JPH06257709A - Device for controlling level of drained water from supply water heater - Google Patents

Abstract

(57) [Summary] [Object] The present invention is to prevent fluctuation of the drain water level due to change of the drain discharge destination of the water heater and to prevent water hammer phenomenon in the pipe. It is to provide a control device. The present invention relates to a plurality of drain discharge systems for discharging the drain of a feed water heater, a drain water level control valve interposed in each of these drain discharge systems, and a water level controller for controlling the drain water level control valve. In the feed water heater drain water level control device provided with, since the water level controller is provided with a circuit for slightly opening the emergency drain water level control valve when the load drops, the drain discharge destination of the feed water heater when the load drops It is possible to prevent changes in the drain water level due to changes. As a result, the water hammer phenomenon in the pipe can be prevented and stable drain water level control can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed water heater drain water level control device for controlling the drain water level of a feed water heater provided in a power plant such as a thermal power plant.

[0002]

2. Description of the Related Art Generally, a power plant such as a thermal power plant is provided with a feed water heater for heating feed water by extraction steam from a turbine. A plurality of such feedwater heaters are provided between the condensate pump and the deaerator or between the feedwater pump and the boiler, and heat the feedwater supplied from the condensate pump to the deaerator or the feedwater pump to the boiler. It is designed to raise the temperature. The former is called a low-pressure feed water heater, from the condensate pump to a low-pressure first feed water heater, a low-pressure second feed water heater,
They are arranged in this order. Similarly, the latter is arranged in the order of the feed pump, the high-pressure first feed water heater, the high-pressure second feed water heater, .... Then, the drain of the feed water heater is discharged and collected to the next stage feed water heater or condenser.

FIG. 1 is a system diagram of a general feed water heater to which the present invention is applied. As shown in the figure, a plurality of drain discharge systems 10 and 11 are connected to the high-pressure third feed water heater 1, and the drains are normally fed to the next-stage feed water heater or the like and to a deaerator or the like when the load is low. Is discharged.

By the way, the drain discharge system 10, 11
The flow rate is controlled by the drain water level control valves 2 and 3 provided in each discharge system. In addition, each drain water level control valve 2,
Control of 3 is performed by the drain water level controller 4. As shown in FIG. 3, this drain water level controller 4 inputs a water level detection signal a from a drain water level detector 5 and outputs control signals b and c to the drain water level control valves 2 and 3 respectively. , 7
Is provided. The set value by each computing unit 6 and 7 is the drain water level control valve (next stage feed water heater line) 2 is usually the standard water level (hereinafter referred to as NWL), drain water level control valve (condenser line)
3 is NWL + a higher than NWL.

In such a drain water level control device,
The drain water level during normal operation is controlled to NWL by the drain water level control valve (next stage feed water heater line) 2, but the drain water level control valve (next stage feed water heater is used when the drain amount is large or the load is low. Line) pressure difference is too small to be discharged to the next stage feed water heater, the drain water level rises to N
Drain water level control valve (condenser line) when WL + a or more 3
Is controlled to NWL + α.

[0006]

By the way, at the time of start-up, the drain water level is controlled by the drain water level control valve (condenser row) 3, and the set value of the drain water level controller 4 is NWL + α higher than NWL. At this time, the drain water level control valve (row of the next-stage feed water heater) 2 is fully opened. After that, the load rises and the drain water level control valve (to the next stage feed water heater)
When the drain can be discharged to the next-stage feed water heater with only 2, the set value of the drain water level controller 4 becomes NWL, and in that state, the drain water level control valve (condenser line) 3 is fully closed. There is.

Further, when the load is lowered, the opposite of the above is true. However, when the drain water level control valve (next stage feed water heater row) 2 alone cannot discharge to the next stage feed water heater, the drain water level control valve (condenser) Line 3). At this time,
Since the drain with a low temperature stays in the primary side pipe of the drain water level control valve (condenser line) 3, the feed water is heated by the self-boiling of the stay drain due to the inflow of the drain having a higher temperature than the staying drain. Blow-up into the vessel may change the drain water level or cause a water hammer phenomenon.

The present invention has been made in view of the above circumstances, and its purpose is not only to prevent fluctuations in the drain water level due to changes in the drain discharge destination of the feed water heater, but also to perform stable drain control. Another object of the present invention is to provide a feed water heater drain water level control device capable of preventing a water hammer phenomenon in a pipe.

[0009]

To achieve the above object, the present invention provides a plurality of drain discharge systems for discharging the drain of a feed water heater, and a drain water level control valve provided in each of these drain discharge systems. In a feed water heater drain water level control device provided with a water level controller for controlling the drain water level control valve, the water level controller includes a circuit for slightly opening the emergency drain water level control valve when the load drops. Characterize.

[0010]

According to the present invention, since the water level controller is provided with a circuit for slightly opening the emergency drain water level control valve when the load drops, the drain water level can be changed by changing the drain discharge destination of the feed water heater when the load drops. Fluctuations can be prevented, which makes it possible to prevent the water hammer phenomenon in the pipe and to perform stable drain water level control.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a system diagram of an embodiment of a feed water heater drain water level control device to which the present invention is applied. In the figure, the feed water heater 1 is interposed in a condensate pipe or a feed pipe 8 from a condensate pump or a feed pump (not shown) to a deaerator or a boiler,
The feed water is heated by steam extracted from a turbine system (not shown) through the extraction pipe 9. As a discharge system for discharging the drain after heating, a next-stage feed water heater discharge system 10 and a condenser discharge system 11 are provided.
Each drain discharge system 10, 11 has a drain water level control valve 2,
3 is interposed. The drain water level control valves 2 and 3 are controlled by a drain water level controller 4.

The water level controller 4 inputs a water level detection signal a from a water level detector 5 for detecting the drain water level of the feed water heater 1 to the drain water level control valves 2 and 3 as shown in FIG. 2 (a). The computing units 6 and 7 that output the control signals b and c, the switching unit 13 that switches the valve opening of the drain water level control valve 3, and the upper limit that limits the upper limit value of the output of the computing unit 7 and the output of the switching unit 13. And a container 12.

The switching device 13 of the drain water level control valve (condenser line) 3 temporarily increases the load, and after reaching a certain load, changes the valve opening degree from 0% to the valve opening degree d% when the load decreases. Switch. The output of the switch 13 is input to the upper limiter 12 to limit the upper limit value of the output from the calculator 7 to be slightly opened, and the drain is discharged to the condenser.

Next, the operation of the present embodiment will be described with reference to the configuration diagram of the drain water level control device of FIG. 2A and the valve opening switching logic diagram of FIG. 2B. At startup, the drain water level is set to NWL by the drain water level control valve (condenser line) 3.
It is controlled to + α. At this time, the drain water level control valve (row of the next-stage feed water heater) 2 is fully opened, but the required amount of drain cannot be discharged because the differential pressure between the front and rear is small.

After that, when the load increases and the differential pressure between the front and the rear gradually increases, the drain water level control valve (to the next-stage feed water heater) 2
When the amount of drain that can be discharged is increased and can be discharged only by the control valve, the drain water level becomes NWL.

On the other hand, in the process of temporarily increasing the load and then stopping it, the process reverse to the above is performed. At this time, when the load rises to a certain load and then the load falls at a certain rate or more, the switching device 13 switches the valve opening degree from 0% to the valve opening degree d%.
Switch to. The output of the switch 13 is input to the upper limiter 12 to limit the upper limit value of the output from the computing unit 7 to be slightly opened, and the drain is also discharged to the condenser.

After that, if the load further decreases, the drain water level control valve (row of the next-stage feed water heater) 2 cannot control to NWL. Then, the drain water level rises, and the drain water level control valve (condenser line) 3 controls the drain water level to NWL + α.

As described above, according to the present embodiment, in the drain water level control of the feed water heater, the drain is forcibly opened before switching to recover the drain from the next stage feed water heater to the condenser at the time of load drop. As a result, it is possible to prevent the fluctuation of the drain water level and perform stable drain water level control. At the same time, the water hammer phenomenon in the pipe can be prevented. Note that a certain load, load drop rate, and valve opening degree d% can be arbitrarily determined in the actual plant.

[0019]

As described above, according to the drain water level controller for the feed water heater of the present invention, the output of the switching unit, the arithmetic unit, and the switching unit that slightly open the valve opening when the load falls on the water level controller. By providing an upper limiter that limits the upper limit value, the drain is forcibly opened slightly before it is recovered from the next-stage feed water heater to the condenser when the load drops, preventing fluctuations in the drain water level and ensuring stable drainage. It is possible to control the water level and prevent the water hammer phenomenon in the pipe.

[Brief description of drawings]

FIG. 1 is a system diagram of a general feed water heater to which the present invention is applied.

2 (a) is a configuration diagram of a water level controller of a feed water heater drain water level control device according to an embodiment of the present invention, and FIG. 2 (b) is a valve opening of the water level controller of FIG. 2 (a). Logic diagram of degree switching.

FIG. 3 is a configuration diagram of a water level controller of a conventional feed water heater drain water level control device.

[Explanation of symbols]

1 ... High-pressure third feed water heater, 2 ... Drain water level control valve, 3 ...
Drain water level control valve, 4 ... Drain water level controller, 5 ... Drain water level detector, 6, 7 ... Computing device, 8 ... Condensate pipe or water supply pipe,
9 ... Bleed pipe, 10 ... Next stage feed water heater discharge system, 11 ... Condenser discharge system, 12 ... Upper limiter, 13 ... Switching device.

Claims (1)

[Claims] 1. A plurality of drain discharge systems for discharging the drain of a feed water heater, a drain water level control valve provided in each of these drain discharge systems, and a water level controller for controlling the drain water level control valve. In the feed water heater drain water level control device, the water level controller includes a circuit for slightly opening the emergency drain water level control valve when the load drops.