JPH03271603A - Controlling device for boiler feed water pump - Google Patents

Abstract

PURPOSE:To improve the control characteristic of a differential pressure between an inlet port and outlet port for a flow control valve when the number of feed pumps driven is varied, by providing a control means whereby the control gain of a differential pressure-controlled device for the flow control valve is switched corresponding to the number of the boiler feed water pumps driven. CONSTITUTION:A control gain most suitable for the differential pressure control of a flow control valve 6A for a boiler feed water pump 5A, either at the operation of the one boiler feed water pump 5A or at the operation of two boiler feed water pumps 5A, 5B is respectively stored in differential pressure-controlled devices 16A1, 16A2 for the flow control valve 6A. In the same manner, a control gain most suitable for the differential pressure control for a flow control valve 6B corresponding to the operation of these boiler feed water pumps is also respectively stored in differential pressure-controlled devices 16B1, 16B2 for the flow control valve 6B. Contact points 17A1, 17A2 are contact points 17B1, 17B2 are respectively turned on or off corresponding to the operation of these boiler feed pumps, and the differential pressure-controlled devices 16A1, 16A2, 16B1, 16B2 are used for the control thereof. In this way, since the differential pressure control of each of the flow control valves 6A, 6B is done by the most suitable control again corresponding to the number of the boiler feed water pumps driven at that time, the control characteristic thereof is improved.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention provides a boiler feed water flow control valve for use in a steam power generation system that operates in such a way that the boiler outlet pressure also increases when the generator output increases. This relates to a boiler feed water pump control device that controls the differential pressure between the inlet and outlet pressures of the boiler.

(Prior Art) An example of a general steam power generation system is shown in Fig. 2. In the figure, steam generated from a superheater 1 of a boiler is supplied to a turbine 2 and gives rotational energy to a generator 3.
Generate electricity.

The steam that has completed its work in the turbine 2 is condensed into water by the condenser 4, and sent again to the boiler superheater by the boiler feed water pump 5 while the flow rate is adjusted by the boiler feed water control valve 6, where it becomes steam again. It is supplied to the turbine 2.

This boiler feed water control method is a method that stabilizes the adjustment of the boiler feed water flow rate by opening and closing the boiler feed water flow rate control valve 6 by controlling the differential pressure between the inlet pressure and the outlet pressure of the boiler feed water flow rate control valve 6 to a constant value. There is. An example of the control method will be explained with reference to FIG.

By inputting the flow rate adjusting valve hole pressure signal Ga and the flow rate adjusting valve outlet pressure S obtained from the flow rate adjusting valve inlet pressure detector 11 and the flow rate adjusting valve outlet pressure detector 12, respectively, to the adder 3. A flow rate rM regulating valve differential pressure signal C is obtained.

This flow rate control valve differential pressure signal C and the flow rate control valve differential pressure setting device 1
By inputting the flow rate adjustment valve differential pressure deviation signal e obtained by inputting the flow rate adjustment valve differential pressure setting signal d outputted from 5 to the adder 14 to the flow rate adjustment valve differential pressure controller 16,
A boiler feed water pump rotation speed command signal f is obtained.

Based on this boiler feed water pump rotation speed command signal f.

By controlling the rotation speed of the boiler feed water pump 5, the differential pressure between the inlet and the outlet of the flow rate regulating valve 6 is maintained at the value set by the flow rate regulating valve differential pressure setting device 15.

On the other hand, the boiler feed water flow rate deviation obtained by inputting the boiler feed water flow rate setting signal g output from the boiler feed water flow rate setting device 17 and the boiler feed water flow rate signal g obtained from the boiler feed water flow rate detector 18 to the adder 19 By inputting the signal i to the boiler feed water flow rate controller 20, a flow rate control valve opening command signal j is obtained.

By adjusting the opening degree of the flow rate control valve 6 using this flow rate control valve opening degree command signal j, the boiler feed water flow rate passing through the flow rate control valve 6 is maintained at the value set by the boiler feed water flow rate setting device 17. .

Here, as mentioned above, since the differential pressure between the inlet and the outlet of the flow rate control valve 6 is maintained at a constant value by the boiler feed water pump 5, the boiler feed water flow rate control by the flow rate control valve 6 can be performed stably. .

A conventional example in which a plurality of sets of boiler feed water control systems are used to control the differential pressure between the inlet and outlet of the boiler feed water flow control valve 6 using the boiler feed water pump 5 will be described with reference to FIG.

Note that FIG. 4 shows the case where two sets of the boiler feed water control systems are used, and the feed water flow rate control loop is omitted.

The two boiler feed water pumps 5A and 5B are independent of each other, each consisting of flow rate adjustment valve differential pressure setters 15A and 15B, adders 13A and 13B, adders 14A and 14B, and flow rate adjustment valve differential pressure controllers 16A and 16B. It is controlled by boiler feed water pump rotation speed command signals fA and fB, which are outputs of the flow rate adjustment valve differential pressure control system.

The control gain of the flow rate adjustment valve differential pressure controller 16A is a constant value regardless of whether the boiler feed water pump 5B is in operation or stopped, and the control gain of the flow rate adjustment valve differential pressure controller 16B is:
This value is constant regardless of whether the boiler feed water pump 5A is in operation or stopped.

(Problem to be Solved by the Invention) The rotational speed of the boiler feed water pump 5 in FIG. 3, the boiler feed water flow rate, and the inlet pressure of the boiler feed water flow rate control valve 6 have the interrelationship shown in FIG. 5. .

That is, in FIG. 5, the characteristic curves LR, LR, LR
2゜LR, LR, LRs are the rotational speeds of the boiler feed pump 5 at constant values R, , R1, R2, R, , R,
, R5 and shows the inlet pressure of the boiler feed water flow rate control valve 6 when the boiler feed water flow rate is changed.

The characteristic curve LCC shows the relationship between the boiler feed water flow rate and the inlet pressure of the boiler feed water flow rate control valve 6 when the opening degree of the boiler feed water flow rate control valve 6 is kept constant and the rotation speed of the boiler feed water pump 5 is varied. There is.

ao+alta2+affta4t”S is characteristic 4!
The rotation speed of the boiler feed pump 5 on the LCC is R.
0R work, R2, R□, R4°R9 are shown.

On the other hand, in the steam power generation system shown in FIG. 2, as the output of the generator 3 increases after the plant is started, the steam pressure at the outlet of the superheater 1 is generally increased, as shown in FIG. 6, for example. ing. That is, after the plant starts up, the outlet pressure of the superheater 1 is kept constant until the output of the generator 3 is 1,
After the output of generator 3 exceeds rie, the superheater l until υ2
outlet steam pressure.

Increase in proportion to the output of generator 3, then superheater l
Let the outlet steam pressure of P2 be constant.

Now, the boiler feed water pump 5 having the characteristics shown in FIG. 5 is incorporated into two sets of boiler feed water control systems as shown in FIG. If the power generation system is operated such that the relationship between the output of the generator 3 and the steam pressure at the outlet of the superheater 1 is as shown in FIG. 6, the following problems will occur. This will be explained with reference to FIG.

The characteristic curve LL is shown in Fig. 4 when the boiler feed water control is performed using only one system of boiler feed pumps, that is, when the boiler feed water pump 5A is stopped and the boiler feed water flow rate control valve 6A is fully closed, or when the boiler feed water pump 5B is stopped and the boiler feed water flow control valve 6A is fully closed. This is the relationship between the boiler feed water flow rate and the inlet pressure of the boiler feed water flow rate control valve 6 when the boiler feed water control is performed with the boiler feed water flow rate control valve 6B fully open.

The output of the generator 3 is approximately proportional to the boiler feed water flow rate, and the boiler feed water flow rates Q, , Q2 are values when the output of the generator 3 is V□l''2 in FIG. 6, respectively.

In addition, the inlet pressure of the boiler feed water flow rate control valve 6 when the boiler feed water flow rate is Q + Qz is the superheater 1 shown in Fig. 6, respectively.
The output steam pressure is approximately equal to P + pz.

In FIG. 4, the characteristic curve LL' shows the case where boiler water supply control is performed using two systems of boiler feed pumps, that is,
A boiler in which boiler feed water pumps 5A and 5B and boiler feed water flow rate control valves 6A and 5B are used, and boiler feed water control is performed so that the boiler feed water flow rates passing through boiler feed water flow rate control valves 6^ and 6B are equal. Water supply flow rate and
This is the relationship with the inlet pressure of the boiler feed water flow rate control valve 6.

The boiler feed water flow rate passing through the boiler feed water pump 5A or 5B is 2 compared to when operating with the ■ system boiler feed water pump.
When the boiler feed water pump in the system is operated, it is halved, so the characteristic curve LL' has a shape in which LL has moved to the left, so that Q□=20' and Q2=202'.

Points a and las' are points on the characteristic curves LL and LL', respectively, where the rotation speed of the boiler feed pump 5A or 5B becomes R5.

Also, the characteristic curves LCC and LCC are respectively at point a.
The rotation speed of the boiler feed water pump 5A or 5B is changed while the opening degree of the boiler feed water flow rate control valve 6A or 6B passing through s185' is kept constant.

Also, a4184' are characteristic curves LCC1 and LC, respectively.
C,' is the point where the rotation speed of the boiler feed pump 5A or 5B becomes R4.

That is, in the state of aslas', if the rotation speed of the boiler feed water pump 5A or 5B is changed from R5 to R4 while the opening degree of the boiler feed water flow rate control valve 6A or 6B is maintained, the state becomes a4184', and the boiler at this time The change in inlet pressure of the water supply flow rate control valve 6A or 6B is Δ, respectively.
P, ΔP'.

Obviously, since ΔP<ΔP', the change in the inlet pressure of the boiler feed water flow rate control valve 6A or 6B with respect to the change in the rotation speed of the boiler feed water pump 5A or 5B at point 84' is equal to point a4.
It is thicker than that in .

Therefore, in the conventional device, if the control gain of the flow rate adjustment valve differential pressure controller 16A or 16B in Fig. 4 is set to the stable control limit value of the boiler feed water pump operation of the system There was a problem in that when switching to boiler feed water pump operation, differential pressure control between the inlet and outlet of the boiler feed water flow rate control valve 6A or 6B became unstable.

On the other hand, if the control gain of the flow rate adjustment valve differential pressure controller 16A or 16B is adjusted to achieve optimal control when operating the boiler feed water pump of system 2, the above difference will occur when switching to operation of the boiler feed water pump of system 1. There was a problem that the response of pressure control was slow.

Therefore, an object of the present invention is to improve the control characteristics of the differential pressure between the inlet and the outlet of the flow control valve when the number of boiler feed pumps in operation is changed.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention is provided with a control means for switching the control gain of the flow rate regulating valve differential pressure controller depending on the number of operating boiler feed pumps. be.

(Function) With the above configuration, even if the number of boiler feed water pumps in operation is changed while the boiler outlet steam output is being increased at the same time as the generator output is increasing after the plant is started, each boiler feed water pump is Flow control valve differential pressure control can be performed optimally.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a boiler feed water pump control device in a case where there are two boiler feed water pumps according to an embodiment of the present invention.

In this figure, the same parts and corresponding parts as in FIG. 4 are given the same reference numerals.

The flow control valve differential pressure controllers 16A and 16A2 control the differential pressure of the flow rate control valve 6A of the boiler feed water pump 5A when only one boiler picture pump 5A is in operation and when two boiler feed pumps 5A and 5B are in operation. The optimal control gain is stored for each.

Similarly, the flow rate regulating valve differential pressure controllers 16B and 16B2 indicate the difference between the flow rate regulating valve 6B of the boiler feed water pump 5B when only one boiler feed pump 5B is in operation and when two boiler feed pumps 5A and 5B are in operation. The optimum control gains for pressure control are stored respectively.

Contacts 17A and 17A2 are used when only one boiler feed pump 5A is in operation, and when only one boiler feed pump 5A is in operation, respectively.
, will be closed when two 5B units are in operation.

Similarly, contacts 17B and 17B2 are closed when only one boiler feed pump 5B is in operation, and when two boiler feed pumps 5A and 5B are in operation, respectively.

Therefore, when only one boiler feed pump 5A is operated, contact 1
Only the section 7A is closed, and the flow rate adjustment valve differential pressure controller 16A is used to control the boiler feed pump 5A.

Similarly, when only one boiler feed pump 5B is in operation, only the contact 17B□ is closed, and the flow rate adjustment valve differential pressure controller 16B□ is used to control the boiler feed water pump 5B.

Also, when operating two boiler feed pumps 5A and 5B,
Contact points 17A2 and 17B2 are closed, and flow rate adjustment valve controllers 16A2 and 16B2 are used to control boiler feed water pumps 5A and 5B, respectively.

In this way, the flow rate control valve differential pressure controllers 16A, 16A2 and 16B, and 16B2 are switched and operated according to the number of boiler feed pumps 5A and 5B in operation, so the flow rate control valves 6A, 16B2 are operated by switching. 6B differential pressure control can now be performed with the optimum control gain commensurate with the number of boiler feed pumps in operation at that time.

This improves the controllability of differential pressure control of the flow rate regulating valve.

In addition, although the above-mentioned actual cross-sectional example has been explained by taking as an example the case where two boiler feed pumps are in operation, the present invention is not limited to this, and it is clear that the present invention can be applied to two or more boiler feed pumps.

[Effects of the Invention] As explained above, according to the present invention, even when the number of operating boiler feed water pumps is changed while the boiler outlet steam pressure is being increased at the same time as the generator output is increasing after the plant is started, It becomes possible to effectively control the differential pressure of the flow rate regulating valve of each boiler feed pump.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a boiler feed water pump control device according to an embodiment of the present invention, Fig. 2 is a block diagram for explaining the outline of a steam power generation system, and Fig. 3 is a block diagram for explaining the outline of a steam power generation system. Figure 4 is a block configuration diagram of a boiler feed water pump control device for explaining the conventional flow control valve differential pressure control when two boiler feed pumps are installed; The figure is a graph to explain the relationship between the rotation speed of the boiler feed water pump, the flow rate control valve inlet pressure, and the boiler feed water flow rate. Figure 6 shows a steam power generation system that increases the boiler outlet pressure as the generator output increases at the time of plant startup. FIG. 7 is a graph diagram for explaining that the controllability of the flow rate regulating valve differential pressure control deteriorates when the number of operating boiler feed pumps is changed. 5. Boiler feed water pump, 6. Boiler feed water flow rate control valve, 16. Stream i control valve differential pressure controller.

Claims (1)

[Claims] In a plurality of boiler water supply systems having boiler feed water pumps and boiler feed water flow rate control valves for supplying boiler water, each of the boiler feed water pumps is configured such that the differential pressure between the outlet and inlet of each of the boiler feed water flow rate control valves becomes a predetermined value. a plurality of flow rate adjustment differential pressure controllers each having an optimal control gain according to the number of operating units of the plurality of boiler water supply systems for controlling each of the boiler feedwater pumps, respectively; A boiler feed water pump control device comprising: a switch for selecting one of the plurality of flow rate adjustment differential pressure controllers according to the number of units in operation.