JPH02259301A - Waste heat recovery boiler - Google Patents

Abstract

PURPOSE:To improve a cooling effect of a reheating device and further improve a thermal efficiency of a plant in a boiler of a waste heat recovery type combined cycle power generating plant by a method wherein a medium pressure part heat exchanger device is arranged in a side-by-side relation between a higher pressure heat exchanger and a low pressure heat exchanger and then medium pressure steam is mixed with steam at an outlet of a turbine high pressure and then guided to the reheating unit. CONSTITUTION:A high pressure steam trap valve, an adjusting valve 34, a reheating steam trap valve and an intercepting valve 37 are closed and steam generated at a high pressure evaporator 14 is guided from a high pressure drum 15 to a condensor 5 through a high pressure bypassing valve 51. In turn, the steam generated at a medium pressure evaporator 42 is flowed from a medium pressure drum 43 into a reheating device 12 through a conduit extending from a low temperature reheating pipe of a high pressure turbine 31 of a steam turbine 3 to the reheater 12 and then a cooling operation is carried out by this steam. The steam passes through the medium and low pressure part turbine bypassing valve 38 and then this steam is discharged to a condensor 5. With such a configuration as above, it is possible to cool the reheater efficiently and at the same time to improve a thermal efficiency of the plant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Field of Application) The present invention relates to an improvement of an exhaust heat recovery boiler in an exhaust heat recovery type combined cycle power plant, particularly a reburning type exhaust heat recovery boiler.

(Prior Art) Conventional exhaust heat recovery type combined cycle power plants have generally adopted a non-rekindling mixed pressure cycle. However, in recent years, as the inlet temperature of gas turbines has increased, the temperature of gas turbine exhaust gas has also increased to around 600°C.
This makes it possible to adopt a reburning steam cycle that combines a reburning exhaust heat recovery boiler and a reburning steam turbine.

For this reason, as shown in FIG.
A reburning waste heat recovery combined cycle power plant has been developed, which mainly consists of:

In this plant, the exhaust gas from the gas turbine 2 is introduced into the exhaust heat recovery boiler 1, where it undergoes heat exchange with water and steam, and is discharged to the outside.

Water is supplied to the exhaust heat recovery boiler 1 by supplying condensate accumulated in the condenser 5 to the low pressure section of the exhaust heat recovery boiler 1 via the low pressure water supply pump 6. Inside the boiler 1, it is heated by a low-pressure economizer 19, and a part of it enters the low-pressure drum 18, where it is heated and evaporated by the low-pressure evaporator 17.

On the other hand, some of the other water is pressurized by the high-pressure water supply pump 20 and heated via the high-pressure economizer 16 to form the high-pressure drum 15.
It is sent to the high-pressure evaporator 14 and evaporated into high-pressure steam.

This high-pressure steam passes from the first high-pressure superheater 13 to the second ^-pressure superheater 11, is superheated, and is sent to the high-pressure part turbine 31 of the steam turbine 3 through the high-pressure steam stop valve and pressure reducing valve 34, where it is It performs expansion work, lowers pressure and temperature, and becomes low-temperature reburned steam.

This low-temperature reburned steam passes through the check valve 35 and is sent to the reheater 12 installed inside the exhaust heat recovery boiler 1, where it is heated again and then passes through the reheat steam stop valve and intercept valve 37. It is sent to the intermediate pressure turbine 32 of the steam turbine 3, where it performs expansion work.

The low pressure steam generated in the low pressure drum 18 is mixed into the outlet steam of the intermediate pressure turbine 32, and the steam turbine 3
The steam enters the low-pressure turbine 33, performs expansion work, and is discharged to the condenser 5. In the condenser 5, the steam is condensed to become condensed water, and the low-pressure water supply pump 6 supplies water to the exhaust heat recovery boiler 1 again.

A heat quantity-temperature diagram in the exhaust heat recovery boiler 1 at this time is shown in FIG.

Thereby, the shaft torque generated by the gas turbine 2 and the steam turbine 3 is transmitted to the generator 4 coupled to the -shaft to generate electricity.

Note that 36 transfers the steam from the second high-pressure superheater 11 to the reheater 1.
38 is a medium and low pressure turbine bypass valve that guides the steam exiting the reheater 12 to the condenser 5; 39 is a turbine bypass valve for guiding the steam exiting the low pressure drum 18 to the condenser 5; This is a low pressure turbine bypass valve that leads to

FIG. 7 shows the starting curve of the above-mentioned -shaft type combined cycle during cold starting.

After starting rotation via a starter device (not shown) such as a starter motor, purge operation of the gas turbine 2 is performed at approximately 30% rotation speed, and the ignition speed is returned to ignite the combustor of the gas turbine 2. do. Thereafter, the rotational speed is increased and kept constant at an intermediate rotational speed, thereby heating the exhaust heat recovery boiler 1 with the exhaust gas of the gas turbine 2.

Since the exhaust gas temperature at this time is lower than the design gas temperature of the reheater 12, it is possible to run the reheater 12 dry.

On the other hand, if the final stage of the steam turbine 3 is brought to its rated speed without any steam input, it will be heated by rotational friction and exceed the allowable temperature. In this case as well, it is necessary to maintain a constant rotational speed midway through the process and use the steam generated.

Therefore, as shown in FIG. 5, a high-pressure section turbine bypass valve 36 is provided, and the steam generated in the high-pressure section of the waste heat recovery boiler 1 is passed through the bypass valve 36 and transferred from the reheater 12 to the intermediate-pressure section turbine. 32 to cool the rotor blades.

(Problem to be solved by the invention) However, when the warm-up operation of the boiler using exhaust gas is completed and it becomes possible to introduce medium- or low-pressure main steam to the turbine, the rotation speed is further increased from this maintained rotation speed. However, at this time, the artificial gas temperature of the exhaust heat recovery boiler 1 rises rapidly as shown in Fig. 7, and the high-pressure steam temperature also rises accordingly. Even if this high temperature steam is passed through 36 and enters the reheater 12, the reheater 12 cannot be effectively cooled.

Further, FIG. 8 shows a startup curve in the case of high temperature startup.

That is, since the inlet gas temperature of the waste heat recovery boiler 1 rises in a short time after ignition, it is necessary to introduce cooling steam into the reheater 12 before ignition, and the high pressure turbine bypass valve 36 must be opened. The steam generated by the heat retained in the high-pressure drum 15 can be introduced into the reheater 12, but when the rotation speed increases and the inlet gas temperature of the exhaust heat recovery boiler 1 rises, the same as in the case of cold startup described above Therefore, the reheater 12 cannot be effectively cooled.

In this way, when a reburning cycle as shown in Fig. 5 is adopted to improve efficiency in a -shaft type combined cycle plant, when the inlet gas temperature of the exhaust heat recovery boiler rises as the rotation speed rises, There was a problem in that it was not possible to secure low-temperature steam to effectively cool the reheater.

In view of the above, the present invention employs a reburning cycle - in an axial heat recovery combined cycle power plant, the reheater can be effectively cooled at the time of plant startup, and
Furthermore, the present invention provides an exhaust heat recovery boiler that can effectively secure cooling steam to prevent temperature rise in the low pressure section of the steam turbine due to rotational friction during cold start-up and high-temperature start-up, and further improve plant thermal efficiency. The purpose is to

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the waste heat recovery boiler according to the present invention includes a heat exchanger for a high pressure section and a low pressure section, and
In an exhaust heat recovery boiler in which outlet steam from a turbine high-pressure section is guided to a reheater disposed inside, a heat exchanger for the intermediate-pressure section consisting of an intermediate-pressure evaporator, an intermediate-pressure drum, and an intermediate-pressure economizer. are interposed in parallel between the heat exchangers of the high-pressure section and the low-pressure section, and the intermediate-pressure steam generated in the intermediate-pressure section heat exchanger is mixed with the outlet steam from the high-pressure section of the turbine to generate the recycle gas. It is configured to be introduced into a heating device.

(Function) According to the present invention configured as described above, the low-pitched intermediate pressure steam generated by the intermediate pressure heat exchanger at startup etc. is guided into the inside of the reheater to effectively cool the reheater. As a result, even if the inlet temperature of the exhaust heat recovery boiler suddenly increases, it can be coped with.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

This embodiment has the following configuration added to the conventional example shown in FIG. 5 above.

That is, the water pressurized by the high-pressure water pump 20 passes through the first high-pressure economizer 45 and the second high-pressure economizer 46 and is supplied to the high-pressure drum 15, while the water passes through the low-pressure economizer 19. A portion of the water supply is pressurized by the medium pressure water supply pump 46 and heated by the medium pressure economizer 44, and then supplied to the medium pressure drum 43. The steam generated in the intermediate-pressure steam generator 42 exits the intermediate-pressure drum 43 and mixes with the outlet steam of the steam turbine high-pressure section 31, and then is supplied to the reheater 12, where it becomes heated steam and enters the steam turbine. It is designed to be supplied to the pressure section 32.

Furthermore, a bypass line 53 is provided at the outlet of the second high-pressure superheater 11 and is equipped with a high-pressure steam bypass valve 51 for releasing high-pressure steam to the condenser 5 during startup. A bypass line 54 equipped with a reheater bypass valve 52 for releasing steam to the condenser 5 is also provided at the outlet.

Hereinafter, the operation of the above embodiment will be explained.

In the case of cold starting as shown in Fig. 7, after the starting device (not shown) such as a starting motor is connected and rotation is started, approximately 30 to 50
Perform purge operation at % rotation speed, return to ignition speed and ignite the combustor. Thereafter, the rotational speed is increased and kept at a constant rotational speed in the middle for warming the exhaust heat recovery boiler 1.

At this time, as shown in FIG. 2, the high pressure steam stop valve and control valve 34 and the reheat steam stop valve and intercept valve 37 are closed. Then, the steam generated in the high-pressure evaporator 14 is
After leaving the high-pressure drum 15 and passing through the first high-pressure superheater 13 and the second high-pressure superheater 11 to be superheated, the steam is discharged through the high-pressure steam bypass valve 51 to the condenser, etc., and then to the low-pressure evaporator 17. After leaving the low pressure drum 18, the generated steam passes through the low pressure turbine bypass valve 39 and is discharged to the condenser 5.

On the other hand, the steam generated in the medium pressure evaporator 42 is transferred to the medium pressure drum 4.
3 and enters the reheater 12 from the outlet pipe (low-temperature reburning pipe) of the high-pressure turbine 31 of the steam turbine 3, and enters the reheater 12.
After cooling the air 2, it exits here and is discharged to the condenser 5 through the medium and low pressure turbine bypass valve 38.

FIG. 4 shows a heat quantity-temperature diagram in the exhaust heat recovery boiler 1.

In the case of cold startup, the pressure of the intermediate pressure steam increases in this state, and when it reaches the predetermined pressure required for cooling the turbine, the reheat steam stop valve and intercept valve are closed as shown in Figure 3. 37 by a necessary opening degree, thereby allowing steam for cooling the steam turbine to flow into the inside of the reheater 12 and the medium and low pressure section of the steam turbine 3.

Thereby, the cooling steam for the reheater 12 and the cooling steam for the steam turbine 3 can be secured, so the rotation speed can be increased to the rated rotation speed.

Note that when this rotation increases, the inlet gas temperature of the exhaust heat recovery boiler 1 rises, but since the low temperature steam flows through the tube of the reheater 12 as described above and is cooled, this tube is not damaged. This will prevent you from doing so.

Additionally, if steam is present in the high-pressure turbine 31 when the rotation increases, the temperature will rise due to rotational friction, so the reheater bypass valve 52 is opened to communicate with the condenser 5. By keeping the inside of the high-pressure turbine 31 in a vacuum, this temperature rise can be prevented.

On the other hand, in the case of high-temperature startup as shown in FIG. can be introduced into the reheater 12 and used as cooling steam for the reheater 12.

However, in this case, the steam coming out of the reheater 12 has a high temperature, so even if this steam is introduced into the intermediate pressure section turbine 32, the low pressure section of the steam turbine will not be cooled. In this way, when the outlet temperature of the reheater 12 is higher than a predetermined temperature, by opening the low pressure steam bypass valve 53, the low pressure steam generated by the heat capacity of the low pressure drum 18 is used as cooling steam for the low pressure turbine 33. can do.

〔Effect of the invention〕

Since the present invention has the above-described configuration, medium-pressure low-temperature steam can be used to cool the reheater during plant startup, etc., so that the reheater can be effectively cooled.

In addition, during cold start-up, steam from the reheater is input from the intermediate-pressure turbine inlet, and during high-temperature start-up, low-pressure steam is input from the low-pressure turbine inlet to secure steam for cooling the steam turbine. can do.

Furthermore, by installing an intermediate pressure evaporator, an intermediate pressure drum, and an intermediate pressure economizer, the area between the steam/water side line shown in Figure 4 and the gas side line can be changed as shown in Figure 6. Since it can be made smaller than the conventional example, there is an effect that the plant thermal efficiency of the combined cycle can be increased by, for example, about 1% in relative value.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a reburning type exhaust heat recovery combined cycle power plant equipped with an embodiment of the present invention, Figures 2 and 3 are operating state diagrams during cold startup in Figure 1, and Figure 4. is a graph showing the heat quantity-temperature diagram in the exhaust heat recovery boiler of Fig. 1, Fig. 5 is a graph showing the conventional example, Fig. 6 is a diagram equivalent to Fig. 1,
Figure 7 is a graph showing the startup curve during cold startup, Figure 7 is a graph showing the startup curve during high temperature startup, and Figure 8 is a graph showing the heat quantity-temperature diagram in the exhaust heat recovery boiler of Figure 5. . 1...Exhaust heat recovery boiler, 2...Gas turbine, 3.
...Steam turbine, 4... Generator, 5... Condenser,
11...Second high pressure superheater, 12...Reheater, 13.
...First high pressure superheater, 14...High pressure evaporator, 15...
- High pressure drum, 16... High pressure economizer, 17... Low pressure evaporator, 18... Low pressure drum, 19... Low pressure economizer, 31... High pressure part turbine, 32... Medium Pressure section turbine, 33... Low pressure section turbine, 34... High pressure steam stop valve and adjustment valve, 37... Reheat steam stop valve and intercept valve, 38... Medium and low pressure section turbine bypass valve,
39...Low pressure turbine bypass valve, 41...Second high pressure economizer, 42...Intermediate pressure evaporator, 43...Intermediate pressure drum, 44...Intermediate pressure economizer, 45...・First high pressure economizer, 46... Medium pressure water supply pump, 51... High pressure steam bypass valve, 52... Reheater bypass L 53, 54...
・Bypass line.

Claims (1)

[Claims] In an exhaust heat recovery boiler that is equipped with a heat exchanger for a high-pressure section and a low-pressure section, and that directs outlet steam from the turbine high-pressure section to an internal reheater, it is equipped with an intermediate-pressure evaporator, an intermediate-pressure drum, and an intermediate-pressure drum. A heat exchanger for the intermediate pressure section consisting of a energy saver is interposed in parallel between the heat exchangers for the high pressure section and the low pressure section, and the intermediate pressure steam generated in the heat exchanger for the intermediate pressure section is transferred to the above heat exchanger. An exhaust heat recovery boiler characterized in that it is configured to be mixed with outlet steam from a turbine high pressure section and introduced into the reheater.