JP2008069763A - Load setter follow-up boiler-turbine parallel control runback control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable safe and certain runback drive in a thermal power plant controlled by a boiler-turbine cooperative control system. <P>SOLUTION: Output of a load setter is so planned as to serve as a runback target load command also at the time of runback by having the load setter follow the output of a runback fall rate setter. As a result, since the load setter maintains the runback target load command value as it is even after resetting the runback, a stability of the drive can be improved at the time of transition to the boiler-turbine cooperative control. Furthermore, controlled variables such as main steam pressure and drum level are changed not excessively at the time of the runback by the parallel control with a fall rate different from that of the boiler by separating the target load command into a boiler input amount control command and a turbine control valve aperture control command for providing a change rate limitter also in the turbine control valve aperture control command. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the case of a thermal power plant that is operated and controlled with a boiler and a turbine cooperative control system, the present invention, when one of the main auxiliary equipment such as a feed pump, a forced draft fan (FDF), a suction ventilator (IDF), etc. loses an accidental stop, It relates to the run-back operation function that prevents the unit from stopping by reducing the load to the point where it can be operated with the remaining auxiliary equipment.

FIG. 2 is a schematic diagram of a run-back control method that is generally employed in thermal power plants. In this conventional runback control system, the runback control circuit is 1) target value selection logic circuit 47 for each runback factor.
2) Runback target load setting value 48
3) Runback detection 49
4) Switcher (also available with low selector) 45
5) Runback descent rate setter 46
And is arranged downstream of an output command setting circuit including a load setting unit 41 and a load change rate setting unit 43. When any auxiliary machine stops and runback occurs, the runback target load set value 48 corresponding to the cause is selected and the runback target load is set at a predetermined descent rate set by the runback descent rate setter 46. The command is lowered to the target value. The operation mode during the runback is a turbine follow-up mode in which the turbine control valve controls the main steam pressure that is lowered by the boiler input amount drop due to the drop in the target value, and as a result, the generator output (MW) balances with the boiler input amount. During the runback, the load setting device 41 and the load change rate setting device 43 are disconnected from the runback control circuit and follow the generator output (MW) during that time. That is, the MW is a standby signal at the time of a runback reset. The MW tracking of the load setting device 41 and the load change rate setting device 43 is an unnatural form of returning to the front through the switch 44 disposed behind the load change rate setting device 43. In this way, the signal flow is divided into two complicated parts during the runback. At the time of the runback reset, the runback target load command is changed from the runback target load set value 48 to the value of the load setting device 41 corresponding to the MW at that time, so the runback target load command is deviated from the target value. Note that the resetting of the runback is a method by resetting the runback detection 49.

If the operation method during run-back is the turbine follow-up method, the steam input is reduced and the steam flow rate is reduced by the turbine control valve controlling the main steam pressure after the result is effective on the main steam pressure. There is a flaw that slows down the search.
It is effective to narrow down the steam flow rate, that is, the turbine control valve in parallel with the boiler input amount simultaneously with the occurrence of the runback in both the drum boiler and the transformer once-through boiler. In particular, defects in the turbine follow-up method are significant in feed pumps and runbacks.

In addition, the following patent document can be mentioned as a well-known technique regarding this invention.

[Patent
JP 2002-41094 A JP-A-10-122549

Problems to be solved by the invention

  As described above, in the related art, the runback target load set value set by a certain runback factor is not held as the output of the load setter after the runback reset.

In the conventional runback control circuit, the target load setting value is provided for each different target load setting for each runback factor, so that the logic configuration is extremely complicated.
For example, in the case of a runback that has lost feedwater pumps, in the case of a typical plant with two turbine-driven feedwater pumps (TBFP) and one electrically-driven feedwater pump (MBFP), one unit stops during operation of two TBFPs. In the conventional system, the runback target load is 50%, 80% load when one TBFP stops during operation of 3 units, and 30% target load when one MBFP remains. Complicated logic is formed in which logic is created for each factor and the target load setting value is selected.

  Since the operation mode during the runback is the turbine follow-up mode, the steam flow rate cannot be reduced simultaneously with the decrease in the boiler input amount at the same time as the runback.

Runback reset method. In the conventional method, an unexpected situation occurs on the turbine side during the runback, and the MW suddenly drops. If the turbine master is set to manual operation, the MW tracking mode is activated and the boiler input command follows the MW. Risk of worst misfire.

  A simple circuit configuration that follows the signal flow.

  The present invention has been made to solve the above problems, and provides a simple circuit configuration that can safely and reliably execute a runback operation under severe conditions such as loss of auxiliary equipment without stopping the unit. For the purpose.

Means for solving the problem

The present invention relates to the following aspects.
1. A method of performing a run-back operation in the following form in a boiler and turbine cooperative control device of a thermal power plant.
1) When the runback target load command is lowered at a predetermined rate of change, the load setter and negative change rate setter are made to follow the output of the runback drop rate setter as a follow-up operation.
2) Divide the runback target load command into the boiler input amount control command and the turbine control valve opening control command, and control the turbine control valve by installing a change rate limiter in the turbine control valve opening control command.
2. A method of setting one runback target load setting device and detecting that the runback target load command has reached the target value and holding it at the target value.
3. For a transformer once-through boiler where the turbine valve opening is constant in the transformation range, a bias value is created by time delay and digital addition for each runback, and this is biased to the turbine valve opening command by the change rate limiter. How to apply.
4 A method to set the target load at the time of water pump (BFP) run-back using digital addition.
5. A method in which the signal flow is unified from the generator output (MW) to the load setter and load change rate setter to perform the generator output follow-up mode (MW tracking mode) operation.
6. Method to perform runback reset by time.

The invention's effect

The signal flow during runback operation and MW tracking mode operation is unified, and the circuit configuration is extremely simple. In addition, the runback target load set value selection logic circuit, the target load set value, and the detection circuit provided for each runback factor have been simplified.
During the runback, the load setter follows the output of the runback descent rate setter, so there is no change in the runback target load command even after the runback reset and stable operation is obtained when shifting to the boiler / turbine cooperative control mode. It came to be able to. Furthermore, the turbine controlled valve can be lowered to the target opening by the rate-of-change limiting operation that can adjust the change speed in parallel with the boiler input amount at the same time as the runback occurs. It became possible to reduce the fluctuation. In particular, in the conventional system, in a drum boiler runback that often results in a unit trip (stop), excessive runoff of the drum level is suppressed and stable runback operation can be obtained as a result of the present invention.
Similarly, in a transformer once-through boiler, when the feedwater pump was lost, the turbine control valve was throttled in parallel with the boiler input to prevent the feedwater pump overload trip. In addition, safety in the following cases was ensured by the method of performing the runback reset by time. If an unexpected situation occurs on the turbine side during the runback and the MW falls too rapidly, and the turbine master is switched to manual operation, the boiler input amount control command follows the MW and does not drop. So that the confusion of boiler operation can be avoided.

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

  1, 3, 4, and 5 relate to an embodiment of the present invention, FIG. 1 is a functional diagram, FIG. 3 is a detailed diagram of a runback target load setting and reset circuit, and FIG. 4 is a turbine control valve control command. It is a circuit diagram. FIG. 5 shows a target load setting circuit at the time when the feed water pump is lost.

  As shown in FIG. 1, the runback target load setting device 1, the switching devices 10 and 2, and the runback drop rate setting device 3 are arranged upstream of the load setting device 4 and the load change rate setting device 6. When the runback occurs, the switching units 10 and 2 are switched to the signal from the runback target load setting unit 1. Here, 1 is set to the lowest value among the runback factors (e.g., corresponding to 25%). This value takes 3 and the output of 3 drops at a preset drop rate (usually 100% / min). When the runback target load command reaches the target value during the descent, the switch 10 is switched to the b side and held and stopped. 4 and 6 are follow-up operations during tracking (tracking operation), and the output of 3 passes as it is and becomes a run-back target load command. The runback target load command is divided into two, one is a boiler input amount control command, and the other is a turbine control valve opening control command through a turbine control valve lowering rate setting device 7 and a turbine control valve opening program 8. . During the runback, the load setting device 4 follows the runback lowering rate setting device, so that the runback target load command is lowered from the load setting device 4. The generator output (MW) is stopped at the switch 2 and is not related to the target load command during the runback or after the runback reset. When the MW tracking mode is set during normal operation, the load setting device 4 and the load change rate setting device 6 follow the MW.

FIG. 3 is a detailed diagram of setting the runback target value. An example of FAN runback will be described. The Hi side of the height detector (Hi / Lo monitor) 11 arranged in the runback target load command is an allowable load condition for the runback factor, and the Lo side set value becomes the runback target value. In the case of FAN runback, when either FDF or IDF stops with a load of 50% or more, the runback is activated and the load is reduced to 50%. Therefore, the Hi side of the Hi / Lo monitor 11 is set to 51% to 52%, and the Lo side is set to the target descent value 50%. If FDF-A trips (stops) during 100% load operation, the 13 FAN runback generation logic becomes “1” and the 14 runback generation logic also becomes “1”. At the same time, the memory 16 is set and the runback operation is in progress. Become. As a result, the switches 10 and 2 are switched to the a side, and the output of the runback target load setting device 1 is guided to the runback lowering rate setting device 3. During the runback, the load setting device 4 and the load change rate setting device 6 are in a follow-up operation and follow the output value of the runback descent rate setting device 3. The output of the runback descent rate setter drops at a preset rate, for example 100% / min. In the middle of the descent, when the Lo side of the Hi / Lo monitor 11 detects 50%, the memory 12 is reset, and the 13FAN runback generation logic and the 14 runback generation logic become “0”. As a result, the switching device 10 is switched to the b side, and the output of the runback lowering rate setting device 3 is held and stopped. At this time, the tracking mode of the load setting unit 4 and the load change rate setting unit 6 may be canceled at the same time. However, since the output of 3 is already held, the tracking mode is canceled when the runback operation is reset. Even if the 14 runback generation logic is reset, the logic during the runback operation is still held and is reset after the time limit (on the order of 6 to 8 minutes) by the time delay (on-delay) 15. When the memory 16 is reset and the runback operation is reset, the boiler turbine cooperative mode operation is performed, and the runback operation ends. As described above, the load setting device 4 and the load change rate setting device 6 are operated by the operator after the tracking mode is canceled.
Even if an unexpected situation occurs on the turbine side during the runback due to the method of performing the runback reset, the boiler input amount control command can be held even when the MW suddenly drops, and the boiler operation is disrupted. Can be prevented.

FIG. 4 shows a turbine control valve opening control command generation circuit for a transformer once-through boiler in which the turbine control valve opening is constant in the transformer region. The circuit is a circuit constituted by a time delay (wipeout) 20, 21, a digital addition 22, and a change rate limiter 23 after an adder 24 is placed behind the turbine adjustment valve lowering rate setting device 7 and the turbine adjustment valve opening degree program 8. It is composed by adding. The operation of this circuit will be described below. For example, when the lost runback of the water supply pump occurs, the 17BFP runback generation logic becomes 1, so that the time delay 20 is turned on, and the bias amount set by the digital addition 22 is sent to the change rate limiter 23, where it has a predetermined change rate. Lower the turbine control valve opening command. The time delay 20 is reset after the time limit, and the output of the digital adder 22 returns to zero. This return is optimally adjusted by the rate of change limiter.
In the case of a drum boiler, the turbine adjusting valve lowering rate setting unit 7 and the turbine adjusting valve opening degree program 8 are preferable only, so the adder 24 is not attached from the beginning, or the S2 input of the adder 24 is input in the circuit of FIG. Set the gain to zero. 7 and 8 may be reversed in arrangement.

FIG. 5 shows a target load setting circuit at the time of BFP runback. The load of each pump is given by the digital addition 30. For example, the turbine-driven feed pump (TBFP) is 50%, and the motor-driven feed pump (MBFP) is 30%. This result is detected by the height detector (Hi / Lo monitor) 32 in association with the target load command. For example, when two TBFP units are operating at 100% load, the output of the digital adder 30 corresponds to 100% load. Here, if one TBFP is stopped, the output of the digital adder 30 becomes 50%. That is, when one of the TBFP pumps stops, the high / low detector 32 is turned on on the Hi side, the memory 33 is set and the output is "1", and the 17BFP runback generation and 14 runback generation logics are turned on simultaneously. 3 is set and the runback operation is in progress. As a result, the switcher 10 and the switcher 2 in FIG. 3 select the output value of the runback target load setting device 1, and the runback lowering rate setting device 3 lowers the runback target load command. When the runback target load command falls to 50% and coincides with the output of the digital adder 30, Lo of the high / low detector 32 is turned on and the memory 33 is reset. As a result, the switch 10 in FIG. 3 switches from the a side to the b side, selects the runback target load command, and the output is held and stops.
This circuit can also be applied to target load setting during mill runback.

It is a functional diagram concerning embodiment of this invention. It is a schematic diagram of a conventional runback control method according to the background art of the present invention. FIG. 2 is a detailed explanatory diagram of a runback target load setting circuit according to the embodiment of the function of FIG. 1. It is a method figure of the turbine control valve opening degree control concerning embodiment of FIG. It is a target load setting circuit diagram at the time of BFP pump loss runback according to the embodiment of FIG.

Explanation of symbols

1, runback target load setting device 2, 9, 10, 42, 44, 45 switching device 3, 46 runback descent rate setting device 6, 43 negative caustic change rate setting device 7, 23, 4 change rate limiting device 4, 41 Load setters 5, 50, Load setter output increase / decrease 8, Turbine boost / decrease valve opening programs 11, 32 Height detector (Hi / Lo monitor)
12, 16, 33 Memory 15, time delay (on delay)
0, 21 Time delay (wipe out)
22, 30 Digital addition 24, adder 31, subtractor 47, target load selection logic 48 for each runback factor, runback target load set value 49, runback detection

Claims (6)

A method of performing a run-back operation in a boiler and turbine cooperative control apparatus of a thermal power plant in the following form.
1) When the runback target load command is lowered with a predetermined change rate, the load setter and the load change rate setter are caused to follow the output of the runback drop rate setter as a follow-up operation.
2) Divide the runback target load command into a boiler input amount control command and a turbine control valve opening control command, and provide a change rate limiter in the turbine control valve opening control command to control the turbine control valve. A method of setting one runback target load setting device and detecting that the runback target load command has reached the target value and holding it at the target value. For a transformer once-through boiler whose turbine adjustment valve opening is constant in the transformation range, a bias value is generated by a time limit timer and digital addition for each runback, and this is biased to the turbine adjustment valve opening command by a change rate limiter. Method. A method of setting a target load at the time of runback of a feed pump (BFP) using digital addition. A method of performing a generator output follow-up mode (MW tracking mode) operation by unifying a signal flow from a generator output (MW) with a load setter and a load change rate setter. A method of performing a runback reset over time.

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