JP6707058B2 - Waste heat boiler, waste heat recovery system, and waste heat recovery method - Google Patents

Description

The present invention mainly relates to a waste heat boiler that recovers heat of exhaust gas discharged from a waste incinerator.

BACKGROUND ART Conventionally, in a waste heat boiler that recovers heat of exhaust gas discharged from a waste incinerator, a configuration including a economizer is known. The economizer is to preheat the boiler water by exchanging heat between the boiler water before being supplied to the evaporator and the relatively low temperature exhaust gas that has passed through the evaporator and the like. Patent documents 1 and 2 disclose a waste heat boiler provided with a economizer.

In Patent Document 1, waste heat having a configuration in which the boiler feed water (boiler water) that has passed through the economizer (coal saver) is connected (supplied) to the evaporator, and is also connected (supplied) to the deaerator inlet side. A boiler is disclosed. As a result, the boiler feed water (boiler water) that has been heated from the deaerator through the economizer is supplied to the evaporator and part of it is returned to the deaerator inlet side. As a result, the boiler feed water (boiler water) temperature at the economizer inlet is early and steady during the time when the boiler feed water (boiler water) temperature from the deaerator is not high enough when starting the waste treatment furnace and the waste heat boiler. Since it is possible to heat up to the temperature of the operating state, the economizer can be shifted to the steady operating state at an early stage.

In Patent Document 2, in a waste incineration treatment facility in which combustion exhaust gas discharged from a waste incinerator is flowed in the order of a waste heat boiler, an economizer, and an exhaust gas treatment facility, low-temperature exhaust gas from which an acidic gas in the latter stage of the exhaust gas treatment facility is removed Disclosed is a configuration including an independent economizer that heats the boiler feed water by recovering heat from the boiler.

JP, 2002-5401, A JP, 2011-237048, A

Here, in Patent Document 1, the temperature of the boiler feed water (boiler water) flowing through the economizer is shifted (heated up) to a steady operation state at an early stage to make it difficult for the economizer to condense the exhaust gas that is in contact heat exchange, so that low temperature corrosion It is described that the occurrence can be prevented. However, Patent Document 1 is a technique used in a state where the waste treatment furnace and the waste heat boiler are not sufficiently heated at the time of startup, and when the waste treatment furnace and the waste heat boiler are in a steady operation, this technique is It does not have the effect of preventing low temperature corrosion.

Further, Patent Document 2 describes that the independent economizer does not easily cause low temperature corrosion because it recovers heat from the exhaust gas from which the acid gas has been removed. However, in the waste incinerator, the nature of the input waste is diverse and unpredictable.Therefore, depending on the waste, the moisture concentration of the exhaust gas becomes high, and the exhaust gas is passed through the exhaust gas treatment facility because it is placed in the latter stage of the exhaust gas treatment facility. In the independent economizer part where the temperature is considerably low, a large amount of dew condensation may occur, and even if heat recovery is performed from the exhaust gas from which the acid gas has been removed, low temperature corrosion cannot be sufficiently prevented. Moreover, since the temperature of the exhaust gas passing through the independent economizer is considerably low, the boiler water cannot be sufficiently heated, and there is a possibility that it will not contribute much to the increase in waste heat recovery efficiency.

If the temperature of the boiler water at the inlet of the economizer is raised by raising the temperature higher in the deaerator, the temperature of the economizer surface rises and the condensation of exhaust gas can be prevented, so that low temperature corrosion can be prevented. However, in this case, in order to raise the temperature of the boiler water at the inlet of the economizer by raising the temperature higher in the deaerator, more steam must be consumed by the deaerator in the boiler. , The waste heat recovery efficiency of the entire system will be reduced.

The present invention has been made in view of the above circumstances, and a main object thereof is to provide a waste heat boiler capable of improving waste heat recovery efficiency while preventing low temperature corrosion.

The problem to be solved by the present invention is as described above. Next, means for solving the problem and its effect will be described.

According to the viewpoint of the present invention, the waste heat boiler of the following composition is provided. That is, this waste heat boiler recovers the heat of the exhaust gas discharged from the waste incinerator. This waste heat boiler includes a economizer, an evaporator, a superheater, a supply path, and an adjusting unit. The economizer heats boiler water by heat exchange with exhaust gas. The evaporator exchanges heat between the boiler water heated by the economizer and the exhaust gas to generate steam. The superheater heats (superheats) the vapor generated by the evaporator. The supply route is a route for supplying boiler water to the economizer. The economizer is configured to include a front economizer and a main economizer. The front economizer is arranged in a boiler body region in which the evaporator and the superheater are arranged. The main economizer is arranged downstream of the boiler body region in the exhaust gas flow direction. The supply route includes a first route, a second route, a third route, and a fourth route. The first route is a route from a deaerator to the front economizer and the main economizer, and is a route to a branch point between the second route and the third route. The second route is a route from the branch point of the first route to the main economizer after passing through the front economizer. The third route is a route from the branch point of the first route, bypassing the front economizer to the main economizer. The fourth route is a route where the second route and the third route join, and is a route connected to the main economizer. The adjusting unit has a mechanism that adjusts a ratio of a flow rate of boiler water passing through the second route and a flow rate of boiler water passing through the third route with respect to a flow rate of boiler water flowing through the first route. . The temperature of the boiler water supplied to the main economizer is adjusted by adjusting the ratio between the boiler water passing through the second route and the boiler water passing through the third route by the adjusting unit. The temperature is to prevent low temperature corrosion in the economizer.

Thereby, for example, the flow rate of the boiler water flowing through the first route and the fourth route remains the same, the proportion of the boiler water flowing into the fourth route via the second route is increased, and the boiler water passing through the third route is increased. By decreasing the proportion of the boiler water flowing into the fourth path through the second path and the third path, the temperature of the boiler water that joins the fourth path and is supplied to the main economizer is increased, The probability of dew condensation on the main economizer can be reduced, and low temperature corrosion is less likely to occur. On the other hand, by decreasing the proportion of boiler water flowing into the fourth path via the second path and increasing the proportion of boiler water flowing into the fourth path via the third path, It is possible to improve the heat recovery performance in the main economizer by lowering the temperature of the boiler water supplied to the main economizer by merging in the 4th path through the path and the 3rd path, and recovering waste heat. The efficiency can be improved. As described above, by adjusting the adjusting unit manually or automatically according to the situation, the waste heat recovery efficiency can be improved while preventing low temperature corrosion in the entire boiler system. Further, since the position of the front economizer is located within the boiler body region, dew condensation does not occur when the exhaust gas comes into contact with the front economizer, and low temperature corrosion does not occur.

According to the present invention, it is possible to provide a waste heat boiler capable of enhancing the waste heat recovery efficiency while preventing low temperature corrosion.

1 is a schematic configuration diagram of a waste heat recovery system including a waste heat boiler according to an embodiment of the present invention. The control block diagram of a waste heat recovery system.

<Overall Configuration of Waste Heat Recovery System> First, the waste heat recovery system 1 including the waste heat boiler 2 of the present embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic configuration diagram of a waste heat recovery system 1 including a waste heat boiler 2 according to an embodiment of the present invention. FIG. 2 is a control block diagram of the waste heat recovery system.

The waste heat recovery system 1 is provided in a waste incineration facility, and is a system that recovers heat generated by combustion of waste in an incinerator (waste incinerator) 10 and generates electricity. As shown in FIG. 1, the waste heat recovery system 1 includes an incinerator 10, a waste heat boiler 2, and a steam turbine generator 60 as main components.

In the incinerator 10, a waste gas supplied from the outside is combusted to generate a high temperature combustion gas. The generated combustion gas is sent to the waste heat boiler 2 as exhaust gas. The exhaust gas contains acid gases such as SOx and HCl, depending on the properties of the waste. Further, the water concentration of the exhaust gas becomes relatively high.

The incinerator 10 is provided with a combustion sensor 11 that detects data related to combustion in the incinerator 10 (for example, the temperature of the combustion chamber). The data detected by the combustion sensor 11 is output to the control device 71 shown in FIG.

The control device 71 includes a CPU, a RAM, a ROM, and the like, performs various calculations, and controls the entire waste heat recovery system 1. Note that the control device 71 may control only the waste heat boiler 2, and the incinerator 10, the steam turbine generator 60, and the like may be controlled by another control device.

The waste heat boiler 2 uses the exhaust gas discharged from the incinerator 10 to generate steam and supplies the steam to the steam turbine generator 60. As shown in FIG. 1, the waste heat boiler 2 includes an evaporator 20, a superheater 30, a economizer 40, a deaerator 50, and a condensate tank 51. Further, the economizer 40 is configured to include a main economizer 41 and a front economizer 42.

In the steam turbine generator 60, power is generated using the steam supplied from the waste heat boiler 2 (specifically, the superheater 30). Further, the steam used for power generation in the steam turbine generator 60 is cooled and condensed in the condenser 61 and returned to the waste heat boiler 2 (specifically, the condensate tank 51) as boiler water. Will be used again.

<Flow of Exhaust Gas in Waste Heat Boiler> Next, the flow of exhaust gas in the waste heat boiler 2 will be described. Exhaust gas generated in the incinerator 10 first passes through the boiler body region 2a as shown in FIG. The boiler body region 2a is a region in which the evaporator 20 and the superheater 30 are arranged, and in the present invention, a front economizer 42 is further arranged. Specifically, the front economizer 42 is arranged near the region where the superheater 30 is arranged and upstream in the exhaust gas flow direction, that is, near the downstream end of the evaporator 20.

The exhaust gas passes through the boiler main body region 2a and then passes through the main economizer 41. After that, the exhaust gas passes through a dust collector, an acid gas remover, a NOx remover, etc., which are not shown, and is then discharged to the outside from the chimney 90. An exhaust gas component detection sensor 72 that detects a component of the exhaust gas is arranged in the path from the main economizer 41 to the chimney 90. The exhaust gas component detection sensor 72 specifically detects the acid gas concentration and the water concentration contained in the exhaust gas and outputs them to the control device 71.

As described above, the waste heat boiler 2 of the present embodiment is configured to further include the front economizer 42 in addition to the main economizer 41 corresponding to a general economizer.

<Flow of Boiler Water and Steam in Waste Heat Boiler> Next, the flow of boiler water and steam in the waste heat boiler 2 will be described. The boiler water is a concept including boiler feed water supplied to the waste heat boiler 2 and boiler water used in the waste heat boiler 2. The condensate tank 51 stores boiler water in which steam that has been used in the steam turbine generator 60 is liquefied. The boiler water stored in the condensate tank 51 is sent to the deaerator 50 by a deaerator water supply pump (not shown).

The deaerator 50 separates and removes gas components such as oxygen dissolved in boiler water by injecting steam inside. Note that, of the high-temperature steam that has entered the steam turbine generator 60, part of the high-temperature steam is extracted (bleeded) while energy is being lost, and is sent to the deaerator 50 as atomized steam for deaeration. In the deaerator 50, the temperature of the boiler water at the outlet of the deaerator rises because high temperature steam is mixed in the boiler water. The boiler water from which the gas such as oxygen has been removed and the temperature has risen as described above is sent to the economizer 40 by a boiler feed pump (not shown). The economizer 40 (main economizer 41 and pre economizer 42) is composed of a plurality of heat transfer tubes for exchanging heat with the exhaust gas, and heats boiler water by exchanging heat with the exhaust gas.

The waste heat boiler 2 of the present embodiment includes a supply path 80 for supplying boiler water from the deaerator 50 to the economizer 40. The supply path 80 includes a first path 81, a second path 82, a third path 83, and a fourth path 84. The first route 81 is a route from the deaerator 50 to the front economizer 42 and the main economizer 41, and is a route to a branch point between the second route 82 and the third route 83. The second route 82 is a route from the branch point of the first route 81 toward the main economizer 41 after passing through the front economizer 42 (connected to the fourth route 84). The third path 83 is a path that bypasses the front economizer 42 from the branch point of the first path 81 toward the main economizer 41 (connected to the fourth economizer 84). The fourth route 84 is a route in which the second route 82 and the third route 83 join (a route on the downstream side of the second route 82 and the third route 83) and is a route connected to the main economizer 41, The flow rate is the same as that of the first path 81.

A regulating valve (adjusting section) 70 is provided in the third path 83, and by changing the valve opening, the flow rate of boiler water flowing through the first path 81 and the fourth path 84 remains the same, It is possible to adjust the ratio between the flow rate of the boiler water passing through the second route 82 and the flow rate of the boiler water passing through the third route 83. The adjusting valve 70 is controlled by the control device 71. The regulating valve 70 may be provided as a three-way valve type at the branch portion of the first passage 81 or the confluence portion of the fourth passage 84.

Here, since the front economizer 42 is arranged on the upstream side of the main economizer 41 in the exhaust gas flow direction, heat exchange with higher temperature exhaust gas is performed. Specifically, the front economizer 42 is arranged in a portion of the boiler body region 2a where the temperature of the exhaust gas is 400°C or higher and 650°C or lower. More specifically, the temperature of the exhaust gas flowing through the part (inlet part) of the pre-coal economizer 42 into which the boiler water is introduced is 400° C. or higher and 650° C. or lower.

On the other hand, since the main economizer 41 is arranged on the downstream side of the front economizer 42 in the exhaust gas flow direction, heat is exchanged with the exhaust gas of a lower temperature. Specifically, the temperature of the exhaust gas flowing through the main economizer 41 (specifically, the inlet portion) is about 200°C. Although the temperature of the exhaust gas changes depending on the combustion state of the incinerator 10 and the like, it is, for example, an average temperature in steady operation.

Since the temperatures of the exhaust gas passing through the main economizer 41 and the pre economizer 42 are thus significantly different, the pre economizer can be used by increasing the proportion of boiler water passing through the second path 82, for example. Since the proportion of the boiler water that passes through 42 and is heat-exchanged with the high-temperature exhaust gas increases, the temperature of the boiler water supplied from the fourth path 84 to the main economizer 41 increases. On the other hand, by increasing the proportion of the boiler water that passes through the third path 83, the proportion of the boiler water that is not heated by the front economizer 42 increases, so that it is supplied from the fourth path 84 to the main economizer 41. Boiler water temperature drops. As described above, in the present embodiment, the controller 71 adjusts the adjusting valve 70 to adjust the temperature of the boiler water supplied to the main economizer 41.

Similar to the front economizer 42, the main economizer 41 heats boiler water by heat exchange with exhaust gas. The boiler water heated by the main economizer 41 is supplied to the evaporator 20. The low temperature corrosion that may occur in the main economizer 41 will be described later.

The evaporator 20 is configured to include a plurality of evaporation pipes arranged in a path through which exhaust gas flows. In the evaporator 20, the boiler water is heat-exchanged with the exhaust gas to generate steam. The steam generated by the evaporator 20 is supplied to the superheater 30.

The superheater 30 is configured to include a plurality of superheat pipes arranged in a path through which exhaust gas flows. The superheater 30 heats (overheats) the steam generated by the evaporator 20. In the superheater 30, the steam is heated (overheated) to, for example, 400° C. or higher, and the exhaust gas is cooled to about 200° C. The high-temperature steam heated (superheated) by the superheater 30 is supplied to the steam turbine generator 60.

<Configuration for Preventing Low Temperature Corrosion and Increasing Waste Heat Recovery Efficiency> Next, a configuration of the waste heat boiler 2 for preventing low temperature corrosion of the main economizer 41 and increasing waste heat recovery efficiency will be described. .. First, the waste heat recovery efficiency and low temperature corrosion in a general waste heat boiler equipped with a economizer (corresponding to the main economizer 41 of this embodiment) will be described.

In general, the economizer is arranged downstream of the superheater in the exhaust gas flow direction, like the main economizer 41 of the present embodiment. Therefore, the economizer will be heat-exchanged with the exhaust gas having a relatively low temperature. Here, in order to recover a larger amount of heat from the exhaust gas by the waste heat boiler, it is preferable to lower the temperature of the boiler water supplied to the economizer and heat exchange the exhaust gas to a lower temperature.

In general, exhaust gas discharged from an incinerator contains corrosive components such as the above-mentioned acidic gas and water, so if the temperature of the exhaust gas is lowered to a temperature below the dew condensation temperature that is commensurate with the moisture content, condensation and dew condensation will occur. It will be. Further, since the acidic gas contained in the exhaust gas has a high solubility in water, it will continuously dissolve in the dew condensation water generated by the dew condensation, but with the passage of time, the dew condensation water will be 100°C or higher. Since a part of the reaction gas evaporates due to the exhaust gas at the temperature, the ratio of the acidic gas component contained in the dew condensation water increases, so-called concentration occurs, and the dew condensation water generation part is easily corroded. Corrosion of iron products etc. that occurs on this principle is called low temperature corrosion. Since the exhaust gas discharged from the incinerator has such a property, when the temperature of the boiler water that passes through the economizer is lowered, the surface temperature of the heat transfer pipes of the economizer will decrease and the temperature of the exhaust gas will decrease. May fall below the dew condensation temperature commensurate with the water content ratio, dew condensation may occur on the surface of the heat transfer tube, the acid gas component contained in the dew condensation water may rise, and the heat transfer tube may cause low temperature corrosion.

The acid gas concentration and moisture concentration contained in the exhaust gas change depending on the waste supplied to the incinerator and the combustion state in the incinerator, and thus are required to prevent low temperature corrosion in the economizer. The temperature of the boiler water supplied to the economizer is also not constant. Here, as described above, the temperature of the boiler water supplied to the economizer is increased by mixing a part of the steam supplied to the steam turbine generator into the deaerator. It is not easy to change the temperature of the boiler water supplied to the economizer due to the nature of the heating method of. Therefore, in the past, in order to reliably prevent low temperature corrosion, the temperature of boiler water supplied to the economizer was often set relatively high (about 140° C.).

In this respect, in the waste heat boiler 2 of the present embodiment, it is only necessary to adjust the adjusting valve 70 to change the proportion of the boiler water that is passed through the front economizer 42. It is possible to adjust the temperature of the boiler water supplied to the vessel). Therefore, for example, when the concentration of acid gas and water contained in the exhaust gas is low and low temperature corrosion is unlikely to occur, the temperature of the boiler water supplied to the main economizer 41 is set lower than 140° C. It is possible to improve the waste heat recovery efficiency while preventing it. After that, when the concentration of acid gas and the concentration of water contained in the exhaust gas become high, the low temperature corrosion can be prevented by raising the temperature of the boiler water supplied to the main economizer 41 to, for example, about 140°C.

In the present embodiment, the adjustment of the adjustment valve 70 is performed by the control device 71 based on various measurement data in the waste heat recovery system 1. Explaining an example of this measurement data, as shown in FIG. 2, there is data on the properties of the exhaust gas, such as the concentration of acidic gas and the concentration of water contained in the exhaust gas, measured by the exhaust gas component detection sensor 72. As described above, when the acid gas concentration and the water concentration are high, low temperature corrosion is likely to occur, so it is preferable to perform control to increase the proportion of boiler water that passes through the front economizer 42.

Further, as another example of the measurement data, there is data on combustion in the incinerator 10 detected by the combustion sensor 11. For example, when the temperature of the combustion chamber (particularly the temperature of the outlet of the combustion chamber) is high, the temperature of the exhaust gas at the time of being supplied to the waste heat boiler 2 is high, which is related to heat exchange efficiency and the like. The temperature of the exhaust gas at the time of passing through the vessel 41 may also increase. In this case, since low temperature corrosion is unlikely to occur, it is preferable to perform control to reduce the proportion of boiler water that passes through the front economizer 42.

Further, as another example of the measurement data, there is data regarding the state of the waste heat boiler 2. For example, the temperature of the boiler water supplied to the main economizer 41 (the temperature of the boiler water passing through the fourth path 84) is compared with the target temperature to bring the temperature of the boiler water close to the target temperature. The adjusting valve 70 may be adjusted.

In this way, the control device 71 adjusts the adjusting valve 70 based on the measurement data, so that the low temperature corrosion can be prevented and the waste heat recovery efficiency can be improved.

In the above description, how to adjust the adjusting valve 70 according to individual measurement data has been described. However, in reality, the control device 71 makes a comprehensive judgment based on a plurality of measurement data to adjust the adjusting valve 70. The adjustment content of 70 is determined. The above measurement data is an example, and other measurement data may be used, or the adjustment content of the adjustment valve 70 may be determined without using at least one of the above measurement data.

Further, in the present embodiment, the control device 71 determines the adjustment content of the adjustment valve 70 based on each measurement data, but the operator adjusts the adjustment valve 70 based on each measurement data. Good.

As described above, the waste heat boiler 2 of the present embodiment includes the economizer 40, the evaporator 20, the superheater 30, the supply path 80, and the adjustment valve 70. The economizer 40 heats boiler water by heat exchange with exhaust gas. The evaporator 20 heat-exchanges the boiler water heated by the economizer 40 with the exhaust gas to generate steam. The superheater 30 heats (superheats) the steam generated by the evaporator 20. The supply path 80 is a path for supplying boiler water to the economizer 40. The economizer 40 is configured to include a front economizer 42 and a main economizer 41. The front economizer 42 is arranged in the boiler body region 2a in which the evaporator 20 and the superheater 30 are arranged. The main economizer 41 is arranged downstream of the boiler body region 2a in the exhaust gas flow direction. The supply path 80 is configured to include a first path 81, a second path 82, a third path 83, and a fourth path 84. The first route 81 is a route from the deaerator to the front economizer 42 and the main economizer 41, and is a route to a branch point between the second route 82 and the third route 83. The second route 82 is a route from the branch point of the first route 81 to the main economizer 41 after passing through the front economizer 42. The third route 83 is a route from the branch point of the first route 81, bypassing the front economizer 42 to the main economizer 41. The fourth route 84 is a route in which the second route 82 and the third route 83 merge, and is a route connected to the main economizer 41. The adjusting valve 70 has a mechanism for adjusting the ratio between the boiler water passing through the second route 82 and the boiler water passing through the third route 83.

Thereby, for example, by increasing the proportion of the boiler water passing through the second path 82, the temperature of the boiler water supplied from the fourth path 84 to the main economizer 41 can be increased, so that the low temperature corrosion is prevented. Less likely to occur. On the other hand, by increasing the proportion of the boiler water that passes through the third route 83, the temperature of the boiler water that is supplied from the fourth route 84 to the main economizer 41 can be lowered, so that the waste heat recovery efficiency is high. Can be improved. As described above, by adjusting the adjusting valve 70 manually or automatically according to the situation, it is possible to improve the waste heat recovery efficiency while preventing low temperature corrosion. Further, since the position of the front economizer 42 is located within the boiler body region 2a, dew condensation does not occur when the exhaust gas comes into contact with the front economizer 42, and low temperature corrosion does not occur.

Although the preferred embodiment of the present invention has been described above, the above configuration can be modified as follows, for example.

The shapes, positions, and configurations of the respective parts constituting the waste heat boiler 2 described in the above embodiment are examples, and other shapes or configurations may be used. For example, the front economizer 42 may be located on the superheater 30 side instead of the evaporator 20 side. Further, it may be located so as to straddle the evaporator 20 and the superheater 30.

In the above embodiment, the steam generated by the waste heat boiler 2 is used for power generation in the steam turbine generator 60 and for heating the boiler water, but the method of using steam may be different. For example, instead of or in addition to heating the boiler water, it can be used to heat the air supplied to the incinerator 10.

1 Waste Heat Recovery System 2 Waste Heat Boiler 2a Boiler Main Area 10 Incinerator (Waste Incinerator)
20 Evaporator 30 Superheater 40 Economizer 41 Main economizer 42 Preliminary economizer 70 Regulator valve (regulator)
71 Control Device 80 Supply Route 81 First Route 82 Second Route 83 Third Route 84 Fourth Route

Claims (5)

In the waste heat boiler that recovers the heat of the exhaust gas discharged from the waste incinerator,
A economizer that heats boiler water by heat exchange with exhaust gas,
An evaporator that generates steam by exchanging heat between the boiler water heated by the economizer and the exhaust gas,
A superheater for heating (superheating) the vapor generated by the evaporator,
A supply route that is a route for supplying boiler water to the economizer,
The adjustment section,
Equipped with
The economizer is
A pre economizer arranged in the boiler body region in which the evaporator and the superheater are arranged,
A main economizer arranged downstream of the boiler body region in the exhaust gas flow direction,
Is configured to include,
The supply path is configured to include a first path, a second path, a third path, and a fourth path,
The first route is a route from a deaerator to the front economizer and the main economizer, and is a route to a branch point between the second route and the third route,
The second route is a route from the branch point of the first route to the main economizer after passing through the front economizer,
The third route is a route from the branch point of the first route, bypassing the front economizer to the main economizer,
The fourth route is a route where the second route and the third route join, and is a route connected to the main economizer,
The adjusting unit has a mechanism for adjusting a ratio of boiler water passing through the second route and boiler water passing through the third route,
The temperature of the boiler water supplied to the main economizer is adjusted by adjusting the ratio between the boiler water passing through the second route and the boiler water passing through the third route by the adjusting unit. A waste heat boiler characterized by a temperature that prevents low-temperature corrosion in the economizer. The waste heat boiler according to claim 1, wherein
The said front economizer is a waste heat boiler characterized by being arrange|positioned in the said boiler main body area|region in the temperature range of the exhaust gas which passes 400 to 650 degreeC. The waste heat boiler according to claim 1 or 2, wherein
The waste heat boiler, wherein the front economizer is arranged in the vicinity of an area where the superheater is arranged and upstream in the exhaust gas flow direction. A waste heat boiler according to any one of claims 1 to 3,
A boiler that controls the adjusting unit based on at least one of data regarding combustion in the waste incinerator, data indicating exhaust gas properties, and data regarding the state of the waste heat boiler, and that passes through the second path. A controller for adjusting the ratio of water and boiler water passing through the third path;
A waste heat recovery system comprising: A waste heat recovery method using the waste heat boiler according to any one of claims 1 to 3,
A method for recovering waste heat, comprising the step of adjusting the adjusting unit so that the temperature of the boiler water supplied to the main economizer is a temperature that prevents low temperature corrosion in the main economizer.

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