JPS6135441B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a gas turbine device, an exhaust 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 is related to drum water level control of an exhaust heat recovery boiler in a combined cycle plant.

First, the general configuration of a combined cycle plant will be explained with reference to FIG.

A combined cycle plant generally includes one or more gas turbine devices 1, the same number of exhaust 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 generates high-temperature, high-pressure combustion gas by burning fuel sent from a fuel pipe 4 using air pressurized by the compressor 2, and a combustor 3 that generates combustion gas. It is composed of a combustor 3 and a gas turbine 5 that is driven by combustion gas and rotates a gas turbine generator 6. Combustion gas discharged from this gas turbine device 1 is led to an exhaust 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 exhaust heat recovery boiler 11, and the exhaust 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 exhaust heat recovery boiler 11 is
an economizer 15 which is a drum boiler and heats the feed water introduced through the water supply pipe 14;
It is composed of a drum 16 for steam generation, an evaporator 17, and a superheater 18. Steam coming out of the superheater 18 passes through a steam pipe 19 and a boiler valve 20, and is collected into a steam header 21. The water is fed into the steam turbine 23 through the control valve 22 to drive the generator 24, and is condensed in the condenser 32. revenge〓〓〓
The supplied water is returned to the exhaust heat recovery boiler 11 by a water supply pump 12 through a water supply pipe 14 equipped with a water supply regulating valve 13 . The steam pipe 19 also includes a turbine bypass valve 25 on the upstream side of the boiler outlet valve 20.
A bypass steam pipe 26 equipped with Steam is introduced into the condenser 32 in order to match the steam pressure generated by the exhaust heat recovery boiler 11, and is not used during normal operation. 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 the exhaust 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 exhaust heat recovery boiler.

However, during the pressure increase process when starting up the exhaust heat recovery boiler 11, the drum pressure of the exhaust heat recovery boiler 11 suddenly decreases due to the start of control of the turbine bypass valve 25, and the saturated water in the drum 16 self-evaporates. It exhibits a so-called reverse response characteristic in which the drum water level rises transiently due to the generated steam bubbles. If the drum water level rises abnormally in this manner, water droplets will be mixed into the generated steam, causing erosion in the superheater 18, steam turbine 23, etc. in the exhaust heat recovery boiler 11. This phenomenon will be explained with reference to FIG. In FIG. 2, 71 is the pressure rise characteristic of the waste heat recovery boiler 11, and 72 is the pressure rise characteristic of the waste heat recovery boiler 11.
shows the saturated steam pressure characteristics commensurate with the steam temperature change rate allowed by When the steam pressure is increased using this curve 72 as the pressure setting of the turbine bypass valve, the steam pressure rises above the control setting at point C, and the turbine bypass valve 25 opens to adjust the steam pressure to the characteristic of 72. Control. When the turbine bypass valve 25 opens, the steam pressure changes following the course of A → B → C → D, but after point C, it is forcibly controlled to have the characteristic of 72, so the steam pressure change rate suddenly changes. It will be in a decreasing direction. When the rate of change in steam pressure suddenly changes to the negative side, the saturated steam pressure in the drum 16 decreases, causing self-evaporation of the saturated water, causing a reverse response phenomenon in the drum water level.

An object of the present invention is to provide a stable drum water level control device that can prevent the above-mentioned abnormal rise in drum water level in advance.

The feature of the present invention is that when the steam pressure change rate exceeds the steam pressure change rate corresponding to the allowable steam temperature change rate, the drum water level set value is lowered by the expected water level rise, and the steam pressure changes. The purpose is to prevent an abnormal rise in the drum water level by opening the can water reduction valve until the rate returns to the specified value.

An embodiment of the present invention will be described below with reference to FIG. The signal from the drum water level detector 51 is compared with the drum water level setting value set by the signal generator 41 in a subtracter 42, and a flow rate command to the water supply regulating valve 13 is issued by a proportional/integral action controller 45 in accordance with the deviation. Steam flow meter 52 by adder 46
The signal is added to the output signal of the proportional/integral controller 45, and the signal is given to the subtractor 47 as the water supply flow rate setting value, and compared with the signal of the water supply flow meter 53, the proportional/integral controller is activated according to the deviation. An opening command is issued to the water supply regulating valve 13 from 48, and control is performed so that the drum water level becomes equal to the set value. The signal from the steam pressure detector 56 is calculated by a differential calculator 82 as a steam pressure rate. In FIG. 2, the pressure setting value 72 of the turbine bypass valve 25 and the steam pressure increase characteristic 7 of the exhaust heat recovery boiler 11 are shown.
The turbine bypass valve 25 starts opening control at the intersection point C with the curve 71 in FIG. The subtracter 83 detects that the rate of change of has become larger than the curve 72 by comparing the allowable rate of change in pressure set by the signal generator 82 with the rate of change in steam pressure calculated by the differential calculator 82, and calculates the rate of change. The gain of the multiplier 44 is changed according to the deviation of the drum water level, and the bias amount of the drum water level set value set by the signal generator 43 is varied, and the drum water level is set so as to substantially rise.
Change the value and throttle the water supply regulating valve 13 in advance. On the other hand, the signal of the subtractor 83 is the logical sum of the output of the comparison alarm 49 which calculates that the drum water level is above the specified value and the condition that the turbine bypass valve 25 is opened.
6, the can water level reducing valve control device 57 opens the can water level reducing valve 31 to prevent the drum water level from rising abnormally. The can water level reduction valve 31 is controlled to open until the drum water level falls to a specified value. When the water level falls to the specified value, the output of the comparison alarm 49 is turned off, the condition of the logical sum 86 is broken, and the can water level reduction valve 31 is closed.

As a result of the above, as the boiler pressure change rate increases, the drum water level set value is lowered and the water supply flow rate is quickly throttled, and furthermore, at point A in Figure 2, the turbine bypass valve 2 is
5 opens and the rate of change in steam pressure suddenly decreases, the can water level reduction valve 31 is opened. These two controls can prevent an abnormal rise in the drum water level.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a combined cycle plant, Figure 2
The figure shows steam pressure rise characteristics, and FIG. 3 is a diagram showing a drum water level control device according to the present invention. DESCRIPTION OF SYMBOLS 1...Gas turbine, 11...Exhaust heat recovery boiler, 17...Drum, 23...Steam turbine device, 31...Can water level reduction valve, 51...Drum water level detector, 52...Steam flow meter, 53 ... Water supply flow meter, 54 ... Drum water level control device, 56 ... Steam pressure detector, 57 ... Can water level reduction valve control device, 4
1... Signal generator, 42... Subtractor, 43... Signal generator, 44... Multiplier, 45... Proportional/integral controller, 46... Adder, 47... Subtractor, 48... Proportional・Integral controller, 49...
Comparison alarm, 82...Differentiator, 83...Subtractor, 84...Signal generator, 86...Order, 13
... Water supply adjustment valve, 31 ... Can water level reduction valve. 〓〓〓

Claims (1)

[Claims] 1 one or more gas turbine devices,
It includes an exhaust 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 using the steam generated by the exhaust heat recovery boiler. In a combined cycle plant equipped with a turbine bypass valve that bypasses, a can water reduction valve is provided to release drum water of the waste heat recovery boiler, and the drum water level exceeds a specified value and the rate of change of the steam pressure signal exceeds the set value. a first control system that opens the can water level reduction valve when the turbine bypass valve opens; and a steam flow rate flowing out from the heat recovery boiler.
The feed water flow rate is controlled based on the inflow feed water amount and the drum water level, and when the steam pressure change rate exceeds a predetermined value, the set value of the drum water level in controlling the feed water flow rate is adjusted to match the magnitude of the steam pressure change rate. A drum water level control device comprising: a second control system that lowers the water level by a certain amount;