JP2592061B2 - Waste heat recovery boiler - Google Patents

Description

The present invention relates to an exhaust heat recovery boiler in, for example, a combined cycle power plant, and more particularly, to sulfur oxides (SOx) in exhaust gas.
The present invention relates to an exhaust heat recovery boiler that can cope with the presence or absence of a waste heat.

[Conventional technology]

Large-capacity thermal power plants are being constructed to meet the rapidly increasing demand for electric power. However, these boilers are required to perform a voltage-changing operation in order to obtain high power generation efficiency even at a partial load.

As a characteristic of recent power demand, the difference between the maximum and minimum loads increases with the increase in nuclear power generation, and thermal power generation tends to shift from base load use to load adjustment.

In other words, when operating thermal power generation for load adjustment,
There are very few boiler loads that are always operated at full load. So-called daily startup and shutdown, such as raising or lowering the load to 75%, 50%, or 25% load, or running or stopping operation (Daily Start Stop, hereafter simply referred to as DSS) operation to carry the intermediate load. This DSS operation allows operation only during daytime when power demand is high, and stops operation at night to improve power generation efficiency.

For example, as part of high-efficiency power generation, a combined cycle power plant has recently been receiving attention. This combined cycle power plant first generates power using a gas turbine, recovers the retained heat in the exhaust gas discharged from the gas turbine using a waste heat recovery boiler, and uses the steam generated by the waste heat recovery boiler to recover heat. The steam turbine is operated to generate power.

As described above, since the combined cycle power plant performs power generation by the gas turbine and power generation by the steam turbine, the power generation efficiency is high and the load response, which is a characteristic of the gas turbine, is excellent. For this reason, it can sufficiently cope with sudden rise and fall of power demand, and is excellent in load followability, which is convenient for performing DSS operation.

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

In FIG. 1, combustion air A from an air supply pipe 1 and fuel F from a fuel supply pipe 2 are mixed and burned in a combustor 3, and the combustion gas is used to rotate a gas turbine 4 so that the gas turbine 4
Power generation is performed. The exhaust gas G rotating the gas turbine 4 is introduced into the exhaust gas passage 6 of the exhaust heat recovery boiler 5. The exhaust gas passage 6 has a low-pressure boiler 10 composed of a low-pressure economizer 7, a low-pressure evaporator 8 and a low-pressure drum 9, and a high-pressure economizer 11, a high-pressure evaporator 12, a high-pressure drum 13, from the downstream side to the upstream side. A high-pressure boiler 15 including a superheater 14 is provided.

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

The water supplied to the low-pressure drum 9 is naturally circulated or forcedly circulated in the order of the low-pressure evaporator 8 and the low-pressure drum 9 through the low-pressure downcomer pipe 19 of the low-pressure drum 9, and is heated during this time to be mixed with water in the low-pressure drum 9. Separated into steam. The separated water is again recycled to the low-pressure downcomer 19, the low-pressure evaporator 8, and the low-pressure drum 9, and the steam is sent from the low-pressure main steam pipe 20 to the steam turbine.
Supplied to 21.

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

The water supplied to the high-pressure drum 13 is supplied to the high-pressure evaporator 12 via the high-pressure downcomer 25 of the high-pressure drum 13, similarly to the low-pressure boiler 10.
Circulation is performed in the order of the high-pressure drum 13. The steam separated in the high-pressure drum 13 is sent to the superheater 14 via the drum steam outlet pipe 26, where the temperature is further raised, and then the steam is supplied to the steam turbine 21 from the high-pressure steam pipe 27. Do.

The water separated by the high pressure drum 13 is supplied to the high pressure downcomer 2
5. Recirculated to high-pressure evaporator 12 and high-pressure drum 13. The water supply levels of the high-pressure drum 13 and the low-pressure drum 9 correspond to the high-pressure drum water supply valve 28 and the low-pressure drum water supply valve 29, respectively.
Is operated to control the amount of water supply. In the figure, 30 is a condenser, and 31 is a generator.

On the other hand, the steam used for rotating the steam turbine 21 becomes water in the condenser 30 and is supplied again to the exhaust heat recovery boiler 5 by the water supply pump 16. Since the water supply WF of the water supply pipe 17 is as low as about 34 ° C., if water is supplied to the low-pressure economizer 7 at the same temperature, low-temperature corrosion occurs in the low-pressure economizer 7. Therefore, it is necessary to mix with a part of the high-temperature water WR passing through the high-pressure water supply pipe 23, raise the temperature of the water supply to a predetermined temperature at which low-temperature corrosion does not occur, and supply the low-pressure coal economizer 7 with water.

That is, a part of the high-temperature water WR of the high-pressure water supply pipe 23 is supplied from the outlet of the boiler transfer pump 22 to the water supply pipe 17 through the recirculation flow path 33 having the recirculation flow control valve 32, Prevents corrosion.

Meanwhile, the exhaust heat recovery boiler 5 shown in the schematic system diagram of FIG. 13 shows a case in which a clean gas-based fuel containing no sulfur such as LNG is burned as the fuel F. In some cases, a dirty oil-based fuel containing sulfur, such as naphtha, may be used as the fuel F.

[Problems to be solved by the invention]

As described above, in the conventional waste heat recovery boiler 5, when planning a waste heat recovery boiler corresponding to a variety of fuels, the transmission of the low-pressure economizer 7 using fuel that does not contain SOx in the exhaust gas (hereinafter referred to as clean gas) is performed. When the heat area is designed, when recovering the retained heat from the exhaust gas containing SOx (hereinafter referred to as dirty gas), in order to raise the inlet feed water temperature of the low-pressure economizer 7 in order to prevent low-temperature corrosion, Disadvantages. This will be described with reference to FIG.

FIGS. 7A and 7B are characteristic curve diagrams showing the SOx amount in the exhaust gas G on the horizontal axis and the exhaust gas temperature and the feedwater temperature at the outlet of the exhaust heat recovery boiler 5 on the vertical axis. Vertical line B is clean gas and SOx amount is zero, vertical line C is dirty gas and SOx amount is 10pp
Shows the case of m.

The curve D in FIG. 7A 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 increased, and the curve E is the heat-transfer area of the low-pressure economizer 7. Shows the exhaust gas temperature at the outlet of the low-pressure economizer 7 when the temperature is reduced.

Also, the curve H in FIG. 4B is the inlet feedwater temperature of the low-pressure economizer 7, the curve I is the outlet feedwater temperature of the low-pressure economizer 7 when the heat transfer area of the low-pressure economizer 7 is increased, and the curve J Is a low pressure economizer 7
Is the outlet feedwater temperature of the low-pressure economizer 7 when the heat transfer area of the low-pressure economizer 7 is reduced.
Indicates a steam generation region in the low-pressure economizer 7.

That is, as described above, in the case of clean gas and dirty gas, in order to prevent low-temperature corrosion in the low-pressure economizer 7, it is necessary to increase the high-temperature water WR from the recirculation passage 33 as shown in FIG. However, when the high-temperature water WR is increased, the inlet feedwater temperature of the low-pressure economizer 7 rises from the point M on the curve H to the point N.

For this reason, the outlet feedwater temperature of the low-pressure economizer 7 rises from the point O to the point P as shown by the curve I, reaches the evaporation region indicated by the oblique line L in the low-pressure economizer 7, and evaporates in the low-pressure economizer 7. phenomenon,
There is a disadvantage that the low-pressure economizer 7 is damaged due to unstable flow, water hammer or the like.

In addition, there is a disadvantage that the capacity of the boiler transfer pump 22 increases with an increase in the high-temperature water WR. According to a trial calculation, the pump capacity of the boiler transfer pump 22 is approximately doubled in the case of dirty gas compared to the case of clean gas. Increase.

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 the curve I to the curve J, the outlet feedwater temperature at the low-pressure economizer 7 is reduced from the point P to the point Q, so that the evaporation can be prevented from decreasing. The exhaust gas temperature at the outlet rises from the point R to the point S, thereby preventing low-temperature corrosion.

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

Conventionally, low temperature corrosion of waste heat recovery boiler
A steam recovery method as described in -86501 has been proposed. This method uses. The temperature of the exhaust gas, the amount of SO ₃ in the exhaust gas, and the vapor pressure in the drum were measured. Converting the measured SO ₃ amount into a sulfuric acid dew point temperature and obtaining a difference between the converted temperature and the measured exhaust gas temperature; The temperature difference is converted into the steam set pressure difference in the drum,
Adding the steam set pressure difference and the measured steam power to obtain a new set pressure value; By comparing the new set pressure area with the measured steam power and controlling the pressure regulating valve provided on the outlet side of the drum based on the comparison result, the exhaust gas temperature is always maintained at the sulfuric acid dew point temperature or higher. However, it is intended to set the minimum recovered steam pressure.

However, in this method, a large amount of steam is present in the drum and in the steam pipe, and the exhaust gas temperature is maintained at a temperature slightly higher than the sulfuric acid dew point while adjusting the amount of the extracted steam. There is a disadvantage that the response to corrosion prevention is poor. Further, in this proposal, no consideration was given to preventing the evaporation phenomenon occurring in the heat exchanger.

A first object of the present invention is to provide an exhaust heat recovery boiler that can safely operate by eliminating the evaporation phenomenon in a heat exchanger, regardless of whether dirty gas or clean gas is used. It is in.

A second object of the present invention is to provide a waste heat recovery boiler that can safely operate at low temperature with good responsiveness even when dirty gas is used.

[Means for solving the problem]

In order to achieve the first object, a first aspect of the present invention is to provide a heat exchanger having a heat transfer area changing means capable of changing a heat transfer area between the exhaust gas and the feed water of the heat exchanger when the sulfur oxide concentration in the exhaust gas is low. The heat transfer area is increased by the heat transfer area changing means, and the heat transfer area is reduced by the heat transfer area changing means when the sulfur oxide concentration in the exhaust gas is high. is there.

In order to achieve the second object, the second present invention provides a feedwater temperature changing means capable of changing a feedwater temperature to a heat exchanger, and when the sulfur oxide concentration in exhaust gas is low, the feedwater temperature changing means is provided. The feedwater temperature is lowered, and when the sulfur oxide concentration in the exhaust gas is high, the feedwater temperature is changed by the feedwater temperature changing means to increase the feedwater temperature.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic system diagram of a combined cycle power plant according to a first embodiment of the present invention, and FIG. 2 is a schematic system diagram in which main parts of FIG. 1 are enlarged.

In the drawings for explaining the embodiments of the present invention, reference numerals 1 to 31 are the same as the conventional ones.

34 in the figure is a first circulating flow control valve, 35 is a first circulating flow path,
36 is a second circulation flow regulating valve, 37 is a second circulation flow path, 38, 39, 40
Is an inlet header, an intermediate header, and an outlet header of the low pressure economizer 7, 41 is a distributor, 42 is a SOx sensor installed in the exhaust gas passage 6 to detect the concentration of SOx in the exhaust gas G, and 43 is the SOx sensor.
A control section for outputting a valve opening command signal to the first circulating flow regulating valve 34 and the second circulating flow regulating valve 36 based on a detection signal from the x sensor 42, and includes a valve switching means 44 therein. I have. In a storage unit (not shown) of the control unit 43, a SOx reference value (for example, 0.1 ppm) is set in advance in order to determine whether the gas is clean gas or dirty gas, and a detection value from the SOx sensor 42 and the reference value are used. Are compared by the control unit 43, and when the detected value is smaller than the reference value, it is determined that the gas is clean gas, and an opening command signal as described later is given to the flow control valves 34 and 36. When the detected value is equal to or larger than the reference value, the gas is determined to be dirty gas, and an opening command signal as described later is given to the flow rate adjusting valves 34 and 36.

In this embodiment, the SOx sensor 42 is provided to directly detect the concentration of SOx in the exhaust gas to determine whether or not the exhaust gas is a clean gas. However, the SOx sensor 42 is not necessarily provided. That is, depending on the fuel used, for example, LNG
Use of a gaseous fuel that does not contain sulfur, such as naphtha, results in a clean gas.On the other hand, use of an oil-based fuel, such as naphtha, results in a dirty gas. Flow control valve 34 depending on the type,
An opening command signal may be given to 36.

1 and 2, when the exhaust gas G is a clean gas, the second circulation flow control valve 36 is closed and the supply of the high-temperature water WR to the second circulation flow path 37 is stopped. On the other hand, the first circulation flow control valve 34 is opened to supply the high-temperature water WR at the outlet of the boiler transfer pump 22 to the first circulation flow path 35, mix with the water WF of the water supply pipe 17, and mix the inlet of the low-pressure economizer 7. Supply to

That is, the high temperature water WR of the first circulation channel 35 and the water supply of the water supply pipe 17
As shown in FIG. 2, the WF is connected to the inlet header 38 of the low-pressure economizer 7.
Then, the heat flows from the point M to the point O in FIG.

On the other hand, when the exhaust gas G is dirty gas, the first circulation flow control valve 34 is closed, and the supply of the high-temperature water WR to the first circulation flow path 35 is stopped. On the other hand, the second circulation flow control valve 36 is opened, and the high temperature water WR at the outlet of the boiler transfer pump 22 is supplied to the second circulation flow path.
37 and mixed with the feedwater WF in the water supply pipe 17
To the intermediate header 39.

That is, the high temperature water WR of the second circulation channel 37 and the water supply of the water supply pipe 17
As shown in FIG. 2, the WF is an intermediate header 39 of the low-pressure economizer 7.
Through the outlet header 40 to use a part of the heat transfer surface of the low-pressure economizer 7, thereby reducing the heat transfer area of the low-pressure economizer 7 as compared with the case of clean gas.

By reducing the heat transfer area in the low-pressure economizer 7, heat recovery from the point N to the point Q shown in FIG. 14 (b) can be achieved. Generation of steam can be prevented.

In the case of dirty gas, water is not supplied between the inlet header 38 of the low-pressure economizer 7 and the intermediate header 39,
Since the exhaust gas temperature of the exhaust gas G is sufficiently low, there is no problem in strength.

As described above, according to the present embodiment, in order to eliminate the disadvantages of the prior art, when the exhaust gas G is a clean gas, the heat recovery efficiency is increased by using all the heat transfer surfaces of the low-pressure economizer 7. . When the exhaust gas G is dirty gas, the heat transfer surface of the low-pressure economizer 7 can be reduced to prevent steaming in the low-pressure economizer 7.

The first embodiment is an example in which the change of the heat transfer area and the change of the feedwater temperature are combined as described above. FIG. 3 is a diagram for explaining a second embodiment relating to the change of the supply water temperature.

In this embodiment, the difference from the first embodiment is that in the first embodiment, both the first circulation channel 35 and the second circulation channel 37 have their inlets branched from the outlet of the boiler transfer pump 22, Its outlet is connected to the inlet header 39 of the low-pressure economizer 7 as well as to the intermediate header 39. On the other hand, in the second embodiment, the inlet of the first circulation channel 35 branches off from the outlet of the boiler transfer pump 22, and the inlet of the second circulation channel 37 is connected to the high pressure economizer 11.
From the outlets of the low pressure economizer 7
It is connected to the entrance header.

Therefore, when the exhaust gas G is clean gas by a command signal of a valve switching means (not shown), the first circulating flow regulating valve
34 is opened, and the second circulation flow control valve 36 is closed. And the first
The high-temperature water WR from the circulation channel 35 and the feedwater WF from the supply pipe 17 are 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 control valve 34 is closed and the second circulation flow control valve 36 is opened. The high-temperature water WR from the second circulation flow rate 37 and the water supply WF from the water supply pipe 17 are mixed and supplied to the low-pressure economizer 7.

That is, in this embodiment, the take-out position of the high-temperature water WR is switched between the outlet of the high-pressure economizer 11 and the outlet of the low-pressure economizer 7 in order to suppress the increase of the high-temperature water WR. . That is, in the case of clean gas whose inlet feedwater temperature to the low-pressure economizer 7 may be low, the high-temperature water WR at the outlet of the low-pressure economizer 7 is circulated from the first circulation channel 35. On the other hand, in the case of a dirty guy who needs to set the inlet feedwater temperature of the low-pressure economizer 7 to a high temperature, the high-temperature water WR at the outlet of the high-pressure economizer 11 having a higher temperature than the low-pressure economizer 7 is supplied to the second circulation passage 37. It is made to circulate by the. As a result, in the case of the dirty guy, the supply water temperature of the high-temperature water WR is high, so that an increase in the circulation flow rate of the second circulation passage 37 can be suppressed, and 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 differs from the second embodiment in that:
The high-temperature water WR is taken out from the distributor 41 of the high-pressure downcomer 25 and supplied to the second circulation channel 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 supplied to the low-pressure economizer 7 from the first circulation channel 35. On the other hand, when the exhaust gas G is a dirty gas, the higher temperature hot water WR from the distributor 41 is supplied from the second circulation channel 37 to the low pressure economizer 7.
Since the generation of steam and low-temperature corrosion in the low-pressure economizer 7 are prevented, and the high-temperature water WR from the second circulation channel 37 is 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 embodiment in that, in the first embodiment, a first circulation flow path 35 and a second circulation flow path 37 are provided in parallel on the inlet side of the low-pressure economizer 7, and the transmission is performed. Change of thermal area was made possible. On the other hand, in this embodiment, the first extraction flow path 46 having the first extraction flow rate control valve 45 is connected to the final outlet header 40a of the low-pressure economizer 7, and the second extraction flow path 48 having the second extraction flow rate control valve 47. To the middle header 40b on the outlet side of the low-pressure economizer 7.
Respectively. Note that these extraction channels 4
The other ends of 6, 48 are connected to a drum water supply pipe 18, as shown in the drawing.

That is, in this embodiment, when the exhaust gas G is a clean gas, the second extraction flow control valve 47 is closed and the second extraction flow path is closed.
Stop taking out from 48. And the first extraction flow control valve
Open 45 and take water from final exit header 40a.

On the other hand, when the exhaust gas G is dirty gas, the first extraction flow control valve 45 is closed to stop the extraction from the first extraction flow path 46. Then, the second extraction flow control valve 47 is opened, and the supply water is extracted from the intermediate outlet header 40b.

As described above, the heat transfer area of the low-pressure economizer 7 is changed depending on whether the exhaust gas G is a clean gas or a dirty gas, whereby the generation of steam and low-temperature corrosion in the low-pressure economizer 7 are reduced. In addition to preventing the exhaust gas, the heat retained in the exhaust gas can be recovered to the maximum.

In the case of dirty gas, water does not flow between the intermediate outlet header 40b of the low-pressure economizer 7 and the final outlet header 40a, but the inlet-side gas temperature of the low-pressure economizer 7 is low and the heat transfer surface is low. There is no worry about burning.

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

This embodiment is different from the first embodiment in that a main circulation flow path 50 having a flow control valve 49 is provided from the outlet side of the boiler transfer pump 22 to the water supply pipe 17.
A first stop valve is provided at the tip end of the main circulation passage 50.
An inlet header water supply pipe 53 having a first stop valve 52;
And an intermediate header water supply pipe 54 having the following. Although not shown, the inlet header water supply pipe 53 is connected to the inlet header of the low-pressure economizer 7, and the intermediate header water supply pipe 54 is connected to the intermediate header of the low-pressure economizer 7.

In this embodiment, when the exhaust 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 and the feedwater WF from the main circulation channel 50 are mixed, and Water is supplied from the water supply pipe 53 for hedder. When the exhaust gas G is dirty gas, the first stop valve 51 is closed,
Open the second stop valve 52 and remove the high-temperature water from the main circulation passage 50.
The WR and the water supply WF are mixed, and water is supplied from the water supply pipe 54 for the intermediate header.

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

This embodiment is different from the second embodiment (see FIG. 3) in that the first stop valve is provided as in the fifth embodiment.
An inlet header water supply pipe 53 having a first stop valve 52;
The point is that a water supply pipe 54 for an intermediate header having the following is provided.

According to this embodiment, two flow control valves 3
By properly switching between the stop valves 4 and 36 and the two stop valves 51 and 52, finer control of the low-pressure economizer 7 becomes possible.

That is, according to the properties of the exhaust gas G, (1) the first circulating flow regulating valve 34 is opened and the second circulating flow regulating valve 36 is closed to control the opening and closing of the first stop valve 51 and the second stop valve 52.

(2) The first circulating flow regulating valve 34 is closed and the second circulating flow regulating valve 36 is opened to control the opening and closing of the first stop valve 51 and the second stop valve 52.

(3) The first stop valve 51 is opened and the second stop valve 52 is closed to control the opening and closing of the first circulating flow regulating valve 34 and the second circulating flow regulating valve 36.

(4) The first stop valve 51 is closed and the second stop valve 52 is opened to control the opening and closing of the first circulating flow regulating valve 34 and the second circulating flow regulating valve 36.

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

This embodiment is different from the fourth embodiment (see FIG. 5) in that the fourth embodiment is a single-pressure boiler, whereas the present embodiment is a condensing boiler. The point is that the high-pressure water supply pipe 23 is provided, and a part of the high-temperature water WR is mixed with the water supply WF through the circulation channel 35.

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

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

FIG. 10 is a diagram for explaining a ninth embodiment of the present invention. This embodiment differs from the eighth embodiment (see FIG. 9) in that a part of the high-temperature water WR is circulated from the distributor 41 of the high-pressure downcomer 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 part of the high-temperature fluid (a 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 part of the high-pressure steam is circulated from the high-pressure steam pipe 27.

If a higher temperature fluid is circulated as in the eighth to eleventh embodiments, the circulating flow rate can be reduced.

Some of the above embodiments use two circulation systems, but two or more circulation systems may be provided.

In the above-described embodiment, there are two water supply positions or two water discharge positions. However, these water supply positions or (and) water discharge positions may be three or more.

Further, in the above-described embodiment, the control in the economizer of the low-pressure boiler has been described. However, the same control as in the above-described embodiment can be performed for other heat exchangers.

According to the embodiment of the present invention, (1) by changing the water supply position or the water supply take-out position to the heat exchanger in accordance with various fuels to substantially adjust the heat transfer area, It is possible to achieve maximum heat recovery even with fuel. According to the calculation example, since the heat recovery is improved by about 5% compared with the conventional waste heat recovery boiler,
The fuel cost is saved about 1500M ￥ / 4 cans / year. However, 100
0MW plant (4 waste heat recovery boilers), operation time 6000Hr /
Calculated based on yearly plant efficiency of 40% and fuel cost of 7 $ / 1000Kcal.

(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.

[Example of calculation]

1. When the gas turbine fuel is LNG (no SOx in the exhaust gas): (1) Boiler transfer pump shaft power = 600KW.

2.Gas turbine fuel is naphtha (SOx in exhaust gas)
In the case of (1) When hot water WR is taken out from the outlet of the low pressure economizer…
… Boiler transfer pump shaft power = 1200KW.

(2) When high-temperature water WR is taken out of the high-pressure economizer outlet ...
… Boiler transfer pump shaft power = 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.

〔The invention's effect〕

As described above, the first aspect of the present invention is provided with a heat transfer area changing means capable of changing the heat transfer area between the exhaust gas and the feedwater of the heat exchanger, and when the sulfur oxide concentration in the exhaust gas is low, the heat transfer area changing means is provided. Means for increasing the heat transfer area, and when the sulfur oxide concentration in the exhaust gas is high, the heat transfer area changing means is configured to narrow the heat transfer area. It is possible to provide a waste heat recovery boiler that can achieve maximum heat recovery and can operate safely without eliminating evaporation in the exchanger.

As described above, the second invention is provided with a feedwater temperature changing means capable of changing the feedwater temperature to the heat exchanger. When the sulfur oxide concentration in the exhaust gas is low, the feedwater temperature is lowered by the feedwater temperature changing means, When the concentration of sulfur oxides in the exhaust gas is high, the feedwater temperature is changed by the feedwater temperature changing means. Since the feedwater temperature is directly related to the heat exchange with the exhaust gas as described above, the exhaust gas temperature can be quickly and finely controlled. In comparison with the method of maintaining the sulfuric acid temperature above the sulfuric acid dew point, it has advantages such as easy control and low-temperature corrosion prevention with good responsiveness.

[Brief description of the drawings]

FIG. 1 is a schematic system diagram of a combined cycle power plant according to a first embodiment of the present invention, FIG. 2 is a schematic system diagram in which main parts of the plant are enlarged, FIG. 3, FIG. 6, FIG. 7,
8, 9, 10, 11 and 12 are schematic system diagrams of a combined cycle power plant showing another embodiment of the present invention.
FIG. 13 is a schematic system diagram of a conventional combined cycle power plant, and FIGS. 14 (a) and (b) are characteristic curves of feed water temperature and exhaust gas temperature in a low-pressure economizer. 7 low-pressure economizer, 8 low-pressure evaporator, 9 low-pressure drum, 10 low-pressure boiler, 11 high-pressure economizer, 12 high-pressure evaporator, 13 high-pressure drum, 17, 18,23,24… water supply pipe, 3
4... 1st circulation flow control valve, 35... 1st circulation flow path, 36.
... Second circulation flow regulating valve, 37 ... Second circulation flow path, 38 ... Inlet header, 39 ... Intermediate header, 40 ... Outlet header, 40a
…… Final exit header, 40b …… Intermediate exit header, 42 …… S
Ox sensor, 43 ... Control unit, 44 ... Valve switching means, 45 ... First extraction flow rate adjustment valve, 46 ... First extraction flow path, 47 ... Second extraction flow rate adjustment valve, 48 ... Second Take-out channel, 49 ... Flow control valve, 50 ... Main circulation channel, 51 ... First stop valve, 52 ...
2nd stop valve, 53 ... Inlet header water supply pipe, 54 ... Middle header water supply pipe.

Claims (5)

(57) [Claims] A heat transfer area changing means for changing a heat transfer area between exhaust gas and feed water of a heat exchanger is provided. When the concentration of sulfur oxides in exhaust gas is low, the heat transfer area is changed by the heat transfer area changing means. An exhaust heat recovery boiler, wherein the heat transfer area is reduced by the heat transfer area changing means when the sulfur oxide concentration in the exhaust gas is high. 2. In claim (1),
The exhaust heat recovery boiler, wherein the heat transfer area changing unit is a unit that can change a water supply position with respect to the heat exchanger. 3. In claim (1),
The exhaust heat recovery boiler, wherein the heat transfer area changing unit is a unit that can change a feed water take-out position with respect to the heat exchanger. 4. A feed water temperature changing means for changing a feed water temperature to a heat exchanger, wherein when the sulfur oxide concentration in the exhaust gas is low, the feed water temperature is lowered by the feed water temperature changing means,
An exhaust heat recovery boiler, wherein the feedwater temperature is increased by the feedwater temperature changing means when the sulfur oxide concentration in the exhaust gas is high. 5. In claim (4),
A plurality of high-temperature fluid supply systems capable of supplying high-temperature fluids having different temperatures to a water supply system to the heat exchanger are provided, and the high-temperature fluid supply system is switched so that the supply water temperature can be changed. An exhaust heat recovery boiler characterized in that: