Plant for producing gaseous nitrogen

Claim 1

A plant for producing gaseous nitrogen, which plant comprises means designed for enabling rapid variation in production rate while maintaining product quality, including a heat exchanger for cooling feed air, a distillation column for receiving at least part of said feed air, a vessel, a reflux condenser disposed in said vessel and arranged to receive, in use, vapour from said distillation column and return liquid reflux thereto, a line connecting the lower portion of said distillation column to said vessel and having an expansion valve mounted therein, a line for withdrawing nitrogen product from said distillation column and bringing said nitrogen product into heat exchange with said feed air, a crude liquid oxygen (LOX) storage tank communicating with said vessel, means to bring crude liquid oxygen from said crude LOX storage tank into heat exchange with vapour from said distillation column to provide reflux for said distillation column, a liquid nitrogen (LIN) storage tank communicating with said distillation column, means to return liquid nitrogen from said liquid nitrogen storage tank to said distillation column and/or vessel, a line for conveying waste gas from said vessel, means to warm said waste gas, an expander to expand said waste gas, means to control the flow of waste gas through said expander, and means to effect heat exchange between the expanded waste gas and the feed air.