Working principle of exhaust gas scrubber

The scrubbing tower is also called spray tower and wet scrubber. It consists of four parts: tower body, trays, reboiler and condenser. The scrubber is a device for rough separation, so the number of trays is generally small, usually not more than ten stages. The scrubber is suitable for the separation of mixed gas containing a small amount of dust, the components will not react, and the product is easy to liquefy, and impurities such as dust are not easy to liquefy or solidify.

When the mixed gas passes into the scrubbing tower from the middle of the scrubbing tower, due to the presence of product component liquid between the trays, the product component gas is liquefied while evaporating part, and the impurities cannot be liquefied or solidified, when passing through the trays with liquid It will be fixed by the product component liquid to produce a washing effect. The washing tower is designed and manufactured according to this principle.

The principle of the scrubber is to use strong acid (sulfuric acid), strong alkali (sodium hydroxide), and strong oxidizer (sodium hypochlorite) as the washing spray solution to contact the odor molecules in the gas according to the odor components to make the gas phase odor components Transfer to the liquid phase, and remove the odorous substances with the help of chemical agents and odor components to neutralize and oxidize.

The commonly used washing equipment is a packed tower. The chemical absorption liquid is sprayed down from the top of the tower, the exhaust gas flows upward, and the odor is fully contacted and reacted with the absorption liquid to be removed. The flow ratio of the absorption liquid to the exhaust gas (liquid/gas ratio) is generally 1-3 L/m3, the height of the packing is generally 2-5 meters, and the flow velocity of the gas empty tower is generally 0.5-1 m/s. A well-operated packed tower can achieve a deodorizing effect of more than 90%.

Commonly used chemical absorbents in waste gas scrubbers

1. Alkaline solution

Alkaline absorbents usually contain 1%~10% sodium hydroxide solution, which has a significant effect on eliminating hydrogen sulfide waste gas. Others such as methyl mercaptan, methyl sulfide, methyl disulfide, and lower fatty acids often cause odor in wastewater treatment plants. The treatment effect is also very significant for flavor substances.

2. Acidic solution

Acid washing is mainly used to eliminate the odor caused by alkaline gases such as ammonia and trimethylamine. Generally, sulfuric acid (0.5%-5% solution) is used as the washing liquid.

3. Sodium hypochlorite solution

Sodium hypochlorite is generally used together with acid-base absorbents. For methyl sulfide which is difficult to eliminate by other methods, the control effect of sodium hypochlorite absorbent is very good.

When dealing with high-concentration odors, the concentration of sodium hypochlorite solution (effective chlorine concentration) is about 500-2000 ppm; when dealing with lower-concentration odors, the concentration of sodium hypochlorite solution is about 50-500 ppm. In terms of the performance of various oxidants, sodium hypochlorite is the cheapest and has a good treatment effect, so it is widely used. The sodium hypochlorite in the solution is in the form of hypochlorous acid (HOCl):

NaOCl+ H2O→HOCl+ NaOH

At pH=7.5, the available chlorine of the hypochlorite solution exists as 50% HOCI and hypochlorite ion (OCl-);

At pH=l0, only 0.3% of available chlorine exists as HOCl;

pH=l1 or 12, HOCl is almost completely dissociated into useless hypochlorite ions, so pH control is very heavy.

Performance characteristics of waste gas scrubber

1. Washing tower treatment system, cheap and simple treatment method;

2. The vertical structure is most suitable for installation in economical space;

3. Suitable for gaseous and liquid pollution sources;

4. Deal with a single source of pollution;

5. Suitable for medium and low air volume;

Scope of application of waste gas scrubber

1. Treatment of various harmful gases such as H2S, SOx, NOx, HCI, NH3, CI2 and other gases;

2. Deodorizing devices in garbage transfer stations and sewage treatment plants;

3. Exhaust treatment of semiconductor optoelectronics industry;

4. Treatment of seepage water and waste gas from storage ponds in landfills;

5. Treatment of waste gas from incinerators and industrial furnaces.