JPS613901A - Method of controlling water level in drum on starting of combined power plant - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a method for controlling a thermal power plant, and particularly to a method for controlling a thermal power plant.

The present invention relates to a control method for a multi-shaft combined power generation plant in which a gas turbine and a steam turbine are each provided with a generator.

[Background of the invention]

In conventional drum water level control, it is common to calculate the difference between the drum water level setting value and the actual water level value, and perform PI control on this difference. In this control, in order to prevent the swelling characteristic of combined power generation Plato, the drum water level is set to a low position before startup, and as the gas turbine ignites, the drum water level is gradually raised to the standard level while the economizer recirculation flow is started. As a result, almost no water is supplied to the drum, and the water level drops. In response to this drop, PI control based only on the difference between the drum water level set value and the actual water level value is slow, and if the control constants of PI control are matched at startup to speed up the response, the water level after load addition is Since the response is fast in areas with small fluctuations, there is a risk of severe water level fluctuations. Therefore, with the conventional control method, it is difficult to control the water level at startup.

[Purpose of the invention]

The purpose of the present invention is to control the drum inlet water level ai at the time of startup of a combined power generation Plato equipped with an exhaust heat recovery boiler, and to control the recirculation flow rate of #'Cph to the drum when the gas turbine ignites. While the water supply decreases, by rapidly increasing the water supply at startup, especially at ignition, it is possible to prevent the drum water level from dropping near the gas turbine ignition.

[Embodiments of the invention]

An outline of the exhaust heat recovery type combined power generation Plato to which the present invention is applied will be explained with reference to FIG.

First, a gas compressed by a compressor 1 of a gas turbine is combusted in a combustor 2. Combustion gas expanded by this combustion is sent to a turbine 3 to drive a generator 4. Exhaust gas discharged from the gas turbine is led to an exhaust gas duct 5, passes through an exhaust heat recovery boiler consisting of a superheater 7, an evaporator 8, an economizer 9, and a drum 6, and is then heat-exchanged. is discharged to.

On the other hand, the water supplied from the condenser 13 passes through the water supply pump 15, and the water supply flow rate control valve 10 supplies the required water supply flow rate. The supplied water is heated by the economizer 9 (thereby, a part of the water is passed through the economizer recirculation flow rate control valve 17 as the economizer recirculation flow rate).
The flow rate is controlled by , and the water is recovered to the condenser 13 . The remaining feed water is supplied to the drum 6. The water in the drum 6 is further heated by an evaporator 8 to become steam, the steam is turned into superheated steam by a superheater 7, the flow rate of which is adjusted through a control valve 11, and supplied to a steam turbine 12, which drives a generator 14. drive The other is a turbine bypass valve [6], and the steam whose flow rate is adjusted is recovered into a condenser 13 and becomes condensed water.

Next, an overview of a conventional drum water level control system will be explained. FIG. 2 shows a conventional drum water level control system. First, a water level setter 29 is given a set value by a host computer or a programmable setter.

A feedback signal is given from the drum water level transmitter 30 to a given water level set value, a subtracter 20 calculates the deviation between the set value and the actual water level, and a proportional integrator 21 performs a proportional integral calculation. Since the drum water level control is a four-element control, the subtractor 22 subtracts the water supply flow rate from the transmitter 31, the steam flow rate from the transmitter 32, the economizer recirculation flow rate from the transmitter 33, and the proportional integral value of the drum water level deviation. The resulting deviation output is subjected to a proportional integral calculation in the proportional integrator 23, and the water supply flow 1kIlliJ control valve is controlled by the output. In addition, the subtracter 26, the signal generator M825, the proportional integrator 27. The high value selection 24 is a circuit for ensuring the minimum flow rate of the water supply flow rate.

Conventional drum water level (a) and water supply flow rate (b) at startup
), the behavior of the economizer recirculation flow rate (c) is explained in FIG.

First, the drum water level set value 40 is set in a ramp-like manner from the gas turbine ignition, and reaches the standard level when the gas turbine is added. The reason why the water level decreases around 1 ignition with respect to the set value is that the exhaust gas in the exhaust gas duct 5 is discharged from the start of the gas turbine to the ignition, so the temperature of the exhaust gas boiler decreases, which causes the temperature of the drum 6, economizer 9, and evaporator to decrease. The water in the container 8 contracts and the drum water level 41 decreases. In addition, water supply 42
is supplied by starting the gas turbine, and when the gas turbine ignites, the economizer recirculation flow rate 43
control begins, but the recirculation flow rate set value a T / H may be overshot due to a transient response.

Because of the recirculation flow rate value exceeding the feedwater flow rate a T/H,
Depending on the structure of the water supply piping to the drum 6, the drum ls 6
Water may flow backwards and flow out as recirculation flow.

Due to these causes, the drum water level may drop near the gas turbine ignition and may reach the low water level alarm set value or trip value.

From this, it is possible to prevent the water level from dropping at the time of ignition by rapidly increasing the water supply together with No. 1 ignition f8 in response to the drop in the drum water level at the time of ignition of the gas tough pin.

Figure 4 shows a conventional control system in which a circuit for increasing the water supply flow rate during ignition is added.

The added circuits include an adder 30, a differentiator 34, and a switch 3.
5. There are signal generators 36, 37, and this circuit switches the bias value of the signal generators 36, 37 with the gas turbine ignition signal. In other words, the bias value It O#
1, but is switched to a predetermined set bias value together with the ignition signal. The bias value is input to the differential book, and a differential signal is outputted in which the set bias attenuates as the R question increases.

The bias value of this t warrant is added to the adder 38. With this circuit, a differential bias value is further added to the deviation between the level setting value and the actual drum level, and the water supply flow rate is increased only at the time of ignition.

Figure 5 shows the behavior of the drum water level and water supply flow rate 2 economizer recirculation flow rate due to the addition of this circuit.

The recirculation flow rate for excellent coal savings behaves as before, but the water supply flow rate is instantaneously equal to the set bias when the gas turbine ignites.

After ignition, it decays transiently until the flow *a T/H. During this period, the drum water level rises to the standard level without falling due to the flow rate of the water supply flowing.

By adding the differential bias value, the drum water level set value changes from a ramp-like change to a water level as shown by the broken line with the differential bias added, as shown in Figure 4. This is the set value.

13,,,*. 0. B1. ．． Yo 9, yay. 5 rum,
The lower the water level, the greater the deviation, and the water supply flow rate is controlled to increase further.

It is possible to prevent the drum water level from decreasing after ignition. In the figure, 28 is a water supply flow rate control valve.

〔Effect of the invention〕

According to the present invention, it is possible to sufficiently prevent a drop in the drum water level after ignition and to sufficiently follow the ramp-shaped drum water level set value, which is optimal as control and highly effective.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a multi-shaft Humbind power generation plant, Figure 2 is a conventional drum water level control system diagram, and Figure 3 is a drum water level feed water flow rate with conventional drum water level control.
Figure 4 is a diagram of the behavior of the recirculation flow rate, Figure 4 is a drum water level control system diagram of an embodiment of the present invention, Figure 5 is a behavior diagram of the drum water level and the water supply flow rate of 2 economizers and the 411 ft flow rate according to the drum water level control of the present invention. be. 34... Differentiator, 35... Signal switch, 36...
Signal generator, 37... Signal generator.

Claims (1)

[Claims] 1. In the exhaust heat recovery type combined power generation Plato, an adder, a differentiator, a signal generator, and a switch are provided in the drum water level control system to control the energy saving recirculation flow rate that starts when the gas turbine ignites. The starting of the combined power generation Plato is characterized in that a means is provided for adding a differential bias value to the difference between the drum water level set value and the actual water level value only at the time of starting, in response to a drop in the drum water level that occurs due to the drop in drum water level. drum water level control method.