Patent ID: 7296437

Claim:
A method which may be used for separating air by cryogenic distillation with a thermally coupled medium pressure column and low pressure column, said method comprising: a) cooling compressed and purified air to a cryogenic temperature in an exchanger, wherein the ratio of the volumetric flow rate of said air entering said exchanger to the total volume of said exchanger is greater than about 3,000 Nm 3 /h/m 3 ; b) sending at least part of said air to said medium pressure column; c) sending at least one oxygen enriched stream, and at least one nitrogen enriched stream from said medium pressure column to said low pressure column; d) withdrawing at least one nitrogen enriched stream and at least one oxygen enriched stream from said low pressure column; e) sending said withdrawn streams to said exchanger; and f) withdrawing at least one oxygen stream from said exchanger, wherein the ratio of the volumetric flow rate of said oxygen stream withdrawn from said exchanger to the total flow area of the exchanger passages through which said stream is withdrawn is less than about 25 Nm 3 /h/cm 2 .