Cryogenic processes for separating air

In a cryogenic process for separating air with the production of oxygen under high pressure, of the kind in which air is separated in a cryogenic separation apparatus comprising a medium-pressure upstream section and a low-pressure downstream section into at least one fraction rich in nitrogen and into at least one fraction rich in oxygen in the liquid state under low pressure, in which the said oxygen fraction is pumped in the liquid state from the said low pressure to the said high pressure, the said liquid oxygen fraction under high pressure being exposed to total vaporization by heat exchange in counterflow with fluids one of which is a first fluid which comprises at least one of the two principal components of air, and during the said exchange is under a high pressure of the order of the said high pressure, and is then expanded to the said medium pressure before being fed in an at least partially liquid state into at least one said separation section, and the other of which is a second fluid comprising air under an intermediate pressure greater than said medium pressure but also lower than said high pressure, and is fed in the gaseous state into said upstream separation section;

• the improvement in which an expansion of all of said second fluid to said medium pressure is carried out in turbine means at an intermediate temperature between the hot and cold temperature of said heat exchange.