JPH07293816A - Control device for fluidized bed type boiler and controlling method - Google Patents

Abstract

PURPOSE:To eliminate a delay in control of a height of a fluidized bed when a load is changed and to improve a load following-up characteristic. CONSTITUTION:This control device is comprised of an offset amount calculation element 1 for outputting an offset amount at each of a load increasing time and a load decreasing time; an adding element 2 for adding a target value of a height of a fluidized bed to an output of the offset amount calculation element 1; a subtracting element 3 for subtracting a detected value of the fluidized bed height sensing element from an output of the adding element 2 and adding an output of a control deviation; an air valve 8 for adjusting a supplying amount of fluidized medium in response to the controlling deviation; and an air valve 9 for adjusting a discharging amount of the fluidized medium in response to the controlling deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fluidized bed height control for a fluidized bed boiler, and more particularly to a fluidized bed boiler control apparatus and method suitable for improving fluidized bed height followability during load changes.

[0002]

2. Description of the Related Art First, a general fluidized bed boiler will be described.

FIG. 3 is an explanatory view showing a furnace of a general fluidized bed boiler.

As shown in the figure, 10 is a furnace having a fluidized bed, 11 is a fluidized bed in which a fluidized medium such as silica sand flows, 12 is fluid air and combustion air for the fluidized medium, and 13 is solid fuel such as coal. Limestone mixed fuel, 14 is combustion gas, 15
Is a fluid medium supply system, and 16 is a fluid medium discharge system.

The volume of the fluidized bed 11 is caused by the cumulative increase of the ash produced by the combustion of the fuel of the mixed fuel and the compound produced by the desulfurization reaction of limestone and sulfur oxides of the mixed fuel. There is a factor that the fluidized medium, ash, and compounds due to the desulfurization reaction are accompanied and discharged in the combustion gas 14 and are reduced. The height h of the fluidized bed 11 changes when the balance between factors that increase or decrease the volume is lost, and a deviation from the control target value occurs. Further, when the load of the fluidized bed boiler is changed, the control target value itself changes according to the load change in order to change the fluidized bed height to change the heat transfer area and control the steam generation amount. The fluidized bed height control of the fluidized bed boiler is basically an operation of supplying a fluidized medium to the fluidized bed 11 to increase the fluidized bed height h, and discharging the fluidized medium, ash and compounds from the fluidized bed 11 to obtain the fluidized bed height h. To lower the temperature. The mixed fuel and the fluidized medium are supplied to the fluidized bed 11 by intermittent gas transfer.

FIG. 4 is an explanatory view for explaining a fluidized bed height control of a fluidized bed boiler according to the prior art. As shown in this figure,
When the load rises, the operation of increasing the fluidized bed height is performed, but when the fluidized bed height is equal to or less than the target value -α, the supply operation of the fluidized medium is started, and when the fluidized bed height rises to the target value -β, the supply operation is stopped. . On the other hand, when the load drops, the operation of lowering the fluidized bed height is performed, but when the fluidized bed height is equal to or higher than the target value + α, the discharge operation of the fluidized medium is started, and when the fluidized bed height drops to the target value + β, the discharge operation is stopped. .

The fluidized bed height control of the fluidized bed boiler does not perform proportional control but performs on / off control with different fluidized bed heights for starting and stopping the operation. The control target is not a liquid like other plants. This is because the fluidized particles are unstable and the height of the fluidized bed constantly fluctuates, and a stable process value cannot be detected. In addition, the fact that the fluidized bed height at which each of the supply operation and the discharge operation is stopped is separated from the target value by β is due to the phenomenon peculiar to the fluidized bed boiler in which the operation operation goes too far and exceeds the target value. .

[0008]

The above-mentioned fluidized bed height control technique is to control the fluidized bed height control operation when the fluidized bed height target value increases when the load rises due to the behavior change of the fluidized bed height when the load changes. The height of the fluidized bed is generally controlled between the target value −α and the target value −β. When the fluidized bed height target value decreases when the load drops, the fluidized bed height control is only the discharge operation, and the fluidized bed height is generally controlled between the target value + β and the target value + α.

FIG. 5 is a table for explaining the relationship between the time and the fluidized bed height of the conventional fluidized bed boiler when the load changes.

As shown in FIG. 5, the fluidized bed height is (α +) on average in both cases of load increase and load decrease when the load changes.
This results in a delay of β) / 2, which results in a factor that hinders load followability and control stability.

An object of the present invention is to improve the drawbacks of the above-mentioned prior art, eliminate the delay of the fluidized bed height control when the load changes, and improve the load followability.

[0012]

[Means for Solving the Problems] The above objects are a fluidized bed height detecting means for detecting a fluidized bed height of a fluidized bed and a fluidized bed height target for setting a fluidized bed height determined according to a load as a target value. Setting means, first adding means for inputting the target value output by the fluidized bed height target setting means and the fluidized bed height output by the fluidized bed height detecting means and outputting a control deviation, and the control when the load is increased A fluid medium supply control means for inputting a deviation and controlling a fluid medium supplied to the fluidized bed, and a fluid medium discharge control means for inputting the control deviation and controlling a fluid medium discharged from the fluidized bed when a load drops. In the controller of the fluidized bed boiler, the fluidized bed height at which the supply of the fluidized medium is started when the load is increased and the fluidized bed height difference from the target value are α, and the fluidized bed height at which the supply of the fluidized medium is stopped and the target value are Let β be the fluidized bed height difference of (α β) / 2, the fluidized bed height at which the discharge of the fluidized medium starts when the load drops and the fluidized bed height difference from the target value α, and the fluidized bed height at which the discharge of the fluidized medium stops and the target The fluidized bed height difference from the value is β, the offset amount output means outputs the offset amount represented by − (α + β) / 2, the offset amount output by the offset output means and the fluidized bed height target setting means output A target value to be added and output to the first adding means.
It is achieved by the addition means of.

The above-mentioned objects are as follows: a fluidized bed height detecting means for detecting the fluidized bed height of the fluidized bed, a fluidized bed height for starting the supply of the fluidized medium when the load rises, and a fluidized bed height difference from the target value α,
The fluidized bed height at which the supply of the fluidized medium is stopped and the fluidized bed height difference from the target value are set to β, and the offset amount is represented by (α + β) / 2. An offset for outputting an offset amount represented by-(α + β) / 2, where α is a fluidized bed height difference from a target value, and β is a fluidized bed height from which the fluid medium is stopped to be discharged. Quantity output means, first addition means for adding the offset amount output by the offset output means and fluidized bed height output by the fluidized bed height detection means, and a fluidized bed height determined according to the load The fluidized bed height target setting means set as a value, the target value output by the fluidized bed height target setting means, the sum of the offset amount and the fluidized bed height detected value output by the first adding means are input and the control deviation is set. Second adding means for outputting and when the load increases The fluidized medium supply control means for inputting the control deviation output by the second adding means to control the fluidized medium supplied to the fluidized bed, and the control deviation output by the second adding means at the time of load drop are input. And a fluidized medium discharge control means for controlling the fluidized medium discharged from the fluidized bed.

The above object is to set a fluidized bed height according to a load demand as a target value, and discharge the fluidized medium in the fluidized bed or supply the fluidized medium to the fluidized bed to control the fluidized bed height. In the control method, when the load rises, the offset amount, which is the average value of the fluidized bed height at which the fluidized medium starts to be supplied and the fluidized bed stop, is added to the target value of the fluidized bed height, and when the load falls, the fluidized bed height This is achieved by subtracting the offset amount, which is the average value of the fluidized bed height at which the discharge of the fluidized medium is started and the fluidized bed height at which it is stopped, from the target value.

[0015]

According to the above construction, by adding the offset amount to the target value of the fluidized bed height, during the load increase,
Deviation −α from the target value where (α + β) / 2 is biased
The target value ± (α-β)
Controlled within a deviation of / 2. Similarly when the load drops,
The discharging operation is performed between the deviations α and β with respect to the target value in which (α + β) / 2 is biased, and the target value ± (α−β) / 2
Controlled within the deviation of. Therefore, since the deviation of the fluidized bed height occurs around the target value, the fluidized bed height is controlled on average without delay with respect to the target value.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a fluidized bed height control system according to an embodiment of the present invention.

First, the structure of this embodiment will be described.

1 is an offset amount calculation element that outputs an offset amount when the load is rising and 2 is a load decrease, 2 is an addition element that adds the target value of the fluidized bed height and the output of the offset amount calculation element 1, and 3 is an addition Subtraction element 4 which subtracts the detection value of the unillustrated fluidized bed height detection element from the output of element 2 and adds the control deviation to the output.
Hysteresis element that outputs ON at α and OFF at target value −β, 5 is a hysteresis element that outputs ON when the fluidized bed height is target value + α when the load drops, and is a hysteresis element that outputs OFF at target value + β. 6 is proportional to the output of the hysteresis element A valve operation amount control element for outputting the valve operation amount in the control or on / off control mode, 7 is a valve operation amount control element for outputting the valve operation amount in the proportional control or on / off control mode by the output of the hysteresis element,
Reference numeral 8 is an air valve for adjusting the supply amount of the fluid medium by the valve operation amount output by the valve operation amount control element 6, and 9 is air for adjusting the discharge amount of the fluid medium by the valve operation amount output by the valve operation amount control element 7. It is a valve.

Next, the operation of this embodiment will be described.

FIG. 2 is a chart showing the correlation between time and fluidized bed height for explaining the operation of the embodiment of the present invention.

The fluidized bed height at which the supply of the fluidized medium starts when the load increases to the target value and the fluidized bed height difference from the target value are α, and the fluidized bed height at which the fluidized medium supply is stopped and the fluidized bed height difference from the target value. Where β is the amount of offset represented by (α + β) / 2, the fluidized bed height at which fluid medium discharge starts when the load drops and the fluidized bed height difference from the target value α, and the fluidized bed height at which fluid medium discharge is stopped And the fluidized bed height difference from the target value is β- (α + β) / 2
As shown in FIG. 2, the offset amount (α + β) is added during the load increase by adding the offset amount represented by
Fluidized bed height deviation -α to -β with respect to the target value with / 2 added
The fluid medium supply start / stop operation is repeated in the range of, and the control operation is performed in the range of ± (α-β) / 2 with respect to the original target value.

During the load drop,-(α +
β) / 2 is added to the target value and the fluidized bed height deviation is repeated within the range of + α to + β, and the fluid medium discharge start / stop operation is repeated, and ± (α-
Control operation is performed in the range of β) / 2.

Further, in the prior art, the fluidized bed height deviation at the end of the load change is -α to -β at the end of the load increase and + α to + β at the end of the load decrease as shown in FIG. In the present embodiment, as shown in FIG. 2, the load is in the range of ± (α-β) / 2 both when the load rises and when the load falls, and the fluidized bed height deviation at the end of the load change is also reduced.

In the above embodiment, the offset amount 1 is ± (α +
β) / 2 was set, but in consideration of the set values of the hysteresis elements 4 and 5 on the supply side and the discharge side, the effect of the supply and discharge characteristics, and the bed height deviation on the plant output, etc. Optimal control can be obtained by giving

In the above embodiment, the control deviation was calculated in addition to the target value as a partner for adding the offset amount. However, the control deviation is calculated by the difference between the measured fluidized bed height value and the target value. In addition to hysteresis elements 4, 5
Can also be input.

[0027]

According to the present invention, by adding the offset amount to the target value of the fluidized bed height, the delay operation of the fluidized bed height during the load change is eliminated and the output deviation can be reduced, so that the load followability is improved. To do. Further, disturbance elements to other control systems are reduced, and control stability is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a fluidized bed height control system of an embodiment of the present invention.

FIG. 2 is a chart showing the correlation between time and fluidized bed height, which explains the operation of the embodiment of the present invention.

FIG. 3 is an explanatory view showing a furnace of a general fluidized bed boiler.

FIG. 4 is an explanatory diagram illustrating a fluidized bed height control of a fluidized bed boiler according to a conventional technique.

FIG. 5 is a table for explaining a relationship between a fluidized bed boiler time and a fluidized bed height when a conventional load changes.

[Explanation of symbols]

 1 Offset amount calculation element 2 Addition element 3 Subtraction element 4 Sterisis element 5 Sterisis element 6 Valve operation amount control element 7 Valve operation amount control element 8 Fluid medium supply amount adjusting air valve 9 Fluid medium discharge amount adjusting air valve 10 Furnace 11 Fluidized bed 12 air 13 mixed fuel 14 combustion gas 15 supply system 16 exhaust system

Claims (3)

[Claims] 1. A fluidized bed height detecting means for detecting a fluidized bed height of a fluidized bed, a fluidized bed height target setting means for setting a fluidized bed height determined according to a load as a target value, and the fluidized bed height. First adding means for inputting the target value output by the target setting means and the fluidized bed height output by the fluidized bed height detecting means to output a control deviation, and inputting the control deviation when the load increases to the fluidized bed A fluidized bed boiler control device comprising fluidized medium supply control means for controlling a fluidized medium to be supplied, and fluidized medium discharge control means for controlling the fluidized medium discharged from the fluidized bed by inputting the control deviation when the load drops. , Α is the difference between the fluidized bed height at which the fluidized medium starts to be supplied when the load increases and the fluidized bed height from the target value, and the fluidized bed height at which the fluidized medium supply is stopped and the fluidized bed height from the target value is β. (Α
+ Β) / 2, the fluidized bed height at which fluid medium discharge starts when the load drops and the fluidized bed height difference from the target value α, and the fluidized bed height at which fluid medium discharge stops and the target The fluidized bed height difference from the value is β, the offset amount output means outputs the offset amount represented by − (α + β) / 2, the offset amount output by the offset output means and the fluidized bed height target setting means output And a second adding means for adding the target value to be output to the first adding means, and a controller for the fluidized bed boiler. 2. A fluidized bed height detecting means for detecting a fluidized bed height of the fluidized bed, a fluidized bed height at which supply of the fluidized medium is started when the load rises, and a fluidized bed height difference from the target value, α, Of the fluidized bed height at which the supply of the fluid is stopped and the fluidized bed height from the target value is β, and the offset amount is represented by (α + β) / 2, the fluidized bed height at which the discharge of the fluid medium is started when the load is reduced, and the target value. Is the fluidized bed height difference from the target value and the fluidized bed height at which the discharge of the fluidized medium is stopped is β- (α +
β) / 2, an offset amount output means for outputting an offset amount, and a first adding means for adding the offset amount output by the offset output means and the fluidized bed height output by the fluidized bed height detecting means. And a fluidized bed height target setting means for setting a fluidized bed height determined according to a load as a target value, a target value output by the fluidized bed height target setting means, and an offset amount output by the first adding means. And second addition means for inputting the sum of the fluidized bed height detection value and outputting the control deviation,
A fluid medium supply control means for controlling the fluid medium supplied to the fluidized bed by inputting the control deviation output by the second adding means when the load rises, and a control deviation output by the second adding means when the load falls. And a fluidized medium discharge control means for controlling a fluidized medium that is input and discharged from the fluidized bed. 3. A fluidized bed boiler control for controlling a fluidized bed height by setting a fluidized bed height according to a load demand as a target value and discharging the fluidized medium in the fluidized bed or supplying the fluidized medium to the fluidized bed. In the method, when the load rises, the offset amount, which is the average value of the fluidized bed height at which the fluidized medium supply starts and the fluidized bed stop, is added to the target value of the fluidized bed height, and when the load falls, the target value of the fluidized bed height. A method for controlling a fluidized bed boiler, wherein an offset amount, which is an average value of a fluidized bed height at which the fluidized medium is discharged and a fluidized bed height at which the fluidized medium is stopped, is subtracted from