technical NOTES

• Disadvantages
  ƒ The operating cost of the system is higher due to the high chemical cost.
  ƒ The water requirement is higher than the dry fog system.
  ƒ The moisture ingress in the system is 1.2 % approx. which is higher than the
  dry fog system.
  ƒ The limited number of system presently operating in the cement plant.

6.4 Dry Fog with Compressed Air
This system operates with compressed air at 5 bar max and the water 1 bar, synchronized
through a twin port nozzle atomizing water in to mist of microscopic particles as
small as one micron. The fine droplets evaporate before wetting anything except
the dust particles. With a small droplets size and the fog effective dispersal pattern,
moisture addition is approx.0.1% by weight of material conveyed.

• Advantages
  ƒ Low pressure system so only standard piping will be used.
  ƒ Less moisture ingression in water than chemical water spray.
  ƒ More Effective than the chemical water spray system


• Disadvantages
  ƒ The fog is turbulent so the effectiveness of the dust suppression is less effective
  than the Cold fog system.
  ƒ Water consumption is higher than Cold fog system.
  ƒ Require expensive compressed air.

6.5 Cost Comparison
For example, a common layout has been considered for costing purpose.

S.N. Description UOM Cold

Fog

Bag

filters

Water

spray with

Chemical

Dry fog with

compressed

air

1 Transfer points Nos. 23 23 23 23

2 Bag filters required Nos. Nil 12 Nil Nil

3 Weight of Equipment Ton 2 75 5 5

4 Weight of Ducting Ton Nil 25 Nil Nil

5 Steel structure Ton Nil 35 Nil Nil

6 Steel structure cost Rs.in Lacs Nil 21 Nil Nil

7 Equipment cost Rs.in Lacs 94 78 40.0 110

8 Erection Cost Rs.in Lacs 6 8 6 6

9 Cost of Ducting Rs.in Lacs Nil 15 Nil Nil

10 Compressed air

requirement

m3/hour Nil 300 Nil 1700

11 Compressor cost Rs.in Lacs Nil 5 Nil 20