JPH02238187A - Supply water pump recirculation flow controller - Google Patents

Abstract

PURPOSE:To prevent water hammer phenomenon by opening a recirculation flow control valve disposed in a supply water pump recirculation line in a thermal power plant for a predetermined opening degree by a supply pump changing signal precedingly for making it possible to preheat valve exit side pipings of a steam line. CONSTITUTION:In a supply water system consisting of a supply water booster pump 3, a supply water pump 4, a supply water heating, etc., disposed in the middle of supply water pipings 2 for introducing condensed water deaerated by a deaerator 1 to a boiler, unillustrated, the supply water pump 4 is connected with the deaerator 1 by a supply water pump recirculation line 5 including a recirculation flow control valve 6. A control signal generated by a flow regulator 12 based on a deviation between the output of a flow detector 9 and the output of a set value generator 11 is sent to the recirculation flow control valve 6. In this case, an opening degree generator 14 is provided to which a supply water pump changing signal 13 is inputted, and its output is introduced to a signal changer 15 to be compared with a signal from the flow regulator 12, and its deviation signal is given to the flow control valve 6.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to a feed water pump recirculation flow control device used in power plants equipped with a feed water pump recirculation line.

(Prior art) In a thermal power plant, steam that has completed its work in a steam turbine becomes condensed water in a condenser, is deaerated in a deaerator, is heated in a feed water heater, and is heated by a feed water pump. It is then pressurized and reintroduced into the boiler.

The above-mentioned water supply pump must always ensure a minimum water supply flow rate due to its pump characteristics. Therefore, a water pump recirculation line is installed between the discharge side of the water pump and the deaerator, and when the water supply flow rate falls below a certain limit, a recirculation flow rate control valve inserted in the water pump recirculation line is installed. Open the
By circulating the insufficient flow rate, the flow rate of the water supply pump is kept at the minimum required flow rate.

Figure 3 shows the main parts of a conventional feed water pump recirculation flow rate control device. A booster pump 3, a water supply pump 4, a water supply heater (not shown), and the like are inserted.

A water pump recirculation line 5 that connects the water pump 4 and the deaerator 1 is a valve that connects a recirculation flow rate control valve 6 and the water supply pipe 2 on the inlet side of the water pump 4 and the water supply pipe 2 on the discharge side of the water pump 4. It is composed of an inlet side pipe 7 and a valve outlet side pipe 8 that connects the outlet side of the recirculation flow rate control valve 6 and the deaerator 1.

The water supply flow rate of the water supply pump 4 is detected by a flow rate detector 9, and the rotation speed of the water supply pump 4 is detected by a rotation speed detector 10. The output of this rotational speed detector 10 is led to a setpoint generator 11 .

The output of the flow rate detector 9 and the output of the set value generator 11 are led to a flow rate regulator 12 and compared, and their deviation is outputted to the recirculation flow rate regulating valve 6 as a control signal.

In the water supply pump recirculation flow rate control device having such a configuration, when the water supply flow rate is sufficiently large, the discharge flow rate of the water supply pump 4 exceeds the minimum required flow rate of the water supply pump 4, so that the water supply is caused to flow through the recirculation line 5. There is no need, and the recirculation flow control valve 6 is fully open. Further, in order to reduce energy loss, power plants are usually designed so that the recirculation flow control valve 6 is fully open when the power plant is under rated load.

Therefore, the recirculation flow WL control valve 6 is normally fully open, the water in the valve outlet side pipe 8 does not move, and its temperature is as low as atmospheric temperature.

On the other hand, the valve port side pipe 7 is directly connected to the water supply pipe 2,
A portion of the high-temperature, high-pressure hot water flowing through the water supply pipe 2 circulates within the valve inlet side pipe 7 due to turbulence and convection. Therefore, the water in the valve inlet side pipe 7 has a very high temperature.

Generally, when a sudden flow occurs in the pipe while the pipe is shielded, a water hammer phenomenon occurs at the resistance section at the rear of the pipe. Furthermore, when high-temperature water flows into low-temperature water, the high-temperature water is vaporized within the pipe and flows through the pipe as a two-phase flow of water and steam. In this case, if the piping is a vertical piping, the water pushed up by the steam falls instead of the steam, causing the water to collide with each other, resulting in a severe water hammer phenomenon.

In the case of FIG. 3, the recirculation flow rate control valve 6 has a fast valve opening speed, and the temperature difference before and after the valve is very large, so the water pump recirculation line 5 has the above-mentioned conditions for the occurrence of the water hammer phenomenon. This means that

Therefore, when switching the water supply pump 4 under the rated load condition, the water supply pump on the stop side must operate the recirculation flow rate control valve 6 rapidly and at a high opening degree in the process of reducing the water supply flow rate. However, in that case, a water hammer phenomenon will occur.

That is, as shown in FIG. 4, when the water supply flow mQ gradually decreases and becomes less than the minimum required flow rate, the recirculation flow rate control valve 6, which had been fully closed until then, begins to open (at time t
l) causes a water hammer phenomenon immediately after this opening operation. A chain line R indicates the opening degree of the recirculation flow rate control valve 6.

(Problems to be Solved by the Invention) As described above, when the water hammer phenomenon occurs in the water supply pump recirculation line 5, cracks occur in the valve inlet side piping 7 and valve outlet side piping 8, and the piping support and orifice (
(none of which are shown), or the recirculation flow rate control valve 6 may be damaged.

SUMMARY OF THE INVENTION An object of the present invention is to provide a water pump recirculation flow rate control device that solves the above-mentioned problems in the prior art and can prevent the water hammer phenomenon from occurring.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a water pump recirculation flow control device equipped with a water pump recirculation line, in which a recirculation flow rate control valve inserted in the water pump recirculation line is activated by a water pump switching signal. The water supply pump recirculation line is opened to a predetermined opening degree in advance to preheat the valve outlet side piping of the water supply pump recirculation line.

(Function) According to the water supply pump circular circulation flow rate control device of the present invention configured as described above, the water supply pump recirculation flow rate control valve is opened in advance by a certain opening degree in response to the switching signal of the water supply pump. As a result, high-temperature water also flows into the valve outlet side piping of the water pump recirculation line and is preheated, thereby preventing the occurrence of water hammer.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. In the following description, the same parts as in FIGS. 3 and 4 are denoted by the same reference numerals, and detailed description will be omitted unless necessary.

In FIG. 1, a water pump switching signal 13 is introduced into an opening generator 14. The output of this opening degree generator 14 is led to a signal switch 15, where it is compared with the signal from the flow rate regulator 12, and the recirculation flow rate control valve 6 is opened based on their deviation signal.

FIG. 2 shows the operation of the device shown in FIG. 1. When the feed water pump switching signal 13 is generated at the water pump switching point to, the recirculation flow rate control valve 6 is immediately advanced to a certain opening Ro. open. As a result, the high temperature water of the small melon also flows to the valve outlet side piping 8 of the water pump recirculation line 5, and the recirculation line 5 is warmed.

Meanwhile, the feed water flow fflQ gradually decreases, and when it reaches the time t1 when it reaches the minimum required flow rate, the recirculation flow rate control valve 6
By the operation of the signal switch 15, the opening degree is controlled by the flow rate controller 12, and increases step by step as shown by the curve R in FIG.

As described above, in the device of the present invention, the recirculation flow rate control valve 6 opens to a predetermined opening degree immediately after the input of the feedwater pump switching signal, and a small amount of high-temperature water flows into the feedwater pump recirculation line. The piping 8 is also gradually heated and is sufficiently preheated at the time of transition to opening control by the flow rate controller 12, so that the minimum required flow rate of the water pump is reached at time t1.
Even if the opening degree of the recirculation flow m control valve 6 is shifted to the flow rate controller 12, the water hammer phenomenon will not occur.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to reliably prevent the water hammer phenomenon from occurring in the feedwater pump recirculation line, and to ensure the health of the plant.

[Brief explanation of drawings]

Figure 1 is a system diagram showing the configuration of the main parts of the device of the present invention;
Figure 3 is a graph showing its operation, Figure 3 is a system diagram showing the configuration of the main parts of a conventional water pump recirculation flow control device, and Figure 4
The figure is a graph showing its operation. DESCRIPTION OF SYMBOLS 1... Deaerator, 2... Water supply piping, 3... Water supply booster pump, 4... Water supply pump, 5... Water supply pump recirculation line, 6... Recirculation flow rate control valve, 7...
Valve inlet side piping, 8... Valve outlet side piping, 9... Flow rate detector, 10... Rotation speed detector, 11... Set value generator, 12... Flow rate controller, 13. ...Water pump switching signal, 14...Opening degree generator, 15...Signal switching device. Juku t Figure applicant's agent Kazuo Sato 2 z

Claims (1)

[Claims] In a water supply pump recirculation flow rate control device equipped with a water supply pump recirculation line, a recirculation flow rate control valve inserted in the water supply pump recirculation line is opened to a predetermined opening degree in advance by a water supply pump switching signal, and the water supply pump A water supply pump recirculation flow rate control device, characterized in that it is configured to preheat a valve outlet side piping of a recirculation line.