Process and device for producing nitrogen-purified liquid methane from a feed gas stream containing at least 98 mol % of methane and between 0.1 and 2 mol % of nitrogen, in which the feed gas stream is cooled to a temperature of between 110 K and 200 K in a first heat exchanger in countercurrent with a stream of nitrogen vapour to produce a cooled stream, a bath of liquid nitrogen is in heat exchange with the cooled stream via a second heat exchanger through which the cooled stream passes, the liquid nitrogen bath producing nitrogen vapour supplied to the first heat exchanger to produce the cooled stream, the cooled stream leaving the second heat exchanger is introduced into a distillation column with a view to its distillation, and a liquid containing at least 99.5 mol % of methane is withdrawn from the bottom of the distillation column as the final product.

A liquefier device which may be a retrofit to an air separation plant or utilized as part of a new design. The flow needed for the liquefier comes from an air separation plant running in a maxim oxygen state, in a stable mode. The three gas flows are low pressure oxygen, low pressure nitrogen, and higher pressure nitrogen. All of the flows are found on the side of the main heat exchanger with a temperature of about 37 degrees Fahrenheit. All of the gases put into the liquefier come out as a subcooled liquid, for storage or return to the air separation plant. This new liquefier does not include a front end electrical compressor, and will take a self-produced liquid nitrogen, pump it up to a runnable 420 PSIG pressure, and with the use of turbines, condensers, flash pots, and multi pass heat exchangers. The liquefier will make liquid from a planned amount of any pure gas oxygen or nitrogen an air separation plant can produce.

To provide an air separation unit capable of reducing the risk of combustion of a heat exchanger connected to an oxygen turbine. An air separation unit A1 including a main heat exchanger 1; an intermediate-pressure rectification column 2; a low-pressure rectification column 4; a crude-argon column 5; a nitrogen condenser 3; a crude-argon condenser 6; an oxygen turbine 9; an oxygen turbine inlet pipe L32 for feeding oxygen gas drawn out from a bottom section of the low-pressure rectification column 4 or a gas phase in a refrigerant storage section of the nitrogen condenser 3 into the oxygen turbine 9 via the main heat exchanger 1, and feeding the oxygen gas to the main heat exchanger 1 again; an oxygen bypass pipe L321 which branches from the oxygen turbine inlet pipe L32; and a dilution stream pipe L42 for drawing out a nitrogen-containing gas.