Process and apparatus for separating off particulate impurities from a flowable medium

In a housing (1) which is provided with a crude gas inlet nozzle (2) and a clean gas outlet nozzle (7) a gas-permeable drum (3) is arranged so as to rotate. Inside the drum (3) there is situated a granular flowable filter material which forms a continuous layer (5) of uniform thickness on the drum interior wall at a first drum rotary speed (n1). At the same time, on the outer circumferential surface of the drum (3) a corotating gas roller (W) forms, which acts as a cyclone preseparater. The crude gas thus prepurified flows through the drum from the outside to the inside and gives up the relatively fine dust particles to the filter material. To clean the dust-laden filter material, the rotary speed of the drum is reduced (n2) to the extent that the filter material rolls off from the interior surface of the drum, the flushing gas then flowing through the drum from the inside to the outside entraining the dust detaching from the filter material. Advantages in comparison with conventional design: simple, compact and cost-effective construction, in particular by dispensing with the complex cyclone preseparater including its auxiliary units, intensive cleaning of the filter material and accordingly short cleaning times, overall reduction of the energy consumption by decreasing the resistances to flow through.