Method and apparatus for producing liquid products from air in various

Abstract

A cryogenic method and apparatus using a liquefier and a two stage distillation column capable of operating in two modes, namely a first mode of operation during which only liquid nitrogen is produced and a second mode of operation during which liquid nitrogen and liquid oxygen are produced. By adjusting the time of operation in each mode, any ratio of liquid nitrogen to liquid oxygen greater than the ratio achieved during the second mode of operation can be achieved. In the first mode of operation, a condenser is used to condense the lower pressure stage gaseous nitrogen into lower pressure stage nitrogen condensate. To condense the lower pressure stage gaseous nitrogen, either at least a portion of the crude oxygen liquid from the higher pressure stage, at least a portion of the oxygen-enriched liquid from the lower pressure stage, at least a portion of the liquefied air, or mixtures thereof, are introduced to the condenser. In the second mode of operation, the top condenser is not used; instead, all of the crude oxygen liquid is introduced into the lower pressure stage, which produces a bottom liquid oxygen stream and a low pressure overhead waste stream containing nitrogen. The system includes fluid flow lines and valves for directing the flow of certain fluids, particularly the crude oxygen liquid and the oxygen-enriched liquid, during the two modes of operation.