JPS63253105A - Combined power plant - Google Patents

Abstract

(57) [Summary] 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 is directed to heating and
The present invention relates to a heat recovery method, and particularly to a combined power generation plant suitable for a large-capacity multi-shaft combined plant using a high-temperature turbine.

[Conventional technology]

In conventional combined plants, an attempt is made to recover as much of the heat in the exhaust gas from the gas turbine as possible using an exhaust heat recovery boiler, and methods for heating feed water in this case are described, for example, in Japanese Patent Publication No. 60-10162. Similarly, the condensate from the condenser was heated and then divided into high-pressure water supply and low-pressure water supply.

However, no consideration has been given to a system configuration in which high-pressure water supply and low-pressure water supply are separated into separate systems and then only the high-pressure water supply is heated.

[Problem that the invention seeks to solve]

In order to recover as much heat as possible with the exhaust heat recovery boiler, it is necessary to lower the exhaust gas temperature as much as possible and plan the water supply temperature at the inlet of the most downstream economizer to be lower than the exhaust gas temperature at the exhaust heat recovery boiler outlet.

In a combined plant that uses a high-temperature gas turbine, the temperature of the gas at the exhaust heat recovery boiler inlet increases, so it is desirable to improve the thermal efficiency by upgrading the steam conditions. The pressure difference becomes larger and larger, and the optimal conditions such as pressure, temperature, water quality, etc. required for water supply also become larger.

In conventional technology, the pressure of water sent to the waste heat recovery boiler was treated separately, but the temperature and water quality were treated the same, so the water temperature was low for the high-pressure system, and the water was low for the low-pressure system. There was a problem with the water supply being of excessive quality.

The purpose of the present invention is to divide the water supply into high-pressure systems and low-pressure systems, and then add means such as heating and deaeration to satisfy the water supply conditions of each system to obtain the optimum water supply conditions. Regarding deaeration, deaeration condenser technology has been developed and put into practical use mainly in single-shaft plants (steam turbines and gas turbines are directly connected by the same shaft and drive a common generator), but many In shaft-type plants (composed of one steam turbine and one or more gas turbines, each driving a generator), the steam turbine has a large capacity and a deaerator is usually installed. There is.

When a deaerator is installed, the water supply will be approximately equal to the saturated water temperature corresponding to the pressure inside the deaerator, and the temperature will be approximately 1.2 to 1.5 at.
At the pressure a, the temperature is about 105°C, and it becomes difficult to lower the exhaust gas temperature at the exit of the exhaust heat recovery boiler to about 110°C, which is possible with a gas-fired gas turbine, in terms of heat exchange between water and gas. This is because a temperature difference of about 30 to 50' is usually required, and the water supply temperature is preferably about 60°C to 80°C. As means for lowering the feed water temperature, there are known methods of lowering the deaerator operating pressure and methods of exchanging heat between the feed water and condensate at the deaerator inlet and outlet.

Lowering the operating pressure of the deaerator and operating it under negative pressure (vacuum) is sometimes done at startup in thermal power plants, but it is preferable during normal operation because there is a concern that air may leak into the deaerator performance. isn't it. Normally, it is 0.2 to 0.
A method of steam sealing is used at a pressure higher than 5 kg/rf, which is the lowest operating pressure above atmospheric pressure.

In addition, heat exchange between feed water and condensate requires a large heat transfer area, and since the withstand pressure is determined by the water supply pressure on the high pressure side, the weight is also large, and when considering the operating characteristics at startup, etc., the control may become complicated. It's large.

Regarding deaeration of feed water, the higher the pressure, the more carefully it is necessary to plan and ensure reliability. It is said that it is possible to do so using the deaeration capacity of the deaerator, and that it is not necessarily necessary to provide a deaerator.

[Means for solving problems]

The objective of optimizing the high-pressure and low-pressure water supply conditions is achieved by separating the high-pressure water supply system and the low-pressure water supply system after or in the manner in which the condensate from the condenser is extracted.

High-pressure water supply is heated upstream of the gas flow from the low-pressure energy saver of the heat recovery boiler after heating the feed water using a feed water heater that uses turbine extraction air or a deaerator that uses turbine extraction air or low-pressure boiler steam. The fuel is guided to a high-pressure economizer installed in the The exhaust gas at the outlet of the high-pressure economizer is planned by adjusting the water supply temperature and the location of the economizer (including placing it separately) so that the exhaust gas has the temperature and heat required for heating the water supply with the low-pressure economizer. All you have to do is The low-pressure water supply system uses condensate extracted from the condenser as feed water and sends water at a low temperature to the low-pressure economizer of the exhaust heat recovery boiler. The feed water in this system is heated by exhaust heat recovery (Guracon,
Heat recovery heating by economizer recirculation) may be used, but a regeneration cycle using turbine bleed air is not used. The low-pressure economizer is located at the downstream end of the heat recovery boiler.

[Effect]

In the heat recovery boiler, there is a high-pressure superheater and a high-pressure evaporator.

It is equipped with a high-pressure energy saver, low-pressure superheater, low-pressure evaporator, and low-pressure energy saver. In some cases, a low-pressure superheater is not installed. The role of the low-pressure superheater is that when the pressure of the high-pressure steam is planned to be high, the expansion line in the steam turbine shifts to the wet side (lower entropy side), so the temperature difference with the low-pressure saturated steam decreases, but the Humidity tends to be excessive. Therefore, it becomes necessary to superheat the low-pressure steam and guide it to the steam turbine.7
This was not necessarily necessary at a main steam pressure temperature of about 538°C.

High-pressure economizers may be installed separately before and after the low-pressure evaporator. This is because the exhaust gas temperature is affected by the heat recovery of the low-pressure economizer and how the pinch point of the low-pressure evaporator is taken. equipment to recover heat.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. It is composed of a gas turbine 1, an exhaust heat recovery boiler 4, a steam turbine 17, a generator 18, and a condenser 19. The gas turbine exhaust gas 2 is converted into exhaust gas 3 after exhaust heat is recovered by the exhaust heat recovery boiler 4.
released as.

High pressure superheater7. High pressure evaporation'rji8. Low pressure coal feeder 10° High pressure coal saver 9. Low pressure evaporator 11. A low-pressure energy saver 12° High-pressure steam 13 is generated from a high-pressure water supply 15 and low-pressure steam 14 is generated from a low-pressure water supply 16 in an exhaust heat recovery boiler 4 composed of a high-pressure drum 5 and a low-pressure drum 6.

The exhaust gas of the steam turbine 17 is condensed into condensate in a condenser 19, extracted with a low-pressure water supply pump 20, and supplied to the turbine bleed air 2.
The water is sent to a deaerator 23 via a low-pressure feed water heater 22 heated at step 5. A system that branches from the outlet of the low-pressure water supply pump 20 and is led to the low-pressure energy saver 12 as the low-pressure water supply 16, and a system that is led from the high-pressure water supply pump 21 to the high-pressure energy saver 9 as the high-pressure water supply 15 through the high-pressure water heater 24. It has a configuration with.

The condensate in the condenser 19 is, for example, 3 kg by a low-pressure water pump.
/ m and about 1/4 to 115 of the water is branched off as the low-pressure water supply 16, and the rest is heated and sent to the deaerator 23. The deaerator 23 has a sealing pressure of 0.2 to 0.5 kg.
/rr?・Operate at G pressure to perform deaeration. As the heating steam, turbine extraction air is normally used, and low pressure steam 14 is used at low loads. The high-pressure feed water heater does not need to be installed when heat recovery in the exhaust heat recovery boiler 4 is insufficient and the temperature of the exhaust gas 3 is higher than the limit by a margin. Low pressure water supply is 30
It can be sent at ~60'C, and high-pressure water can be sent at around 100-120'C. Furthermore, it is preferable in terms of thermal efficiency and stage planning that at least one low-pressure feed water heater bleeds air from a stage lower than the mixing pressure of the low-pressure steam.

The embodiment shown in FIG. 2 has a system configuration in which high-pressure feed water is heated and sent to the exhaust heat recovery boiler 4 without providing a deaerator. Although the water supply pump extracts low pressure and high pressure from the condenser 19, it is of course possible to use a system configuration in which water is extracted at low pressure and pressurized, and then the high pressure water pump is used to increase the pressure.

The example in FIG. 3 shows an example of a system configuration in which a low-pressure superheater is not provided. If the pressure of the high-pressure steam 13 is not very high and the exhaust steam humidity of the steam turbine 17 is not large, it can be used in a water system configuration.

FIG. 4 is an example in which the exhaust heat recovery boiler is a vertical type and the high pressure steam system is a once-through boiler. A high-pressure water supply system may require the installation of a condensate desalination device.

FIG. 5 shows a conventional example of the temperature distribution in the exhaust heat recovery boiler and the ratio of the amount of heat recovered in each part. 6th
The figure shows a similar comparison of one example of the present invention. By increasing the pressure of the high-pressure steam 13, the amount of evaporation is slightly reduced, and the amount of heat exchanged by the high-pressure evaporator 8 is slightly reduced, but the work in the steam turbine is thermodynamically increased. For this reason, the steam turbine output increases slightly, but the humidity of the turbine exhaust increases. In the conventional example shown in FIG.
Although the difference between the gas temperature and the steam saturation temperature in the evaporator 1 is large, in one example of the present invention, the low-pressure steam 14 is generated under optimal conditions to the same extent as the high-pressure evaporator 8. The high-pressure water supply 15 can also be supplied at a higher temperature than the exhaust gas 3, which was not possible in the prior art.

FIG. 7 is an example in which the high-pressure steam expansion line is shown as the turbine expansion line 26 in an enthalpy-entropy diagram. The high pressure steam condition is 1, for example 60ata.

With respect to the turbine expansion line 26 set at 500° C., both steam pressure and temperature are increased to, for example, 70 ata.

In the case of 540'C, the length of the turbine expansion line to the end point becomes longer, and more output is produced with the same amount of steam. However, only the pressure should be further increased, for example, 130at.
If the temperature is increased to 540° C. and the temperature remains at 540° C., the turbine expansion line will become longer, but the steam humidity at the end point will also increase, which may impair the reliability of the blade. By superheating the mixed low pressure steam 14, steam having a higher temperature than the turbine stage can be mixed, thereby reducing the humidity of the exhaust steam. Therefore, in a combined power generation plant that maximizes the heat recovery in the exhaust heat recovery boiler 4 and lowers the temperature of the exhaust gas 3 to the limit, it is possible to use the high temperature gas turbine exhaust gas 2 generated by the high temperature gas turbine to generate high-grade steam. This has been made possible by the present invention.

Low-pressure natural air should be actively used not only for recovering power but also as a countermeasure against turbine exhaust humidity.

It is desirable to obtain a large amount of evaporation at as low a pressure as possible, and the example in FIG. 6 shows that this is possible.

[Effects of the Invention] According to the present invention, the pressure of high-pressure steam can be reduced from 70 to 80 a
By increasing the ta to about 130 ata, there is an effect of optimizing the steam conditions of a large capacity steam turbine used in a multi-shaft combined power generation plant. In addition, regarding the water supply system, a deaerator is installed in the high-pressure water supply system, which operates at above atmospheric pressure, and by sending low-pressure water at a lower temperature than the high-pressure water supply to the low-pressure economizer, exhaust gas is reduced to a low temperature. It has the effect of recovering heat.

With the present invention, a plant efficiency of about 2% relative value can be expected in the steam cycle. The output ratio of the steam turbine plant is about 30% to 40%, and the total output of the entire plant is 0.7%.
It will be about %. Furthermore, by increasing the pressure of the steam, the volume of the main steam system can be reduced, ensuring reliable deaeration of feed water, and greatly improving reliability by reducing the humidity of the steam turbine exhaust. The effect of improving efficiency tends to become even greater as the temperature of the gas turbine increases.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram of an embodiment of the present invention, Fig. 2 is an embodiment without a deaerator, and Fig. 3 is a system configuration diagram of an embodiment without a low-pressure superheater. It is. FIG. 4 is a system configuration diagram of an embodiment in which the high-pressure steam system does not have a drum. FIG. 5 is a temperature distribution diagram of an exhaust heat recovery boiler according to an example of the prior art, and FIG. 6 is a temperature distribution diagram of an exhaust heat recovery boiler according to an embodiment of the present invention. FIG. 7 is an enthalpy-entropy diagram showing an example of the present invention and a conventional example using turbine expansion lines. 1... Gas turbine, 2... Gas turbine exhaust gas,
3...Exhaust gas, 4...Exhaust heat recovery board, S...
high pressure drum.

Claims (1)

[Scope of Claims] 1. A gas turbine, an exhaust heat recovery boiler installed in the exhaust gas flow path to generate steam through heat exchange with the gas turbine exhaust gas, and steam driven by the steam generated by the exhaust heat recovery boiler. In a plant equipped with a turbine, a condenser for condensing exhaust steam of a steam turbine, and a water supply pump for sending water condensed in the condenser, at least two types of pressures having different pressures are used in the exhaust heat recovery boiler. The above steam is generated, the high-pressure steam supply water is separated from the low-pressure steam water supply system, and the high-pressure water supply system is heated to a higher water temperature than the low-pressure water supply system using turbine extraction, etc., and then exhaust heat is recovered. A combined power generation plant with a boiler equipped with a system that sends water to a high-pressure economizer installed separately from a low-pressure economizer. 2. In claim 1, there is a combined power generation system that is equipped with a deaerator only for high-pressure water supply and that uses steam turbine extraction and/or exhaust heat recovery boiler steam to generate heating steam. plant. 3. A combined power generation plant according to claim 1, comprising a low-pressure heater in a gas flow path that turns low-pressure steam generated in an exhaust heat recovery boiler into superheated steam.