Highly pure nitrogen gas producing apparatus

In an apparatus comprising means designed for producing highly pure nitrogen gas from the rectification of air, for precluding the need for a subsequent high-temperature catalytic step and for precluding the need of purging large quantities of cooling nitrogen, the combination which comprises means effective to compress the air taken from the outside, a means to remove the carbon dioxide gas and water in the compressed air by the said air compression means, a means to store liquefied nitrogen supplied from the outside, a heat exchanger connected to cool down the compressed air passed through said removing means to ultra low temperature, a rectifying column connected to turn a part of the compressed air cooled by the heat exchanger to ultra low temperature into liquid and to keep only nitrogen in gas form, said rectifying column having evaporating means for converting said liquid nitrogen to gaseous nitrogen, a lead channel connected lead consistently the liquefied nitrogen in said liquefied nitrogen storage means into said evaporating means as a source of cooling for compressed air liquefication in place of cold generated from a gas expander, a means to control the feed rate of said liquefied nitrogen in order to maintain constant rectifying conditions in said rectifying column which is provided to said lead channel, and an outlet channel connected to combine and remove both of the gasified said liquid nitrogen after use as the cooling source and also the gasified nitrogen from the outside source, pass them through said heat exchanger and heat them by exchanging heat with said compressed air, as the product nitrogen gas.