JPH03282102A - Exhaust heat recovery boiler and controller of temperature reducing device used for it - Google Patents

Abstract

PURPOSE:To prevent the reheated steam that flows via an attemperator even when a large volume of steam is drawn from reducing its superheating by dividing the heat transfer face of a reheater into two parts, a second reheater and a first reheater and providing an attemperator in an intermediate position of those two reheaters. CONSTITUTION:The heat transfer faces of a high pressure superheater and a reheater are divided into two parts, and a high pressure superheater 12, first and second reheaters 4, 42, and high pressure superheater 14 are arranged in this order from the upstream side of the exhaust gas, and attemperators 36 and 35 are respectively provided in the passages between the reheaters 41 and 42 and between the superheaters 12 and 14. When the volume of bleeding becomes large, the flow rate of the steam that flows through the reheaters 41 and 42 drops and the flow rate of the cooling water becomes large in order to keep the temperature of the outlet steam below limit value, but with the installation of the attemperators 36 the temperature of the steam that flows into the attemperators 36 is kept high, and the temperature at the outlet of the attemperator does not fall lower than a limit value even if the flow rate of the water increases. An attemperator controller which controls the temperature of the outlet steam of the superheaters and reheaters detects the generator load by a load detector 45 and detected loads are converted to signals, and the deviation values are given from its output signals and the output signal of a temperature sensor 47 for the temperature of the outlet steam of the high pressure second superheater 12, and the deviation values are converted to flow rate instruction signals and change the opening of an adjustment valve 43.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a reheat type waste heat recovery boiler, and particularly when extracting a large amount of steam from the reheater inlet. The present invention relates to an exhaust heat recovery boiler suitable for suppressing a decrease in the degree of superheating of the outlet steam of a desuperheater provided in a boiler. The present invention also relates to a desuperheater control device used in the exhaust heat recovery boiler.

(Conventional technology) In keeping with the trend toward higher gas turbine inlet gas temperatures, the exhaust heat recovery boiler of the combined cycle power generation plant has been developed to make the most efficient use of the high-temperature exhaust gas of the gas turbine. There are attempts to configure it as a heat recovery boiler. The general configuration of this three-pressure reheat type waste heat recovery boiler is as follows. That is, as shown in FIG. 7, the exhaust heat recovery boiler, which is generally designated by the reference numeral 11, includes, from the exhaust gas upstream side, a high-pressure second superheater 12, a reheater 13, a high-pressure first superheater 14, a high-pressure evaporator 15, low pressure superheater 16, high pressure second economizer 17, medium pressure superheater 18, medium pressure evaporator 19,
Medium pressure economizer 20, high pressure first economizer 21, low pressure evaporator 2
2, and a low-pressure economizer 23 are arranged in sequence.

The high-pressure, medium-pressure and low-pressure evaporators 15, 19, 22 are each equipped with a high-pressure steam drum 24, an intermediate-pressure steam drum 25 and a low-pressure steam drum 25, respectively a high-pressure feed water pump 27, a medium-pressure feed water pump 28 and a low-pressure Water pump 2
9, the feed water is fed through the first high-pressure economizer 21, the second high-pressure economizer 17, the intermediate-pressure economizer 20, and the low-pressure economizer 23. The exhaust gas is sent to the vessel 19 and the low-pressure evaporator 22, where it receives and removes the heat of the exhaust gas through the heat transfer surface and is evaporated. The high-pressure steam generated in the high-pressure evaporator 15 passes through the high-pressure first superheater 14 and the high-pressure second superheater 12, and the medium-pressure steam generated in the medium-pressure evaporator 19 passes through the medium-pressure superheater 18. and a reheater 13, a high pressure turbine 31 and an intermediate pressure turbine 32 are used as the working medium of a steam turbine, generally designated by the reference numeral 30.
The steam from the low-pressure evaporator 22 is further introduced into the low-pressure turbine 33 via the low-pressure superheater 16.

Note that the exhaust gas from the high-pressure turbine 31 is mixed with intermediate-pressure steam led from the intermediate-pressure evaporator 19 and led to the reheater 13, where it is heated again to raise the temperature and then supplied to the intermediate-pressure turbine 32.

Generally, when the exhaust gas temperature of the gas turbine 34 increases,
The superheated steam temperature and reheated steam temperature become too high, and it becomes necessary to lower them below the maximum operating temperature. For this reason,
Attemperators 35 and 36 are provided on the inlet sides of the high-pressure second superheater 12 and the reheater 13, and cooling water is mixed with the steam passing through the attemperators to lower the temperature.

In addition, in the figure, numeral 37 is a bleed air connection pipe, 38 is a condenser, and 3
9 indicates a generator.

(Problem to be Solved by the Invention) Normally, in a combined cycle power plant using such an exhaust heat recovery boiler, a plurality of units each consisting of a gas turbine 34, an exhaust heat recovery boiler 11, a steam turbine 30, and a generator 39 are provided. When the plant is started up, extracted steam is sent from the unit in operation to the unit to be started up to be used as driving steam for the steam turbine, or as auxiliary steam or steam for cooling the steam turbine. In this case, the reheater 13 is used for the driving steam of the steam turbine.
A part of the medium pressure steam extracted from the inlet side of the
7 and a low pressure turbine 33 for auxiliary steam.
A portion of the low-pressure steam flowing to the two is respectively supplied through a bleed connection pipe (not shown). However, if multiple units are to be started, a large amount of steam must be extracted and supplied to the steam turbines of the respective units to be started, which inevitably reduces the flow rate of steam flowing into the reheater 13. As a result, the temperature of the steam flowing to the outlet of the reheater 13 increases. To prevent this, the amount of cooling water supplied to the desuperheater 36 can be increased to lower the steam temperature.
Since the steam sent to the reheater 13 is a mixed steam of the exhaust gas of the high-pressure turbine 31 and the outlet steam of the intermediate-pressure superheater 18, the degree of superheating of the steam is not very high. If a large amount of cooling water is supplied to the desuperheater 36 in an attempt to lower the temperature, the temperature of the steam passing through the outlet of the desuperheater 36 will drop significantly, and the degree of superheating of the steam flowing into the reheater 13 will drop below the limit value. It goes down to That is, FIG. 8 shows the change in the steam temperature at the outlet of the attemperator with respect to the amount of cooling water in the attemperator.

When the amount of extracted air is small, if the amount of cooling water is increased to lower the steam temperature at the reheater outlet to the limit value, the steam temperature at the reheater outlet will change from (E) to (E) in Figure 8, line C. drop along. At this time, the outlet steam temperature of the desuperheater 36 is also
It decreases along line A' from point (a) to point (b) in the figure.

On the other hand, as the amount of extracted air increases, the flow rate of steam flowing through the reheater 13 decreases. The amount of cooling water will be larger than when the amount of extracted air is small, and the temperature at the desuperheater outlet will be lower than when the amount of extracted air is small. When the amount of cooling water to the desuperheater 36 is increased in order to lower the reheater outlet temperature from (g) to (te) in FIG. 8 along line C',
The temperature at the outlet of the desuperheater is B from point (c) to point (d) in Figure 8.
' line, and at some point it enters a region where it becomes below the limit value of the desuperheater outlet temperature.

This phenomenon is explained in Japanese Unexamined Patent Publications No. 61-186702, No. 81-289201, and Unexamined Japanese Patent Application No. 1-75802. This problem is even more noticeable in an exhaust heat recovery boiler in which the outlet (high temperature side) of the heater 13 is located at the location where the exhaust gas temperature is highest, making it impossible to supply steam to other units.

If some of the steam becomes drain and is carried to the reheater 13 in this way, there is a risk that the heat exchanger tubes will be damaged due to repeated thermal shocks. If the reheater 13 were to be installed in a higher temperature exhaust gas region in an attempt to reduce the drop in reheated steam temperature during partial load, the effect of this phenomenon would be greatly increased.

On the other hand, generally, the amount of cooling water injected changes greatly when there is a load change. Gas turbine 3 as shown in FIG.
The temperature of the exhaust gas in No. 4 is highest when the load is equivalent to 75%,
Even if the load is higher or lower than this, the temperature will continue to drop. The amount of cooling water injected into the desuperheater 36 is determined based on the steam flow rate and the exhaust gas temperature, and cooling water injection starts at a load equivalent to 50%, reaches the maximum at a load equivalent to 75% to 85%, and thereafter is as described above. It gradually decreases as the exhaust gas temperature decreases, and reaches zero at 100% load. Such a large change in the injection amount, for example, when the injection amount is small, causes chattering of the control valve that regulates the flow rate of cooling water flowing into the attemperator 36, making the control operation unstable. This chattering occurs at a load equivalent to 50% and at a load equivalent to 1
00% load, that is, the rated load, and the exhaust heat recovery boiler 11 may not be able to maintain a stable injection amount near the rated load. If cooling water were to be injected intermittently, there is a concern that the heat exchanger tubes would be damaged by repeated thermal shocks.

An object of the present invention is to provide a heat recovery heat boiler that suppresses a decrease in the degree of superheating of reheated steam flowing through a desuperheater even when a large amount of steam is extracted at the inlet of the reheater. There is a particular thing.

Another object is to provide a desuperheater control device that eliminates unstable operation of the cooling water control valve of the desuperheater in a normal load range.

[Configuration of the Invention (Means for Solving the Problems) The exhaust heat recovery boiler according to the present invention is an exhaust heat recovery boiler in which a high-pressure superheater and a reheater are sequentially provided along the direction of exhaust gas flowing inside the vessel. The high-pressure superheater and reheater each divide the heat transfer surface into two, and from the upstream side of the exhaust gas, the high-pressure second superheater,
The second reheater, the first reheater, and the high-pressure first superheater are arranged in this order, and the desuperheater is connected to the steam path connecting the high-pressure first and second superheaters and the first and second reheater. It is characterized in that it is provided in each of the steam paths.

Further, a desuperheater control device according to another invention includes desuperheaters in each of the steam path connecting the high-pressure first and second superheaters and the steam path connecting the first and second reheaters, In a desuperheater control device that adjusts the amount of cooling water supplied to the desuperheater by changing the opening degree of a control valve in order to maintain the superheated steam or reheated steam temperature appropriately, the superheater outlet steam temperature and means for switching the set value of the reheater outlet steam temperature in accordance with the load signal of the generator.

(Function) The heat transfer surface of the reheater is divided into two parts to form a second and a first reheater. The attemperator is installed between both reheaters, and the reheater outlet steam temperature is controlled by adjusting the amount of cooling water supplied to the attemperator. The steam passes through the first reheater to increase the degree of superheat to some extent, thereby increasing the amount of cooling water injected into the attemperator.

Therefore, even if the amount of extracted steam is increased when supplying extracted steam to other units, no problem will occur in the operation of the exhaust heat recovery boiler.

Further, the set values of the outlet steam temperatures of the second superheater and the second reheater are switched according to the load signal of the generator, and when the load increases, the temperature is slightly increased once, and then brought to the specified temperature. This allows the increase in the amount of cooling water to flow smoothly and prevents the control operation from becoming unstable. and,
When the load is close to the rated load, lower the set value of the outlet steam temperature so that the amount of cooling water exceeds the minimum flow rate.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 3. In these figures, the same components as those explained in FIG. 7 are given the same reference numerals, and the explanation thereof will be omitted.

In FIG. 1, the heat transfer surface of the high pressure superheater and reheater is divided into two when according to the present invention. In other words, the heat transfer surface includes the high-pressure second superheater 12 and the second reheater 4 when viewed from the exhaust gas upstream side.
1, the first reheater 42, and the high-pressure first superheater 14 are arranged in this order. Further, the desuperheater 36 is interposed in the path between the second reheater 41 and the first reheater 42 . Note that the desuperheater 35 is provided in a path connecting both superheaters 12 and 14, as in the conventional case.

On the other hand, when the arrangement of these heat transfer surfaces is depicted in a plan view, it becomes as shown in FIG.

Further, FIG. 3 shows the configuration of a desuperheater control device that controls the outlet steam temperature of the superheater and reheater. This control device changes the set value according to the generator load and changes the opening degree of the control valves 43, 44 based on the deviation from the actual steam temperature to adjust the amount of cooling water.

That is, the generator load is detected by the load detector 45 and input to the temperature signal generator 46 . The output signal of this temperature signal generator 46 is compared with the output signal of a temperature detector 47 detecting the outlet steam temperature of the high-pressure second superheater 12 in a temperature difference calculator 48 to obtain a control deviation. This deviation signal is converted into a flow rate command signal by the regulator 49,
The signal is outputted to the control valve 43 via the amplifier 50, and its opening degree is changed, and the amount of cooling water is increased or decreased in accordance with the flow rate command signal. Although not shown, the control valve 44 is also provided with the same control device.

Next, the operation of this embodiment will be explained with reference to FIGS. 4 to 6. FIG. 4 shows one of the units of the combined cycle power plant configured as described above is in operation, and the reheater is used as driving steam for the steam turbine 30 from this operating unit to the other unit that is about to start up. This figure shows the changes in temperature of each part when steam is supplied from the inlet side of the bleed through the bleed communication pipe 37. In addition,
For comparison, the change in temperature in the case of the prior art is also shown. When the amount of extracted air is small, increasing the amount of cooling water in order to lower the steam temperature at the reheater outlet to the limit value, the steam temperature at the reheater outlet will change to line D from point (e) to point (f) in Figure 4. decreases along. At this time, the outlet steam temperature of the desuperheater 36 decreases along line A from point (a) to point (b) in FIG. The outlet steam temperature of No. 36 is much higher than the outlet limit temperature, and there is no problem in operation.

When the amount of extracted air increases, the flow rate of steam flowing through the reheaters 41 and 42 decreases, so the outlet steam temperature of each reheater 41 and 42 is kept below the limit value as when the amount of extracted air is small. However, since the attemperator 36 is installed between both reheaters 41 and 42, the steam flowing into the attemperator 36 Can keep temperature high. In this case, due to the increase in the amount of cooling water, the steam temperature at the outlet of the reheater will decrease (as shown in Figure 4).
g) to (h) along line D', and as a result, the desuperheater outlet temperature decreases from point (C) to point (d) in Figure 4.
However, even if the amount of cooling water increases, the desuperheater outlet temperature will not fall below the limit value.

The amount of heat absorbed at each heat transfer surface of the exhaust heat recovery boiler constructed in this way is shown in FIG.

Next, the operation when the steam temperature control at the outlet of the high-pressure second superheater 12 and the second reheater 41 is performed by the control device shown in FIG. 3 will be explained.

As described above, due to the characteristics of the gas turbine 34, the temperature of the exhaust gas flowing into the exhaust heat recovery boiler 11 reaches a peak at a load equivalent to 75%. If the steam temperature is not controlled, the upper limit will be reached at a load equivalent to 75%, but since the steam temperature will become too high when this upper limit is reached, the outlet steam temperature is controlled by cooling water. As shown in FIG. 6, the set value of the outlet temperature is set higher than the set value during normal operation while the load is kept low. In this way, control is not started until the exhaust gas temperature approaches the peak value temperature, so when the load increases, the steam temperature increases accordingly and slightly exceeds the temperature during normal operation. This steam temperature slightly exceeding the temperature during normal operation corresponds to a load where the steam temperature becomes lower than the material's service limit temperature.For example, when the load is 60%, the outlet steam temperature setting value is changed to the initial value. Switch from the set value to the set value during normal operation. At this time, since the steam temperature exceeds the temperature setting value during normal operation, cooling water is rapidly injected into the steam, causing hunting when the cooling water amount is near zero flow rate, and the control valve 43.
4 does not cause chattering and the load can continue to increase. Furthermore, when the load increases, the exhaust gas temperature decreases, so the steam temperature also decreases, and the amount of cooling water decreases. Therefore, when the load reaches a point where the amount of cooling water falls below the minimum flow rate, the steam temperature setting value is switched to a temperature lower than the temperature during normal operation, and when the load reaches full load, the cooling water flow exceeds the minimum flow rate. Let it flow.

For the above control operation, the generator load is detected by the load detector 45, and the set value of the temperature signal generator 46 is switched at a predetermined load (for example, 60% load), and the same applies even after the load increases. Can be switched. When a deviation occurs between the set value and the actual steam temperature, a flow rate command signal corresponding to the positive or negative value is outputted by the control valves 43, 44, thereby increasing or decreasing the amount of cooling water.

In this way, even when extracting a large amount of steam from the inlet sides of the second and first reheaters 41, 42, it is possible to prevent the degree of superheating of the steam at the outlet of the attemperator 36 from decreasing, and other It is possible to supply large amounts of auxiliary steam to the unit.

[Effects of the Invention] As explained above, the present invention divides the heat transfer surface of the reheater into two to form the second and first reheaters, and places the desuperheater between both reheaters. This prevents the degree of superheating of the reheated steam flowing through the desuperheater from decreasing.
It becomes possible to supply a large amount of auxiliary steam when starting up other units.

In addition, since the set values of the superheater outlet steam temperature and the reheater outlet steam temperature are switched by the generator load signal, it is possible to eliminate unstable operation of the cooling water control valve of the desuperheater. .

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the exhaust heat recovery boiler according to the present invention, Fig. 2 is a plan view showing the arrangement of heat transfer surfaces, and Fig. 3 is a desuperheater control device according to the present invention. A configuration diagram showing an example, Fig. 4 is a diagram showing the relationship between the amount of cooling water and steam temperature, Fig. 5 is a diagram showing the amount of heat absorbed by the heat transfer surface, and Fig. 6 is a diagram showing the load and outlet steam temperature setting value. 7 is a configuration diagram showing an example of a conventional exhaust heat recovery boiler, and FIG. 8 is a diagram showing the relationship between cooling water amount and steam temperature in the conventional technology.
FIG. 9 is a diagram showing the relationship between load and amount of cooling water. 11...Exhaust heat recovery boiler 12...
...High pressure second superheater 14...High pressure first superheater 30...
...... Steam turbine 34 ...... Gas turbine 35.36 ...... Desuperheater 37 ...... Bleed communication pipe 41 ... ...Second reheater 42...First reheater 46...Temperature signal generator 48...
...Temperature difference calculator 49...Adjuster

Claims (2)

[Claims] (1) In an exhaust heat recovery boiler in which a high-pressure superheater and a reheater are sequentially installed following the direction of exhaust gas flowing inside the vessel, the high-pressure superheater and the reheater each divide the heat transfer surface into two, and the exhaust gas a high-pressure second superheater, a second reheater, a first reheater, and a high-pressure first superheater are arranged in this order from the upstream side of , and a steam path connecting the first and second reheaters. (2) In the steam path connecting the high-pressure first and second superheaters;
A desuperheater is provided in each steam path connecting the first and second reheaters, and in order to maintain an appropriate temperature of superheated steam or reheated steam, the amount of cooling water supplied to the desuperheater is controlled by a control valve. A desuperheater control device that adjusts the opening degree by changing the degree of opening, characterized by comprising means for switching the set values of the high-pressure superheater outlet steam temperature and the reheater outlet steam temperature using a generator load signal. Desuperheater control device.