JPH0741141B2 - Wet flue gas desulfurization equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an absorption liquid oxidation control device for a wet flue gas desulfurization device, and in particular, it is produced by absorbing and removing sulfur oxides in exhaust gas using an absorption liquid. The present invention relates to an absorbent liquid oxidation control device for a wet flue gas desulfurization device, which is suitable for oxidizing a sulfite.

[Conventional technology]

FIG. 5 is a configuration diagram showing a conventional wet flue gas desulfurization system, in which a dust removal tower 1 into which exhaust gas 101 is introduced, is communicated with this dust removal tower 1 in the middle stage, and an absorbent slurry (absorption liquid) 102 is provided at the bottom. The absorption tower circulation tank 3 for storing the is mainly composed of the absorption tower 2. A dust removing tower circulation tank 4 in which the dust removing tower circulation slurry 103 is stored is connected to the lower portion of the dust removing tower 1, and an agitator 6 is provided in the circulation tank 4. A stirrer 5 is also provided in the absorption tower circulation tank 3.

A nozzle 16 is arranged above the absorption tower 2, and the nozzle 16
An absorption tower circulation pump 7 for supplying the absorption liquid is connected to. Similarly, a nozzle 17 provided above the dust removing tower 1
A dust removing tower circulation pump 8 for supplying the slurry 103 is provided. Further, an absorption tower bleed pump 9 is connected to the absorption tower circulation tank 3, and an oxidation tower supply tank 10 for storing sulfuric acid 105 is connected to the pump 9. pump
An oxidation tower 11 is connected to the tank 10 via 18, and a thickener 12 and a centrifugal separator 13 are sequentially connected to the oxidation tower 11.

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

Exhaust gas 101 from the boiler or the like is removed and cooled in the dust removing tower 1 (or is directly supplied to the absorption tower 2). Then, the sulfur oxides in the exhaust gas 101 are absorbed and removed in the absorption tower 2. Here, the absorbent slurry used for absorbing and removing the sulfur oxides in the exhaust gas 101 is once held in the absorption tower circulation tank 3 and circulated to remove the sulfur oxides. Here, the agitator 5 stirs and mixes the absorbent.
After the SO ₂ absorption performance is restored 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 (CaCO ₃ ) in the absorbent slurry is changed to calcium sulfite (CaS 3
O ₃ ) and part of it (or the total amount depending on conditions)
Is oxidized by oxygen in the exhaust gas to form calcium sulfate (gypsum). This slurry is extracted from the circulation tank 3 by the absorption tower bleed pump 9, and is supplied to the oxidation tower supply tank 10
Unreacted CaC by adding sulfuric acid (H ₂ SO ₄ ) at
After being adjusted to a pH suitable for the decomposition of O ₃ and the oxidation of sulfite, it is supplied to the oxidation tower 11. In the oxidation tower 11, the air 106 from the bottom of the tower is forced to generate fine bubbles by an atomizer for air refining to dissolve oxygen in the air, and the dissolved oxygen reacts with calcium sulfite to give calcium sulfate (gypsum). ) And is withdrawn from the bottom of the tower. The gypsum slurry extracted from the oxidation tower 11 is supplied to the thickener 12 and concentrated, and then the centrifuge 13 causes the gypsum 10% of the adhered water to be 10% or less.
8 is separated and collected from the filtered water 107. However, the system shown in FIG. 5 has the problems that the cooling, absorption and oxidation steps are performed in separate columns, so that the process is complicated and the installation space is wide. Therefore,
In order to solve these problems, the inventors have already proposed a wet flue gas desulfurization apparatus in which the steps of cooling, absorption and oxidation are combined in one tower as shown in FIG.

That is, this apparatus is composed of one tower in which a circulation tank 32 for storing the circulation slurry 102 is provided below the desulfurization tower 31 into which the exhaust gas 101 is introduced, and a demister 36 is provided above. A pump 33 is connected to the circulation tank 32.
Thickener 37 and centrifuge 38 are sequentially connected to 33.
Further, in the desulfurization tower 31, a spray portion 39 to which the circulating slurry from the pump 33 is supplied is arranged.

In this apparatus, the exhaust gas 101 such as a boiler is guided to a desulfurization tower 31, contacted with a sprayed calcium-based absorbent slurry to remove dust, cool, and desulfurize, and then the entrained mist is demitted.
It is removed by 36 and comes out of the desulfurization tower 31. On the other hand, the limestone slurry 104, which is the absorbent, is supplied to the circulation tank 102 according to the amount of SO _{2 to be} removed, and the hydrogen ion (H ⁺ ) in the slurry after contact with the exhaust gas is reduced to recover the absorption performance of the absorption slurry. Let The circulation tank 32 is provided with stirrers 34 and 35 for preventing solids from settling and for refining and dispersing air (for oxidation). Sulfurous acid generated by absorbing SO ₂ in exhaust gas by stirring these air. It oxidizes the ions to form stable sulfates, which lowers the SO ₂ equilibrium partial pressure in the absorption liquid to increase the absorption capacity and prevents sedimentation and deposition of the absorbent.

The absorption slurry thus regenerated is supplied to the spray section 39 by the circulation pump 33 and comes into countercurrent contact with the exhaust gas. A part of the absorption slurry is extracted from the circulation tank 32, concentrated (or directly) in the thickener 37, dehydrated in the centrifuge 38, and recovered as the powdered gypsum 108 containing 10% or less of the adhered water. Incidentally, 107
Is filtered water.

[Problems to be solved by the invention]

However, the above-mentioned prior art does not consider the low utility required by the user. That is, for the purpose of lowering the utility of the desulfurizer, (a) reduction of pressure loss in the absorption tower (reduction of ventilation system power) and (b) absorption tower circulation liquid amount control (reduction of circulation pump power) are performed. However, no specific control method has been established for the process of oxidizing CaSO ₃ to gypsum, and constantly spends a certain amount of oxidation utility on changes in boiler load and exhaust gas conditions. . Therefore, there has been a problem in a method of grasping the oxidation state of calcium sulfite in the absorbing solution in the desulfurization apparatus and how to utilize the method to reduce the utility for oxidation.

The object of the present invention is to solve the above-mentioned problems of the prior art,
It is an object of the present invention to provide a wet flue gas desulfurization device capable of favorably performing an oxidation reaction with a minimum required utility.

[Means for solving problems]

In order to achieve the above object, the present invention measures the dissolved oxygen concentration in the absorption liquid, provided with a control means for controlling the supply state of the air blown into the absorption liquid based on the measurement result, the natural in the desulfurization tower The basic air amount is calculated from the oxidation rate, and the air amount depending on the dissolved oxygen concentration is calculated to control the supply state of the blown air.

[Action]

Dissolved oxygen in the absorbent is detected when the sulfite concentration is almost zero. As a result, when the oxidation reaction of the slurry (absorption liquid) in the tank is well performed, the concentration of dissolved oxygen immersed in the absorption liquid is 0 within the range of the saturated solubility of air or less.
When the indication is larger, and on the contrary, when the oxidation reaction is insufficient, the dissolved oxygen concentration shows a value of apparently zero, so by controlling the air supply state accordingly, the oxidation state is good. Kept in.

Example of Invention

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

FIG. 1 is a block diagram showing an embodiment of the present invention. In addition,
In FIG. 1, the same elements as those in FIG. 6 are designated by the same reference numerals, and the duplicated description will be omitted.

The exhaust gas supply pipe is provided with an analyzer 40 for analyzing SO ₂ and O ₂ in the exhaust gas 101 and an exhaust gas flow 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 for adjusting the amount of air 106 supplied into the circulation tank 32 are provided. In addition, these valves 43a and 43b or the agitator 35 for oxidation are used as a dissolved oxygen meter.
A control unit 44 is provided to control the operation by 42.

Next, the function and effect of the above configuration will be described.

Exhaust gas 101 from a boiler or the like is introduced into the desulfurization tower 31 and comes into contact with the sprayed calcium-based absorbent slurry to remove dust, cool, and desulfurize, and then is removed from the desulfurization tower 31 by removing entrained mist by the demister 36. On the other hand, limestone slurry that is an absorbent
104 is supplied to the circulation tank 32 according to the amount of SO _{2 to be} removed, and comes into contact with the exhaust gas 101 to reduce hydrogen ions (H ⁺ ) in the absorption slurry having a lowered pH. For a plurality of oxidation in the circulating tank 32 (air fine dispersion) stirrer 35 is installed, sulfite ions raised slurry absorbs SO ₂ SO ₂ partial pressure (SO _^2-3) oxide Then, the partial pressure is lowered to recover the SO ₂ absorption performance and calcium sulfate (gypsum) is obtained. The absorbent slurry thus regenerated is supplied to the spray section 39 by the circulation pump 33 and drops 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 the dissolved oxygen meter 42 immersed in the absorption liquid, and when the measured value becomes zero, the operating number of the oxidation agitator 35 is increased. Also, apart from this,
The exhaust gas flow meter 41 measures the amount of exhaust gas at the desulfurization tower inlet, and the SO ₂ concentration
The O ₂ analyzer 40 measures the respective signals, and the signals are taken into the control unit 44 to indirectly determine the number of operating agitators 35 required for oxidation based on exhaust gas conditions, and perform on / off control. (Note that the stirrer
It is desirable that not only the number control of 35, but also the circulation flow rate and the O ₂ concentration in the gas be processed by the control unit 44. ) The target is achieved with the minimum required oxidation utility by the required operation value of the oxidation stirrer 35 from the gas side and the signal from the measurement side on the liquid side by the dissolved oxygen meter 42.

Part of the absorption slurry that is circulated and used in the desulfurization tower 31 is extracted from the circulation tank 32, concentrated in the thickener 37, and finally dehydrated in the centrifuge 38 to be recovered as the gypsum 108 having 10% or less of the adhered water ( In some cases, it is possible to omit the thickener 37 and directly supply the centrifuge 38).

In this way, the presence or absence of dissolved oxygen is continuously monitored using the dissolved oxygen meter 42 in order to maintain the sulfite ion concentration, which is an important determinant of desulfurization performance, at almost zero with the minimum required utility. Based on the measurement result of the dissolved oxygen meter 42, the absorption liquid having a high absorption capacity can be constantly held in the circulation tank 32. Moreover, for this reason, it is not necessary to carry out a chemical analysis of the absorbing liquid.

It should be noted that when the indicated value of the dissolved oxygen meter indicates zero, it suggests that the oxidation performance at that time is not sufficient. To increase.

(2) Increase the number of revolutions of the agitation stirrer (this makes it possible to further miniaturize the bubbles of the oxidizing air.) (3) Increase the number of operating agitation stirrers.

There is a means such as the above, but the objective is achieved by either method. However, the method of (3) is the easiest and most effective.

Next, the principle that the oxidation state of sulfite can be understood by measuring the dissolved oxygen concentration will be described.

FIGS. 2 (a) and 2 (b) show the relationship between the oxidation state of sulfite and the dissolved oxygen, which is an example of what the present inventors have conducted for the purpose of understanding the oxidation state of sulfite. According to this result, the dissolved oxygen meter 42
Indicates 0, and dissolved oxygen is detected when the oxidation reaction is almost completed. By using this relationship, the oxidation state in the tank 32 can be grasped more easily and continuously than the concentration of sulfite in the absorbing solution is determined by chemical analysis.

Next, specific means for oxidizing the cooling liquid 102 based on the measurement result of the dissolved oxygen meter 42 will be described.

1) A method of arranging a nozzle or sparger ring in the tank 32 for oxidation.

In this case, it is possible to achieve the object by controlling the valves 43a and 43b to increase or decrease the air supply amount. However, if this change width is large, the nozzles, the ejection holes, etc. will be clogged, so be careful.

2) A method of efficiently oxidizing air by mechanically atomizing air with a stirring blade, a rotating body, or the like.

In this case, the factors related to the oxidation performance include the air supply amount, the rotation speed, and the operating number.

The following is a description of these factors.

 How to change the air supply.

By changing the amount of air, some objects can be achieved, but they also have the following problems. That is, when shutting off air with a high-speed rotating body,
The apparent density of the liquid around the rotating body is small, which is a fraction of the power consumption when the liquid is rotated without blowing air. On the other hand, when the air supply amount is increased above the rated value, there is no problem because the power tends to decrease. However, when reducing the amount of air, the power consumption increases,
In some cases, it may cause a motor trip, etc., so that consideration must be taken when reducing the air supply amount.

FIG. 3 shows a specific configuration of the control unit 44 for performing this air supply amount control.

The calculator 25 for calculating and outputting the base signal F is an exhaust gas flow meter.
Exhaust gas amount signal B output from 41, SO _{2 in} inlet exhaust gas
SO in the inlet exhaust gas output from the concentration detector (analyzer) 22
₂ concentration signal C, exhaust gas O ₂ concentration detector (analyzer) 23 output O ₂ concentration signal D, circulating fluid amount detector (flow meter) 24 circulating fluid amount signal E and pH Each output signal of the pH value signal G output from the detector 29 is input. The indicating controller 26, which calculates and outputs the control signal H based on the base signal F, the dissolved oxygen signal A of the dissolved oxygen meter 32, and the dissolved oxygen set value S, includes a subtracter (Δ) 26a and a proportional integrator (PI) 2
6b, adder (Σ) 26c and manual / automatic switch (H / A) 26d
It is composed of The opening degree of the valve 43 is adjusted by the control signal H output from the instruction controller 26.

The calculator 25 calculates the natural oxidation rate from O ₂ in the exhaust gas 101 based on the signals B to E and G according to the equations (1) and (2).

Natural oxidation amount Q _N = k × [L] (1) Required oxidation amount Q _R = [G] × [SO ₂ ] × C (2) Based on these, the base air amount Vair is calculated by the formula (3) And the output signal F of the calculator 25 is obtained.

Base air amount Vair = α × [Q _R −Q _N ] (3) where k: natural oxidation coefficient k∝ [O ₂ ], pH α, C: constant Most of the air amount to be supplied is a calculator. Determined by 25,
The rest is finely adjusted by the actual measurement 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, when the control that depends only on the signal A is performed without using the signal F,
Since the variable range is widened, the response becomes slow and hunting or the like easily occurs. Valves 43a and 43b are indicating controllers
According to the control signal H output from 26, the valve opening degree is 0 to 10
It is adjusted in the range of 0%.

 A method of changing the rotation speed of the agitator for oxidation 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.
A rotation speed controller 27 is provided between the agitator 26 and the agitator 35. Therefore, the same operation as in FIG. 3 is performed, and the rotation speed information is output as the signal I from the indicating controller 26 instead of the valve opening information. In response to this signal I, the rotation speed controller 27 controls the rotation speed of the stirrer 35.

 A method of changing the number of operating agitators 35.

This is the most effective method as compared with the above methods and. Since the rotation speed and the air supply amount of one rotating body are constant and the control can be performed depending on whether the operation is performed or not, the maintenance cost is relatively low and the variable range is wide from 0 to all units. This unit number control is executed by the control unit 44 shown in FIG. 1 based on the output value of the dissolved oxygen meter 42.

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

[Example] An experiment was conducted using an absorption / oxidation one-column type flue gas desulfurization apparatus having a treatment gas amount of 580 Nm ³ / h (rated). The desulfurization tower 31 has a diameter of 0.3 m.
Height about 9.5m, circulation tank 32 at the bottom of the tower is φ1.0m, height 1.5m
Then, four side stirrers (using a three-blade propeller having a diameter of 120 m for the blades) for sulfite sulfation and prevention of slurry settling were installed in four equal parts at a height of 150 mm from the tank bottom. The rotation number of the stirrer 35 was fixed at 1500 rpm, and the amount of air supplied per unit was 1.0 Nm ³ / h. About 20wt as absorbent
% Limestone slurry was fed to the circulation tank 32. And
The circulation tank 32 holds 410 liters of absorbent slurry containing CaCO ₃ and CaSO ₄ .2H ₂ O as main components, and is extracted from the circulation tank 32 by the circulation pump 33 and circulated at a flow rate of 8.7 t / h. . The pH setting value of the circulation tank 32 was set to 5.5 to control the limestone flow rate. A small-capacity liquid reservoir was installed in the middle of the circulating liquid return line, the dissolved oxygen electrode was immersed, and the measured value was sent to the control panel.
The dissolved oxygen set value was set to zero, and when it became zero, the control system was constructed so that the operations of Nos. 1 to 4 of the oxidation agitator and the air shutoff valve associated therewith were opened. The upper limit setting value of dissolved oxygen was set to 5 ppm, and the stirrer was stopped and the air shutoff valve was closed.

(Example 1) When automatic operation was performed under exhaust gas conditions of exhaust gas amount: 580 Nm ³ / h and inlet SO ₂ concentration: 740 ppm, the number of operating agitators for oxidation was steady at 3 units and the dissolved oxygen at that time was 2 to 5 ppm. Kept in. At this time, samples the several degrees absorption liquid, SO ^2-
_{When 3} concentrations were chemically analyzed (iodometry method), 2m mo
It was confirmed to be less than l / l. Also, the desulfurization rate is 9
It was 0%.

(Example 2) Under the exhaust gas condition of exhaust gas amount: 305 Nm ³ / h, inlet SO ₂ concentration: 630 ppm (corresponding to 1/4 load as boiler load), the number of operating units becomes steady when operating automatically, and it is in the absorbing liquid. of
SO _^2-3 concentrations were kept below 2m mol / l. The desulfurization rate at this time was 92%.

Reference Example 1 Switching to manual operation under the same exhaust gas conditions as in Example 2, and changing the number of agitators operating to four, the desulfurization rate was 92%, and
SO _^2-3 concentration was almost zero.

〔The invention's effect〕

As described above, according to the present invention, in a wet flue gas desulfurization apparatus, it becomes possible to always perform an excellent oxidation reaction with a minimum required utility. In particular, when the load of a boiler or the like is low or when a fuel having a low S content is burned, the amount of air, motor power, etc. in the tower can be reduced, so that there is a remarkable effect in reducing utility.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are characteristic diagrams showing the relationship between sulfite ion concentration and dissolved oxygen, and FIGS. 3 and 4 are control units 44. FIG. 5 is a block diagram showing the details of FIG. 5, FIG. 5 is a configuration diagram showing an example of a conventional wet flue gas desulfurization system, and FIG. 6 is a configuration diagram showing an example of a one-tower type desulfurization device. 22 …… SO ₂ concentration detector, 23 …… O ₂ concentration detector, 24 …… Circulating flow detector, 25 …… Computer, 26 …… Indicating controller, 27…
… Rotation speed controller, 31 …… Desulfurization tower, 32 …… Circulation tank, 33 …… Circulation pump, 35 …… Stirrer, 36 …… Demister, 37 …… Thickener, 38 …… Centrifuge, 39 …… Spray section , 40 …… analyzer, 41 …… exhaust gas flowmeter, 43a, 43b ……
Valve, 44 ... Control part.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location B01D 53/34 ZAB (72) Inventor Toshio Katsube 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Ltd. Kure Factory (72) Inventor Hiroshi Masutomi 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Ltd. Kure Factory (72) Inventor Fujimura, 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Ltd. Kure Factory (56) References JP-A-62-193630 (JP, A)

Claims (5)

[Claims] 1. A desulfurization tower for contacting an absorbent with an exhaust gas introduced into a boiler or the like to absorb and remove sulfur oxides in the exhaust gas, and a tank provided under the tower for storing the absorbent. In a wet flue gas desulfurization device for forcibly oxidizing sulfite in the absorbent of the tank with air blown into the absorbent, means for measuring the dissolved oxygen concentration in the absorbent, and the means Provided with a control means for controlling the supply state of the air to be blown based on the measured dissolved oxygen concentration, to calculate the basic air amount by the natural oxidation rate in the desulfurization tower, further air amount dependent on the dissolved oxygen concentration And controlling the supply state of the blown air. 2. The wet flue gas desulfurization apparatus according to claim 1, wherein the control means increases or decreases the amount of air blown in. 3. The wet flue gas desulfurization apparatus according to claim 1, wherein the control means controls the rotation speed of an agitator that agitates the absorbing liquid in the tank. 4. The wet flue gas desulfurization apparatus according to claim 1, wherein the control means controls the number of operating agitators that agitate the absorbing liquid in the tank. 5. A desulfurization tower for adsorbing and removing the sulfur oxides in the exhaust gas by bringing the absorbent into contact with the introduced exhaust gas such as a boiler, and a tank provided under the tower for storing the absorption liquid. In a wet flue gas desulfurization device for forcibly oxidizing sulfite in the absorbent of the tank with air blown into the absorbent, means for measuring the dissolved oxygen concentration in the absorbent, and the means Measured dissolved oxygen concentration, amount of equipment exhaust gas, sulfur oxide concentration in gas, O _{2 in} gas
The number of revolutions of a stirrer that calculates the oxidation state of sulfite due to oxygen in the exhaust gas based on the concentration and the signal of the circulating amount of the absorbing liquid, and stirs the absorbing liquid in the tank based on the deviation between the value and the dissolved oxygen concentration. Alternatively, a wet flue gas desulfurization device characterized by controlling the number of operating units.