N2 flow needed for blanketing
N2 flow needed for blanketing
(OP)
Dear all,
I'm trying to calculate the nitrogen flow needed for purging a hopper. This hopper (with a volume of 0.40 m3) is a bin in which different solids (polymer, additives, ..) are collected and via which they are discharged in a mixer (here all the components are mixed together at high temperature), this is a continuous process.
To ensure a safe operation, the oxygen concentration in the hopper should be reduced to 5 vol%. The polymer and other additives take air in the hopper and this air flow was calculated as 4 m3/hr. My question is: how do I calculate the nitrogen flow needed to purge this continuous air flow and have an oxygen concentration of 5 vol%?
The N2 flow shall be continuous as well and going from the bottom of the hopper to the top (where the polymer and feed enters) and shall be extracted via an outlet on the hopper together with other fumes.
I attached a schematic drawing.
Best regards,
Orsiz
I'm trying to calculate the nitrogen flow needed for purging a hopper. This hopper (with a volume of 0.40 m3) is a bin in which different solids (polymer, additives, ..) are collected and via which they are discharged in a mixer (here all the components are mixed together at high temperature), this is a continuous process.
To ensure a safe operation, the oxygen concentration in the hopper should be reduced to 5 vol%. The polymer and other additives take air in the hopper and this air flow was calculated as 4 m3/hr. My question is: how do I calculate the nitrogen flow needed to purge this continuous air flow and have an oxygen concentration of 5 vol%?
The N2 flow shall be continuous as well and going from the bottom of the hopper to the top (where the polymer and feed enters) and shall be extracted via an outlet on the hopper together with other fumes.
I attached a schematic drawing.
Best regards,
Orsiz





RE: N2 flow needed for blanketing
Do you believe the estimate of 4cum/hr?
If so, then you need 3-4 times that for purge flow.
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P.E. Metallurgy, Plymouth Tube
RE: N2 flow needed for blanketing
4:1 dilution results in 4.2% oxygen, assuming complete mixing.
TTFN (ta ta for now)
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RE: N2 flow needed for blanketing
Don't you have to take the volume of the hopper into account? Will I immediately reach the needed oxygen concentration of 5 vol% when I start up then? Isn't there a certain time needed in order to purge the oxygen? The concept of nitrogen purging is relatively new to me so I still have to learn a lot about it.
RE: N2 flow needed for blanketing
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: N2 flow needed for blanketing
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P.E. Metallurgy, Plymouth Tube
RE: N2 flow needed for blanketing
If y m3/hr is the N2 purge rate, and N2 purity is say 99%, and say we add a 20% safety margin to this estimated 4m3/hr of free air getting into the hopper, we will have
0.99y + (4 x 1.2 x 0.79) = ((4 x 1.2) + y) x 0.95, which gives y = 25.2m3/hr.
If you dont include a safety margin, y = 21m3/hr.
This is the continous rate.
RE: N2 flow needed for blanketing
RE: N2 flow needed for blanketing
Only for further evaluation, Orsiz:
if I'm not wrong, from 0.99y + (4 x 1.2 x 0.79) = ((4 x 1.2) + y) x 0.95
y = 16 (19.2) Actual m3/h
that happens without fumes and if all streams with gas/vapour are at the same temperature:
1) fumes with low or neglected O2 content reduce nitrogen request;
2) if nitrogen is colder than air feeded, y becomes lower and if hotter, y becomes higher (but rarely the last cond. happens)