JP2003126650A - Control method and apparatus for wet flue gas desulfurization plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out control following SO2 concentration even if the SO2 concentration of a flue gas at an inlet of a desulfurization plant is abruptly increased. SOLUTION: The control apparatus 4 for the desulfurization plant 1 comprises a pump control means 20 for controlling operation of pumps 3 and an absorbent injection amount control means 30 for controlling the injection amount of an absorbent, the pump control means 20 comprises a pump number determination means 21 for determining the number of pumps 3 necessary to be operated corresponding to the load of the boiler and a pump starting and stopping means 22 for starting to stopping pumps 3 based on the determination of the change of the number of the pumps 3 to be operated, and since the pump starting and stopping means 22 increases the number of the pumps 3 to be operated in the case the SO2 concentration at an outlet is a first set value or higher at the time of reception of a starting signal or a stopping signal of a coal mill, even if the SO2 concentration at the inlet is sharply increased at the time of starting or stopping the coal mill, the desulfurization plant 1 can be controlled so as to follow the change and the SO2 concentration at the outlet can be suppressed to a standardized value or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a wet flue gas desulfurization apparatus and a control apparatus therefor, and relates to a technology capable of following control even when the concentration of sulfur oxides in exhaust gas rises sharply. .

[0002]

2. Description of the Related Art In a boiler of a thermal power plant that uses coal, oil, etc. as a fuel, the fuel contains sulfur, so that
Exhaust gas discharged from the boiler contains a considerable amount of sulfur dioxide (SO ₂ ) as sulfur oxide. This SO ₂
If the exhaust gas is diffused into the atmosphere while containing the above, it has an adverse effect on the environment such as causing acid rain. Therefore, after the SO ₂ is removed from the exhaust gas by the desulfurization device, the exhaust gas is diffused into the atmosphere. Although various types of desulfurization devices are adopted, for example, Japanese Patent No. 2538184 discloses a wet flue gas desulfurization device configured as follows.

This wet flue gas desulfurization apparatus comprises an absorption tower and a plurality of pumps for circulating an absorption liquid containing an alkaline absorbent such as CaCO _{3 in the} absorption tower. Exhaust gas discharged from the boiler flows into the absorption tower, and this exhaust gas passes through the inside of the absorption tower and is discharged from the absorption tower while being in contact with the absorbing liquid sprayed from above inside the absorption tower. At this time, the sulfur oxides in the exhaust gas react with the absorbent in the absorbing liquid to be removed as CaSO ₄ . This wet flue gas desulfurization apparatus is configured to control the number of operating pumps and the pH of the absorbing liquid to suppress the SO ₂ concentration of exhaust gas at the outlet of the absorption tower to a regulated value or less.

For example, the applicant of the present application has proposed the following method for controlling a wet flue gas desulfurization apparatus in the above publication. In this control method, the upper limit value and the lower limit value of the pH of the absorbing liquid with respect to the predicted load of the boiler are obtained in advance, and the load of the boiler and the required operating number of pumps are calculated with respect to these upper limit values and the lower limit values. The relations are obtained respectively, and the number of operating pumps is controlled so that the pH such as absorption falls between the upper limit value and the lower limit value of these pH values. The upper limit value is provided to prevent the utilization rate of the absorbent from decreasing due to too high pH,
On the other hand, the lower limit value is provided for the purpose of preventing the metal material in the absorption tower from corroding due to too low pH.

When the boiler load is stable, p
The number of operating pumps can be increased or decreased so that the H set value falls between the upper limit value and the lower limit value, and the number of operating pumps can be minimized. On the other hand, when the load of the boiler is fluctuating rapidly, the absorbent input amount is controlled and the number of operating pumps is increased / decreased to control the pH set value to be constant. It can be suppressed.

[0006]

In the control method of the wet flue gas desulfurization apparatus described in the above publication, the control of the desulfurization apparatus can be made to follow the fluctuation of the load of the boiler to some extent. However, for example, in the case of a boiler that uses coal as a fuel, coal is crushed by a coal mill and pulverized coal is supplied to the boiler, but when the coal mill is started or stopped, the residual pulverized coal in the coal mill is crushed. To purge the boiler into the boiler. Prior to the purging work, sulfur content such as iron sulfide having a large specific gravity is retained in the coal mill, and depending on the type of coal used, the SO ₂ concentration of the exhaust gas may be 150 to ₂₀₀ ppm when the coal mill is started or stopped. It can rise sharply.

Rapid SO as described above₂Against changes in concentration
Then, the control method described in the above publication cannot be followed at all.
Therefore, at the time of starting and stopping the mill,
SO ₂Depending on the concentration, it may be
It is necessary to start the pump to increase the circulating amount of absorbing liquid.
Yes, the work load on the operator increases. Boiler negative
When the load is stable, the pH setting value of the absorption tower is the upper limit
The number of pumps operating is controlled so that it falls between the value and the lower limit.
However, for example, the pH of the absorption tower is the lower limit of the pH setting value.
When driving in the vicinity, the exhaust gas suddenly increases as described above.
SO₂If the concentration increases or there is a sudden load increase,
The pH value of the absorbent is below the lower limit of the pH setting value and desulfurization
The exhaust gas at the outlet of the absorption tower becomes SO₂Concentration is regulated value
There is a possibility that it will greatly exceed.

Furthermore, the upper and lower limits of pH are calculated,
Since the relationship between the boiler load and the required number of operating pumps for these upper and lower limit values is determined and the number of operating pumps is controlled so that the pH setting value falls between the upper limit value and the lower limit value, control is complicated. Therefore, it takes time to perform these arithmetic processing. An object of the present invention is to make it possible to follow the control of the desulfurization device even when the SO ₂ concentration of exhaust gas rises sharply, to simplify the control, and to shorten the calculation processing time.

[0009]

A method for controlling a wet flue gas desulfurization apparatus according to a first aspect of the present invention is directed to a method for controlling a wet flue gas desulfurization apparatus in which exhaust gas discharged from a boiler is circulated in an absorption tower while circulating an absorbent containing an alkaline absorbent by a plurality of pumps. In a method for controlling a wet flue gas desulfurization device for removing sulfur oxides, pump control means for driving and controlling the plurality of pumps, when receiving a start signal or a stop signal of a fuel supply device for supplying fuel to a boiler,
When the sulfur oxide concentration of the exhaust gas at the outlet of the absorption tower is equal to or higher than the first set value, the number of operating pumps is increased.

For example, in a fuel supply system for supplying coal to a coal boiler, purging work in the fuel supply system performed when starting or stopping the fuel supply system causes the exhaust gas from the boiler to be discharged depending on the type of coal. The SO ₂ concentration rises sharply. Therefore, the pump control means receives the start signal or the stop signal of the fuel supply device, and at that time, the SO ₂ concentration of the exhaust gas at the outlet of the absorption tower (hereinafter referred to as the outlet SO ₂
When the (concentration) is equal to or greater than the first set value, the number of operating pumps is forcibly increased. As the number of operating pumps increases, the circulation flow rate of the absorption liquid in the absorption tower increases, and the reaction between the absorption liquid and SO ₂ in the exhaust gas is promoted.

The pump control means causes the fuel supply device to start.
Or as soon as the stop signal is received, the number of pumps
It is possible to increase the exit SO₂Concentration is steep
Even if it rises sharply, the control will follow the exit SO₂Control concentration
It can be kept below the threshold. Also, exit SO₂Concentration
Increase the number of pumps operating only when it is above the first set value
SO to exit₂Concentration is sufficiently lower than the regulation value
SO of the exhaust gas at the inlet ₂Concentration (hereinafter, inlet SO₂concentration
Even if the) temporarily increases rapidly, the exit SO ₂concentration
Is below the regulation value, start an extra pump.
Never.

According to a second aspect of the present invention, there is provided a method for controlling a wet flue gas desulfurization apparatus according to the first aspect, wherein the pump control means receives the start signal or the stop signal to increase the number of operating pumps, and then the absorption tower outlet. When the concentration of sulfur oxides in the exhaust gas falls below a second set value that is smaller than the first set value, the number of operating pumps is reduced.

When the pump control means receives the start signal or the stop signal of the fuel supply device and the pump control means increases the number of operating pumps, when the increase in the concentration of SO ₂ at the inlet stops, the SO _{2 at} the outlet is reduced. The concentration gradually decreases. When the outlet SO ₂ concentration drops below the second set value that is smaller than the first set value, the pump control means stops the extra pumps and reduces the number of pumps operating.

According to a third aspect of the present invention, there is provided a method for controlling a wet flue gas desulfurization apparatus, wherein when the pump control means receives a start signal or a stop signal of the fuel supply device, all pumps are in operation. In this case, the amount of the absorbent added is increased. If the pump control means receives the start signal or stop signal of the fuel supply device, but it is not possible to increase the operating number of pumps because all operable pumps are in operation, increase the amount of absorbent to be supplied. By increasing the pH of the absorbing solution, the reaction between the absorbing solution and SO ₂ in the exhaust gas is promoted,
The control can be made to follow the rapid increase in the inlet SO ₂ concentration.

The control device for the wet flue gas desulfurization apparatus according to claim 4 removes the sulfur oxides in the exhaust gas discharged from the boiler while circulating the absorption liquid containing the alkaline absorbent through the absorption tower by a plurality of pumps. In a wet flue gas desulfurization apparatus, a pump control means for driving and controlling a plurality of pumps, a pump number determining means for determining the required number of pumps to be operated according to the load of the boiler, and the required number of operating pumps and the actual operation of the pumps. A pump control unit including a pump start / stop unit for starting or stopping the pump by determining the number of pumps to be increased or decreased from the number of pumps, and an absorbent input amount control unit for controlling the input amount of the alkaline absorbent, A pH setting value determining means for determining the pH setting value of the liquid and an input amount determining means for determining the input amount of the alkaline absorbent using the determined pH setting value are provided. A adsorbents input amount control means,
The pump start / stop means of the pump control means has a sulfur oxide concentration of exhaust gas at the outlet of the absorption tower that is equal to or higher than a first set value when receiving a start signal or a stop signal of a fuel supply device that supplies fuel to a boiler. In this case, the number of operating pumps is increased.

When the fuel supply device is started or stopped, the inlet exhaust gas SO ₂ concentration rises sharply, but the pump start / stop means of the pump control means receives the start signal or the stop signal of the fuel supply device, and at that time. Outlet SO ₂ concentration is first
If it is equal to or greater than the set value, the number of operating pumps is forcibly increased. As the number of operating pumps increases,
The circulation flow rate of the absorption liquid in the absorption tower is increased, and the reaction between the absorption liquid and SO ₂ in the exhaust gas is promoted. The other operations are the same as those in claim 1, and the description thereof is omitted.

According to a fifth aspect of the present invention, in the wet flue gas desulfurization apparatus control device according to the fourth aspect of the invention, the pump start / stop means receives a start signal or a stop signal of the fuel supply device to determine the number of pumps operating. After the increase, the number of operating pumps is decreased when the sulfur oxide concentration of the exhaust gas at the outlet of the absorption tower decreases to a second set value that is smaller than the first set value. Since the operation of the invention of claim 5 is almost the same as that of claim 2, the description thereof will be omitted.

According to a sixth aspect of the present invention, in the wet flue gas desulfurization apparatus control apparatus according to the fifth aspect of the invention, when the pump start / stop means receives a start signal or a stop signal of the fuel supply apparatus, all pumps are activated. When the engine is in operation, a command to increase the amount of the absorbent to be input is output to the input amount determining means. Since the operation of the invention of claim 6 is almost the same as that of claim 3, the description thereof will be omitted.

According to a seventh aspect of the present invention, in the wet flue gas desulfurization apparatus control device according to any one of the fourth to sixth aspects of the invention, the pH set value determining means preliminarily uniquely establishes the relationship between the boiler load and the pH set value. It is characterized in that it has a pH set value characteristic that is set in a physical manner. Therefore, even if the inlet SO ₂ concentration rises abruptly, the pH of the absorption liquid does not fluctuate significantly.
It is possible to stabilize the pH control by suppressing the fluctuation of pH.

The control device for a wet flue gas desulfurization device according to claim 8 is the control device for a wet flue gas desulfurization device according to any one of claims 4 to 7, wherein the pH set value determining means is a sulfur oxide concentration and a sulfur oxide concentration at the outlet of the absorption tower. It is characterized in that a pH set value correction means for correcting the pH set value according to the deviation from the target value is provided. If the deviation between the outlet SO ₂ concentration and the target value of the SO ₂ concentration is positive, that is, if the outlet SO ₂ concentration exceeds the target value of the SO ₂ concentration, the pH set value correction means determines the magnitude of the deviation. A corresponding correction amount is determined and this correction amount is added to the pH set value. By correcting the pH set value in this way, the pH of the absorbing liquid rises, the reaction between the absorbing liquid and SO ₂ in the exhaust gas is promoted, and the outlet SO ₂ concentration approaches the target value.

On the other hand, when the deviation is negative, that is, when the outlet SO ₂ concentration is lower than the target value of the SO ₂ concentration, a negative correction amount corresponding to the magnitude of the negative deviation is added to the pH set value. In this case, since the pH set value is lowered, the introduction of the alkaline absorbent is suppressed.

A control device for a wet flue gas desulfurization device according to a ninth aspect is the control device for a wet flue gas desulfurization device according to any one of the fourth to eighth aspects, wherein the input amount determining means inputs the alkaline absorbent according to a changing speed of a load of the boiler. It is characterized in that it comprises an input amount correction means for correcting the amount. When the boiler load changes abruptly, the input amount correction means determines a correction amount according to the changing speed of the load of the boiler, and this correction amount is added to the input amount of the alkaline absorbent, so the load of the boiler is reduced. It is possible to follow the control of the pH of the absorbing solution even when it changes abruptly.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described. This embodiment is an example in which the present invention is applied to a wet flue gas desulfurization device for a coal-fired boiler for a thermal power plant. still,
The following description includes a description of both the method of controlling the wet flue gas desulfurization apparatus and the controller. As shown in FIG. 1, a wet flue gas desulfurization apparatus 1 (hereinafter referred to as a desulfurization apparatus) is for removing SO ₂ from exhaust gas discharged from a boiler (not shown). Absorption tower 2, a plurality of pumps 3 that circulate an absorption liquid containing an alkaline absorbent (hereinafter referred to as an absorbent) in the absorption tower 2, and a control device 4 that controls the number of pumps 3 operating and the pH of the absorption liquid. And so on. Coal crushed into fine powder by a coal mill (not shown) is supplied to the boiler as fuel.

Exhaust gas from the boiler flows into the absorption tower 2 through the duct 5, and the exhaust gas passes through the absorption tower 2 and is discharged from the duct 6. The duct 5 is provided with a concentration detector 7 for detecting the inlet SO ₂ concentration, and the duct 6 is provided with a concentration detector 8 for detecting the outlet SO ₂ concentration and a flow rate detector 9 for detecting the exhaust gas flow rate. ing. In the absorption tower 2,
A nozzle 10 for spraying the absorbing liquid from above and a storage tank 11 for storing the absorbing liquid are provided. The storage tank 11 is
A plurality of pumps 3 connected to the suction line 12 of the pump 3
The discharge lines 13 of are connected to the nozzles 10, respectively. The suction line 12 has a pH for measuring the pH of the absorbing liquid.
A detector 14 is provided. The absorption liquid discharged from the storage tank 11 is pressurized by the pump 3 through the suction line 12, is pressure-fed to the nozzle 10 from the discharge line 13, and the absorption liquid is sprayed from the nozzle 10 in the absorption tower 2.

Calcium carbonate (CaCO ₃ ) as an absorbent is charged into the storage tank 11 via a charging line 15, and the charging line 15 has a flow rate control valve 16 and a flow rate detector for detecting the flow rate of the absorbent. 17 and a flow rate controller 18 that controls the flow rate control valve 16 based on a signal from the flow rate detector 17.
Is provided.

Next, the control device 4 and its control system will be described. Although not shown, the control device 4 includes a CPU and an RO.
It has a microcomputer including M and RAM and a bus connecting them, an input / output interface, and a drive circuit for driving the pump 3. Pump 3 in ROM
A program for controlling the number of operating vehicles and the amount of absorbent input are stored. The RAM is used as a work memory or the like. The input / output interface includes a concentration detector 7,
8, a plurality of A / D converters for converting the detection signals from the exhaust gas flow rate detector 9, the pH detector 14, and the flow rate detector 17 into digital signals are connected.

FIG. 2 is a functional block diagram for functionally explaining the control of the control device 4. The control device 4 controls the pump control means 20 for driving and controlling the plurality of pumps 3 and the amount of absorbent to be introduced. The absorbent input control means 30 is provided. The pump control means 20 determines the number of pumps required to operate the pump 3 in accordance with the load of the boiler.
And the required number of pumps 3 and the actual number of pumps 3
And a pump starting / stopping unit 22 for starting or stopping the pump 3 by determining the number of increased / decreased units.

First, the pump number control means 21 will be described. The boiler load command value is input to the pump number determining means 21 from the controller of the boiler. This boiler load command value is input to the prediction calculation means 23 that predicts the boiler load. The predictive calculation means 23 predicts the boiler load from the boiler load command value in order to enable control to follow a sudden load change, and as shown in FIG. The exponential smoothing calculation means 24 and the high selector 25 are provided. Triple exponent calculation means 24
Derives a triple exponential smoothing operation value from the boiler load command value and outputs it to the high selector 25. The high selector 25 compares the triple exponential smoothing operation value with the boiler load command value, and derives the larger value as the predicted value.

The triple exponential smoothing operation will be described. Time-series data x _t is, as according to _{x t = a + bt + ct} 2/2 ··· (1), represents an exponential smoothing value as second equation. S ⁽¹⁾ _t = αx _t + (1-α) S ⁽¹⁾ _t-1 (2) Here, if β = (1-α), then S ⁽¹⁾ _t = α−βb / alpha + obtained as ^{β (2α) c / 2α 2} + (b-βc / α) t + ct 2/2 ··· (3). Furthermore, S ⁽²⁾ _t = αS ⁽¹⁾ _t + βS ⁽²⁾ _t-1 (4) S ⁽³⁾ _t = αS ⁽²⁾ _t + βS ⁽³⁾ _t-1 (5) You can put it like. The smoothed value data X _i is X _t = 3S ⁽¹⁾ _t -3S ⁽²⁾ _t + S ⁽³⁾ _t (6), and the predicted value of the τ period ahead in the n period is the third formula, Four
Formula, a determined from Equation 5, b, than the value of c, the _{X n + τ = X n +} b n τ + c n τ 2/2 ··· (7).

When the boiler load command value changes as shown by the solid line in FIG. 4, the predicted value by triple exponential smoothing changes as shown by the broken line in FIG. In FIG. 4, when the boiler load command value increases from time t1 to t2, the predicted value rises prior to the boiler load command value, and overshoot occurs at time t2. This predicted value falls below the boiler load at time t3, and the change in the predicted value stabilizes at time t4.
Similarly, when the boiler load command value decreases from time t5 to t6, the predicted value decreases prior to the boiler load command value, and an undershoot occurs at time t6 and time t7.
The change in the predicted value stabilizes at. However, high selector 25
In the above, since the larger value of the boiler load command value and the predicted value is selected, the predicted value is selected from time t1 to t3, and the boiler load command value is selected after time t3. According to the prediction calculation means 24, the boiler load can be accurately predicted, especially when the load on the boiler is increased.

The boiler load command value from the boiler control device is input to the predictive calculation means 23, and at the same time, to the map M1 showing the relationship of the reference SO ₂ concentration of the exhaust gas with respect to the boiler load X. As shown in FIG. 5, the map M1
Is preset according to the exhaust gas property plan value, but is normally automatically updated based on the operation data during the operation of the desulfurization apparatus 1. Reference S determined by this map M1
A correction coefficient is obtained in the calculating means 26 from the ratio of the O ₂ concentration and the inlet SO ₂ concentration detected by the concentration detector 7, and the predicted boiler load described above is corrected by this correction factor. That is, the standard SO ₂ concentration is a and the inlet SO ₂ concentration is
When the density is b and the correction coefficient is c, the correction coefficient c is given by the eighth equation. c = (b / a) ^d (8) Here, d is a predetermined constant. The final boiler load predicted value is determined by multiplying the boiler load predicted by the prediction calculation means by the multiplier 27 with this correction coefficient c.

Next, based on the boiler load predicted value determined as described above, the required number of operating pumps 3 is determined by the map M2 as shown in FIG. This map M2
Represents the relationship between the boiler load X and the required number of pumps 3 to be operated. The map M2 is set in advance based on the operation data, but may be appropriately updated by changing the operating state during the operation of the desulfurization apparatus 1.

Next, the pump start / stop means 22 will be described. The actual number of operating pumps 3 and the required number of operating pumps 3 determined by the pump number determining means 21 are input to the pump start / stop means 22. First, in the subtractor 28, the shortage number of pumps 3 (excessive number in the case of a negative number) is obtained from the difference between the required number of pumps 3 and the actual number of pumps, and the number of shortages of the pumps 3 starts the pump. It is input to the stopped number calculation means 29.

The start-up signal or stop signal of the coal mill and the outlet SO ₂ concentration detected by the concentration detector 8 are also input to the pump start-up / stopping number calculation means 29. As shown in FIG.
At time t1, the pump start / stop number calculation means 29
Receives the start signal or stop signal of the coal mill, and at this time t1, if the outlet SO ₂ concentration is higher than the predetermined first set value, the pump start / stop number calculation means 29.
To increase the number of operating pumps 3,
Increase the shortage of vehicles by 1. The number obtained by adding 1 to this shortage number becomes the number of pumps 3 to be activated, and the pump start / stop means 22 issues a start command to the number of pumps 3 to be activated. For example, when the boiler load fluctuation is stable and the number of shortages is zero, as shown in FIG. 7, the number of operating pumps 3 increases by one at time t1. Of course, when the number of activated pumps is negative, the pump start / stop means 22 issues a stop command to the pumps 3 of that number.

After the number of operating pumps 3 is increased by starting or stopping the coal mill, at the time t2, the outlet SO ₂
When the concentration is reduced to the second predetermined value or less, which is smaller than the first predetermined value, the pump start / stop number calculation means 29 reduces the number of pumps 3 in shortage by one in order to reduce the number of pumps 3 in operation. Let The number obtained by subtracting 1 from this shortage number becomes the number of pumps 3 that can be started,
In response to this, the pump start / stop means 22 issues a start command. For example, when the boiler load fluctuation is stable and the number of shortages is zero, as shown in FIG. 7, the number of operating pumps 3 decreases by one at time t2.

When all the pumps 3 are in operation when the pump start / stop means 22 receives the start signal or stop signal of the coal mill, the pump start / stop means 23.
Outputs an instruction to increase the input amount of the absorbent to the input amount determining means 40 described later. This will be described later in detail.

Next, the absorbent input control means 30 will be described. As shown in FIG. 2, the absorbent input amount control means 3
0 is provided with a pH setting value determining means 31 for determining the pH setting value of the absorbing liquid, and an input amount determining means 32 for determining the input amount of the alkaline absorbent using the determined pH setting value. As shown in FIG. 2, the pH set value determination means 31
Is a map M showing the relationship between the boiler load X and the pH set value.
3 (pH set value characteristic), outlet SO ₂ concentration and predetermined SO
₂ pH setting value correcting means 33 for correcting the pH setting value obtained from the map M3 according to the deviation from the target concentration value.

As shown in FIG. 8, the map M3 is a map in which the relationship between the boiler load and the pH set value is uniquely set in advance. From the predicted value of the boiler load calculated by the number-of-pumps determining unit 21, the basic pH set value of the absorbing liquid is determined based on the map M3. As shown in FIG. 8, when the boiler load is low, the pH set value is set high.
This is to prevent the pH of the absorbing solution from decreasing and the outlet SO ₂ concentration exceeding the regulation value when the boiler load suddenly increases in this state when the operation is continued under a low load. Further, the pH set value is constant in the other boiler load ranges, and even if the inlet SO ₂ concentration rises rapidly, the fluctuation of the pH of the absorbing liquid becomes small, so that the pH control can be stabilized.

The outlet SO ₂ concentration is input to the pH set value correction means 33, and the subtractor 34 obtains the deviation between the outlet SO ₂ concentration and a predetermined target value of the outlet SO ₂ concentration.
The deviation amount multiplied by a predetermined positive constant K1 by the constant device 35 becomes the correction amount α1. However, the lower limit limiter 3
6, the lower limit value α ₀ of the correction amount α ₁ (α ₀ is a negative value)
Is provided and when the correction amount α1 is smaller than the lower limit value α ₀ , α1 = α ₀ . Correction amount α obtained from the above
1 is added to the basic pH set value in the adder 37 to determine the final pH set value. The correction amount α
The negative lower limit value α ₀ is set to 1 because the correction amount α 1 is negative, that is, when the outlet SO ₂ concentration is lower than the target value, the pH setting value correction means 33 decreases the pH setting value. However, if the correction amount is large, the absorption liquid pH
When the inlet SO ₂ concentration suddenly fluctuates due to undershoot from the set value or boiler load increase at the time when the pH decreases, the pH follow-up is delayed and the outlet SO ₂ concentration is delayed.
This is because the concentration may exceed the regulation value.

As shown in FIG. 2, the input amount determining means 32
Is a basic input amount determining means 38 for determining the basic input amount of the absorbent, an input amount correcting means 39 for correcting the basic input amount according to the changing speed of the boiler load, and a pump start / stop means 22.
And an input amount increasing means 40 for increasing the input amount according to the input amount increase command from.

As shown in FIG. 2, the basic input amount determining means 3
In FIG. 8, the boiler air flow rate (corresponding to the exhaust gas flow rate) and the inlet SO ₂ concentration are input from the boiler control device, and the total SO in the exhaust gas is input through the multiplier 41 and the constant unit 42.
₂ Amount is calculated. The gain schedule calculation means 43 calculates the gain for ratio control used in the PID calculation means 45 described later. On the other hand, the pH of the absorption liquid detected by the pH detector 14 and the pH set value determined by the pH set value determining means 31 are input, and the subtractor 44 calculates the deviation of the pH.

Here, the total amount of SO _{2 in} the exhaust gas,
The input amount is calculated by the PID calculating means 45 from the deviation of the pH. The input amount is the boiler air flow rate and the inlet SO ₂
SO calculated from concentration by multiplier 46 and constant unit 47
Adder 48 with feedforward control using ₂ variables
Is corrected and the basic input amount is determined.

In the input amount correcting means 39, the changing speed β of the boiler load is calculated from the boiler load command value by the differentiator 50.
1 is required. The rate of change β1 multiplied by a predetermined positive constant K4 in the constant unit 52 is the correction amount for the basic input amount. However, if the rate of change β1 is negative,
That is, when the boiler load decreases, the input amount correcting means 39 corrects the input amount in the direction of decreasing. However, when the input amount is largely corrected to the decreasing side due to the large decrease rate of the boiler load, the absorption liquid pH may decrease, and at this time, the inlet SO ₂ concentration rapidly changes. At this time, the follow-up of the absorption liquid pH may be delayed and the outlet SO ₂ concentration may exceed the regulation value. Therefore, if the lower limit limiter 51 sets a lower limit value β ₀ (zero or a negative value) to the changing speed β 1 and the changing speed β is equal to or lower than the lower limit value β ₀ , β =
The correction amount is calculated as β ₀ . The correction amount above is the adder 5
In step 3, the amount added is added to the basic amount to determine the amount of absorbent input.

When all the pumps 3 are in operation when the pump start / stop means 22 receives the start signal or stop signal of the coal mill, the pump start / stop means 2
The command to increase the input amount is output from 2 to the input amount increasing means 40. As shown in FIG. 9, the input amount increasing means 40 is provided with a map M4 showing the relationship of the increase amount with respect to the time t, and when a command to increase the input amount is received, the input amount increasing means 40 corresponds to each time based on the map M4. The increase amount is automatically determined, and the input amount is increased by the adder 54 by this increase amount. Therefore, even when all the pumps 3 are in operation and the circulation amount of the absorption liquid cannot be further increased at the time of starting or stopping the coal mill, it is possible to increase the pH of the absorption liquid by increasing the input amount. , Exit SO ₂
Prevents the concentration from exceeding the regulation value.

Next, the operation of the control device 4 will be described. In the pump control means 20, the pump number determination means 21 calculates a boiler load predicted value from the boiler load command value, and the required operating number of pumps 3 is determined from this boiler load predicted value. The pump start / stop means 22 calculates the number of pumps 3 that is insufficient based on the required number of pumps 3 and the actual number of pumps 3. At this time, if the pump start / stop means 22 does not receive the start signal or stop signal of the coal mill,
For the pumps 3 corresponding to the shortage number, a start command is issued if the shortage number is a positive value, and a stop command is issued if the shortage number is a negative value.

When the pump start / stop means 22 receives the start signal or stop signal of the coal mill, and the outlet S
When the O ₂ concentration is equal to or higher than the predetermined first set value, the pump 3
1 in order to increase the number of operating vehicles forcibly
Is added as the start-up number, and a start-up command is issued to the pumps 3 corresponding to this start-up number. Therefore, as soon as the start signal or stop signal of the coal mill is received, the new pump 3 is started, and the circulation amount of the absorbing liquid increases, so that the start or stop of the coal mill causes the inlet SO ₂ concentration to rise rapidly. Also, the outlet SO ₂ concentration can be suppressed below the regulation value.

After that, when the increase of the inlet SO ₂ concentration stops, the outlet SO ₂ concentration decreases, but when it decreases below the second set value that is smaller than the first set value, the number of operating units is forced. In order to reduce the number of pumps to 3, the number of the pumps 3 to be activated is set to the number obtained by subtracting 1 from the insufficient number. Thus, even if the coal mill is started or stopped, if the outlet SO ₂ concentration is equal to or lower than the predetermined first set value, the pump 3 is not forcibly started, and the pump 3 is forcibly started. Even in such a case, when the outlet SO ₂ concentration falls below the second set value that is smaller than the first set value, the pump 3 that has been started is forcibly stopped, so that the extra pump 3 is not operated. When all the pumps 3 are in operation when the pump start / stop means 22 receives the start signal or the stop signal of the coal mill, the pump start / stop means 22 causes the charge determining means 40 to determine the charge amount of the absorbent. Output a command to increase.

Next, in the absorbent input amount control means 30, first, the pH set value determination means 31 determines the basic pH set value based on the map M3, and the pH set value correction means 33 sets the basic pH set value. The value is corrected by the deviation between the outlet SO ₂ concentration and its target value to determine the final pH setpoint. In the input amount determining means 32, the basic input amount determining means 38 determines the basic input amount of the absorbent from the boiler air flow rate, the inlet SO ₂ concentration and the pH of the absorbing liquid based on the corrected pH set value. .

Next, the input amount correction means 39 corrects the basic input amount in accordance with the changing speed of the boiler load to determine the input amount. Furthermore, when a command to increase the input amount of the absorbent is input to the input amount increasing means 40 from the pump start / stop means 22, the increase amount for each time is automatically determined based on the map M4. , The input amount is increased by this increase amount.

According to the control method of the desulfurization apparatus 1 and the control apparatus 4 thereof described above, the following effects can be obtained. 1) When the pump start / stop means 22 receives the start signal or the stop signal of the coal mill, the number of operating pumps 3 is increased, so that the inlet SO ₂ concentration rapidly increases when the coal mill is started or stopped. However, since the circulation flow rate of the absorbing liquid can be immediately increased, it is possible to keep the outlet SO ₂ concentration below the regulation value by making the control follow the fluctuation of the inlet SO ₂ concentration. Further, the number of operating pumps 3 is increased only when the outlet SO ₂ concentration is equal to or higher than the first set value,
When the outlet SO ₂ concentration falls below the second set value, the number of pumps 3 to be operated is reduced, so that the extra pumps 3 are not operated, which is advantageous in terms of operation cost.

2) When the pump start / stop means 22 receives the start signal or the stop signal of the coal mill, if all the pumps 3 which can be operated are in operation, the charging amount increasing means 40 stores the absorbent Since the command to increase the input amount is output and the input amount is increased by the input amount increasing means 40, the pH of the absorption liquid can be increased even in a state where the circulating amount of the absorption liquid cannot be increased without the startable pump 3. to promote the reaction of the SO ₂ absorption liquid and flue gas by increasing the outlet SO ₂
Keep the concentration below the regulation value.

3) The pH set value determining means 31 has a map M3 in which the relationship between the boiler load and the pH set value is uniquely set in advance, and the pH set value obtained from this map M3 has little fluctuation. Therefore, even if the SO ₂ concentration at the inlet suddenly rises, the fluctuation of the pH of the absorbing liquid can be suppressed,
It enables stable pH control. Further, the pH control is simplified, and the time required for the arithmetic processing can be shortened.

4) Since the pH set value correction means 33 corrects the pH set value according to the deviation between the outlet SO ₂ concentration and its target value, the deviation is positive, that is, the outlet SO ₂ concentration is S.
If the O ₂ concentration exceeds the target value, the pH of the absorption liquid
The reaction between the absorbing liquid and the SO ₂ of the exhaust gas is promoted by increasing the value of, and the outlet SO ₂ concentration approaches the target value. On the other hand, when the deviation is negative, that is, when the outlet SO ₂ concentration is lower than the target value of the SO ₂ concentration, the correction amount of the negative value is determined and the pH set value is lowered, so Input is suppressed. Here, by setting an appropriate lower limit value for this negative correction amount, it is possible to prevent the pH set value from dropping too low, and even if the boiler load or the inlet SO ₂ concentration changes suddenly, The SO ₂ concentration can be suppressed below the regulation value.

5) Boiler load by the input amount correcting means 39
To correct the amount of absorbent input according to the rate of change β1
So, even if the boiler load changes suddenly,
Follow the control of H and exit SO₂Concentration below regulation value
Can be suppressed. When the changing speed of the boiler load is negative
Is the lower limit value β to the rate of change β1 for determining the correction amount.
₀By providing a
Do not correct to the inlet SO₂The concentration rises sharply
If the follow-up of the input amount correction is delayed when the ₂concentration
Can be kept below a specified value.

It should be noted that, for example, when one of the pumps 3 is under maintenance, and the pump start / stop means 22 receives the start signal or the stop signal of the coal mill while all of the operable pumps 3 are in operation. Sometimes, pump starting and stopping means 2
A command to increase the input amount may be output from 2 to the input amount increasing means 40.

[0056]

According to the invention of claim 1, when the pump control means increases the number of operating pumps when receiving the start signal or the stop signal of the fuel supply device, the fuel supply device starts or stops. Even if the inlet SO ₂ concentration rises rapidly, the circulating flow rate of the absorbing liquid can be immediately increased. Therefore, the control is made to follow the variation of the inlet SO ₂ concentration so that the outlet SO ₂ concentration is below the regulation value. It becomes possible to suppress it. Further, in order to increase the number of operating seen the pump when the outlet SO ₂ concentration is equal to or greater than the first set value, the outlet SO ₂
Since the concentration is sufficiently lower than the regulation value, even if the inlet SO ₂ concentration increases suddenly temporarily, if the outlet SO ₂ concentration falls below the regulation value, it is not necessary to start the pump further. It is advantageous in terms of operating cost.

According to the second aspect of the present invention, after the pump control means receives the start signal or the stop signal of the fuel supply device and the pump control means increases the number of operating pumps,
When the outlet SO ₂ concentration drops below a second set value that is smaller than the first set value, the number of pumps operating is reduced, so that the outlet SO ₂ concentration falls below a second set value that is smaller than the first set value. When it drops, reduce the number of
The number of pumps to be operated can be reduced at an appropriate timing, and an extra pump is not operated, which is advantageous in operating cost. In addition, the same effect as that of the first aspect can be obtained.

According to the invention of claim 3, the pump control means receives the start signal or the stop signal of the fuel supply device,
If it is not possible to increase the number of pumps that can be operated because all the pumps that can be operated are in operation, increase the amount of absorbent to raise the pH of the absorbent to increase the absorption liquid and exhaust gas. The reaction of SO ₂ with SO ₂
Since the control can be made to follow the rapid increase in the O ₂ concentration, it becomes possible to suppress the outlet SO ₂ concentration below the regulation value. In addition, the same effect as that of claim 1 or 2 can be obtained.

According to the invention of claim 4, the pump starting and stopping means increases the number of operating pumps when the starting signal or the stopping signal of the fuel supply device is received. Therefore, the effect is the same as that of claim 1. Yes, and the description is omitted. According to the invention of claim 5, after the pump control means receives the start signal or the stop signal of the fuel supply device and the number of operating pumps is increased by the pump start / stop means, the outlet SO ₂ concentration is set to the first setting. When the number of pumps is decreased to the second set value or less, which is smaller than the value, the number of operating pumps is reduced. Therefore, the effect is the same as that of claim 2, and the description thereof is omitted.

According to the sixth aspect of the present invention, when the pump starting / stopping means receives the starting signal or the stopping signal of the fuel supply device, but all the operable pumps are in operation and there is no further operable pump. Causes an increase in the amount of the absorbent charged, and therefore the effect is the same as that of claim 3, and the description thereof is omitted. According to the invention of claim 7, the pH set value determining means comprises:
Since it has a pH set value characteristic in which the relationship between the boiler load and the pH set value is uniquely set in advance, the pH set value does not fluctuate, so that even if the inlet SO ₂ concentration rises sharply, The fluctuation of the absorption liquid is small, and even if the inlet SO ₂ concentration rises sharply,
The control of can be stabilized. Further, the pH control is simplified, and the time required for the arithmetic processing can be shortened.
In addition, the same effect as that of any one of claims 4 to 6 can be obtained.

According to the eighth aspect of the invention, when the deviation between the outlet SO ₂ concentration and its target value is positive, that is, when the outlet SO ₂ concentration exceeds the target value, the pH set value correction means is used. Determine the correction amount corresponding to the magnitude of the deviation,
Since this correction amount is added to the pH set value, the pH of the absorption liquid rises and the reaction between the absorption liquid and SO ₂ of the exhaust gas is promoted,
The outlet SO ₂ concentration is brought close to the target value.

On the other hand, when the deviation is negative, that is, when the outlet SO ₂ concentration is below the target value, a negative correction amount corresponding to the magnitude of the negative deviation is added to the pH set value. In this case, since the pH set value is lowered, the introduction of the alkaline absorbent is suppressed. Here, by setting an appropriate lower limit value for this negative correction amount,
Even if the boiler load or the inlet SO ₂ concentration changes abruptly, it is possible to suppress the outlet SO ₂ concentration to be equal to or lower than the regulation value by preventing the pH set value from being corrected too much. In addition, the same effect as that of any one of claims 4 to 7 can be obtained.

According to the invention of claim 9, when the boiler load changes abruptly, the correction amount according to the changing speed is determined by the injection amount correcting means, and this correction amount is the injection amount of the alkaline absorbent. Therefore, even if the boiler load changes abruptly, the pH control of the absorption liquid is made to follow,
The SO ₂ concentration at the outlet can be suppressed below the regulation value. In addition, the same effect as that of any one of claims 4 to 8 can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a desulfurization device according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a desulfurization device.

FIG. 3 is a block diagram showing a configuration of a prediction calculation means.

FIG. 4 is a diagram showing a relationship between a predicted value of a boiler load and a time.

FIG. 5 is a diagram showing a relationship between boiler load and inlet SO ₂ concentration.

FIG. 6 is a diagram showing a relationship between a boiler load and a required number of pumps to be operated.

FIG. 7 is a diagram showing increase / decrease in the number of operating pumps when starting / stopping the coal mill in the pump start / stop means.

FIG. 8 is a diagram showing a relationship between a boiler load and a pH set value.

FIG. 9 is a diagram showing the amount of increase in the amount of adsorbent charged when starting / stopping the coal mill when all pumps are operating.

[Explanation of symbols]

1 desulfurization equipment 2 absorption tower 3 pumps 4 control device 20 Pump control means 21 means for determining the number of pumps 22 Pump start / stop means 30 Absorbent input amount control means 31 pH setting value determining means 32 Input amount determining means 33 pH setting value correction means 39 Input amount correction means

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3H045 AA16 AA22 AA39 BA19 BA28                       CA23 DA01 DA32 DA47                 4D002 AA02 AC01 BA02 CA01 DA05                       DA16 GA02 GA03 GB02 GB05                       GB09

Claims (9)

[Claims] 1. A method for controlling a wet flue gas desulfurization apparatus, which removes sulfur oxides in exhaust gas discharged from a boiler while circulating an absorbent containing an alkaline absorbent through an absorption tower by a plurality of pumps. When the pump control means for controlling the drive of the pump receives the start signal or the stop signal of the fuel supply device for supplying the fuel to the boiler, the sulfur oxide concentration of the exhaust gas at the outlet of the absorption tower is the first set value or more. In this case, the method for controlling a wet flue gas desulfurization device is characterized in that the number of pumps operated is increased. 2. The second setting in which the sulfur oxide concentration of the exhaust gas at the outlet of the absorption tower is smaller than the first set value after the pump control means receives the start signal or the stop signal and increases the number of pumps operating. The method for controlling a wet flue gas desulfurization apparatus according to claim 1, wherein the number of operating pumps is reduced when the value falls below a value. 3. When the pump control means receives a start signal or a stop signal of the fuel supply device, and when all the pumps are in operation, the amount of the absorbent admixed is increased. The method for controlling the wet flue gas desulfurization apparatus according to claim 2. 4. A wet flue gas desulfurization device for removing sulfur oxides in exhaust gas discharged from a boiler while circulating an absorbent containing an alkaline absorbent through a plurality of pumps to an absorption tower, and driving a plurality of pumps. A pump control means for controlling, which determines the required number of pumps to be operated according to the load of the boiler, and the number of pumps to be increased / decreased from the required number of pumps to be operated and the actual number of pumps to be operated. A pump control unit that includes a pump start-stop unit that starts or stops, and an adsorbent input amount control unit that controls the input amount of the alkaline absorbent, the pH setting value determining unit determining a pH setting value of the absorbing liquid. Means and
An absorbent input amount control means having an input amount determining means for determining the input amount of the alkaline absorbent using the determined pH set value, and a pump start / stop means of the pump control means is provided in the boiler. The number of operating pumps is increased when the concentration of sulfur oxides in the exhaust gas at the outlet of the absorption tower is equal to or higher than a first set value when a start signal or a stop signal of a fuel supply device that supplies fuel is received. Wet flue gas desulfurization equipment control device. 5. The pump start / stop means receives a start signal or a stop signal of the fuel supply device to increase the number of pumps in operation, and then the sulfur oxide concentration of the exhaust gas at the outlet of the absorption tower is set to the first set value. The controller for the wet flue gas desulfurization apparatus according to claim 4, wherein the number of operating pumps is reduced when the value is reduced to a second set value that is smaller than the second set value. 6. The pump start / stop means, when all the pumps are in operation when receiving the start signal or the stop signal of the fuel supply device, the input amount determining means causes the input amount of the absorbent to be input. The control device for the wet flue gas desulfurization device according to claim 5, wherein a command to increase is output. 7. The wet method according to claim 4, wherein the pH setting value determining means has a pH setting value characteristic in which the relationship between the boiler load and the pH setting value is uniquely set in advance. Control device for flue gas desulfurization equipment. 8. The pH setting value determining means includes a pH setting value correcting means for correcting the pH setting value according to the deviation between the sulfur oxide concentration at the outlet of the absorption tower and the sulfur oxide concentration target value. The control device for a wet flue gas desulfurization device according to any one of claims 4 to 7. 9. The charging amount determining means comprises charging amount correcting means for correcting the charging amount of the alkaline absorbent according to the changing speed of the load of the boiler.
A control device for a wet flue gas desulfurization device according to any one of 1.