Re: Downsize Pipe To Help Elevate Plugging?
Solid loading ratio is the ratio between air and solid mass flow rates.
If you change the pipe from 3” to 2” using the same flow rates; solid
loading ratio will remain the same only your air velocity in the pipe
will increase.If you need to reduce the solid loading ratio you need
a higher air flow rate or reduced solids flow rate in the system.
400 m3/hr air gives air velocity of about 21.5 m/s at atom. conditions
in 3"and 50.3 m/s in 2 “line. Stepping down will actually increase your
system pressure drop and reduce the solids rate. ■
Re: Downsize Pipe To Help Elevate Plugging?
Dear Sam,
I understand you are operating a vacuum system.
Solid loading ratio = (kg/sec product) / (kg/sec air)
I think you are using the pipe volume instead of kg/sec of air.
Pulsing your filters reduces (or stop) the air flow through the pipe for a moment.
(As you describe).
This can cause the pneumatic conveying to stop for a while and a plug is induced.
Increasing your rpm on the 3 inch pipe could help (reducing SLR)
Reducing the 3 inch pipe to a 2 inch pipe will cause capacity reduction at the same pressure drop and with the same air flow.
As we are not aware of the material you are conveying nor the geometry of you pipeline, it is very difficult to be more precise.
Read the threads in the pneumatic conveying section of this forum and you will get to understand pneumatic conveying better.
success.
teus ■
Teus
Re: Downsize Pipe To Help Elevate Plugging?
hi mantoo,
thank you for your explanation of SLR.
can you help me understand a bit more. having the same Roots blower, downsizing of line from 3 inch to 2 inch will increase my air velocity but at the same time increase my system pressure drop, but why the reduction in solids rate? what is the impact of increasing air velocity? to ensure the transported product remains suspended? and with greater air velocity, wouldn't i be moving more product, i.e. increase solid mass flow, instead? that is if i increase my feed rate, but since feed rate is also fixed, why then decrease in solids rate?
as mentioned stepping down also increase my system pressure drop, will that increase my chance of chokage, especially when the line is purged with positive air for 2-3 seconds every 30 minutes, since i didn't increase my blower capacity to accomodate for smaller pipe size?
thanks..........
Originally posted by Mantoo
Solid loading ratio is the ratio between air and solid mass flow rates.
If you change the pipe from 3” to 2” using the same flow rates; solid
loading ratio will remain the same only your air velocity in the pipe
will increase.If you need to reduce the solid loading ratio you need
a higher air flow rate or reduced solids flow rate in the system.
400 m3/hr air gives air velocity of about 21.5 m/s at atom. conditions
in 3"and 50.3 m/s in 2 “line. Stepping down will actually increase your
system pressure drop and reduce the solids rate.
■
Re: Downsize Pipe To Help Elevate Plugging?
hi Teus,
can you help me, does down-sizing reduce my system pressure drop or maintain? Mantoo explains to me downsizing will cause system pressure to drop at the expense of increase in air velocity.
thank you.............
oh...btw....read most of the thread in this forum...never knew there was so much to pneumatic conveying till now...
thanks to everyone!!! =)
Originally posted by Teus Tuinenburg
Increasing your rpm on the 3 inch pipe could help (reducing SLR)
Reducing the 3 inch pipe to a 2 inch pipe will cause capacity reduction at the same pressure drop and with the same air flow.
teus
■
Re: Downsize Pipe To Help Elevate Plugging?
Total System pressure losses can be divided into Air + solids contributions.
As the air velocity increases in the pipe the air only losses also go up ( darcy / fanning equation).
So for the same system pressure loss there is less pressure left for conveying the solids.
Hence lower solid rate.
“ In Pneumatic conveying more air doesn’t mean more solid rate.” ■
Downsize pipe to help elevate plugging?
can someone help me out here and critic my train of thought on pneumatic system. thanks.
Roots blower rated at 400m3/hr
if i have two lines, one 3 inch, and the other 2 inch. for the same 400m3/hr blower,
3 inch line will have a slower pickup velocity as compared to 2 inch line, right? since capacity of blower is similar, a smaller pipe with smaller volume will have its volume of air move faster. but smaller pipe will have lower pressure as compared to 3 inch pipe. and if so what is the impact of lower pressure? does it has anything to do with pressure drop across system?
3 inch line will have higher solid-gas ratio as compared to 2 inch line, if the feed ratio is similar, right? since 3 inch line has more volume and slower gas velocity.
the background of these questions, is that i am trying to convince myself weather if a dilute-system consisting of 3 inch lines facing frequent plugging and low vacuum pressure, could be resolved by going to a 2 inch line, having the same feed rate from a rotary valve. incidentally, the plugging only occurs when the system is purged with positive air during filter bag cleaning. [during this period, the conveyor line sees no vacuum, but slight positive air] thereafter the first purge, the first bend upwards will plug, near the pickup point. But just before the plugging, i.e. first purging of the system, vacuum readings were low, but transfer were still possible.
my intention is to reduce pipe diameter to 2 inch from 3 inch, in hopes of increasing the pickup velocity, as well as increase the vacuum pressure to assist in pulling the plug at the first bend when the system is purged with positive air at the filter bags area. at the same time reduce by half the vertical lift near the pickup point. but because of this reduction, i will have to add an additional two bends to bring the height back further downstream. am i on the right track? another option i may pursue is increase the speed of the blower to increase the capacity. will this help more than downsizing the pipe from 2 inch to 3 inch?
thanks all for your kind advise and critic.
sam ■