JPS61195937A - Treatment of mercury-containing waste gas - Google Patents

Abstract

PURPOSE:To recover efficiently metallic mercury at a high yield and to make non-polluting a mercury vapor-contg. waste gas by treating the waste gas with a condenser using cooling water and treating further the gas after the treatment with a scrubbing and cooling column using cooling water. CONSTITUTION:The mercury-contg. waste gas discharged from a mercury ion reducing and evaporating device (not shown) is treated with the condenser 1 using the cooling water. The mercury and condensate are fed into a mercury settling tank 2 where the metallic mercury is separated and recovered. The outlet gas thereof is passed to the scrubbing and cooling column 3. The above- mentioned gas is treated by the countercurrent contact with the cooling water supplied by a circulation pump 9 in a packed bed. The cooling water contg. mercury is put into a storage tank 4 where the water is cooled to about 5 deg.C by a cooler 5 and further the metallic mercury is separated and recovered by a liquid cyclone 6, etc. The cooling water is returned to the scrubbing and cooling column top. On the other hand, the waste gas is brought into contact with an absorbent liquid such as KMnO4-H2SO4 soln. mixture in a mercury absorption column 7 by which the remaining mercury is absorbed away from the gas. The gas is then released into the atmosphere.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a method for treating mercury-containing waste gas.

Specifically, the present invention relates to a method for efficiently recovering mercury as metallic mercury by cooling mercury-containing waste gas in two stages.

[Prior art]

When waste containing mercury or mercury compounds, such as batteries and fluorescent lamps, is incinerated, the flue gas (incineration waste gas) contains mercury, so it is not possible to release the incineration waste gas directly into the atmosphere. Can not. This is the same for gases containing mercury, such as mercury mine waste gas, etc. Therefore, these incineration waste gases are usually washed with water, alkaline liquid, etc. before being released into the atmosphere. Because the wastewater or anti-acid wastewater will contain mercury,
The water cannot be released unless this mercury is removed. Mercury-containing wastewater is treated by the ferrite method, reduction vaporization method, etc., but generally most of the mercury is removed by the ferrite method, and then the treatment liquid obtained by the ferrite method is mixed with a reducing agent and air. (or nitrogen gas).

Metal mercury and mercury compounds are vaporized by making a reducing agent exist in the mercury-containing wastewater and passing air or nitrogen gas through it.

Therefore, this vaporized mercury is recovered as metallic mercury or mercury compounds by means such as 1.2.3.4 below (reductive vaporization method).

Incidentally, if necessary, these means 1 to 4 may be applied to the treatment of the above-mentioned acid washing waste gas (also, mercury mine wastewater may be used instead of the above-mentioned anti-acid waste liquid, etc.). .

l) Gas cooling method: Indirect cooling using cooling water (room temperature or cold water) to cool the gas to a low temperature (for example, 10° C. or lower) requires a large cooler. Even after treatment, the mercury concentration in the gas remains high.

2) Cryogenic method: The equipment for deep cooling with NaOH or KOH solution is complicated.

3) Absorption method: Potassium permanganate-sulfuric acid mixture.

Aqueous solutions containing available chlorine such as ammonium persulfate and Na0IQ are mainly used.

The waste and absorption liquid containing a high concentration of Hf ions must be treated with a reducing agent, etc. to recover metallic mercury. 4) Adsorption method: Activated carbon carrying 0aC4, 101, etc. is mainly used to remove mercury. Recover as mercury chloride. The disadvantage is that activated carbon, which has a low mercury concentration in the gas and is suitable for small-scale processing, is difficult to regenerate.

However, in recent years, with the increase in waste, the content of mercury and mercury compounds in the wastewater generated from books, incineration waste gas, and the washing of the waste gas with water has tended to increase. It is requested.

〔the purpose〕

The present invention provides a method for removing mercury that can almost completely recover metallic mercury from gas containing mercury vapor when mercury-containing wastewater is treated with a mercury ion reduction vaporizer.

〔composition〕

The method for treating mercury-containing waste gas according to the present invention includes treating gas discharged from a mercury ion reduction vaporization device with a condenser using cooling water;

It is characterized in that the condenser outlet gas is treated in a water washing cooling tower using cooling water to recover the mercury in the gas as metallic mercury.

By the way, inventor #i said that the treatment and mercury recovery of conventional mercury ion reduction vaporization equipment exhaust gas (mercury-containing gas generated by implementing the reduction vaporization method) is achieved by indirect cooling (see 1 above) and adsorption method (see 4 above).
), it was confirmed that the reason why the mercury recovery was still unsatisfactory was because the temperature of the cooled gas was above room temperature. That is, when the temperature of the cooled gas is above room temperature, Htflk in the gas
The Hf adsorption capacity is relatively high, increasing the load on the adsorber and reducing the Hf adsorption capacity due to wet gas. The present invention has been made based on this knowledge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in more detail below by means of embodiments according to the accompanying drawings. Here, waste water containing heavy metals (including CHf) is treated by the ferrite method, and a reducing agent (for example, tin chloride) is added to the treatment liquid.

For convenience, the gas to be treated is the exhaust gas (Hp vapor-containing gas) obtained by adding Hp vapor and exploding a mixture containing sodium borohydride (sodium borohydride, etc.). The pHFi of the liquid is on the alkaline side.

Now, the exhaust gas at about 60℃ saturated with water vapor is 75N&/
The 1-1f concentration of hr (dry gas) is 240.5 cape/N
d-dry gas, which was used as the test gas.

This gas is passed through a condenser 1 and cooled with cooling water (22℃).
Cooled indirectly to 0°C. The Hf concentration in the outlet gas is 34
It was M97Nd-dry gas. Metal Hf and condensed water generated in the condenser 1 are transferred to a mercury settling tank 2.

In the mercury settling tank 2, the gold H4klf is precipitated as grayish-black fine particles, but they gradually combine to form Hf grains of 1 to 3 diameters. Furthermore, since the auto-safe flow water in the mercury settling tank 2 contains 70 pI)b of mercury, it is returned to a ferrite reaction tank or a mercury ion reduction vaporizer (not shown). Hf recovery rate in condenser 1 and mercury settling tank 2 is approximately 86%
Since the mercury concentration in the condenser outlet gas is still high, it is reprocessed. Of course, it is possible to keep the Hf concentration in the condenser outlet gas low by lowering the temperature change of the cooling water in condenser 1 to near 0°C, but indirect cooling using a gas-liquid system cannot achieve a large heat transfer coefficient. Since the temperature difference between the gas and liquid is small, the heat transfer area of the condenser 1 must be widened. Therefore, in the present invention, the temperature of the condenser outlet gas is simultaneously lowered by direct contact of the gas and liquid system.

Condenser outlet gas I/i introduced into water washing cooling tower 3
Cooled to 5°C. The water washing cooling tower 3 has a diameter of 300 wφ and 1
A groove was filled with an Inchraschig ring, and cooling water at 5°C was supplied from the top of the tower and brought into contact with the gas in a countercurrent flow.

Here, since the gas and liquid come into direct contact, heat transfer between the gas and liquid is easy and gas cooling can be easily performed. By going through the steps so far, it was possible to recover 98.5% of the metallic mercury in the ferrite treatment exhaust gas (sample gas).

The cooling water used in the washing cooling tower 3 is cooled to 5°C by the cooler 5 in the storage tank 4, but it is 0°C.
In this embodiment, the difference between the inlet gas (condenser outlet gas) and the outlet gas (5°C exhaust gas) of the water washing cooling tower 3 is approximately 20Kca.
A/~-Dry gas, and the cooler 5 only needs to have a small capacity.

After the cooling water in the storage tank 4 separates fine mercury particles in a liquid cyclone 6, it is returned to the top of the water washing cooling tower 36.Moreover, the water condensed in the tower is dropped into the storage tank 4 together with the cooling water. However, the OATSAFE flow in the storage tank 4 passes through the mercury sedimentation tank 2 through an OJR-FLO hole (not shown) provided in the storage tank 4, and together with the drain of the condenser 1.

It is returned to the ferrite reaction tank or mercury ion reduction vaporizer.

As inferred from the above, the operation in the water washing cooling tower 3 is as follows:
This has not only the effect of gas cooling but also the ability to collect Hf fine particles that were not collected by the condenser 1. However, the permissible indoor Hf concentration is O, O due to labor administration.
Since the CHf concentration of the outlet gas from the water washing cooling tower 3 is 3.6 Cape/N-, it is necessary to reprocess it.

Various methods can be used to treat low-concentration mercury-containing gas, but in this example shown in the drawing, Hf absorption is carried out using #'io, 2s sulfuric acid mixed solution of manganese peroxide and potash SOZ. . That is, the water washing cooling tower outlet gas was led to the mercury absorption tower 7, and brought into contact with the liquid mixture to oxidize and absorb mercury. As a result, the outlet gas of mercury absorption tower 7 Hf @ degree qo, 03 Misaki/Nn? - It became a dry gas and could be released into the atmosphere.

The above mixed solution (Hf absorption solution) IIi had the ability to absorb mercury until the reddish-pink color of potassium permanganate disappeared, and this absorption ability was maintained for about two months. The collected wastewater, which has lost its mercury absorption capacity, is divided into 58 small portions (]01) and returned to a water tank (20m'K) in the -Hf ion reduction and vaporization equipment for ferrite processing (not shown). did. As a result, the mercury ion concentration of raw water for ferrite treatment is 4"IFA, and the manganese ion concentration is 4.411117t.
However, this degree of increase in the concentration of each metal ion #
"t, Removal of mercury and manganese in the implementation of ferrite method,
In addition, it did not affect the reductive vaporization of mercury.

In addition, in the drawing, 8 represents an absorption liquid storage tank, and 9 and 10 represent a circulation pump.

As mentioned above, the method of the present invention uses cooling water in the condenser and cooling water in the washing cooling tower, and by combining these condensers and washing cooling towers, the Hf vapor-containing gas can be heated to about 0 to 10°C. Examples of mercury-containing waste gas that can be treated by implementing the method of the present invention, which allows easy and effective cooling and condensation recovery of gold tIHf, include incineration waste gas as well as waste gas from factories that use mercury. examples include mercury mine waste gas and mercury mine waste gas.

The water washing cooling tower outlet gas is as described above.

It is treated with a mercury absorption liquid (potassium permanganate-sulfuric acid mixture, absorption liquid containing available chlorine, etc.), and the collected waste liquid containing Hf ions is led to a mercury ion reduction vaporization process, such as a ferritization process. and rendered harmless. In addition, since the water washing cooling tower outlet gas is at a low temperature, the moisture content in the gas is low.
Even if the outlet gas is dry-treated with mercury-adsorbing activated carbon, etc., the HP
It has little effect on the decrease in adsorption capacity.

〔effect〕

According to the mercury-containing waste gas treatment method of the present invention, the following effects are brought about: 1) Hf absorption tower by providing a water washing cooling tower.

The load on Hf adsorption towers etc. is reduced.

II) The gas-liquid heat transfer in the water-washed cooling tower is greater than that in indirect cooling, thus reducing effective gas cooling and gold j14Hf
Can wash and collect fine particles with water.

-) The water washing cooling tower outlet gas is almost completely demercuryed by treatment with a mercury absorption liquid, and the Hf-containing waste and absorption liquid is treated with heavy metal processing equipment that reduces and vaporizes Hf ions in ferrite processing, etc. Hf ions in the liquid are converted into metal Hf
A closed system is adopted in which waste is collected as waste.

lv) Almost perfect mercury recovery is possible.

[Brief explanation of drawings]

The drawing is a flow sheet for explaining the method of the present invention. l...Condenser 2...Mercury settling tank 3...
・Water washing cooling tower 4...Storage tank 5...Cooler
6...Liquid cyclone 7...Mercury absorption tower
8...Absorption liquid storage tank 9, lO...Circulation M1/ump

Claims (1)

[Claims] 1. The gas discharged from the mercury ion reduction vaporization device is treated with a condenser using cooling water, and the condenser outlet gas is further treated with a washing cooling tower using cooling water to produce the gas. A method for treating mercury-containing waste gas, characterized by recovering the mercury contained therein as metallic mercury. 2. The treatment method according to claim 1, wherein the water washing cooling tower outlet gas is treated with a mercury absorption liquid, and the obtained wastewater silver absorption liquid is led to a mercury ion reduction vaporization device.