as indicated by the arrows and exits the drying hopper 1 through an exit air line 8 emanating from the lid of the drying hopper 1 the moisture laden exit air from drying hopper 1 is conducted through exit air line 8 to a drying air dryer generally designated by reference numeral 10 in which the entrained moisture is extracted from the exit air the exit air from line 8 is thereby conveyed to drying air dryer 10 via a first solid filter 12 a flap valve 14 and the intake line 16 of a fan 18 whose outlet conduit 20 leads to an outer annular chamber 22 of drying vessel 24 the moist exit air flows radially through an adsorption agent 26 which is contained in the drying vessel 24 and which extracts the moisture from the exit air adsorption agent 26 may take the form of silica gel and or a molecular sieve the dried air flows from the adsorption agent 26 into a central duct 28 of the drying vessel 24 and then passes through a flap valve 29 into an outlet line 30 of the drying air dryer 10 in this embodiment of the invention drying air dryer 10 serves as the source of flowing gas having a fluctuating moisture content outlet line 30 leads into a chamber 32 which is completely filled with a moisture adsorption medium such as a molecular sieve from chamber 32 a line 34 leads through heater 7 to the drying air line 5 outside the drying vessel 24 central duct 28 has a branch line 40 along which an additional flap valve 42 and a solid filter 44 are arranged and which.