How to design the air/cloth ratio according to the operation condition?
The end users sometimes are confused on the air/cloth ratio design from the filter bag dust collector manufacturers, because the same operation condition offered to different dust collector manufacturers the air/cloth ratio may different, some designed from the experiences, and some according to your budget expected, some just offering a list simply for different kinds of dust collection, while what’s the theory support for the air/cloth ratio design? Then following is the answer for this question from Zonel Filtech.
Let’s say the air/cloth ratio design is Qt:
The Qt= Qn * C1*C2*C3*C4*C5
Qn is standard air/cloth ratio, which is related to the particle type and coherence properties, basically:
The sublimation of ferrous & nonferrous metal, active carbon chooses 1.2m/min;
The dust air from coke production, volatile residue, metal powders (polishing, etc.), oxidation of metal chooses 1.7m/min;
The dust air of alumina, cement, coal, lime, ores chooses 2.0m/min.
So the similar kind of the dust air can decide according to the above.
C1 is the index of purging type:
If choose the pulse jet purging method:
Woven filter fabric dust bags, C1 choose 1.0;
Nonwoven filter cloth dust bags, C1 choose 1.1.
If choose the reverse blown purging plus mechanical shake, the C1 choose 0.1~0.85;
If choose the reverse blown purging only, the C1 choose 0.55~0.7.
C2 is the index related to the inlet dust content:
If the inlet dust content such as at 20g/m3, the C2 choose 0.95;
If the inlet dust content such as at 40g/m3, the C2 choose 0.90;
If the inlet dust content such as at 60g/m3, the C2 choose 0.87;
If the inlet dust content such as at 80g/m3, the C2 choose 0.85;
If the inlet dust content such as at 100g/m3, the C2 choose 0.825;
If the inlet dust content such as at 150g/m3, the C2 choose about 0.80;
C3 is the index related the particle sizes/ median diameter:
If the median diameter of the particle:
> 100 microns, choose 1.2~1.4;
100~50 micron, choose 1.1;
50~10 micron, choose 1.0;
10~3 micron, choose 0.9;
C4 is the index related to the dust air temperature:
For the dust air temperature at (degree C):
20, choose 1.0;
40, choose 0.9;
60, choose 0.84;
80, choose 0.78;
100, choose 0.75;
120, choose 0.73;
140, choose 0.72;
>160, can choose 0.70 or less some properly.
C5 is the index related to the emission:
If the emission request less than 30mg/m3, the C5 choose 1.0;
If the emission request less than 10mg/m3, the C5 choose 0.95;
Design for cement kiln dust collection, with Nomex nonwoven filter bags dust collector, operation temperature at 170 degree C, inlet dust content is 50g/m3, median particle size is 10 microns, emission request is less than 30mg/m3.
So, the Qt=2*1.1*0.88*0.9*0.7*1=1.21m/min.
When design the DC, this air/cloth ratio can be taken into consideration.