Managing make-up gas composition variation for a high pressure expander process

A method for liquefying a feed gas stream rich in methane in a system having a first heat exchanger zone and a second heat exchanger zone, comprising:

• (a) providing a compressed refrigerant stream with a pressure greater than or equal to 1,500 psia;
• (b) cooling the compressed refrigerant stream by indirect heat exchange with ambient temperature air or water to produce a compressed, cooled refrigerant stream;
• (c) directing the compressed, cooled refrigerant stream to the second heat exchanger zone to additionally cool the compressed, cooled refrigerant stream below ambient temperature to produce a compressed, additionally cooled refrigerant stream;
• (d) expanding the compressed, additionally cooled refrigerant stream in at least one work producing expander, thereby producing an expanded, cooled refrigerant stream;
• (e) routing part the expanded, cooled refrigerant stream to at least one separator, and mixing said expanded, cooled refrigerant stream with a make-up refrigerant gas stream, to thereby condition the make-up refrigerant gas stream by condensing heavy hydrocarbon components therefrom and producing a gaseous overhead refrigerant stream;
• (f) combining the gaseous overhead refrigerant stream with a remaining portion of the expanded, cooled refrigerant stream to form a cold primary refrigerant mixture;
• (g) passing the cold primary refrigerant mixture through the first heat exchanger zone to form a warm refrigerant stream, whereby the warm refrigerant stream has a temperature that is cooler by at least 5° F. of a highest fluid temperature within the first heat exchanger zone;
• (h) passing the feed gas stream through the first heat exchanger zone but not the second heat exchanger zone to cool at least part of the feed gas stream by indirect heat exchange with the cold primary refrigerant mixture, thereby forming a liquefied gas stream;
• and
• (i) compressing the warm refrigerant stream to produce the compressed refrigerant stream.