Page 13 - dust collection systems

It is recommended that during the initial cake construction
period, the air flow rate be lowered to half of the standard

for about two hours and then increased stage by stage to

prevent the finer particles from clogging the filter.

As the dust cake is formed on surface of the woven fabric,

they are suitable for low energy cleaning methods such as

shaking or reverse air flow through the filter bags.

In a nonwoven fabric, particles are mostly caught by their

impingement on the fibres within the fabric. Hence, this type

of filtration is often referred to as ‘depth filtration’ to

distinguish it from ‘sieving’. The actual flow paths followed by

the gas passing through a depth filter are extremely tortuous,

and a particle unable to follow these paths is given a

trajectory which sooner or later brings it into contact with a

fiber where it adheres, largely as a result of Van der Waal’s

forces. Since particles have to be removed from depth, a high

energy cleaning technique such as pulse jet is required for

their cleaning.

Dust cake forms slower in a nonwoven fabric than in a woven

fabric because the flow is relatively uniform across the fabric

surface rather than concentrated through a discrete number

of openings in the weave of woven fabric. In a woven fabric,

filling of the openings (the free area) with dust occurs more

rapidly because of the concentrated flow through them. The

relatively high cleaning frequency, characteristic of