cleaning machine the drier is indirectly heated with vapour or steam 20 a rotating drum may be employed the conditions in the drier are controlled via a microprocessor control an o2 measuring device inspires fresh air prior to the drying operation a system is passed to the n2 apparatus a flushing with n2 is carried out until the oxygen content drops below 6 another signal indicates readiness for operation in fig2 which shows a detail of the drier arrangement and n2 preparation the same reference numerals as in fig1 have been used for identical elements the drying drum 50 has been emphasized as the central element nitrogen generated from the air is injected into the drum of the drier 50 via the conduit 40 past a heating register 60 the still moist material is transferred from the cleaning machine 10 not illustrated here the heating to the aforementioned temperature takes place in the drum 50 the moisture and solvent are expelled 62 recycling is effected via a fan 64 the mixture flows on at 66 and enters an evaporator 68 the liquid n2 being supplied together with condensed water via 70 to a water separator 72 the condensate is removed via 22 the steam returns in the cycle at 20 to the heat register following the evaporator 68 a measuring conduit 44 branches off to an o2 analyzer 74 an o2 value of 6 is set in the drier the n2 apparatus 30 takes up.