JPH11347352A - Wet exhaust desulfurizing method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the filling of the circulating tank of an absorbing tower with fine air bubbles when salts are conc. in the absorbing tower or the diameter of the absorbing tower is contracted or the amt. of an absorbing soln. is increased and to keep a liquid surface level constant. SOLUTION: A wet exhaust gas desulfurizing method wherein the combustion exhaust gas discharged from the combustion device of a boiler or the like is brought into contact with an absorbing soln. in an absorbing tower 2 to treat sulfur oxide in the exhaust gas and the absorbing soln. having absorbed sulfur oxide is stored in the circulating tank 7 of the absorbing tower and, after a defoaming agent is supplied to the absorbing soln. during the storage of the absorbing soln., the absorbing soln. is again brought into contact with the combustion exhaust gas, there is no special limit as the defoaming agent, it is pref. to use a defoaming agent based on a higher alcoholic surfactant. It is unnecessary to make the concn. of the defoaming agent in the absorbing soln. too high and, if the defoaming agent is supplied so that the concn. thereof is set to 3-50 ppm, effect is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet type flue gas desulfurization apparatus, and more particularly to a wet type flue gas desulfurization apparatus suitable for preventing an abnormal rise in the liquid level due to the filling of bubbles in an absorption tower liquid reservoir.

[0002]

2. Description of the Related Art In order to prevent air pollution, wet limestone-gypsum desulfurization apparatuses are widely used as apparatuses for removing sulfur oxides in exhaust gas. FIG. 5 shows a conventional technique of this wet limestone-gypsum desulfurization apparatus.

[0003] Exhaust gas 1 containing sulfur oxides generated from a thermal power plant or the like is led to an absorption tower 2 of a desulfurizer. Absorption tower 2
Inside, a spray header 3 having a large number of spray nozzles 4 is installed, and by contacting the absorbing liquid sprayed as fine droplets from the spray nozzle 4 with the exhaust gas 1, the sulfur oxides in the exhaust gas are converted into absorbing droplets. Chemically removed at the surface. Small droplets accompanying the exhaust gas flow are removed by a mist eliminator 5 installed on the upper part of the absorption tower 2, and the purified gas 6 is raised by a reheating facility (not shown) installed on the downstream side of the absorption tower 2 as necessary. Heated and discharged from the chimney.
Most of the droplets sprayed from the spray nozzle 4 absorb the sulfur oxide and then fall into the absorption tower circulation tank 7 provided at the lower part of the absorption tower 2.

[0004] Sulfur oxide (SO ₂ ) absorbed in the absorbing solution
Reacts with limestone (CaCO ₃ ) contained in the absorbing solution, and is further oxidized by the air 8 supplied to the absorbing solution circulating tank 7 to form gypsum 14 (CaSO ₄ .2H ₂ O). This series of reactions is represented by the following formula.

SO ₂ + 2H ₂ O + CaCO ₃ + 1 / 2O
₂ → CaSO ₄ .2H ₂ O + CO ₂ On the other hand, limestone 9 as an absorbent is stored as limestone slurry in a limestone supply facility 10 and a limestone slurry pump 11
Is supplied to the absorption tower circulation tank 7. Further, in order to collect the gypsum generated in the absorption tower 2, a part of the absorption liquid in the absorption tower circulation tank 7 is extracted and sent to the gypsum dewatering equipment 13 by the pump 12, and the gypsum contained in the absorption liquid is removed. And soot is collected as gypsum 14. A part of the gypsum 14 and soot dewatered filtrate is discharged out of the system from the drainage line 15 to prevent the in-system impurities from being concentrated, and the remaining liquid is sent to the limestone supply facility 10, where it is supplied for limestone slurry production. It is used as water, and the remainder is sent to the absorption tower circulation tank 7 of the absorption tower 2 via the dehydration filtrate line 16.

Here, the desulfurization wastewater extracted from the wastewater line 15 is sent to a wastewater treatment facility, where it is discharged after removing fluorine, precious metals and the like. Since the equipment cost of the wastewater treatment equipment depends on the amount of desulfurization wastewater, it is necessary to reduce the amount of desulfurization wastewater as much as possible in order to reduce equipment costs. When the desulfurization wastewater is reduced, impurities, particularly salts (NH ₄ , Mg)
^2+, Cl ^-, etc.) is easily concentrated.

Further, in recent years, the concentration of sulfur oxides in exhaust gas has been high due to diversification of boiler fuels, and high desulfurization performance has been required for desulfurization equipment. I have.

[0008]

The above-mentioned prior art is based on the problem that when the salts are concentrated in the absorption tower 2, when the diameter of the absorption tower is reduced, or when the amount of the absorbing solution is increased, the absorption tank circulation tank 7 is used. There was a problem that the microbubbles were slowly filled and the liquid level rose abnormally and flowed back to the absorption tower inlet duct.

An object of the present invention is to prevent the absorption tower from being filled with fine bubbles in the absorption tower circulation tank when salts are concentrated in the absorption tower, when the diameter of the absorption tower is reduced, or when the amount of the absorbing solution is increased. It is an object of the present invention to provide a desulfurization method and a device in which a liquid level is maintained stably.

[0010]

The above object of the present invention is attained by the following constitution. That is, the combustion exhaust gas discharged from the combustion device is brought into contact with the absorbing solution to treat the sulfur oxides in the exhaust gas, the absorbing solution absorbing the sulfur oxide is stored, and the absorbing solution is consumed during the storing of the absorbing solution. This is a wet flue gas desulfurization method in which after supplying a foaming agent, the absorbent is used to contact the combustion exhaust gas again.

The defoaming agent is not particularly limited, but it is desirable to use a defoaming agent containing a higher alcohol surfactant as a main component. It is not necessary to make the concentration of the antifoaming agent in the absorbing solution so high, and an effect can be obtained if the supply is performed so as to maintain the concentration in the range of 3 to 50 ppm.

Further, since a part of the defoaming agent flows out of the system due to drainage, gypsum-adhered water, etc., the amount of the defoaming agent in the absorption tower circulation tank varies depending on the boiler load. Therefore, stable operation becomes possible by controlling the supply amount of the defoaming agent based on the load signal of a combustion device such as a boiler. Since there is a correlation between the load of the combustion device and the amount of exhaust gas, the same effect can be obtained even if the defoaming agent supply amount is controlled based on the amount of exhaust gas instead of the load signal.

Further, the present invention provides an absorption tower for treating a sulfur oxide in an exhaust gas by contacting a combustion exhaust gas discharged from a combustion device with an absorbing solution, and storing an absorbing solution having absorbed the sulfur oxide therein. Also included is a wet flue gas desulfurization device provided with an absorption tower circulation tank that supplies the absorbing solution while circulating it to the absorption tower, and a defoaming agent supply unit that supplies a defoaming agent into the absorbing solution in the absorption tower circulation tank. .

[0014]

[Function] By supplying the defoamer to the absorption tower circulation tank, the generation of fine bubbles is controlled even if the absorption liquid after gas-liquid contact with the exhaust gas falls and collides with the liquid surface of the absorption liquid in the tank. You. As a result, the number of fine bubbles drawn into the descending flow velocity of the absorption tower circulation tank is reduced, so that an abnormal rise in the liquid level due to the filling of the fine bubbles can be controlled.

[0015]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In the desulfurization apparatus shown in FIG. 1, the same components as those of the desulfurization apparatus described with reference to FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.

In the desulfurization apparatus shown in FIG. 1, a defoaming agent tank 18, a defoaming agent injection pump 19 and a defoaming agent injection line 2
0, and a specified amount of defoamer is supplied to the absorption tower circulation tank 7
To be injected.

FIG. 2 (a) shows a control system diagram of the amount of the defoaming agent injected into the absorption tower circulation tank 7. A predetermined signal (calculated from the relationship shown in FIG. 2B) is obtained for the load request signal by the function generator 22, and a correction value from the bias setting unit 23 is added to this value, and the calculation is performed by the calculation unit 24. Then, the operation amount of the defoaming agent injection pump 19 is determined.

The injection amount of the antifoaming agent is an amount that keeps the concentration of the antifoaming agent in the absorbent almost constant, that is, an amount that flows out of the system of the desulfurizer. Here, the amount flowing out of the system is the sum of the amount taken out from the drainage line 15, the amount taken out by being contained in the attached water in the gypsum 14, and the amount taken out attached to the gypsum particles.

When the desulfurizer is actually operated, the amount of gas and the concentration of SO _{2 at the} inlet change due to a change in the boiler load, so that the outflow amount of the defoamer outside the system changes. In order to cope with this, the defoaming agent injection amount control may be performed based on the relationship between the boiler load and the defoaming agent injection amount shown in FIG. 2 in consideration of the drainage amount, the recovered gypsum amount, and the attached water amount of each load. .

Since the injection amount of the antifoaming agent is very small, the antifoaming agent injection pump 19 is preferably a diaphragm type or plunger type pump, and it is desirable to remotely control the pump pulse (number of strokes per unit time). desirable. In addition, the rate of diluting the defoaming agent with water may be increased, and the injection amount of the defoaming agent may be controlled by a combination of a vortex pump, a flow meter, and a regulating valve, but the equipment configuration is similar to a diaphragm type or a plunger type. It is preferable to directly control the pump pulse to change the injection amount because the minute flow rate can be easily controlled. However, when the supply amount of the antifoaming agent is large in a large-capacity plant, a means for controlling the injection amount of the antifoaming agent by a combination of a vortex pump, a flow meter and a regulating valve is also effective.

FIG. 3 shows the mechanism of occurrence of an abnormal rise in the liquid level caused by the filling of the absorption tower circulation tank 7 with fine bubbles in the absorption tower 2. The absorption liquid sprayed from the spray nozzle 4 of the absorption tower 2 falls and collides with the liquid surface of the absorption tower circulation tank 7 to generate fine bubbles.

On the other hand, since the absorption liquid is extracted from the absorption tower circulation tank 7 and is circulated and sprayed, a downward flow is generated in the absorption tower tank 7. The downflow velocity also increases. Therefore, when the flow rate of the descending flow in the absorption tower circulation tank 7 is higher than the rising speed of the fine bubbles generated on the liquid level in the absorption tower circulation tank 7, the fine bubbles are stored in the lower part of the absorption tower circulation tank 7. To reach.

When the above phenomenon occurs, the liquid level in the absorption tower circulating tank 7 rises to about 1.5 to 2 times the set value, causing gas flow obstruction at the absorption tower inlet. And a large amount of overflow in the absorption tower occurs. For this reason, an antifoaming agent is injected to suppress the generation of fine bubbles near the liquid surface.

(Experiment) The type of antifoaming agent (denatured oil type antifoaming agent and higher alcohol-based surfactant) and the defoaming in the absorbent were measured using a test device capable of reproducing the behavior in the absorption tower circulation tank 7. FIG. 4 shows the results of a test in which the agent concentration was changed. The antifoaming agent is composed mainly of a higher alcohol surfactant (Kurita Industries Co., Ltd .: Krilles P666), and it is confirmed that sufficient effects can be obtained if the antifoaming agent concentration in the absorbing solution is about 3 to 50 ppm. did.

[0025]

According to the present invention, the generation of fine bubbles in the liquid storage section of the absorption tower can be suppressed, and safe operation can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a system diagram of a desulfurization apparatus according to an embodiment of the present invention.

FIG. 2 is a control system diagram (FIG. 2 (a)) for controlling an injection amount of an antifoaming agent into the absorption tower circulation tank 7 using the desulfurization apparatus of FIG. FIG.
(B)).

FIG. 3 is a view for explaining a mechanism of occurrence of abnormal rise in liquid level due to filling of fine bubbles in an absorption tower circulation tank in the desulfurization apparatus of FIG. 1;

FIG. 4 is a diagram showing the results of a test in which the type of antifoaming agent and the concentration of the antifoaming agent in the absorbing solution are changed using a test device capable of reproducing the behavior in the absorption tower circulation tank in the desulfurization device of FIG. It is.

FIG. 5 is a diagram showing a system diagram of a conventional desulfurization apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Exhaust gas 2 Absorption tower 3 Spray header 4 Spray nozzle 5 Mist eliminator 7 Absorption tower circulation tank 8 Air 10 Limestone supply equipment 11 Limestone slurry pump 12 Absorbing liquid extraction pump 13 Gypsum dehydration equipment 14 Gypsum 15 Dehydration line 16 Dehydration filtrate line 18 Defoaming agent Tank 19 Defoamer injection pump 20 Defoamer injection line

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hisato Tahara 5-3 Takaracho, Kure City, Hiroshima Prefecture Inside Bab Hitachi Industrial Co., Ltd.

Claims (5)

[Claims] 1. A method of treating a sulfur oxide in an exhaust gas by bringing a flue gas discharged from a combustion device into contact with an absorbing solution, storing the absorbing solution having absorbed the sulfur oxide, and absorbing the absorbing solution in the storing of the absorbing solution. After supplying the defoamer to the liquid, using the absorbing liquid,
A wet flue gas desulfurization method comprising bringing the flue gas into contact with the combustion exhaust gas again. 2. The wet flue gas desulfurization method according to claim 1, wherein an antifoaming agent containing a higher alcohol surfactant as a main component is used. 3. An antifoaming agent concentration in the absorbing solution of 3 to 50 pp.
The wet flue gas desulfurization method according to claim 1, wherein the supply is performed so as to be maintained in a range of m. 4. The wet exhaust desulfurization method according to claim 1, wherein the supply amount of the defoaming agent is controlled according to a load signal of the combustion device or an exhaust gas amount. 5. An absorption tower for treating a sulfur oxide in an exhaust gas by bringing a flue gas discharged from a combustion device into contact with an absorbent, storing the absorbent absorbing the sulfur oxide, and absorbing the absorbent. A wet type flue gas desulfurization apparatus comprising: an absorption tower circulation tank for supplying a defoaming agent into the absorption liquid in the absorption tower circulation tank;