Maximum Discharge Pressure of a Flooded Screw 2

[EmmanuelTop]

One of the projects we have in our scope (pre-feasibility phase) considers 2-stage compression trains, from 1-3 barg suction pressure to 25-30 barg discharge pressure. We intend to look more deeper into flooded screws for this particular case.

I have looked into various literature (Hanlon, Bloch) and compressor manufacturer sites (Howden, Mycom, Kobelco), trying to find the maximum discharge pressure (or maximum pressure ratio) for flooded screws. Hanlon, Bloch, and Howden quote the maximum discharge pressure range of 20-20 barg (without mentioning the minimum suction pressure), whereas Kobelco and Mycon quote much higher figures (Mycom = 50 barg @ 5 barg minimum suction pressure, Kobelco = 100 barg @ unspecified suction pressure). I ended up this reasearch without having a final conclusion - what would be the figures applicable for our project case, considering suction and discharge pressures as given in the first paragraph of this post? Is it achieveble with a single-stage flooded screw?

Any help is much appreciated.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[zdas04]

I generally consider "feasible" as within +/-10% of peak efficiency. That range is highly dependent on the VI selected. For a 4.6 VI the peak efficiency occurs at around 4.75 compression ratios and the range is 2.8-11.0. This means that for a 31 bara discharge you should try to keep suction above 2.8 bara with a 4.61 VI. For a 2.5 VI the peak is at 3.5 ratios and the range is 2.0-6.25 so for 31 bara discharge you'd want to stay above 4.7 bara.

With the 4.6 VI case, above 4.75 ratios you are "under compressing" which means that you are making the gas compress gas instead of using steel to compress the gas. That part of the efficiency vs. compression ratio graph is reasonably flat. The peak efficiency is around 76% and 11 ratios is at 68%. By the time you get to 20 ratios (which several authors claim is a physical limit, but I'm not sure that is true) the number is still above 60% for a 4.61 VI.

I'd go for it, making sure that I got the max VI that the vendor offered and building everything to ANSI 300.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[bcs5274]

have used some 2 stage leroi flooded screws with success in the past