JPS58198602A - Controller for feed pump of boiler - 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 The present invention is a control device for a boiler feed pump that uses both a feed water flow rate control valve and pump rotation speed control, and is particularly suitable for a boiler feed pump for a variable pressure operation plant! ll1llllK1
11.

In a thermal power plant using a variable pressure operation method, when the load is small, the discharge pressure of the boiler feed water pump (hereinafter simply referred to as pump) is also lowered and operated.

However, due to the operation characteristics of the pump, excessive flow I occurs at a flow rate below the rated flow rate of the pump. This will be explained with reference to FIG.

In FIG. 1, the vertical axis shows pressure and the horizontal axis shows flow rate, and the fan-shaped range in the figure is the operating head of the pump.

Since the discharge pressure of the pump is operated according to the solid line L1 in the figure, the pump cannot increase the flow rate beyond point P1,
Therefore, conventionally, it is necessary to start the second pump early. Moreover, in a region where the power generation output is high, the discharge pressure of the pump is also high, so the pump can output at the rated flow tQ1t, but the operator monitors the power generation output and pump discharge output and adjusts the pump flow rate accordingly. You have to decide how much you can increase it.

An object of the present invention is to provide a pump control device that can control the operating state of a pump from an overflow region to a region where the pump can operate, thereby expanding the operating range of a single pump.

In order to achieve such an objective, in the present invention, when the water supply pressure to the boiler is used at a pressure lower than the pump rated specification, the pump The unique feature is that the pump can be operated by increasing the pump discharge pressure according to the characteristics of the pump.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a graph explaining the present invention in detail, and like FIG. 1, the vertical axis shows pressure and the horizontal axis shows All.

In the control device for the boiler feed water pump, the feed water flow 1 control valve installed on the pump outlet side controls the pump flow 1k1111Ogl, and the rotation speed of the pump is controlled by the pump discharge pressure.

When the differential pressure of the feed water flow 1 control valve is held constant, the pump discharge pressure (differential pressure constant) is shown by a solid line L1, and the feed water flow rate control valve outlet pressure is shown by a dashed line L2 in FIG. This is to reduce the pump discharge pressure as much as possible and reduce the shaft power by setting the water supply flow rate control valve to the minimum differential pressure necessary for control, but in that case, the problems mentioned above occur. be.

Therefore, in the present invention, by making the differential pressure of the water supply flow rate control valve variable, the pump discharge pressure is set as indicated by the broken line L3 in FIG. 2, and an excessive flow rate is prevented.

Figure 3 shows an embodiment of the pump control device according to the present invention, including a 1-piece pump, a 2-piece variable speed device, a 3-piece pump, and a 4-piece pump.
is a water supply flow rate control valve, 5 and 6 are pressure detectors, 7 is a subtractor, & is a deviation calculator, 9 is a proportional integral calculator, 9 is a proportional integral calculator, 10 is a differential pressure signal generator, and 11 is a high value. selector,
12 and 13 #i differential pressure generators, 14 Ifi bias device, and 15 digit subtractor.

In such a configuration, the pump 1 is connected to the prime mover 3 via the variable speed device 2, and the rotation speed of the pump 1 is controlled by adjusting the variable speed device 2.

Conventionally, as differential pressure-volume control, the pressure after cocooning of the water supply flow rate control valve 4 is detected by a pressure detector 5.6, the differential pressure of the water supply flow rate control valve is obtained by a subtractor 7, and this differential pressure is calculated by a deviation calculation. The signal is input to the variable speed unit #2 through the unit 8 and the proportional integral calculator 9, and the variable speed unit lt2 is operated so that there is always no deviation from the preset output of the running differential pressure signal generator 10.

In the embodiment of the present invention, a flow rate detection differential pressure generator 12, a differential pressure detector 13, and a bias device 1 are installed at the inlet of the pump 1.
4. A subtracter 15 and a high value selector 11 are newly added.

The relationship between the discharge pressure PA of the pump l and the maximum flow rate Q1 at that pressure is expressed by the following equation (1).

Q, middle k [・・・・・・(1) However, it is a k constant.

Here, conversely, a certain pump inlet flow rate Q! The lowest value P of the pump discharge pressure at can be expressed by the following equation (2).

p , * to / Q I * ・・・・・・(2
) However, k' is a constant.

Therefore, in the present invention, the pump discharge pressure P is changed to the pump inlet flow rate Q! The pressure is controlled so that it is at least the lowest pressure that can be obtained. Therefore, the pump inlet flow rate Q at the differential pressure generator 12
1, but since the signal extracted in the case of differential pressure type flow rate detection is proportional to the square of the flow, the obtained signal is a signal of the bottom pressure P. A slight bias is added to this signal by the bias device 14, but this is done to prevent the pump from overflowing due to delays in the control device, etc.
This is to ensure a margin on tlJa. The signal obtained in this manner becomes the pump discharge pressure setting value indicated by the broken line L3 in FIG.

Signal from bias device 14 and water supply flow! A subtracter 15 takes the difference between the signal from the control lunchbox pressure detector 6 and calculates the differential pressure setting value of the water supply flow rate control valve 4.

This differential pressure setting value and a setting signal generator 1 for differential pressure/volume control
The output of 0 is input to the high value selector 11, and the larger signal among these human input signals is controlled as the differential pressure setting value.

If this is done, the pump discharge pressure will rise before entering the overflow region, so no overflow will occur.

As described above, according to the present invention, when the pressure is lowered for variable pressure operation, the discharge pressure of the pump can be controlled to be high according to the pump characteristics. For example, in the example shown in FIG. 1, operation is now possible from point P1 to a point near the rated flow IQI.

In this way, by controlling the operating state of the pump from the excess flow Wkta to the region where the pump can be operated,
The operating range of a single pump can be significantly expanded.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the operating characteristics of a conventional pump, FIG. 2 is a diagram explaining the operating characteristics of a pump according to the present invention, and FIG. 3 is a diagram showing the configuration of an embodiment of a pump control device according to the present invention. be.

Claims (1)

[Claims] 1. A boiler comprising a boiler feed water pump, a control means for controlling the rotation speed of the pump, and a water feed flow rate control valve installed at the outlet of the pump to control the water feed flow rate of the pump. In a control device for a water supply pump, in a region where the pump has an excessive flow rate below the rated flow rate of the pump,
A boiler feed water pump control device characterized by comprising means for increasing the discharge pressure of the pump in accordance with the characteristics of the pump to enable operation. 2. The boiler feed water pump control device according to claim 1, wherein the pump discharge pressure according to the characteristics of the pump is determined from the inlet flow rate of the pump.