JPS61257223A - Method for removing mercury incorporated in exhaust gas - Google Patents

Abstract

PURPOSE:To selectively remove mercury in a high degree of removal by washing an exhaust gas with an alkaline washing liquid contg. a reducing agent and thereafter trapping the mercury vapor incorporated in the exhaust gas. CONSTITUTION:An exhaust gas contg. mercury is washed in a washing tower 1 with an alkaline washing liquid contg. a reducing agent such as HI and H2S. Therefore the greator parts of mercury are incorporated in the exhaust gas and the washing liquid is induced to an aeration vessel 2 (vaporization) and the mercury incorporated in the liquid is vaporized by the aeration treatment. Both the exhaust gas drawn from the washing tower 1 and the mercury vapor drawn from the aeration vessel 2 are induced to a mercury trapping tower 3 and herein it is trapped with a mercury vapor adsorbent and the treated gas is discharged in the atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for selectively and efficiently removing mercury contained in exhaust gas discharged from an incinerator for waste such as municipal waste.

BACKGROUND OF THE INVENTION The exhaust gas from incinerators contains various harmful substances, but especially if the waste contains dry batteries, fluorescent lamps, etc., the mercury derived from these can be vaporized. It is included as a substance or a compound. Therefore, there is a strong need for a new method for effectively removing mercury contained in exhaust gas.

Prior Art and its Problems Conventionally, as a method for treating this type of exhaust gas, a method of cleaning the exhaust gas with an alkaline cleaning liquid and then releasing it into the atmosphere has been a common method. According to this method, acidic components such as hydrogen chloride and sulfur oxides in exhaust gas are efficiently removed, and about 60% of mercury is removed, but there are still problems such as staining.

1.) Generally, mercury or its compounds are designated as poisonous substances, and their emission is strictly restricted.
The removal rate as mentioned above, ie, 60%, was completely insufficient. Therefore, it is necessary to significantly improve the removal rate of mercury from exhaust gas and to suppress the emission of mercury into the atmosphere υ1 as much as possible.

2) In addition, it is necessary to reliably dispose of the mercury that has migrated into the cleaning solution during the cleaning process, to reduce the mercury concentration in the solution to below the regulatory value, and to completely dispose of the recovered mercury. Due to its unique characteristics, the above-mentioned disposal cannot always be carried out completely.

This invention was made with the intention of solving the above-mentioned problems, and is a mercury that can selectively remove mercury contained in exhaust gas from an incinerator at a high removal rate. The purpose is to provide a method for removing.

Means for Solving the Problems In order to achieve the above object, the method for removing mercury according to the present invention is characterized in that exhaust gas is cleaned with an alkaline cleaning liquid containing a reducing agent, and then mercury vapor in the exhaust gas is captured.

Further, in a preferred embodiment of the present invention, the mercury transferred into the cleaning liquid during cleaning is vaporized, and the generated mercury vapor is captured together with the mercury vapor in the exhaust gas after cleaning. The mercury that has migrated into the cleaning liquid is vaporized, for example, by aeration.

The reducing agent is not particularly limited, and representative examples thereof include hydrogen compounds such as HI and H2S, sulfite and sulfites, alkali metals, metals such as MalCa and Zn, salts such as Fe (II) and 3n, Examples include organic substances such as formic acid and oxalic acid, and hydrazine. Addition of the reducing agent may be continuous or intermittent.

Mercury vapor is captured by a dry method using a mercury vapor adsorbent or the like, or a wet method using an absorption liquid containing a liquid chelating agent, a sulfur compound, or the like.

The exhaust gas after mercury vapor capture treatment is released into the public domain after necessary measures such as preventing the generation of white smoke.

Function When exhaust gas is washed with an alkaline cleaning solution, acidic components such as hydrogen chloride and sulfur oxides in the exhaust gas are efficiently transferred to the cleaning solution.On the other hand, mercury in the exhaust gas is inhibited from transferring to the cleaning solution by the action of the reducing agent. and most of it remains in the exhaust gas,
Some of it migrates into the cleaning solution.

The mercury in the cleaning liquid is reduced to a form that is easily vaporized by the action of the reducing agent in the cleaning liquid.

The cleaning liquid containing mercury in this form is then subjected to a vaporization treatment, and the generated mercury vapor is subjected to a mercury vapor capture treatment together with the mercury-containing exhaust gas after cleaning, and the mercury is further recovered.

Effects of the Invention According to the present invention, since the exhaust gas is first cleaned with an alkaline cleaning liquid containing a reducing agent, transfer of mercury in the exhaust gas to the cleaning liquid can be suppressed as much as possible. Therefore, since the cleaning liquid after cleaning contains only a small amount of mercury, the treatment of the liquid and the final disposal of the sludge derived from the liquid can be easily carried out.

In addition, components other than mercury in the exhaust gas, such as hydrogen chloride and sulfur oxides, are absorbed into the cleaning solution as a result of cleaning with the alkaline cleaning solution. Mainly only mercury. Therefore, the waste adsorbent, waste absorption liquid, and waste sludge discharged from the mercury vapor capture stage can be easily treated, and mercury can be easily recovered from them.

Thus, according to the mercury removal method of the present invention, mercury contained in the exhaust gas from the W furnace can be selectively removed at a high removal rate.

EXAMPLES Next, examples of the present invention will be shown to demonstrate the above effects.

In the drawing, mercury-containing exhaust gas is introduced into a cleaning tower (1) where it is cleaned with an alkaline cleaning liquid. As a result, hydrogen chloride, sulfur oxide, etc. in the exhaust gas are absorbed into the liquid. A reducing agent is added to the alkaline cleaning solution. Therefore, most of the mercury in the exhaust gas remains in the exhaust gas, and only a portion of it migrates into the liquid. The cleaning liquid discharged from the cleaning tower (1) is led to an aeration tank (2) for vaporization, where it is aerated and more than 90% of the mercury contained in the liquid is vaporized.

Mercury-containing exhaust gas (and aeration Wt(2) from the cleaning tower (1)
) is guided to the mercury trapping group (3), where the mercury vapor is trapped by a dry adsorption treatment using a mercury vapor adsorbent. The treated exhaust gas is released into the atmosphere through the white smoke generation prevention i@.

[Brief explanation of drawings]

The drawing is a flow sheet showing an embodiment of the invention. that's all 4 other people

Claims (2)

[Claims] (1) A method for removing mercury from exhaust gas, which comprises cleaning the exhaust gas with an alkaline cleaning liquid containing a reducing agent, and then capturing mercury vapor in the exhaust gas. (2) The method according to claim 1, wherein the mercury transferred into the cleaning liquid during cleaning is vaporized, and the generated mercury vapor is captured together with the mercury vapor in the exhaust gas after cleaning.