Removing nitrogen from and subsequently liquefying natural gas stream

Abstract

Abstract A natural gas containing substantial nitrogen is refrigerated to below minus 120*F in usual propane-ethylene refrigeration system using a cascade arrangement. Vapor and liquid thus obtained are separated and the liquid passed into the tubes of a refrigeration heat exchanger. The vapor and liquid, which has been further refrigerated, as a liquid, are recombined to effect uniform distribution of the vapors into the further refrigerated liquid for a flow through the heat exchanger tubes. Thus, admixed liquid and vapor streams are further refrigerated by heat interchange with bottoms from a fractionation zone into which the feed has been flashed, thus reboiling the fractionation zone bottoms. The nitrogen to be separated and some hydrocarbon, e.g., methane, are taken as overhead from the fractionation zone. Also, the overhead is used to refrigerate the liquid first obtained when refrigerating the feed after separation of vapors therefrom. Further, refrigeration of the recombined vapor and liquid is effected by flashing the natural gas containing fractionation zone bottoms in several stages, using liquid obtained upon a first flashing of said bottoms to refrigerate the recombined vapor and liquid streams described and using vapors from each flashing step practiced upon the fractionation zone bottoms to further refrigerate in order the liquid first separated from the feed after separation of vapors therefrom and the incoming feed gas resulting in a fuel gas containing some nitrogen. The remainder of the several times flashed fractionation bottoms is now substantially at atmospheric pressure and constitutes liquefied natural gas substantially free from nitrogen which is the product of the process. A controls system designed to render the system essentially automatic and to keep it in balanced operation is described.

Inventors

• 👤 Ernest A Harper
• 👤 Martin R Reber

Bibliographic Details