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Reciprocating compressor power follows the adiabatic head relation, roughly 22 brake horsepower per MMscf/day per stage at a ratio of 2 to 3. Splitting the overall ratio evenly between stages minimises total power and keeps discharge temperature within material limits, which is why staging with interstage cooling is standard.
Compression power
BHP per stage = 22 x q (MMscfd) x k/(k-1) x (r^((k-1)/k) - 1)
Staging
Ratio per stage = (overall ratio)^(1/stages)
Compressor selection, relief protection and gas handling must follow the applicable machinery and pressure system standards, with vendor performance data used for final design.
Discharge temperature rises with ratio and must stay below about 300 F for lubricant and valve life. Ratios above 3-4 per stage also cut volumetric efficiency sharply.
Enough to keep each stage ratio between 2 and 4. A 9:1 overall ratio is normally two stages; 30:1 needs three.