Vacuum Pump Performance above Sea Level

[Mike4chemic]

Hello,
We design a Vapor Recovery Unit, which its main part is a screw vacuum pump. The system will be located at a site in South America (elevation is about 2,000 m above sea level. The required vacuum level is 0.069 bara.
Based on the pump's operation curve, which was received from a vendor, the maximum vacuum level which can be achieved at sea level by this pump is 29 in HgV (0.03 bara).
I try to evaluate, whether the required vacuum level of 0.069 bara can be achieved at 2000 m above sea level by this pump. I used the following methodology:
This vacuum pump with a maximum capability of 29 in HgV at sea level is rated of 97%.
(29 in HgV/29.92 in HgV)= 0.97
Then, I assumed the 97% rating can be used to the vacuum pump to determine its performance at 2000 m above sea level. The ambient pressure at 2000 m above sea level is about 0.763 bara.
Therefore, the pump’s performance at 2000 m is 0.763 bara X 0.97= 0.74 bara.
Based on this, the vacuum pump can only achieve a maximum absolute pressure of 0.273 bara (1.013 bara-0.74 bara). It means the required vacuum level of 0.069 bara can’t be achieved at 2000 m above sea level.
I asked this question a pump’s vendor. Based on his evaluation, the maximum vacuum level which can be achieved with the pump is 0.023 bara (0.763 bara- 0.74 bara), and therefore he don’t see any problem to achieve the vacuum required level of 0.069 bara.
I'm a little confused. Who is right?
Thanks in advance, Mike

 

[EmmanuelTop]

See:

http://www.dekkervacuum.com/pdfs/uploads/s2p040-alt.pdf

http://www.hargravesfluidics.com/alt_standard.php

http://www.powerexinc.com/images/PWX/download/Vac_Altitude.pdf

Dejan IVANOVIC
Process Engineer, MSChE

 

[crshears]

Maybe it's just me, but my approach to answering this question is "Which parameters define the dimensions of the box?"

More specifically, will the operation of said device be adversely affected by pumping against a lower discharge pressure than that encountered at standard temperature and pressure at mean sea level?

I used to have operating engineers argue with me that the Rankine / thermal efficiency of a power plant was affected by changes in atmospheric pressure, since the "degree of vacuum" changed; my contention was that any given plant operates between two absolute pressures, therefore atmospheric pressure changes are not applicable...

Although I can't PROVE it, it is my suspicion that the degree of vacuum a particular pump can draw is defined by its design and the characteristics of the vapour mixture it must work with, and not by the pressure level it discharges to.

Hope this helps.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]