improve the dust collection efficiency in the filter cloth 6a.

  In this embodiment, the temperature of the exhaust gas led to the bag filter 6 is adjusted by mixing the exhaust gas subjected to heat exchange and the exhaust gas not subjected to heat exchange. Here, even in the technique described in Patent Document 1, the temperature of the exhaust gas at the boiler outlet is adjusted by mixing exhaust gases having different temperatures. However, the present embodiment (the present invention) adjusts the temperature of the exhaust gas with a configuration different from that of Patent Document 1.

  That is, in the present embodiment, the region (region C2, C3) in which the heat transfer tube 12a is disposed in the movement path (in the water cooling wall) of the exhaust gas in the boiler 4 and the region (region) in which the exhaust gas bypass control valve 15 is disposed. C1). If comprised in this way, the temperature of the waste gas guide | induced to the bag filter 6 can be adjusted with a simple structure. On the other hand, in the configuration described in Patent Document 1, since a new duct is added, the structure becomes complicated.

1: Gasification melting furnace 2: Gas pipe 3: Combustion chamber 4: Boiler 4a: Steam-water separation drum 4b: Carbon-saving device 4c: Evaporator 4d: Superheater 4e: Radiation cooling unit 6: Bag filter 6a: Filter cloth 7 : Induction blower 8: Combustion air blower 9: Boiler feed pump 10: Waste crane 11: Waste pit 11a: Waste 12: Exhaust gas heat exchanger 13: Circulation pump 14: Combustion air heat exchanger 15: Exhaust gas bypass control valve 15a: Casing 15b: Rotating shaft 15c: Valve plate 16: Actuator 17: Water supply tank 18: Vent pipe 19: Exhaust gas temperature control device 20: Gas temperature sensor 21: Water temperature control device 22: Water amount control valve 23: Water temperature sensor 24: Heater 25-28 :duct

Claims (9)

In an exhaust heat recovery method for recovering sensible heat of exhaust gas generated by combustion and incineration of waste and burned,
The heat of the exhaust gas is recovered by a boiler,
Cooling water in a first temperature state of 90 ° C. or higher and lower than 100 ° C. is brought into a second temperature state in which an air-water mixed state is obtained at approximately 100 ° C. by heat exchange with the exhaust gas that has passed through the boiler. Convert and
An exhaust heat recovery method characterized by warming combustion air used for the combustion process using the cooling water in the second temperature state . The cooling water After warming the combustion air, wherein at a first temperature state, the exhaust heat recovery method according to claim 1, characterized by using again the heat exchange with the exhaust gas. The cooling water in the second temperature state is used for heating the combustion air and is used for maintaining the cooling water used for heat exchange with the exhaust gas in the first temperature state. The exhaust heat recovery method according to claim 1 or 2 . In an exhaust heat recovery system that recovers sensible heat of exhaust gas that is generated by gasification melting treatment or incineration treatment of waste and burned,
A boiler that recovers heat by generating steam by heat exchange with the exhaust gas;
A heat exchanger for exhaust gas that causes heat exchange using cooling water for the exhaust gas that has passed through the boiler,
A supply mechanism for supplying the cooling water at a first temperature state of 90 ° C. or higher and lower than 100 ° C. to the exhaust gas heat exchanger;
The exhaust gas heat exchanger converts the cooling water supplied from the supply mechanism into a second temperature state that is in an air-water mixed state at approximately 100 ° C. by heat exchange with the exhaust gas ,
The second with the cooling water temperature state of the exhaust heat recovery system, characterized by have a heat exchanger for the combustion air to warm the combustion air used in the combustion process. A passage that is disposed adjacent to the exhaust gas heat exchanger, and allows the exhaust gas from the boiler to pass through without heat exchange;
A damper for adjusting the amount of movement of the exhaust gas in the passage;
The exhaust heat recovery system according to claim 4 , comprising: The exhaust heat recovery according to claim 4 , further comprising: a water supply tank that accommodates the cooling water to which the cooling water after heating the combustion air is guided and supplied to the heat exchanger for exhaust gas. system. A branch duct branched from a duct for guiding the cooling water in the second temperature state to the heat exchanger for combustion air, and leading the cooling water in the second temperature state to the water supply tank;
A valve for adjusting the amount of the cooling water guided to the water supply tank via the branch duct;
A water temperature sensor for detecting the water temperature in the water supply tank;
A controller for controlling the driving of the valve based on the temperature detected by the water temperature sensor,
The controller controls the open / close state of the valve so that the detected temperature is 90 ° C. or higher and lower than 100 ° C. The exhaust heat recovery system according to claim 6 , wherein the exhaust heat recovery system is adjusted. A controller for controlling the driving of the damper;
A temperature sensor for detecting the exhaust gas heat exchanger and the temperature of the exhaust gas that has passed through the passage;
If the temperature detected by the temperature sensor is lower than the lower limit value of the reference temperature range, the controller drives the damper to increase the amount of movement of the exhaust gas in the passage, and the detected temperature is within the reference temperature range. 6. The exhaust heat recovery system according to claim 5, wherein if it is higher than an upper limit value, the damper is driven to reduce the amount of movement of the exhaust gas in the passage. The exhaust heat recovery system according to any one of claims 4 to 8, wherein the exhaust gas heat exchanger includes a heat transfer tube for moving the cooling water.

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