JPH02192501A - Water feed control device during fcb of drum boiler - Google Patents

Abstract

PURPOSE:To prevent the excessive increase of a drum level due to the excessive feed of water by a method wherein simultaneously with the starting of FCB, a regulating valve for the feed of steam to a turbine for driving a boiler water feed pump is rapidly controlled for opening operation, and after the starting of the rise of a drum level, the valve is throttled according to a load and then returned to normal control. CONSTITUTION:A steam feed regulating valve 13 is rapidly controlled for opening to a set specified opening simultaneously with FCB (forced load cutoff). Lowering phenomenon of a drum level is stopped, and converted into a rise. A differentiator 40 raptures the rise phenomenon to control a switching device 42. A change rate controller 45 outputs a target value signal, outputted according to a load from a function generator 43, and an opening signal, corresponding to a rate of change single outputted according to a load from a function generator 44, to a steam feed regulating control derive part 12, and the opening of the regulating valve is controlled according to restoration of a drum level. When the drum level is restored to a value within an allowable deviation based on a given set value, an H/L monitor 41 raptures the restoration to switch a switching device 7, and transfer to drum level single element control corresponding to a drum level signal is effected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a feed water control device for a drum boiler during FCB (rapid load shedding), and particularly to control of steam supply to a turbine for driving a boiler feed water pump during FCB. Regarding.

[Conventional technology]

The amount of steam supplied to the turbine, which operates the boiler feed water pump that supplies water to the drum boiler, is controlled by controlling the opening degree of the steam supply control valve so that the drum level becomes a predetermined value.

Figure 4 shows a conventional water supply control device of this type.
1 is a subtractor, 2 is a P+I1 node (3 elements).

3 is P+I regulator (single element), 4 is adder, 5 is P+I
regulator, 6 is a switch (3 elements - single element), 7 is a switch,
8 is a switch (for hold), 9 is a function generator, 10 is an adder, and 11 is a switch (for hold).

Reference numeral 12 indicates a steam supply control valve operation drive unit, and 13 indicates a steam supply control valve.

In the water supply control device as described above, during FCB, P
At the same time as the CB, the opening of the steam supply control valve 13 is rapidly controlled to a specified opening to prevent the drum level from dropping (due to pressure increase due to turbine control valve throttling and air bubble contraction due to rapid fuel throttling). If the flow rate of feed water becomes larger than the flow rate of steam generated by the boiler when returning to normal control after that, the drum level will rise, and the drum level may rise excessively due to overshoot.

In feed water control using a turbine-driven boiler feed water pump, the difficulty in controlling the feed water during PCB is that the turbine oil steam, which is the driving steam source for the turbine that drives the boiler feed water pump, is lost at the same time as the PCB, so the steam of the zero-can boiler is lost. At this time, it is necessary to secure the driving steam source and control the steam supply control valve to the boiler feed water pump driving turbine.

[Problem to be solved by the invention]

In particular, conventional water supply control devices do not take into account excessive water supply after preventing a drop in the drum level during PCB, and there is a problem in which the drum level rises excessively.

Therefore, an object of the present invention is to provide a water supply control device that can not only prevent the drum level from decreasing during PCB but also prevent the drum level from rising excessively due to excessive water supply thereafter.

[Means to solve the problem]

In order to achieve this object, the present invention provides a feed water control system for Fe2 of a drum boiler using a turbine-driven boiler feed water pump, in which the steam supply control valve to the turbine for driving the boiler feed water pump is controlled at the same time as the start of PCB. Opening control is performed rapidly to a specified opening degree, and after the drum level starts to rise, the steam supply control valve is controlled to be narrowed down according to a rate of change determined according to the load, and then the control valve is returned to normal control. It is characterized by being equipped with a control circuit.

[Effect]

Since the steam supply control valve is rapidly opened to the specified opening at the same time as the PCB, the boiler feed water pump ensures a sufficient amount of water supply and suppresses a drop in the drum level. When the drum level stops decreasing and begins to rise, the steam supply control valve is throttled and controlled according to the rate of change determined according to the load, and then returns to normal control, so that the drum level due to excessive water supply is reduced. Excessive rise can be prevented.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to FIGS. 1 to 3.

Figure 2 is a system diagram of a steam turbine operating plant;
21 is a boiler, 22 is a turbine steam control valve, 23 is a high and intermediate pressure turbine, 24 is a low pressure turbine, 25 is a condenser, 26
．． 27 is a turbine-driven boiler feed pump, 28 is an electric motor-driven boiler feed pump, 29 is a feed water flow rate control valve, 3
0 is a turbine oil pipe, and 31 is a 2SH inlet steam pipe.

Reference numeral 13 denotes a steam supply control valve for the boiler feed water pump 26, 27 to the turbine for operation, which is the same as the conventional steam supply control valve described above with reference to FIG.

As a steam supply source to the driving turbine of the boiler feed water pump 26, 27, normally, turbine oil is used at a load of 45% or more, low-temperature reheated steam is used at a load of less than 45%, and in the case of Fe2, both of the above are used. It is also lost as steam, so it is 0.
Can boiler steam is used (switched over).

FIG. 1 is a block diagram of a water supply control device that controls the opening/closing operation of the steam supply control valve 13, and the same components as those of the conventional water supply control device described above with reference to FIG. 4 are given the same reference numerals. The explanation will be omitted.

40 is a differentiator that differentiates the amount of change in the drum level, and 41 is a H/L that monitors the level of the drum level relative to the set value.
A monitor, 42 a switch provided between the switch 7 and the switch 11, 43 a function generator that generates a target value signal according to the load, and 44 a function generator that generates a rate of change signal according to the load. 45 is a rate of change limiter.

Next, the control operation will be explained with reference to FIG.

The opening/closing operation of the steam supply control valve 13 is controlled by the switching device 7 so that the opening degree is set to the specified opening degree by the adder 10 at the same time as the PCB.
and is switched by the switch 42.

The steam supply control valve 13 is rapidly opened to this prescribed opening degree. At this time, the adder 10 adds the opening correction signal output from the function generator 9 according to the load and the current opening signal to generate a specified opening signal.・This specified opening signal becomes larger as the load becomes larger.

The drum level falls at the same time as the PCB, but as the opening degree of the steam supply control valve 13 increases and the water supply flow rate increases, the downward phenomenon eventually stops and begins to rise. The differentiator 40 captures this rising phenomenon and controls the switch 42, and provides the opening signal output from the rate of change limiter 45 to the steam supply control valve operation drive unit 12 to perform opening/closing operation control (narrowing operation control). Start.

At this time, the rate of change limiter 45 outputs an opening signal according to the target value signal output from the function generator 43 according to the load and the rate of change signal output from the function generator 44 according to the load. Recovery speed from the lowest point of drum level is slow for PCB under high load.

It is fast for PCB with low load. For this purpose, function generator 4
4 generates a change rate signal according to the load to control the opening degree of the adjustment valve in accordance with the recovery of the drum level.

When the drum level recovers to within the allowable deviation with respect to the predetermined set value, the H/L monitor 41 detects this and switches the switch 7 to switch to drum level single element control according to the drum level signal.

〔Effect of the invention〕

As described above, the present invention rapidly controls the opening of the steam supply control valve to the turbine for driving the boiler feed water pump to a specified opening at the same time as the start of PCB, and after the drum level starts to rise, the control valve is opened according to the load. Since the steam supply control valve is controlled in a narrow manner according to the rate of change, and then returned to normal control, it is possible to prevent the drum level from rising excessively due to excessive water supply.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the feed water control device during PCB of the drum boiler according to the present invention, Fig. 2 is a system diagram of a steam turbine operation plant, Fig. 3 is a control characteristic diagram, and Fig. 4 is a diagram of a conventional drum boiler. It is a block diagram of a water supply control device at the time of PCB. 12... Steam supply control valve operation drive unit. 13... Steam supply control valve, 40...
・Differentiator, 41...H/L monitor, 42・
......Switcher, 43.44...Function generator, 45...Change rate limiter. Part tv! J Fig. 2 Steam, 77D Fukai Fig. 3 O t Time According to the present invention, the custom-made conventional method has 1 or I River Fig. 4 Water supply flow rate God Ram and bell smoke mysterious sink amount 0 no entry into the supply sword

Claims (1)

[Claims] 1. In a water supply control device during FCB of a drum boiler using a turbine-driven boiler feed pump, at the same time as FCB starts, the steam supply control valve to the turbine for driving the boiler feed water pump is adjusted to a specified opening degree. A regulating valve operation control circuit that rapidly controls the opening operation, and after the drum level starts to rise, controls the steam supply regulating valve to narrow down according to a rate of change determined according to the load, and then returns to normal regulating operation control. A water supply control device for FCB of a drum boiler, characterized in that it is provided with: