comparision between screw and centrifugal compressors

[turbo65]

Dear friends.

hi.

Presently one of the compressor suppliers is convecing us to buy centrifugal air compressor instead of buying screw air compressor. We require 500m3/min air compressor for 8 bar pressure and air should be oil free. The supplier (Ingersoll) claims that centrifugal compressors are more efficint(unit m3 of air/kW) as compare to screw air compressor of similar range. They also claims that the long term maintenance cost for centrfugal compressor is far less then screw. If you friends have any syggestion.
Also i want to knoe how to calculate the efficiency of screw and centrifugal compressor. For recip god knoledge is available in marine books but i am un able to find any thing for screw and centrifugal.

awaiting replies.

turbo65

 

[imok2]

turbo65
As I deal with air conditioning this is what I know about Screws vs Centrifugals
Prosscrews)
1. full load efficiency = to single stage centrifugals
2. part load eff 10 to 15% better then single stage cent.
3. excellent for air cooled application
4. surge not a factor
Con;
1. less efficient then 2 stage centrifugals
2. requires more maintenance then cent. If I get more info I will pass it on!

 

[imok2]

Thought this might interest you:

http://216.239.41.104/search?q=cache:WrtUyV1UlhUJ:

http://www.bobby-sc.com/Brewery%20A...s+centrifugals+air+compressors&hl=en&ie=UTF-8

 

[chicopee]

screw type compressor is positive displacement whereas centrifugal is not. screw compressor is more expensive to repair when comparing cost and may require extensive leed time to replace.

 

[jay165]

They're right about maintenance, wrong about efficiency.

One thing about a dry screw machine is that they are extremely noisy and require intake and exhaust silencers. Even with the silencers, they are still loud and will cause enough vibration to loosen bolts and break small fittings.

 

[zdas04]

Turbo65
See faq378-764 in the Piping and Fluid Mechanics Forum for some general discussion of the relative effeciency of Screws, Centrifuguls, and Recips. If your salesman was comparing a centrifugul to a dry screw, he was about right.

For your 500 m3/min (25 MMCF/d) and 8 bar (117 psig) oil-free application, a 3 or 4 stage centrifugul is probably the best choice since coalescing filters never take all the oil from a flooded screw (which would be the best choice by far if you could tolerate a small amount of oil).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com