Liquid absorption generally includes water washing and alkali neutralization. The commonly used absorbents for alkali liquor absorption are 10% Na2CO3, 4%~6% NaOH and NH3. Purification equipment mainly includes washing tower, foam tower, packing tower, inclined orifice tower and turbulent ball tower. Its main purification mechanism is to make gas-liquid contact fully and neutralize acid and alkali, thus improving purification efficiency. The advantages of liquid absorption method are less equipment investment and simple process. Disadvantages are: (1) large energy and water consumption, high operating costs; (2) It is easy to cause secondary pollution; (3) In the northern winter, it is easy to cause the equipment to fail to operate normally due to icing; (4) Because nitric acid mist contains NO insoluble in water, the purification efficiency of nitric acid mist by liquid absorption method is relatively low.
Solid adsorption method
Commonly used adsorbents include activated carbon, molecular sieve, silica gel, ammonia-containing coal slime, etc. Beijing University of Technology has successfully developed an adsorbent-SDG adsorbent, which can treat a variety of acid mist. It was once listed as 1992 best practical technology and 1995 feasible practical technology by the State Environmental Protection Administration. The adsorbent has been successfully applied in many industries. It can purify various acidic gases (fog) such as sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, acetic acid and phosphoric acid. It is especially suitable for pickling workplaces where the concentration is less than 1000 mg/m3.
Compared with other existing adsorbents, SDG acid mist adsorbent has the following advantages: (1) The raw material and manufacturing cost of adsorbent are low; ⑵ High adsorption efficiency and large adsorption capacity; ⑶ The adsorption process is mainly chemical adsorption, and the properties of the products formed are stable. The adsorbents after adsorption can be directly discarded without regeneration, which saves the corresponding process and equipment consumption. Adsorption purification equipment includes fixed bed adsorber, moving bed adsorber and rotating adsorber.
The advantages of purifying acid mist by adsorption method are as follows: (1) nitrogen oxide pollution associated with nitric acid mist can be removed well; ⑵ Simple equipment and convenient operation; (3) Dry process, no secondary pollution. Its disadvantage is that the adsorption capacity of adsorbent is limited, which leads to huge equipment and intermittent operation. Therefore, adsorption method is only suitable for purifying waste gas with low acid mist concentration.
filtration method
There are three main filter layers of acid mist filter: screen, wire mesh and fiber. The filter layer of mesh demister is usually made of PVC material and staggered in the equipment. The screen in the screen demister is generally made of polyethylene or corrosion-resistant stainless steel. The fiber materials of fiber demister are mostly polypropylene and glass fiber.
Electrostatic defogging method
Acid mist electrostatic precipitator is a kind of electrostatic precipitator series products. After the electrostatic precipitator became a patented technology, the first successful practical application was 1907 for capturing sulfuric acid mist.
Mechanical defogging method
The principle of this method is to separate liquid droplets from gas by gravity, inertia force or centrifugal force, so as to achieve the purpose of purification. Commonly used equipment includes baffle demister and centrifugal demister.
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