JPS6349231A - Oxidation control device for absorbing liquid in wet type stack gas desulfurization apparatus - Google Patents

Abstract

PURPOSE:To preferably carry out oxidation with the minimum necessary amount of utilities by providing a dissolved oxygen meter measuring the concn. of dissolved oxygen in an absorbing liquid, and control means controlling the supply condition of air to be blown into according to the measured value by the dissolved oxygen meter. CONSTITUTION:A stack gas 101 is introduced into a desulfurization tower 31 and brought into contact with the sprayed absorbent slurry to be desulfurized. On the other hand, the corresponding amount of absorbent slurry with the removing amount of SO2 is supplied to a circulating tank 32. Plural oxidizing agitators 35 are provided to the circulating tank 32 to regenerate the absorbent slurry absorbing SO2 to restore the absorbing capacity for SO2. The regenerated absorbent slurry is supplied to a spray part 39 by a circulating pump 33. In this constitution, the amount of dissolved oxygen in the absorbent slurry is continuously measured by the dissolved oxygen meter 12. When the measured value becomes zero, the number of the operating agitators for oxidation is increased. Moreover, the amount of stack gas and the concn. of SO2 are measured by a flow meter 41 and an analyzer 40, and the operation of the agitators 35 is decided through a controlling part 44.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an absorption liquid oxidation control device for a wet flue gas desulfurization equipment, and particularly relates to an absorption liquid oxidation control device for a wet flue gas desulfurization equipment, and in particular, sulfur oxides generated by absorbing and removing sulfur oxides from exhaust gas using an absorption liquid. The present invention relates to an absorption liquid oxidation control device for a wet flue gas desulfurization device suitable for oxidizing sulfites.

[Conventional technology]

FIG. 5 is a configuration diagram showing a conventional wet flue gas desulfurization system, including a dust removal tower 1 into which flue gas 101 is introduced, and a dust removal tower 1.
The absorbent slurry 102 is communicated with the tower at the middle stage and at the bottom of the tower.
The main structure is an absorption tower 2 equipped with an absorption tower circulation tank 3 for storing the water.

A dust removal tower circulation tank 4 in which a dust removal tower circulating slurry 103 is stored is connected to the lower part of the dust removal tower 1, and a stirrer 6 is provided in this circulation tank 4. A stirrer 5 is also provided within the absorption tower circulation tank 3.

A nozzle 16 is provided in the upper part of the absorption tower 2, and an absorption tower circulation pump 7 for supplying absorption liquid to the nozzle 16 is connected to the nozzle 16. Similarly, a dust removal tower circulation pump 8 is provided for supplying slurry 103 to a nozzle 17 provided at the upper part of the dust removal tower 1. Further, an absorption tower bleed, I-min pump 9 is connected to the absorption tower circulation tank 3, and this pump 9
An oxidation tower supply tank 10 storing sulfuric acid 105 is connected to the oxidation tower supply tank 10 . Oxidation tower 1 is supplied to tank 10 via pump 18.
) is connected to the oxidation tower 1), and a sifter 12 and a centrifugal separator 13 are sequentially connected to this oxidation tower 1).

Next, the operation of the wet flue gas desulfurization system configured as described above will be explained.

Exhaust gas 101 from a boiler or the like is removed and cooled in a dust removal tower 1 (or directly supplied to an absorption tower 2). Then, sulfur oxides in the exhaust gas 101 are absorbed and removed within the absorption tower 2. The absorbent slurry used here to absorb and remove sulfur oxides in the exhaust gas 101 is temporarily held in the absorption tower circulation tank 3, and is circulated to remove sulfur oxides.

Here, the absorbent is stirred and mixed by the stirrer 5.

After attempting to recover the So2 absorption performance in the absorption tower circulation tank 3, it is supplied to the absorption tower 2 again by the absorption tower circulation pump 7. By repeating this step by step, the limestone (CaCOl) in the absorbent slurry becomes calcium sulfite (CaS○, ), and a portion (or the entire amount depending on the conditions) is oxidized by oxygen in the exhaust gas and becomes calcium sulfate (gypsum). becomes. This slurry was extracted from the circulation tank 3 by the absorption tower bleed pump 9, and was adjusted to a pH suitable for decomposing unreacted CaCO3 and oxidizing sulfite by adding sulfuric acid (H2304) in the oxidation tower supply tank 10. Afterwards, it is supplied to the oxidation tower 1). In the oxidation tower 1), the air 106 from the bottom of the tower is forcibly generated with an air atomization atomizer to dissolve oxygen in the air, and the dissolved oxygen and calcium sulfite react to form calcium sulfate ( gypsum) and is extracted from the bottom of the tower. The gypsum slurry extracted from the oxidation tower 1) is supplied to the sifufuna 12 and concentrated, and then passed through the centrifugal separator 13 to remove the filtrated water 1 as 10 days of gypsum with less than 10% adhering water.
07 and will be separated and recovered.

However, in the system shown in FIG. 5, the cooling, absorption, and oxidation steps are performed in separate towers, which makes the process complicated and requires a large installation space. Therefore, in order to solve these problems, the inventors have already combined the steps of cooling, absorption and oxidation into one as shown in FIG.
We proposed an l-temperature flue gas desulfurization system that is combined into two towers.

That is, this device includes a desulfurization tower 31 into which exhaust gas 101 is introduced.
A circulation tank 32 for storing circulating slurry 102 is provided at the bottom of the tower, and a demister 36 is provided at the top. A pump 33 is connected to the circulation tank 32, and a sifter 37 and a centrifugal separator are connected to this pump 33 in this order. Furthermore, a spray section 39 is provided within the desulfurization tower 31 to which the circulating slurry from the pump 33 is supplied.

In this device, exhaust gas 101 from a boiler etc. is sent to a desulfurization tower 3
1 and comes into contact with the sprayed calcium-based absorbent slurry to be dedusted, cooled and desulfurized, and then the entrained mist is removed by a demitasse 36 and exits from the desulfurization tower 31. On the other hand, the limestone slurry 104, which is an absorbent, is supplied to the circulation tank 102 in proportion to the amount of 802 to be removed, reducing hydrogen ions (H') in the slurry after contact with the exhaust gas, and recovering the absorption performance of the absorption slurry. In addition, the circulation tank 32 has a stirring R3 for preventing solid matter settling and for air atomization and dispersion (for oxidation).
4 and 35 are installed, and these air agitation absorbs SO2 in the exhaust gas and oxidizes the sulfite ions generated to form stable sulfate salts, lowering the equilibrium partial pressure of SO2 in the absorption liquid and increasing the absorption capacity. As well as increasing the sedimentation of the absorbent,
Prevents buildup.

The absorption slurry regenerated in this way is transferred to the circulation pump 33.
The gas is supplied to the spray section 39 and comes into countercurrent contact with the exhaust gas.

A portion of the absorbed slurry is extracted from the circulation tank 32, compressed (or directly) in a syringe 37, dehydrated in a centrifugal separator 38, and recovered as powdered gypsum 108 with adhering water of 10% or less. In addition, 107 is filtered water.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional technology does not take into consideration the reduction in utility required by users. In other words, for the purpose of reducing the utility of the desulfurization equipment, (a) reducing the pressure inside the absorption tower by setting a fire (reducing the power of the ventilation system) and (b) controlling the amount of circulating liquid in the absorption tower (reducing the power of the circulation pump), etc. However, a specific control method has not been established for the process of oxidizing Ca5Oz to gypsum, and a certain amount of oxidation utility is always required to respond to changes in boiler load and exhaust gas conditions. There is. Therefore, the problem has been how to grasp the oxidation state of calcium sulfite in the absorption liquid in the desulfurization equipment, and how to utilize this to reduce the utility for oxidation.

The purpose of the present invention is to solve the problems of the prior art described above,
It is an object of the present invention to provide an absorption liquid oxidation control device for a wet flue gas desulfurization device, which allows the oxidation reaction to be performed satisfactorily with the minimum necessary utilities.

[Means for solving problems]

In order to achieve the above object, the present invention measures the dissolved oxygen concentration in the absorption liquid with a dissolved oxygen needle, and based on this measurement result, the air supply condition B (air amount , agitation M).

[Effect]

Dissolved oxygen in the absorption liquid is detected when the sulfite concentration is almost zero. As a result, if the oxidation reaction of the slurry (absorbing liquid) in the desulfurization equipment circulation tank is occurring well, the dissolved oxygen meter immersed in the absorbing liquid will indicate a value greater than O in the range below the saturated solubility of air. On the other hand, if the oxidation reaction is insufficient, the dissolved oxygen will appear to be zero, so
By controlling the aeration amount and stirring conditions necessary for oxidation accordingly, the oxidation state can be maintained in a good condition.

[Embodiments of the invention]

The following is a detailed explanation of the present invention based on the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention.

In FIG. 1, the same reference numerals are used for the same parts as in FIG. 6, so redundant explanation will be omitted.

The exhaust gas supply pipe is provided with an analyzer 40 for analyzing SO2 and 0□ in the exhaust gas 101 and an exhaust gas>t ffl meter 41. Further, a dissolved oxygen meter 42 is provided between the outlet side of the pump 33 and the desulfurization tower 31. In addition, valves 43a and 43b are provided to adjust the amount of air 106 supplied into the circulating air pump 32. Furthermore, these valves 43
a, 43bi<or the oxidation stirrer 35 is connected to the dissolved oxygen meter 42
A control section 44 is provided to control the operation.

Next, (Y
I will explain the effects of using it.

Exhaust gas 101 from a boiler or the like is led to a desulfurization tower 31 and comes into contact with the sprayed calcium-based absorbent slurry to be removed, cooled, and desulfurized, and then entrained mist is removed by a demister 36 and discharged from the desulfurization tower 31. On the other hand, the limestone slurry 104, which is an absorbent, is supplied to the circulation tank 32 in proportion to the removal so,1, and comes into contact with the exhaust gas 101 to reduce hydrogen ions (H') in the absorption slurry whose pH has decreased.

A plurality of oxidation (air atomization and dispersion) agitators 8135 are installed in the circulation tank 32, which absorbs S02 and converts it into S
Sulfite ions (So”) in the slurry with high Oz partial pressure
-1) to reduce the partial pressure, recover the S02 absorption performance, and obtain calcium sulfate (gypsum). The absorbent slurry thus regenerated is supplied to the spray section 39 by the circulation pump 33 and falls into the circulation tank 32 while being in countercurrent contact with the exhaust gas 101. The dissolved oxygen concentration in the absorbent slurry is continuously measured by a dissolved oxygen meter 42 immersed in the absorbent liquid, and when the measured value becomes zero, the number of oxidizing stirring R35 in operation is increased.

Separately, the amount of exhaust gas at the inlet of the desulfurization tower is measured with an exhaust gas flow meter 41, and the SO□ concentration is measured with a 50202 analyzer 40, and the signals are taken into the control unit 44 and indirectly calculated from the exhaust gas conditions necessary for oxidation. The number of stirrers 35 to be operated is determined and on/off control is performed. (In addition, it is desirable that the control unit 44 not only control the number of stirrers 35, but also handle the circulation flow rate and 0 tfH degree in the gas.The operation request value of the oxidation stirrer 35 from the gas side and the 1 volume oxygen Total 4
The purpose is achieved with the minimum necessary oxidation utility by the signal from the actual measured value on the liquid side according to 2.

A portion of the absorption slurry that is circulated in the desulfurization tower 31 is extracted from the circulation tank 32, concentrated in the sifter 37, and finally dehydrated in the centrifuge 38 to form gypsum 1 with less than 10% adhering water.
08 (in some cases, Shirafuna 37
It is also possible to omit the step and directly feed the sample to the centrifugal separation fi3B).

In this manner, the dissolved oxygen meter 42 is used to continuously monitor the presence or absence of dissolved oxygen in order to maintain the sulfite ion concentration, which is important as a factor determining desulfurization performance, at almost atmospheric level with the minimum necessary utility. Based on the measurement result of the dissolved oxygen meter 42, the absorption liquid can be constantly held in the circulation tank 32 depending on the absorption capacity. Moreover, there is no need to carry out chemical analysis of the absorption liquid for this purpose.

If the reading on the dissolved oxygen meter shows zero, it suggests that the oxidation performance at that point is insufficient. increase.

(2) Increase the rotational speed of the oxidation stirrer (this makes the oxidation air bubbles even finer.) (3) Oxidation stirrer? Increase the number of machines in operation.

There are several methods available, but either method will achieve the goal. However, method (3) is the simplest and most effective.

Next, the principle behind how the oxidation state of sulfite can be determined by measuring the dissolved oxygen concentration will be explained.

FIGS. 2(a) and 2(b) show the relationship between the oxidation state of sulfite and dissolved oxygen, and are an example of experiments conducted by the present inventors for the purpose of understanding the oxidation state of sulfite. According to this result, if sulfite is present in the liquid, the dissolved oxygen meter 4
The indicated value of 2 becomes zero, and dissolved oxygen comes to be detected when the oxidation reaction is almost completed. By utilizing this relationship, the oxidation state within the tank 32 can be more easily and continuously determined than by determining the sulfite concentration in the absorption liquid by chemical analysis.

Next, based on the measurement results of the dissolved oxygen meter 42, the coolant 10
A specific means for oxidizing No. 2 will be explained.

1) A method in which a nozzle or sparger ring is placed inside the tank 32 to perform oxidation.

In this case, it is possible to achieve the objective by controlling the valves 43a and 43b to increase or decrease the amount of air supplied, but care must be taken because if the range of change is large, the nozzle, ejection hole, etc. will be clogged.

2) A method of efficiently oxidizing air by mechanically atomizing the air using stirring blades, rotating bodies, etc.

In this case, factors related to oxidation performance include: (1) air supply amount, (2) rotation speed, and (2) number of operating units.

These factors will be explained as follows.

■ Method of changing the air supply amount.

Although the objective can be achieved to a certain degree by changing the amount of air, it also has the following problems. In other words, when blocking air with a high-speed rotating body,
The apparent density of the liquid around this rotating body is low, and the power consumption is a fraction of the power consumed when rotating without blowing air.

On the other hand, if you increase the air supply amount above the rated value, there is no problem because the power tends to decrease. However, if you decrease the air amount, the power consumption will increase, and in some cases, it may cause motor trip etc. Consideration must be given when reducing the air supply amount.

FIG. 3 shows a specific configuration of the control section 44 for controlling the air supply amount.

The computing unit 25 that calculates and outputs the base signal F includes an exhaust gas amount signal B outputted from the exhaust gas flowmeter 41 and an SO□ concentration signal in the inlet exhaust gas outputted from the 5Ota degree detector (analysis needle) 22 in the inlet exhaust gas. C1 6tR degree signal in exhaust gas output from the 1 degree Oz detector (analysis needle) 23, circulating fluid IH! Circulating fluid amount signal E output from the output device (flow meter) 24 and pH value signal G output from the pH detector 29
Each output signal of is input. The indicating controller 26 calculates and outputs the control signal H based on the base signal F, the dissolved oxygen signal A of the dissolved oxygen meter 42, and the dissolved oxygen set value S.
Δ) 26a, proportional integrator (Pl) 26b, adder (Σ)
26c and a manual/automatic switch (H/A) 26d. Control signal H output from this indicating controller 26
The opening degree of the pulp 43 is adjusted by.

The computing unit 25 calculates the exhaust gas 10 based on the signals B-E and G.
Using 02 in 1, the natural oxidation rate is calculated using equations (1) and (2).

Natural oxidation amount QN = kX (L)...River...
(1) Required oxidation amount Qa = CG)X (Sow)X
C... (2) Based on these, the base air 1) Vair is determined by equation (3), and this is used as the output signal F of the calculator 25.

Base air amount Va i r =ax [QR-QH)・
・・・・・・・・・・・・(3) However, k: natural oxidation coefficient kcc (Ox), p
Hα, C: Constant Most of the amount of air to be supplied is determined by the calculator 25, and the rest is finely adjusted by the actual measured value depending on the output value of the dissolved oxygen meter 42. Therefore, control with excellent controllability such as responsiveness and continuity can be performed. By the way, signal F
If control is performed solely depending on the signal without using the control, the variable range will be widened, resulting in slow response and a tendency to cause hunting and the like. The valve opening degrees of the valves 43a and 43b are adjusted in a range of 0 to 100% according to a control signal H output from the indicating controller 26.

■Method of changing the rotation speed of the oxidation stirrer 35.

This can be realized by the configuration shown in FIG. In FIG. 4, the pH detector 29 is removed from the configuration of FIG.
It is configured by providing. Therefore, the operation is similar to that shown in FIG. 3, and instead of valve opening information, rotation speed information is sent to the indicating controller
It is output as signal I. The rotational speed controller 27 controls the rotational speed of the stirrer 35 in accordance with this signal (2).

■Method of changing the number of stirrers 35 in operation.

This is the most effective method compared to methods (1) and (2) above. - Since the rotation speed and air supply amount of the rotating body of the machine are kept constant and can be controlled depending on whether or not to operate, maintenance costs are relatively low. The number control is executed by the control section 44 shown in FIG. 1 based on the output value of the dissolved oxygen meter 42.

Table 1 shows the relationship between phenomena and control contents corresponding to the above three control forms.

Table 1 [Example] Experiments were conducted using a single absorption/oxidation tower type flue gas desulfurization apparatus with a processing gas amount of 51) 1 ONm''/h (rated).

The desulfurization tower 31 has a diameter of 0.3 m and a height of about 9.5 m, and the circulation tank 32 at the bottom of the tower has a diameter of 10 m and a height of I.

The length of the tank was 5 m, and four side-type stirrers (using a three-blade propeller type with a diameter of 120 m as blades) were installed at a height of 150 mm from the tank bottom for sulfite oxidation and slurry sedimentation prevention. The rotational speed of this agitator 35 is kept constant at 150 rpm, and the amount of air supplied per unit is 1. ONm'/
It was set as h. Approximately 20 wt % limestone slurry was supplied to the circulation tank 32 as an absorbent. The ii tank 32 holds an absorbent slurry 4101 mainly composed of CaCO2 and Ca5Oa 2 Hz○, which is extracted from the Wi ring tank 32 by the circulation pump 33.
It was circulated at a flow rate of t/h. The pH setting value of the circulation tank 32 was set to 5.5, and the limestone flow rate was controlled.

A small-capacity liquid reservoir is set up in the middle of the return line of the i-method, and the dissolved oxygen electrode is immersed in it, and the measured value is sent to the control panel, and the dissolved oxygen set value is used as the atmosphere. A control system was set up so that the oxidation stirrer was operated and the associated air cutoff valve was opened, and the upper limit set value of dissolved oxygen was set to sppm. 1) The stirrer was stopped and the air cutoff valve was closed.

(Example 1) When automatic operation was performed under the exhaust gas conditions of exhaust gas l: 58ONm'/h and population sow concentration near 40Ppm, the number of oxidation stirrers in operation was steady at 3, and the dissolved oxygen at that time was 2 to 2 sppm. was maintained. At this time, the absorption liquid was sampled several times and the So''-x concentration was chemically analyzed (iodometric method), and it was confirmed that it was less than 2mmoilIt.The desulfurization rate was also 90%.
Met.

(Example 2) Exhaust gas I: 305Nm/h, population S Oz 93 degrees:
When automatically operated under exhaust gas conditions of 630 ppm (equivalent to 1/4 boiler load), the number of units in operation was 1.
It becomes steady at the stand, and the So''-3 concentration in the absorption liquid is also '1 m
It was kept below mo171. The desulfurization rate at this time was 92%
Met.

(Reference Example 1) When the operation was changed to manual operation under the same exhaust gas conditions as in Example 2 and the number of stirrers in operation was set to four, the desulfurization rate was 92% and the 5oz-z concentration in the absorption liquid was almost at atmospheric pressure.

〔Effect of the invention〕

As described above, according to the present invention, in a desulfurization apparatus having an oxidizing ability, it is possible to always perform an oxidation reaction satisfactorily with the minimum necessary utility.

In particular, when the load of the boiler is low or when a low fuel of 3 minutes is burned, the amount of air in the tower, the motor power, etc. can be reduced, so there is a remarkable effect on reducing utility.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2(a)
, (b) is a characteristic diagram showing the relationship between sulfite ion concentration and dissolved oxygen, FIGS. 3 and 4 are block diagrams showing details of the control unit 44, and FIG. 5 is an example of a conventional wet flue gas desulfurization system. FIG. 6 is a block diagram showing an example of a one-tower type desulfurization apparatus. 22...S○2? Agriculture rate detector, 23...
・0□Concentration detector, 24... Circulation flow rate detector,
25... Arithmetic unit, 26... Indicating controller, 27... Rotation speed controller, 31...
...Desulfurization tower, 32...Circulation tank, 33...
... Circulation pump, 35... Stirrer, 36...
... Demister, 37 ... Shisovna, 38.
... Centrifugal separator, 39 ... Spray section, 4
0...Analyzer, 41...Exhaust gas flow meter, 43a, 43b...Pulp, 44...
・Control unit. Agent Patent Attorney Masaru Nishimoto - Figure 1 ↑ Figure 2 Time (min) → (b) Ginma (min) → Figure 3 Figure 4 Figure 5 Figure 6

Claims (6)

[Claims] (1) A desulfurization tower that absorbs and removes sulfur oxides from the flue gas by bringing the sprayed absorption liquid into contact with the flue gas from the introduced boiler, etc., and a desulfurization tower that is installed at the bottom of the tower to store the absorption liquid and remove the spray In a wet flue gas desulfurization equipment, the wet flue gas desulfurization equipment is equipped with a circulation tank that circulates dissolved oxygen in the absorption liquid in the tank, and forcibly oxidizes sulfite in the absorption liquid in the tank by air blown into the absorption liquid. Absorbent oxidation control for wet flue gas desulfurization equipment, characterized in that it is provided with a dissolved oxygen meter that measures the concentration, and a control means that controls the supply state of the air to be blown based on the measured value of the dissolved oxygen meter. Device. (2) The absorption liquid oxidation control device for a wet flue gas desulfurization device according to claim (1), wherein the control means is an increase or decrease in the amount of air blown into the device. (3) Inlet exhaust gas amount, SO_2 concentration in gas, O_ in gas
2 Calculate the basic air amount based on the natural oxidation rate estimated based on the concentration, absorption liquid circulation flow rate, and absorption liquid pH value,
The wet flue gas desulfurization apparatus according to claim (2), wherein the blown air amount is obtained by adding an air amount calculated depending on the dissolved oxygen measurement value to this air amount. absorption liquid circulation flow rate control device. (4) Absorbing liquid oxidation control of the wet flue gas desulfurization apparatus according to claim (1), wherein the control means is a rotation speed control of a stirrer that stirs the absorbing liquid in the tank. Device. (5) Absorbent liquid oxidation in the wet flue gas desulfurization apparatus according to claim (1), characterized in that the control means controls the number of agitators in operation that stir the absorbent in the tank. Control device. (6) Calculate the oxidation state of sulfite by oxygen in the exhaust gas based on the signals of the exhaust gas amount at the equipment inlet, the sulfur oxide concentration in the gas, the O_2 concentration in the gas, and the absorption liquid circulation amount, and combine that value with the dissolved oxygen value. An absorbing liquid oxidation control device for a wet flue gas desulfurization apparatus according to claim 4 or claim 4, wherein the rotational speed or the number of operating units of the stirrer is controlled based on the deviation of the agitator.