The refinery flare gas can be considered one of the most challenging, but it can be handled with the right compressor.

So how can we compress flare gas from a refinery?

Several types of compressors are being used. 

Centrifugal compressors should not be recommended in refinery flare gas applications because they cannot easily deal with wide swings of mole weight and are sensitive to any solids or liquids entrained by the gas stream. 

Positive displacement machines are best suited for these conditions because they can handle easily wide changes in the composition of the gas.  I know of five types of mechanical compressors being used, more of less successfully in flare gas applications:

• - Sliding vane compressors
• - Liquid ring compressors
• - Reciprocating piston compressors
• - Oil-flooded screw compressors
• - Oil-free screw compressors

Each of these technologies has its place and can be successful when applied correctly. 

A few pros and cons of each of these types of machines:

Sliding vane compressors are simple compressors with a single shaft off-center in a cylindrical housing.  They work best in low pressure clean gas applications.  They are not very reliable when dust or liquid is ingested in the machine and prevent the vanes from sliding back-and-forth in the rotor slots.  Jacket-cooling is required and oil needs to be injected continuously for lubricating the vanes that slide along the housing.  They may require relatively frequent overhauls, but these are relatively easy to handle. Initial costs are low.

Like the sliding vane compressors, the liquid ring compressors are also simple machines. The principle of operation is very similar to that of sliding vane compressors with the exception that a ring of liquid, generally water, is used instead of vanes that slide radially.  Liquid ring compressors are therefore well suited for wet gas,

dirty gas applications.  The gas maintains a low temperature during compression as the heat is absorbed by the liquid.  These compressors are available in a variety of materials to handle a wide range of gases.  As compressors, these machines are not very energy efficient, as it takes power to maintain the liquid ring in proper motion under all operating conditions. Moreover, the liquid will scrub and cool the gas.  This requires the liquid to be treated, before being discharged, and also cooled, filtered if it is used in a closed loop.  Of course, large amounts of water are not available...(Read whole article)