JPH05337327A - Wet-type exhaust gas desulfurization device and method for desulfurization - Google Patents

Abstract

PURPOSE:To provide a wet-type exhaust gas desulfurization method by which to reduce the quantity of alkali agent used for separating fluorine and metal ion dissolved in a drained liquid, when discharging a drained absorbent slurry to a drainage treatment device, in a wet-type exhaust gas desulfurization device using a calcium compound absorbent slurry. CONSTITUTION:Part of a calcium compound absorbent slurry which comes in contact with an exhaust gas containing sulfur oxide in an absorption column 2, is extracted through a pump 5, then the extracted slurry is dehydrated using a dehydrator 13 to recover gypsum 14, and part of the water drained by the dehydrator is recycled to the absorption column 2. The other part, of the water drained by the defydrator, which corresponds to the drainage amount of a desulfurization device is supplied to a neutralization tank 6 and an alkali agent 7 is added to adjust the pH value. After that, the drained water with the adjusted pH value is sent to a thickener 8 where a supernatant is discharged to a drainage treatment device. On the other hand, an underflow slurry containing a solid component is supplied to the absorption column or the dehydrator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet exhaust gas desulfurization apparatus and a desulfurization method, and more particularly to a wet exhaust gas desulfurization apparatus and a desulfurization method capable of reducing the F (fluorine) concentration in desulfurization effluent with a small amount of chemicals.

[0002]

2. Description of the Related Art Among exhaust gas desulfurization apparatuses currently used for treating exhaust gas from boilers and the like, after absorbing SOx in the exhaust gas from boilers and the like, they are oxidized and recovered as calcium sulfate, that is, gypsum. A wet limestone / gypsum method is generally used in which lime or the like is used as an absorbent (hereinafter, limestone / lime or the like is referred to as an absorbent, and a slurry containing the absorbent supplied to an absorption tower is referred to as an absorbent slurry).

A system diagram of a conventional wet exhaust gas desulfurization apparatus is shown in FIG.
Shown in. Exhaust gas from a boiler or the like is introduced into the absorption tower 2 through the inlet flue 1, where it is cooled to the saturation temperature by gas-liquid contact with the absorbing liquid slurry pre-spray 2a supplied by the circulation pump 3 and, at the same time, in the exhaust gas. SOx, dust, H
Cl, HF, etc. are removed and discharged from the outlet flue 4.

The absorber 2 is supplied with an amount of absorbent slurry that corresponds to the amount of SOx to be absorbed and removed from the absorbent slurry tank 19 through the absorbent slurry pump 20. On the other hand, SO
The slurry containing gypsum produced by absorbing x and being oxidized is withdrawn by the absorption tower withdrawing pump 5 in proportion to the amount of the absorbent slurry input, and is supplied to the neutralization tank 6. In the neutralization tank 6, an alkaline agent solution 7 such as caustic soda is supplied, and the pH of the extracted absorbent slurry is increased from 4 to 6 to 6 or more, so that it is simultaneously removed with SOx in the absorption tower 2, Metal ions (M ⁺ ) in the F ⁻ and dust dissolved in the absorbent slurry are CaF
₂ and precipitated as MOH. This CaF ₂ , MOH
The gypsum slurry containing is separated by the gypsum thickener 8 into a concentrated slurry in which the solid concentration of gypsum, CaF ₂ and MOH is increased by natural sedimentation, and a supernatant. The concentrated slurry is stored in the dehydrator supply tank 10 by the thickener underflow pump 9, then supplied to the dehydrator 13 by the dehydrator supply pump 11, and discharged as the powdered gypsum 14. The dehydrated filtrate is stored in the dehydrator drainage pit 15, and the dehydrator drainage pump 1
It is returned to the gypsum thickener 8 by 6 and concentrated again. On the other hand, the overflow liquid from the gypsum thickener 8 is stored in the thickener overflow tank 17, and partly discharged by the thickener overflow pump 18 to a wastewater treatment device (not shown) to suppress the concentration of Cl concentration in the system, and the rest. It is reused in the absorption tower 2.

In the above system, the purpose of adding the alkaline agent 7 in the neutralization tank 6 to precipitate the dissolved F- ^{and the} like and separate it with the gypsum thickener 8 is to discharge a portion of the thickener overflow water to the wastewater treatment equipment. F in wastewater ^- by reducing the concentration of such, F wastewater treatment apparatus
^- not only to reduce the drug amount for processing or the like, is to reduce the amount of sludge to be industrial waste generated by the process.

[0006]

In the above-mentioned prior art, the purpose of the alkaline agent supplied to the neutralization tank is to reduce the utility of the wastewater treatment equipment and to reduce the amount of sludge generated. Nevertheless, the total amount of slurry extracted from the absorption tower is supplied to raise the pH, and the total amount of the slurry is put into the thickener 8 and concentrated and separated, so the amount of alkali agent used is Not only is it too large, but there is also the problem that the thickener 8 becomes too large.

An object of the present invention is to provide a wet exhaust gas desulfurization apparatus and a desulfurization method capable of reducing the size of the gypsum thickener 8 while minimizing the amount of the alkaline agent necessary for removing the F (fluorine) component. To do.

[0008]

In order to achieve the above object, a first invention of the present application is to provide an absorption tower in which exhaust gas containing sulfur oxide is brought into gas-liquid contact with an absorbent slurry containing a calcium compound, and gas-liquid contact is made. In a wet exhaust gas desulfurization device equipped with a dehydrator for extracting a part of the absorbent slurry in the absorption tower and separating and recovering the gypsum in the slurry, one of the residual liquid of the slurry separated from the gypsum by the dehydrator Part to the absorption tower, a means for adding an alkaline agent to the other part of the slurry residual liquid to precipitate a dissolved substance in the liquid and separate it into a filtrate and a precipitated solid concentrated slurry, and the filtrate is discharged and solidified. The present invention relates to a wet exhaust gas desulfurization device, which is provided with means for returning the product slurry to the desulfurization device.

A second aspect of the invention is to bring the sulfur oxide-containing exhaust gas and the calcium compound absorbent slurry into contact with each other in the absorption tower to absorb and remove the sulfur oxide in the exhaust gas, and at the same time, a part of the absorbent slurry in the absorption tower. In a wet exhaust gas desulfurization device for recovering gypsum in the slurry, the slurry extracted from the absorption tower is dehydrated by a dehydrator to recover the gypsum, and an alkaline agent is added to at least a part of the dehydrated effluent to adjust the pH. To precipitate the dissolved matter in the effluent, separate it into a filtrate and precipitate solids concentrated slurry, discharge the filtrate to the wastewater treatment equipment, and supply the solids slurry to the dehydrator or absorption tower. The present invention relates to a wet exhaust gas desulfurization method.

A third invention is the above-mentioned second invention,
The present invention relates to a wet exhaust gas desulfurization method, characterized in that the amount of the alkaline agent added to the other part of the slurry residual liquid is controlled so that the pH value of the slurry residual liquid after the addition of the alkaline agent becomes a predetermined value.

[0011]

Since the amount of slurry supplied to the neutralization tank 6 is limited to the amount required to secure the required amount of waste water from the desulfurization device,
The amount of alkali agent required to raise the pH is kept to a minimum, and the amount of slurry flowing into the thickener 8 is also reduced, so that wasteful use of chemicals and excessive equipment will not occur.

[0012]

EXAMPLE A system of a wet exhaust gas desulfurization apparatus according to the present invention is shown in FIG. The operation of the absorption tower is similar to that of the conventional technology, but the slurry extracted from the absorption tower 2 is stored in the dehydrator supply tank 10. This slurry is supplied to the dehydrator 13 by the dehydrator supply pump 11, and the gypsum 14 is dehydrated and recovered. On the other hand, the dehydrated filtrate is collected in the dehydrator drain pit 15, supplied by the dehydrator drain pump 16 to the absorption tower 2 and the absorbent slurry pit 19 as make-up water, and partly supplied to the neutralization tank 6. In the neutralization tank 6, the pH is measured by the pH meter 12, and the alkaline agent 7 is added so that the pH becomes a predetermined value. The overflow liquid sent from the neutralization tank 6 to the gypsum thickener 8 and separated from the solid matter is stored in the thickener overflow tank 17 and discharged to the wastewater treatment device by the thickener overflow pump 18. On the other hand, the slurry containing solid matter such as CaF ₂ is returned to the dehydrator supply tank 10 again.

As described above, according to this embodiment, the supply amount of the dehydrated filtrate to the neutralization tank 6 can be reduced, so that the addition amount of the alkaline agent 7 can be reduced and the gypsum thickener 8 can be made compact. The effect of the present invention will be described in comparison with the prior art using mass balance. 1000 as an example
2 and 4 show the mass balance around the neutralization tank of the present invention and the prior art in the case of the desulfurization plant for MW, respectively.

In the conventional desulfurization apparatus shown in FIG. 4, the slurry amount 51 flowing into the neutralization tank 6 is 168 tons / h, and the addition amount 57 of the alkaline agent required for raising the pH of this slurry is 0.16 tons / h. h. On the other hand, in the present invention shown in FIG. 2, the amount of slurry flowing into the neutralization tank 6 is 5
6 can be reduced to 26 tons / h,
7 is about 0.03 ton / h, which can be reduced to ⅕ or less of the conventional technique.

Regarding the amount of slurry flowing into the thickener 8, in the prior art, as shown in FIG. 4, the above-mentioned absorption tower withdrawal amount is 51: 168 tons / h and the alkali agent addition amount is 57: 0.16 tons / h. And the dehydrator drainage pump 16
It is necessary to treat 270 tons / h, which is the sum of 55: 102 tons / h of outlet of the dehydrator drain pump supplied from
In order to handle this amount, the thickener 8 becomes very large with a diameter of 17 m.

On the other hand, in the present invention, the amount of slurry flowing into the thickener 8 is, as shown in FIG. 2, the above neutralization tank inlet flow rate of 56:26 tons / h and the amount of alkali agent addition of 5
7: 0.03 ton / h added to about 26 ton / h,
It can be reduced to 1/10 of the conventional technology, and thicker 8 has a diameter of 5 m
It is possible to make the size very small as follows. As another embodiment of the present invention, a dehydrator supply tank 10 and a pump 1 shown in FIG.
Although there is a method of omitting 1 and returning the underflow slurry of the thickener 8 to the absorption tower, the same effect can be obtained.

[0017]

According to the present invention, since the amount of slurry flowing into the neutralization tank and thickener can be reduced, the amount of chemicals used to remove fluorine and the like and the equipment cost of thickener can be reduced.

[Brief description of drawings]

FIG. 1 is a system diagram of a wet flue gas desulfurization apparatus according to the present invention.

FIG. 2 is a diagram showing a mass balance of the wet flue gas desulfurization apparatus according to the present invention.

FIG. 3 and

FIG. 4 is a system diagram of a conventional wet flue gas desulfurization apparatus and a diagram showing a mass balance thereof.

[Explanation of symbols]

1 ... Inlet flue, 2 ... Absorption tower, 3 ... Circulation pump, 4 ... Exit flue, 5 ... Extraction pump, 6 ... Neutralization tank, 7 ... Alkaline agent, 8 ... Gypsum thickener, 9 ... Thickener underflow pump, 10 ... Dehydrator supply tank, 11 ... Dehydrator supply pump, 12 ... pH meter, 13 ... Dehydrator, 14 ... Gypsum, 15 ...
Dewatering machine drainage pit, 16 ... Dewatering machine drainage pump, 17 ... Thickener overflow tank, 18 ... Thickener overflow pump, 19 ... Absorber slurry pit, 20 ... Absorber slurry pump, 51 ... Absorption tower extraction amount, 52 ... Dehydrator supply amount , 53 ... Gypsum production amount, 54 ... Dehydration filtration amount, 55 ... Dehydrator drainage pump outlet amount, 56 ... Neutralization tank inlet flow amount, 57
… Alkaline agent addition amount, 58… Thickener overflow amount,
59 ... Thickener underflow amount, 60 ... Drainage flow rate.

Claims (3)

[Claims] 1. An absorption tower in which an exhaust gas containing sulfur oxides is brought into gas-liquid contact with an absorbent slurry containing a calcium compound, and a part of the absorbent slurry in the gas-liquid contacted absorption tower is extracted to obtain gypsum in the slurry. In a wet exhaust gas desulfurization device equipped with a dehydrating device for separating and recovering, the means for supplying a part of the residual liquid of the slurry separated from the gypsum by the dehydrating device to the absorption tower, and the other part of the residual liquid of the slurry. A wet process characterized in that means for adding an alkaline agent to precipitate a dissolved substance in the liquid to separate it into a filtrate and a precipitated solid concentrated slurry, and means for discharging the filtrate and returning the solid slurry to a desulfurization apparatus are provided. Exhaust gas desulfurization equipment. 2. A sulfur oxide-containing exhaust gas and a calcium compound absorbent slurry are brought into contact with each other in the absorption tower to absorb and remove the sulfur oxide in the exhaust gas, and a part of the absorbent slurry in the absorption tower is extracted into the slurry. In the wet exhaust gas desulfurization device for recovering gypsum, the slurry extracted from the absorption tower is dehydrated by a dehydrator to recover gypsum, and the pH is increased by adding an alkaline agent to at least a part of the dehydrated effluent, After the dissolved matter in the effluent is precipitated, it is separated into a filtrate and a precipitate solids concentrated slurry, the filtrate is discharged to a wastewater treatment device, and the solids slurry is supplied to a dehydrator or an absorption tower. Wet exhaust gas desulfurization method. 3. The wet method according to claim 2, wherein the amount of the alkaline agent added to the other part of the residual slurry liquid is controlled so that the pH value of the residual slurry liquid after the alkaline agent is added becomes a predetermined value. Exhaust gas desulfurization method.