JP2000015051A - Control method for absorption tower bleed liquid flow rate in flue gas desulfurization apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce rise of the concentration of a suspending substance contained in overflow water of a gypsum thickener, avoid deterioration of dewatering performance and reduce operation cost by alleviating load on a waste water treatment apparatus side. SOLUTION: Actual absorption tower bleed liquid flow rate 29 is controlled in such a manner as to be prevented from exceeding an absorption tower bleed liquid flow rate upper limit set value 64' by additionally providing in a controller 41 a divider 76 which divides soot dust inflow quantity 73 per unit section area of a gypsum thickener by soot dust concentration 74 in an absorption tower to output a quotient 75 and a multiplier 78 which multiplies the quotient 75 outputted by the divider 76 by a section area 77 of the gypsum thickener to obtain the absorption tower bleed liquid flow rate upper limit set value 64' and output the value to a low selector 66.

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 flow rate of a bleed liquid in an absorption tower of a flue gas desulfurization apparatus.

[0002]

2. Description of the Related Art In general, coal-fired
SO from exhaust gas discharged from irrigation _Two(Sulfur oxides)
To absorb and remove calcium carbonate as absorbent
(CaCO_Three) Is installed,
The flue gas desulfurization unit is usually equipped with a lower part as shown in FIG.
A liquid reservoir 1a for absorbing liquid 1 is formed in
An absorption tower 3 in which a play nozzle 2 is disposed;
The absorption liquid 1 in the liquid reservoir 1a is pumped up and the spray nozzle 2
A plurality of circulation pumps 4 for spraying and circulating
Oxidizing air for supplying oxidizing air to the liquid reservoir 1a of the absorption tower 3
Blower 5 and liquid extracted from liquid reservoir 1a of absorption tower 3
Gypsum recovery from gypsum 6 from absorption tower bleed liquid 1 '
And a device 7.

[0003] The gypsum recovery apparatus 7 is provided with a caustic soda supplied via a neutralizing agent supply line 9 to an absorption tower bleed liquid 1 ′ extracted from a liquid reservoir 1 a of the absorption tower 3 via an extraction line 8. A neutralization tank 10 for adding a neutralizing agent such as (NaOH) and an absorption tower bleed liquid 11 neutralized in the neutralization tank 10 are introduced through a neutralization absorption liquid line 12, and the absorption tower bleed liquid A gypsum thickener 16 for sedimenting the solid content in 11 and leading the supernatant overflow water 13 to a wastewater treatment device 15 via a drainage line 14, and a slurry 17 containing the solid content settled by the gypsum thickener 16 is a slurry line 18. The slurry 17 is dewatered to separate the gypsum 6 and the filtrate 19 from the slurry 17 and the filtrate 19 separated from the gypsum 6 is filtered through the filtrate line 20 into the gypsum thickener 1.
6 and a gypsum dewatering machine 21 for guiding to 6. In the middle of the slurry line 18, a gypsum dewatering machine supply tank 22 for temporarily storing the slurry 17 introduced from the gypsum thickener 16 to the gypsum dewatering machine 21 is provided, and in the middle of the filtrate line 20. A gypsum dewatering machine drain pit 23 for temporarily storing the filtrate 19 returned from the gypsum dewatering machine 21 to the gypsum thickener 16 is provided. An overflow water tank 24 for temporarily storing the overflow water 13 to be discharged is provided. In the middle of the neutralizing agent supply line 9, there is provided a flow rate adjusting valve 25 for adjusting the flow rate of the neutralizing agent supplied to the neutralizing tank 10. PH instruction control for detecting the pH of the bleed liquid 11 in the absorption tower 10 and outputting an opening command 26 to the flow control valve 25 so that the pH becomes a preset pH set value (usually 7.0). A total of 27 are provided.

[0004] In the case of the above-mentioned flue gas desulfurization apparatus, the absorption liquid 1
Is circulated while being sprayed from the spray nozzle 2 by the operation of the circulation pump 4, and the exhaust gas sent to the absorption tower 3 from a coal-fired boiler or the like (not shown) is mixed with the absorbent 1 sprayed from the spray nozzle 2. By contacting
After SO ₂ (sulfur oxide) is absorbed and removed, it is discharged to the outside.

On the other hand, the absorbent 1 having absorbed SO ₂ from the exhaust gas drops into the liquid reservoir 1a and is forcibly oxidized by the oxidizing air supplied into the liquid reservoir 1a by the operation of the oxidizing air blower 5. , Gypsum (calcium sulfate (CaS
O ₄ )) is produced, and a part of the absorbent 1 in the liquid reservoir 1 a containing the gypsum is converted into an absorption tower bleed liquid 1 ′ via the extraction line 8 through the neutralization tank 10 And neutralized by a neutralizing agent such as caustic soda (NaOH) supplied through a neutralizing agent supply line 9 in the neutralizing tank 10, and neutralized in the neutralizing tank 10. The bleed liquid 11 is introduced into the gypsum thickener 16 through the neutralizing absorption liquid line 12, and the solid content in the absorption tower bleed liquid 11 settles in the gypsum thickener 16, and the slurry 17 containing the solid content is converted into a slurry. The slurry 17 is introduced into the gypsum dewatering machine 21 through the line 18 and the gypsum dewatering machine supply tank 22, and the slurry 17 is dewatered in the gypsum dewatering machine 21 to be separated into the gypsum 6 and the filtrate 19, and the filtrate separated from the gypsum 6 19 is a filter The liquid is returned to the gypsum thickener 16 via the liquid line 20 and the gypsum dehydrator drain pit 23, and the overflow water 13 of the supernatant in the gypsum thickener 16 is
The wastewater is led to a wastewater treatment device 15 through a wastewater line 14 and an overflow water tank 24, and in the wastewater treatment device 15, harmful nitrogen compounds are decomposed by the action of nitrifying bacteria and are expressed by COD (chemical oxygen demand). After the reducing substance is adsorbed by the adsorption resin made of a polymer material, it is discharged to the outside.

Further, a required amount of absorbent slurry is supplied to the absorption tower 3 from an absorbent slurry supply line 28 as needed.

In the flue gas desulfurization apparatus as described above,
And neutralization of the gypsum recovery device 7 from the liquid reservoir 1a of the absorption tower 3.
Flow rate of the absorption tower bleed liquid 1 'withdrawn to the tank 10.
Is the flow control of the bleed liquid in the absorption tower provided in the middle of the extraction line 8.
As controlled by adjusting the opening of the valve 39
However, the control system is the liquid reservoir 1a of the absorption tower 3.
Extracted from the gypsum into the neutralization tank 10 of the gypsum collection device 7
Absorption tower bleed liquid flow to detect the collection tower bleed liquid flow rate 29
Gas flow rate for detecting the desulfurization gas flow rate 31
A total of 32 and SO at the entrance of the absorption tower_TwoAbsorption tower that detects concentration 33
Entrance SO_TwoBranching from the middle of the concentration line 34 and the extraction line 8
Return for returning part of the absorption tower bleed liquid 1 ′ to the absorption tower 3
Line 8 'is provided in the middle of the absorption line bleed liquid 1'.
A slurry concentration meter 36 for detecting a slurry concentration 35;
A level meter 3 for detecting the level 37 of the liquid reservoir 1a of the collection tower 3.
8 and the absorption detected by the absorption tower bleed liquid flow meter 30.
With the bleed liquid flow rate of the collecting tower 29 and the desulfurization gas flow meter 32,
The detected desulfurization gas flow rate 31 and the absorption tower inlet SO _Two
Absorption tower inlet SO detected by densitometer 34_TwoConcentration 33,
The slurry concentration 35 detected by the slurry concentration meter 36
And the level 37 detected by the level meter 38 are input.
The opening degree command is sent to the absorption tower bleed liquid flow control valve 39.
And a controller 41 that outputs a signal 40.
I have.

[0008] As shown in FIG.
The set desulfurization rate 42 (for example, 90%) with respect to the absorption tower inlet SO ₂ concentration 33 detected by the absorption tower inlet SO ₂ concentration meter 34.
[%]) To obtain a desulfurization SO ₂ concentration 43 and output the same, and a desulfurization output from the multiplier 44 to the desulfurization gas flow rate 31 detected by the desulfurization gas flow meter 32. By multiplying the SO ₂ concentration 43,
A multiplier 46 for obtaining and outputting the SO ₂ amount 45 to be absorbed from the exhaust gas, and a desired conversion coefficient 47 for multiplying the SO ₂ amount 45 to be absorbed output from the multiplier 46 by an absorption tower. A multiplier 49 for outputting a bleed liquid flow rate set value 48; a slurry concentration 35 detected by the slurry concentration meter 36 and a slurry concentration set value 50 (for example, 1
5 [wt%]), and a subtractor 52 for outputting a slurry concentration deviation 51, and a proportional integration process for the slurry concentration deviation 51 output from the subtracter 52 to eliminate the slurry concentration deviation 51. A proportional-integral controller 54 for outputting a correction value 53 for the conversion of the absorption tower bleed liquid required for the operation, and an output from the proportional-integral controller 54 for the set value 48 of the absorption tower bleed liquid flow output from the multiplier 49. The adder 56 calculates and outputs an absorption tower bleed liquid flow rate correction set value 55 by adding the absorption tower bleed liquid flow rate conversion correction value 53, and the liquid storage section of the absorption tower 3 detected by the level meter 38. The difference between the level 37 of 1a and the level set value 57 (for example, 9.5 [m]) is obtained, and a subtractor 59 that outputs a level deviation 58 is compared with a level deviation 58 output from the subtracter 59. Integration processing to be required in order to eliminate the level difference 58 absorption column bleed fluid flow rate setpoint 60
Of the absorption tower bleed liquid flow rate correction value 55 output from the adder 56 and the absorption tower bleed liquid flow rate setting value 60 output from the proportional integration controller 61. And a high selector 63 that outputs the selected value and outputs it as an absorption tower bleed liquid flow rate set value 62, an absorption tower bleed liquid flow rate set value 62 and an absorption tower bleed liquid flow upper limit set value 64 output from the high selector 63. A low selector 66 that selects the lower one of the two and outputs it as an absorption tower bleed liquid flow rate set value 65, an absorption tower bleed liquid flow rate set value 65 output from the low selector 66, and an absorption tower bleed liquid flow rate lower limit setting High selector 69 which selects the higher one of the values 67 and outputs it as the set value 68 of the bleed liquid flow rate of the absorption tower.
And the difference between the absorption tower bleed liquid flow rate set value 68 output from the high selector 69 and the absorption tower bleed liquid flow rate 29 output from the absorption tower bleed liquid flow meter 30 is determined. A subtracter 71 for outputting the bleed liquid 70 from the subtractor 71;
0 is proportionally integrated and the bleed liquid flow rate deviation 70
And a proportional-integral controller 72 for outputting an opening command 40 for eliminating the pressure to the absorption tower bleed liquid flow rate regulating valve 39.

During operation of the flue gas desulfurization apparatus, the absorption tower bleed liquid flow rate 29 detected by the absorption tower bleed liquid flow meter 30, the desulfurization gas flow rate 31 detected by the desulfurization gas flow meter 32, and the absorption The absorption tower inlet SO ₂ concentration 33 detected by the tower inlet SO ₂ concentration meter 34, the slurry concentration 35 detected by the slurry concentration meter 36, and the level 37 detected by the level meter 38 are sent to the controller 41. The SO ₂ concentration 33 detected at the absorption tower inlet SO ₂ concentration meter 34 by the multiplier 44 of the controller 41
Is multiplied by the set desulfurization rate 42 to obtain the desulfurized SO.
₂ concentration 43 is obtained and output to a multiplier 46, and the desulfurization SO ₂ concentration 43 output from the multiplier 44 is output to the multiplier 46 with respect to the desulfurization gas flow rate 31 detected by the desulfurization gas flow meter 32. By multiplying, the SO ₂ amount 45 to be absorbed from the exhaust gas is obtained and output to the multiplier 49, where the SO ₂ amount 45 output from the multiplier 46 is multiplied by a conversion coefficient 47. Thus, the absorption tower bleed liquid flow rate set value 48 is output to the adder 56.

In a subtractor 52 of the controller 41, a difference between the slurry concentration 35 detected by the slurry concentration meter 36 and the slurry concentration set value 50 is obtained. Slurry concentration deviation 51 output from the subtracter 52 is proportionally integrated in the proportional integration controller 54, and the bleed liquid flow rate correction for the absorption tower required to eliminate the slurry concentration deviation 51 is performed. The value 53 is output to the adder 56, where the absorption tower bleed liquid output from the proportional-integral controller 54 is compared with the absorption tower bleed liquid flow rate set value 48 output from the multiplier 49. By adding the flow rate conversion correction value 53, an absorption tower bleed liquid flow rate correction set value 55 is obtained and output to the high selector 63.

Further, a subtractor 59 of the controller 41 obtains a difference between the level 37 of the liquid reservoir 1a of the absorption tower 3 detected by the level meter 38 and the level set value 57, and obtains a level deviation. 58 is output to the proportional-plus-integral controller 61,
In the proportional integral controller 61, the level deviation 58 output from the subtractor 59 is proportionally integrated, and the absorption column bleed liquid flow rate set value 60 necessary for eliminating the level deviation 58 is set to the high selector 63. Is output to the high selector 63, and the absorption bleed liquid flow rate correction set value 55 output from the adder 56 and the proportional integral controller 6
The higher one is selected from the absorption tower bleed liquid flow rate set value 60 output from 1 and the absorption tower bleed liquid flow rate set value 6
2 is output to the low selector 66, and the low selector 66 sets the absorption tower bleed liquid flow rate set value 62 and the absorption tower bleed liquid flow upper limit set value 6 output from the high selector 63.
4 is selected and output to the high selector 69 as the absorption tower bleed liquid flow rate set value 65.
In 9, the higher one of the absorption tower bleed liquid flow rate setting value 65 and the absorption tower bleed liquid flow rate lower limit setting value 67 output from the low selector 66 is selected, and the subtractor is used as the absorption tower bleed liquid flow rate setting value 68. The difference between the set value 68 of the absorption tower bleed liquid flow output from the high selector 69 and the absorption tower bleed liquid flow rate 29 output from the absorption tower bleed liquid flow meter 30 is output to the subtractor 71. Is calculated, and the absorption tower bleed liquid flow rate deviation 70 is output to the proportional integral controller 72. In the proportional integration controller 72, the absorption tower bleed liquid flow deviation 70 output from the subtracter 71 is proportionally integrated. An opening command 40 for eliminating the absorption tower bleed liquid flow deviation 70 is output to the absorption tower bleed liquid flow adjustment valve 39, and the opening degree of the absorption tower bleed liquid flow adjustment valve 39 is adjusted. It is adjusted, the liquid reservoir portion 1a of the absorption tower 3
Is controlled so that the flow rate 29 of the absorption tower bleed liquid extracted from the wastewater into the neutralization tank 10 of the gypsum recovery apparatus 7 becomes equal to the set value 68 of the absorption tower bleed liquid flow rate.

That is, the flow rate 29 of the absorption tower bleed liquid extracted from the liquid storage section 1a of the absorption tower 3 to the neutralization tank 10 of the gypsum recovery device 7 is basically to ensure the quality of the gypsum 6. For the absorption tower bleed liquid flow rate set value 48 obtained by multiplying the SO ₂ amount 45 to be absorbed by the conversion coefficient 47,
The control is performed based on the absorption tower bleed liquid flow rate correction set value 55 obtained by adding a correction to maintain the slurry concentration 35 of the absorption tower bleed liquid 1 ′ at the slurry concentration set value 50, whereby, for example, the slurry concentration 35 is reduced. When it becomes, the opening of the absorption tower bleed liquid flow rate adjustment valve 39 is reduced,
A correction operation is performed so that the absorption tower bleed liquid flow rate 29 decreases.

When the level 37 of the liquid reservoir 1a of the absorption tower 3 approaches the overflow level, the opening of the absorption tower bleed liquid flow control valve 39 is widened, and the absorption tower bleed liquid flow 29 increases. Correction operation is performed as follows.

Further, if the flow rate 29 of the bleed liquid in the absorption tower is extremely increased, the processing capacity of the gypsum thickener 16 may be exceeded.
Since it is necessary to secure the overflow water 13 of the gypsum thickener 16 to a minimum in view of the liquid balance of the entire system, the absorption tower bleed liquid flow rate 29 exceeds a preset absorption tower bleed liquid flow rate upper limit value 64. Without lowering below the lower limit 67 of the bleed liquid flow rate of the absorption tower.

[0015]

However, in the case of the above-mentioned flue gas desulfurization apparatus, the combustion conditions in the coal-fired boiler (not shown) upstream of the absorption tower 3, the type of coal to be charged, and Depending on the operation state of the dust collector, a large amount of dust as impurities flows into the absorption tower 3 and the concentration of suspended solids contained in the overflow water 13 of the gypsum thickener 16 may increase. When the concentration of the suspended substance contained in the overflow water 13 of the gypsum thickener 16 increases, as shown in FIG. 5, the sedimentation rate of the solid in the gypsum thickener 16 decreases, which may cause a decrease in dewatering performance. On the other hand, since the overflow water 13 containing a large amount of suspended substances is introduced into the wastewater treatment device 15,
As the amount of the coagulating sedimentation agent used in the wastewater treatment device 15 increases, a large amount of sludge is generated, and the burden on the wastewater treatment device 15 increases, leading to a significant increase in operating costs. Was.

In view of such circumstances, the present invention can suppress an increase in the concentration of suspended substances contained in the gypsum thickener overflow water, can avoid a decrease in dewatering performance, and can improve the efficiency of the wastewater treatment apparatus. An object of the present invention is to provide a method for controlling a flow rate of a bleed liquid in an absorption tower of a flue gas desulfurization apparatus capable of reducing a burden and reducing an operation cost.

[0017]

Means for Solving the Problems The present invention, absorption liquid circulated while spraying pumped from reservoir part with lime, and contacted with the flue gas to remove absorbed SO ₂ in the flue gas absorber as an absorbent A tower, a neutralization tank for adding a neutralizing agent to the absorption tower bleed liquid withdrawn from the liquid reservoir of the absorption tower, and allowing the solid content in the absorption tower bleed liquid neutralized in the neutralization tank to settle. And a gypsum thickener for guiding the overflow water of the supernatant to a wastewater treatment device, and a slurry containing a solid content settled by the gypsum thickener is dewatered to be separated into gypsum and a filtrate, and the filtrate separated from the gypsum is sent to the gypsum thickener. In a method for controlling the flow rate of bleed liquid from an absorption tower of a flue gas desulfurization apparatus having a gypsum recovery device having a gypsum dewatering device and a gypsum dewatering device, the concentration of suspended solids in the overflow water of gypsum thickener falls within a planned value. The dust inflow per gypsum thickener unit cross-sectional area is obtained, the dust inflow per gypsum thickener unit cross-sectional area is divided by the dust concentration in the absorption tower, and the value is multiplied by the gypsum thickener cross-section to obtain the absorption tower. A method for controlling the flow rate of an absorption tower bleed liquid in a flue gas desulfurization apparatus, wherein the upper limit set value of a bleed liquid flow rate is determined and the actual flow rate of the absorption tower bleed liquid is controlled so as not to exceed the upper limit set value of the absorption tower bleed liquid flow rate. It depends on.

According to the above means, the following effects can be obtained.

During operation of the flue gas desulfurization unit, an allowable amount of dust inflow per unit area of the gypsum thickener permissible to keep the concentration of suspended solids in the overflow water of the gypsum thickener within a plan value is determined. The dust inflow per cross-sectional area is divided by the dust concentration in the absorption tower, and the value is multiplied by the gypsum thickener cross-sectional area to obtain the upper limit of the bleed liquid flow rate of the absorption tower. The actual absorption tower bleed liquid flow rate is controlled so as not to exceed.

As a result, it is assumed that a large amount of dust as impurities flows into the absorption tower depending on the combustion conditions in the coal-fired boiler on the upstream side of the absorption tower, the type of coal input, and the operating state of the electric dust collector. Also, since the concentration of the suspended substance contained in the gypsum thickener overflow water does not excessively increase, the solid sedimentation speed in the gypsum thickener does not decrease, and a decrease in dewatering performance is avoided. Since the overflow water containing a large amount of suspended substances is not introduced into the wastewater treatment equipment, the amount of the coagulating sedimentation agent used in the wastewater treatment equipment does not increase, and a large amount of sludge is not generated. Burden is reduced, and operation costs can be reduced.

[0021]

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

FIG. 1 shows an example of an embodiment of the present invention. In the figure, the parts denoted by the same reference numerals as those in FIGS. 3 and 4 represent the same parts, and the basic structure is shown in FIGS. 4 is the same as the conventional one shown in FIG. 4, but the feature of the illustrated example is that, as shown in FIG. 1, the dust inflow 73 per unit sectional area of the gypsum thickener is divided by the dust concentration 74 in the absorption tower, A divider 76 for outputting the quotient 75 and a quotient 75 output from the divider 76 are multiplied by a gypsum thickener cross-sectional area 77 to obtain an upper limit set value 64 ′ of the absorption tower bleed liquid flow rate. And a multiplier 78 for outputting to the controller 41.
And the actual absorption tower bleed liquid flow rate 2 is set so as not to exceed the absorption tower bleed liquid flow rate upper limit set value 64 '.
9 is controlled.

The dust inflow amount 73 per unit area of the gypsum thickener is based on a diagram as shown in FIG.
The concentration of suspended solids in the overflow water 13 of the gypsum thickener 16 is determined as an allowable value to fall within the planned value. However, as shown in FIG. A diagram representing the relationship between the amount 73 and the suspended solids concentration in the overflow water 13 of the gypsum thickener 16 is stored in the controller 41 in advance based on data obtained during operation.

The dust concentration 74 in the absorption tower is the concentration of the dust dissolved in the absorption liquid 1 in the liquid reservoir 1a of the absorption tower 3, and this is the concentration of the dust in the absorption tower 3 with respect to the absorption tower 3. It can be obtained by sequentially calculating based on various data during operation, including the supply amount, the flow rate of the exhaust gas introduced into the absorption tower 3, and the like.

Next, the operation of the above illustrated example will be described.

At the time of operation of the flue gas desulfurization apparatus, the overflow water 13 of the gypsum thickener 16 is based on the diagram shown in FIG.
The dust inflow 73 per unit area of the gypsum thickener allowed to keep the concentration of suspended solids within the planned value is determined, and the dust inflow 73 per unit area of the gypsum thickener is absorbed by the divider 76. By dividing the quotient 75 by the gypsum thickener cross-sectional area 77 in a multiplier 78, a quotient 75 is multiplied by a multiplier 78 to obtain an upper limit value 64 ′ of the absorption tower bleed liquid flow rate, which is output to the low selector 66.

In the low selector 66, the high selector 6
The lower one of the absorption tower bleed liquid flow rate setting value 62 and the absorption tower bleed liquid flow rate upper limit setting value 64 ′ output from 3 is selected and output to the high selector 69 as the absorption tower bleed liquid flow rate setting value 65, In the high selector 69, a higher one of the set value 65 of the absorption tower bleed liquid and the lower set value 67 of the absorption tower bleed liquid output from the low selector 66 is selected, and the set value of the absorption tower bleed liquid flow rate is set. 68, which is output to the subtracter 71, where the set value 68 of the absorption tower bleed liquid flow rate output from the high selector 69 and the flow rate of the absorption tower bleed liquid output from the absorption tower bleed liquid flow meter 30 are output. 29 is obtained, and an absorption tower bleed liquid flow rate deviation 70 is output to a proportional-integral controller 72. In the proportional-integral controller 72, the absorption tower output from the subtractor 71 is output. The bleed liquid flow deviation 70 is proportionally integrated, and an opening command 40 for eliminating the absorption tower bleed liquid flow deviation 70 is output to the absorption tower bleed liquid flow adjustment valve 39. The opening degree is adjusted, and the absorption tower bleed liquid flow rate 2 which is extracted from the liquid reservoir 1a of the absorption tower 3 to the neutralization tank 10 of the gypsum recovery device 7
Control is performed so that 9 becomes equal to the absorption tower bleed liquid flow rate set value 68.

As a result, the actual absorption tower bleed liquid flow rate 2
Since 9 is controlled so as not to exceed the upper limit value 64 ′ of the bleed liquid flow rate of the absorption tower, the combustion conditions in the coal-fired boiler on the upstream side of the absorption tower 3, the type of coal of the input coal, or Even if a large amount of dust as impurities flows into the absorption tower 3 depending on the operation state of the electric precipitator, the concentration of suspended substances contained in the overflow water 13 of the gypsum thickener 16 does not excessively increase. Therefore, the sedimentation speed of the solid in the gypsum thickener 16 does not decrease, and a decrease in the dewatering performance is avoided. On the other hand, since the overflow water 13 containing a large amount of suspended substances is not introduced into the wastewater treatment device 15, wastewater treatment is performed. The use amount of the coagulating sedimentation agent in the device 15 does not increase, and a large amount of sludge is not generated, so that the burden on the wastewater treatment device 15 side is reduced and the operation cost can be reduced.

In this way, an increase in the concentration of suspended substances contained in the overflow water 13 of the gypsum thickener 16 can be suppressed, a decrease in dewatering performance can be avoided, and a burden on the wastewater treatment device 15 can be reduced. Operating cost can be reduced.

It should be noted that the method of controlling the flow rate of the bleed liquid in the absorption tower of the flue gas desulfurization apparatus of the present invention is not limited to the above-described example, and various changes can be made without departing from the gist of the present invention. Of course.

[0031]

As described above, according to the method for controlling the flow rate of the bleed liquid in the absorption tower of the flue gas desulfurization apparatus of the present invention, it is possible to suppress an increase in the concentration of suspended substances contained in the overflow water of the gypsum thickener. , Can avoid a decrease in dehydration performance,
In addition, it is possible to achieve an excellent effect that the burden on the wastewater treatment device can be reduced and the operating cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a controller according to an example of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a dust inflow amount per unit sectional area of a gypsum thickener and a suspended solids concentration in a gypsum thickener overflow in water.

FIG. 3 is an overall schematic configuration diagram of a conventional example.

FIG. 4 is a control block diagram of a controller in a conventional example.

FIG. 5 is a diagram showing the relationship between the concentration of suspended solids in gypsum thickener overflow water and the sedimentation velocity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Absorption liquid 1 'Absorption tower bleed liquid 1a Liquid storage part 3 Absorption tower 6 Gypsum 7 Gypsum collection apparatus 10 Neutralization tank 11 Absorption tower bleed liquid 13 Overflow water 15 Wastewater treatment equipment 16 Gypsum thickener 17 Slurry 19 Filtrate 21 Gypsum dehydrator 29 Absorber bleed liquid flow 31 Desulfurization gas flow 39 Absorber bleed liquid flow control valve 40 Opening command 41 Controller 62 Absorber bleed liquid flow set value 64 'Absorber bleed liquid flow upper limit set value 65 Absorber bleed liquid flow set value 66 Low selector 73 Dust inflow per unit area of gypsum thickener 74 Dust concentration in absorption tower 76 Divider 77 Gypsum thickener cross section 78 Multiplier

Claims (1)

[Claims] 1. An absorption tower for pumping an absorbent using lime as an absorbent from a liquid reservoir, circulating it while spraying, and contacting the exhaust gas to absorb and remove SO ₂ in the exhaust gas; A neutralization tank for adding a neutralizing agent to the bleed liquid of the absorption tower withdrawn from the reservoir, a sedimentation of solids in the bleed liquid of the absorption tower neutralized in the neutralization tank, and a drainage treatment of the overflow water of the supernatant. A gypsum having a gypsum thickener leading to an apparatus and a gypsum dewatering machine for dewatering a slurry containing solids precipitated by the gypsum thickener to separate gypsum and a filtrate, and leading the gypsum and the separated filtrate to the gypsum thickener A method for controlling a flow rate of a bleed liquid in an absorption tower of a flue gas desulfurization apparatus provided with a recovery device, comprising: The dust inflow per cross-sectional area is determined, the dust inflow per unit cross-section of the gypsum thickener is divided by the dust concentration in the absorption tower, and the value is multiplied by the gypsum thickener cross-section to obtain an upper limit value of the absorption tower bleed liquid flow rate. And controlling an actual absorption tower bleed liquid flow rate so as not to exceed the upper limit set value of the absorption tower bleed liquid flow rate.