Filter dust collectors

Filter dust collectors

1. how they work

   • sieving, or catching any size larger than the openings in the media
   • interrupting particles' path when they pass whitinhalf their dianeter of a filter element
   • acting as a target for impaction or direct collision by a particle
   • particle diffusion
   • gravitational settling
   • electrostatic attraction
   • caking of collected process dust
   • action of a precoat cake of a filter aid

2. filter media

   • material: woven fabric, needled felt, paper, plastic, ceramic, metal surface membranes of polytetrafluoroethylene
     • selction of filter material should be based on experience, or on actual test whit the gas stream to be filtered

3. removing the recovered dust

   • relying on on-off or intermittent operation of the baghouse
   • shaking the filter bags
   • using a reverse air flow
   • pulsejet dislodging and reverse air flow combined

4. bag filtration velocities

   • calculated by dividing the volumetric flowrate by the filter
   • filter area= (volumetric flowrate through filter)/(filtration velocity)
   • filtration velocitie should be refined by multiplying by factors depending on the application
     • applicarion factors: 0.8 for oily, 0.9 for continous-collection materials, 1.0 for lower dust loading and intermittent operation
     • temperature factors: 1.0 for temperatures up to 110°F, 0.9 110-225°F and 0.8 above 225°F
     • particle size factors: 0.8 under 3
     • dust load factors: 1.2 for less grains/ft3, 1.1 10-20 grains/ft3, 1.0 20-50 grains/ft3, 50-80 grains/ft3, 0.8 above 80 grains/ft3

5. the right size

   • using optimum filter media and filtration velocity, help in optimizing velocity, lenght and number of filter bags snd required floor space.
   • the price depends on the relative value placed on filter cloth, accessory equipment, operating cost, and floorspace.
   • the engineer must also take into acount a number of other process-related factors when sizing a baghouse installation.

6. don't forget about pressure

   • pressure drop across the filter bag depends on
     • dust characteristics
     • filtration velocity
     • can velocity
     • choice of filter media
     • cleanability of the collected dust
   • the resistance of pressure drop across a clean filter ia usually around 0.5 t0 1.5 in w.c

7. measuring performance

   • efficiency= [(inlet dust load - dust emission)/ inlet dust load][100]