JPS61159009A - Controller for boiler feedwater - 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 boiler feed water control device for a thermal power plant, and particularly to a water feed water control device with an i o'o s capacity.

[Background of the invention]

BACKGROUND OF THE INVENTION Conventionally, water supply to a boiler in a thermal power plant has been carried out using two water supply pumps with a capacity of 5O1s and one standby water pump. At thermal power plants, load is cut off when there is a disturbance in the power system, but at this time one of the two water supply pumps is stopped, and the remaining water pump covers the boiler water supply flow rate. We have secured power to various power generation facilities and are preparing for the re-incorporation of loads. At this time, in order to reliably ensure the boiler feed water flow rate, a method is used in which the regulating valve of the feed water pump driving turbine is determined in advance and positioned at a set value (see % Application No. 53-21042).

This is because various state quantities change significantly when the load is cut off, so while a normal feedback control system cannot keep up with the situation, reliable control is performed using the feeder and backward. In such a conventional case, the required boiler feed water flow rate is greater than the required minimum flow rate of the feed water pump, and the recirculation valve remains closed and does not need to be particularly controlled. By the way, in order to reduce the cost of thermal power plant equipment, a configuration with one 100% capacity water supply pump and one standby water supply pump has been considered. The boiler water supply flow rate will be secured with one water supply pump, but the required minimum flow rate for a 100% capacity water supply pump is twice that of a 50-capacity water supply pump, so the necessary boiler water supply flow rate ( This is the same regardless of pump capacity). Therefore, when the load is cut off, it is necessary not only to control the valve opening of the water supply pump, but also to control the recirculation valve so that it quickly reaches a predetermined value to ensure the minimum flow rate of the water supply pump. It wasn't.

[Purpose of the invention]

An object of the present invention is to provide a boiler feed water control device that can reliably secure the required boiler feed water flow rate and the minimum flow rate of the feed water pump when the load is cut off, even in a thermal power plant using a 100-capacity feed water pump. It is on offer.

[Summary of the invention]

The present invention provides a means for determining the required minimum flow rate of the water supply pump and the recirculation flow rate required at the time of load cutoff according to the magnitude of the load immediately before the load cutoff, and the output of this means is used to drive the water supply pump and the recirculation flow rate at the time of load cutoff. This is characterized in that the opening degree of the recirculation valve is controlled.

[Embodiments of the invention]

The present invention will be explained in detail below using examples.

FIG. 1 shows an embodiment of the present invention, in which a water pump 1 with a capacity of 100 cm is driven by a water pump driving turbine 2, and the drive of this turbine 2 is adjusted by operating a control valve 3. On the other hand, pump water is supplied only to the boiler when the amount of water supplied is large, and the recirculation valve 4 is closed at this time, but when the required amount of water supplied to the boiler decreases and becomes less than the required minimum flow rate of the water pump 1, it is recirculated. Open the circulation valve 4t to ensure the required minimum flow rate of the pump. Control for this is usually performed as follows: subtract the recirculation flow rate 6 from the Umazu feed water pump inlet flow rate 5 by -101 to obtain the actual water supply flow rate to the boiler, and calculate the actual water supply flow rate to the boiler by combining this with the boiler water supply demand. The deviation of 9 is calculated by the subtracter 102 and then sent to the control calculator 1
11, its output is applied to the actuator 13 via contact a of the switch 12 (normally, the 3 side is connected), and the output of the subtractor 102 becomes O (actual water supply flow rate). is controlled so that (matches demand 9). On the other hand, the minimum required pump flow rate corresponding to the pump rotation speed 7 or the pump discharge pressure 8 is given by the setter 14, and a value obtained by subtracting the pump water supply flow rate 5t from this is determined by the subtractor 103.

If this is positive, it corresponds to the flow rate that must flow to the recirculation valve 4, so this amount is sent to the recirculation valve 4 via the control calculator 112 and the a contact of the switch 15 (which is normally connected to the a side). is applied to the actuator 16, and the opening degree of the recirculation valve 4 is operated to a required value. During normal operation when the water supply flow rate is large, the recirculation valve 4 is fully closed.

FIG. 2 shows the characteristics of such a water supply system, where the curve β is the characteristic of the water supply pressure and r is the characteristic of the main steam pressure. As an example of the above-mentioned normal operation in which the water supply flow rate is large, in terms of the water supply pressure β, the operating point A for 100% flow rate is raised. If a load cutoff occurs during operation in this state of point A, the required water supply flow rate of the boiler becomes the water supply amount expressed by Fury.

At this time, the feed water pump discharge pressure 8 (FIG. 1) needs to be a point B1, which is the sum of the pressure increase on the boiler main steam side to the point A, which corresponds to the reduction in resistance due to the reduction in the feed water flow rate. #
) The water supply pump should have a driving force corresponding to point B. In the case of a conventional configuration with two 5Oqk water supply pumps, one is stopped at the same time as the load is cut off, and water is supplied by the remaining pump, but at point B (in Figure 2), 50% water supply Since the flow rate was higher than point B on the minimum required flow rate curve α of the pump and was within the normal operating range of the pump, there was no need to open the recirculation valve 4t. But 100-
In the case of a water supply pump, the required minimum flow f of the pump is represented by a curve α, and the pump discharge pressure is B.

If a pressure equivalent to
is required. Since efficient operation is at point B, the feedwater pump driving turbine 2 requires a driving force corresponding to point B0, and the recirculation valve 4 is opened to recirculate the flow rate corresponding to B and BI. is ideal. When the normal operation point is point C, when a load cutoff occurs, the water supply pump 1 and the drive turbine 2 turn on, requiring a driving force of 400, and the recirculation valve 4t opens, just as in the above explanation. Teri. Retil the flow rate corresponding to D.
It will make you l. In this way, when load interruption occurs,
Since the target values of the driving force of the water supply pump 1 and the opening degree of the recirculation valve 4 are uniquely determined according to the load just before that, in the embodiment shown in FIG. a function generator 18 that determines the opening degree of the control valve 3 and a recirculation valve 4;
A function generator 19 is provided to determine the opening degree of the switches 12 and 15t, and the switches 12 and 15t are moved to the b side when the load is cut off. Then, the operating point of the feed water pump moves to Bo or 00 point on the pump's required minimum flow rate (curve α) line, and the required recirculation flow rate B
(L B t , D@D s, etc. are obtained. An example of the characteristics of the function generator 19 is shown in Figure @3.

As described above, feedforward control is performed in order to cope with the extremely wide change in state quantity when the load is cut off, but after the system has stabilized for a certain period of time, switches 12 and 15 are returned to side a. It is common to return to normal water supply control (feedback control). Further, the function generators 18 and 19 that set the necessary opening degree of the regulating valve 3 and the opening degree of the recirculation valve 4 are used to set the equivalent water supply flow rate 5 or Water supply bo/pu ◎Rotation number 7,
Alternatively, the water supply pump discharge pressure can also be set to 8.

Fig. 4 shows another embodiment of the present invention, in which the normal control system is the same as Fig. 1, but when the load is cut off, the switch
2.15 are both connected to the b side, and the general operates as follows. That is, the required pump water supply flow rate (on the curve α in FIG. 2) is determined by the function generator 20 corresponding to the load 17 immediately before the cutoff, and the water supply pump is controlled by the function generator 21 using the corresponding regulating valve 3.
This is done by finding the degree of opening. On the other hand, the recirculation valve 40 is controlled by subtracting the boiler required water supply amount 22 from the required pump water supply flow rate using the subtractor 23 to obtain the required recirculation flow rate, and then determining the opening degree of the recirculation valve 4 corresponding to this using the function generator 24. Seek and do. Note that the function generator 24 calculates the required recirculation flow rate and pump rotation speed 7.
Alternatively, the accuracy can be increased as a function of two parameters: pump discharge pressure 8.

〔Effect of the invention〕

As is clear from the above embodiments, according to the present invention, 1
Even in a plant using a water pump with a capacity of 0.00m, the effect is that the boiler water flow rate and the required flow rate of the pump can be efficiently and reliably secured even during load interruption such as during isolated operation within the plant.

[Brief explanation of drawings]

Figure 1 is a diagram showing an embodiment of the present invention, Figure 2 is a diagram showing the characteristics of a water supply system, and Figure 3 is a diagram showing the characteristics of a function generator that sets the optimal opening degree of the recirculation valve according to the load. FIG. 4 is a diagram showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Water supply pump, 2... Water supply pump drive turbine, 3... Turbine adjustment valve, 4... Recirculation valve, 13.
... Adjustment valve actuator, 16 ... Recirculation actuator, 17 ... Load signal, 18 ... Load / adjustment valve opening function generator, 19 ... Load / Recirculation valve opening function generator, 20...Load/minimum required water supply pump flow rate function generator, 21...Feed water pump flow rate/regulating valve opening function generator, 22...Boiler required water supply flow rate at load cutoff, 23
... Subtractor, 24 ... Required recirculation flow rate/recirculation valve opening function generator.

Claims (1)

[Scope of Claims] 1. A boiler for a thermal power plant equipped with a feed water pump that has a recirculation path and whose required minimum flow rate during load interruption is greater than the boiler's required feed water flow rate during load interruption. In the water supply control device, the opening degree of the recirculation valve and the water supply in order to ensure the boiler required water supply flow rate and the required minimum flow rate of the water supply pump in response to the state variables of the power generation plant at the time of load interruption. A setting means is provided to set the driving force of the pump,
A boiler feed water control device, characterized in that, when a load interruption occurs, the driving force of the feed water pump and the opening degree of the recirculation valve are controlled by the output of the setting means. 2. The state quantity set forth in claim 1 is characterized in that the state quantity is the load amount immediately before the load disconnection occurs, the water supply flow rate by the water supply pump, the rotation speed of the water supply pump, or the discharge pressure of the water supply pump. Boiler water supply control device. 3. The setting means includes a function generator that sets the required small flow rate of the feed water pump according to the state quantity, and a function generator that subtracts the set value of the boiler required feed water flow rate from the output of the function generator. 2. The boiler feedwater control device according to claim 1, further comprising a recirculation flow rate setting device for determining a recirculation flow rate.