JPH0243881B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control device for a geothermal steam turbine in a steam turbine plant that utilizes geothermal steam.

[Technical background of the invention and its problems]

Generally, in a power generation plant using geothermal heat, the pressure of steam flowing into a steam turbine varies depending on the state of the steam well, the amount of steam ejected, and the like. Therefore, the steam pressure flowing into the steam turbine is often higher than the rated value. A steam turbine operated at a rated pressure and a rated load increases the amount of steam flowing into the steam turbine due to an increase in steam pressure, and the load on the steam turbine becomes overloaded. In order to avoid this overload operation, conventionally, control is performed to throttle the steam regulating valve so that the outlet pressure (ball pressure) of the steam regulating valve does not rise above a certain value.
Furthermore, in the case of geothermal power generation plants, there has been an aspect in which partial load efficiency has not been given much importance in the past, and a throttle control method is generally adopted, and in this case, steam is Therefore, if any one of the steam control valves is narrowed down, the inflow to the steam control valve as a whole is reduced, and the steam control valve outlet pressure can be kept within a specified value. In addition, in the case of this throttle control, the steam regulator valve outlet pressure and the steam turbine output are almost proportional, so the steam regulator valve outlet pressure will only exceed the specified value when the steam turbine output is above the rated value. It won't happen. Therefore, the steam control valve outlet pressure can be controlled relatively easily.

That is, FIG. 1 is a system diagram of a geothermal steam turbine control device incorporating steam control valve outlet pressure control using a conventional control method. Steam ejected from a well 1 is separated into steam and hot water by a drain separator 2. The steam that exits the drain separator 2 is passed through the isolation valve 3 and the main steam stop valve 4.
a, 4b, enters the steam control valves 5a, 5b,
The amount of steam flowing into the steam turbine 6 is adjusted by the steam control valves 5a and 5b, and the steam flows into the steam turbine 6. The steam flowing into the steam turbine 6 performs work there and drives the generator 7, and the exhaust gas from the steam turbine 6 flows into the condenser 8, where it is condensed and returned to the ground.

By the way, a gear 9 is directly connected to the rotor shaft of the steam turbine 6, and a non-contact electromagnetic pickup 10 is disposed opposite the gear 9.
The non-contact electromagnetic pickup 10 detects a frequency signal proportional to the turbine rotation speed. The frequency signal detected by the electromagnetic pickup 10 is converted by a frequency/voltage converter 11 into an analog quantity proportional to the turbine rotation speed, and is applied to an adder 12.

In the adder 12, the rotation speed signal from the frequency/voltage converter 11 is compared with the setting signal from the speed setter 13, and the error signal is sent to the adjustment rate circuit 14 to match the adjustment rate. A speed control signal is generated and applied to the low value priority circuit 15. The low value priority circuit 15 compares and calculates the speed control signal, a limit signal from the load limiter 16, and a pressure control signal from a steam control valve outlet pressure control circuit (to be described later), and determines which of the lower control signals is selected. ,
This becomes the output signal of the low value priority circuit 15. One of the output signals is power amplified by the power amplifier 17a and then input to the electric/hydraulic converter 18a. The electric/hydraulic converter 18a converts the input current into a mechanical displacement proportional to the input current, and the displacement operates the control pilot of the steam control valve oil cylinder 19a, thereby controlling the opening of the oil cylinder 19a. The position of the steam control valve 5 is controlled by this oil cylinder 19a.
The opening degree of a is controlled, and the amount of steam flowing into the steam turbine is controlled. The other output of the low value priority circuit 15 controls the opening degree of the steam control valve 5b through a power amplifier 17b, an electro-hydraulic converter 18b, and a steam control valve oil cylinder 19b, similarly to the above-mentioned one. FIG. 1 shows an example in which there are two steam control valves, and in this case both steam control valves 5a and 5b perform the same operation.

Since the incoming steam is mixed within the turbine casing, the outlet pressures of the steam control valves 5a and 5b are the same regardless of the outlet pressure. This pressure is detected by the pressure detector 20, and the detected pressure signal is applied to the adder 21.
A pressure error signal is obtained by comparison with the setting signal from the pressure setting device 22, and the pressure control circuit 23 generates a pressure control signal according to the pressure adjustment rate from the pressure error signal. This pressure control signal passes through the exclusion circuit 24 and becomes an input to the low value priority circuit 15. The pressure setting value is generally set higher than the specified value, and is usually set to the limit pressure. Therefore, when the steam control valve inlet pressure is at the specified value and the pressure is at the rated load operation, the pressure control circuit 2
The output signal from 3 is an opening control signal that fully opens the steam regulating valve, and when the inlet pressure of the steam regulating valve becomes higher than the specified value and the outlet pressure of the steam regulating valve becomes higher than the specified value, the adder The output error signal of 21 becomes smaller, and the output of pressure control circuit 23 also becomes smaller. For this reason, the pressure control signal becomes smaller than the speed control signal from the speed control circuit, and the output of the low value priority circuit 15 is such that the pressure control signal takes priority, so that the steam turbine automatically switches from speed control to pressure control. Transition.

FIG. 2 shows the relationship between the steam control valves 5a, 5b and the nozzle 6a in the throttle control system,
Nozzles are provided around the entire circumference, and the incoming steam from each steam control valve 5a, 5b is mixed in front of the nozzle 6a and flows into the nozzle. Therefore, as described above, the outlet pressures of the steam control valves 5a and 5b are the same pressure.

However, in recent geothermal power plants, partial load operation is often considered important, and in order to improve efficiency at partial load,
Nozzle control methods are increasingly being adopted. By the way, in the case of this nozzle control method, in order to improve efficiency at partial loads, the steam control valves are opened sequentially, and the divided nozzles and steam control valves are paired. ,
The outlet pressure of each steam control valve will differ depending on the load of the steam turbine. In other words, even under partial load, if the steam control valve is fully open, the outlet pressure of the steam control valve will rise above the specified value due to the rise in steam pressure. Moreover, since the main steam pressure of a geothermal turbine is relatively low, a large-capacity steam turbine has long blades, and if the steam control valve outlet pressure rises to a specified value or higher, a problem arises in the strength of the blades.

Therefore, it is impossible to use a conventional throttle control system control system as is in a turbine control system using a nozzle control system.

[Purpose of the invention]

In view of these points, the present invention provides a turbine control device using a nozzle control method, in which when the generated steam pressure on the steam well side increases, the outlet pressure of the steam control valve in the fully open state becomes equal to or higher than a specified value. An object of the present invention is to provide a steam turbine control device that can reliably prevent steam turbine overload.

[Summary of the invention]

The present invention has a nozzle control method in which a plurality of steam control valves are opened in sequence, and the next steam control valve is opened when the first steam control valve is fully open or close to fully open. In the steam turbine control device of a geothermal steam turbine plant, the outlet pressure signal of the steam regulator valve that first reaches full open is detected, and that pressure signal is used as an input signal to the pressure control circuit, and the outlet pressure of the steam regulator valve is determined to be equal to or higher than a specified value. When the pressure rises to 1, the pressure control circuit is activated to first narrow down the opening degree of the steam control valve, which is already fully open.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 3 to 5. Note that the same parts as in FIG. 1 are given the same reference numerals, and the explanation thereof will be omitted.

Figure 3 shows a geothermal turbine control device that has steam control valve outlet pressure control using a nozzle control method. The steam control valves and nozzles are designed so that they are at their highest efficiency when each steam control valve is fully open, increasing efficiency at partial loads. Further, in the case of nozzle control, by sequentially opening each steam regulating valve, the full opening point of each steam regulating valve becomes the highest efficiency point. In FIG. 3, steam control valves 5a and 5
b is written the same as in Fig. 1, but as mentioned above, the nozzle control system is used in Fig. 3, and the outlets of the steam control valves 5a and 5b are connected to pipes to separate nozzles. It is then connected.

FIG. 4 shows the connection between the steam control valve and the nozzle in the nozzle control system. As shown, the nozzles 6a and 6b are connected to the partition plates 6c, 6d, 6e,
6f, and a steam control valve 5a.
is the nozzle 6a, and the steam control valve 5b is the nozzle 6b.
are connected to each other.

In addition, in the case of the nozzle control method, since each steam control valve is sequentially opened, one of the control signals output from the low value priority circuit 15 becomes the control signal for the steam control valve 5a that is opened first. The constant 25 adjusts the opening speed of the steam control valve 5a. In other words, in the case of the throttle control method, it was sufficient to fully close and fully open all the steam control valves in the same way according to the output signal of the low value priority circuit 15, but in the nozzle control method, the steam control Since the valves are opened sequentially, it is necessary to increase the opening speed of each steam control valve in response to the control signal.

The other output of the low value priority circuit 15 is sent to the adder 26
Accordingly, a bias signal, which is a negative signal, is added to the steam control valve opening start bias 27 to adjust the second valve 5b to open from the time when the first valve 5a is fully opened. The control signal to which the bias signal is added increases the rate of increase of the control signal at constant 28, which has the same meaning as constant 25.
The detection seat of the pressure detector 20 is provided on the outlet side of the first steam control valve because the first valve is the first valve to open and the first to fully open. That is, the outlet pressure of the fully open steam regulating valve is the maximum, and if pressure control is performed using this pressure, the outlet pressures of all other steam regulating valves will be held within the specified pressure. This pressure detection signal is compared with a set value from a pressure setting device 22 by an adder 21.
This error signal is used by the pressure control circuit 23 to generate a pressure control signal in accordance with the pressure adjustment rate. This pressure control signal passes through an exclusion circuit 24 and is connected on the one hand to the control signal of the steam control valve 5a by a first low value priority circuit 29. The other pressure control signal leaving the exclusion circuit 24 is connected by a second low value priority circuit 30 to the control signal of the steam control valve 5b.

The pressure of the pressure control circuit is set so that if the outlet pressure of the steam control valve is within a specified value, the output signal from the pressure control circuit is a control signal that fully opens each steam control valve. When the steam regulator outlet pressure exceeds a specified value, the error signal from the adder 21 decreases, producing a control signal that throttles the steam regulator. This control signal is applied to each low value priority circuit 2.
9 and 30, each of which compares and calculates the steam control valve signal from the speed control circuit, and when it becomes smaller than the control signal from the speed control circuit, the steam control valve shifts to pressure control.

However, in the case of throttle control, when the outlet pressure of the steam regulating valve exceeds a specified value, all the steam regulating valves are throttled down to control the outlet pressure of the steam regulating valve so as not to exceed the specified value. In the case of the nozzle control system in the embodiment, the pressure control signal is connected to each steam valve by the low value priority circuits 29 and 30, so even if the output of the steam turbine is below the rated value, the steam regulator valve inlet pressure remains unchanged. If the pressure at the outlet of a fully open steam regulator exceeds the specified value, the pressure control circuit generates a signal that throttles the steam regulator; Only steam control valves lower than the control signal transition to pressure control. That is, in the case of the nozzle control method, the steam control valves are sequentially opened according to the load of the steam turbine, and in the case of partial load, all the steam control valves are not fully opened. Therefore, the steam control valve that is fully open or the steam control valve that is controlling the speed near full open will shift to pressure control first. In the case of a geothermal plant, the inlet steam pressure tends to increase by closing the steam control valve, but the rate of increase can be controlled by narrowing the steam control valve.
Since it is smaller than the decreasing steam regulating valve outlet pressure, the steam regulating valve outlet pressure can be held within the specified value by narrowing down the steam regulating valve to some extent.

FIG. 5 shows the state of pressure control in the present invention. In FIG. 5, the X-axis shows the passage of time, and the Y-axis shows the respective states. Also, A is the steam control valve 5
A is the valve opening degree, B is the valve opening degree of the steam regulator valve 5b, C is the rotation speed of the steam turbine, D is the output of the steam turbine, E is the output signal of the pressure control circuit, F is the steam regulator valve outlet pressure, G indicates the state of the inlet pressure of the steam control valve. Point a is the starting point of the turbine, and the rated rotational speed is reached at point b, and the load on the turbine begins to increase after joining. At point C, the first valve 5a of the steam control valve becomes fully open, and the second valve 5b begins to open. At point d, the second valve is also fully opened, resulting in rated load operation. In this state, the main steam pressure (steam control valve inlet pressure) increases (e
point), and as the pressure rises, the steam control valve outlet pressure also rises, and the output of the steam turbine also begins to increase. The outlet pressure of the steam control valve exceeds the specified value (f
point), the output of the pressure control circuit starts decreasing, and the steam control valves 5a and 5b start throttling (g
point). The pressure control circuit throttles the outlet pressure of the steam control valve to a specified value, and once the specified value is reached, pressure control is continued to maintain that pressure. When the inlet pressure of the steam regulating valve decreases and becomes equal to or less than the specified value pressure, the pressure control circuit generates a control signal to fully open the steam regulating valve again, so that the steam turbine shifts to a speed control state. Although FIG. 5 shows the control state when the pressure rises when both the first valve 5a and the second valve 5b are fully open, the same control is performed even if the pressure rises when only the first valve 5a is fully open. It will be done. However, in this case, only the first valve shifts to pressure control, and the second valve 5b remains under speed control.

〔Effect of the invention〕

A geothermal power generation plant having a nozzle control method in which a plurality of steam control valves are opened in sequence, and the next steam control valve is opened when the first steam control valve is fully open or close to fully open. A steam turbine control device includes a pressure control circuit that outputs a steam regulating valve control signal in response to an outlet pressure signal of the steam regulating valve that first reaches full open, and a pressure control circuit that outputs a steam regulating valve control signal in response to a turbine rotational speed signal. a first low value priority circuit that outputs a low value signal of the output signals from the speed control circuit and the pressure control circuit as a control signal for the steam control valve that first reaches full open; A second low-value signal that outputs the low value signal of the output signal from the speed control circuit to the steam control valve that reaches full open and the output signal from the pressure control circuit as a control signal for the steam control valve that reaches full open next. Since a value priority circuit is provided,
During partial load operation, if the steam pressure flowing into the steam turbine exceeds the specified value due to the condition of the steam well, fluctuations in the amount of steam ejected, etc., the steam control valve, which is fully open or close to fully open, may Only the valves are transferred to pressure control to prevent overloading of the steam turbine, and the other steam control valves are controlled by the output signal from the speed control circuit. Therefore, all the steam control valves do not shift to pressure control at the same time, the load is not reduced more than necessary, the output of the turbine can be maintained at a predetermined value, and the steam pressure etc. It is possible to effectively utilize geothermal heat, which is subject to fluctuations. Moreover, even though each steam control valve is connected to correspond to one of the nozzles partitioned off from each other, each steam control valve can be adjusted by simply installing a pressure sensor at the outlet of the steam control valve that reaches full open first. The valves can be sequentially shifted to pressure control, and the configuration can be extremely simple.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a control system for a steam turbine in a geothermal power plant that incorporates steam regulator outlet pressure control using the conventional throttle control method. Figure 2 is a system showing the connection between the steam regulator and nozzle in the throttle control method. 3 is a system diagram of a control system for a steam turbine in a geothermal power plant according to an embodiment of the present invention, FIG. 4 is a system diagram showing the connection state of a steam control valve and a nozzle in a nozzle control system, and FIG. FIG. 3 is a diagram showing changes in the steam regulator, the output of the pressure control circuit, and the pressures at the steam regulator inlet and outlet during steam regulator outlet pressure control in the present invention. 5a, 5b...Steam control valve, 6...Steam turbine, 6a, 6b...Nozzle, 6c, 6d, 6e,
6f...Partition plate, 10...Electromagnetic pick-up, 1
1... Frequency/voltage converter, 12, 21, 26...
... Adder, 13 ... Speed setting device, 15, 29, 3
0...Low value priority circuit, 17a, 17b...Power amplifier, 18a, 18b...Electric/hydraulic converter,
19a, 19b...Steam control valve oil cylinder, 22...Pressure setting device, 23...Pressure control circuit, 27...Bias.

Claims (1)

[Claims] 1 Geothermal power generation with a nozzle control method in which multiple steam control valves are opened in sequence, and the next steam control valve is opened when the first steam control valve is fully open or close to fully open. In a control device for a steam turbine in a plant, there is a pressure control circuit that outputs a steam regulating valve control signal in response to an outlet pressure signal of the steam regulating valve that first reaches full open, and a steam regulating valve control circuit that outputs a steam regulating valve control signal in response to a turbine rotation speed signal. a speed control circuit that outputs a signal; a first low value priority circuit that outputs a low value signal of the output signals from the speed control circuit and the pressure control circuit as a control signal for the steam control valve that first reaches full open; A second controller outputs a low value signal between the output signal from the speed control circuit and the output signal from the pressure control circuit to the steam control valve that next reaches full open as a control signal for the steam control valve that next reaches full open. A control device for a steam turbine, comprising a low value priority circuit.