Propane recovery methods

Abstract

The present invention is directed to methods for separating and recovering propane, propylene and heavier hydrocarbons, i.e., the C.sub.3 + hydrocarbons, from a gas feed, e.g., raw natural gas or a refinery or petroleum plant gas stream. These methods employ sequentially configured first and second distillation columns, e.g., a de-methanizer tower followed by a de-ethanizer tower. A cooled gas feed condensate is separated in the first column into methane and a liquid phase comprising ethane and heavier hydrocarbons. The liquid phase is separated in the second column into a gas phase primarily comprising ethane and a second liquid phase primarily comprising the desired C.sub.3+ hydrocarbons. At least a portion of the second gas phase is introduced into the first distillation column as an overhead reflux to improve the separation of C.sub.3+ hydrocarbons. The methods of the present invention permit separation and recovery of more than about 99% of the C.sub.3+ hydrocarbons in the gas feed at higher operating pressures. Further, by cooling the second gas phase with a liquid condensed in a lower tray of the first column, significant capital and operating costs may be saved. By using the self refrigeration system, the need for external refrigeration is eliminated and the separation efficiency is improved in the first column. Accordingly, the processes of the present invention result in achieving higher liquid recovery levels with lower capital requirements and significant savings in operation.