ENHANCED NGL RECOVERY PROCESSES

The present invention is directed to methods for improving the efficiency and economy of processes for the recovery of natural gas liquids (NGL) from a gas feed, e.g., raw natural gas or a refinery or petrochemical plant gas stream. These methods may be employed with most, if not all, conventional separation methods using a distillation tower, e.g., a demethanizer or deethanizer column. In the methods of the present invention, a portion of a hydrocarbon liquid condensed on a chimney tray disposed below the lowest feed tray of the column is withdrawn from the tower. This withdrawn liquid hydrocarbon is expanded and heated to produce a two-phase system for separation into a heavy, liquid hydrocarbon product and a vapor phase for recycle to the column, preferably as a stripping gas. The withdrawn hydrocarbon liquid is preferably heated by indirect heat exchange with the inlet gas, thus reducing or eliminating the external refrigeration requirements of the process. The expanded, heated vapor recycled to the column increases the ethane and propane concentration in the column, this reducing the tray temperature profile and increasing the separation efficiency. Accordingly, the column may be operated at lower temperatures and higher pressures, resulting in significant energy savings and economies of operation.