USE OF GRAVITATIONAL SETTLING CHAMBERS AND CYCLONES COLLECTORS FOR AIR EMISSION CONTROL

The air particles emission must control the particles emissions ranging in size from 1 µm to more than 100 µm in diameter. Collectors are designed according to the physics of collecting mechanisms.

GRAVITATIONAL SETTLING CHAMBERS

These are simple chambers and expensive. In this gravitational forces dominate vertical particle motion. These are simple expansions in duct where horizontal velocity of particles is reduced to give time to settle the particles by gravity. On particle viscous force and gravitational forces are equal but in opposite direction and the particle is expected to fall at terminal velocity. The horizontal component of viscous force is negligible because the particle moves with the velocity of gas stream.

The expressions used for the efficiency of the collector are:

η_g= 1- exp {-µ_tL/µH}

η_g= 1- exp {-gd2p _PpL/18µuH}

exp is used to represent exponential

η_{g = efficiency of removal as a fraction}

_{L=Length of collector in meter}

_{H= Depth of collector in meter}

_{u= horizontal velocity of gas and particles through collector}

d_{p=diameter of particle}

_{Pp= density of particle}

_{The performance of the collector varied from design prediction due to turbulence and variation in flow in collector.}

CYCLONES/ INTERNAL COLLECTORS

These collectors depends upon centrifugal forces to separate the heavier particles from lighter gas molecules. Particles laden gases enter in cyclone at top and spiral downward along casing in solid body rotation at entrance velocity u. Particles move outside of spiral. The only exit for particles is upward from central pipe. 

The magnitude of centrifugal force is 

F_c= m_p u²_T/r

UT= tragential velocity of particle

r= radius of curvature of particle trajectory

The pressure drop through conventional cyclone is 5 to 15 cm of 

water by high efficiency cyclone is 10 to 30 cm. of water.

Gravitational settling chambers and simple inertial separators have 

no moving parts. They may be fabricated by metals that can 

withstand the high temperature and resist corrosion. They are 

effective for solid and liquid particles.