Cryogenic distillation process for the production of oxygen and nitrogen

Abstract From the Canadian patent

According to the invention, an intermediate column having its lower end in heat exchange with the top of the high pressure column, and its upper end in heat exchange with an intermediate location above the bottom tray of the lower pressure column is used. This intermediate column separates the oxygen rich liquid produced at the bottom of the high pressure column into two liquid fractions which are then introduced as feeds to the low pressure column which still has, it's lower end in heat exchange with the top of the high pressure column, therefore, its pressure will be essentially the same as the low pressure column of a classical double column process operated at the same air pressure.