JPS6115961B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas boiler, and particularly to a method for starting an exhaust gas boiler that sequentially passes gas turbine exhaust gas through a superheater, an evaporator, and an economizer to generate steam that drives a turbine. The present invention relates to a method for controlling the outlet water supply temperature of an economizer for an exhaust gas boiler, which is suitable for preventing the occurrence of water hammer.

Exhaust gas boilers in combined plants exchange heat between the gas turbine's high-temperature exhaust gas and feed water to generate superheated steam for driving the turbine.
Due to the characteristics of a gas turbine, exhaust gas flows in at a flow rate close to the rated value from the time of startup, and exhaust gas flows in at a temperature that rises to the rated value within several tens of minutes. For this reason, even though the drum pressurization speed is fast,
Because the rate of increase in the temperature of the feed water in the economizer installed on the downstream side of the exhaust gas of the evaporator is slow, the temperature of the feed water at the outlet of the economizer continues to rise even after the drum pressure increase stops, reaching the drum saturation temperature. , steam is generated in the economizer, becomes steam-mixed water, and is sent to the drum, resulting in a water hammer phenomenon.

In addition, when the gas turbine exhaust gas has to be operated at a particularly low temperature during low load, the drum pressure does not increase, so the temperature of the outlet water supply of the energy saver is controlled below the drum saturation temperature to prevent the water hammer phenomenon. In order to do this, a large amount of water must be supplied into the economizer.

An object of the present invention is to provide an exhaust gas boiler that can prevent water hammer from occurring without increasing the amount of water supplied.

The present invention reduces the amount of gas turbine exhaust gas passing through the economizer when the temperature of the feed water at the outlet of the economizer increases after the drum pressure is increased. A bypass duct for gas turbine exhaust gas that bypasses only the economizer is provided, and this bypass duct is provided with an exhaust gas flow rate control means.

Embodiments of the present invention will be described below based on the accompanying drawings.

In Figure 1, during normal operation, water is supplied to water supply pipe 1.
A portion of this water supply is discharged from a blow line (not shown) to the outside of the exhaust gas boiler, and the remaining water supply is introduced into the drum 3. The feed water introduced into the drum 3 is supplied to the evaporator 5 through the downcomer pipe 4, where it is heated by the gas turbine exhaust gas to generate steam and become steam-mixed water. The generated steam is separated into gas and liquid in the drum 3, and introduced into the superheater 7 through the saturated steam pipe 6.
Furthermore, it is superheated by gas turbine exhaust gas and becomes superheated steam. This superheated steam is introduced from the main steam pipe 8 to a steam turbine (not shown).

On the other hand, the gas turbine exhaust gas sequentially passes through the superheater 7, the evaporator 5, and the economizer 2, exchanges heat with the feed water, and is then discharged from the chimney 9 to the outside of the exhaust gas boiler.

Such normal operation and the equipment components for this operation are the same as those of the prior art.

In this embodiment, the economizer 2 is provided with a gas turbine exhaust gas bypass duct 10 that bypasses only the economizer 2, and a damper 11 and a damper 1 are provided on the upstream and downstream sides of the bypass duct 10, respectively.
2 is provided, and a damper 1 is provided downstream of the economizer 2.
3 is provided.

That is, each damper 11, 12, 13 forms exhaust gas flow rate control means.

Next, the operating method at startup in this embodiment will be explained. When the exhaust gas turbine is started, the pressure A in the drum 3 approximately corresponds to the gas turbine load B, as shown in FIG. For this reason, conventionally, the outlet water supply temperature D of the economizer 2 has a portion T exceeding the drum saturation temperature, which is indicated by C in the figure. Therefore, when passing through this portion T, steam is generated and is sent to the drum 3 as steam-mixed water, resulting in a water hammer phenomenon.

Therefore, in this embodiment, after the drum pressure increase is completed,
When the temperature of the outlet water supply of the economizer 2 rises (that is, at time _t1 in FIG. 2), the damper 13 is operated to reduce the amount of exhaust gas passing through the economizer 2, and at the same time the damper 11 and the damper 12 are operate each,
Exhaust gas is passed through the bypass duct 10. Since the heat absorption amount in the economizer 2 is reduced by such an operation, the temperature of the outlet water supply of the economizer 2 is controlled to be below the drum saturation temperature, as shown by E in FIG. After a certain period of time (that is, time t ₂ in FIG. 2), the dampers 11 and 12 are closed, the damper 13 is opened, the exhaust gas passes only through the economizer 2, and normal operation begins.

Also, when the load is low, the pressure of the drum 3 does not increase,
When the temperature of the outlet water supply of the economizer 2 rises and the drum pressure increase ends, that is, when it approaches the drum saturation temperature, a part of the exhaust gas is passed through the bypass duct 10 in the same manner as described above, and the heat in the economizer 2 is reduced. By lowering the absorption amount, the outlet water supply temperature of the economizer 2 can be controlled to be below the drum saturation temperature. Therefore, there is no need to supply a large amount of water to the economizer 2 in order to control the outlet water supply temperature of the economizer 2 to be below the drum saturation temperature.

Note that the present invention can also be applied to a mixed pressure type exhaust gas boiler. In the case of a mixed pressure exhaust gas boiler, an evaporator is installed on the exhaust gas downstream side of the economizer in order to utilize the residual heat of the exhaust gas. Therefore, if such an economizer is equipped with an exhaust gas bypass duct, and the drum pressure does not increase during low loads, some of the exhaust gas will pass through the bypass duct and then join with the exhaust gas that has passed through the economizer. can be passed to a downstream evaporator. As a result, the amount of heat absorbed by the economizer on the high-pressure side decreases, and the high-temperature exhaust gas passes through the evaporator on the low-pressure side (downstream side), increasing the pressure of the drum faster and reducing the amount of heat absorbed by the economizer on the high-pressure side. The outlet water supply temperature can be controlled below the drum saturation temperature.

As described above, according to the present invention, water hammer can be prevented from occurring during startup without increasing the water supply flow rate, and stable operation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of the present invention, and FIG. 2 is a diagram showing drum pressure increase characteristics and economizer outlet water supply temperature characteristics at startup, and when operating a bypass damper. 1... Water supply pipe, 2... Energy saver, 3... Drum,
4... Downpipe, 5... Evaporator, 6... Saturated steam pipe, 7... Superheater, 8... Main steam pipe, 9... Chimney, 10... Bypass duct, 11, 12, 13
……damper.

Claims (1)

[Claims] 1. In an exhaust gas boiler that sequentially passes gas turbine exhaust gas through a superheater, an evaporator, and a economizer to thereby generate steam for driving a steam turbine, a gas that bypasses only the economizer is used in the economizer. A bypass duct for turbine exhaust gas is provided, and an exhaust gas flow rate control means is provided in this bypass duct to receive the feed water heated by the economizer, send it to the evaporator, and heat the steam mixture in the evaporator to generate steam. When the pressurization of the drum that receives water, separates the gas and liquid, and sends the steam to the superheater is completed,
A method for controlling an outlet water supply temperature of an economizer for an exhaust gas boiler, characterized in that the bypass duct is opened by the exhaust gas flow rate control means and closed after a certain period of time has elapsed.