HYDROCARBON GAS PROCESSING.

Abstract

The present invention relates to a process and apparatus for separating a hydrocarbon gas stream containing methane and heavier hydrocarbons, as well as significant amounts of nitrogen and carbon dioxide. The gas stream is cooled and expanded, then fractionated in a first distillation column into a first overhead vapor stream and a hydrocarbon liquid stream containing most of the carbon dioxide. The hydrocarbon liquid stream is further fractionated into a hydrocarbon vapor stream and a less volatile fraction consisting of heavier hydrocarbons. The first overhead vapor stream is cooled, expanded, and separated into vapor and liquid streams. Both streams are cooled and expanded before feeding a second distillation column, which produces a second overhead vapor stream that is predominantly nitrogen and a bottoms liquid stream that is predominantly methane.The bottom liquid stream is vaporized and combined with the hydrocarbon vapor stream to form a volatile residual gas fraction containing most of the methane.