JPH0661424B2 - Method for removing mercury and acid gas in combustion exhaust gas - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust gas treatment method for an incinerator for municipal solid waste, an incinerator for industrial waste, an incinerator for night soil / sewage sludge, wherein mercury (or mercury compound) and acid are contained in the exhaust gas. It relates to a method for simultaneously removing gases.

[Prior Art] Acidic gas (eg HCl, SOx) contained in combustion exhaust gas
And mercury (or mercury compounds) can be removed by a wet method, that is, by adding a liquid chelate to an alkali absorbing liquid whose pH is adjusted to 7-9, and contacting this absorbing liquid with exhaust gas. There is a method of transferring acidic gas and mercury to the absorption liquid side at the same time. {Ide, Furukaku, Shigenaka "Urban and Waste" vol.15, No.5, 67-86 (1985)} However, the method of simultaneously removing acid gas and mercury by the dry method has never been used.

[Problems to be solved by the invention]

The present invention is intended to provide a method capable of simultaneously removing acid gas and mercury contained in a combustion exhaust gas, which has never been performed so far, by a dry method.

That is, since the method of removing the acidic gas by the dry method has been conventionally provided, the present invention provides a method for removing mercury in the combustion exhaust gas by the dry method in harmony with the method for removing the acidic gas by the dry method. It is a technical object to provide a joining method.

[Means for solving problems]

The present invention sprays a mixed powder of a reaction aid and a mercury reactant into a flue of a combustion exhaust gas to fix mercury in the exhaust gas to the powder side, and sprays an acid gas neutralizer powder into the exhaust gas. The method for removing mercury and acid gas in combustion exhaust gas is characterized in that the acid gas is removed, and a bag filter is provided behind the injection to discharge the gas together with the combustion dust from the exhaust gas to the outside of the system.

In the present invention, a mercury reactant that is injected into exhaust gas in order to increase the air permeability of the bag filter and prevent moisture absorption.
(S, FeS, ZnS, CaS, Cus) powder on the reaction aid (zeolite,
Powders of alumina, diatomaceous earth, perlite, activated clay, kaolin, feldspar, etc.) are mixed in advance, and these are simultaneously injected into the exhaust gas flue. The mixing ratio of the reaction auxiliary agent and the mercury reaction agent depends on the exhaust gas conditions, but generally, the weight ratio is as follows: mercury reaction agent: reaction auxiliary agent = 1: 1 to 50, preferably 1: 1 to It is 10.

Also, the acid gas neutralizing agent (slaked lime, calcium carbonate, calcium oxide, magnesium hydroxide, magnesium carbonate, magnesium oxide, etc.) powder is injected into the exhaust gas flue before or after the injection of the mixed powder. Since the mercury reactant is easily activated in the coexistence of the acidic gas, it is preferable to inject the acidic gas neutralizing agent after injecting the mixed powder.

In this way, each reaction product with the powder injected into the flue and combustion dust are efficiently collected and removed by the bag filter.

[Action]

(1) Acid gas and mercury can be removed simultaneously by the method of the present invention.

(2) Since the mercury reactant can be mixed with the reaction aid and injected into the exhaust gas at the same time, no new equipment is required for mercury removal.

(3) Since the mercury reactant is mixed with the reaction aid, the mercury reactant can be diluted with powder, and the dispersion effect in the exhaust gas is enhanced as compared with the case of single injection.

(4) Since a cake layer of partially unreacted mercury reactant and acid gas neutralizer is formed on the bag filter, when exhaust gas passes through the layer, mercury and reactant and acid gas and neutralizer are formed. The solid-gas reaction with and progresses, and each removal efficiency improves.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG.

In FIG. 1, 1 is a combustion exhaust gas generation source (eg, municipal waste incinerator, industrial waste incinerator, human waste / sewage sludge incinerator), 2 is an exhaust gas duct, 3 is a bag filter, 4 is an exhaust fan, and 5
Is a chimney, 6 is a silo for mixing a reaction aid and a mercury reactant, 7,7 '
Is a powder quantitative feeder, 8,8 'is a powder transportation air fan, 9 is an acid gas neutralizer silo, 10 and 10' are powder feeding nozzles, 11
Is the collected ash.

The reaction aid and the mercury reaction mixed powder are injected into the combustion exhaust gas containing mercury and acid gas generated in the combustion exhaust gas generation source 1 from the exhaust gas duct 2 in front of the gas flow of the bag filter 3 by the powder supply nozzle 10. To do. A predetermined amount of the reaction aid and the mercury reaction mixed powder are cut out from the mixing silo 6 by the powder quantitative feeder 7 and are transported to the powder feeding nozzle 10 by the air sent from the powder transport fan 8. Next, the acidic gas neutralizing agent is similarly injected into the exhaust gas from the exhaust gas duct 2 behind the gas flow to which the reaction aid and the mercury reaction mixed powder have been supplied.

The injection positions of the reaction aid and the mercury reaction mixed powder and the injection position of the acid gas neutralizing agent may be before or after the above position, but the present description position is preferable.

The mercury reactant and the acid gas neutralizer injected into the exhaust gas rapidly react with the mercury and the acid gas in the exhaust gas to fix the mercury and the acid gas from the gas side to the powder side.

Reactants and neutralizers with fixed mercury and acid gas, unreacted reactants and neutralizers, and combustion dust are collected on the bag filter 3 located downstream and washed off by backwashing operation. It is discharged outside the system.

Since the unreacted mercury reactant and the acid gas neutralizer together form a cake layer on the bag filter 3, when the exhaust gas passes through the layer, the solid gas of the mercury and the acid gas with the reactant and the neutralizer is further added. The reaction proceeds and the removal rate of each increases. Combustion gas from which mercury and acid gas have been removed is exhaust fan 4
It is discharged from the chimney 5 via the.

FIG. 2 shows a conceptual diagram of the powder deposit layer on the surface of the bag filter 3 cloth.

As shown in FIG. 2, the mercury reactant, the acid gas neutralizer, the reaction aid, and the combustion dust injected into the exhaust gas are 3 cloths 12 pieces.
Sequentially deposit on the surface. In the figure, G ₁ is exhaust gas, 13 is a precoat layer made of a reaction aid, 14 is a deposition layer, 15 is a mercury reaction agent, 16 is an acid gas neutralizing agent, and 17 is the presence of the reaction aid.

Examples of the acid gas neutralizing agent include alkali neutralizing agents such as slaked lime, calcium carbonate, calcium oxide, magnesium hydroxide, magnesium carbonate and magnesium oxide.

Examples of the mercury reactant include S, FeS, ZnS, CaS and CuS.

As the reaction aid, one or more mixed powders selected from powders of zeolite, alumina, diatomaceous earth, perlite, activated clay, kaolin, feldspar, etc. are used.

<Example> The mercury and HCl discharged from the municipal waste incinerator were removed under the following conditions. Conditions: Incineration amount: 150 T / day Exhaust gas amount: 30,000 Nm ³ / h Hg concentration: 0.3 mg / Nm ³ HCl concentration: 700 ppm Gas temperature: 200 to 230 ° C. Procedure: 50 kg of mixed powder of reaction aid and mercury reactant / H {mixing ratio: reaction aid / mercury reactant (weight ratio) 1 to 50}. Perlite was used as the reaction aid, and ZnS powder with a particle size of 200 to 300 mesh was used as the mercury reaction agent. After spraying the mixed powder, 0 to 2-3 seconds later, the mixed powder was blown in, and 100 kg / h of slaked lime powder was blown in the wake, and mercury and HCl were blown.
(Acid gas) was removed. Results: As a result of the above test, mercury in the exhaust gas could be removed at a maximum of 76% and HCl at 98.6%.

〔The invention's effect〕

-According to the present invention, mercury and acid gas in combustion exhaust gas can be treated dry and simultaneously.

-A high removal rate can be achieved by using a bag filter that also collects dust and accelerates the reaction.

・ By mixing and injecting the mercury reactant and the reaction aid,
It is possible to simplify the equipment and improve the dispersibility when the mercury reactant is injected into the exhaust gas.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention, and FIG. 2 is a conceptual diagram of a surface deposition layer of a bag filter 3 cloth according to the present invention.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Mitsuhiro Doroguchi 12 Nishiki-cho, Naka-ku, Yokohama-shi, Kanagawa Mitsubishi Heavy Industries, Ltd.Yokohama Works (72) Inventor Jouji Tonomura 12 Nishiki-cho, Naka-ku, Yokohama, Japan Mitsubishi Heavy Industries Yokohama Works Co., Ltd. (56) Reference JP-A-62-186925 (JP, A)

Claims (1)

[Claims] 1. A mixed powder of a reaction aid and a mercury reactant is injected into a flue of a combustion exhaust gas to fix mercury in the exhaust gas to the powder side, and an acidic gas neutralizer powder is injected to the exhaust gas. A method for removing mercury and acid gas in combustion exhaust gas, characterized in that the acid gas therein is removed, and a bag filter is provided behind the injection to discharge the gas together with the combustion dust from the exhaust gas to the outside of the system.