Reciprocating Compressors – Discharge Temperature

Discharge temperature is an important factor, as it must be limited to prevent material damage. Additionally, higher discharge temperatures mean higher differential temperatures which cause greater differences in thermal expansion of components made of dissimilar materials. This in turn, causes higher stresses and larger deviations from design clearances.

300°F is a good all-around limit for process and oil-field compressors. The limit often applied to machines compressing hydrogen-rich gases is 275°F.

Although temperatures as high as 350–375°F have been used with a fair amount of success, 300°F provides a better margin of safety for several design factors, thus improving reliability and availability. The widely used PTFE piston ring and packing materials last longer and perform better at lower temperatures. With a calculated or observed temperature of 300°F, there are likely localized temperatures 50 degrees higher or more.

The 300°F limit sometimes causes a machine to have a greater number of stages than a higher temperature limit. More stages reduce rod loading by reducing the differential pressure. Another benefit of lower discharge temperatures is a reduced tendency toward deposits of solids on the discharge valves. This is likely to occur in dirty gas and heavy hydrocarbon services.

The penalties of lower discharge temperatures are cost, more working parts, and increase in footprint size. However, experience has shown that the benefits outweigh the penalties in the long run. There may be isolated cases where higher discharge temperatures may be justified, but these cases should be carefully studied.

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