JP2012057860A - Exhaust heat recovery device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust heat recovery device capable suppressing the occurrence of problems such as the corrosion of a heat transfer tube caused by the alternate wetting and drying of an economizer by the load fluctuation of a burning appliance.SOLUTION: In the exhaust heat recovery device 10 in which the dry-type economizer 11 for heating supply water by utilizing the sensible heat of an exhaust gas and a condensation economizer 12 disposed at a downstream side in the exhaust gas flowing direction with respect to the dry-type economizer for heating the supply water by utilizing the condensation latent heat of the exhaust gas are disposed in a duct 5 in which the exhaust gas is circulated, and which is constituted to guide the supply water to the dry-type economizer 11 through the condensation economizer 12, an exhaust gas temperature changing means 20 for changing the temperature of the exhaust gas is disposed between the dry-type economizer 11 and the condensation-type economizer 12, and the exhaust gas temperature changing means 20 is a means for changing an exhaust gas temperature so that an exhaust gas temperature at an outlet of the dry-type economizer reaches a water dew point or higher, or a means for changing the exhaust gas temperature so that the exhaust gas temperature at an inlet of the condensation economizer reaches the water dew point or lower.

Description

  The present invention relates to an exhaust heat recovery apparatus including an economizer that heats feed water by residual heat of exhaust gas, and more particularly to an exhaust heat recovery apparatus in which a dry economizer and a condensation economizer are arranged in series on an exhaust gas duct.

  Conventionally, in a combustion device such as a boiler, an exhaust heat recovery device is provided to improve thermal efficiency. As one of the exhaust heat recovery devices, an economizer that is provided in an exhaust gas duct and heats feed water by the residual heat of the exhaust gas flowing through the duct is widely known. This economizer is generally a dry economizer that recovers only the sensible heat of exhaust gas, but as a device configuration that further improves the heat recovery rate, a condensing economizer that condenses water vapor in exhaust gas and recovers latent heat is called a dry economizer. A combined waste heat recovery device has been proposed and put into practical use.

In the case of a boiler, for example, about 300 ° C. combustion exhaust gas generated in the combustion chamber first flows into a dry economizer, where sensible heat is recovered, and then flows into a condensing economizer to mainly recover condensing latent heat. It is discharged from the chimney as an exhaust gas of about ℃.
The condensation economizer is generally composed of a multi-stage heat transfer tube group. Combustion exhaust gas is supplied to the outside of the tube, and feed water is supplied to the inside of the tube. Sensible heat from the exhaust gas (convection heat transfer) and latent heat accompanying moisture condensation on the surface of the heat transfer tube Recover. As is well known, when combustion is performed in a combustion device using hydrocarbons such as coal, heavy oil, and gas as fuel, hydrogen constituting the hydrocarbons reacts with oxygen to generate water vapor, which is a large amount in the exhaust gas. include. Therefore, a condensation economizer that condenses water vapor in exhaust gas and recovers latent heat is an extremely effective means for improving thermal efficiency.

  As an exhaust heat recovery device using both a dry economizer and a condensing economizer, Patent Document 1 (Japanese Patent Laid-Open No. 60-213757) has a main heat exchange part and a latent heat recovery heat exchange part integrated in the lower part of the combustion chamber. The structure of the heat exchanger arranged in the form is disclosed. In this heat exchanger, the feed water is introduced into the main heat exchange section through the latent heat recovery heat exchange section, while the combustion exhaust gas is first subjected to sensible heat recovery in the main heat exchange section and then the latent heat. The steam in the exhaust gas is actively condensed in the heat exchanger for recovery to recover the latent heat of steam.

  As another device configuration, in Patent Document 2 (Japanese Patent Laid-Open No. 11-118104), a dry economizer is arranged following the boiler outlet duct, and an air preheater and a condensing economizer are sequentially arranged in series on the downstream side thereof. A boiler configuration is disclosed. In this boiler, the amount of heat remaining in the exhaust gas at the outlet of the dry economizer is effectively recovered by the air preheater and the condensing economizer together with the amount of heat held by the water vapor contained in the exhaust gas to improve the thermal efficiency. Is.

JP 60-213757 A JP 11-118104 A

  However, as disclosed in Patent Documents 1 and 2, in the exhaust heat recovery device in which the dry economizer and the condensing economizer are arranged in series, the condensation of moisture in the exhaust gas can be performed even if the gas side mainstream does not reach the water dew point. Since condensation occurs when the heat transfer tube temperature is at the water dew point, condensation may partially occur in the dry economizer depending on the heat transfer tube temperature. As a result of the condensation, a partial wet region is formed in the heat transfer tube, and the heat transfer tube has a wet region and a dry region in one economizer.

The positions of the wet area and the dry area vary as the load of the combustion device varies. In other words, when the load on the combustion equipment fluctuates, the exhaust gas temperature that passes through the dry economizer or the condensation economizer fluctuates, so the position where the exhaust gas reaches the condensing temperature fluctuates, and the boundary position between the wet and dry regions fluctuates .
Thereby, the area | region which repeats wet and dry will arise in a heat exchanger tube. The heat transfer tube is mainly made of metal, and the heat transfer tube is likely to cause stress corrosion cracking by repeated drying and wetting. Moreover, when the surface of the heat transfer tube repeats drying and wetting, dust and scale are likely to adhere and solidify, which may cause a decrease in heat exchange efficiency.

  Therefore, in view of the problems of the prior art, the present invention has an object to provide an exhaust heat recovery device capable of suppressing the occurrence of problems such as corrosion of a heat transfer tube due to the economizer repeatedly drying and wetting due to load fluctuations of combustion equipment. To do.

  In order to solve the above problems, an exhaust heat recovery apparatus according to the present invention includes a dry economizer that heats feed water using sensible heat of the exhaust gas in a duct through which the exhaust gas circulates, and an exhaust gas flow direction from the dry economizer. In the exhaust heat recovery apparatus, which is provided on the downstream side and is provided with a condensation economizer configured to heat feed water using the condensation latent heat of the exhaust gas, and configured to introduce the feed water to the dry economizer through the condensation economizer An exhaust gas temperature changing means for changing the temperature of the exhaust gas is interposed between the dry economizer and the condensation economizer so that the exhaust gas temperature changing means has an exhaust gas temperature at the outlet of the dry economizer equal to or higher than a water dew point. Means for changing the exhaust gas temperature, or exhaust gas so that the exhaust gas temperature at the condenser economizer inlet is below the water dew point. Characterized in that it is a means for changing the scan temperature.

  According to the present invention, the exhaust gas temperature changing means is interposed between the dry economizer and the condensation economizer so that the exhaust gas temperature changing means causes the exhaust gas temperature at the outlet of the dry economizer to be equal to or higher than the water dew point, or the exhaust gas at the condensing economizer inlet. Since the exhaust gas temperature is changed so that the temperature is below the water dew point, it is possible to prevent heat transfer tubes that repeat drying and wetting with a dry economizer or condensation economizer, and to prevent corrosion of the heat transfer tubes and adhesion of scales to the heat transfer tubes. It becomes possible to suppress.

Specifically, when the exhaust gas temperature changing means is a means for changing the exhaust gas temperature so that the exhaust gas temperature at the outlet of the dry economizer is equal to or higher than the water dew point, moisture in the exhaust gas does not condense in the dry economizer, Almost all heat transfer tube surfaces of the dry economizer can be kept dry at all times. On the other hand, if the exhaust gas temperature changing means is a means for changing the exhaust gas temperature so that the exhaust gas temperature at the inlet of the condensing economizer is lower than the water dew point, condensation will surely occur in the condensing economizer, All heat transfer tube surfaces can be kept wet all the time. Here, the exhaust gas temperature changing means may be configured to have both the former and the latter, and in that case, it is possible to reliably maintain the dry economizer in a constantly dry state and the condensation economizer in a constantly wet state. It becomes.
The exhaust gas temperature at the dry economizer outlet is preferably the heat transfer tube metal temperature at the exhaust gas outlet side of the dry economizer, and the exhaust gas temperature at the condensation economizer inlet is the heat transfer tube metal temperature at the exhaust gas inlet side of the condensation economizer. Preferably there is. Thereby, it is possible to appropriately manage the presence or absence of condensation on the heat transfer tube surface.

  Further, the exhaust gas temperature changing means is a branch gas introduction section for introducing a branch gas obtained by branching a part of the exhaust gas from the upstream side of the dry economizer between the dry economizer and the condensation economizer, and the dry economizer A first temperature detection means for detecting a feed water inlet temperature or a heat transfer tube metal temperature on the exhaust gas outlet side of the dry economizer, and the duct from the branch gas introduction part based on the temperature detected by the first temperature detection means A branch gas amount adjusting means for adjusting the amount of branch gas introduced into the branch gas amount adjusting means, and when the temperature detected by the first temperature detecting means falls below a water dew point, the branch gas amount adjusting means adjusts the branch gas. It is preferable to increase the introduction amount.

In this configuration, a part of the exhaust gas is branched from the upstream side of the dry economizer, and this branch gas is introduced from a branch gas introduction section provided between the dry economizer and the condensation economizer. Since this branch gas does not pass through the dry economizer, it has a large amount of heat, and by supplying this directly to the condensing economizer, the exchange heat amount in the condensing economizer is increased and the feed water temperature is raised. Therefore, by adjusting the branch gas introduction amount, it is possible to adjust the temperature of the feed water flowing into the dry economizer, and thus the heat transfer tube metal temperature of the dry economizer. Here, the heat transfer tube metal temperature depends on both the exhaust gas temperature and the feed water temperature, but the heat transfer coefficient of the exhaust gas is extremely small compared to the heat transfer coefficient of the feed water. Receive a lot. Therefore, in this structure, the presence or absence of condensation on the surface of the heat transfer tube can be adjusted by the feed water temperature.
And by adjusting the amount of branch gas introduction based on the feed water inlet temperature of the dry economizer or the heat transfer pipe metal temperature on the exhaust gas outlet side of the dry economizer, the heat transfer pipe metal temperature of the dry economizer can be maintained above the water dew point. The surface of the heat transfer tube is always kept in a dry state, and corrosion of the heat transfer tube of the dry economizer and adhesion of scales to the heat transfer tube can be suppressed.

  Further, a second temperature detection means for detecting a feed water outlet temperature of the condensation economizer or a heat transfer pipe metal temperature on an exhaust gas inlet side of the condensation economizer, and a moisture supply means for supplying moisture to the inlet side of the condensation economizer And when the temperature detected by the second temperature detection means is equal to or higher than the water dew point, the water supply means sprays water or steam on the inlet side of the condensation economizer, or directly sprays the condensation economizer. Is preferred.

  In this way, the water supply outlet temperature of the condensing economizer or the heat transfer pipe metal temperature on the exhaust gas inlet side of the condensing economizer is detected, and when the detected temperature exceeds the water dew point, water is supplied to the condensing economizer by the water supply means. The heat transfer tube surface of the economizer can be wetted. Specifically, by spraying water or steam on the inlet side of the condensation economizer, it is possible to increase the humidity of the exhaust gas and promote condensation. Alternatively, the heat transfer tube can be forcibly moistened by spraying water directly onto the condensation economizer.

  Further, the exhaust gas temperature changing means is a dry / condensation economizer that is detachably interposed between the dry economizer and the condensation economizer, and heats the feed water using sensible heat and latent heat of condensation of the exhaust gas. The feed water discharged through the condensation economizer is introduced into the dry economizer through the dry / condensation economizer, and the dry / condensation economizer is disposed from the inlet side of the dry / condensation economizer. It is preferable to provide a bypass pipe that bypasses and is connected to the outlet side and through which the water supply flows.

  In this way, by arranging the dry / condensation economizer between the dry economizer and the condensing economizer, and by configuring the dry / condensing economizer to reliably start condensation, the dry economizer is always in a dry state and the condensing economizer. Is always maintained in a wet state, whereby corrosion of the heat transfer tubes in each economizer and adhesion of scales to the heat transfer tubes can be suppressed. Preferably, on the duct extending from the dry economizer to the wet economizer, a wet / dry mixed area including the condensation start point of the exhaust gas is estimated in advance, and the dry / condensed economizer is disposed in the dry / humid mixed area. As a method for estimating the wet and dry mixed area, the condensation start point can be estimated based on the metal temperature calculated from the exhaust gas temperature and the feed water temperature, and the wet and dry based on the condensation start point and the operation fluctuation range (load fluctuation width). The mixed area can be estimated. The driving fluctuation range is obtained from experience values (including past actual measurement data), experimental data, or simulation.

  In this configuration, the heat transfer tube of the dry / condensation economizer partially repeats a dry state and a wet state. However, since this dry / condensation economizer is detachable, corrosion or scale adhesion occurs. Only a dry / condensing economizer can be removed and repaired or replaced. In addition, a bypass pipe is provided that bypasses the dry / condensation economizer to distribute the water supply.If a problem occurs in the dry / condensation economizer, the dry / condensation economizer is temporarily stopped and the bypass pipe is opened. It is possible to continue the steady operation by circulating the water supply.

  Furthermore, the exhaust gas temperature changing means is a dry / condensation economizer that is detachably interposed between the dry economizer and the condensation economizer, and that heats the feed water using sensible heat and latent heat of condensation of the exhaust gas. The feed water introduced into the dry / condensation economizer is configured to circulate through a feed water system independent of the dry economizer and the feed water introduced into the condensation economizer, and the feed water temperature at the dry / condensation economizer inlet Is preferably below the water dew point.

In this way, by placing the dry / condensation economizer between the dry economizer and the condensing economizer, the dry economizer is always kept in the dry state and the condensing economizer is always in the moist state as described above. Corrosion of heat transfer tubes and adhesion of scales to the heat transfer tubes in each economizer can be suppressed. Also in this configuration, it is preferable to preliminarily estimate the dry and wet mixed region including the exhaust gas condensation start point, and arrange the dry / condensation economizer in this dry and wet mixed region.
Furthermore, the water supply system of the dry / condensation economizer is configured independently, and the water supply temperature at the inlet of the dry / condensation economizer is set to be equal to or lower than the water dew point, whereby condensation can be reliably generated in the dry / condensation economizer.

  As described above, in the present invention, the exhaust gas temperature changing means is interposed between the dry economizer and the condensing economizer so that the exhaust gas temperature at the outlet of the dry economizer becomes higher than the water dew point by the exhaust gas temperature changing means, or the condensing economizer. Since the exhaust gas temperature is changed so that the exhaust gas temperature at the inlet is below the water dew point, it is possible to prevent heat transfer tubes that repeat drying and wetting with a dry economizer or a condensation economizer, and corrosion of the heat transfer tubes, scale to the heat transfer tubes, etc. Can be suppressed.

1 is an overall configuration diagram of a boiler to which an embodiment of the present invention is applied. It is a lineblock diagram of the exhaust heat recovery device concerning a 1st embodiment of the present invention. It is a block diagram of the waste heat recovery apparatus which concerns on 2nd Embodiment of this invention. It is a block diagram of the waste heat recovery apparatus which concerns on 3rd Embodiment of this invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.
An exhaust heat recovery apparatus according to an embodiment of the present invention is an apparatus that recovers exhaust heat from exhaust gas generated in combustion equipment such as a boiler, a diesel engine, a gas turbine, an incinerator, and a heating furnace.

First, a configuration of a boiler to which an exhaust heat recovery apparatus according to an embodiment of the present invention is applied will be described with reference to FIG. The boiler 1 mainly includes a combustion chamber 2 in which a burner 3 is provided, a heat transfer tube 4 that generates steam using combustion gas, a duct 5 that extends from the outlet of the combustion chamber 2, and a duct 5. An exhaust heat recovery apparatus 10 disposed and a chimney 6 connected to the duct 5 are provided.
In the combustion chamber 2 of the boiler 1, the fuel and combustion air supplied from the burner 3 are combusted to generate high-temperature combustion gas. The combustion gas is heat-exchanged in the heat transfer tube 4 to heat the water in the tube and generate steam. The exhaust gas generated in this process passes through the duct 5 extended from the outlet of the combustion chamber 2 and is recovered by the exhaust heat recovery device 10 and then discharged from the chimney 6.

The exhaust heat recovery apparatus 10 has a plurality of heat exchangers arranged in series on the duct 5. In this embodiment, at least a dry economizer 11 and a wet economizer 12 are provided in this embodiment as the heat exchanger in order from the upstream side in the exhaust gas flow direction.
The dry economizer 11 is a heat exchanger that is composed of a multi-stage heat transfer tube group, heat-exchanges the feed water flowing through the pipe and the exhaust gas flowing outside the pipe, and heats the feed water using the sensible heat of the exhaust gas.
The condensation economizer 12 is composed of a multi-stage heat transfer tube group, and is a heat exchanger that exchanges heat between the feed water flowing inside the tube and the exhaust gas flowing outside the tube, and heats the feed water using the condensation latent heat of the exhaust gas.

  As the first water supply system 14 of these economizers, the feed water pumped from the pump 13 is introduced into the heat transfer pipe from the downstream side in the exhaust gas flow direction of the condensation economizer 12, and passes through the condensation economizer 12 in the upstream side in the exhaust gas flow direction. Then, it is introduced into the heat transfer pipe from the downstream side in the exhaust gas flow direction of the dry economizer 11 and is discharged from the upstream side in the exhaust gas flow direction through the dry economizer 11.

  In FIG. 1, as an example, an exhaust gas flow is formed from the upper side to the lower side of the duct 5 extending in the vertical direction, a dry economizer 11 is disposed above the duct portion, and a condensing economizer 12 is disposed below. Although the arrangement is shown, the present invention is not limited to this, and each economizer may be arranged in a duct portion where the exhaust gas flow is formed from below to above, or the exhaust gas flow is formed in the horizontal direction. Each economizer may be arranged in a duct part.

Further, in the present embodiment, an exhaust gas temperature changing means for changing the temperature of the exhaust gas is interposed between the dry economizer 11 and the condensation economizer 12.
The exhaust gas temperature changing means changes the exhaust gas temperature so that the exhaust gas temperature at the dry economizer outlet 11a is higher than the water dew point, or changes the exhaust gas temperature so that the exhaust gas temperature at the condensed economizer inlet 12a is lower than the water dew point. Means.
Thereby, it is possible to prevent a heat transfer tube that repeats drying and wetting with the dry economizer 11 or the condensation economizer 12, and to suppress corrosion of the heat transfer tube and adhesion of scales to the heat transfer tube.

Specifically, when the exhaust gas temperature changing means is a means for changing the exhaust gas temperature so that the exhaust gas temperature at the dry economizer outlet 11a becomes equal to or higher than the water dew point, moisture in the exhaust gas may be condensed in the dry economizer 11. In addition, almost all the heat transfer tube surfaces of the dry economizer 11 can be kept dry at all times.
On the other hand, when the exhaust gas temperature changing means is a means for changing the exhaust gas temperature so that the exhaust gas temperature at the condensing economizer inlet 12a is equal to or lower than the water dew point, condensation is reliably generated in the condensing economizer 12, and the condensing economizer Almost all twelve heat transfer tube surfaces can be kept moist at all times.

The exhaust gas temperature changing means may be configured to have both the former and the latter, and in that case, the dry economizer 11 can be always kept in a dry state and the condensing economizer 12 can be always kept in a wet state. It becomes.
The exhaust gas temperature at the dry economizer outlet 11a is preferably the heat transfer tube metal temperature on the exhaust gas outlet 11a side of the dry economizer 11, and the exhaust gas temperature at the condensation economizer inlet 12a is the exhaust gas inlet 12a side of the condensation economizer 12 The heat transfer tube metal temperature is preferred. Thereby, it is possible to appropriately manage the presence or absence of condensation on the heat transfer tube surface.
Next, a specific configuration of the exhaust heat recovery apparatus 10 will be described in the following first to third embodiments.

(First embodiment)
FIG. 2 is a configuration diagram of the exhaust heat recovery apparatus according to the first embodiment of the present invention.
The exhaust heat recovery apparatus 10 according to the first embodiment includes a dry economizer 11 disposed in a duct 5 through which exhaust gas flows, a condensing economizer 12 disposed downstream in the exhaust gas flow direction, and a dry type as an exhaust gas temperature changing means. A branch gas introducing unit 20 interposed between the economizer 11 and the condensing economizer 12 and a first temperature detecting means 23 for detecting a water supply temperature or a heat transfer tube metal temperature of the dry economizer 11 are provided.

  The branch gas introduction unit 20 is configured such that a branch gas obtained by branching a part of the exhaust gas from the upstream side of the dry economizer 11 is introduced between the dry economizer 11 and the condensation economizer 12 by bypassing the dry economizer 11. ing. Specifically, a branch pipe 21 having one end connected to the duct 5 on the upstream side of the dry economizer 11 and the other end connected to the duct 5 between the dry economizer 11 and the condensation economizer 12 is provided. A branch gas amount adjusting means for adjusting the amount of branch gas introduced from 20 is provided.

  The branch gas amount adjusting means is, as an example in FIG. 2, a three-way valve 22 disposed at a connection portion between the branch pipe 21 and the duct 5 on the upstream side of the dry economizer 11. By this three-way valve 22, a predetermined flow rate of the exhaust gas branches from the duct 5 and is introduced from the branch gas introduction unit 20 as a branch gas. The valve arrangement of the branch pipe 21 is not limited to this, and may be an on-off valve arranged on the branch pipe 21.

The first temperature detection means 23 detects the feed water inlet temperature of the dry economizer 11 or the heat transfer tube metal temperature on the exhaust gas outlet side 11 a of the dry economizer 11.
Based on the temperature detected by the first temperature detecting means 23, the branch gas introduction amount is adjusted by the branch gas amount adjusting means. At this time, the control means 25 may be provided. In this case, the control means 25 obtains the opening degree of the three-way valve 22 based on the temperature detection signal input from the first temperature detection means 23, and sends an opening degree control signal to the three-way valve 22 so as to be this opening degree. Send.
The heat transfer tube metal temperature depends on both the exhaust gas temperature and the feed water temperature, but the heat transfer coefficient of the exhaust gas is extremely small compared to the heat transfer coefficient of the feed water, so the heat transfer tube metal temperature greatly affects the feed water temperature. receive. Therefore, in this embodiment, the presence or absence of condensation on the heat transfer tube surface can be adjusted by the feed water temperature.

Here, the operation of the exhaust heat recovery apparatus 10 according to the first embodiment will be described.
In the steady operation, the exhaust gas flowing through the duct 5 is first introduced into the dry economizer 11, and the dry economizer 11 uses the sensible heat of the exhaust gas to heat the feed water. The exhaust gas discharged from the dry economizer 11 is then introduced into the condensing economizer 12, and the condensing economizer 12 heats the feed water mainly using the condensing latent heat of the exhaust gas.

  During operation of the exhaust heat recovery device 10, the first temperature detection means 23 detects the feed water inlet temperature of the dry economizer 11 or the heat transfer pipe metal temperature on the exhaust gas outlet side 11 a of the dry economizer 11 and detects it. Based on the temperature, the control means 25 controls the three-way valve 22 to adjust the amount of branch gas introduced from the branch gas introduction section 20. Specifically, when the temperature detected by the first temperature detection means 23 is equal to or lower than the water dew point, the control means 25 controls the three-way valve 22 to increase the branch gas introduction amount.

  As described above, according to the first embodiment, a part of the exhaust gas is branched from the upstream side of the dry economizer, and this branch gas is introduced from the branch gas introduction unit 20 provided between the dry economizer 11 and the condensation economizer 12. Yes. Since this branch gas does not pass through the dry economizer 11, it has a large amount of heat. By supplying this directly to the condensing economizer 12, the amount of exchange heat in the condensing economizer 12 is increased and the feed water temperature is raised. Therefore, by adjusting the branch gas introduction amount, it is possible to adjust the temperature of the feed water flowing into the dry economizer 11, and consequently the heat transfer tube metal temperature of the dry economizer 11.

  And by adjusting the amount of branch gas introduction based on the feed water inlet temperature of the dry economizer 11 or the heat transfer pipe metal temperature on the exhaust gas outlet side of the dry economizer, the heat transfer pipe surface temperature of the dry economizer 11 can be maintained above the water dew point, As a result, the heat transfer tube surface can be kept dry at all times, and corrosion of the heat transfer tube of the dry economizer 11 and adhesion of scales to the heat transfer tube can be suppressed.

In the first embodiment, the water supply outlet temperature of the condensation economizer 12 or the heat transfer pipe metal temperature on the exhaust gas inlet side 12a of the condensation economizer 12 and the moisture on the inlet side 12a of the condensation economizer 12 It is preferable to have a water supply means 27 for supplying water.
As the water supply means 27, means for spraying water or steam on the inlet side 12 a of the condensation economizer 12 or means for spraying water directly on the condensation economizer 12 can be used.
With these configurations, when the temperature detected by the second temperature detection means 26 is equal to or higher than the water dew point, the water supply means 27 sprays water or steam on the inlet side 12a of the condensation economizer 12, or the condensation economizer 11 Water directly. When the control means 25 is provided, the control means 25 transmits a control signal for operating the water supply means 27 based on the temperature detection signal input from the second temperature detection means 26.

  Thus, the water supply outlet temperature of the condensing economizer 12 or the heat transfer pipe metal temperature on the exhaust gas inlet side 12a of the condensing economizer 12 is detected, and water is supplied to the condensing economizer 12 by the water supply means 27 when the detected temperature becomes equal to or higher than the water dew point. By doing so, the heat transfer tube surface of the condensation economizer 12 can be wetted. Specifically, by spraying water or steam on the inlet side 12a of the condensation economizer 12, the humidity of the exhaust gas can be increased to promote condensation. Alternatively, the heat transfer tube surface can be forcibly moistened by directly spraying the condensation economizer 12 with water.

  Next, an application example of the first embodiment will be described. All of the configurations shown below prevent condensation from occurring in the dry economizer 11 and are preferably used in combination with the configuration of the first embodiment already described.

  As a first application example, an auxiliary branch pipe 30 in which the branch pipe 21 is further branched from the middle is provided, and the downstream end of the auxiliary branch pipe 30 is connected to the middle stage of the dry economizer 11. A three-way valve 31 is provided at the connection between the branch pipe 21 and the auxiliary branch pipe 30. Then, the three-way valve 31 is controlled based on the temperature detected by the first temperature detecting means 23, and the branch gas introduction amount introduced into the middle stage of the dry economizer 11 through the auxiliary branch pipe 30 is adjusted. Specifically, when the temperature detected by the first temperature detection means 23 is equal to or lower than the water dew point, the three-way valve 31 is controlled so that the auxiliary branch pipe 30 is opened, and the branch gas is passed through the auxiliary branch pipe 30. Is introduced into the middle of the dry economizer 11.

  In this way, when the feed water inlet temperature of the dry economizer 11 or the heat transfer pipe metal temperature on the exhaust gas outlet side 11a of the dry economizer 11 becomes below the water dew point, the branch gas is introduced into the middle stage of the dry economizer 11 via the auxiliary branch pipe 30. By doing so, the exhaust gas temperature in the dry economizer 11 is raised, thereby reducing the humidity in the exhaust gas and suppressing condensation.

  As a second application example, an auxiliary branch pipe 32 in which the branch pipe 21 is further branched from the middle is provided, and the downstream end of the auxiliary branch pipe 32 is connected to the downstream duct of the condensation economizer 12. A three-way valve 33 is provided at the connection between the branch pipe 21 and the auxiliary branch pipe 32. Then, the three-way valve 33 is controlled based on the temperature detected by the first temperature detecting means 23, and the branch gas introduction amount introduced into the downstream side of the condensation economizer 12 through the auxiliary branch pipe 32 is adjusted. Specifically, when the temperature detected by the first temperature detection means 23 is equal to or lower than the water dew point, the three-way valve 33 is controlled so that the amount of branch gas flowing through the auxiliary branch pipe 32 is reduced, and the dry economizer 11 is controlled. Increase the amount of exhaust gas introduced. As a result, the exhaust gas temperature in the dry economizer 11 rises and the humidity in the exhaust gas decreases, so that condensation of moisture in the exhaust gas can be suppressed.

  The auxiliary branch pipe 32 may be one conventionally used for white smoke prevention. Normally, when the exhaust gas is released from the chimney 6 (see FIG. 1) into the atmosphere, the water vapor in the exhaust gas is cooled and white smoke is generated. Released after heating. For heating, exhaust gas upstream from the exhaust heat recovery device 10 is used. That is, the exhaust gas upstream of the dry economizer 11 is partially branched, and this branched gas is merged before the chimney. By reducing the amount of branch gas branched from the auxiliary branch pipe 32, the amount of exhaust gas introduced into the dry economizer 11 is increased, and moisture condensation in the dry economizer 11 is suppressed.

(Second Embodiment)
FIG. 3 is a configuration diagram of the exhaust heat recovery apparatus according to the second embodiment of the present invention.
The exhaust heat recovery apparatus 10 according to the second embodiment includes a dry economizer 11 disposed in a duct 5 through which exhaust gas flows, a condensing economizer 12 disposed downstream in the exhaust gas flow direction, and an exhaust gas temperature changing means as a dry type. A dry / condensation economizer 35 is interposed between the economizer 11 and the condensing economizer 12.

The dry / condensation economizer 35 is a heat exchanger that heats feed water using sensible heat of exhaust gas and latent heat of condensation, and is detachably attached to the duct 5.
Preferably, on the duct 5 extending from the dry economizer 11 to the wet economizer 12, a wet / dry mixed area including the condensation start point of the exhaust gas is estimated in advance, and the dry / condensed economizer 35 is disposed in the dry / humid mixed area. As a method of estimating the wet and dry mixed area, the condensation start point can be estimated based on the metal temperature calculated from the exhaust gas temperature and the feed water temperature, and the wet and dry based on the condensation start point and the operation fluctuation range (load fluctuation range) of the boiler. The mixed area can be estimated. The driving fluctuation range is obtained from experience values (including past actual measurement data), experimental data, or simulation.

  As the first water supply system 14 of these economizers 11, 35, and 12, the feed water pumped from the pump 13 (see FIG. 1) is introduced into the heat transfer pipe from the downstream side in the exhaust gas flow direction of the condensation economizer 12, and the condensation is performed. It is discharged from the upstream side in the exhaust gas flow direction through the economizer 12, then introduced into the heat transfer pipe from the downstream side in the exhaust gas flow direction of the dry / condensation economizer 35, and discharged from the upstream side in the exhaust gas flow direction through the dry / condensation economizer 35 Furthermore, it is introduced into the heat transfer pipe from the downstream side of the exhaust gas flow direction of the dry economizer 11 and discharged from the upstream side of the exhaust gas flow direction through the dry economizer 11.

  In addition, the first water supply system 14 has a bypass pipe 36 that bypasses the dry / condensation economizer 35 from the inlet side of the dry / condensation economizer 35 and is connected to the outlet side of the dry / condensation economizer 35. A three-way valve 37 is provided at the connection portion between the inlet side of the dry / condensation economizer 35 and the bypass pipe 36.

Here, the operation of the exhaust heat recovery apparatus 10 according to the second embodiment will be described.
The exhaust gas flowing through the duct 5 is first introduced into the dry economizer 11, and the dry economizer 11 uses the sensible heat of the exhaust gas to heat the feed water. The exhaust gas discharged from the dry economizer 11 is then introduced into the dry / condensation economizer 35, where the feed water is heated using the sensible heat and latent heat of condensation of the exhaust gas. In the dry / condensation economizer 35, moisture may be supplied by the moisture supply means 38 so that condensation occurs reliably. The moisture supply means 38 has the same configuration as the moisture supply means 27 shown in FIG. The exhaust gas discharged from the dry / condensation economizer 35 is further introduced into the condensing economizer 12, and the condensing economizer 12 mainly heats the feed water using the condensing latent heat of the exhaust gas.

  In this way, by arranging the dry / condensation economizer 35 between the dry economizer 11 and the condensing economizer 12, and by configuring the dry / condensing economizer 35 to reliably start condensing, the dry economizer 11 is always in a dry state. In addition, the condensation economizer 12 is always maintained in a wet state, whereby corrosion of the heat transfer tubes in each economizer and adhesion of scales to the heat transfer tubes can be suppressed.

  In the second embodiment described above, the heat transfer tube of the dry / condensation economizer 35 partially repeats a dry state and a wet state. However, since the dry / condensation economizer 35 is detachable, corrosion and scale can be removed. When adhesion or the like occurs, only the dry / condensation economizer 35 can be removed and repaired or replaced. Further, since the bypass pipe 36 through which the feed water flows is arranged by bypassing the dry / condensation economizer 35, when a problem occurs in the dry / condensation economizer 35, the three-way valve 37 is controlled to supply water only to the bypass pipe 36. The dry / condensing economizer 35 may be temporarily stopped and the steady operation may be continued. The dry / condensation economizer 35 is repaired and replaced during regular maintenance.

(Third embodiment)
FIG. 4 is a configuration diagram of an exhaust heat recovery apparatus according to the third embodiment of the present invention.
The exhaust heat recovery apparatus 10 according to the third embodiment includes a dry economizer 11 disposed in a duct 5 through which exhaust gas flows, a condensing economizer 12 disposed downstream in the exhaust gas flow direction, and a dry type as an exhaust gas temperature changing means. A dry / condensation economizer 40 is interposed between the economizer 11 and the condensing economizer 12.

As the first water supply system 14 of these economizers, water supplied by pump 13 (see FIG. 1) is introduced into the heat transfer pipe from the downstream side in the exhaust gas flow direction of the condensing economizer 12 and passes through the condensing economizer 12. It is discharged from the upstream side in the exhaust gas flow direction, then introduced into the heat transfer pipe from the downstream side in the exhaust gas flow direction of the dry economizer 11, and discharged from the upstream side in the exhaust gas flow direction through the dry economizer 11.
Further, as a second water supply system 41 provided independently of the first water supply system 14, the dry / condensation economizer 40 is introduced into the heat transfer pipe from the downstream side in the exhaust gas flow direction of the dry / condensation economizer 40. It has a water supply system that is discharged from the upstream side in the exhaust gas flow direction. The second feed water system 41 is supplied with feed water such that the feed water temperature at the dry / condensation economizer inlet is equal to or lower than the water dew point.

As described above, by arranging the dry / condensation economizer 40 between the dry economizer 11 and the condensing economizer 12, the dry economizer 11 is always in a dry state and the condensing economizer 12 is the same as the operation effect described in the second embodiment. Is always maintained in a wet state, whereby corrosion of the heat transfer tubes in each economizer and adhesion of scales to the heat transfer tubes can be suppressed.
In addition, the water supply system of the dry / condensation economizer 40 is configured as an independent second water supply system 41, and the water supply temperature at the dry / condensation economizer inlet is set to a water dew point or less, so that the dry / condensation economizer 40 can reliably Condensation can occur.

DESCRIPTION OF SYMBOLS 1 Boiler 5 Duct 10 Waste heat recovery apparatus 11 Dry type economizer 12 Condensation economizer 14 1st water supply system 20 Branch gas introduction part 21 Branch pipe 22 Three-way valve 23 1st temperature detection means 25 Control means 26 2nd temperature detection means 27 Water supply means 30, 32 Auxiliary branch pipes 31, 33 Three-way valve 35 Dry / condensation economizer 37 Three-way valve 38 Water supply means 40 Dry / condensation economizer 41 Second water supply system

Claims (5)

A dry economizer that heats feed water using sensible heat of the exhaust gas in a duct through which the exhaust gas circulates, and a condenser that is disposed downstream of the dry economizer in the direction of exhaust gas flow and heats the feed water using latent heat of condensation of the exhaust gas In an exhaust heat recovery apparatus provided with an economizer and configured to introduce the water supply to the dry economizer through the condensation economizer,
An exhaust gas temperature changing means for changing the temperature of the exhaust gas is interposed between the dry economizer and the condensation economizer,
The exhaust gas temperature changing means changes the exhaust gas temperature so that the exhaust gas temperature at the dry economizer outlet becomes equal to or higher than the water dew point, or changes the exhaust gas temperature so that the exhaust gas temperature at the condensed economizer inlet becomes equal to or lower than the water dew point. An exhaust heat recovery apparatus characterized by being a means. The exhaust gas temperature changing means is a branch gas introduction section for introducing a branch gas obtained by branching a part of the exhaust gas from the upstream side of the dry economizer between the dry economizer and the condensation economizer;
First temperature detecting means for detecting a feed water inlet temperature of the dry economizer or a heat transfer pipe metal temperature on an exhaust gas outlet side of the dry economizer, and the branch gas introducing section based on the temperature detected by the first temperature detecting means And further comprising a branch gas amount adjusting means for adjusting the amount of branch gas introduced into the duct.
2. The exhaust heat recovery apparatus according to claim 1, wherein when the temperature detected by the first temperature detection unit becomes equal to or lower than a water dew point, the branch gas introduction amount is increased by the branch gas amount adjustment unit. A second temperature detection means for detecting a feed water outlet temperature of the condensation economizer or a heat transfer pipe metal temperature on an exhaust gas inlet side of the condensation economizer; and a water supply means for supplying moisture to the inlet side of the condensation economizer,
When the temperature detected by the second temperature detection means becomes equal to or higher than the water dew point, water or steam is sprayed on the inlet side of the condensation economizer by the moisture supply means, or water is sprayed directly on the condensation economizer. The exhaust heat recovery apparatus according to claim 2. The exhaust gas temperature changing means is a dry / condensation economizer that is detachably interposed between the dry economizer and the condensation economizer and heats the feed water using sensible heat and latent heat of condensation of the exhaust gas,
The feed water discharged through the condensing economizer is configured to be introduced into the dry economizer through the dry / condensing economizer, and bypassing the dry / condensing economizer from the inlet side of the dry / condensing economizer The exhaust heat recovery apparatus according to any one of claims 1 to 3, further comprising a bypass pipe connected to the outlet side through which the water supply flows. The exhaust gas temperature changing means is a dry / condensation economizer that is detachably interposed between the dry economizer and the condensation economizer and heats the feed water using sensible heat and latent heat of condensation of the exhaust gas,
The feed water introduced into the dry / condensation economizer is configured to circulate through a water supply system independent of the dry economizer and the feed water introduced into the condensation economizer, and the feed water temperature at the dry / condensation economizer inlet is water. The exhaust heat recovery apparatus according to any one of claims 1 to 3, wherein the exhaust heat recovery apparatus has a dew point or less.

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