Positive or Negative Pressure Filtration

[bif]

I am looking at installing a new dust conveying and filtration system as part of a plant expansion.

The unit we currently have uses positve pressure filtration to remove the dust fines (cyclone to remove most of the particles, then a fan blowing any entrained dust into cloth filter bags).

My previous experience has been having the entire system under negative pressure and so my concept would be cyclone to remove most of the dust then the some type of reverse jet pulse air filter and then the fan after that.

This begs the question how do I compare the 2 systems in terms of operating efficiency and cost? Is it better to use positive or negative pressure filtration?

 

[fredt]

I would generally favour a negative pressure system mainly because of potential fan erosion with a pressurised system where the fan is upstream. It isn't always essential to have a cyclone pre-collector with a fabric filter unless dust loadings are extremely high.

Because the greatest plate areas exposed to differential pressure with atmosphere on a fabric filter are on the downstream side the structure can be lighter in a pressurised system. However this advantage is quickly off-set if your fan wears out quickly.

Every case is different and best to get specialised advice taking account of all factors in your application.

 

[berkshire]

Bif
One thing to look at is the fan type.
In the first system you describe, a paddle wheel fan is generally used, because they handle entrained dust better, they are also not very efficient.
In the second system where the fan is behind all of the dust filters a more efficient fan can be used.
B.E.