JPH04311608A - Repowering system of previously provided steam power facility - Google Patents

Abstract

PURPOSE:To suppress over-raising of the inlet temperature of the economizer of a boiler, and prevent its steaming by cooling feed water at a deaerator outlet by a drain, at a low temperature, of a low pressure feed water heater so as to lower inlet temperature of a struck gas cooler at the time of partial loading of a plant. CONSTITUTION:A repowering system of previously provided steam power facility is provided with a steam power facility in which turbines 3, 7, 9 are operated by steam supplied from a boiler 1 so as to drive a power generator 10, and then steam is condensed by a condenser 11 to be returned into the boiler 1 through low/high pressure feed water heaters 14a, 14c, 18a to 18c, a deaerator 15, and the like. A gas turbine 22 is additionally provided on the power facility, and exhaust thereof is used as combustion air of the boiler 1. And a stuck gas cooler 25 is additionally provided in order to lower the temperature of exhaust gas so as to heat feed water branched from a feed water pipe 16. In this case, a heat exchanger 28 is provided to exchange heat between the outlet feed water of the deaerator 15 and the lower pressure feed water heater 14a, and water supplied through the stuck gas cooler 25 is introduced into the heat exchanger 28.

Description

[Detailed description of the invention]

[Object of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a repowering system for existing steam power generation equipment.

0002

2. Description of the Related Art As a repowering system for existing steam power generation facilities, there is an exhaust gas reheating combined cycle plant. This involves adding a gas turbine plant to existing steam power generation equipment and using the gas turbine exhaust gas as combustion air for the boiler. In addition, instead of the air preheater of the existing steam power generation equipment, a stack gas cooler is installed that uses boiler exhaust gas to heat the condensate or feed water of the steam turbine cycle system. This repowering system has the following advantages.

[0003] First, power generation efficiency can be improved by combining existing power generation plants. Second, since a gas turbine is additionally installed, the amount of power generated by the power plant as a whole can be increased. Third, since there are few modifications to existing equipment, repowering can be carried out in a relatively short period of time.

[0004] In recent years, there has been a significant increase in the demand for electric power, and there has been a remarkable tendency for the power reserve margin of each electric power company to decrease accordingly. Considering the fact that it is difficult to quickly construct new power plants to deal with this problem, repowering is one of the effective means to solve these problems.

FIG. 2 shows an example of a conventional steam power generation facility.

[0006] Steam generated by the boiler 1 is guided to a high pressure steam turbine 3 through a main steam pipe 2. The steam that has done work in the high-pressure steam turbine 3 reaches the reheater 5 of the boiler 1 via a low-temperature reheat steam pipe 4. The steam heated in the reheater 5 is guided to an intermediate pressure steam turbine 7 through a high temperature reheat steam pipe 6. The steam that has done work in the intermediate pressure steam turbine 7 is guided to a low pressure steam turbine 9 through a crossover pipe 8.

High pressure steam turbine 3, intermediate pressure steam turbine 7
and the low pressure steam turbine 9 is connected to the generator 10,
Electricity is generated by a generator 10.

[0008] The steam that has done work in the low pressure steam turbine 9 is
It is guided to the condenser 11 and becomes condensate. Condensate in the condenser 11 is pressurized by a condensate pump 12 and heated via a condensate pipe 13 by low-pressure feed water heaters 14a, 14b, and 14c.

The water deaerated by the deaerator 15 is transferred to the water supply pipe 16.
The water is further pressurized by the water supply pump 17 and heated by the high pressure water heaters 18a, 18b, and 18c. After that, it reaches the boiler 1 and generates electricity while repeating the cycle of the system described above.

Reference numeral 19 denotes an air preheater, which is a heat exchanger that is installed to increase the combustion efficiency of the boiler 1 and heats boiler combustion air with the high-temperature exhaust gas of the boiler 1.

Next, FIG. 3 shows an example of a repowering system in which a gas turbine plant is added to the above-described conventional steam power generation equipment to create an exhaust reheating combined cycle system.

As shown in the figure, conventional steam power generation equipment includes
A compressor 20, a combustor 21, a gas turbine 22, a gas turbine generator 23, a gas damper 24, etc. are additionally installed. Furthermore, a stack gas cooler 25 is additionally installed in order to effectively utilize the high temperature exhaust gas of the boiler 1 and to lower the temperature of the exhaust gas since high pressure exhaust gas cannot be directly discharged from the chimney. Note that 26 indicates a gas turbine exhaust pipe, and 27 indicates a boiler exhaust gas duct.

The stack gas cooler 25 is connected to the water supply pipe 16
The feed water is heated by exchanging heat with water branched from the steam turbine, and then returned to the steam turbine cycle system for heat recovery. Note that since the exhaust gas of the gas turbine 22 is used as boiler combustion air, the air preheater 19 is not required.

[0014]

[Problems to be Solved by the Invention] However, the above repowering system for existing steam power generation equipment has the following problems.

Since the gas turbine always rotates at a constant rate, the amount of air compressed by the compressor 20 does not change significantly even under partial load. Therefore, the amount of exhaust gas discharged from the boiler 1 to the stack gas cooler 25 during partial load does not change significantly from that during rated operation.

On the other hand, in a steam turbine cycle system, when a partial load is reached, the flow rates of the condensate pipe 13 and the water supply pipe 16 decrease depending on the load. Moreover, since the extraction pressure of the steam turbine also decreases as the load decreases, the internal pressure of each low-pressure feedwater heater 14a, 14b, 14c, deaerator 15, and high-pressure feedwater heater 18a, 18b, 18c also decreases. As a result, the amount and temperature of water flowing into the stack gas cooler 25 decrease.

For this reason, there is a problem in that the temperature of the outlet water supply of the stack gas cooler 25 rises too much, causing steaming in the economizer of the boiler 1.

[0018] Therefore, the present invention provides a repowering system for existing steam power generation equipment that prevents the temperature of the outlet water supply of the stack gas cooler from rising too high and allows the system to operate safely and economically even during partial load. The purpose is to provide.

[Configuration of the invention]

[Means for Solving the Problems] The present invention allows steam generated in a boiler to flow into a condenser through a turbine, and further through a low-pressure feedwater heater, a deaerator, and a high-pressure feedwater heater. A gas turbine is added to the existing steam power generation equipment that forms a steam turbine cycle system, and the exhaust gas of this gas turbine is used as combustion air for the boiler, and the outlet side of the deaerator of the steam turbine cycle system and the Install a stack gas cooler that bypasses the outlet side of the high-pressure feedwater heater and heats the feedwater by exchanging heat between a portion of the feedwater that flows into the high-pressure feedwater heater from the deaerator and the boiler exhaust gas. In the repowering system of existing steam power generation equipment, which converts to exhaust reheating combined cycle,
The water supply branched from the water supply line to the stack gas cooler passes through the heat exchanger and the first control valve to join the water supply line to the stack gas cooler, and the water supply branch pipe branches from the drain line of the low-pressure feed water heater. The drain exchanges heat with the water supply branched from the water supply line to the stack gas cooler of the heat exchanger and returns to the condenser via the second control valve. A computing unit is provided for controlling the opening and closing of the first control valve and the second control valve based on the outlet water supply temperature.

[0020]

[Operation] With the above structure, the inlet temperature of the stack gas cooler is lowered when the plant is under partial load by cooling the outlet feed water of the deaerator with the drain of the low-temperature, low-pressure feed water heater. It then exchanges heat with the boiler exhaust gas to prevent the stack gas cooler outlet water supply temperature from rising too high. Therefore, the inlet temperature of the boiler economizer is prevented from rising too much, and steaming within the boiler economizer can be prevented.

[0021]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a repowering system for an existing steam power generation facility showing an embodiment of the present invention. The same reference numerals as in FIG. 3 indicate the same or equivalent parts. The differences from FIG. 3 include a heat exchanger 28, a heat exchanger feed water flow rate control valve 29, a feed water branch pipe 30, a low pressure feed water heater drain flow control valve 31, a low pressure feed water heater drain branch pipe 32, and a low pressure feed water heater drain. The difference is that a pump 33, a temperature detector 34, and a computing unit 35 are additionally provided.

[0023] In this embodiment, a gas turbine plant is added to the conventional steam power generation equipment, and the deaerator outlet water supply and
A heat exchanger is installed to exchange heat with the drain of the low-pressure feedwater heater, creating an exhaust reburning combined cycle system.

The heat exchanger 28 exchanges heat between the outlet feed water of the deaerator 15 and the drain of the low pressure feed water heater 14a.

The heat exchanger water supply flow rate control valve 29 adjusts the amount of water supplied to the heat exchanger 28 .

The water supply branch pipe 30 branches from the inlet water supply line of the stack gas cooler 25 and supplies water to the heat exchanger 28.

[0027] The low pressure feed water heater drain flow rate control valve 31 is as follows:
The amount of drain flowing into the heat exchanger 28 from the low pressure feed water heater 14a is adjusted.

The low-pressure feedwater heater drain branch pipe 32 is a branch pipe that branches from the low-pressure feedwater heater 14a and returns to the condenser 11 via the heat exchanger 28.

The low pressure feed water heater drain pump 33 sends drain from the low pressure feed water heater 14a to the heat exchanger 28.

The temperature detector 34 detects the outlet temperature of the stack gas cooler 25.

The computing unit 35 outputs an opening signal to the heat exchanger feed water flow rate control valve 29 and the low pressure feed water heater drain flow rate control valve 31 based on the detection signal of the temperature detector 34.

Note that 36 indicates a low-pressure feedwater heater drain pipe, and 37 indicates a high-pressure feedwater heater drain pipe.

With the above configuration, during normal operation, the heat exchanger 2
8 is not necessary, the heat exchanger water supply flow rate control valve 29 is fully closed, and the water supply flowing through the water supply branch pipe 30 is stopped. At the same time, the low-pressure feed water heater drain flow control valve 31 is also fully closed to stop the drain flowing through the low-pressure feed water heater drain branch pipe 32.

Next, when the load becomes partial, an imbalance occurs in the relationship between the amount of condensate, drain, and water supply in the steam turbine cycle system and the amount of exhaust gas from the boiler, so the outlet temperature of the stack gas cooler 25 increases. A situation where the price rises too much occurs.

Then, the temperature detector 34 detects the temperature at point A shown in the figure near the outlet of the stack gas cooler 25,
Based on the detection signal, the calculator 35 performs control calculations,
The opening signal is sent to the heat exchanger feed water flow rate control valve 29 and the low pressure feed water heater drain flow rate control valve 31. Thereby, the heat exchanger water supply flow rate control valve 29 opens and closes based on the opening degree signal from the computing unit 35 to control the water supply amount of the water supply branch pipe 30.

On the other hand, the low pressure feed water heater drain flow control valve 3
1 opens and closes based on the opening command from the computing unit 35,
The drain amount of the low pressure feed water heater drain branch pipe 32 is controlled.

That is, for example, when the detection signal of the temperature detector 34 is larger than a predetermined value set by the calculator 35, the control calculation signal causes the heat exchanger feed water flow rate control valve 29 and the low pressure feed water heater drain flow rate control valve 31 to be activated. Move in the opening direction. As a result, the water supply branch pipe 3 flowing on the secondary side of the heat exchanger 28
0 water supply amount increases. Furthermore, the amount of low-temperature low-pressure feedwater heater drain flowing from the low-pressure feedwater heater 14a to the primary side of the heat exchanger 28 via the low-pressure feedwater heater drain branch pipe 32 increases.

As a result, the feed water on the secondary side of the heat exchanger 28 is cooled and flows into the stack gas cooler 25. In this case, since the amount of exhaust gas from the boiler 1 is the same even during partial load operation as during normal operation, the outlet side of the stack gas cooler 25 is also supplied with low temperature water. Therefore, the rise in the outlet temperature of the stack gas cooler 25 is suppressed and controlled within a predetermined temperature range.

[0039]

As explained above, according to the present invention, the outlet temperature of the stack gas cooler can be maintained at a specific temperature even during partial load operation. This makes it possible to prevent steaming in the boiler economizer, thereby improving the reliability of each device and making it possible to safely operate the repowering system.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a repowering system for existing steam power generation equipment, showing one embodiment of the present invention.

FIG. 2 is a system diagram of a conventional existing steam power generation facility.

FIG. 3 is a system diagram of a repowering system for an existing steam power generation facility, showing a conventional example.

[Explanation of symbols]

1 Boiler 2 Main steam pipe 3 High pressure steam turbine 4 Low temperature reheat steam pipe 5 Reheater 7 Intermediate pressure steam turbine 9 Low pressure steam turbine 10 Generator 11 Condenser 14a Low pressure feed water heater 15 Deaerator 21 Combustor 22 Gas Turbine 23 Gas turbine generator 25 Stack gas cooler 26 Gas turbine exhaust pipe 27 Boiler exhaust gas duct 28 Heat exchanger 29 Heat exchanger feed water flow rate control valve 30 Water supply branch pipe 31 Low pressure feed water heater drain flow rate control valve 32
Low-pressure feed water heater drain branch pipe 33 Low-pressure feed water heater drain pump 34 Temperature detector 35 Arithmetic unit

Claims (1)

[Claims] [Claim 1] An existing system in which steam generated in a boiler flows through a turbine to a condenser, and further passes through a low-pressure feedwater heater, a deaerator, and a high-pressure feedwater heater to form a steam turbine cycle system. A gas turbine is added to the steam power generation equipment, the exhaust gas of the gas turbine is used as combustion air for the boiler, and the outlet side of the deaerator of the steam turbine cycle system and the high pressure feed water heater are connected. Exhaust reheating is achieved by bypassing the outlet side and installing a stack gas cooler to heat the feedwater by exchanging heat between a part of the feedwater flowing from the deaerator into the high-pressure feedwater heater and the exhaust gas of the boiler. In a repowering system for existing steam power generation equipment that is converted to a combined cycle type, water supply branched from the water supply line to the stack gas cooler passes through a heat exchanger and a first control valve to the water supply line to the stack gas cooler. The merging water supply branch pipe and the drain branched from the drain line of the low-pressure feed water heater exchange heat with the water supply branched from the water supply line to the stack gas cooler of the heat exchanger, and pass through the second control valve. and a low-pressure feed water heater drain branch pipe that returns to the condenser, and a computing unit that controls opening and closing of a first control valve and a second control valve based on the temperature of the outlet feed water of the stack gas cooler. A repowering system for existing steam power generation equipment.