Single mixed refrigerant, closed loop process for liquefying natural gas

Abstract

A fluid material is cooled through a temperature range exceeding 200.degree. F. by heat exchange with a single mixed refrigerant composition in a heat exchange zone forming a part of a closed loop refrigeration cycle thus assuring high reliability and low investment by virtue of simplification of the equipment required and ease of control thereof. The process is especially useful for liquefaction of natural gas. Refrigerant in the refrigeration loop containing constituents having increasingly lower boiling points is successively directed from a compression zone to a condensation zone, thence to a heat exchange zone, next expanded in an expansion zone, returned to the heat exchange zone for countercurrent flow against the refrigerant flowing therethrough from the condensation zone to the expansion zone, and finally returned to the compression zone. The natural gas is directed to the heat exchange zone and liquefied therein by countercurrent flow against the cold refrigerant stream flowing from the expansion zone to the compression zone. The refrigerant is made up of C.sub.1 to C.sub.5 hydrocarbons plus nitrogen as an optional constituent with the relative proportions of the constituents being controlled so that the combined cooling curve of the hot refrigerant stream and the feed gas closely matches the heating curve of the cold refrigerant stream in a sense that the curves are in close proximity at the lowest temperature levels thereof and relatively uniformly and slowly diverge as the highest temperature points on the curves are approached.