JPS6154123B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a gas turbine device, a waste heat recovery boiler that generates steam using the heat of the gas turbine exhaust gas, and a steam turbine device that is driven by the steam emitted from the boiler. This paper relates to a drum water level control system for a waste heat recovery boiler in a combined cycle plant.

First, the general configuration of a combined cycle plant will be explained with reference to FIG. 3, which shows a conventional example thereof.

A combined cycle plant generally includes one or more gas turbine devices 1, the same number of waste heat recovery boilers 11 as the gas turbine devices, and one steam turbine device 40. The gas turbine device 1 includes a compressor 2, a combustor 3 that burns fuel sent from a fuel pipe 4 using air pressurized by the compressor 2 to generate high temperature and high pressure combustion gas, and a combustor 3 that generates high temperature and high pressure combustion gas. The gas turbine 5 is driven to rotate a gas turbine generator 6. Combustion gas discharged from this gas turbine device is led to a waste heat recovery boiler 11 through an exhaust gas duct 7. Further, the exhaust gas duct 7 is provided with a bypass duct 10 that bypasses the waste heat recovery boiler 11, and the gas duct 7 and the bypass duct 10 are provided with a boiler inlet damper 8 and a boiler bypass damper 9, respectively, that adjust the flow of exhaust gas. It is provided. The waste heat recovery boiler 11 is a drum-type boiler, and is composed of an economizer 15 that heats water supplied through the water supply pipe 14, a drum 16 for steam generation, an evaporator 17, and a superheater 18. Superheater 1
The steam coming out from the steam pipe 19 and the boiler valve 20 are collected in the steam header 21, and from the steam header 21, it is sent through the control valve 22 into the steam turbine 23 to drive the generator 24, and the condensate water is The water is condensed in a vessel 32. The condensed feed water is returned to the waste heat recovery boiler 11 by a feed water pump 12 through a water feed pipe 14 equipped with a feed water control valve 13 . Further, a bypass steam pipe 26 equipped with a bypass valve 25 is branched from the steam pipe 19 on the upstream side of the boiler outlet valve 20 and communicates with the condenser 32 via a desuperheater 27. , Steam is introduced into the condenser 32 to match the steam pressure in the steam header 21 and the steam pressure generated by the waste heat recovery boiler 11, such as when starting the waste heat recovery boiler, and is used during normal operation. Not done. 28 is a spray pipe branched from the water supply pipe downstream of the water supply pump 12 and connected to the desuperheater 27, and 29 is a spray adjustment valve.

The conventional water supply system control device is a waste heat recovery boiler 1.
a drum water level detector 51 that detects and transmits a drum water level signal so as to keep the water level of the drum 16 constant; a steam flow meter 52 that transmits a signal of the amount of steam generated in the drum; and a feed water flow rate signal. A water supply control device 54 using so-called three-element control is installed, which adjusts the water supply regulating valve 13 in order to control the drum water level to a constant level in accordance with signals from three measuring devices of the water supply flowmeter 53 that transmits the water.

This water supply control device 54 can realize sufficiently stable control against fluctuations in water level due to changes in the amount of heat supplied to the waste heat recovery boiler.

However, when this condensate cycle plant is made to follow transient minute load changes, not only the load change of the gas turbine but also the steam turbine 2
There is a load control method that changes the load in advance. In this control method, especially when the regulating valve 22 is opened in advance, the pressure in the boiler 11 suddenly decreases and the saturated water in the drum 16 self-evaporates. The drum water level rises transiently due to the generated steam bubbles, which is a so-called reverse response characteristic. When the drum water level rises abnormally in this way, water droplets are mixed into the generated steam and the superheater 1 in the waste heat recovery boiler 11
This may cause erosion in the steam turbine 8, steam turbine 23, etc. In addition to the above-mentioned opening operation of the control valve 22, the cause of the sudden drop in the boiler pressure is the sudden opening operation of the boiler outlet valve 20 or the bypass valve 25.

An object of the present invention is to provide a stable drum water level control system that can proactively prevent the above-mentioned abnormal drum water level. The purpose of the present invention is to provide a control device that can automatically respond to transient steam pressure fluctuations and prevent a rise in drum water level.

In order to achieve the above object, the drum water level control device according to the present invention is a composite device comprising three-element control means for controlling the feed water flow rate based on the steam flow rate outflowing from the waste heat recovery boiler, the inflow feed water flow rate, and the drum water level. In the cycle plant, A. A can water blowing system is provided in the drum of the waste heat recovery boiler, and a can water reduction valve is provided in the can water blowing system, B. When the set value is exceeded, and (b) the rate of change of the signal representing the internal pressure of the waste heat recovery boiler exceeds the set value,
A can water level reducing valve control device for opening the can water level reducing valve is provided, and the structure is such that drum water is released through a can water blowing system independently of the operation of the three-element control means,
The present invention is characterized in that when the conditions (a) and (b) are compatible, the drum water level is lowered prior to the operation of the three-element control means.

An embodiment of the present invention will be described below with reference to the drawings.
This embodiment is an improvement of the conventional example shown in FIG. 3 by applying the present invention. The difference from the conventional example is that the configuration of section E shown surrounded by a phantom line is added. 32 is a blow tank, 30
55 is a pressure gauge installed to measure the steam pressure generated by the waste heat recovery boiler 11, and 56 is a pressure signal that is the output of the pressure gauge. A change rate calculator 54 inputs the water level signal which is the output of the drum water level detector 51 and the pressure change rate signal which is the output of the change rate calculator, and when both signals are equal to or higher than the set value. At some point, the canned water reduction valve 31
If the drum water level is above a set level when the generated steam pressure suddenly decreases, for example, by suddenly opening the control valve 22, the control device 57 Canned water reduction valve 31
opens and blows the canned water in the drum 16 into the blow tank 3.
By discharging water into the drum 16, the water level in the drum 16 is prevented from rising.

FIG. 2 shows this canned water reduction valve control device 57 in more detail. 58 is a comparator that outputs a signal _X1 when the output signal of the rate of change calculator 56 exceeds the value set by the rate of change setter 59; 60 is a comparator that outputs a signal 62 is a comparator that outputs _the signal X ₂ when _the value exceeds the set value.
This is a valve opening degree control device that opens the canned water reduction valve 31 when both are input. The set value of the drum water level is
The water level is set equal to or slightly higher than the standard water level.

In the configuration shown in FIG. 2, if the level detected by the water level detector ₅₁ is below the set value, the output signal Even if the required pressure change rate is large, the control device 6
2 does not open the canned water reduction valve 31. Also, even if the water level exceeds the set value,
Similarly, if the pressure change rate is below the set value, the control device 62 will not open the canned water reduction valve 31. This is because in these cases, there is no risk that the drum water level will become abnormally high.

On the other hand, in a state where the actual drum water level is higher than the drum water level for actuating the can water reduction valve, which is temporarily set equal to or slightly higher than the standard water level,
The internal pressure of the waste heat recovery boiler 11 is set by the change rate setting device 5.
If the drum water level drops suddenly beyond the value set in step 9, if left as it is, the drum water level will become abnormally high due to steam bubbles caused by self-evaporation of the drum water.
When X ₁ and X ₂ occur, the can water reduction valve 31 is opened and the drum water is released into the blow tank 32 through the blowdown pipe 30. By letting the drum water escape in this way, the drum water level decreases, and when it becomes lower than the set drum water level for operating the can water reduction valve, the output signal _X1 of the comparator 58 disappears, and the can water reduction valve 31 closes. becomes.

In the above embodiment, an example was shown in which the internal pressure of the waste heat recovery boiler 11 is directly input to the rate of change calculator 56. However, as can be easily understood from the operation and effect of the above example, Instead of a pressure signal,
A signal that represents a quantity that changes with the pressure inside the boiler,
In other words, abnormalities in the drum water level can also be detected by converting the sudden opening of the control valve 11 shown in FIG. rise can be prevented. Also, blowdown pipe 3
The drum water discharged by the pump 0 may be discharged to the condenser 32 or the heat source side of the deaerator (not shown).

As described above, in addition to conventional three-element control to control the drum water level, the present invention provides an advance method in which the can water reduction valve is opened when the rate of pressure change is large and the water level is high to allow can water to flow out of the drum. Since this is a control system that performs control, it is possible to prevent the drum water level from becoming abnormally high even if the boiler internal pressure suddenly decreases. Therefore, carryover of water droplets into the steam generated by the boiler can be prevented, and erosion of the boiler heat exchanger tubes, main steam pipes, and steam turbine can be prevented. For this reason,
In a combined cycle plant, by making the gas turbine load follow the rapid minute load fluctuations and proactively operating the control valve at the steam turbine inlet, it is possible to make effective transient use of the boiler heat. The responsiveness of the steam turbine can be improved. Moreover, in connection with this, the responsiveness of the combined cycle plant can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a combined cycle plant showing one embodiment of the present invention, and FIG. 2 is a system diagram showing details of the portion of FIG. 1 relating to the present invention. FIG. 3 is an explanatory diagram of a drum water level control device equipped with a conventional three-element control means. 1...Gas turbine device, 11...Waste heat recovery boiler, 16...Drum, 21...Steam header, 2
2...Adjustment valve, 23...Steam turbine, 30...
Blowdown pipe, 31... Canned water reduction valve, 32...
Blow tank, 51...Drum water level detector, 52
... Steam flow meter, 53 ... Water supply flow meter, 54 ...
Water supply control device, 55... Pressure gauge, 56... Rate of change calculator, 57... Canned water reduction valve control device, 58...
Comparator, 60... Comparator, 59...
Change rate setting device, 61... Drum water level setting device for actuating canned water reduction valve, 62... Valve opening degree control device.

Claims (1)

[Claims] 1. One or more gas turbine devices;
It consists of a combination of a waste heat recovery boiler device that generates steam using the exhaust gas of the gas turbine device as a heat source, and a steam turbine device that performs work with the steam generated by the waste heat recovery boiler, and the steam that flows out from the waste heat recovery boiler In a combined cycle plant equipped with a three-element control means for controlling the feed water flow rate based on the steam flow rate, the inflow feed water flow rate, and the drum water level, A. A can water blowing system is provided in the drum of the waste heat recovery boiler, and the can water A can water reduction valve is installed in the blow system, and B (a) the drum water level exceeds the set value for operating the can water reduction valve, and (b) the rate of change of the signal representing the internal pressure of the waste heat recovery boiler is set. When the value is exceeded,
A can water level reducing valve control device for opening the can water level reducing valve is provided, and the structure is such that drum water is released through a can water blowing system independently of the operation of the three-element control means,
A drum water level control device for a combined cycle plant, characterized in that when the conditions (a) and (b) are compatible, the drum water level is lowered prior to the operation of the three-element control means.