This article contains excerpts from the paper, “Your Gas Compression Application – Reciprocating, Centrifugal, or Screw?” presented at the 2016 Turbomachinery Symposium by Greg Phillippi of Ariel Corporation, Tim Manthey of Aerzen USA, Jonathan Sutter of Elliott Group, Ben Williams of Ariel Corporation, Bruce McCain, an engineering consultant.
Flare Gas MW – 20.0
The challenge for a reciprocating compressor in this application is the varied molecular weight of the gas. Although reciprocating compressors can compress a wide variety of gas molecular weights, in order to achieve the reliability required in the process industry, the compressor valves are configured based on the operating conditions and the gas molecular weight.
In considering the use of a centrifugal compressor for this application, the first problematic attribute is the low flow rate of 550 ACFM. Due to the size of the flow passages in the centrifugal compressor the efficiency will suffer. Secondly, the ratio of specific heats, K, coupled with the lower efficiency will require at least one intercooler. Although there are centrifugal compressors that accommodate connections for up to two process-intercoolers on a single casing, the number of impellers required to reach the final discharge pressure at the lower mole weight of 10 will require multiple compressor bodies (due to rotor dynamics). Finally, there is the large mole weight variation between the operating cases.