JPH0544407A - Exhaust heat recovery method of pressurized fluidized bed combined generating system - Google Patents

Abstract

PURPOSE:To enhance thermal efficiency of the whole plant by providing a feed water circulation adjusting valve, a flash tank, and a drain adjusting valve in the course of a feed water circulation return system pipe line from the feed water outlet of a gas turbine exhaust gas cooler positioned in a boiler high pressure feed water system to a deaerator. CONSTITUTION:A pressurized fluidized bed combined generating system is composed of a pressurized fluidized bed boiler 2, a gas turbine generator 1, and a steam turbine generator 3. A feed water circulation return system from the feed water outlet of a gas turbine exhaust gas cooler 8 to a deaerator positioned in a boiler high pressure feed water system is provided, and a feed water circulation adjusting valve 13, a flash tank 14, and a drain adjusting valve 15 are provided in the course of it. Since the flash tank 14 has comparatively low pressure inside, flash steam is recovered to the deaerator 6, and flash drain is likewise to the deaerator 6 through the drain adjusting valve 15. Thus, at the partial load time of a plant, exhaust gas of high temperature is not shed to a smokestack, and this surplus emission heat quantity is recovered to prevent lowering of plant thermal efficiency.

Description

Detailed Description of the Invention

[0001]

This invention relates to a pressurized fluidized bed combustion boiler,
In a pressurized fluidized bed combined cycle power generation system including a gas turbine and a steam turbine, the present invention relates to an exhaust heat recovery method for gas turbine exhaust gas.

[0002]

2. Description of the Related Art In a pressurized fluidized bed boiler, a combined power generation system is used in which a gas turbine is driven by combustion exhaust gas and a steam turbine is driven by generated steam. In this case, since the combustion exhaust gas that has exited the gas turbine maintains a high temperature, in order to recover this thermal energy and reduce the heat load on the chimney, heat is exchanged with the boiler feed water by the gas turbine exhaust gas cooler, The temperature is lowered and discharged to the chimney.

A flow diagram of this conventional combined cycle power generation system is shown in FIG. In FIG. 3, 1 is a gas turbine generator, 2 is a pressurized fluidized bed boiler, 3 is a steam turbine generator, 4 is a condenser, 5 is a low-pressure feed water heater, 6 is a deaerator,
7 is a high pressure feed water heater, 8 is a gas turbine exhaust gas cooler,
Reference numeral 9 is a gas bypass damper, 10 is a chimney, 11 is a water supply pump, and 12 is a water supply adjusting valve.

Fuel and compressed air from the gas turbine generator 1 are supplied to the pressurized fluidized bed boiler 2 and burned, and the generated steam drives the steam turbine generator 3. On the other hand, the exhaust gas of the pressurized fluidized bed boiler 2 drives the gas turbine generator 1. Exhaust gas from the steam turbine 3 is condensed in a condenser 4, and then, a low-pressure feed water heater 5, a deaerator 6, a feed water pump 11,
After passing through the high-pressure feed water heater 7 and the feed water adjusting valve 12, the pressure fluidized bed boiler 2 is reached and a steam side cycle is formed.

The gas turbine exhaust gas is exhausted to the boiler feed water side by the gas turbine exhaust gas cooler 8 and then discharged to the atmosphere through the chimney 10. The extraction steam of the steam turbine 3 is applied to the heating steam of the low-pressure feed water heater 5, the deaerator 6, and the high-pressure feed water heater 7. The high-pressure feed water heater 7 and the gas turbine exhaust gas cooler 8 serve as a system for branching the boiler feed water, but for heat balance reasons, the high-pressure feed water heater 7 is not used and depends only on the gas turbine exhaust gas cooler 8. The method is general.

The gas turbine exhaust gas cooler 8 functions at the time of rated load for the purpose of recovering the heat quantity of exhaust gas possessed when viewed from the gas side, and as a high pressure feed water heater when viewed from the boiler feed water side. However, at the partial load when the plant output decreases, the equilibrium state of heat exchange between the gas side and the water supply side shows a state different from that at the rated load. That is, generally, as a result that the amount of heat transferred from the gas side to the water supply side exceeds the capacity of the water supply heater, a part of the outlet water supply of the exhaust gas cooler 8 is accompanied by steam generation. The steam generation, which is a function originally not provided to the exhaust gas cooler 8, causes a serious operational obstacle such as a water hammer, which causes a problem that the operation of the plant cannot be continued.

The gas turbine exhaust gas cooler 8 is provided with a gas side bypass system and a gas bypass damper 9. As a means for avoiding the above-mentioned problems in the conventional method, this gas side bypass circuit is provided, and the gas flow rate to the exhaust gas cooler 8 is reduced by opening the gas bypass damper 9 during partial load, whereby the exhaust gas is reduced. Measures are taken to reduce the heat load on the cooler and prevent steam generation at partial load.

However, the above gas bypass damper system causes a rise in the temperature of the exhaust gas discharged from the chimney at the time of partial load, and in addition to the problem of requiring a heat-resistant structure for the exhaust gas duct and the chimney, the final exhaust gas This is a serious problem in that it causes an increase in heat loss, that is, a decrease in plant thermal efficiency.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to improve the capacity as a feed water heater by the amount of heat transfer from the gas side to the feed water side during partial load when the plant output of the pressurized fluidized bed combined cycle power generation system decreases. Even when the temperature exceeds the limit, it is an object to provide a means for preventing the reduction of the thermal efficiency of the plant by collecting the surplus discharged heat amount without flowing the high-temperature exhaust gas to the chimney.

[0010]

As a result of intensive studies to solve the above-mentioned problems, the present inventors have increased the amount of water supplied through the gas turbine exhaust gas cooler by providing a circulation circuit to increase the excess heat of exhaust gas. Is absorbed and flashed in the circulation circuit to contribute to the improvement of the thermal efficiency of the entire plant by reducing the extraction steam from the steam turbine to the deaerator or supplying it to the low temperature reheat steam system of the steam turbine. The present invention has been completed by finding that it can be obtained.

That is, the present invention is as follows: (1) In a pressurized fluidized bed combined cycle power generation system comprising a pressurized fluidized bed combustion system boiler, a gas turbine and a steam turbine, from a feed water outlet of a gas turbine exhaust gas cooler located in a boiler high pressure feed water system. Install a water supply circulation return system pipe to the deaerator, install a water supply circulation adjustment valve, a flash tank, and a drain adjustment valve in the middle of the pipe, set the flash tank to a low pressure, and flush flash steam to the deaerator and flush drain. Is an exhaust heat recovery system for a pressurized fluidized bed combined cycle power generation system characterized by recovering and circulating the

(2) In a pressurized fluidized bed combined cycle power generation system consisting of a pressurized fluidized bed combustion system boiler, a gas turbine, and a steam turbine, from the water supply outlet of the gas turbine exhaust gas cooler located in the boiler high pressure water supply system to the deaerator. A water supply circulation return system pipe is provided, and a water supply circulation adjusting valve is provided in the middle of the pipe.
A pressurized fluidized bed combined cycle power generation characterized by installing a flash tank and a drain adjustment valve, setting the flash tank to an intermediate pressure, collecting the flash steam to a low temperature reheat steam system and collecting the flash drain to a deaerator and circulating it. This is the system exhaust heat recovery method.

The details of the present invention will be described with reference to FIGS. FIG. 1 is a flow diagram of a first system according to claim 1, which is a low pressure flash system, and FIG. 2 is a flow diagram of a second system according to claim 2, which is a medium pressure flash system.

Referring to FIG. A circulation return system is provided from the water supply outlet of the gas turbine exhaust gas cooler 8 to the deaerator, and a water supply circulation adjusting valve 13, a flash tank 14, and a drain adjusting valve 15 are installed on the way. The flash tank 14 has a relatively low pressure in this first system,
Flash vapor is collected in the deaerator 6, and flash drain is collected in the deaerator 6 via the drain adjusting valve 15.

The gas-side bypass system of the gas turbine exhaust gas cooler 8 is not installed. At the time of partial load when the plant output decreases, the amount of heat transfer from the gas side to the water supply side exceeds the capacity as a water supply heater, so the amount of water that is passed by the pump 11 to the gas turbine exhaust gas cooler 8 is controlled by the pressurized fluidized bed boiler 2. By increasing the amount of water supply or more and balancing the amount of heat transfer in the exhaust gas cooler 8 with the gas side, and suppressing steam generation in the exhaust gas cooler, excess water is sent to the circulation return system to the deaerator. Normally, the feed water temperature at the outlet of the exhaust gas cooler 8 is detected, and the feed water circulation adjusting valve 13 is controlled to open.

This water is flushed in the flash tank 14 by reducing the pressure to about the deaerator 6, and is cooled by the latent heat of vaporization. The water is returned to the deaerator 6 by adjusting the drain adjusting valve 15 with the liquid level gauge of the flash tank, and the vapor is also recovered to the deaerator because the pressure is about the same as that of the deaerator. Eventually, the amount of heat transferred in the exhaust gas cooler 8 becomes an amount of steam from the flash tank 14, and the extracted steam 16 from the middle of the steam turbine to the deaerator 6 can be saved.
This is, of course, automatically balanced from the thermal equilibrium relationship in the deaerator and does not require special control.

Next, FIG. 2 will be described. The configuration of the second system is basically similar to that of the first system, but the flash tank 14 has a relatively medium pressure in the second system, and the flash steam is recovered to the low temperature reheat steam 17. Is different from the first system. That is, the steam that has once driven the turbine in the steam turbine 3 is at a lower temperature than the steam that has exited the boiler, and this steam is returned to the boiler 2 and reheated to drive the steam turbine 3 again. The flash steam in the flash tank 14 is supplied to the low temperature reheat steam system 17.

As a result, the amount of low-temperature reheated steam is increased, and eventually the amount of steam supplied to the steam turbine 3 is increased, and the extra heat amount in the exhaust gas cooler is recovered. The point that the drain of the flash tank is circulated to the deaerator 6 and the point that the gas side bypass system of the gas turbine exhaust gas cooler 8 is not installed is the same as the first system.

That is, in the present invention, by installing the circulation return system from the feed water outlet of the gas turbine exhaust gas cooler 8 to the deaerator, the load condition of the whole plant is controlled when the whole plant is partially loaded. Without it, it becomes possible to secure a sufficient amount of water supply to the gas turbine exhaust gas cooler 8 to prevent the generation of steam at the time of partial load in the gas turbine exhaust gas cooler 8.

As described above, in the first system, the flash vapor in the flash tank 14 is recovered by the deaerator 6 as the deaerator heating vapor, and as a result, the extraction amount of the deaerator turbine bleed air 16 is reduced, so Contributes to increased turbine output. In the second system, the flash steam in the flash tank 14 has an intermediate pressure and the low temperature reheat system 1
By recovering to No. 7, heat recovery at a higher level than that of the first system can be achieved, and as a result, it contributes greatly to the improvement of thermal efficiency under partial load.

[0021]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. (Embodiment 1) FIG. 4 shows one embodiment of the first system of the present invention in the case where there is no steam reheat system from the steam turbine middle portion, and in order to make it easy to understand, the flow rate of each portion, It is the figure which entered the temperature.

FIG. 5 also shows the case without a reheat system.
It is a corresponding conventional example in which the bypass 9 for the conventional gas turbine exhaust gas is provided without the circulation and return system of the water supply of the present invention.
Conventionally, a gas turbine exhaust gas of 40 T / hr (25%) is bypassed in order to prevent steam generation in the water supply system at a partial load with a water supply amount of 60 T / hr from a deaerator. Therefore, the exhaust gas temperature at the chimney is 195 ° C., and the damage to the flue and the chimney is large, and an expensive special heat-resistant wall structure is required to prevent this.

In the invention of FIG. 4, the circulating water supply 20T /
The amount of water to be sent to the exhaust gas cooler 8 including hr is 80 T / hr, which allows the exhaust gas system to be bypassed without
Since the entire amount of exhaust gas can recover exhaust heat, the final exhaust gas temperature can be reduced to the originally intended 140 ° C.

The flash vapor (5 T / hr) and flash drain (15 T / hr) in the circulation return system to the deaerator 6, which is the essence of the present invention, are recovered to the deaerator. As a result, the bleed air for the deaerator is reduced from 6T / hr in the conventional example to 2T / hr.
The electric power is reduced to hr, and the difference of 4 T / hr generates additional electric power in the steam turbine 3, the output of 15 MW is increased to 15.5 MW in the illustrated example, and the thermal efficiency of the entire plant is improved.

(Embodiment 2) FIG. 6 shows a second embodiment of the present invention in the case where there is a reheat system for steam from the middle part of a steam turbine.
FIG. 3 is a diagram showing an example of the system, and is a diagram in which flow rates and temperatures of respective parts are entered for easy understanding.

FIG. 7 is a corresponding conventional example in which the conventional gas turbine exhaust gas bypass 9 is provided without the circulation system of the feed water of the present invention, also in the case of the reheat system. Also in this case, the exhaust gas temperature in the flue and the stack becomes 195 ° C. due to the exhaust gas bypass as in FIG. 5, and the same problem as described above occurs.

In the invention of FIG. 6, by setting the amount of water to be sent to the exhaust gas cooler to 75 T / hr, exhaust heat recovery of the entire exhaust gas is possible without providing a bypass in the exhaust gas system, so the final exhaust gas temperature is It can be reduced to the originally intended 140 ° C. Of the supply water circulation amount of 20 T / hr, 2 T / hr of steam is flashed in the flash tank 14, which is sent to the reheat steam system 17, reheated by the boiler, and used again for driving the steam turbine.

The flash drain 18T / hr is circulated to the deaerator 6. As a result of the present invention, in Example 2 of FIG. 6, the extraction air for the deaerator is changed from 5.5 T / hr in FIG. 7 of the conventional example to 3 in FIG.
T / hr and the amount of high temperature reheated steam is 2T /
By increasing hr, the amount of electric power generated in the steam turbine 3 is increased from 16 MW to 17 MW, and the thermal efficiency of the entire plant is improved.

[0029]

EFFECTS OF THE INVENTION In addition to solving structural problems, which are problems in the conventional combined cycle power generation system, due to harmful steam generation in the gas turbine exhaust gas cooler at partial load or excessive rise in exhaust gas temperature in the gas bypass damper system, The increase in final exhaust gas heat loss, that is, the decrease in plant thermal efficiency is eliminated, and the thermal efficiency of the entire plant is improved.

[Brief description of drawings]

FIG. 1 is a flow diagram of a first system of the present invention, which is a low pressure flash method.

FIG. 2 is a flow diagram of the second system of the present invention, which is a medium pressure flash system.

FIG. 3 is a flow diagram of a conventional combined cycle power generation system.

FIG. 4 is a flow diagram of a first system in which a flow rate and temperature corresponding to Example 1 of the present invention are entered.

5 is a flow diagram in which a flow rate and a temperature of a conventional example corresponding to FIG. 4 are entered.

FIG. 6 is a flow diagram of a second system in which a flow rate and temperature corresponding to Example 2 of the present invention are entered.

FIG. 7 is a flow diagram in which the flow rate and temperature of the conventional example corresponding to FIG. 6 are entered.

[Explanation of symbols]

 1 Gas Turbine Generator 2 Pressurized Fluidized Bed Boiler 3 Steam Turbine Generator 4 Condenser 5 Low Pressure Water Heater 6 Deaerator 7 High Pressure Water Heater 8 Gas Turbine Exhaust Cooler 9 Gas Bypass Damper 10 Chimney 11 Water Pump 12 Water Supply Regulator valve 13 Water supply circulation regulator valve 14 Flash tank 15 Drain regulator valve 16 Turbine extraction for deaerator 17 Low temperature reheat steam

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location F22D 1/40 7715-3L F23J 15/00 6850-3K

Claims (2)

[Claims] 1. A pressurized fluidized bed combustion boiler, a gas turbine,
In a pressurized fluidized bed combined cycle power generation system consisting of a steam turbine, a water supply circulation return system pipe from the water supply outlet of the gas turbine exhaust gas cooler located in the boiler high pressure water supply system to the deaerator is provided, and the water supply circulation adjustment is performed in the middle of the pipe. Valve, flash tank, and drain adjustment valve are installed, the pressure of the flash tank is kept low, and the flash vapor is collected in the deaerator and the flash drain is circulated in the deaerator for circulation. System waste heat recovery method. 2. A pressurized fluidized bed combustion boiler, a gas turbine,
In a pressurized fluidized bed combined cycle power generation system consisting of a steam turbine, a water supply circulation return system pipe from the water supply outlet of the gas turbine exhaust gas cooler located in the boiler high pressure water supply system to the deaerator is provided, and the water supply circulation adjustment is performed in the middle of the pipe. A pressurized fluidized bed characterized by installing a valve, a flash tank, and a drain adjustment valve, setting the flash tank to an intermediate pressure, collecting the flash steam to the low temperature reheat steam system and collecting the flash drain to the deaerator and circulating it. Exhaust heat recovery method for combined power generation system.