JPH0726908A - Combined cycle power plant - Google Patents

Abstract

PURPOSE:To prevent generation of steaming in fed water flowing through an economizer in a boiler when a combined cycle power plant falls into a negative load (partial load) operating range. CONSTITUTION:Steam is extracted from an opening of an overheater 18 in a boiler 1, and then the extracted steam is fed to an exhaust recovery heat- exchanger 15 where heat-exchange is carried out between the steam and exhaust heat from a gas turbine plant GTP. After the heat-exchange, the steam is returned to the overheater 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combined cycle power generation plant which is a combination of a steam turbine plant and a gas turbine plant, and is particularly useful for reducing the amount of steam sent from a boiler to a steam turbine, such as during partial load. The present invention relates to an improved combined cycle power plant suitable for suppressing the steaming phenomenon occurring in a boiler.

[0002]

2. Description of the Related Art Recently, in the electric power industry, a combined cycle power plant having excellent plant thermal efficiency has been in the limelight as the power consumption increases. This power plant is a combined cycle of a steam turbine plant and a gas turbine plant.

A combined cycle power plant may be a combination of a new gas turbine plant and a new steam turbine plant. However, considering the site conditions and the long period from construction to installation, the steam turbines that have already accumulated a lot of achievements have been accumulated. A so-called repowering power plant, which cleverly combines a plant and a new gas turbine plant to shorten the construction period, is general.

This type of power plant that has already been proposed is one in which a new gas turbine plant is added to an existing steam turbine plant and combined together to form a combined cycle. The exhaust heat from the gas turbine is recovered as exhaust heat. This is an improved combined cycle power plant that recovers heat with a heat exchanger and heats part of the exhaust steam from the steam turbine or the water of the condensate / water supply system.

In this type of power plant, a new gas turbine plant is added to an existing steam turbine plant to form a combined cycle, so that the exhaust heat of the gas turbine can be effectively utilized, so that the fuel consumption of the boiler is reduced. It is possible to improve the power generation efficiency. Further, since the gas turbine plant is additionally installed, it is possible to increase the amount of power generated by the power plant as a whole.

Further, in the combined cycle power plant, the existing steam turbine plant is rarely modified, and the additional gas turbine plant adjacent to the steam turbine plant can be installed in advance, so that the plant suspension period can be shortened. And so on. And in order to cope with the recent significant growth in power demand and the sharp decrease in the power reserve ratio of each power company due to the growth in power demand, it is required to start up new power generation facilities immediately. From the request, repowering of the existing steam turbine plant is considered to be one of the effective means.

An example of a conventional improved combined cycle power plant is shown in FIG. This combined cycle power generation plant is a combined cycle system in which a gas turbine plant GTP is added to an existing steam turbine plant STP.

In the steam turbine plant STP, the boiler 1, the steam turbine ST and various heat exchangers are sequentially connected to form a closed cycle. The steam generated in the boiler 1 is guided to the turbine high pressure section 2 of the steam turbine ST and performs expansion work. The steam that has worked in the turbine high-pressure section 2 of the steam turbine ST is sent to the boiler reheater 3 and the exhaust heat recovery heat exchanger 15 to be reheated or heated. The steam reheated or heated by the boiler reheater 3 and the exhaust heat recovery heat exchanger 15 joins again at the outlet of the boiler reheater 3 and is guided to the turbine intermediate pressure portion 4 of the steam turbine ST to perform work. The steam that has worked in the turbine intermediate pressure section 4 is subsequently guided to the turbine low pressure section 5 of the steam turbine ST, where it further performs work, and then the condenser 6
Is led to and cooled to condensate.

The respective parts 5, 9 of the steam turbine ST are
The work done in 10 drives a turbine generator 7 connected to the end of the steam turbine shaft, which is converted into electrical energy.

On the other hand, the condensate cooled and condensed in the condenser 6 is sent from the condenser 6 to the condensate water supply system by the condensate pump 8, and is fed to the low pressure feed water heater 9 and the low pressure (first) gas. It is heated by the feed water heater (low-pressure gas cooler) 10 and sent to the deaerator 11, where it is deaerated. The water deaerated by the deaerator 11 is pressurized by the water supply pump 12, further heated by the high-pressure water supply heater 13 and the high-pressure (second) gas water supply heater (high-pressure gas cooler) 14, and then supplied to the boiler 1. In the boiler 1, the temperature of the feed water rises in the economizer 16, the steam becomes steam in the evaporator 17, and the superheated steam becomes in the boiler superheater 18. The superheated steam from the boiler superheater 22 and the exhaust steam extracted from the turbine high-pressure part 2 of the steam turbine ST and heated by the exhaust heat recovery heat exchanger 15 join at the outlet of the boiler reheater 3 to become main steam. , To the turbine intermediate pressure portion 4 of the steam turbine ST again.

The gas turbine plant G additionally installed
The TP includes a compressor 19a and a gas turbine 19b and constitutes an open cycle. The gas turbine 19b has a shaft end connected to a turbine generator 20, and drives the turbine generator 20 to generate electric energy. At the same time, the gas turbine exhaust heat discharged from the gas turbine 19b is guided to the boiler 1 for boiler combustion. Used as air for use. Gas turbine exhaust heat is 600 ° C
Since it is a high temperature, it is impossible to guide it to the boiler 1 as it is. Once the exhaust heat recovery heat exchanger 15 exchanges heat with the exhaust steam from the turbine high pressure part 2, the temperature is lowered and then the boiler is cooled. Guided to 1. The exhaust heat introduced to the boiler 1 is used as boiler combustion air here, and then in order to make more effective use of that heat, the condensate / water supply and heat of the high pressure gas feed water heater 14 and the low pressure gas feed water heater 10 are used. After replacement, the temperature is lowered to around 100 ° C, which is the same level as the conventional plant, and then released from the stack 21 into the atmosphere.

FIG. 4 shows another embodiment of the prior art, in which the condensate / feed water that has passed through the high pressure gas feed water heater 14 is further heated by the exhaust heat recovery heat exchanger 15 and then reheated. The condensate water / water supply of the high-pressure feed water heater 13 is merged with the water / water supply to guide it to the boiler 1.

The above-mentioned embodiment shown in FIG. 3 and the embodiment shown in FIG. 4 are referred to. The gas turbine exhaust heat contributes to steam generation, condensate / feed water preheating, and is further utilized for boiler combustion air. Therefore, a large amount of fuel can be saved in the boiler 1 and its significance is extremely large.

[0014]

Conventionally, in a single steam turbine plant STP, when there is a load change command, the steam generation amount of the boiler 1 is increased or decreased according to the command.
Specifically, the amount of steam to be generated in the boiler 1 is controlled by adjusting the amount of condensate / water supply sent to the boiler 1 with the water supply pump 12 or the like.

However, in this type of power plant in which the steam turbine plant STP and the gas turbine plant GTP are combined, for example, when there is a load reduction (partial load) command, the exhaust heat sent from the gas turbine plant GTP to the boiler 1 is discharged. Despite the decrease, a peculiar phenomenon that the temperature of the feed water sent to the boiler 1 rises may appear. FIG. 5 is a graph showing the relationship between the upper temperature limit characteristic of the feed water sent to the economizer in the boiler 1 and the actual temperature characteristic of the feed water, in which the load on the plant increases on the horizontal axis and the feed water temperature rises on the vertical axis. Shows. In this figure, with the load P as the boundary, the actual feed water temperature falls apart from the upper limit temperature limit value as the load increases. However, as the load decreases, the actual feed water temperature exceeds the upper limit temperature limit value as indicated by the broken line.

Such a phenomenon means that the pressure of the water supply is higher than the internal pressure of the economizer. Under such circumstances, if water is supplied to the economizer, steaming may occur. Has become. The occurrence of steaming hinders the water supply passing through the economizer and induces a water hammer, so that the heat transfer tube of the economizer has the disadvantage of being corroded or damaged.

In view of such a point, the present invention suppresses the temperature of the feed water passing through the economizer within the upper limit temperature limit value even if the plant of this kind enters a load reduction (partial load) operation range, The purpose is to publicize a combined cycle power plant that prevents accidents of equipment wear.

[0018]

In order to solve the above-mentioned problems, a combined cycle power plant according to the present invention has a boiler, a steam turbine, a condenser and a condensate water supply system as described in claim 1. A gas turbine plant equipped with a compressor and a gas turbine is installed in the provided steam turbine plant, an exhaust heat recovery heat exchanger is installed in the exhaust heat system of this gas turbine plant, and the heat source of this exhaust heat recovery heat exchanger is used. In a combined cycle power plant that uses exhaust heat from a gas turbine plant, uses exhaust steam from a steam turbine as a heat source, and returns the heat source after heat exchange to a steam turbine, the exhaust heat recovery heat exchanger uses a heat source as a gas turbine plant. The exhaust heat of the heat source is used, and the heat source after heat exchange is output from the superheater by using the steam extracted from the inlet side of the superheater incorporated in the boiler. And returning to the side.

[0019]

In the combined cycle power plant according to the first aspect of the present invention, when the load reduction operation area is entered, the steam passing through the inlet side of the superheater is extracted and sent to the heat recovery heat exchanger. In this case, the withdrawal of steam lowers the temperature of the feed water passing through the economizer, and the pressure accompanying the temperature drop also drops proportionally.

Therefore, the water supply while passing through the economizer can be suppressed within the upper limit temperature limit value. As a result, the pressure of the supplied water can be suppressed below the pressure inside the economizer, so that steaming in the economizer can be prevented.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a combined cycle power plant according to the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, this combined cycle power plant is a new gas turbine plant GTP added to an existing steam turbine plant STP, but both the steam turbine plant STP and the gas turbine plant GTP are new. It may be a combination of each other.

In the figure, the steam turbine plant ST
P sequentially connects the boiler 1 that generates steam, the steam turbine ST that drives the turbine generator 7, the condenser 6, the condensate water supply system CF, and the like to form a closed cycle.

The steam turbine plant STP is a boiler 1
The steam generated in the turbine is used as the turbine high pressure part 2 of the steam turbine ST.
I'll guide you to the work of expansion. The steam that has worked in the turbine high-pressure section 2 is sent to the boiler reheater 3 and reheated to compensate for the temperature drop. The reheated steam of the boiler reheater 3 is sent to the turbine intermediate pressure section 4 of the steam turbine ST,
Do the expansion work here. The steam that has worked in the turbine intermediate pressure section 4 is further guided to the turbine low pressure section 5, where it also undergoes expansion work and is then guided to the condenser 6 where it is cooled and becomes condensate feed water.

The steam turbine plant STP is connected to a turbine generator 7 via a turbine shaft and a coupling (not shown), and the turbine generator 12 is driven by the work performed by each part 2, 4 and 5 of the steam turbine ST. Generating electrical energy.

On the other hand, the condensate cooled by the condenser 11 is sent to the condensate feed water system CF by the condensate pump 8 and is fed to the first stage by the low pressure feed water heater 9 and the low pressure gas feed water heater 10 having a multi-stage structure. Is heated. The heated condensate feed water is guided to the deaerator 11 and is deaerated there, and then sent by the feed water pump 12 to the multi-stage high pressure feed water heater 13 and the high pressure gas feed water heater 14.
The second stage feed water heating is performed, and then the water is supplied to the boiler 1.

On the other hand, the gas turbine plant GTP is equipped with a compressor 19a and a gas turbine 19b.
By the operation of b, the turbine generator 20 is driven to generate electricity. Further, an exhaust heat recovery heat exchanger 15 is installed in the exhaust heat system GTE of the gas turbine 19b to effectively use the exhaust heat from the gas turbine 19b.

The boiler 1 is provided with a economizer 16, an evaporator 17 and a superheater 18 in sequence, and the feed water from the condensate feed water system CF provided in the boiler 1 is preheated by the economizer 16. ,
It is vaporized by the evaporator 17 to become vapor. The steam generated in the evaporator 17 is sent to the superheater 18 to become superheated steam, which is used as an operation source of the turbine high pressure section 2 of the steam turbine ST.

At the inlet of the superheater 18, an exhaust heat recovery heat exchanger 15
The conduit SHP connecting to the is branched and conducted, and this conduit SHP is connected to the outlet of the superheater 18 via the exhaust heat recovery heat exchanger 15.
It is configured to be closed.

In the above closed circuit configuration, when a load reduction command is input to the steam turbine plant STP or the gas turbine plant GTP, the condensate water supply system CF causes the coal economizer of the boiler 1 to operate.
Although the feed water sent to 16 is quantitatively controlled and reduced, its temperature rises as shown in FIG. 5 while passing through the economizer 16, and exceeds the upper limit temperature limit value. In this case, the superheater
When the steam is drawn out from the inlet of 18 through the conduit SHP, the feed water temperature during passage through the economizer 18 is lowered, and as shown in FIG. 2, it can be suppressed below the upper limit temperature limit value. The steam temperature is
There is a proportional relationship with that pressure, and eventually the water supply pressure drops,
Since the internal pressure of the economizer 16 can be suppressed to be equal to or lower than the internal pressure, steaming can be prevented. Thus, under the decrease of the feed water pressure, the steam withdrawn from the inlet of the superheater 18 reaches the exhaust heat recovery heat exchanger 15, where it exchanges heat with the exhaust heat of the gas turbine 19b to raise the temperature and superheat. Is returned to the outlet of the superheater 18 and merges with the superheated steam of the superheater 18, and the steam turbine S
It is provided to the turbine high pressure section 2 of T.

In order to reduce the water supply pressure of the economizer 16, it is necessary to draw steam from the inlet of the superheater 18
In consideration of the thermal balance in joining with the superheated steam that has exited, the extraction of steam from the inlet of the superheater 18 is a preferred embodiment.

[0031]

As described above, in the combined cycle power generation plant according to the present invention, when the steam turbine plant or the gas turbine plant enters the operation area of reduced load, steam is drawn out from the inlet of the superheater,
The extracted steam was guided to the exhaust heat recovery heat exchanger, where it exchanged heat with the exhaust heat of the gas turbine plant, and the temperature-raising steam was combined with the superheated steam discharged from the superheater. The water supply pressure can be reduced, and as a result, steaming of the water supply can be prevented. Furthermore, since the exhaust heat from the gas turbine plant is used for the exhaust heat recovery heat exchanger as a heat source for raising the temperature of the extracted steam that joins the superheated steam that has exited the superheater, it is excellent in that it can be used effectively. Produce an effect.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a combined cycle power generation plant according to the present invention.

FIG. 2 is a graph showing that the temperature characteristic of the feed water passing through the economizer of the boiler of the combined cycle power plant according to the present invention is not more than the upper limit temperature limit value.

FIG. 3 is a schematic diagram showing an example of a conventional combined cycle power plant.

FIG. 4 is a schematic diagram showing another embodiment of a conventional combined cycle power plant.

FIG. 5 is a graph showing characteristics of feed water temperature passing through a economizer of a boiler of a conventional combined cycle power plant.

[Explanation of symbols]

 STP steam turbine plant GTP gas turbine plant SHP conduit ST steam turbine CF condensate feed water system GTE gas turbine exhaust heat system 1 boiler 3 boiler reheater 6 condenser 15 waste heat recovery heat exchanger 16 coal saver 17 evaporator 18 Superheater 19a Compressor 19b Gas turbine

Claims (1)

[Claims] 1. A steam turbine plant equipped with a boiler, a steam turbine, a condenser and a condensate water supply system is provided with a gas turbine plant equipped with a compressor and a gas turbine,
An exhaust heat recovery heat exchanger is installed in the exhaust heat system of this gas turbine plant, the exhaust heat of the gas turbine plant is used as the heat source of this exhaust heat recovery heat exchanger, and the exhaust steam of the steam turbine is used as the heat source. In a combined cycle power plant that returns a heat source after replacement to a steam turbine, the exhaust heat recovery heat exchanger uses exhaust heat of a gas turbine plant as a heat source,
A combined cycle power plant characterized by using steam extracted from the inlet side of a superheater incorporated in a boiler to return the heated source to the outlet side of the superheater after heat exchange.