Method and device for producing compressed nitrogen

An apparatus for producing compressed nitrogen by low-temperature fractionation of air comprising

• a distillation column system having a high-pressure column and a low-pressure column, and a high-pressure column top condenser and a low-pressure column top condenser, both in the form of condenser-evaporators, wherein
• the low-pressure column in the operation of the plant has the lowest operating pressure of all the separating columns in the distillation column system, and comprising
• a main air compressor for production of a high-pressure overall air stream by compressing feed air to an overall air pressure, wherein
• the main air compressor is the only external energy-driven gas compressor in the apparatus,
• means of work-performing decompression a first substream of the high-pressure overall air stream,
• means of introducing the first substream decompressed to perform work into the distillation column system,
• a main heat exchanger for cooling a second substream of the high-pressure overall air stream.
• means of introducing the cold second substream at least partly in the liquid state into the distillation column system,
• means of introducing gaseous top nitrogen from the high-pressure column into the liquefaction space of the high-pressure column top condenser,
• means of withdrawing a first liquid nitrogen stream from the liquefaction space of the high-pressure column top condenser,
• means of introducing a first substream of the first liquid nitrogen stream as reflux liquid into the high-pressure column,
• means of introducing top nitrogen from the low-pressure column into the liquefaction space of the low-pressure column top condenser,
• means of withdrawing a second liquid nitrogen stream from the liquefaction space of the low-pressure column top condenser,
• means of introducing a first substream of the second liquid nitrogen stream as reflux liquid into the low-pressure column,
• means of forming an internal compression nitrogen stream by a second substream of the first liquid nitrogen stream and/or a second substream of the second liquid nitrogen stream,
• means of increasing the pressure of the internal compression nitrogen stream in the liquid state to a product pressure higher than the operating pressure of the high-pressure column,
• means of warming the internal compression nitrogen stream brought to the product pressure in the main heat exchanger,
• means of drawing off the warmed internal compression nitrogen stream as gaseous compressed nitrogen product stream below the product pressure,
• means of drawing off at least one oxygen-enriched product gas stream from the distillation column system,
• means of warming the oxygen-enriched product gas stream in the main heat exchanger, and comprising
• means of drawing off all oxygen-enriched product gas streams in the gaseous state from the distillation column system,
• characterized in that
• the exit of the means for work-performing decompression is flow-connected to the high-pressure column,
• the main air compressor is designed for the compression of the feed air to an overall air pressure at least 5 bar above the operating pressure of the high-pressure column, and
• the means of increasing the pressure of the internal compression nitrogen stream in the liquid state are designed for increasing the pressure to a product pressure between 20 and 100 bar.