JPH11179145A - Absorbent supply control method and apparatus for flue gas desulfurization facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fluctuation of pH value of an absorbing solution in an absorption tower at the time of starting and stopping a circulation pump. SOLUTION: A controller 17 outputs to an absorbent slurry regulating valve 9a valve command signal for increasing an absorbent slurry supply amount read by a flow meter 15 by a specified increase amount S for a specified time upon an input of a circulation pump increase signal 19a and outputs to the absorbent slurry regulating valve 9a valve command signal 14 for decreasing the absorbent slurry supply amount 13 read by the flow meter 15 by a specified decrease amount S' for a specified time t' upon an input of a circulation pump decrease signal 19b. A normal absorbent slurry supply control is executed by using a pH value 11 detected by a pH meter 10 as a reference while the circulation pump increase/decrease signals 19 are not outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sulfur pump for exhaust gas fed into an absorption tower in which a liquid reservoir for absorbing liquid is formed in the lower part and a number of spray nozzles are provided in the upper part, by means of a circulation pump. The present invention relates to a method and an apparatus for controlling the supply of an absorbent in a flue gas desulfurization apparatus for removing with an absorbing liquid which is pumped from a reservoir and sprayed from a spray nozzle.

[0002]

2. Description of the Related Art A flue gas desulfurization apparatus for desulfurizing exhaust gas using limestone, calcium carbonate and other absorbents generally has a liquid reservoir 1a for absorbing liquid 1 formed at a lower portion as shown in FIG. An absorption tower 3 having a large number of spray nozzles 2 disposed thereon, a circulating pump 4 for pumping up the absorption liquid 1 in a liquid reservoir 1a of the absorption tower 3 and spraying and circulating it from the spray nozzle 2; And an oxidizing air blower 5 for supplying oxidizing air to the liquid reservoir 1a. 6 is a circulation pipe on which a circulation pump 4 is installed,
Reference numeral 7 denotes a valve for an operator to periodically extract a part of the absorption liquid 1 in the absorption tower 3.

[0003] 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 from the coal-fired boiler to the absorption tower 3 comes into contact with the absorbing liquid 1 sprayed from the spray nozzle 2, thereby reducing SO 2. ₂ (Sulfur oxide)
Is absorbed and removed and then discharged outside.

On the other hand, a part of the absorbing liquid 1 that has absorbed SO ₂ from the exhaust gas is recovered as gypsum slurry from the bottom of the liquid reservoir 1 a of the absorption tower 3, water is removed from the gypsum slurry, and gypsum is generated. It has become. Also, in the absorption tower 3,
The absorbent slurry 8 is supplied via an absorbent slurry adjusting valve 9.

[0005] By the way, as long as the sulfur in the exhaust gas and the calcium in the absorbent react normally one-to-one, the amount of the unreacted absorbent is almost zero, and the desulfurization of the exhaust gas is surely performed. Therefore, it has been conventionally performed to control the pH (pH) of the absorbing solution in the absorption tower to be constant.

That is, a pH meter 10 for detecting a pH value 11 of an absorbing solution is installed, for example, in a circulation pipe 6 having a circulation pump 4 connected between the liquid reservoir 1a and the spray nozzle 2 and provided with a pH meter. The control is performed so that the pH value 11 detected at 10 becomes a preset pH value 16.

More specifically, the controller 11 compares the detected pH value 11 with a preset set pH value 16 (for example, pH value 5.0), and based on the comparison result, supplies the absorbent slurry. The controller 12 outputs a valve command signal 14 to the absorbent slurry adjusting valve 9 to control the valve opening of the absorbent slurry adjusting valve 9 for adjusting the amount 13. Further, a flow meter 15 for detecting the amount 13 of absorbent slurry supplied is provided, and the amount 13 of absorbent slurry supplied by adjustment of the absorbent slurry adjusting valve 9 is corrected to be a valve command signal 14.

[0008]

As described above, in a wet type flue gas desulfurization apparatus, the supply amount of the absorbent slurry 8 has conventionally been determined by measuring the pH value 11 of the absorbent 1 in the absorption tower 3 by a pH meter 1.
It is detected at 0, compared with the set pH value 16 set in the controller 12, and controlled by the valve command signal 14 based on the deviation so that the pH value of the absorbent 1 in the absorption tower 3 is always constant. I have.

Therefore, when the flow rate of the exhaust gas sent to the absorption tower 3 increases, that is, when the load on the boiler increases, or when the concentration of sulfur oxides in the exhaust gas increases, the absorption pumped up from the liquid reservoir 1a. In order to increase the amount of the liquid 1 and spray more of the absorbing liquid 1 from the spray nozzle 2, among the many circulation pumps 4, some of the circulation pumps 4 in the currently stopped state are activated. .

[0010] Immediately after the circulation pump 4 is started, the amount of the absorbing liquid 1 sprayed from the spray nozzle 2 rapidly increases, so that a large amount of sulfur oxide is absorbed from the exhaust gas. As a result, the pH value 11 of the absorbing solution in the absorption tower 3 temporarily drops below the set pH value 16. As described above, when the pH value 11 decreases rapidly,
In an attempt to maintain the value 11 at the set pH value 16, the supply of the absorbent slurry 8 is increased.

FIG. 4 shows the process values of the pH value 11 of the absorbing solution 1 in the absorption tower 3 and the supply amount 13 of the absorbent slurry before and after the start and stop of the circulation pump in the above-mentioned conventional flue gas desulfurization apparatus. FIG. 4 is a characteristic diagram illustrating a relationship.

As shown by the solid line A in FIG. 4, immediately after the start of the circulation pump, the pH value 11 of the absorbing solution 1 in the absorption tower 3 drops rapidly from the set pH value 16, and thereafter, the set pH value 16 Is temporarily exceeded.

That is, immediately after the circulation pump 4 is started,
Since the amount of the absorbing liquid 1 sprayed from the spray nozzle 2 rapidly increases, a large amount of sulfur oxide is absorbed from the exhaust gas, and the absorbing liquid 1 sprayed from the spray nozzle 2 is discharged from the liquid reservoir 1a. By being mixed with the absorbing solution 1, the pH value of the absorbing solution 1 decreases, and the absorbing solution 1 having the reduced pH value is supplied to the circulating pipe 6 by the circulating pump 4 so that the pH value is reduced.
There is a required time delay before the pH value 11 is detected by the pH meter 10, and therefore, the pH value 1
1, the controller 12 changes the valve command signal 14 so that the set pH value 16 is maintained.
To control the supply amount 13 of the absorbent slurry so as to increase with a time delay as shown by the solid line B in FIG.

As shown by the broken line A 'in FIG. 4, immediately after the circulation pump is stopped, the pH value of the absorbent 1 in the absorption tower 3 rises rapidly from the set pH value 16, and thereafter, the pH value of the set pH value increases.
It can be seen that the H value is temporarily lower than 16.

That is, immediately after the circulation pump 4 is started,
Since the amount of the absorbing liquid 1 sprayed from the spray nozzle 2 is rapidly reduced, the absorption of the sulfur oxide from the exhaust gas is reduced, and the absorbing liquid 1 injected from the spray nozzle 2 is stored in the liquid reservoir 1a. Is mixed with the absorption liquid 1 of
The pH value of the absorbing solution 1 rises, and the absorbing solution 1 whose pH value has risen is supplied to the circulation pipe 6 by the circulation pump 4 and p
There is a time delay before it is detected by the H meter 10, and therefore, based on the increase in the pH value from the pH meter 10,
The controller 12 outputs a valve command signal 14 to the absorbent slurry adjusting valve 9 so that the set pH value 16 is maintained, and the absorbent slurry supply amount 13 has a time delay as shown by a broken line B ′ in FIG. Then, control is performed so as to decrease.

That is, in the conventional pH control, since the start / stop of the circulation pump 4 is not considered, the pH value fluctuates up and down with respect to the set pH value 16 immediately after the start / stop of the pump. Since the absorbent slurry supply amount 13 is controlled with a time delay with respect to the fluctuation of the value 11, it is uneconomical to supply an excessive amount of the absorbent slurry 8 particularly when the circulation pump is started. There was a problem.

This phenomenon is particularly remarkable when a plurality of circulating pumps 4 are continuously started and stopped due to a sudden rise and fall of the boiler load.

The present invention solves the above disadvantages of the prior art,
It is an object of the present invention to provide a method and an apparatus for controlling the supply of an absorbent of a flue gas desulfurization apparatus, which can suppress the fluctuation of the pH value of the absorbent in the absorption tower when the circulation pump is started.

[0019]

In order to achieve the above object, a method of controlling the supply of an absorbent according to the present invention comprises forming a liquid reservoir for absorbing liquid in a lower part and disposing a number of spray nozzles in an upper part. The method for controlling the supply of an absorbent in a flue gas desulfurization apparatus, wherein the sulfur content of the exhaust gas sent into the absorption tower is pumped up from a liquid reservoir by a circulation pump and removed by an absorbing solution sprayed from a spray nozzle. The amount of the slurry supplied to the absorbent is controlled so that the pH value of the absorbent in the absorption tower becomes the set pH value. When the slurry supply amount is increased by a predetermined amount and the circulation pump decrease signal is output,
For a predetermined time, the supply amount of the absorbent slurry is reduced by a predetermined amount.

Further, in the absorbent supply control device of the present invention, the sulfur content of the exhaust gas sent to an absorption tower in which a liquid reservoir part is formed at a lower part and a number of spray nozzles are arranged at an upper part is determined. An absorbent supply control device of a flue gas desulfurization device that is pumped up from a liquid reservoir by a circulation pump and removed by an absorbent sprayed from a spray nozzle, and detects a pH value of the absorbent in the absorption tower. a pH meter, an absorbent slurry adjusting valve for adjusting an absorbent slurry supply amount supplied to the absorption tower, a flow meter for detecting the absorbent slurry supply amount, the pH value, an absorbent slurry supply amount, and setting. a controller for receiving a pH value, a circulating pump increase / decrease signal, and setting and inputting a predetermined time and a predetermined amount increase and a predetermined amount decrease.
The absorbent slurry supply amount is increased by a predetermined amount, and when a circulating pump decrease signal is input, a valve command signal for decreasing the absorbent slurry supply amount by a predetermined amount is output to the absorbent slurry adjusting valve for a predetermined time. It is characterized by having made it.

In the above means, the controller usually comprises p
The opening degree of the absorbent slurry adjusting valve is controlled based on the pH value of the H meter and the supply amount of the absorbent slurry by the flow meter so that the pH value of the absorbent becomes the set pH value.

On the other hand, when the circulation pump increase signal is output,
The controller immediately outputs a valve command signal for increasing the supply amount of the absorbent slurry to the absorbent slurry adjusting valve for a predetermined time, and when the circulating pump decrease signal is output, the controller immediately performs the predetermined time,
A valve command signal for reducing the supply amount of the absorbent slurry is output to the absorbent slurry adjusting valve.

Accordingly, the pH value can always be kept constant by controlling the increase / decrease of the supply amount of the absorbent slurry in advance by the increase / decrease signal of the circulation pump, and the excess amount of the absorbent slurry is supplied when the circulation pump is started. Is also prevented.

[0024]

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

FIG. 1 is an overall configuration diagram of a flue gas desulfurization apparatus according to an embodiment of the present invention.

The set pH meter 10 provided in the circulation pipe 6
Has detected the pH value 11 of the absorbing solution 1,
A controller 17 is provided for controlling the opening degree of the absorbent slurry adjusting valve 9 by the valve command signal 14 so that the value 11 becomes a set pH value 16 (for example, pH value 5.0). Further, the supply amount 13 of the absorbent slurry detected by the flow meter 15 provided downstream of the absorbent slurry adjusting valve 9 is input to the controller 17, and the flow rate of the absorbent slurry 8 supplied to the absorption tower 3 is controlled by a valve. The correction is made so as to match the command signal 14.

Further, in the present invention, a circulating pump increase / decrease signal 19 comprising a circulating pump increasing signal 19a for starting the circulating pump 4 and a circulating pump decreasing signal 19b for stopping the circulating pump 4 is input to the controller 17. ing.

The controller 17 also includes a circulating pump increase signal 1
At the time of the output of 9a, in order to supply the absorbent slurry 8 to the absorption tower 3 for a predetermined time, the amount of the absorbent slurry 8 being larger than the supplied amount 13 of the absorbent slurry read by the flow meter 15, as shown in FIG. A predetermined amount increase ΔS and a short predetermined time t are set and input.

Further, when the circulating pump decrease signal 19b is output, the controller 17 supplies the absorbent slurry 8 having a smaller amount than the absorbent slurry supply amount 13 read by the flow meter 15 to the absorber 3 for a predetermined time. For this purpose, as shown in FIG. 2, a predetermined amount decrease ΔS ′ of the absorbent slurry 8 and a short predetermined time t ′ are set and input.

The predetermined amount increase ΔS is set at a ratio of 1.2, 1.3, 1.4, etc. when the supply amount of the absorbent slurry normally supplied to keep the pH value constant is 1, for example. The predetermined amount decrease ΔS ′ can be set at a ratio of 0.9, 0.8, 0.7 or the like when the supply amount of the absorbent slurry is 1, for example.

The operation of the above embodiment will be described below.

In the above-mentioned flue gas desulfurization apparatus, the absorbing 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 from the coal-fired boiler tower to the absorption tower 3 is sprayed. By contacting with the absorbing liquid 1 sprayed from 2, the sulfur oxides are absorbed and removed and then discharged to the outside. On the other hand, a part of the absorbing solution 1 that has absorbed the sulfur oxides from the exhaust gas is
A gypsum slurry is collected from the bottom of a, and water is removed from the gypsum slurry to produce gypsum.

At this time, the absorbent slurry 8 is supplied into the absorption tower 3 so that the pH value of the absorption liquid 1 in the absorption tower 3 is always constant. When the increase / decrease signal 19 is not output, the pH meter 10
The supply amount of the absorbent slurry 8 is controlled based only on the pH value 11 detected by the above.

On the other hand, when the load of the boiler suddenly increases, the circulation pump increase signal 19a is output to an appropriate number of the circulation pumps 4 that are stopped during operation, and a predetermined number of circulation pumps are output. The circulation pump 4 is started. This circulation pump increase signal 19a is also taken into the controller 17 as described above.

In response to the input of the circulating pump increase signal 19a, the controller 17 changes the absorbent slurry supply amount 13 read by the flow meter 15 by a predetermined amount increase ΔS set and inputted as shown by the solid line in FIG. A valve command signal 14 that is increased for a predetermined time t is output to the absorbent slurry adjusting valve 9.

The absorbent slurry adjusting valve 9 increases the valve opening for a predetermined time in response to a valve command signal 14 from the controller 17 to increase the amount 13 of the absorbent slurry supplied to the absorption tower 3. Thereafter, the normal absorbent slurry supply control is performed based on the pH value 11 detected by the pH meter 10.

When the boiler load suddenly decreases, the circulating pump decrease signal 19b is output to an appropriate number of operating circulating pumps 4 among a large number of circulating pumps 4, and a predetermined circulating pump signal is output. The pump 4 is stopped. The circulation pump decrease signal 19b is also taken in by the controller 17 as described above.

In response to the input of the circulating pump decrease signal 19b, the controller 17 changes the absorbent slurry supply amount 13 read by the flow meter 15 by a predetermined amount decrease ΔS ′ set and inputted as shown by a broken line in FIG. The valve command signal 14 that is reduced for the predetermined time t ′ is output to the absorbent slurry adjusting valve 9.

The valve opening degree of the absorbent slurry adjusting valve 9 is reduced by a predetermined time in accordance with a valve command signal 14 from a controller 17, and the supply amount 13 of the absorbent slurry to the absorption tower 3 is reduced. Thereafter, the normal absorbent slurry supply control is performed based on the pH value 11 detected by the pH meter 10.

By increasing or decreasing the supply amount 13 of the absorbent slurry only when the circulation pump 4 is started and stopped, the pH value of the absorbent 1 in the absorption tower 3 is set to the set pH value as shown in FIG. It becomes possible to control almost constant so as to match the value 16.

Note that the predetermined amount increase ΔS and the predetermined amount decrease Δ
The size of S ′ and the length of the predetermined times t and t ′ are determined by determining the relationship between the fluctuation of the pH value 11 due to the activation of the circulation pump 4 and the supply amount 13 of the absorbent slurry during the test operation of the apparatus, and determining the optimum value. To the controller 17.

[0042]

As described above, according to the method and the apparatus for controlling the supply of the absorbent in the flue gas desulfurization apparatus of the present invention, the fluctuation of the pH value of the absorbent in the absorption tower due to the start or stop of the circulation pump is prevented. However, there can be provided an effect that stable pH value control can always be performed and a problem that the absorbent slurry is excessively supplied at the time of starting the circulation pump can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a flue gas desulfurization device according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a pH value of an absorption tower and a supply amount of an absorbent slurry before and after a circulation pump is started and stopped in a flue gas desulfurization apparatus according to an embodiment of the present invention.

FIG. 3 is an overall configuration diagram showing an example of a conventional flue gas desulfurization device.

FIG. 4 shows the operation of a circulation pump in a conventional flue gas desulfurization system.
It is a characteristic view which shows the relationship between the absorption tower pH value and the amount of absorbent slurry supply before and after a stop.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Absorbent liquid 1a Liquid reservoir 2 Spray nozzle 3 Absorption tower 4 Circulation pump 9 Absorbent slurry adjusting valve 10 pH meter 11 pH value 13 Absorbent slurry supply amount 14 Valve command signal 15 Flow meter 16 Set pH value 17 Controller 19 Circulation Pump increase / decrease signal 19a Circulation pump increase signal 19b Circulation pump decrease signal t, t 'Predetermined time ΔS Predetermined amount increase ΔS' Predetermined amount decrease

Claims (2)

[Claims] A circulating pump pumps up sulfur from exhaust gas fed into an absorption tower in which a liquid reservoir for absorbing liquid is formed at a lower portion and a number of spray nozzles are disposed at an upper portion. A method for controlling the supply of an absorbent in a flue gas desulfurization apparatus, wherein the absorbent is removed by an absorbent sprayed from a nozzle, wherein the pH of the absorbent in the absorber is set to a set pH value. In addition to controlling the amount of the absorbent slurry supplied to the circulating pump, the amount of the absorbent slurry supplied is increased by a predetermined amount when the circulation pump increase signal is output, and the absorption amount is increased by a predetermined time when the circulation pump decrease signal is output. A method for controlling the supply of an absorbent for a flue gas desulfurization device, wherein the supply amount of the agent slurry is reduced by a predetermined amount. 2. A circulating pump is used to pump the sulfur content of the exhaust gas sent to an absorption tower having a lower part in which a liquid reservoir for absorbing liquid is formed and a plurality of spray nozzles disposed in the upper part, and spray the sulfur. An absorbent supply control device for a flue gas desulfurization device configured to remove with an absorbing solution sprayed from a nozzle, wherein the pH meter detects a pH value of the absorbing solution in the absorption tower, and is supplied to the absorption tower. An absorbent slurry adjusting valve for adjusting the supplied amount of the absorbent slurry, a flow meter for detecting the supplied amount of the absorbent slurry, the pH value, the supplied amount of the absorbent slurry, a set pH value, and a circulating pump increase / decrease signal. And a controller for setting and inputting a predetermined time, a predetermined amount increase and a predetermined amount decrease, and the controller increases the absorbent slurry supply amount by a predetermined amount for a predetermined time when the circulation pump increase signal is input. And circulation pump When a signal is inputted, a valve command signal for decreasing the supply amount of the absorbent slurry by a predetermined amount for a predetermined time is outputted to the absorbent slurry adjusting valve, wherein the absorbent supply of the flue gas desulfurization device is performed. Control device.