Process for recovering C4 + hydrocarbons using a dephlegmator

Claim 1

A process for separating C 4 and heavier hydrocarbons in high recovery and a purity of at least 60 mole %, from a feed gas comprising about 0-5 mole % C 5 and heavier hydrocarbons, 1-10% C 4 hydrocarbons, 0-10% C 3 hydrocarbons, 0-10% C 2 hydrocarbons, and the balance CH 4 and light inerts, which comprises: (a) pressurizing the feed gas to a level from 10 to 40 atmospheres if not at said level; (b) establishing and maintaining said feed gas at a temperature of from 2° to 38° C.; (c) passing said feed gas, prior to fractionation, to a dephlegmator, thereby cooling said feed gas to a preselected overhead temperature, within the range from -52° to -76° C., for forming a liquid condensate containing C 4 + hydrocarbons of a purity of at least 60 mole % and an overhead vapor fraction; (d) withdrawing said liquid condensate from the dephlegmator; (e) withdrawing said overhead vapor fraction from said dephlegmator and warming by indirect heat exchange against the feed in said dephlegmator; (f) work expanding the resulting warmed overhead vapor fraction in an expander to a pressure sufficient to generate a cold fraction having the required refrigeration value and having a temperature from about 2° to 15° C. below the preselected overhead temperature in said dephlegmator; and (g) withdrawing said cold fraction from the expander and again warming by indirect heat exchange against the feed in said dephlegmator.