Re: Pneumatic Conveying At High Altitudes.
I have designed a few systems for mining industry working at height of 2500m.
I agree with the comment that due to lower atmospheric pressure higher volumetric
flow is required for compressor (this is simple physics cant argue with it).
For pressure conveying systems there is no noticeable change suspension velocity
pressure drops etc. Only thing which changes is the exit velocity due to lower ambient
atmospheric pressure. Also you need to take into account higher air volume at the end
for filter sizing.
For vacuum systems i agree lower Dp is available due to lower air density this could result in
higher pickup velocities. ■
Re: Pneumatic Conveying At High Altitudes.
Dear Mr. Mantoo.
Thanks to your reply. I was triggered to look at the suspension velocity issue, which I did not address in my formula building as such.
For pressure conveying systems there is no noticeable change suspension velocity
I found:
v(suspension-altitude)=√((air-sea level)/(air-altitude) )*v(suspension-sea level)
The suspension velocity at 2500m is, compared to the suspension velocity at sea level:
v(suspension-altitude)=√(746/1000)*v(suspension-sea level)
The issue for keeping the particles in suspension is more complex to figure out, because this is influenced by the Reynolds number: influencing the Reynolds number which in return is influenced by the gas density and the gas velocity.
Also, you need to take into account higher air volume at the end
for filter sizing.
And the lower ambient pressure at high altitudes must also be accounted for
For vacuum systems i agree lower Dp is available due to lower air density this could result in
higher pickup velocities
I agree to the requirement of higher velocities at a vacuum intake, causing higher pickup velocities
This accounts also for pressure systems when the compression ratio at high altitude equals the compression ratio at low altitudes.
Describing the consequences for a compressor, operating at high altitude is not the complete story to describe the consequences for pneumatic conveying at high altitudes.
That seems to be much more complex, due to the many parameters involved.
The software of Yarca pcs is accounting for all the relevant parameters of pneumatic conveying automatically in the algorithm, either at sea level or at high altitude systems. ■
Teus
Re: Pneumatic Conveying At High Altitudes.
Dear Mr Teus Tuinenburg
In my opinion the only difference between sea level and 2500m conveying system will be
the difference of 0.26 atm of ambient pressure. if you add this pressure to gauge pressure
at higher altitude then both system will have same conveying characteristics for a positive
pressure system.
I am not sure why you think it is has a major impact on conveying calculations. In engineering
it is very common to account for pressure at altitude.
Have a nice day ■
Re: Pneumatic Conveying At High Altitudes.
Dear Dr. Mantoo,
In my opinion the only difference between sea level and 2500m conveying system will be
the difference of 0.26 atm of ambient pressure. if you add this pressure to gauge pressure
at higher altitude then both systems will have same conveying characteristics for a positive
pressure system.
If I understand correctly:
p-absolute atmospheric is 1.0 bara
p-absolute 2500m is 0.75 bara
Gauge pressure at sea-level is gauge pressure at 2500m (dp system)
Then:
Absolute conveying pressure at sea level is 1.0+dp
Absolute conveying pressure at 2500m is 0.75+dp
Pressure ratio at sea level = (1.0+dp)/1
Pressure ratio at 2500m = (0.75+dp)/0.75
Example for dp conveying = 2 barg:
Pressure ratio at sea level = (1.0+2)/1=3
Pressure ratio at 2500m = (0.75+2)/0.75=2.75/0.75=3.66
Conclusion:
-The pressure ratio of a system at high altitude is higher than the pressure ratio of a system at sea level at equal pressure drop.
-The air delivers more energy for pneumatic conveying at high altitude than at sea level at equal pressure drop
-A pneumatic conveying design with equal pressure ratio at a high altitude and sea level results in lower dp.
Remark:
Calculations show indeed a lower achievable stable conveying pressure at higher altitudes.
If we consider the pressure ratio as a conveying characteristic for a positive pressure system, then
a pneumatic conveying system does not have the same conveying characteristics at equal gauge pressure (pressure drop)
I am not sure why you think it is having a major impact on conveying calculations. In engineering it is very common to account for pressure at altitude.
The calculations will show the overall effect of the influence of the lower density of air at higher altitudes.
And that appears to be a very complex system.
Also:
-At higher altitudes, the compressor volume needs to be higher for equal SLR at sea level.
-As higher air velocities are required at higher altitudes, to match the lower suspension velocities, the compressor needs to have a higher volume displacement.
In engineering it is always a must to account for pressure at altitude. ■
Teus
Pneumatic conveying at high altitudes.
Designing a pneumatic conveying system operating at sea level results in a different installation than designing a pneumatic conveying system operating at high altitudes.
At high altitudes, the atmospheric pressure is lower and thereby the air density is lower.
paltitude=1013.25*(288.15/(288.15-0.0065*Altitude))^(-5.2559)
This has the following consequences:
At high altitudes, the suspension velocity will be lower.
This requires higher air velocities, to keep the particles in suspension.
Compressors at high altitudes.
As higher air velocities are required at higher altitudes, to match the lower suspension velocities, the compressor needs to have a higher volume displacement.
Pressure ratio (available pressure drop) at high altitudes.
[b}Vacuum system:[/b]
As the ambient pressure at high altitudes is lower, the available vacuum is also lower.
Conclusions:
The pressure ratio at higher altitudes is higher than the pressure ratio at sea level for the same vacuum
A pneumatic conveying design with equal pressure ratio at a high altitude and sea level results in lower vacuum
Pressure system.
Conclusions:
The pressure ratio at higher altitudes is higher than the pressure ratio at sea level for the same ∆p
A pneumatic conveying design with equal pressure ratio at a high altitude and sea level results in lower ∆p
Solid Loading Ratio at high altitudes.
At higher altitudes, the compressor volume needs to be higher for equal SLR.
[b]Summary consequences at higher altitudes.[b/]
Higher required airflow/air velocities due to lower suspension velocity.
Lower pressure/vacuum due equal pressure ratio.
Higher required airflow at equal SLR.
All the above requirements result in a required air mass flow, showing that pneumatic conveying is a mass flow technology and not a volume flow technology (like a belt conveyor)
Equipment at high altitudes.
Above requirements lead to bigger pneumatic conveying installations (compressors, pipelines
Due to the lower air density at higher altitudes, the heat capacity of the air is reduced, requiring bigger coolers to maintain the same cooling capacity.
A software program must be capable of performing the calculations for a pneumatic conveying system, whereby the ambient conditions are not limited to “at sea level”.
Calculations for an installation must generate the correct results, based on just the input of the relevant altitude (sea level or at an altitude).
Altitude at sea level = 0 m, corrected for a high pressure- or a low-pressure atmospheric system
At a high-altitude level the average ambient pressure in mbar is calculated from the formula ambient pressure=function(altitude), corrected for a high pressure- or a low-pressure atmospheric system ■
Teus