The spray exhaust gas purification tower, a new type of spray absorption equipment, has been widely used in exhaust gas purification. It develops the concept of a fluidized bed into a vapor-liquid mass transfer device, fluidizing the packing within the spray exhaust gas purification tower, thereby facilitating the mass transfer process. Its characteristics include high gas velocity, high processing capacity, light tower weight, relatively uniform vapor-liquid distribution, and resistance to clogging by solid and viscous materials. In particular, the strong turbulence within the tower facilitates mass and energy transfer, allowing for a significant reduction in tower diameter and height. This tower handles a large air volume, with an overhead gas velocity of 1.5 to 6.0 m/s, a spray density of 20 to 110 m³/(m²·h), and a pressure drop of 1,500 to 3,800 Pa. The spray exhaust gas purification tower’s demisting device utilizes a cyclone plate demister. By swirling the gas through the tower plates, centrifugal force removes the mist, resulting in a demisting efficiency of 98%-99%. Its simple structure and low pressure drop also contribute to its low pressure drop.
Acid mist waste gas is introduced into the purification tower through the air duct. After passing through the packing layer, the waste gas and the sodium hydroxide absorption liquid are fully contacted and absorbed and neutralized. After purification, the acid mist waste gas is dehydrated and demisted by the demister plate before being discharged into the atmosphere by the fan. The absorption liquid is pressurized by the water pump at the bottom of the tower and sprayed down from the top of the tower, returning to the bottom of the tower for recycling.
The packing layer within a spray tower serves as a mass transfer device, providing contact between the gas and liquid phases. A packing support plate is installed at the bottom of the packed tower, on which the packing is placed in a random pile. A packing pressure plate is installed above the packing to prevent it from being blown by the rising airflow. Spray liquid from the spray tower is sprayed onto the packing from the top through a liquid distributor, flowing down along the packing surface. Gas is introduced from the bottom of the tower and, after being distributed by the gas distributor, continuously passes through the gaps in the packing layer in a countercurrent to the liquid. On the packing surface, the gas and liquid phases come into close contact and transfer mass. As the liquid flows down the packing layer, wall flow sometimes occurs. This wall flow effect causes uneven distribution of the gas and liquid phases within the packing layer, reducing mass transfer efficiency. Therefore, the packing layer within the spray tower is divided into two sections, with a redistribution device located in the middle to spray the redistributed liquid onto the lower packing layer.
Spray exhaust gas purification towers are available in single and double towers. They utilize a circular tower structure connected in sections with flanges. They consist of a liquid storage tank, tower body, air inlet section, spray layer, packing layer, cyclone demisting layer, inspection window, and air outlet.
Treatment methods of spray exhaust gas purification tower for various types of exhaust gas:
(1) Chromium-containing waste gas
A combination of filtration recovery pretreatment and wet spray treatment is required. A grid-type chromic acid mist recovery device can initially recover 60%-80% of the chromic acid in the exhaust gas. To meet emission standards, spray absorption purification is required. Sulfurous acid solution can reduce highly toxic hexavalent chromium to less toxic trivalent chromium:
H2CrO7+3Na2SO3+3H2SO4→Cr2(SO4)3+3NaSO4+4H2O
(2) Nitrogen oxides (NOX)
Nitric acid solution is highly oxidizing and unstable, and its oxide forms are diverse. Its purification requires the combination of its reducing agent to react and generate stable N2.
2NO + O2 → 2NO2
2Na2S2O3+NO2+2 NaOH→2N2↑+4 Na2SO4+2H2O
(2) Treatment of acidic and alkaline waste gas
Because these waste gases are water-soluble and easily absorbed by water, absorption methods can effectively remove them*. Acidic waste gases are absorbed with alkaline solutions, while alkaline gases are absorbed with acidic solutions. For example, sulfuric acid waste gases can be neutralized and absorbed with sodium hydroxide solution or ammonia water, while ammonia-containing waste gases can be directly absorbed with water to produce ammonia water. The reaction formula is as follows:
H2SO4+2NaOH→Na2SO4+2 H2O
NH3+H2O→NH3·H2O
The spray exhaust gas purification tower is applicable to: oil refineries, rubber factories, leather factories, printing factories, chemical factories, Chinese and Western medicine factories, metal foundries, plastic factories, spray solvents, food processing plants, meat processing plants, slaughterhouses, poultry feed plants, paper mills, sewage treatment plants, garbage stations, etc. and inorganic waste gas purification.
