TECHNOLOGY FOR AIR POLLUTION CONTROL - College of …：学院的空气污染控制技术….ppt

WET SCRUBBERS (CONTD.) Construction and Operation (contd.) Smaller droplets provide better cleaning, but are more difficult to remove from the cleaned stream. The polluted spray is collected. Particles are settled out or otherwise removed from the liquid. The liquid is recycled. Wet scrubbers are also used for the removal of gases from the air streams. SCRUBBER Efficiency where, k = Scrubber coefficient (m3 of gas/ m3 of liquid) R = Liquid-to-gas flow rate (QL/QG) ψ = internal impaction parameter Internal impaction parameter where, c = cunningham correction factor ρp = particle density (kg/m3) Vg = speed of gas at throat (m/sec) dp = diameter of particle (m) dd = diameter of droplet (m) μ = dynamic viscosity of gas, (Pa-S) WET SCRUBBERS (CONTD.) Advantages of Wet Scrubbers Wet Scrubbers can handle incoming streams at high temperature, thus removing the need for temperature control equipment. Wet scrubbers can handle high particle loading. Loading fluctuations do not affect the removal efficiency. They can handle explosive gases with little risk. Gas adsorption and dust collection are handled in one unit. Corrosive gases and dusts are neutralized. Disadvantages of Wet Scrubbers High potential for corrosive problems Effluent scrubbing liquid poses a water pollution problem. CYCLONE SPRAY CHAMBERS These scrubbers combine a cyclone with a spray nozzle. The added centrifugal force permits good separation of the droplets, hence a smaller droplet size can be used. Cyclone spray chambers provide up to 95% removal of particles 5 micron. ORIFICE SCRUBBERS The gas is impacted onto a layer of the scrubbing liquid. The gas passes through the liquid, thus removing almost all the particulate matter, and a large portion of the probable gases. After coming out of the liquid, the gas is passed through baffles to remove the liquid droplets. IMPINGEMENT SCRUBBERS In Impingement scrubbers, the gas impacts a layer of liquid/froth through a perf