Dust collector purging system problem – blowing pipe design
When Zonel Filtech help clients to improve their dust collectors, some of them were complained that the purging systems of their bag filter housing is not works well even if they using the air leading pipe on the air blowing pipe, also with the venturi, and also with a correct pressure for the compressed air, so they cannot find the solution to improving the purging works.
After analyzed their purging system, the Zonel engineers were found the main reason is that the distance between their air leading pipe to bag tube sheet is not correct. If the distance too big, the air may blow some to the bag tube sheet instead into the filter bags; on the contrary, if too small, the pressed air cannot leading enough air outside into the filter bags, the purging effect sure won't be good.
But how to define this distance (H1 in the following drawing) ?
１.First step, you need to define the average value of the Øp in the drawing.
As usual, we calculate the Øp with the following formula:
C=Coefficient, as usual choose 50%~65%.
D=pulse jet valve outlet diameter, as usual the same to air blowing pipe.
n=the filter bag number per row (purging with the same pulse jet valve)
As usual, C we choose 0.55.
Mostly, the air leading pipe the diameter is 2~3 times of the Øp.
２.Define the length of the air leading pipe.
Air leading pipe as usual use the following formula:
Ck=coefficient, as usual choose 0.2~0.25
K=is jet turbulence coefficient, cylindrical choose 0.076.
i.e. L= about 0.2* Øp/0.076=2.65 Øp
３.It’s very easy to get that tg a degree =(1/2 Øb)/H2
tg a degree= 3.4K=0.272 (can be treat as a constant)
So a degree choose 15 degree.
If choose 3” immerged pulse jet valve, leading pipe d=30mm, filter bag diameter is 160mm, how to get H1.
Obviously, the H1=H2-L
So we have to define the H2 and L.
tg a degree =(1/2 Øb)/H2=3.4K=0.272
i.e. H2=1.838 Øb
Øb = 160mm
So the H2=294 mm
3”as usual the average Øp=15 mm (also can calculate when the bag qty be offered, or according to the experience data, appended please find.)
From the previous result, L=2.65 Øp, so the L=2.65*15=40 mm
So the H1=294-40=254mm.
For the Qp, generally the average data can be chosen as following:
Pulse jet valve size ---- Qp
1” ---- 6~8mm
As usual, when the Qp design will divided into 3~4 groups, closer to the pulse jet valve, the open size bigger, and group to group the diameter differences about 1mm.