JPH0443803A - Control method for combined cycle electric power plant - Google Patents

Abstract

PURPOSE:To shorten starting time as the whole electric power plant by connecting together the high pressure drum and the low pressure drum of an exhaust heat boiler through a connecting pipe, and providing a control valve on the way of the connecting pipe. CONSTITUTION:A combined-cycle electric power plant is constituted out of a gas turbine l, a steam turbine 15, and an exhaust heat boiler 2. The high pressure drum 17 and the low pressure drum 11 of the exhaust heat boiler 2 are connected together through a connecting pipe 30. A control valve 31 is provided on the way of the connecting pipe 30. By circulating water between the low pressure drum 11 and the high pressure drum at starting, rise of steam pressure and temperature of the low pressure drum 11 can be quickened. By decrease of the water flow from a high pressure circulating pump 18 to a high pressure evaporator 4, heat absorption of the high pressure evaporator 4 is decreased and the heat absorbing quantity of a low pressure evaporator 7 is increased by the portion. In this way, the rising speed of steam pressure and temperature of the low pressure drum is quickened, the warming time of the exhaust heat boiler can be shortened, and the starting time as the whole plant can be shortened.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for improving the startup characteristics of a combined cycle power plant consisting of a gas turbine, a steam turbine, and a waste heat boiler. .

(Conventional technology) In order to improve energy efficiency, recent thermal power plants often use combined cycle power plants in which exhaust gas from a gas turbine is guided to an exhaust heat boiler to heat steam and rotate a steam turbine. There is a tendency.

FIG. 2 shows the configuration of a conventional single-shaft combined cycle power plant. Gas that has finished its work in a gas turbine 1 is introduced into an exhaust heat boiler 2.

The waste heat boiler has a built-in superheater 3, a high-pressure evaporator 4, a denitration catalyst 5, a high-pressure economizer 6, a low-pressure evaporator 7, and a low-pressure economizer 8, and the exhaust gas from the gas turbine 1 is While flowing through the heat boiler 2, it is cooled and denitrated, and then released into the atmosphere.

On the other hand, the water stored in the condenser 9 is pressurized by the low-pressure water supply pump 10, flows through the low-pressure economizer 8, and is then stored in the low-pressure drum 11. A portion of the water stored in the low-pressure drum 11 is pressurized by the low-pressure circulation pump 12, flows through the low-pressure evaporator 7, is superheated, and then returns to the low-pressure drum 11 again. Steam separated from water in the low pressure drum 11 is guided to an intermediate stage of the steam turbine 15 through a low pressure steam pipe 13 and a low pressure steam valve 14. In addition, a part of the water stored in the low pressure drum 11 is pressurized by the high pressure circulation pump 16, flows through the high pressure economizer 6, is heated, and is heated by the high pressure drum 11.
Guided by 7.

A portion of the water stored in the high-pressure drum 17 is pressurized by the high-pressure circulation pump 18, flows through the high-pressure evaporator 4 and is heated, then returns to the high-pressure drum 17 again and is separated into water and steam.

The steam stored in the high-pressure drum 17 is superheated through the high-pressure steam pipe 19 and the heater 3, and then sent through the high-pressure steam valve 20 to the first stage of the steam turbine 15.

As a result, the steam turbine 15 and the gas turbine 1
rotates and drives the power generation a121.

The above is the operation of the combined cycle power plant during steady operation.

Figure 3 shows the characteristics of the above-mentioned single-shaft combined cycle power plant at startup, and shows the startup device (not shown).
When the gas turbine starts up and reaches about 15% of the rated rotation speed, fuel is introduced into the gas turbine and ignited, increasing the rotation speed.

As a result, the gas turbine exhaust flow rate and temperature increase,
The temperature of the gas flowing into the waste heat boiler also increases. Since the gas turbine shaft and the steam turbine shaft are directly coupled, as the rotation speed of the gas turbine increases, the rotation speed of the steam turbine shaft also increases.

In this state, the temperature and pressure of the steam in the waste heat boiler have not risen enough to send it to the steam turbine, and the steam turbine is forced to idle by the gas turbine.

In the above-mentioned idling state, heat is generated in the blades of the steam turbine, especially the long blades in the rear stage, due to wind damage, and there is a possibility that the temperature may rise beyond a permissible value.

For this reason, the rotation speed of the gas turbine is maintained within a predetermined value until the temperature inside the waste heat boiler rises, steam is generated, and the cooling steam can flow to the steam turbine. Warm up.

(Problem to be Solved by the Invention) Cooling steam in an actual steam turbine flows from a low-pressure drum, and the low-pressure drum has a certain pressure (in the actual example, about 2.5 kg/kg).
The rotation speed is maintained at approximately half of the rated rotation speed for warming until the rotation speed reaches cd).

However, the exhaust heat boiler has a large heat capacity, and at the beginning of warming, heat is taken away by the high-pressure evaporator 4 and the denitrification catalyst 5, and as shown in Figure 3, the inlet gas temperature of the exhaust heat boiler increases. The pre-gas temperature of the low-pressure evaporator does not rise easily, so the steam pressure and temperature inside the low-pressure drum also rise slowly, and it takes 60 to 90 minutes to warm up the waste heat boiler, resulting in energy loss during this time. It's also big.

The present invention was made in order to eliminate the above-mentioned disadvantages in the conventional technology, and an object of the present invention is to provide a control method for a combined cycle power plant that can significantly shorten the warming time of a waste heat boiler. .

[Configuration of the Invention (Means for Solving the Problem) The method for controlling a combined cycle power plant of the present invention is a combined cycle power plant comprising a gas turbine, a steam turbine, and a waste heat boiler. The low-pressure drums are connected by a connecting pipe, and a control valve is installed in the middle of the connecting pipe, and water is circulated between the high-pressure drum and the low-pressure drum at startup to accelerate the generation of low-pressure steam.

(Function) According to the method of the present invention configured as described above, the control valve is opened at startup and water is circulated between the high-pressure drum and the low-pressure drum, thereby accelerating the generation of low-pressure steam.
Plant startup time can be reduced.

(Example) Next, the present invention will be explained in detail with reference to FIG.

Note that in FIG. 1, the same parts as in FIG. 2 are given the same reference numerals, and explanations of overlapping parts will be omitted.

In FIG. 1, in the middle of the piping from the high-pressure drum 17 to the high-pressure evaporator 4, from the downstream side of the high-pressure circulation pump 18,
A connecting pipe 30 is branched, and the other end of this connecting pipe is connected to the low pressure drum 11. A control valve 31 is inserted in the middle of the connecting pipe 30. The pressure calculator 32 detects the pressure of the low-pressure steam pipe 13, compares it with a predetermined pressure setting value, and controls the opening degree of the control valve 31.

The other configurations are the same as in FIG.

In the control method for the combined cycle power plant of the present invention configured as described above, as shown in the startup characteristics in Figure 3, the rise in steam pressure and temperature in the high-pressure drum is greater than that in the low-pressure drum. In order to avoid this problem, the set value of the pressure calculator 32 is set to the exhaust heat boiler warming completion pressure (for example, 2.5 Kg/cj), and the pressure inside the low pressure drum 11 at startup is set to the above set value. If it is lower, the regulating valve 31 is opened, and at startup, part of the water at the outlet of the high-pressure circulation pump 18 flows through the regulating valve 31 to the low-pressure drum 11.

The water flowing into the low pressure drum 11 mixes with the water inside the drum,
Speed up the temperature rise of the water in the low pressure drum.

Further, a part of the water in the low pressure drum 11 returns to the high pressure drum 17 through the high pressure water supply pump 16 and the high pressure economizer 6.

By circulating water between the low-pressure drum 11 and the high-pressure drum 17 in this manner, the rise in steam pressure and temperature in the low-pressure drum can be accelerated. In addition, high pressure circulation pump 1
By reducing the amount of water flowing from 8 to high pressure evaporator 4,
The amount of heat absorbed by the high-pressure evaporator decreases, and the amount of heat absorbed by the low-pressure evaporator 7 increases accordingly.

Due to the above two effects, the rate of increase in the steam pressure and temperature in the low pressure drum becomes faster, the warming time of the waste heat boiler can be shortened, and the startup time of the entire plant can therefore be shortened.

Figure 4 shows the start-up characteristics of a combined cycle power plant employing the method of the present invention. The rate of rise in pressure and temperature of the low pressure drum is faster than in the case of Figure 3, and therefore the exhaust heat boiler warming It can be seen that the startup time is shortened.

Although the above explanation describes an example in which the present invention is applied to a vertical forced circulation type waste heat boiler, the present invention is not limited to this, and can easily be applied to a natural circulation type waste heat boiler. can do.

[Effects of the Invention] In the combined cycle power plant of the present invention, the rate of increase in steam pressure and temperature in the low pressure drum is fast, so the time for warming the exhaust heat boiler is shortened, and the startup time of the power plant as a whole is shortened. I can do it.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing an embodiment of the combined cycle power plant of the present invention, Figure 2 is a system diagram showing the configuration of a conventional single-wheel combined cycle power plant, and Figure 3 is a conventional single-wheel combined cycle power plant. Fig. 4 is a starting characteristic diagram of the combined cycle power plant of the present invention. 1... Gas turbine 2... Exhaust heat boiler 3... Superheater 4... High pressure evaporator 5... Denitration catalyst 6... ...High pressure energy saver 7...Low pressure evaporator 8...Low pressure energy saver 9...Condenser 0...Low pressure water supply pump ...Low pressure drum 2 ...Low pressure circulation pump 3 ...Low pressure steam pipe 4 ...Low pressure steam valve 5 ...Steam turbine 6 ... - High pressure water supply pump 7 ... High pressure drum 8 ... High pressure circulation pump 9 ... High pressure steam pipe 0 ... High pressure steam valve 1 ... Generator 0 ... ...Connection pipe...Control valve 2...Pressure calculator

Claims (1)

[Claims] In a combined cycle power generation plant consisting of a gas turbine, a steam turbine, and a waste heat boiler, the high-pressure drum and low-pressure drum of the waste heat boiler are connected by a connecting pipe, and a control valve is inserted in the connecting pipe, so that the A method for controlling a combined cycle power plant, comprising opening the control valve to circulate water between a high-pressure drum and a low-pressure drum to accelerate the generation of low-pressure steam.