NITROGEN GENERATING METHOD AND APPARATUS FOR USE IN THE SAME

There is provided a method of generating nitrogen which includes cryogenically separating compressed air introduced into a high-pressure column 11, storing liquid air 13 in a bottom portion of the high-pressure column 11 and taking nitrogen in gaseous form from an upper portion of the high-pressure column 11, introducing the liquid air 13 stored in the bottom portion of the high-pressure column 11 into a low-pressure column 12, cryogenically separating the liquid air 13 introduced into the low-pressure column 12, storing oxygen-enriched liquid air 22 in a bottom portion of the low-pressure column 12 and taking nitrogen in gaseous form from an upper portion of the low-pressure column 12 as a product gas, introducing the nitrogen taken from the upper portion of the high-pressure column 11 into a condenser 16 to liquefy the nitrogen, refluxing part of the liquid nitrogen to the high-pressure column 11, feeding the remainder of the liquid nitrogen to the upper portion of the low-pressure column 12, and introducing liquid nitrogen or liquid oxygen from outside a system into the low-pressure column as a coolant, wherein the liquid air 13 taken through an extraction pipe 20 is introduced into a portion of a rectification part 12a of the low-pressure column 12 in which the number of theoretical plates from a column bottom side is set within the range of one to ten. This method significantly reduces the amount of raw material air to accomplish significant reductions in power consumption, the amount of coolant and costs of facilities.