JPH09327616A - Oxidative substance concentration controlling method and apparatus for exhaust gas desulfurization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the concentration of an oxidative substance at a prescribed value or lower, prevent deterioration of the function of a wastewater treatment apparatus, and suppress the deterioration of adsorptive resin of the wastewater treatment apparatus by adjusting the flow rate of oxidative air to be supplied to an absorption tower as to control the concentration of the air prescribed times as high as absorbed SO2 amount. SOLUTION: The flow rate of oxidative air to be supplied to an absorption tower 5 is so controlled as to be a prescribed times as high as the absorbed SO2 amount. That is, a computing apparatus 33 which computes the necessary oxidative air amount 37 to control the concentration of the air to be a prescribed times as high as the absorbed S02 amount and gives an output is installed, a flow rate adjusting damper 43 to adjust the flow rate of the oxidative air to be supplied to the absorption tower 5 is installed in the suction side of an oxidative air blower 6, and a flow rate instructing and adjusting meter 41 which detects the flow rate of the oxidative air to be supplied to the absorption tower 5 and sends out an output of a valve opening instruction signal 42 to the flow rate adjusting damper 43 as to equalize the flow rate of the oxidative air with the necessary oxidative air amount 37 computed by the computing apparatus 33 is installed in the discharge side of the oxidative air blower 6. It is effective that the ratio of the flow rate of the oxidative air to the absorbed SO2 amount is set to be 2.5-3.5 times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for controlling the concentration of oxidizing substances in a flue gas desulfurization device.

[0002]

2. Description of the Related Art Conventionally, a flue gas desulfurization apparatus using lime (limestone, slaked lime or quick lime) as an absorbent, generally absorbs the absorbent 2 in a liquid reservoir 1 formed at the bottom as shown in FIG. By operating the circulation pump 3, the spray nozzle 4 disposed at the upper portion sprays and circulates the exhaust gas, and the exhaust gas supplied from the outside is discharged after being brought into contact with the absorbing liquid 2 sprayed from the spray nozzle 4. An oxidizing air blower 6 for supplying air for oxidation is connected to the liquid reservoir 1 of the absorption tower 5, and a stirrer 7 for stirring the absorbing liquid 2 in the liquid reservoir 1 is provided, and a mother liquor tank 25 described later is provided. Absorbent for kneading the absorbing liquid 23 supplied from the above and the lime 9 supplied from the silo 8 to generate the absorbing slurry 10 and supplying the absorbing slurry 10 to the liquid reservoir 1 of the absorption tower 5. Slurry pick 11, a part of the absorbent 2 is supplied from the bottom of the absorption tower 5 and a part of the neutralizer 12 such as caustic soda supplied to the liquid reservoir 1 of the absorption tower 5 is supplied. A neutralization tank 13 for mixing and stirring 2 and the neutralizing agent 12 is provided, a thickener 15 for concentrating the absorption liquid 14 extracted from the neutralization tank 13 is provided, and the absorption liquid 16 concentrated by the thickener 15 is supplied. The absorption liquid 16
Is provided with a gypsum separator supply tank 17 for stirring, and a gypsum separator 20 for dehydrating the absorption liquid 16 extracted from the gypsum separator supply tank 17 to produce gypsum 19 is provided. The filtrate pit 2 for supplying the purified water 21 and supplying a part of the water 21 to the thickener 15
2 is further provided, and the supernatant absorbing liquid 23 is supplied from the thickener 15 and a part of the absorbing liquid 23 is treated as a waste water treatment device 24.
And a mother liquor tank 25 for supplying the absorbent slurry pit 11 and feeding the rest to the liquid reservoir 1 of the absorption tower 5.

In FIG. 5, reference numeral 18 is make-up water that is appropriately replenished to the absorption tower 5.

In the case of a flue gas desulfurization apparatus as described above, the absorption liquid 2
Is circulated by the operation of the circulation pump 3, and the exhaust gas sent to the absorption tower 5 comes into contact with the absorption liquid 2 sprayed from the spray nozzle 4, whereby SO ₂ (sulfur oxide) is absorbed and removed. Later, it is discharged outside.

On the other hand, a part of the absorbing liquid 2 which has absorbed SO ₂ from the exhaust gas is supplied from the bottom of the liquid reservoir 1 of the absorption tower 5 to a neutralization tank 13 where the neutralizing agent 12 Is mixed and stirred, the mixed and stirred absorption liquid 14 is sent to the thickener 15, concentrated in the thickener 15, and the concentrated absorption liquid 16 is supplied to the gypsum separator supply tank 1.
7 and sent to a gypsum separator 20 where the moisture is removed to produce gypsum 19.

The water 21 dehydrated by the gypsum separator 20
Is returned to the thickener 15 through the filtrate pit 22,
The supernatant absorbent 23 which is discharged when the absorbent 14 is concentrated in the thickener 15 is supplied to a wastewater treatment device 24 and an absorbent slurry pit 11 through a mother liquor tank 25, and is also supplied to a liquid reservoir of the absorption tower 5. Sent to 1.

The absorbent 23 supplied to the absorbent slurry pit 11 is kneaded with the lime 9 supplied from the silo 8 in the absorbent slurry pit 11 to form an absorbent slurry 10 in the liquid reservoir of the absorption tower 5. 1 is supplied.

The absorbing solution 2 sent to the wastewater treatment device 24
No. 3, harmful nitrogen compounds are decomposed by the action of nitrifying bacteria of the wastewater treatment device 24, and COD (chemical oxygen demand)
Is adsorbed by the polymer resin of the wastewater treatment device 24 and then discharged to the outside.

[0009]

In the conventional flue gas desulfurization apparatus as described above, when an amount of oxidizing air exceeding the amount required for the main reaction of desulfurization is supplied, S ₂ O ₈ (persulfuric acid) is generated as a side reaction. ) Or IO ₃ (iodic acid) or the like is generated to increase the concentration of the oxidizing substance, which causes a decrease in the activity of nitrifying bacteria in the wastewater treatment device 24, or kills the nitrifying bacteria. There is a problem that the function of the wastewater treatment device 24 is deteriorated and the adsorbent resin of the wastewater treatment device 24 is rapidly deteriorated.

Therefore, conventionally, the oxidizing air amount [Nm ³ is supplied to the absorption tower 5 by the oxidizing air blower 6].
/ H] was controlled by using an indicator value of an oxidation-reduction potentiometer (not shown) for detecting the oxidation-reduction potential (ORP value) of the absorbent 2 as an index.

The relationship between the concentration of the oxidizing substance and the oxidation-reduction potential is such that the concentration of the oxidizing substance decreases as the oxidation-reduction potential decreases, so that the oxidation-reduction potential reaches a predetermined value. By controlling the amount of oxidizing air, it becomes possible to keep the concentration of the oxidizing substance below a predetermined value.

However, the relationship between the concentration of the oxidizing substance and the redox potential varies greatly depending on the type of coal when desulfurizing exhaust gas from a coal-fired boiler, and it is not always necessary to use the redox potential as an index. It wasn't right.

The redox potential is already present as a result of the supply of oxidizing air into the absorbing liquid 2, and the redox potential already existing in the absorbing liquid 2 is used. If the amount of oxidizing air to be newly supplied is controlled based on this, there is a delay by that amount, and there is room for improvement in the control method.

[0014] In view of the above situation, the present invention maintains the concentration of the oxidizing substance at a predetermined value or less without affecting the coal type even when desulfurizing the exhaust gas from the coal-fired boiler, and Oxidizing substance concentration control method and device for flue gas desulfurization device, which can prevent deterioration of function, can suppress deterioration of adsorbent resin of waste water treatment device, and can improve responsiveness by eliminating delay as a control system Is to provide.

[0015]

According to the present invention, an absorbing liquid containing lime as an absorbent is brought into contact with exhaust gas to absorb and remove SO ₂ in the exhaust gas, and oxidizing air is blown into the absorbing liquid brought into contact with the exhaust gas. A method for controlling the concentration of oxidizing substances in a flue gas desulfurization apparatus equipped with an absorption tower, characterized in that the flow rate of oxidizing air supplied to the absorption tower is adjusted so that the required ratio to the amount of absorbed SO _{2 is} obtained. The present invention relates to a method for controlling the concentration of oxidizing substances in a flue gas desulfurization device.

In the oxidant concentration control method for the flue gas desulfurization apparatus, it is effective to set the ratio of the flow rate of oxidizing air to the absorbed SO ₂ amount to 2.5 to 3.5.

Further, the present invention comprises an absorption tower in which the absorbing solution using lime as the absorbent is brought into contact with the exhaust gas to absorb and remove SO ₂ in the exhaust gas and blow the oxidizing air into the absorbing solution brought into contact with the exhaust gas. An exhaust gas flow rate detector for detecting the exhaust gas flow rate at the outlet side of the absorption tower, and an inlet side for detecting the SO ₂ concentration in the exhaust gas at the inlet side of the absorption tower. and SO ₂ concentration detector, and the outlet side SO ₂ concentration detector for detecting the SO ₂ concentration in the exhaust gas at the outlet side of the absorption tower, is detected by the inlet-side SO ₂ concentration detector SO ₂ concentration and the outlet SO and obtains the difference between the detected SO ₂ concentration ₂ concentration detector obtains the absorption SO ₂ concentration, absorption SO ₂ seeking the product of the exhaust gas flow rate detected by the exhaust gas flow rate detector and said absorbing SO ₂ concentration The amount is calculated and the absorption S
An arithmetic unit that obtains and outputs the required amount of oxidizing air so that the required ratio is obtained with respect to the O ₂ amount, a flow rate adjustment damper that adjusts the flow rate of the oxidizing air that is supplied to the absorption tower, and the oxidation supplied to the absorption tower. A flow rate indicating controller for detecting a flow rate of air and outputting an opening degree instruction signal to a flow rate adjusting damper so that the flow rate of the oxidizing air matches the required oxidizing air amount obtained by the arithmetic unit. The present invention relates to the oxidant concentration control device of the flue gas desulfurization device.

In the oxidant concentration control device of the flue gas desulfurization device, it is effective to set the ratio of the required oxidizing air amount to the absorbed SO ₂ amount to 2.5 to 3.5.

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

In the case of the method for controlling the concentration of oxidizing substances in the flue gas desulfurization apparatus of the present invention, the flow rate of the oxidizing air supplied to the absorption tower is adjusted so that the required SO ₂ amount can be obtained.

Further, in the case of the oxidant concentration control device of the flue gas desulfurization apparatus of the present invention, when the flue gas desulfurization apparatus is operating, the SO ₂ concentration in the exhaust gas at the inlet side of the absorption tower is detected by the SO ₂ concentration detector on the inlet side. Is detected, the SO ₂ concentration detector at the outlet side detects the SO ₂ concentration in the exhaust gas at the outlet side of the absorption tower, and the exhaust gas flow rate detector detects the exhaust gas flow rate at the outlet side of the absorption tower. is input to the vessel, in the arithmetic unit, the inlet-side SO ₂ concentration detector difference between the detected SO ₂ concentration and the detected SO ₂ concentration at the outlet SO ₂ concentration detector and is required absorption SO ₂ concentration is determined, it is demanded product of exhaust gas flow rate detected by the said absorbing SO ₂ concentration the exhaust gas flow rate detector, the absorption SO ₂ amount is determined, required oxidation air quantity on the basis of the absorption SO ₂ amount Flow control controller required Is output, the opening command signal from the flow indicating controller to the flow control damper so that the flow rate of the oxidizing air to meet the required oxidation air amount determined by the arithmetic unit is supplied is outputted to the absorption column, the absorption SO ₂ amount The flow rate of the oxidizing air supplied to the absorption tower is adjusted so that the required magnification is obtained.

As a result, in the method and apparatus for controlling the concentration of oxidative substances in the flue gas desulfurization apparatus of the present invention, side reactions to the main reaction of desulfurization do not easily occur, and oxidative substances such as S ₂ O ₈ and IO ₃ are removed. It is less likely to be generated, the concentration of the oxidizing substance is suppressed from increasing, the activity of nitrifying bacteria in the wastewater treatment device is lowered, or the nitrifying bacteria are not killed, and the function of the wastewater treatment device is reduced. It does not decrease, and deterioration of the adsorbent resin of the wastewater treatment equipment can be suppressed.

Moreover, if the flow rate of the oxidizing air supplied to the absorption tower is adjusted so that the required ratio to the absorbed SO ₂ amount is obtained, even if the exhaust gas from the coal-fired boiler is desulfurized, it varies depending on the coal type. The concentration of oxidizing substances is kept below a certain level, and the amount of oxidizing air to be newly supplied is controlled based on the redox potential already existing in the absorbing liquid as in the past. Absorption S instead of doing
Since the flow rate of the oxidizing air is adjusted in a feed-forward control according to the amount of O ₂ , there is no delay as a control system.
Responsiveness is also improved.

[0024] Particularly, in an oxidizing substance concentration control method and apparatus for flue desulfurization apparatus of the present invention, the magnification of the flow rate of the oxidizing air to absorb SO ₂ amount, i.e. the required oxidation air amount ratio to absorb SO ₂ of 2. When it is from 5 to 3.5, the required desulfurization performance can be secured and the concentration of the oxidizing substance can be reduced to the required value or less, which is more effective.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 4 show an example of an embodiment for carrying out the present invention. In the drawings, the parts denoted by the same reference numerals as those in FIG. 5 represent the same things, and the basic structure is shown in FIG. is similar to the conventional one shown, where the feature of the present illustrated embodiment, as shown in FIGS. 1 to 4, so that a required magnification to the absorption sO ₂ amount 35, supplied to the absorption tower 5 The point is that the A / S control for adjusting the flow rate of the oxidizing air, that is, the oxidizing air blowing ratio control using the absorbed SO ₂ amount 35 as an index is configured.

Incidentally, "A" in the A / S control is "A".
abbreviated “ir” and represents the required amount of oxidizing air 37,
“S” is an abbreviation for “Sulfur”, and the absorbed SO ₂ amount is 3
5 is represented.

In the figure, 26 is an exhaust gas flow rate detector for detecting the exhaust gas flow rate 27 at the outlet side of the absorption tower 5, 28 is an inlet side SO ₂ for detecting the SO ₂ concentration 29 in the exhaust gas at the inlet side of the absorption tower 5. A concentration detector, 30 is an outlet side SO ₂ concentration detector that detects the SO ₂ concentration 31 in the exhaust gas at the outlet side of the absorption tower 5, and 33 is an SO ₂ concentration 29 detected by the inlet side SO ₂ concentration detector 28. And SO ₂ concentration detector 30 on the outlet side
The absorbed SO ₂ concentration 32a is obtained by calculating the difference from the SO ₂ concentration 31 detected in step S1, and the product of the absorbed SO ₂ concentration 32a and the exhaust gas flow rate 27 detected by the exhaust gas flow rate detector 26 is calculated. ₂ is an arithmetic unit that obtains the amount 35, and obtains and outputs the required amount of oxidizing air 37 so that the required SO ₂ amount 35 becomes a required multiplication factor, and supplies it to the suction side of the oxidizing air blower 6 to the absorption tower 5. A flow rate adjusting damper 43 for adjusting the flow rate of the oxidizing air is provided, the flow rate of the oxidizing air supplied to the absorption tower 5 is detected on the discharge side of the oxidizing air blower 6, and the flow rate of the oxidizing air is calculated by the calculator 33. A flow rate indicating controller 41 that outputs an opening degree instruction signal 42 to the flow rate adjusting damper 43 is provided so as to match the required oxidizing air amount 37 obtained in step 1.

As shown in FIG. 2, the computing unit 33 has a SO ₂ concentration 29 detected by the SO ₂ concentration detector 28 on the inlet side and a SO ₂ concentration 31 detected by the SO ₂ concentration detector 30 on the outlet side. Subtractor 32 that obtains the absorbed SO ₂ concentration 32a by obtaining the difference
And the absorbed SO ₂ concentration 32a obtained by the subtractor 32 and the exhaust gas flow rate 27 detected by the exhaust gas flow rate detector 26.
Seeking product of, obtaining the absorption SO ₂ amount 35 multiplier 34
And a function generator 36 that outputs a required oxidizing air amount 37 based on the absorbed SO ₂ amount 35 obtained by the multiplier 34.

A function as shown in FIG. 3 is input to the function generator 36, and the function increases / decreases the required oxidizing air amount 37 substantially in proportion to the increase / decrease in the absorbed SO ₂ amount 35. This means that the values of the oxidizing substance and COD can be set to desired values by appropriately changing the settings of this function.

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

During operation of the flue gas desulfurizer, SO ₂ on the inlet side
The concentration detector 28 detects the SO ₂ concentration 29 in the exhaust gas at the inlet side of the absorption tower 5, and the outlet side SO ₂ concentration detector 30 detects the SO ₂ concentration 31 in the exhaust gas at the outlet side of the absorption tower 5. Further, the exhaust gas flow rate detector 26 detects the exhaust gas flow rate 27 on the outlet side of the absorption tower 5 and inputs it to the calculator 33.

In the calculator 33, the inlet side SO
₂ SO ₂ concentration 29 detected by the concentration detector 28 and S on the outlet side
The difference from the SO ₂ concentration 31 detected by the O ₂ concentration detector 30 is obtained by the subtractor 32 to obtain the absorbed SO ₂ concentration 32a. The absorbed SO ₂ concentration 32a and the exhaust gas flow rate detector 2
The product of the exhaust gas flow rate 27 detected in 6 is obtained by the multiplier 34, and the absorbed SO ₂ amount 35 is obtained.
The required oxidizing air amount 37 is output from the function generator 36 to the flow rate indicator controller 41 based on the absorbed SO ₂ amount 35 obtained in step 4, and the flow rate of the oxidizing air supplied to the absorption tower 5 is obtained by the calculator 33. The opening instruction signal 42 is output from the flow rate indicating controller 41 to the flow rate adjusting damper 43 so as to match the required oxidizing air amount 37, and the absorption tower 5 is moved to the absorption SO ₂ amount 35 so that the required magnification is obtained. The flow rate of the oxidizing air supplied is adjusted.

As a result, a side reaction with respect to the main reaction of desulfurization is less likely to occur, an oxidizing substance such as S ₂ O ₈ or IO ₃ is less likely to be generated, and the concentration of the oxidizing substance is prevented from increasing, and the wastewater is discharged. The activity of the nitrifying bacteria in the treatment device 24 will not be reduced or the nitrifying bacteria will not be killed, the function of the wastewater treatment device 24 will not be reduced, and the deterioration of the adsorption resin of the wastewater treatment device 24 can be suppressed. .

Moreover, when the flow rate of the oxidizing air supplied to the absorption tower 5 is adjusted so that the required SO ₂ amount is 35, the coal type can be used even when the exhaust gas from the coal-fired boiler is desulfurized. The concentration of the oxidizing substance is suppressed to a predetermined value or less, and the oxidizing air to be newly supplied based on the redox potential already existing in the absorbing liquid 2 as in the conventional case. Since the flow rate of the oxidizing air is adjusted in a feedforward control according to the absorbed SO ₂ amount 35 instead of controlling the amount, the delay as a control system is eliminated and the response is improved.

Here, as shown in FIG. 4, the relationship between A / S (oxidizing air blowing ratio) and the concentration of oxidizing substances is that the smaller the A / S is, the more the concentration of oxidizing substances decreases. Therefore, when the oxidizing substance concentration is 5 [mg / l] or less, A / S should be 3.2 or less. However, if A / S is too small, SO ₃ due to insufficient oxidizing air will be generated. When it occurs, the desulfurization performance is deteriorated. Therefore, in order to secure the desulfurization performance and reduce the concentration of the oxidizing substance, it is preferable to set the A / S value to about 2.8 to 3.2. However, the concentration of the oxidizing substance may be suppressed to about 10 [mg / l] or less, and the desulfurization performance required varies depending on the equipment and has a certain range. , A / S may be about 2.5 to 3.5.

Thus, even when desulfurizing the exhaust gas from the coal-fired boiler, the concentration of the oxidizing substance is maintained at a predetermined value or less without being affected by the coal type, and the wastewater treatment equipment 24
Function deterioration can be prevented, deterioration of the adsorbent resin of the waste water treatment device 24 can be suppressed, and further, responsiveness can be improved by eliminating delay as a control system.

The method and apparatus for controlling the concentration of oxidizing substances in the flue gas desulfurization apparatus according to the present invention are not limited to the above illustrated examples, and various modifications may be made without departing from the gist of the present invention. Of course you can get it.

[0039]

As described above, the first aspect of the present invention is as described above.
According to the oxidant concentration control method and device of the flue gas desulfurization apparatus described in 1 to 4, even when desulfurizing the exhaust gas from the coal-fired boiler, the concentration of the oxidant is not more than a predetermined value without being affected by the coal species. It is possible to prevent the deterioration of the function of the wastewater treatment equipment by suppressing the deterioration of the adsorbent resin of the wastewater treatment equipment, and further to improve the response by eliminating the delay as a control system. Can play.

[Brief description of drawings]

FIG. 1 is an overall schematic configuration diagram of an example of an embodiment of the present invention.

FIG. 2 is a block diagram showing details of a computing unit shown in FIG.

FIG. 3 is a diagram showing a function set in a function generator shown in FIG.

FIG. 4 shows an example of A / S according to an embodiment of the present invention.
It is a diagram showing the relationship between (oxidizing air blowing ratio) and the concentration of oxidizing substances.

FIG. 5 is an overall schematic configuration diagram of a conventional example.

[Explanation of symbols]

2 Absorbing liquid 5 Absorption tower 6 Oxidized air blower 9 Lime 24 Wastewater treatment device 26 Exhaust gas flow rate detector 27 Exhaust gas flow rate 28 Inlet side SO ₂ concentration detector 29 SO ₂ concentration 30 Outlet side SO ₂ concentration detector 31 SO ₂ concentration 32a Absorption SO ₂ concentration 33 Operator 35 Absorbed SO ₂ amount 37 Required oxidizing air amount 41 Flow rate indicator controller 42 Opening command signal 43 Flow rate adjustment damper

Claims (4)

[Claims] 1. Flue gas desulfurization provided with an absorption tower in which an absorbing solution using lime as an absorbent is brought into contact with exhaust gas to absorb and remove SO ₂ in the exhaust gas, and oxidizing air is blown into the absorbing solution brought into contact with the exhaust gas. A method for controlling the concentration of oxidizing substances in a device, wherein the flow rate of oxidizing air supplied to the absorption tower is adjusted so that the required SO ₂ amount is multiplied, and the oxidizing property of the flue gas desulfurization device is adjusted. Substance concentration control method. 2. The method for controlling the concentration of oxidizing substances in a flue gas desulfurization device according to claim 1, wherein the ratio of the flow rate of oxidizing air to the absorbed SO ₂ amount is 2.5 to 3.5. 3. Flue gas desulfurization provided with an absorption tower in which an absorbent containing lime as an absorbent is brought into contact with the exhaust gas to absorb and remove SO ₂ in the exhaust gas, and an oxidizing air is blown into the absorbent brought into contact with the exhaust gas. a oxidizer concentration control device of the apparatus, and the exhaust gas flow rate detector for detecting the exhaust gas flow rate at the outlet side of the absorption tower, the inlet-side SO ₂ concentration detection for detecting the SO ₂ concentration in the exhaust gas at the inlet side of the absorption tower vessels and, outlet SO ₂ concentration detector and, SO ₂ concentration and the outlet SO ₂ concentration sensor is detected by the inlet-side SO ₂ concentration detector for detecting the SO ₂ concentration in the exhaust gas at the outlet side of the absorption tower in seeking the difference between the detected SO ₂ concentration calculated absorption SO ₂ concentration, determine the absorption SO ₂ amount seeking the product of the detected exhaust gas flow rate in the said absorbing SO ₂ concentration the exhaust gas flow rate detector, The required magnification for the absorbed SO ₂ amount So as to obtain and output the required amount of oxidizing air, a flow rate adjustment damper that adjusts the flow rate of oxidizing air supplied to the absorption tower, the flow rate of oxidizing air supplied to the absorption tower, and Of the flue gas desulfurization apparatus, and a flow rate indicating controller that outputs an opening degree instruction signal to a flow rate adjusting damper so that the flow rate of the flow rate matches the required oxidizing air amount obtained by the arithmetic unit. Concentration control device. 4. The oxidant concentration control device for a flue gas desulfurization device according to claim 3, wherein the ratio of the required amount of oxidizing air to the amount of absorbed SO ₂ is 2.5 to 3.5.