Process for the recovery of argon

Claim 1

A process for the recovery of argon from a tail gas stream remaining after treating an ammonia synthesis purge gas for the recovery therefrom of hydrogen values, said tail gas stream being at super-atmospheric pressure and containing methane, argon and nitrogen and residual hydrogen and said process comprising: (i) separating said tail gas stream by partial condensation into a condensate containing methane, argon and nitrogen and an uncondensed gas stream containing substantially all of the residual hydrogen in said tail gas stream, said separation being effected by cooling said tail gas stream in a plurality of heat exchange steps, in which condensed gas is separated out after at least the penultimate heat exchange step and thereafter the uncondensed gas is passed upwardly in the final heat exchange step with condensed material formed therein flowing downwards in contact with the rising gas stream and mixing with said condensed gas to form said condensate; and recovering said uncondensed gas stream containing substantially all of the residual hydrogen from said final heat exchange step (ii) expanding and partially evaporating said condensate to produce a fractioning stream; (iii) separating said fractioning stream by fractional distillation at sub-ambient temperature and superatmospheric pressure in two distillation columns in series, wherein in the first distillation column a liquid methane stream is separated as the bottoms product and a gaseous stream containing nitrogen and argon is recovered as the overhead product and passed without an intermediate pressure reduction step to the second distillation column in which it is fractionated to produce argon as the bottoms product and a gaseous nitrogen stream as overhead product; and wherein the heat for reboil and the cooling for reflux for the distillation columns are provided by a single heat pump cycle in which the heat transfer fluid is provided from the said gaseous nitrogen stream; the cold requirements of the process are supplied by an open refrigeration cycle in which the refrigerant is provided from the said gaseous nitrogen stream; and reflux in the final heat exchange step in (i) is provided by evaporation of a coolant passed in indirect countercurrent heat exchange relationship with said rising gas, said coolant comprising a stream containing liquid nitrogen provided from said gaseous nitrogen stream and the bubble point of which has been lowered by combining it with a gas stream obtained by expanding gas provided from the uncondensed gas stream obtained in step (i).