JPH09280504A - Predictive detector for generation of swelling and controller for feed water of boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the level of a steam separator from being lowered owing to the generation of a swelling by providing a delay timer for receiving the output of a set/reset device, receiving a furnace passing flow rate signal after the joint of a boiler water feed line and a furnace recirculating line, resetting and inputting the output. SOLUTION: First high signal detectors 40a to 40c to which the valve opening signals 16as to 16cs of respective level control valves 16a to 16c are inputted send the outputs to an AND element 42 when input values are not lower than a prescribed value. When the AND element 42 simultaneously receives the outputs of a timer 43 and the AND element 42, it sends a set signal to a set/ reset device 46. A second high signal detector 44 to which a furnace passing flow rate signal 26s from a furnace passing flow rate detector 26 is inputted outputs the input when the input value is not lower than a prescribed value. A delay timer 47 receives the output of the set/reset device 46, delays the output by time required for increasing the flow rate of a water feed pump, and outputs the delayed output. When a second AND element 45 receives these signals at the same time, it sends a reset signal to the set/reset device 46.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a swelling occurrence prediction detection device and a boiler feedwater control device applied to a pressure once-through boiler.

[0002]

2. Description of the Related Art A system diagram of a conventional transformer once-through boiler is shown in FIG. The water in the condenser 1 passes through a condensate booster pump 2, a condensate pump 3, a low pressure feed water superheater 4, a deaerator 5, a plurality of boiler feed water pumps 6, a plurality of feed water control valves 17, and a high pressure feed water superheater 7. Sent to. Further, the high-pressure feed water superheater 7 to the economizer 8, the furnace evaporation pipe 9, the furnace outlet brackish water separator 10, the superheater 1
1 is sequentially sent to the high-pressure turbine 12.

The drain of the furnace outlet brackish water separator 10 is sent to the outlet of the high pressure feed water superheater 7 through a brackish water separator drain tank 13, a furnace recirculation pump 14, and a furnace recirculation flow control valve 15 in this order. Further, the water is branched from the outlet of the drain tank 13 and sent to the condenser 1 through the plurality of brackish water separator drain tank level control valves 16.

In the figure, 51 is a furnace recirculation line, and 52 is
Is the water supply line.

FIG. 5 shows a controller for the water supply system. The output of the load indicator 21 is an adder 22, a high selector 23, and a subtractor 2.
5, and is sequentially sent to the feedwater control valve 17 or the boiler feedwater pump 6 through the PI regulator 26. The output of the main steam pressure control device 20 is sent to the adder 22. Further, the output of the minimum water supply flow rate command device 24 is sent to the high selector 23.

[0006] The output of the furnace flow rate detector 26 provided in the line after the merging of the water supply line 52 and the furnace recirculation line 51 is sent to the subtractor 25.

In the above, the load indicator 2 is added by the adder 22.
The load index signal from No. 1 and the boiler pressure control correction signal from the main steam pressure controller 20 are added.

Next, the higher selector 23 selects this signal and the higher one of the minimum feed water flow rate command signals required for the transformer once-through boiler from the minimum flow rate commander 24 and outputs it to the subtractor 25. The subtracter 25 detects this signal and the furnace flow rate detector 2
The deviation from the furnace flow rate signal 26s from 6 was calculated and P
It is sent to the I regulator 26. A control signal is sent from the PI controller 26 to the water supply control valve 17 or the boiler water supply pump 6,
The flow rate through the furnace is adjusted so that the deviation becomes zero.

FIG. 6 shows a control device of the furnace recirculation system.
The output of the drain level meter 28 of the brackish water separator drain tank 13 is sent to the flow rate command function unit 29 and the drain valve opening command function units 32, 33, 34. The output of the flow rate command function unit 29 is sent to the furnace recirculation flow rate control valve 15 through the subtractor 30 and the PI controller 31 in sequence. The outputs of the drain valve opening command function units 32 to 34 are sent to the respective brackish water separator drain tank level control valves 16a to 16b.

In the above, the flow rate command function unit 29 receives the output of the drain level meter 28 and outputs the recirculation flow rate command signal having the characteristic shown in FIG. The subtractor 30 receives this signal and the output of the recirculation flow rate detector 27, and sends a deviation signal to the PI controller 31. A recirculation valve opening control signal is sent from the PI controller 31 to the furnace recirculation flow rate control valve 27, and the recirculation flow rate is adjusted so that the deviation becomes zero. That is, the flow rate control valve 27 is opened when the drain level becomes α or higher, and the valve opening is adjusted so that the recirculation flow rate becomes 20% when the drain level becomes β or higher.

Further, a drain valve opening command function unit (for A valve)
The characteristics of 32, (for B valve) 33, and (for C valve) 34 are as shown in FIG. 8, and the drain level is higher L ₁
When the above is reached, the drain tank level control valve (A valve) 16a
Is opened, and the drain is also flown to the condenser 1 side to adjust the level. For example, when the drain level is am, the drain tank control valves 16a (A valve) and 16b (B valve) are fully opened.

As shown in FIG. 9, a transformer once-through boiler which operates by continuously changing the boiler pressure from a subcritical pressure to a supercritical pressure depending on a load, particularly in a subcritical pressure operating region at low load, In order to protect the tube of the furnace by the boiling phenomenon in which water and steam coexist, a velocity exceeding the critical weight flow rate in the supercritical pressure region is required. Therefore, a circuit (not shown) recirculates the furnace outlet fluid, that is, a part of the drain of the brackish water separator 10, mixes it with the water supply from the water supply pump 6, and keeps the flow rate passing through the furnace at the above limit flow rate. Further, the relationship of the furnace feed water flow rate to the load is expressed as shown in FIG. 10, and the load flow rate is maintained at the so-called minimum feed water flow rate, that is, the above-mentioned limit weight flow rate up to about 30% of the load. After that, the water supply increases proportionally as the load increases, the furnace recirculation flow rate becomes 0, and the entire amount is supplied from the water supply pump 6.

[0013]

Generally, when the boiler water in the furnace transitions from the saturated water to the brackish water mixing region a short time after the burner is ignited at subcritical pressure at the time of boiler start-up, the air bubbles rapidly heated As the specific volume increases and the volume expands,
Pushing up the canned water, the level of the drain tank rises sharply,
A so-called swelling phenomenon occurs.

However, after the can water pushed up is discharged by the water drain valve, the water supply inside the furnace sharply decreases, so that the drain level drops sharply and the water drain valve is fully closed, and further the furnace is re-opened. The circulation flow rate also drops sharply. At this time, the above-mentioned water supply control system operates to increase the flow rate of the water supply pump in order to secure the minimum water supply amount, but the follow-up is delayed, and as a result, the minimum water supply flow rate is interrupted.

Such a decrease in level leads to an emergency stop of the recirculation pump, and a decrease in the flow rate of the feed water leads to an emergency stop of the boiler in terms of boiler furnace protection. In order to prevent this, in general, careful monitoring of the operator can be performed to manually open the water supply control valve 17 in accordance with the swelling sign to prevent the level decrease and the water supply flow rate decrease. However, the operating procedure was extremely complicated, and it was practically impossible.

[0016]

The present invention employs the following means to solve the above-mentioned problems.

(1) A boiler ignition signal of a once-through boiler having a brackish water separator drain tank, a furnace recirculation line connected to the brackish water separator drain tank, a level control line having a level control valve, and a boiler feed water line. And a first high signal detector that receives the opening signal of the level control valve and outputs a predetermined time.
A first AND element that receives the output of the timer and the first high signal detector, a set-reset device that receives the output of the AND element at a set input, a delay timer that receives the output of the set-reset device, and the boiler A second high signal detector for receiving the signal of the flow rate through the furnace after joining the water supply line and the furnace recirculation line, and an output for receiving the outputs of the delay timer and the second high signal detector and inputting the outputs to the set reset device. A swelling occurrence prediction detection device comprising a second AND element for sending to.

In the above, when the boiler is started, the boiler ignition signal is turned on. Upon receiving this signal, the timer outputs a predetermined time corresponding to the time when swelling occurs.

On the other hand, since the valve opening degree of the level control valve increases with the occurrence of swelling, the first high signal detector for inputting this signal outputs when the input is above a predetermined value. The first AND element sends a set signal to the set / reset device when these signals are simultaneously input. The set / reset device is brought into a set state by this signal and outputs a swelling signal.

Further, the flow rate signal through the furnace increases to suppress swelling. The second high signal detector which inputs this signal outputs when the input is equal to or higher than a predetermined value.

On the other hand, the delay timer receives the output of the set / reset device, delays the time required for the feed water pump flow rate increasing operation, and outputs it. The second AND element sends a reset signal to the set / reset device when these signals are simultaneously input. The set / reset device is reset by this signal.

As described above, the occurrence of swelling at the time of starting the boiler can be easily and accurately predicted and detected.

(2) The brackish water separator drain of the once-through boiler having a brackish water separator drain tank, a furnace recirculation line having a flow rate control valve connected to the brackish water separator drain tank, and a level control line having a level control valve A flow rate command function unit that receives the drain level signal of the tank, a subtractor that receives the output of the flow rate command function unit and the furnace recirculation flow rate signal of the furnace recirculation line, and the furnace recirculation line that receives the output of the subtractor In the boiler feed water control device having a PI controller for sending a recirculation valve opening control signal to the flow control valve of the above, a change rate switch inserted between the flow rate command function unit and the subtractor and the output are changed by the same. A reduction flow signal device for sending to the input end of the rate changeover switch, and a swelling occurrence prediction detection device of the above (1) for sending output to the control input end of the same rate changeover switch. Boiler water supply control device.

In the above, normally, the changeover switch with change rate receives and outputs the output of the flow rate command function unit, and the PI control unit regulates the flow rate control valve.

When a swelling symptom occurs and the output of the swelling occurrence prediction detection device is sent to the change rate changeover switch, the change rate changeover switch switches the input at a predetermined change rate and outputs the reduced flow rate signal device. Is output. Since the reduced flow rate signal device outputs a flow rate command signal obtained by subtracting the feed pump flow rate to be increased from the normal recirculation flow rate, this signal is sent to the subtractor. A deviation signal is generated by the subtractor, and a recirculation valve opening control signal is sent to the flow control valve via the PI controller. The flow control valve is throttled according to the input, and the recirculation flow rate decreases.

The flow rate of the water supply pump is increased by this decrease. This increase will prevent the brackish water separator from lowering its level after completion of swelling.

In this way, swelling of the boiler is prevented.

(3) A load indicator for outputting a load indicator signal of a once-through boiler having a feed water line having a boiler feed water pump and a feed water control valve and a furnace recirculation line, and a main steam pressure control for outputting a boiler pressure correction signal. A device, a high selector receiving the output signal of the output of the load indicator and the main steam pressure control device and the output of the minimum flow indicator, and the furnace flow rate signal after the confluence of the water supply line and the furnace recirculation line and the above In a boiler feedwater control device having a subtractor for receiving the output of the high selector and a PI controller for receiving the output of the subtractor and sending a control signal to the boiler feedwater pump or the feedwater control valve, the minimum flow rate commander and A change rate switching device inserted between the high selectors, and an increase flow signal device that sends an output to the input terminal of the same change rate switching device,
Send the output to the control input terminal of the switch with the same rate of change (1)
Boiler water supply control device including the swelling occurrence prediction detection device.

In the above, the changeover rate changer normally receives and outputs the output of the minimum flow rate indicator. The high selector receives this signal and the addition signal of the output of the load indicator and the main steam pressure control device, and outputs the higher one. The subtractor outputs a deviation signal from this signal and the output of the furnace passage flow rate detector.
The PI controller outputs a control signal from this deviation signal to control the flow rate of the water supply line.

When a swelling symptom occurs and the output of the swelling occurrence prediction detection device is sent to the change rate changeover switch, the change rate changeover switch switches the input at a predetermined change rate, and outputs the increase flow rate signal device. Is output. The increased flow rate signal device outputs the feedwater pump flow rate (minimum flow rate + α) signal to be increased.

This output is sent to the subtractor via the high selector. A deviation signal is generated by the subtractor, and a control signal is sent to the boiler feed water pump or the feed water control valve via the PI adjuster. In response to this control signal, the boiler water supply pump or the water supply control valve operates and the flow rate of the water supply line increases.

This increase prevents the level reduction of the brackish water separator after completion of swelling in a preventive manner.

In this way, swelling of the boiler is prevented.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) An embodiment of the present invention 1 will be described with reference to FIG. The parts described in the conventional example are assigned the same reference numerals, and the description thereof will be omitted. The parts related to the present invention will be mainly described.

Brackish water separator drain tank level control valve 16
a, 16b, 16c valve opening signals 16as, 16bs,
16cs is the first high signal detectors 40a, 40, respectively.
b, 40c. First high signal detectors 40a-4
The output of 0c is sent to the set input terminal of the set / reset device 46 via the OR element 41 and the first AND element 42. Further, the boiler ignition signal 43s is sent to the AND element 42 via the timer 43.

The output of the furnace flow rate detector 26 is sent to the reset terminal of the set / reset device 46 via the second high signal detector 44 and the second AND element 45. The output of the set / reset device 46 passes through the delay timer 47 and the AND element 4
Sent to 5.

In the above, when the boiler is started, the boiler ignition signal 43s is turned on. Receiving this signal, the timer 43 outputs a predetermined time corresponding to the time when swelling occurs.

On the other hand, since the level control valves 16a to 16c increase in valve opening with the occurrence of swelling,
The first high signal detectors 40a to 40c, to which the valve opening signals 16as to 16cs are input, output when the input is a predetermined value or more. These outputs are sent to the AND element 42 via the OR element 41. AND element 42 ANDs timer 43
When the outputs of the elements 42 are simultaneously input, a set signal is sent to the set / reset device 46. The set / reset device 46 is brought into a set state by this signal and outputs the swelling signal 46s.

Further, the furnace passage flow rate signal 26s from the furnace passage flow rate detector 26 increases to suppress swelling. The second high signal detector 44, which receives this signal, outputs it when the input is above a predetermined value.

On the other hand, the delay timer 47 receives the output of the set / reset device 46, delays the time required for the feed water pump flow rate increasing operation, and outputs the delayed flow. The second AND element 45 sends a reset signal to the set / reset device 46 when these signals are simultaneously input. The set / reset device 46 is reset by this signal.

As described above, the occurrence of the swelling sign at the time of starting the boiler can be easily and accurately detected.

(2) An embodiment of the present invention 2 will be described with reference to FIG. The parts described in the conventional example are assigned the same reference numerals, and the description thereof will be omitted. The parts related to the present invention will be mainly described.

The output of the flow rate command function unit 29 is sent to the subtractor 30 via the changeover switch 48. The output of the reduced flow rate signal device 49 is sent to the input terminal of the changeover rate changeover device 48. Further, the output 46s of the swelling occurrence prediction detection device of the above (1) is sent to the control input terminal of the changeover rate changer 48.

In the above, the switching unit with change rate 4 is usually used.
Reference numeral 8 receives and outputs the output of the flow rate command function unit 29, and the PI control unit 31 adjusts the flow rate control valve 15.

When swelling occurs and the output 46s of the swelling occurrence prediction detection device is sent to the change rate changeover switch 48, the change rate changeover switch 48 switches the input at a predetermined change rate, and the reduced flow signal 49. Output the output of. The reduced flow rate signal device 49 outputs a flow rate command signal (for example, 20% (recirculation flow rate) -15% = 5% when it is desired to increase 15%) by subtracting the feed pump flow rate to be increased from the normal recirculation flow rate. Therefore, this signal is sent to the subtractor 30. Subtractor 3
A deviation signal is generated at 0, and a recirculation valve opening control signal is sent to the flow control valve 15 via the PI controller 31. The flow control valve 15 is throttled according to the input, and the recirculation flow rate decreases.

On the other hand, by the control system of the boiler feed pump 6,
The water supply pump 6 operates so that the flow rate of the water supply pump increases by this decrease. This increase prevents the brackish water separator 10 from lowering in level after the swelling is completed.

In this way, swelling of the boiler is prevented, and stable startup is possible.

(3) An embodiment of the present invention 3 will be described with reference to FIG. The parts described in the conventional example are assigned the same reference numerals, and the description thereof will be omitted. The parts related to the present invention will be mainly described.

The output of the minimum flow rate commanding device 24 is sent to the high selector 23 via the changeover switch 48. Further, the output of the increase flow rate device 50 is sent to the input terminal of the changeover rate changeover device 48.

Further, the output 46s of the swelling occurrence prediction detection device of the above (1) is sent to the control input terminal of the changeover switch 48.

The output of the high selector 23 is sent to the boiler feed water pump 6 or the feed water control valve 17 through the subtractor 25 and the PI regulator 26 in sequence.

In the above, normally, the changeover rate switch 48
Receives and outputs the output of the minimum flow rate indicator 24. The high selector 23 receives this signal and the addition signal of the output of the load indicator 21 and the main steam pressure control device 20, and outputs the higher one.
The subtractor 25 outputs a deviation signal from this signal and the output of the furnace passage flow rate detector 26. The PI controller 26 outputs a control signal from this deviation signal to control the flow rate of the water supply line 52.

When a swelling sign is generated, the output 46s of the swelling occurrence prediction detection device is changed to a changeover switch 48.
Then, the change rate changeover switch 48 switches the input at a predetermined change rate and outputs the output of the increased flow rate signal device 50. The increase flow rate signal device 50 outputs a signal of the feed pump flow rate (minimum flow rate + flow rate pushed out by swelling) to be increased.

This output passes through the high selector 23 and the subtractor 25.
Sent to A deviation signal is generated by the subtractor 25, and a control signal is sent to the boiler feed water pump 6 or the feed water control valve 17 via the PI adjuster 26. In response to this control signal, the boiler water supply pump 6 or the water supply control valve 17 operates, and the water supply line 5
The flow rate of 2 increases.

This increase prevents the brackish water separator 10 from lowering in level after the swelling is completed.

In this way, swelling of the boiler is prevented and stable startup is possible.

In the present embodiment, the above-mentioned (2) is a route in which the recirculation flow rate is reduced, and as a result, the feed water flow rate is compensated for indirectly, so to speak, the flow rate is directly controlled by the direct water feed pump or control valve. Responsiveness is fast because it increases. Further, the value of the feed water flow rate to be increased is the so-called recirculation flow rate in (2), which is a set value given by the flow rate command function unit 29 of about 2
While the range is limited to 0%, the increase flowmeter 50 is not limited and has the effect of allowing a wide range of set values.

[0058]

As described above, the present invention has the following effects.

(1) The swelling occurrence prediction detection device accurately predicts the occurrence of a swelling phenomenon.

(2) Due to the output of the swelling occurrence prediction detection device, the flow rate of the water supply line is rapidly increased, and the decrease in the level of the brackish water separator due to the occurrence of swelling is suppressed. Therefore, stable startup of the boiler can be realized.

[Brief description of drawings]

FIG. 1 is a configuration system diagram of an embodiment of the present invention 1. FIG.

FIG. 2 is a configuration system diagram of an embodiment of the present invention 2.

FIG. 3 is a configuration system diagram of an embodiment of the present invention 3;

FIG. 4 is a system diagram of a conventional transformer once-through boiler.

FIG. 5 is a configuration system diagram of a control device for a water supply system of the conventional example.

FIG. 6 is a configuration diagram of a conventional furnace recirculation system.

FIG. 7 is an operation explanatory view of the conventional example.

FIG. 8 is an operation explanatory view of the conventional example.

FIG. 9 is an explanatory view of the operation of the conventional example.

FIG. 10 is an operation explanatory view of the conventional example.

[Explanation of symbols]

1 Condenser 2 Condensate booster pump 3 Condensate pump 4 Low pressure feed water superheater 5 Deaerator 6 Boiler water feed pump 7 High pressure feed water heater 8 Coal saver 9 Furnace evaporator 10 Furnace outlet brackish water separator 11 Superheater 12 High pressure Turbine 13 Brackish water separator drain tank 14 Furnace recirculation pump 15 Furnace recirculation pump Flow control valve 16, 16a-16c Brackish water separator drain tank level control valve 20 Main steam pressure controller 21 Load indicator 22 Adder 23 High selector 24 minimum feed water flow rate commander 25 subtractor 26 furnace flow rate detector 27 recirculation flow meter 28, 31 PI controller 29 flow rate command function unit 30 subtractor 32-34 drain valve opening command function unit 40a-40c, 44 high Signal detector 41 OR element 42,45 AND element 43 Timer 46 Set / Reset device 47 Delay timer 48 Change Biasing switch 49 reduced flow signal 50 increase the flow rate signal 51 furnace recirculation line 52 water supply line

Claims (3)

[Claims] 1. A boiler ignition signal of a once-through boiler having a brackish water separator drain tank, a furnace recirculation line connected to the brackish water separator drain tank and a level control line having a level control valve, and a boiler once-through boiler having a boiler feed water line. A timer that outputs a predetermined time, a first high signal detector that receives the opening signal of the level control valve, and a first A that receives the outputs of the timer and the first high signal detector.
An ND element, a set-reset device that receives the output of the AND element as a set input, a delay timer that receives the output of the set-reset device, and a furnace passage flow rate signal after the boiler water supply line and the furnace recirculation line are merged A second AND element for receiving the outputs of the delay timer and the second high signal detector and sending the output to the reset input of the set-reset device. Swelling prediction detection device. 2. The brackish water separator drain tank of a once-through boiler having a brackish water separator drain tank, a furnace recirculation line having a flow rate control valve connected to the brackish water separator drain tank, and a level control line having a level control valve. Flow rate command function unit for receiving the drain level signal of, and a subtractor for receiving the output of the flow rate command function unit and the furnace recirculation flow rate signal of the furnace recirculation line, and the subtractor for receiving the output of the subtractor of the furnace recirculation line In a boiler feedwater control device having a PI controller for sending a recirculation valve opening control signal to a flow control valve, a changeover switch with a change rate inserted between the flow rate command function unit and a subtractor, and the same change rate as the output. 3. A swelling occurrence prediction detection device according to claim 1, further comprising a reduced flow rate signal device for sending to an input end of the switch with switch and an output for sending to a control input end of the switch with change rate. Boiler water supply control device characterized in that 3. A load indexer for outputting a load index signal of a transformer once-through boiler having a water supply line having a boiler water supply pump and a water supply control valve, and a furnace recirculation line, and a main steam pressure control device for outputting a boiler pressure correction signal. And a high selector that receives the added signal of the output of the load indicator and the output of the main steam pressure control device and the output of the minimum flow indicator, and the furnace passage flow signal after the confluence of the water supply line and the furnace recirculation line and the high A subtractor that receives the output of the selector,
In a boiler feed water control device having a PI regulator for receiving the output of the subtractor and sending a control signal to the boiler feed water pump or the feed water control valve, with a change rate inserted between the minimum flow rate commander and the high selector 2. A switching device, an increase flow rate signal device for sending an output to an input end of the switching device with the same change rate, and a swelling occurrence prediction detection device according to claim 1, which sends an output to a control input end of the switching device with the same change ratio. A boiler water supply control device characterized by being provided.