Patent ID: 6705113
Filing Date: 2004-03-16
Classification: F25J,Y10S

Abstract:
In a process for the production of olefins from a charge gas containing hydrogen, methane, ethylene and other C2 and heavier hydrocarbons wherein said charge gas and additional olefin plant process streams are cooled by a refrigeration system having a series of heat exchangers, a method for cooling said charge gas and additional olefin plant process streams by the use of a tertiary refrigerant in said refrigeration system comprising the steps of:(a) compressing a tertiary refrigerant vapor comprising a selected mixture of methane, ethylene and propylene in a multistage compressor having a first stage, at least one intermediate stage and a last stage with a last stage discharge wherein the composition of said last stage discharge is greater than 50 mol percent propylene; (b) cooling to condense a portion of said tertiary refrigerant vapor from said last stage discharge to form a remaining tertiary refrigerant vapor and a heavy liquid refrigerant having a greater percentage of propylene than said selected mixture; (c) separating said heavy liquid refrigerant from said remaining tertiary refrigerant vapor in a separator; (d) cooling to condense at least a portion of said remaining tertiary refrigerant vapor from said separator and thereby forming a medium liquid refrigerant and forming a light vapor refrigerant of any uncondensed portion thereof; (e) bringing said heavy and medium liquid refrigerants and any light vapor refrigerant into heat exchange contact with themselves and each other and with said charge gas and additional olefin plant process streams in said series of heat exchangers whereby said charge gas and additional olefin plant process streams are cooled and said heavy and medium liquid refrigerants are subcooled and then heated and vaporized and said light vapor refrigerant is first cooled and condensed and then vaporized; and (f) returning said light and medium and heavy vaporized refrigerants to said compressor.