JPH11347332A - Flue gas treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the inlet temperature of a flue gas at the inlet of an electric dust collector to at highest an upper limit value even in the case the inlet temperature of the flue gas of a heat recovering apparatus fluctuates. SOLUTION: In the case of suppressing the outlet flue gas temperature of a heat recovering apparatus 13 to a previously set upper limit value of lower, cooling water is supplied through a flow rate adjustment valve 47 to a drain tank 20 installed in a heat medium circulation route 15-2 to lower the temperature of the heat medium flowing into a heat recovering apparatus 11. Consequently, even in the case the inlet flue gas temperature of the heat recovering apparatus 11 fluctuates, the outlet flue gas temperature of the heat recovering apparatus 11 (the inlet flue gas temperature of an electric dust collector) can be suppressed to at highest the upper limit value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas treatment system, and more particularly, to a heat recovery device for reheating flue gas discharged from a wet flue gas treatment device in order to reduce the concentration of soot and dust. The present invention relates to a flue gas treatment system which is arranged on the upstream side of a dry electric precipitator to suppress the smoke exhaust temperature at the inlet of the dry electric precipitator.

[0002]

2. Description of the Related Art Such a flue gas treatment system has conventionally been disclosed in Japanese Patent Publication No. 07-056377 and Japanese Patent Laid-Open No.
The thing described in 122438 gazette is known. The former flue gas treatment system guides the flue gas discharged from the boiler to an air preheater, heats the combustion air used in the boiler, and converts the dust in the flue gas discharged from the air preheater to a dry electric Dust collector (hereinafter simply referred to as electric dust collector)
After being collected by the method, it is led to a wet flue gas treatment device such as a wet desulfurization device. Since the flue gas discharged from the wet flue gas treatment device has a saturated gas temperature, it is heated to a predetermined temperature and discharged from the chimney. A smoke reheater is located. The heat source of this reheater is obtained by arranging a heat recovery unit in the flue gas system upstream of the wet type flue gas treatment device and circulating a heat medium between the heat recovery unit and the reheater. . In particular, in order to further reduce the concentration of dust in the flue gas, a heat recovery device is disposed upstream of the dust collector to lower the temperature of the flue gas flowing into the dust collector, thereby reducing the electrical resistivity of the dust. The size is reduced to improve dust collection performance.

However, in such a flue gas treatment system, if the flue gas temperature is low, such as when starting a boiler,
The temperature of the flue gas falls below the dew point inside the heat recovery unit, causing dust to adhere to the heat transfer tubes of the heat recovery unit and corroding the heat transfer tubes and downstream equipment.

In order to solve such a problem, as described in the latter Japanese Patent Application Laid-Open No. 09-122438, a pipe for a heat medium flowing through a heat recovery unit is bypassed with a heat recovery unit. When the exhaust gas temperature at the outlet of the heat recovery unit falls below the predetermined lower limit, a part of the heat medium is circulated by bypassing the heat recovery unit to reduce the amount of heat recovery, and the heat recovery unit It has been proposed to keep the exit flue gas temperature above a predetermined lower limit.

[0005]

However, the above-mentioned prior art does not deal with fluctuations in the smoke temperature at the outlet of the air preheater, that is, fluctuations in the smoke temperature at the inlet of the heat recovery unit. There is a problem that sufficient consideration has not been given to controlling the temperature range of the smoke temperature, that is, the temperature range of the smoke exhaust gas temperature at the entrance of the electrostatic precipitator, particularly in terms of suppressing the upper limit temperature.

That is, in order to keep the dust collecting performance of the electric precipitator high, the smoke exhaust temperature at the inlet of the electric precipitator must be 75 to 110 ° C. regardless of the fluctuation of the exhaust gas temperature at the outlet of the air preheater.
(Preferably 80 to 95 ° C.). In order to satisfy this condition, generally, the area (heat transfer area) of the heat transfer tube of the heat recovery unit is determined with the upper limit value (for example, 155 ° C.) of the outlet flue gas temperature of the air preheater as a design condition. However, if the heat transfer area of the heat recovery unit is determined under such design conditions, the heat transfer area becomes relatively too large during operation at a normal temperature (for example, 125 ° C.).
As a result, the heat recovery amount becomes unnecessarily large, and the smoke exhaust gas temperature at the inlet of the electrostatic precipitator falls below the lower limit (for example, 75 ° C.), or the smoke exhaust gas temperature inside the heat collecting device falls below the dew point. It may decrease. In such a case, the dust in the flue gas becomes wet and adheres to the heat transfer tube of the heat recovery unit as described above,
In addition to the problem that the hopper of the electric precipitator is clogged, there is a problem that the heat transfer tube and downstream equipment are corroded at low temperature.

In order to solve such a problem, as described in the latter publication, a part of the heat medium flowing through the heat recovery unit is bypassed to reduce the amount of heat recovery. The exhaust gas temperature at the outlet can be maintained at or above the lower limit. However, if the amount of heat recovered by the heat medium is reduced, the temperature of the heat medium flowing through the reheater may become too low. The heat transfer tube of the vessel may be corroded. Therefore, as described in the publication, the heat medium flowing into the reheater is heated by another heat source such as steam, and the temperature of the heat medium at the outlet of the reheater is set to a lower limit (for example, 75 ° C.) or more. Although it is only necessary to maintain the temperature, it is a problem that constantly heating the heat medium flowing into the reheater during the operation at the normal temperature wastes a large amount of energy.

[0008] Such a problem is caused by setting the design temperature of the exhaust gas at the inlet of the heat recovery unit to an appropriate value (for example, 125 ° C) and reducing the area of the heat transfer tube of the heat recovery unit. The described prior art can also generally solve the problem.

However, if the area of the heat transfer tube of the heat recovery unit is designed according to the normal operation, when the ambient air temperature is high as in summer, the temperature of the smoke discharged from the outlet of the air preheater, that is, the temperature of the exhaust discharged from the heat recovery unit, is increased. Since the smoke temperature becomes high, the smoke exhaust temperature at the inlet of the electric precipitator cannot be suppressed to the upper limit, and the dust collection performance may be impaired. In addition, the temperature of the heat medium flowing out of the heat recovery unit rises, the temperature of the flue gas heated by the reheater increases, and the heat-resistant temperature of materials such as the flue gas fan and the chimney may be limited. . The present invention solves the above problems, in other words, even if the inlet smoke exhaust gas temperature of the heat recovery unit fluctuates, it is an object to suppress the inlet smoke exhaust gas temperature of the electrostatic precipitator to at least the upper limit value. I do.

[0010]

The object of the present invention can be solved by the following means. The present invention firstly provides an air preheater that heats combustion air with flue gas discharged from a boiler, a heat recovery device that heats a heating medium with flue gas discharged from the air preheater, and a heat recovery device An electric precipitator that collects the soot and dust in the flue gas discharged from the air conditioner, a wet-type flue gas treatment device that wet-treats the flue gas discharged from the electric dust collector, and a gas that is discharged from the wet-type flue gas treatment device And a heat medium circulating device for circulating the heat medium between the reheater and the heat recovery device. .

[0011] By providing a temperature control means in the heat medium circulating line for suppressing the smoke exhaust gas temperature at the outlet of the heat recovery device to a predetermined upper limit or less, even if the smoke smoke temperature at the inlet of the heat recovery device fluctuates. In addition, it is possible to suppress the smoke exhaust temperature at the inlet of the electric precipitator to at least the upper limit value. In this case, the temperature control means can be realized by providing a device for cooling the heat medium flowing through the heat recovery device when the exhaust gas temperature at the outlet of the heat recovery device exceeds a preset upper limit value.

Another solution is to determine the heat transfer area of the heat recovery unit based on a preset upper limit of the exhaust gas temperature of the heat recovery unit so that the temperature of the exhaust gas at the entrance of the heat recovery unit can be reduced. Even if it fluctuates, the exhaust gas temperature at the inlet of the electrostatic precipitator can be suppressed to at least the upper limit value. In this case, when the inlet temperature of the heat recovery unit decreases during normal operation, and the outlet flue gas temperature falls below a predetermined lower limit, the amount of heating of the heat medium by the reheater is reduced to reduce the heat recovery unit temperature. In order to raise the temperature of the heat transfer medium at the inlet of the electric precipitator, a pipe line that bypasses a part of the heat transfer pipe of the reheater is provided even if the temperature of the smoke at the inlet of the heat recovery unit fluctuates. It can be kept above the lower limit of smoke temperature.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a configuration diagram of a flue gas treatment system according to an embodiment of the present invention. FIG. 2 is an overall configuration diagram of the flue gas treatment system, and FIG. 1 is a configuration diagram of main parts. As shown in FIG. 2, in the flue gas treatment system according to the present embodiment, the flue gas discharged from the boiler 1 is introduced into a denitration device 2, where nitrogen oxides in the flue gas are removed. It is led to the air preheater 3. The flue gas led to the air preheater 3 exchanges heat with the combustion air supplied to the boiler 1, and is cooled to, for example, 120 to 155 ° C.
Introduced in 1. The heat of the flue gas introduced into the heat recovery unit 11 is recovered by the heat medium flowing through the heat transfer tube by heat exchange, cooled to, for example, 75 to 110 ° C., and guided to the electric precipitator 4, where the smoke is discharged. Most of the dust inside is collected. The flue gas that has passed through the electric dust collector 4 is pressurized by an induction fan 5 and introduced into a wet desulfurization device 6 which is an example of a wet flue gas treatment device, and SOx in the flue gas is removed by gas-liquid contact. . The flue gas cooled to the saturated gas temperature in the wet desulfurization device 6 is heated by the reheater 13 and discharged from the chimney 8 via the desulfurization fan 7. The reheater 13 is a heat recovery unit 1
This is a heat exchanger provided with a heat transfer tube through which a heat medium flows as in 1, and the flue gas is heated to, for example, 90 to 110 ° C. by heat exchange with the heat medium flowing in the heat transfer tube. Also, the heat recovery unit 11
And a heat transfer tube of the reheater 13 are connected to a heat medium circulation line 15-1, 1
5-2, the heat recovery unit 11 and the reheating unit 13
And a heat medium is circulated between the heat medium and the heat exchanger.

As described above, in the flue gas treatment system shown in FIG. 2, since the electric precipitator 4 is placed on the downstream side of the heat recovery unit 11, the flue gas flowing into the electric precipitator 4 Since the temperature decreases, the electrical resistivity of the dust decreases, and the dust removal efficiency can be increased.

FIG. 1 shows a detailed view of a heat medium circulation system of a heat recovery unit and a reheater according to a feature of the present invention. Heat recovery unit 11
Heat transfer tube 12 and heat transfer tube 14 of
Are connected annularly by heat medium circulation pipes 15-1 and 15-2, and the heat medium is circulated in the heat transfer pipes 12 and 14 by a circulation pump 16 provided in the middle of the pipes. It has become. As described above, the heat transfer tubes 12, 14
In order to improve the efficiency of heat exchange, a fin tube or the like is used. In addition, a heat medium bypass line 17 is provided to control the outlet smoke temperature of the heat recovery unit 11,
The heat recovery is performed by adjusting the opening degree of the flow control valve 41 so that the temperature of the exhaust gas discharged from the heat recovery unit 11 becomes equal to or higher than a set value according to a signal from the thermometer 32 that measures the temperature of the exhaust gas discharged from the heat recovery unit 11. Controlling the amount. Further, a heat medium tank 18 is provided in the heat medium circulation pipe 15-2 to absorb the expansion of the heat medium in the pipe.

In the case of partial load operation of the boiler, etc.,
When the outlet smoke temperature of the reheater 13 decreases, the heat transfer pipe 14
There is a risk that mist discharged from the wet desulfurization device adheres to the surface of the steel and corrodes. Therefore, a heat medium heater 19 is installed in the heat medium circulation pipe 15-1 at the outlet of the heat transfer tube 12, and steam is supplied to the heat medium heater 19 via the steam supply pipe 22, so that the heat of the outlet of the reheater 13 is reduced. The medium temperature is maintained at a predetermined value (for example, 75 ° C.) or higher, or the exhaust gas temperature at the outlet of the reheater 13 is maintained at a predetermined value (for example, 90 ° C.). That is, a thermometer 34 that measures the temperature of the exhaust gas discharged from the reheater 13
In response to a signal from a thermometer 36 that measures the temperature of the heat medium at the inlet of the heat recovery unit 11, the amount of steam supplied to the heat medium heater 19 is controlled by adjusting the opening of the steam supply amount adjustment valve 42.

The steam supplied to the heat medium heater 19 exchanges heat with the heat medium, and the latent heat is recovered to form a drain.
Through the drain tank 20 with a heat exchanger. The heat exchanger of the drain tank 20 has a heat medium circulation line 1
5-2 is connected, and the latent heat recovered drain is exchanged with a heat medium to further recover the recovered drain heat.
This drain is sent to the collection destination by the drain pump 21 via the on-off valve 48 for reuse in the power plant.

Here, the feature of the embodiment shown in FIG. 1 is that a temperature control means for supplying cooling water to the drain system of the drain tank 20 and cooling the heat medium returning to the heat recovery unit 11 is provided. . The temperature control means connects the cooling water supply pipe 23 provided with the flow regulating valve 47 to the drain inlet of the drain tank 20, and connects the cooling water return pipe 24 to the drain outlet of the drain tank 20 via the on-off valve 49. Is formed.

Next, control and operation of the embodiment shown in FIG. 1 will be described. The flue gas temperature of each part in the flue gas treatment system of FIGS. 1 and 2 is designed or operated based on the following conditions as in the general case. Outlet flue gas temperature of air preheater (inlet flue gas temperature of heat recovery unit): 120-155 ° C Outlet flue gas temperature of heat recovery unit (inlet smoke temperature of electric precipitator): 75-110 ° C Wet flue gas Outlet flue gas temperature of treatment equipment (inlet flue gas temperature of reheater): about 50 ° C Outlet flue gas temperature of reheater (stack chimney exhaust gas temperature): 9
0 to 110 ° C As a precondition, in order to reduce the electric resistivity of the dust and maintain the dust collecting performance of the electric dust collector high, regardless of the fluctuation of the outlet smoke temperature of the air preheater, the electric dust collector At a temperature of 75 to 110 ° C (preferably 80 to 95 ° C).

As the design conditions for the heat transfer area of the heat recovery unit 11, the design conditions for the exhaust gas temperature at the outlet of the air preheater 3 are set as follows: (A) The temperature during normal operation (for example, 125 ° C.). Case (B) The case where the upper limit value of 155 ° C. is set as the design condition will be described separately.

The embodiment shown in FIG. 1 is suitable for the design condition (A). In this case, the design criteria of the smoke exhaust temperature and the heat medium temperature of each part are as shown in the column of “Example of FIG. 1” in Table 1. Further, as shown in Table 1, the heat transfer area of the heat recovery unit 11 in this case is 80% of the heat transfer area of the related art based on the design condition (B). For comparison, Table 1
FIG. 2 also shows a design standard of the temperature of each part when the design is performed under the design condition (B) according to the related art, and an operation example of the temperature of each part depending on the presence or absence of a heat recovery unit bypass operation described later.

[0022]

[Table 1]

As shown in Table 1, in the case of the example of FIG. 1 and when the design condition (A) is met, the smoke exhaust temperature and the heat medium temperature of each part are maintained at the design standard, It can be operated without any problem while maintaining the exhaust gas temperature of the dust collector at 80 ° C. For example, if the inlet flue gas temperature of the heat recovery unit 11 decreases due to partial load operation or the like, as shown in the control block diagram of FIG. Detection value and lower limit set value 80 ℃
And if the detected value is lower than the lower limit,
The opening of the flow control valve 41 is controlled according to the difference. As a result, a part of the heat medium flowing through the heat transfer tube 12 flows to the heat medium bypass line 17, and the temperature of the exhaust gas discharged from the heat recovery unit 11 is maintained at the lower limit or more. If a part of the heat medium flowing through the heat recovery unit is bypassed to reduce the amount of heat recovery, the outlet smoke temperature of the heat recovery unit 11 can be maintained at a predetermined value. As a result, it is possible to prevent problems such as dust being moistened inside the heat recovery unit and adhering to the heat transfer tubes, clogging of the hopper of the electric dust collector, and problems such as low-temperature corrosion of the heat transfer tubes and downstream devices. .

However, if the amount of heat recovery is reduced, the reheater 13
The temperature of the heat medium flowing through the device is too low,
Reheater 1 by the exhaust gas at the saturated gas temperature
The third heat transfer tube 14 may be corroded. In this case, in the present embodiment, the heat medium flowing into the reheater 13 is heated by the heat medium heater 19. That is, as shown in FIG.
The detected value of the exhaust gas temperature at the outlet of the reheater 13 detected by the thermometer 34 is compared with a lower limit set value (for example, 85 ° C.), and the opening of the flow control valve 42 is controlled in accordance with the difference. By heating the heat medium flowing into the reheater 13, the outlet smoke temperature of the reheater 13 is maintained at or above the lower limit.

In this case, as shown in FIG. 4, the detected value of the temperature of the heating medium at the outlet of the reheater 13 detected by the thermometer 36 is compared with a lower limit set value (for example, 75 ° C.).
It is preferable to control the opening of the flow control valve 42 in accordance with the deviation to heat the heat medium flowing into the reheater 13 together. Thus, the temperature of the heat transfer medium at the outlet of the reheater 13 is maintained at or above the lower limit, so that corrosion of the heat transfer tubes 14 of the reheater 13 can be prevented. In this case,
It is important to prevent the cooling water flow control valve 47 and the steam flow control valve 42 from opening at the same time. Therefore, when the flow control valve 47 is “open”, the steam flow control valve 42 and the drain valve on-off valve 46 are controlled to be “fully closed”.

On the other hand, the heat recovery unit 11
Rises to 155 ° C., the temperature of the smoke at the outlet of the heat recovery unit 11 rises accordingly, and the electric dust collector 4
If the exhaust gas temperature at the entrance exceeds the upper limit, the dust collection performance is impaired. In such a case, according to the embodiment of FIG.
As shown in the control block diagram, the detected value of the exhaust gas temperature at the outlet of the heat recovery unit 11 detected by the thermometer 32 is compared with an upper limit set value of 95 ° C., and when the detected value is higher than the upper limit set value, The opening of the flow control valve 47 is controlled according to the difference. Thereby, the cooling water is supplied to the drain tank 20, the heat medium introduced into the heat transfer tube 12 is cooled, and the temperature of the heat medium at the inlet of the heat recovery unit 11 decreases. As a result, as shown in “Operation example of FIG. 1” shown in Table 1, the exhaust gas temperature at the outlet of the heat recovery unit 11 can be kept at or below the upper limit.

Further, the smoke exhaust gas temperature at the inlet of the heat recovery unit 11 is 15
When the temperature rises to 5 ° C., the temperature of the outlet heat medium of the heat recovery unit 11 rises accordingly, and the temperature of the inlet heat medium of the reheater 13 rises, whereby the temperature of the exhaust gas to be heated rises. When the temperature of the flue gas rises, materials such as the desulfurization fan 7 and the chimney 8 must have a high heat-resistant temperature. According to the present embodiment, however, the heat medium introduced into the heat transfer tube 12 is cooled. As a result, the temperature of the heat transfer medium at the inlet of the heat recovery unit 11 decreases, so that the temperature can be suppressed to the above-described range.

As described above, according to the embodiment shown in FIG. 1, even if the inlet flue gas temperature of the heat recovery unit 11 fluctuates, the inlet flue gas temperature of the electric precipitator 4 can be suppressed to at least the upper limit. As a result, the heat transfer area of the heat recovery unit 11 can be reduced, and the dust concentration can be reduced without increasing the size of the electric precipitator 4.

In addition, the temperature of each part can be controlled within a predetermined range of upper and lower limits in response to fluctuations in the smoke exhaust temperature at the inlet of the heat recovery unit 11, and problems such as corrosion, adhesion of dust and clogging, etc. can be prevented. Can be prevented.

FIG. 5 shows a detailed view of a heat medium system of a heat recovery unit and a reheater according to a feature of the second embodiment of the present invention. In the figure, the difference from FIG. 1 is that instead of supplying cooling water for cooling the heat medium to the drain tank 20, a cooling water supply pipe 23 having a flow control valve 43 is connected to the heat medium heater 1.
9 and the cooling water recovery pipe 24 is connected to the steam drain line of the heat medium heater 19 via the on-off valve 45. Other points are the same as those in FIG.

With this configuration, the same control and operation as in the embodiment of FIG. 1 can be realized. here,
In the example of FIG. 1, the cooling water is supplied to the drain tank 20, and in the example of FIG. 5, the cooling water is supplied to the steam supply pipe of the heat medium heater 19, but the present invention is not limited to this. Instead, a heat medium cooler using cooling water may be independently provided in the heat medium circulation pipe 15-2. According to this, the interlock between the cooling water flow control valve 47 and the steam flow control valve 42 becomes unnecessary. Further, it is possible to control to operate both the regulating valves 47 and 42 at the same time. Further, the heat medium cooling systems of FIGS. 1 and 5 may be combined.

Next, FIG. 6 shows a detailed view of a heat medium system of a heat recovery unit and a reheater according to a feature of the third embodiment of the present invention. In the figure, the difference from FIGS. 1 and 5 is that the heat transfer tube 14 of the reheater 13 is divided into two heat transfer tube groups 14-1 and 14-2 without providing a cooling system for the heat medium, 62
Is opened and closed to bypass the heat transfer tube group 14-2 on the downstream side of the reheater 13 and allow the heat medium to flow only to the heat transfer tube group 14-1 on the upstream side.

This embodiment is suitable for the design condition (B). That is, this is a suitable example when the heat transfer area of the heat recovery unit 11 is determined based on the upper limit value (for example, 155 ° C.) of the inlet flue gas temperature. That is, if the design is performed under the design condition (B), even if the temperature rises in summer or the like, the upper limit of the smoke exhaust temperature at the inlet of the electrostatic precipitator 4 is set to, for example, 110 ° C. or 9 ° C.
It can be kept at 5 ° C. However, when the smoke exhaust gas temperature at the inlet of the heat recovery device 11 becomes the temperature for normal operation (for example, 125 ° C.), the smoke smoke temperature at the outlet of the heat recovery device 11 is too low, and the heat transfer tube of the heat recovery device 11 is heated. 13 and the hopper of the electrostatic precipitator 4, and a problem of low-temperature corrosion of the heat transfer tube 13 and the like.

Therefore, in the embodiment of FIG. 6, the amount of heat exchange in the reheater 13 is reduced so that the heat recovery unit 1
1, the amount of heat recovery is reduced so that the exhaust gas temperature at the outlet of the heat recovery unit 11 is maintained at a lower limit (for example, 80 ° C.) or higher. In other words, the outlet flue gas temperature of the heat recovery unit 11 is
As described in FIG. 1, by controlling the amount of the heat medium flowing into the heat recovery unit 11 by the bypass control, the heat medium can be maintained at the lower limit or more. In that case, the heat medium circulation pipe 15-
2, the temperature of the heat medium is further lowered, and the above-described disadvantages occur.
The temperature of the heat medium flowing into the device can be maintained at or above the lower limit.

However, when steam cannot be used or when the amount of steam is reduced, the control is not always appropriate. Therefore, in FIG. 6, the on-off valve 61 is fully opened, the on-off valve 62 is fully closed, and the heat medium flows only into the heat transfer tube group 14-1 while bypassing the heat transfer tube group 14-2 of the reheater 13. By letting
The amount of heat exchanged in the reheater 13 is reduced. This makes it possible to maintain the inlet heat medium temperature of the heat recovery unit 11 at or above the lower limit, as in the operation example shown in the column of “Example of FIG. 6” in Table 1. As a result, the exhaust smoke temperature at the outlet of the heat recovery unit 11 and the exhaust smoke temperature at the outlet of the reheater 13 can be maintained and controlled to be equal to or higher than the lower limit.

As described above, according to the embodiment of FIG.
Even if the heat transfer area of the heat recovery unit is set based on the design condition (B), the temperature of the exhaust gas at the inlet of the electrostatic precipitator can be maintained at a predetermined value or more in the case of the normal operation temperature. Etc., and adhesion and clogging of dust can be prevented, and the dust collection efficiency can be kept high. Further, since the temperature of the heating medium at the outlet of the reheater can be maintained at a predetermined value or more, corrosion of the reheater can be prevented.

On the other hand, according to the prior art, as indicated by an asterisk in the column of the prior art in Table 1, regardless of the presence or absence of the heat recovery unit bypass operation at the normal operation temperature, Since the exhaust gas temperature at the outlet of the recovery unit and the temperature of the heat medium at the entrance of the heat recovery unit (the temperature of the heat medium at the outlet of the reheater) are out of the predetermined temperature range, there is a problem such as the corrosion described above.

[0038]

As described above, according to the present invention,
Even if the outlet flue gas temperature of the air preheater fluctuates, the inlet flue gas temperature of the electrostatic precipitator can be maintained in a predetermined range. In particular, even if the outlet smoke temperature of the air preheater rises, the inlet smoke temperature of the electric precipitator can be suppressed to a predetermined upper limit, so that the reduction of dust collection efficiency is suppressed and the dust concentration is reduced. There is an effect that it can be held.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a temperature control system of a heat recovery unit and a reheater, which are characteristic parts of a flue gas treatment system of the present invention.

FIG. 2 is a block diagram showing the configuration of a flue gas treatment system to which the present invention is applied.

FIG. 3 is a control block diagram of an outlet flue gas temperature of the heat recovery unit according to the embodiment of FIG. 1;

FIG. 4 is a control block diagram of a heat medium temperature of the heat recovery unit and the reheater according to the embodiment of FIG. 1;

FIG. 5 is a configuration diagram of another embodiment of a temperature control system of a heat recovery unit and a reheater, which are characteristic parts of the flue gas treatment system of the present invention.

FIG. 6 is a configuration diagram of still another embodiment of a temperature control system of a heat recovery unit and a reheater, which are characteristic parts of the flue gas treatment system of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Boiler 2 Denitration apparatus 3 Air preheater 4 Electric precipitator 5 Induction fan 6 Wet desulfurization apparatus 7 Desulfurization fan 8 Chimney 11 Heat recovery unit 12, 14 Heat transfer tube 13 Reheater 14-1, 14-2 Heat transfer tube group 15 -1,15-2 Heat medium circulation pipe line 16 Circulation pump 17 Heat medium bypass line 19 Heat medium heater 20 Drain tank 22 Steam supply pipe 23 Cooling water supply pipe 31,32,33,34,35,36,37,38 , 3
9 Thermometer 41, 42, 43, 47 Flow control valve 45, 46, 48, 49, 61, 62 On-off valve

Claims (5)

[Claims] 1. An air preheater for heating combustion air by exhaust gas discharged from a boiler, a heat recovery device for heating a heating medium by exhaust gas discharged from the air preheater, and a heat recovery device An electrostatic precipitator that collects dust in the exhaust smoke,
A wet flue gas treatment device for wet treating flue gas discharged from the electric dust collector, a reheater for heating the flue gas discharged from the wet flue gas treatment device with a heating medium, and the reheater. A heat medium circulating pipe for circulating the heat medium between the heat recovery unit and a heat medium circulation line, wherein a temperature at which an exhaust gas temperature at an outlet of the heat recovery unit is suppressed to a predetermined upper limit or less. A flue gas treatment system, wherein a control means is provided in the heat medium circulation pipe. 2. The flue gas treatment system according to claim 1, wherein the temperature control means is a means for cooling the heat medium in accordance with an exhaust smoke temperature at the outlet of the heat recovery unit. 3. A heat transfer device comprising: a bypass pipe that short-circuits an inlet and an outlet of a heat medium pipe flowing into the heat recovery unit; and a heat medium heater that heats the heat medium flowing into the reheater. The smoke exhaust treatment system according to claim 1 or 2, wherein: 4. An air preheater for heating combustion air by exhaust gas discharged from a boiler, a heat recovery device for heating a heat medium by exhaust gas discharged from the air preheater, and An electrostatic precipitator that collects dust in the exhaust smoke,
A wet flue gas treatment device for wet treating flue gas discharged from the electric dust collector, a reheater for heating the flue gas discharged from the wet flue gas treatment device with a heating medium, and the reheater. A heat medium circulation pipe that circulates the heat medium between the heat recovery unit,
In a flue gas treatment system including a bypass pipe that short-circuits an inlet and an outlet of a heat medium pipe that flows to the heat recovery unit, and a heat medium heater that heats the heat medium flowing into the reheater, In the heat recovery unit, the heat transfer area is determined based on an upper limit value of an outlet smoke temperature of the air preheater, and the outlet smoke temperature of the heat recovery unit is controlled to be equal to or higher than a preset lower limit value. A flue gas treatment system, wherein a temperature control means is provided in the heat medium circulation pipe. 5. The heat recovery unit according to claim 5, wherein the temperature control unit divides the heat transfer tubes of the reheater into a plurality of heat transfer tube groups, and bypasses a part of the heat transfer tube group for a flowing heat medium. The flue gas treatment system according to claim 4, wherein the inlet heat medium temperature is controlled to be equal to or higher than a lower limit value.