JPS6231245B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiler feed pump control device of a variable speed electric motor type, and more particularly to a boiler feed pump control device that stabilizes control when the feed water pump starts up rapidly.

The prior art and its problems will be explained with reference to FIG. In so-called variable pressure boilers, which operate power generation boilers in a manner that changes the steam pressure at the boiler outlet depending on the load, a variable-speed motorized boiler feed pump using a fluid coupling is installed as a feed water control device. In order to control the water supply to the boiler, a configuration is adopted in which the flow rate is controlled by a flow rate control valve installed on the pump outlet side, and the pump rotational speed is controlled so that the differential pressure across the flow rate control valve is constant. ing. That is, in FIG. 1, the pressure before and after the flow control valve 1 is detected by pressure detectors 2 and 3, the differential pressure is calculated by a subtractor 4, and the preset setting in the differential pressure setting device 5 is calculated. This can be done by calculating the deviation from the differential pressure using a proportional integrator 6, proportionally integrating the calculated deviation, and inputting the output of the proportional integrator 6 to the variable speed device 8 via the automatic/manual switch 7. The speed of the water supply pump 9 is controlled by controlling the transmission 8.

However, the conventional method described above has the following problems. In plants with large power generation capacity, a steam turbine-driven feed water pump and an electric motor-driven feed water pump are installed together, and the steam turbine-driven feed water pump is used for normal operation, and the electric motor-driven feed water pump is used only when the plant is started. I am using it. However, in drum-type boiler plants, when the plant is operated independently after a rapid load interruption or when the boiler is operated independently, the required feed water flow rate decreases and stable control cannot be achieved with a steam turbine-driven feed water pump. It is necessary to start up the water pump quickly. However, since the pressure on the outlet side of the water supply flow rate control valve after the rapid load is interrupted is almost the same as the pressure before the load is interrupted, the output of the subtractor 4 and the differential pressure setting device 5 cannot be maintained with the conventional control method described above. The deviation from the output is too large and good control cannot be obtained.
Should the automatic/manual switch 7 be set to manual to increase the speed of the water supply pump 9 to increase the outlet pressure and reduce the deviation before feeding to the automatic side, or should a computer control method be used? method must be adopted. However, the former method has the disadvantage that it takes too much time to stabilize the control, and the latter method has the disadvantage that it is impractical due to the risk of temporary overload.

An object of the present invention is to provide a boiler feed water pump control device that eliminates the above-mentioned disadvantages of the prior art and can perform stable control even when the feed water pump is driven rapidly due to rapid loading or interruption. It is in.

In order to achieve the above object, the features of the present invention are as follows:
Characterizes the proportional integrator that proportionally integrates the deviation between the differential pressure across the flow control valve and the preset differential pressure, and the relationship between the pump outlet pressure and variable speed device input in the minimum flow state of the water pump. and a signal switching device that passes the output of the function generator and inputs it to the variable speed device when the feed water pump starts up rapidly, and passes the output of the proportional integrator and inputs it to the variable speed device after startup is complete. The structure has the following features.

The present invention will be explained below with reference to the drawings.

Figure 2 is a characteristic curve diagram showing the relationship between the water supply flow rate (horizontal axis) and pressure (vertical axis). be done. Therefore, the pressure after the load is broken is almost the same as before the break, but its value changes depending on the load before the break. On the other hand, the rotation speed of a variable speed water pump is changed by controlling the fluid coupling, but the relationship between the input signal of the fluid coupling and the pump outlet pressure is not uniquely determined because it varies depending on the pump flow rate. . However, when the pump is started, water is not being supplied to the boiler side, so the water supply pump is only flowing with a minimum flow to prevent overheating. Focusing on this point, when the water pump is started, the water is not supplied to the boiler side, so the minimum flow is flowing to the water supply pump to prevent overheating. 2, the input to the fluid coupling, that is, the output of the control device can be uniquely determined.

FIG. 3 shows a block configuration diagram of an embodiment of the present invention, and the difference from the conventional example shown in FIG. 1 is that the adder 10,
The point is that a function generator 11 and a signal switch 12 are added. The adder 10 adds the output signal of the pressure detector 3, which detects the rear pressure of the flow rate control valve 1, and the output signal of the differential pressure setting device 5, and uses the addition result as a target pressure signal after starting the water supply pump. Output. Next, as mentioned above, since the relationship between the control device output and the water supply pump outlet pressure is uniquely determined when the water supply pump is in the minimum flow state, the control device output corresponding to the target pressure signal after starting the water supply pump can be determined.
The relationship between this target pressure signal and the control device output is defined as the characteristic of the function generator 11. This provides the target controller output when the water pump is at minimum flow.

Furthermore, the signal switch 12 is used to switch the output of the function generator 11 to pass when the water supply pump is rapidly started at the time of rapid load interruption, and to pass the output of the proportional integrator 6 after the start is completed. ,
By inputting this passage signal to the variable speed device 8 via the automatic/manual switch 7, the rotation speed of the water supply pump is rapidly increased to obtain a predetermined pressure at the time of rapid startup, and the flow rate control valve after startup is completed. It is possible to shift to the flow rate stabilization control according to No. 1.

As described above, according to the present invention, when rapidly starting the water supply pump due to rapid loading or interruption, a signal corresponding to the target pressure is given at the time of rapid starting, so rapid starting is possible. Thereafter, a transition to normal proportional-integral control will be performed within a short period of time.

[Brief explanation of the drawing]

FIG. 1 is a control system diagram for explaining the prior art, FIG. 2 is a diagram showing an operating curve of a water supply pump, and FIG. 3 is a control system diagram of an embodiment of the present invention. 1...Flow control valve, 2, 3...Pressure detector, 4
...Subtractor, 5...Differential pressure setting device, 6...Proportional integrator, 7...Auto/manual switch, 8...Variable speed device, 9...Water pump, 10...Adder, 11...
...Function generator, 12...Signal switch.

Claims (1)

[Claims] 1. A boiler water supply system in which a flow rate control valve is provided on the outlet side of a motor-variable water supply pump, and the water supply flow rate to the boiler is controlled by variable speed control of the water supply pump so that the differential pressure before and after the flow rate control valve is constant. In the pump control device, there is a proportional integrator that proportionally integrates the deviation between the differential pressure across the flow control valve and a preset differential pressure, and a variable speed device that measures the pump outlet side pressure in the minimum flow state of the water supply pump. A function generator that has a characteristic relationship with the input, and when the feed water pump starts rapidly, the output of the function generator is passed through and input to the variable speed device, and after startup is completed, the output of the proportional integrator is passed through and input to the variable speed device. A boiler feed water pump control device characterized by comprising: a signal switching device for inputting an input signal to a signal switch;