Reciprocating Compressor / Centrifugal Compressor Flowrate Limitation 1

[SPanda]

Hi,
Commercially available reciprocating compressors (multistage) are usually used for flow rates upto 1000CFM and similary for multistage centrifugal compressors the usual limit is around 10,000 CFM - see attachment in PDF.

Can anyone help me in explaining what are the usual issues with having Multistage Recips beyond 1000CFM? Are there a limitation on materials, Rod Load, power etc.
Similarly why are multistage centrifugal Compressors usually limited to around 10,000 CFM? What are the factors that limiting the flow rate.

Thanks.

 

[dcasto]

none. Ariels largest cylinders can do 3400 CFM, a single 6 throw single stage ariel compressor can do 11,000CFM in a single stage configuiration.

The selection of recips invloves limits with rod load, piston speed, valve losses, materials, frame torque limits, gas composition....

 

[ARenko]

dcasto's numbers are in line w/ what the graph says f/ single stage recips. Regarding multi-stage...

We have many four throw, four stage Ariels doing 1500 scfm to 5000 psi. We have one doing 1750 scfm. Limitations are as mentioned by dcasto.

It's possible that at the time that graph was made that was reality (also, it just says "typical"). I'm guessing that w/ advances in technology cylinders are getting more displacement relative to pressure rating these days so that you can get more flow out of your second, third, fourth... stages (and your first for that matter).

 

[raphatss]

I think that going beyond 1000 CFM with recips is not usual because the cylinders are going to be huge and that is not economically viable. And recips are not so easy to balance like a centrifugal compressor, and I think this has a big impact on the max speed/flow they can achieve.

 

[zdas04]

SPanda,
What is the source for the graph you attached? DCasto and DJV's numbers make a lot more sense. The 11,000 CFM single stage equates to almost a 5,500 CFM two stage or about a 3,6000 CFM three stage, and over 2,500 CFM is possible for a 4 stage (0-6,000 psig at sea level).

David

 

[zdas04]

I just noticed that SPanda hasn't been back for a month. Hopefully this thread will be useful for others who have come across that chart.

David

 

[ARenko]

raphatss,
Our 1st stage cylinder is 4.75" bore f/ our 1500 cfm machines. Not huge at all. Of course we feed it at 300 - 350 psig.

 

[guizmy]

For centrifugal compressors when you decrease the actual flowrate the flow coefficient tend also to decrease and impellers width becomes very narrow. At such low flow coefficients, the polytropic efficiency drop significantly (efficiencies may fall in the range of 60% - 50% typically).