Equation 5.16(2) shows that settling chambers have high collection efficiency for low gas velocities, high terminal settling velocities, and large ratios of chamber length to height. Thus, gas velocities are usually below 3 m/sec, which has the added benefit of preventing reentrainment. A large L/H ratio ensures a long residence time and a short vertical distance for the particle to travel to be collected. The equation yields high terminal settling velocities for large particle sizes, therefore, these devices efficiently remove particles greater than 50 /m in diameter.
Settling chambers are characterized by low capital costs and low pressure drop (~0.5 in water gauge [w.g.]). They can be used under temperature and pressure extremes (~1000°C and ~100 atm). Settling chambers are used as precleaners to remove dry dusts produced by grinding, e.g. in coal dryers, grain elevators, and rock crushers.
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