JPS6399401A - Waste-heat recovery boiler - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust heat recovery boiler in, for example, a combined cycle power plant, and particularly relates to a waste heat recovery boiler in a combined cycle power plant, etc.
This relates to an exhaust heat recovery boiler that can be used with or without.

[Conventional technology]

Large-capacity thermal power plants are being constructed to meet the rapidly increasing demand for electricity, but these boilers are required to operate at variable voltage in order to obtain high power generation efficiency even during partial load.

This is a recent characteristic of electricity demand, as nuclear power generation has grown and the difference between maximum and minimum loads has also increased.

Thermal power generation tends to shift from base load to load adjustment.

In other words, when operating thermal power plants for load adjustment, there are few cases in which the boiler load is always operated at full load, and the load is increased and decreased to 75% load, 50% load, and 25% load. It performs so-called daily start-stop (hereinafter simply referred to as DSS) operations, such as starting and stopping operation, to carry intermediate loads, and with this DSS operation, it operates only during the day when electricity demand is high, and during the night. The system stops operation to improve power generation efficiency.

For example, combined cycle power plants have recently been attracting attention as a part of high-efficiency power generation. This combined power generation plant first performs charging using a gas turbine, then recovers the heat retained in the exhaust gas discharged from the gas turbine using an exhaust heat recovery boiler, and operates a steam turbine using the steam generated by the exhaust heat recovery boiler. It is used to generate electricity.

In this way, composite Jl! Since the ffi plant generates power using a gas turbine and a steam turbine, it has high power generation efficiency and is excellent in load response, which is a characteristic of gas turbines. Therefore, it can sufficiently cope with sudden increases and decreases in power demand, has excellent load followability, and is convenient for DSS operation.

FIG. 13 is a schematic system diagram of a conventional combined cycle power plant.

In the figure, combustion air A from an air supply pipe 1 and fuel F from a fuel supply pipe 2 are mixed and combusted in a combustion m3, and the combustion gas rotates a gas turbine 4 to generate electricity by the gas turbine 4. The exhaust gas G that rotates the turbine 4 is passed through the exhaust gas passage p of the heat recovery boiler 5. Introduced in I6. In this exhaust gas passage 6, from the downstream side to the upstream side, there are a low pressure boiler 10 consisting of a low pressure economizer 7, a low pressure evaporator i8, and a low pressure drum 9, and a high pressure economizer 11. high pressure evaporation fi
A high pressure boiler 15 consisting of a high pressure boiler 13 and a superheater 14 is arranged.

On the other hand, the feed water WF, which is the fluid to be heated, is supplied from the water supply pump 16 through the water supply pipe 17 to the low-pressure economizer 7, and after being preheated to a predetermined temperature, it is supplied to the low-pressure drum 9 through the drum water supply pipe 18. Ru.

The feed water supplied to the low pressure drum 9 passes through the low pressure downcomer pipe 19 of the low pressure drum 9 to the low pressure evaporator 8. The water is naturally circulated or strongly controlled in the order of the low-pressure drum 9, during which it is heated and separated into water and steam in the low-pressure drum 9. The separated water is returned to the low-pressure downcomer 19, the low-pressure evaporator 8 and the low-pressure While being recirculated to the drum 9, the steam is supplied to a steam turbine 21 via a low pressure main steam pipe 20.

On the other hand, a part of the high-temperature water WR diverted at the outlet of the low-pressure economizer 7 is supplied to the high-pressure economizer 11 from the boiler transfer pump 22 via the high-pressure water supply pipe 23, and after being preheated to a predetermined temperature, The water is supplied to the high pressure drum 13 through the drum water supply pipe 24.

Similar to the low pressure boiler 10, the water supplied to the high pressure drum 13 passes through the high pressure downcomer pipe 25 of the high pressure drum 13 to the high pressure steamer 5.
i! Vessel 12. The high pressure drum 13 is circulated in this order. The steam separated within the high pressure drum 13 is sent to the superheater 14 via the drum steam outlet pipe 26.

After being further heated, the steam is supplied to the steam turbine 21 through the high-pressure steam pipe 27, and the steam turbine 21 generates electricity.

Note that the water separated by the high pressure drum 13 is transferred to the high pressure downcomer pipe 2.
5. High pressure evaporator 12) Recirculated to high pressure drum 13. Then, the water supply level of the high pressure drum 13 and the low pressure drum 9 is determined by the high pressure drum water supply valve 28. The amount of water supplied is controlled by operating the low pressure drum water supply valve 29. In addition, 30 in the figure is a condenser, and 31 is a generator.

On the other hand, the steam used to rotate the steam turbine 21 turns into water in the condenser 30, and I? Water is again supplied to the exhaust heat recovery boiler 5 by the 1llf water pump 16. This is because the water supply WF of this water supply pipe 17 is at a low temperature of about 34°C.

If water is supplied to the low-pressure economizer 7 at the same temperature, low-temperature corrosion will occur in the low-pressure economizer 7. Therefore, it is mixed with a part of the high-temperature water WR passing through the high-pressure water supply pipe 23, and the water supply temperature is raised to a predetermined temperature at which low-temperature corrosion does not occur.
It is necessary to supply water to

In other words, a part of the high-temperature water WR in the high-pressure water supply pipe 23 is supplied from the outlet of the boiler transfer pump 22 to the water supply pipe 17 via the recirculation flow path 33f & having the recirculation flow rate adjustment valve 32, and is supplied to the water supply pipe 17 to reduce the low-temperature corrosion of the low-pressure energy saver 7. is prevented.

By the way, the exhaust heat recovery boiler 5 shown in the schematic system diagram of Fig. 13 shows the case where a clean gas-based fuel that does not contain sulfur such as LNG is fired as the fuel F, and this is due to the diversification of fuels in recent years. In order to cope with this, dirty oil-based fuel containing sulfur such as naphtha is sometimes burned as fuel F.

(Problem that the invention seeks to solve) In this way, in the conventional exhaust heat recovery boiler 5.

When planning an exhaust heat recovery boiler compatible with a variety of fuels, if the heat transfer area of the low-pressure energy saver 7 is designed using a fuel that does not contain SOx in the exhaust gas (hereinafter referred to as clean gas), SOx
(hereinafter referred to as dirty gas), the inlet water temperature of the low-pressure economizer 7 is raised to prevent low-temperature corrosion, but there are the following drawbacks.

The situation will be explained using FIG. 14.

In Figures (a) and (b), the horizontal axis represents SOx in the exhaust gas G.
It is a characteristic curve diagram in which the vertical axis shows the exhaust gas temperature and the feed water temperature at the outlet of the exhaust heat recovery boiler 5. The vertical line B in the figure is clean gas and the SOx amount is zero, and the vertical line LAC is dirty gas and the SOx amount is zero.
The case where the amount of Ox is 10 ppm is shown.

The curve LAD in the figure (a) is the exhaust gas temperature at the outlet of the low-pressure economizer 7 when the heat transfer area of the low-pressure economizer 7 is reduced, and the curve E is the heat transfer area of the low-pressure economizer 7. The figure shows the exhaust gas temperature at the outlet of the low pressure economizer 7 when increasing the temperature.

In addition, the curve H in the same figure (b) is the inlet water supply temperature of the low pressure energy saver 7. The curve L is the low pressure energy saving! Curve J is the outlet water temperature of the low pressure economizer 7 when the heat transfer area of a7 is increased.
The outlet water temperature of the low-pressure economizer 7 when the heat transfer area is reduced, the direct l1IK is the steam generation temperature in the low-pressure economizer 7, and the oblique part, iiL, is the steam generation area in the low-pressure economizer 7. shows.

In other words, as mentioned above, in the case of clean gas and dirty gas, in order to prevent low-temperature corrosion in the low-pressure economizer 7,
As shown in FIG. 13, high temperature water W from the re-Wi circulation path 33
Although it is necessary to increase R.

When the high temperature water WR is increased, the inlet water temperature of the low pressure economizer 7 rises from point M to point N on curve aH.

For this reason, the daily water supply temperature of the low-pressure energy saver 7 is a curve! As shown in the figure, the temperature rises from point Q to point P, and in the low-pressure economizer 7, the evaporation region shown by diagonal lines is reached. Vessel 7
There is a disadvantage that it may damage.

In addition, with the increase in high temperature water WR, the boiler transfer pump 22
According to trial calculations, the pump capacity of the boiler transfer pump 22 increases approximately twice when dirty gas is used compared to when clean gas is used.

On the other hand, in order to prevent the evaporation phenomenon in the low-pressure economizer 7, when the heat transfer area of the low-pressure economizer 7 is reduced from curve I to curve J, the outlet water temperature at the low-pressure economizer 7 changes from point P to The evaporation phenomenon can be prevented by dropping to point Q.

The exhaust gas temperature at the outlet of the exhaust heat recovery boiler 5 also rises from point R to point S, and low-temperature corrosion is also prevented.

However, in the case of clean gas, the exhaust gas temperature at the outlet of the exhaust heat recovery boiler 5 rises from point T to point U in FIG.
The exhaust gas temperature at the outlet increases by approximately 15°C. Therefore, a large amount of recoverable heat is released into the atmosphere, which is uneconomical in terms of heat recovery rate.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, eliminate the evaporation phenomenon in the heat exchanger for both dirty gas and clean gas, maximize heat recovery, and enable safe operation. We also provide waste heat recovery boilers.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides a heat exchanger capable of controlling the amount of heat exchanged between exhaust gas and water supply in a heat exchanger by changing the water supply state according to the concentration of sulfur oxides in exhaust gas. The heat exchanger is characterized in that an exchange amount switching means is provided to maintain the heat exchanger at a temperature at which low-temperature corrosion by exhaust gas does not occur on the downstream side of the heat exchanger in the exhaust gas flow direction.

〔Example〕

Each of the five embodiments of the present invention will be described below with reference to the drawings. 1st
The figure is a schematic system diagram of a combined power generation plan 1- according to the first embodiment of the present invention, and FIG. 2 is a schematic system diagram in which the main parts of FIG. 1 are enlarged.

In addition, in the drawings for explaining the present invention in detail.

Reference numerals 1 to 31 are the same as the conventional one.

In the figure, 34 is the first Wl return flow adjustment valve, 35 is the first circulation flow path, 36 is the second Wi return flow adjustment valve, 37 is the second Wi return flow path, and 38, 39, and 40 are the inlet headers of the low pressure economizer 7. , an intermediate header and an outlet header, 41 is a distributor, 42 is a Sox sensor installed in the exhaust gas passage 6 to detect the SOx concentration in the exhaust gas G, and 43 is the first sensor based on the detection signal from the SOx sensor 42. This is a control section for outputting a valve opening command signal to the circulation flow rate adjustment valve 34 and the second (li! circulation flow rate adjustment valve 36), and includes a valve switching means 44 inside. SOx
The control unit 43 compares the detected value from the sensor 42 and the reference value, and if the detected value is lower than the reference value, it is determined that the gas is clean and the flow rate adjustment valve 34.3G is opened as described below. gives a command signal. In addition, if the detected value is higher than the reference value, it is determined that it is dirty gas, and the flow rate adjustment valve 34.36
It is designed to give an opening degree command signal as described below.

In the case of this embodiment, the SOx sensor 42 is installed to directly detect the SOxm degree in the exhaust gas and determine whether or not it is clean gas, but it is not necessarily necessary to install the SOx sensor 42, that is, when using 1.For example, if a gas-based fuel that does not contain sulfur, such as LNG, is used, the gas will be clean, whereas if an oil-based fuel that contains sulfur, such as naphtha, is used, it will be dirty gas, so use an appropriate valve switching means. It is also possible to provide an opening command signal to the flow rate regulating valves 34 and 36 depending on the H1 class of the fuel used.

In FIGS. 1 and 2, when the exhaust gas G is clean gas, the second @recirculation flow regulating valve 36 is closed and the supply of high temperature water WR to the second circulation flow path 37 is stopped. On the other hand, the first
@ Open the return flow rate adjustment valve 34 to supply the high temperature water WR at the outlet of the boiler transfer pump 22 to the first N return flow path 35, and
It is mixed with the water supply WF of No. 7 and supplied to the inlet of the low-pressure economizer 7.

That is, as shown in FIG. 2, the high-temperature water WR in the first circulation channel 35 and the water supply WF in the water supply pipe 17 are flowed to the inlet of the low-pressure economizer 7 via the ladder 38 and to the outlet header 40. Heat recovery from point M to point O in FIG. 14(b) is attempted using all heat transfer surfaces of 7.

On the other hand, when the exhaust gas G is dirty gas, the first @recirculation flow rate adjustment valve 34 is closed and the high temperature water W to the first circulation flow path 35 is
The supply of R is stopped. On the other hand, the first circulation flow rate adjustment valve 36 is opened to transfer the high temperature water WR at the outlet of the boiler transfer pump 22 to the second circulation flow rate adjustment valve 36.
It is supplied to the circulation path 37, mixed with the water supply WF of the water supply pipe 17, and supplied to the middle of the low pressure coal saving 157 to the ladder 39.

In other words, the high temperature water WR of the first w1 circulation path 35 and the water supply pipe 17
As shown in FIG. 2, the supplied water WF is passed through the intermediate header 39 of the low-pressure economizer 7 to the outlet header 40, and using a part of the heat transfer surface of the low-pressure economizer 7, This also reduces the heat transfer area of the low pressure economizer 7.

By reducing the heat transfer area in the low pressure economizer 7 in this way, it is possible to recover heat from point N to point Q shown in FIG. can be prevented from occurring.

Note that in the case of dirty gas, water is not supplied from the ladder 38 to the inlet of the low-pressure coal saving 817 to the intermediate ladder 39, but this does not pose a problem in terms of strength because the exhaust gas temperature of the exhaust gas G is sufficiently low.

In this way, in order to eliminate the drawbacks of the conventional technology, the present embodiment uses all the heat transfer surfaces of the low pressure economizer 7 to increase heat recovery efficiency when the exhaust gas G is clean gas. .

Furthermore, when the exhaust gas G is dirty gas, the heat transfer surface of the low pressure economizer 7 can be reduced to prevent steaming within the low pressure economizer 7.

FIG. 3 is a diagram for explaining a second embodiment of the present invention.

This embodiment differs from the first embodiment as follows:
In the first embodiment, the inlet of both the first circulation flow path 35 and the second WIi flow M37 is branched from the outlet of the boiler transfer pump 22, and the outlet is connected to the inlet of the low pressure coal saving 1'J7 through the ladder 39 and the intermediate header. Connected to 39. On the other hand, in the second embodiment.

The inlet of the first w1 return flow path 35 is branched from the outlet of the boiler transfer pump 22, and the inlet of the second shield return flow path 37 is connected to the high pressure economizer 1.
Both outlets are connected to the inlet header of the low-pressure economizer 7.

Therefore, when the exhaust gas G is clean gas, the first circulating flow rate a'! is determined by a command signal from a valve switching means (not shown)! I
The i-valve 34 is opened and the second circulation flow rate adjustment valve 36 is closed. And the high temperature water WR from the first shield 1a flow path 35 and the supply pipe 17
The water WF supplied from the WF is mixed and supplied to the low pressure economizer 7. On the other hand, when the exhaust gas G is dirty gas, the first circulation flow rate adjustment valve 34 is closed and the second Wi circulation flow rate adjustment valve 36 is opened.
The high temperature water WR from the second circulation flow path 37 and the water supply pipe 17
The feed water WF is mixed and supplied to the low pressure economizer 7.

In other words, in this embodiment, in order to suppress the increase in high-temperature water WR, the take-out position of high-temperature water WR is set to high-pressure coal-saving 1011.
The outlet of the low-pressure economizer 7 and the outlet of the low-pressure economizer 7 are switched. That is, in the case of clean gas which requires only a low inlet water temperature to be supplied to the low-pressure economizer 7, the high-temperature water WR at the outlet of the low-pressure economizer 7 is circulated from the first circulation flow path 35 to 4! make a circle On the other hand, in the case of dirty water that requires the inlet water temperature of the low-pressure economizer 7 to be high, the high-temperature water WR at the outlet of the high-pressure economizer 11, which has a higher temperature than the low-pressure economizer 7, is passed through the second shield ring. WIQ is performed by path 37. As a result, in the case of dirty gas, it is possible to suppress an increase in the circulation flow rate of the second circulation flow path 37 due to the high temperature of the high-temperature water WR supplied.
Therefore, the capacity of the boiler transfer pump 22 can be reduced.

FIG. 4 is a diagram for explaining a third embodiment of the present invention.

This embodiment is different from the second embodiment in that high-temperature water WR is taken out from a distributor 41 of a high-pressure downcomer pipe 25 and supplied to a second circulation flow path 37.

In this embodiment, when the exhaust gas G is clean gas, the high temperature water WR at the outlet of the boiler transfer pump 22 is
It is supplied to the low pressure economizer 7 from the first ring flow path 35. On the other hand, when the exhaust gas G is dirty gas, the higher temperature water WR from the first distributor 41 is passed from the second circulation flow path 37 to the low pressure energy saver 7.
to generate steam in the low-pressure economizer 7 and reduce the low a
It prevents corrosion and also prevents high-temperature water W from the second circulation flow path 37.
Since R can also be reduced, the capacity of the boiler transfer pump 22 can be reduced.

FIG. 5 is a diagram for explaining a fourth embodiment of the present invention.

This embodiment is different from the first to third embodiments described above. Road 37
It is possible to change the heat transfer area by installing them in parallel. On the other hand, in this embodiment, the first
The take-out flow path 46 is connected to the final outlet of the low-pressure economizer 7 to the ladder 40a, and the second take-out flow path 48 having the second take-out flow rate adjustment valve 47 is connected to the ladder 40b to the middle of the outlet side of the low-pressure economizer 7. This is the point. Note that the other ends of these take-out channels 46 and 48 are connected to the drum water supply pipe 18, as shown in the drawing.

That is, in this embodiment, when the exhaust gas G is clean gas, the second extraction flow m regulating valve 47 is closed and the extraction from the second extraction flow path 48 is stopped. Then, the first extraction flow rate adjustment valve 45 is opened, and the water supply is taken out from the ladder 40a to the final outlet.

On the other hand, when the exhaust gas G is dirty gas, the first extraction flow rate regulating valve 45 is closed to stop the extraction from the first extraction flow path 46. Then, the second extraction flow rate adjustment valve 47 is set to σn,
The water supply is removed from the intermediate outlet header 38.

In this way, the heat transfer area of the low-pressure economizer 7 is changed depending on whether the exhaust gas G is clean gas or dirty gas, thereby preventing the generation of steam and low-temperature corrosion in the low-pressure economizer 7. , the heat retained in the exhaust gas can be recovered to the maximum extent possible.

Note that in the case of dirty gas, feed water does not flow between the intermediate outlet header 40b and the final outlet header 40a of the low-pressure economizer 7, but the gas temperature on the inlet side of the low-pressure economizer 7 is low and the heat transfer surface There is no need to worry about it being burned out.

FIG. 6 is for explaining a fifth embodiment of the present invention.

This embodiment differs from the first embodiment as follows:
A main circulation passage 50 having a flow rate 5I regulating valve 49 is provided from the outlet side of the boiler transfer pump 22 toward the water supply pipe 17. At the tip side of this main circulation flow path 50, there is an inlet header water supply pipe 53 having a first stop valve 51, and a second water supply pipe 53 having a first stop valve 51.
Although not shown, this inlet header water supply pipe 53 is connected to the inlet header of the low-pressure economizer 7.

The intermediate header water supply pipe 54 is connected to the intermediate header of the low pressure economizer 7.

In this example, if the wandering gas G is clean gas,
The first stop valve 51 is opened, the second stop valve 52 is closed, and the high temperature water WR in the main circulation flow path 5o is mixed with the water supply WF, and the water is supplied from the water supply pipe 53 for the inlet header. If the exhaust gas G is dirty gas, on the contrary, the first stop valve 51
is closed, the second stop valve 52 is opened, and the main circulation flow path 5o is opened.
The raw high-temperature water WR and the water supply WF are mixed and supplied from the intermediate header water supply pipe 54.

FIG. 7 is a diagram for explaining a sixth embodiment of the present invention.

This embodiment differs from the second embodiment (see FIG. 3) in that the first stop valve 5 is different from the second embodiment (see FIG. 3).
1 and an intermediate header water supply pipe 54 having a second stop valve 52.

If configured as in this embodiment, two flow rate regulating valves 34
．． 36 and the two stop valves 51, 52 as appropriate, more fine control is possible in the low pressure economizer 7.

That is, depending on the properties of the exhaust gas G, (1) Open the first shield circulation flow rate adjustment valve 34 to
The valve 31a is closed, and the opening and closing of the first stop valve 51 and the second stop valve 52 are controlled.

(2) Close the first circulation flow rate adjustment valve 34 and open the second circulation flow rate adjustment valve 36 to control the opening and closing of the first stop valve 51 and the second stop valve 52. (3) Open the first stop valve 51. The second stop valve 52 is opened and the second stop valve 52 is closed to control the opening and closing of the first circulation flow rate adjustment valve 34 and the 24th ya circulation flow rate adjustment valve 36.

(4) Close the first stop valve 51 and close the second stop valve 5.
2 is opened to control the opening and closing of the first circulation flow rate adjustment valve 34 and the second circulation flow rate adjustment valve 36.

FIG. 8 is a diagram for explaining a seventh embodiment of the present invention.

The difference between this embodiment and the fourth embodiment (see FIG. 5) is that while the fourth embodiment uses a vehicle pressure boiler, this embodiment uses a repressure boiler, and the boiler transfer pump 22
A high-pressure water supply pipe 23 is also provided, and a portion of the high-temperature water WR passes through a circulation flow path 35 and is mixed with the water supply WF.

FIG. 9 is a diagram for explaining the eighth embodiment of the present invention.

This embodiment differs from the sixth embodiment (see FIG. 7) in that the circulation system from the boiler transfer pump 22 outlet is omitted, and a portion of the high-temperature water WR is circulated from the outlet of the high-pressure economizer 11. This is the point.

FIG. 10 is a diagram for explaining a ninth embodiment of the present invention. This embodiment is different from the eighth embodiment (see FIG. 9) in that a portion of the high-temperature water WR is circulated through the WJ from the distributor of the high-pressure downcomer pipe 25.

FIG. 11 is a diagram for explaining a tenth embodiment of the present invention. This embodiment differs from the eighth embodiment (see FIG. 9) in that a portion of the high-temperature fluid (mixture of high-temperature water WR and steam) is circulated from the outlet of the high-pressure evaporator 12.

FIG. 12 is a diagram for explaining an eleventh embodiment of the present invention. This embodiment differs from the eighth embodiment in that a portion of the high-pressure steam is circulated from the high-pressure steam pipe 27.

By circulating a higher temperature fluid as in the eighth to eleventh embodiments, the WJE flow rate can be reduced.

Although some of the above embodiments use two circulation systems, it is also possible to provide two or more circulation systems.

In addition, some of the above embodiments are provided with two water supply positions or two water extraction positions, but there may be three or more water supply positions or (and) water extraction positions. .

Further, in the embodiment described above, the control by the economizer of the low-pressure boiler was explained, but it is also possible to perform the same control as in the embodiment described above for other heat exchangers.

According to an embodiment of the present invention, (1) In response to various types of fuel, the water supply position or the water supply take-out position to the heat exchanger is changed to substantially adjust the heat transfer area. It is also possible to maximize heat recovery from fuel. According to an example calculation, heat recovery is improved by about 5% compared to conventional waste heat recovery boilers, which results in fuel cost savings of about 1,500 M yen/4 cans per year.

However, 10100O plant (4 exhaust heat recovery boilers),
Operating time 6000j (r/year, plant efficiency 40%,
Calculated as cooking cost 7 yen/1000 K ca Q.

(2) Regardless of the presence or absence of SOx in the exhaust gas, it is possible to suppress an increase in the capacity of the boiler transfer lamp.

[Estimation example]

16 Gas turbine fuel is LNG (SOX in exhaust gas)
(1) Boiler transfer pump shaft power = 600KW.

2) When the gas turbine fuel is naphtha (with SOx in the exhaust gas), (1) When high-temperature water WR is taken out from the outlet of the low-pressure economizer... Shaft power of the boiler transfer pump = 1200KW
.

(2) When high-temperature water WR is taken out from the outlet of the high-pressure economizer...The shaft power of the boiler transfer pump = 610KW.

Therefore, by implementing the present invention, the shaft power of the boiler transfer pump can be reduced to about half, and the operating cost can be reduced.

〔Effect of the invention〕

According to the present invention, even when using clean gas or dirty gas, evaporation phenomenon and low-temperature corrosion in the heat exchanger are eliminated,
It has the advantage of being able to recover maximum heat from exhaust gas.

[Brief explanation of the drawing]

Fig. 1 is a schematic system diagram of a combined power generation plant according to the first embodiment of the present invention, Fig. 2 is an enlarged schematic system diagram of the main parts of the plant, and Fig. 3! ! ! 1. 4, 5, 6, 7, 8, 9, and 10. Figures 11 and 12 are schematic system diagrams of a combined power generation plant showing other embodiments of the present invention, Figure 13 is a schematic system diagram of a conventional 41 combined power generation plant, and Figure 14 (aL (b) is a low pressure It is a characteristic curve diagram of the supply water temperature and the exhaust gas temperature in the energy saver. 7...Low pressure energy saver, 8...Low pressure evaporator, 9...Low pressure drum, 10...Low pressure boiler, 11...High pressure economizer, 12...
High pressure evaporator, 13... High pressure boiler, 17, 18
, 23.24... Water supply pipe, 34... First circulation flow rate 7A'Iii valve, 35... First Wi
Recirculation passage, 36...24th g1 recirculation flow adjustment valve, 3
7...Second @recirculation path, 38...Inlet header, 39...Intermediate header. 40...Exit header, 40a...Final quantity roheshida. 40b... Intermediate exit header, 40...
SOx sensor, 43...control unit, 44...
...Valve switching means, 45...First extraction flow rate adjustment valve, 46...First extraction flow path. 47...Second outlet flow rate adjustment valve, 48...
・Second extraction flow path, 49...Flow rate adjustment valve, 50.
...Main wi circulation path, 51...First stop valve, 52...Second stop valve, 53...
... Water supply pipe for inlet header, 54 ... Water supply pipe for intermediate header. Figure 1 Figure 4 Figure 5 W/- Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 1/Figure 12 Figure 13

Claims (8)

[Claims] (1) A heat exchange amount switching means is provided that can control the amount of heat exchange between the exhaust gas and the water supply in the heat exchanger by changing the water supply state according to the concentration of sulfur oxides in the exhaust gas. An exhaust heat recovery boiler characterized by being configured to be maintained at a temperature at which low-temperature corrosion due to exhaust gas does not occur on the downstream side of a heat exchanger in the exhaust gas flow direction. (2) In claim (1), the heat exchange amount switching means is a heat transfer area changing means capable of changing the heat transfer area between the exhaust gas and the feed water of the heat exchanger in multiple stages. An exhaust heat recovery boiler characterized by: (3) The exhaust heat recovery boiler according to claim (2), wherein the heat transfer area changing means is a means that can change the water supply position with respect to the heat exchanger. (4) The exhaust heat recovery boiler as set forth in claim (2), wherein the heat transfer area changing means is a means for changing the feed water extraction position with respect to the heat exchanger. (5) The exhaust heat recovery boiler according to claim (1), wherein the heat exchange amount switching means is a water supply temperature changing means that can change the temperature of the water supplied to the heat exchanger. . (6) A high-temperature fluid mixing system as described in claim (5), in which the feed water temperature changing means mixes a part of the high-temperature fluid heated by a heat exchanger with the feed water of the heat exchanger. 1. A waste heat recovery boiler characterized in that a plurality of high temperature fluid mixing systems are provided, and high temperature fluids having different temperatures can be switched and supplied from the plurality of high temperature fluid mixing systems. (7) In claim (1), the heat exchange amount switching means is heat transfer area changing means that can change the heat transfer area between the exhaust gas and the feed water of the heat exchanger in multiple stages. An exhaust heat recovery boiler, characterized in that it is combined with a feed water temperature changing means that can change the temperature of water fed to the heat exchanger. (8) In claim (1), a sensor is provided to detect the concentration of sulfur oxides in the exhaust gas flowing through the heat exchanger, and the amount of heat exchanged is determined based on the detection signal of the sensor. An exhaust heat recovery boiler characterized in that the switching means is configured to be driven.