Document npRM143bYMREwwXDQZZg9Bj2G

268 W. N. WITHERIDGE A. SPRAY CHAMBERS OR TOWERS Air-washing equipment that depends on liquid sprays or cascades is char acterized by empty or nearly empty enclosures through which air moves against fairly low resistance. The air-liquid contact surface is that of the liquid droplet'1 as they fall through the air, supplemented by the surfaces of any deflecting ele-* ments placed across the air stream (Figure 25). As the air-liquid contact surface! is increased by reduction of droplet size, a critical point is reached where the ai stream begins to entrain or carry over the spray or fog. Spray pressure an nozzle type are therefore related to the velocity of air movement, and practical operation requires a compromise between high contact surface for most effectiv cleaning, and high air-treating capacity. The spray chamber may be constructed as a vertical cylinder with tangentm air inlet (Figure 25). Centrifugal force can be developed by the rotating ai'r, stream as a means of separating the liquid droplets and any large solid particle" entering the chamber. B. DEFLECTION ORIFICE SCRUBBERS Figure 26 illustrates a type of air scrubber that makes use of energy in t'* air stream to generate a liquid spray or cascade. The "orifice" is the space be tween the surface of the liquid and a deflection element or "gate" below whig, the air must pass to reach the scrubbing zone. In some designs the air is imping^; vertically against the liquid surface and escapes in all directions with the eg t'rairie'd"Iiqui3rFully_submerged impingement nozzle? are used in gas-sampli^?' instruments, but the impact velocities are far greater than used in air or g cleaners of practical industrial design. j The orifice scrubber requires close control of liquid level to ensure tl correct amount of liquid entrainment and, at the same time, prevent an excessi|i pressure drop, represented by depression of the liquid surface in the vicinity.; the orifice. Pressure drop generally ranges between 2 and 6 inches of water C. PACKED TOWERS Gas or vapor absorbers used extensively in the chemical industries are ver cal cylinders or towers packed,with,materials,,like,broken stone, hard coke,. < spheres, Berl "sadoffBag'oyhollomcvgaaera br?ritigs;;;made of ceramic, metaljgSn bon, or glass, accb^^pScf^M..efi'emi6|fe'&iil structu'rabproperties required. PaeSejj towers are remarkajij|. effective as air cleaners when correctly "'designed , aS, operated.11 The'height'of'aiFSBsbfptioh towbrihfluencerits effectiveness, while thebfif sectional area determines its air-handling capacity. For convenience in estimable capacity, the movement of air or gas through a packed tower is expressed "Max Leva, Tower Packings and Packed Tower Design. The United States Stone Co., Akron, Ohio, 1953.