JPS5969130A - Treatment of waste gas containing fluorine-containing component - Google Patents

Abstract

PURPOSE:To regenerate an aq. CaCl2 soln. and recycle the same as treating liquid for removal of fluorine-contg. component, by treating waste gas contg. fluorine-contg. component with the CaCl2 soln. to remove fluorine as CaF2 in an absorption column, and adding gypsum dehydrate to the treated liquid contg. Cl ions. CONSTITUTION:Waste gas 2 contg. F-contg. compoent is introduced into an absorption column 1, and an aq. CaCl2 soln. of 4-5.5pH is sprayed from the upper part to deposit F-contg. component in the gas as CaF2. The liquid is supplied into a tank 5 where gypsum dihydrate 6 industrial water 7 are added thereto. CaCl2 is regenerated by the reaction in the tank 5, and CaCl2 is again supplied to the upper part of the column 1 by a pump 8 and is cyclically used as the treating liquid for removal of fluorine-contg. compound from the waste gas contg. F. The residue in the tank 15 is treated with a thickener 9, whereafter CaF2 11 is separated and recovered with a solid-liquid separator 10. The supernatant liquid is returned to the tank 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating exhaust gas containing fluorine-based components, and aims to provide a method that can efficiently and inexpensively treat exhaust gas containing fluorine-based components through a simple process. It is something.

Fluorine-based component-containing exhaust gas is generated from aluminum electrolytic furnaces, ceramic product firing and melting furnaces, fertilizer reaction equipment, stainless steel pickling equipment, etc., and the exhaust gas from these equipment contains HF%F2. In addition, S depending on each equipment
Harmful substances such as OX%Hα and CO2 are present, and silica, iron, and other substances may also be present.

Conventional techniques for treating such fluorine-based component-containing exhaust gas include: (1) After removing fluorine from the exhaust gas by cleaning the exhaust gas with an aqueous NaOH solution, the cleaning solution containing fluorine is treated with ca (OHlz or Ca (OH)). )2
+ A method of precipitating and removing CaF2 by adding Caα2 (so-called double alkali process), ■ converting exhaust gas to Ca(OH)20 Caα2 bath solution, A4g(OH)2+
A4α2 solution or Ba (OH)2 + Ba c
There is a method (mono-alkali process) of contacting with bath removal (mono-alkali process) (see Japanese Patent Publication No. 113482/1982). However, since method (2) uses double alkali norocess, the treatment process is complicated, and in order to avoid the complexity of this process, Ca (OH) is used as the cleaning liquid.
It is possible to use t slurry, but Ca(OH)
.

The problem is that it is impractical due to the low solubility of Ca(OH)2, the loss of Ca(OH)2 due to co-precipitation with Ca-based precipitates, the loss due to CO2 absorption, and a decrease in the ability to absorb harmful mobilization.

In addition, the method (2) above is an improvement on the method (①) above.
This was proposed to solve the problem of using Ca(OH4)2 slurry.
)2 is much higher than the solubility in water, and Caα, 30% solution 10
It is used in a state in which ca(oH)z is dissolved at a maximum of 0.76f for 0y, and is disclosed in Japanese Patent Application Laid-Open No. 1134-1983.
Description of the embodiment described in Publication No. 82 and Figures 2 and 3 of the drawings
In the figure, Ca(O
H)2: Although the exhaust gas is treated with an absorption liquid containing 0.3 to 0.5 wt%, the absorption liquid [Ca(OH
)2Q, 5wt%] is said to be stable at a pH of 18.9, and it is clear that exhaust gas treatment is performed by an absorption liquid in the alkaline region with a pH of at least 7 or higher, and fluorine-based components can be removed at a pH of 7 or higher. The absorption and removal reaction of fluorine-based components in this method is carried out using an absorption liquid of Ca (oHt2+ 2F +2H-+CaF
2 + 2H20, and as a side reaction Ca (OH)2 + CO2- + CaCO3+
It is undeniable that H2O progresses to some extent and CaCO3 is generated to some extent. Therefore, in the method (2) above, QL(OH)2, which is often used as a fluorine-based component removal agent, is expensive and a part of it is lost as CaC0. Since α- is used, there are disadvantages in long-term operation, such as corrosion of the equipment due to α-.

The present invention was devised after repeated studies in view of the above-mentioned actual circumstances. After treating the sharp parts, industrial water gypsum (C
aSO4・2H20)-? Half water level f (CaSO4-H
A calcium chloride-containing absorption liquid whose pH is adjusted to 4.0 to 5.5 by adding a sharp agent such as H20) or anhydrite (caso4) is regenerated, and the regenerated absorption liquid is treated with the above-mentioned fluorine-containing component-containing exhaust gas. By recycling the fluorine component-containing exhaust gas as described above, we succeeded in efficiently and inexpensively treating the above-mentioned fluorine-based component-containing exhaust gas in a simple process.

That is, to further explain the present invention, the present inventors first disclosed the patent No. 1046547 (Japanese Patent Publication No. 55-41) for efficiently treating sharp parts with calcium carbonate.
810), but the present invention uses industrial gypsum (CaSO4.2H20), which is much cheaper than calcium carbonate in the earlier invention, and the demand for gypsum has been decreasing in recent years. On the contrary, by-product gypsum is increasing due to the spread of desulfurization equipment, etc., and its price is extremely low.In the present invention, the inexpensive industrial water gypsum is used as a sharps agent.

The fluorine-based components in the fluorine-based component-containing exhaust and gas react with Caα2 in the absorption liquid, and are precipitated as CaF2 by a chemical reaction as shown in the following equation (1).

CaCZ2 + 2F −→CaF2 + 2α−−−
----- (1) However, Ca'SO4.2H20 is added to the treatment solution containing α- after the sharp part treatment, and the following (2
) CaC/! 2 is played.

CaSO4+2C/! −−+ Cayu±5Q42−
・・・・・(2) In addition, the new absorption liquid before the inflow of the fluorine-based component-containing exhaust gas should be 0.05% or more, preferably 0.
．． By adding Hα to a 1-0.5% CaC42 aqueous solution, p
Li adjusted to 4.0 to 5.5, preferably 4.5±0.5, is used, and the regenerated absorption liquid after the exhaust gas inflow has a p
A sample is used which is operated while adding Ca S04.2H20 so as to maintain H4.0 to 5.5, preferably 4.5±0.5.

The reason why the concentration of Ca in the new absorption liquid was set to be 0.05% or more is because if it is less than 0.05%, the F concentration in the absorption liquid after sharps treatment will be high. The reason for setting the following value is that even if the content is 0.5% or more, there is no significant change in the sharp portion ratio, and economic efficiency was taken into consideration. In addition, J of the above-mentioned absorption liquid should be 4.0 or more, and if it is less than 4.0, the above-mentioned (
This is because the reaction of formula 1) is not carried out efficiently, and 5
, 5 or less is because if it is 5.5 or more, the reaction of formula (2) cannot be carried out smoothly.

Furthermore, when the treatment is performed at a pH of 4.5±0.5 of the absorption liquid, the fluorine removal rate in the exhaust gas is, for example,
When the a degree is about 100 ppm, a quotient value of 98% or more can be obtained, and the F concentration in the exhaust gas after sharp treatment is 2
．． It becomes 0■/N- or less. In addition, the pH range (4,0
~5.5) is in the acidic region, so most of the components (silica and metals) from the dust in the exhaust gas are dissolved in the absorption liquid, and CaF2 is obtained as a precipitate.
can be obtained with extremely high purity.

The accompanying drawing is a schematic diagram showing an example of an apparatus for carrying out the present invention. As shown in the figure, 1 is an absorption tower, and in this absorption tower 1, a fluorine-based component-containing exhaust gas 2 is
After coming into contact with the absorption liquid and removing the fluorine content, it is discharged to the outside as treatment waste water 3. Treatment liquid 4 after the sharp part treatment
is Ca5O from the lower part of the absorption tower 1.

・2H20 is led to the supply tank 5, and in this supply tank 5, No. 08804 2H, 06 and industrial water 7 are added to the treatment liquid 4.
is added to regenerate Caα2, and the resulting C
The aα2 solution is circulated and supplied to the upper part of the absorption tower 1 as a regenerated absorption liquid via an absorption liquid circulation pump f8. In addition,
Said 7”? A part of the Caα2 solution from 77″8 is led to the 7th thickener 9, and the precipitate concentrate from this thickener 9 (
CaF211 is recovered in this solid-liquid separation@10, and the liquid is returned to the supply tank 5 as liquid F together with the supernatant liquid from the thickener 9. A portion 12 of the liquid from the solid-liquid separator 10 contains the heavy metals of the absorption liquid,
After neutralization to prevent condensation of silica, etc., the precipitated products are removed and then discharged as an effluent from the system. The thickener 9 may be installed between the absorption tower 1 and the feeder 5.

Specific embodiments according to the present invention will be described below.

[Example 1] Sj F4 and F2 in air as raw gas to be treated
By mixing and diluting (SiF4:F, = 1:2 molar ratio), a fluorine-based component-containing gas with an F concentration of 23 to 27 η/Nrrl was synthesized. This raw material/' 20 Nt/-
Sharps were treated using the equipment shown in the attached drawings using the gas as a test gas. As the absorption tower 1, a general type absorption tower (inner diameter 25.8 mmφ) with a perforated plate (porosity 18%) was used, and the amount of absorbed liquid was 1.
．． 7 t, Caα2 concentration in absorption liquid 0.05%, L/G
2.5t/ly? , the pg of the absorption liquid is 3, respectively.
．． CaSO4.2 to maintain the set value between 5 and 6.0.
Fluorine in the girth was removed by supplying H20. The results are shown in Table 1.

According to this result, when the F in the raw gas is 23 to 277nfl/N, the Caα2 concentration in the absorption liquid is 0.05%, and L/G
2.5t/- p)l 4. If O ~ 5.5, the desorption rate is 98% or more, and the F in the treated exhaust gas at that time is 1
mg/Nn? The following is obtained, and the F concentration in the absorption liquid p is 5
It was ~9 da/l. When the pH was 3.5 and 6.0, the F content in the absorption liquid F was 15 μ/L or more.

[Example 2] Mix and dilute &F4 and F2 with air as the raw gas (5
j-F4: F2 = 1: 1 molar ratio), Fg degree 98-101 r/Nrr? A gas containing fluorine components was synthesized. Using this raw gas 2ONt/IEII+ as a test gas, sharp treatment was performed using the apparatus shown in the attached drawings. The absorption tower 1 was the same as in Example 1, and CaC in the absorption liquid was
pH at t2 concentration 0.20%, L/G 2.5 L/d
Ca'SO so that they hold 4,0 to 5,5, respectively.
The results of removing fluorine in the gas by supplying 4.2H20 are shown in Table 2.

That is, according to this result, F98-1101Tn in the raw gas
/N-, Caα2 concentration of absorption liquid 0.20%, L/
If G 2.5 t, hawk pg 4.0-5.5,
The desorption rate is 98% or more, and the F in the treated exhaust gas at that time is
#-j: 2η/Nd or less was obtained, and the F concentration in the absorption liquid F was 6 to 8 m9/l.

Note that not only industrial gypsum but also hemihydrate gypsum (C
aSO4@'/2 H2O) or anhydrite (ca
Equivalent results can also be obtained with so, ).

As explained above, in this invention, Caα2, which is used for cutting sharp parts, is used to obtain industrial water gypsum (Ca5O,.2
Since it is regenerated by adding H20) and recycled as a (regenerated) absorption liquid, exhaust gas treatment is extremely economical.Moreover, since the pit of the absorption liquid is treated as an acidic region, most of the impurities are removed. The precipitate (CaF2) is dissolved in the absorption liquid and has extremely high purity, and the concentration of Caα2 is low, so CI! This invention has great industrial effects because problems such as corrosion of equipment due to - can be avoided.

[Brief explanation of drawings]

The drawings illustrate embodiments of the present invention, and are schematic views showing one example of an apparatus for carrying out the present invention. However, in this drawing, 1 is an absorption tower, 2 is a fluorine-based component-containing gas, 3 is a treated exhaust gas, 4 is a treated liquid, 5 is a supply tank,
6 is industrial water gypsum, 7 is industrial water, 8 is an absorption liquid circulation pump, 9 is a thickener, 10 is a solid-liquid separator, 11 is CaF, , 1
2 indicates the liquid extracted from the system. Patent applicant Nippon Kokan Co., Ltd. Inventor Shindo Yamashita Tatsuo Kato Agent Patent attorney Shirakawa −−

Claims (1)

[Claims] Fluorine-based component-containing exhaust gas is converted to p containing calcium chloride.
Defluorination treatment by contacting with an absorption liquid of u 4.0 to 5.5,
A defluoridating agent such as gypsum trihydrate, gypsum hemihydrate, or anhydrite bone is added to the treatment solution after the defluoridation treatment to reduce the pil to 4.0 to 5.5.
A method for treating a fluorine-containing exhaust gas, which comprises regenerating a chlorinated absorbent containing K and recycling the regenerated absorbent for the treatment of the fluorine-containing exhaust gas.