Patent ID: 8429933

Claim:
A method of producing a liquid product stream at a production rate that is selectively varied, said method comprising: producing the liquid product stream as a result of a cryogenic rectification process which employs a distillation column for separating nitrogen from a feed stream comprising the nitrogen and oxygen, the feed stream introduced into the distillation column after having been compressed, purified and cooled; the cryogenic rectification process utilizing a refrigeration cycle that comprises partially warming an oxygen-rich vapor stream within a main heat exchanger used within the cryogenic rectification process for cooling the feed stream, the oxygen-rich vapor stream being produced from the generation of reflux for the distillation column, expanding at least part of the oxygen-rich vapor stream within a variable speed turboexpander to generate an exhaust stream and fully warming the exhaust stream within the main heat exchanger; selectively varying the production rate of the liquid product stream by varying feed stream pressure of the feed stream such that the increasing feed stream pressure will increase pressure within the distillation column and therefore, the oxygen-rich vapor stream, thereby increasing the expansion ratio across the variable speed turboexpander, the refrigeration imparted to the cryogenic rectification process and consequently, the production rate of the liquid product stream and vice-versa; and increasing flow rate of the feed stream during an increase of the feed stream pressure and thereby producing the oxygen-rich vapor stream at an increased flow rate and vice-versa such that efficiency of the variable speed turboexpander remains substantially constant.