Method and apparatus for the production of ultra-high purity nitrogen

摘要

Air separation by low temperature liquefaction and fractionation wherein feed air is compressed and cooled and supplied to a single stage air separation column from which gaseous nitrogen is removed frown the top and wherein an oxygen-rich liquid is removed from the bottom. The column contains solid material providing solid surfaces on which mass and energy transfer takes place to effect fractionation over a substantial vertical height in the single stage of the column. Liquid is removed from the column intermediate that height, and the removed liquid is subcooled and expanded to produce a gas and a liquid. The liquid is an ultra-high purity nitrogen product, and can be withdrawn from the cycle in liquid or vapor phase. Vapor is removed from the top of the column, cooled and partially condensed and phase separated. Vapor from the last-mentioned phase separation is discharged, thereby to eliminate from the cycle most of the impurities boiling lower than nitrogen. Liquid from the last-mentioned phase separation is returned to the top of the column as reflux.