Process and installation for the cryogenic purification of hydrogen

In an installation for the cryogenic purification of impure hydrogen, comprising:

• a heat exchange line having a warm end and a cold end, at least one phase separator at the cold end of said heat exchange line for separating a liquid phase from a gas phase, a hydrogen expansion turbine having an input, a labyrinthine seal, a rotor, a stator and gas bearings, means for circulating a current of impure hydrogen in one direction in the heat exchange line, means for expanding to a low pressure the liquid phase from the phase separator, means for adding hydrogen under the low pressure to a residual fraction resulting from the expansion, and means to cause to circulate a mixture obtained under the low pressure in countercurrent to the impure hydrogen;
• the improvement wherein the heat exchange line comprises passages for cooling the gas leaving the bearings of the turbine, said passages being connected to the input of the turbine at the cold end of the heat exchange line and means for withdrawing a leakage flow of hydrogen from the labyrinthine seal of the turbine, under a pressure slightly less than an interstitial pressure Pi which prevails between the rotor and the stator of said turbine.