Patent ID: 7219513
Filing Date: 2007-05-22
Classification: F25J

Abstract:
1. A method for separation of methane and more volatile components from ethane and less volatile components making up a high pressure feed gas stream, the improvement comprising: (a) cooling the feed gas stream, which consists of a cooling stream and a first heat exchanger feed stream, in a first heat exchanger to form a partly condensed first stream, where heat is exchanged only against a low pressure, heated overhead gas stream to form a compressor feed stream; (b) separating the first stream into a vapor second stream and a liquid third stream; (c) passing the second stream through an expander to a low pressure to form a partly condensed fourth stream and thereafter feeding the fourth stream to a mid-level stage in a demethanizer column; (d) flashing to a low pressure the third stream to form a partly vaporized fifth stream and thereafter feeding the fifth stream to a stage in the demethanizer column just below the feed stage of the fourth stream; (e) operating the demethanizer column with upper and lower side reboilers and a bottom reboiler, whereby the upper reboiler withdraws from and returns to the demethanizer column an upper reboiler stream at stages above the feed stage of the fourth stream and the lower reboiler withdraws from and returns to the demethanizer column a lower reboiler stream at stages below the feed stage of the fifth stream; (f) operating the demethanizer column so that a cooled overhead gas stream is removed from a top stage and indirectly heated in an overhead condenser heat exchanger to form the heated overhead gas stream; (g) splitting the compressor feed stream into a first recycle stream and a product stream, thereafter operating a first compressor only with expansion power supplied from operation of the expander and compressing the first recycle stream to form a second recycle stream; (h) compressing to high pressure in a second compressor the product stream to form a sales gas stream consisting substantially of methane and more volatile components; and (i) cooling the first recycle stream sequentially in a first cooler, the bottom reboiler, the lower reboiler, the upper reboiler and the overhead condenser to form a sub-cooled reflux stream; (j) flashing the reflux stream to low pressure and feeding the flashed stream to the top stage of the demethanizer; and (k) operating the demethanizer column to produce a liquid bottom stream from a bottom stage consisting substantially of ethane and less volatile components.