The state of development of multilayer sand bed filters

The state of development of multilayer sand bed filters may be described as follows: 1) Sand bed filters are generally suitable for the filtration of aggressive aerosols, in particular in cases of additional thermal loads, pressure peaks (fire safety, earthquakes). 2) Sand bed filters permit high flow rates, GfK filters (GfK = Gesellschaft fuer Kernforschung) reach 10 m3/min x m2 with charges of more than 1 kg/m2 and a separating efficiency > 99%. (use as pre-filters for the separation of large amounts of aerosols). 3) With proper optimization, the separating efficiency is better than that of class S filters (99.97%), while no significant reduction of the charge is required. 4) Exchange of sand bed filters is possible with a suitable vertical arrangement of the sand layers. 5) Sand bed filters may be combined with class S filters. The experience so far with sand bed filters was gained on the basis of experiments with aerosols from metal combustion. (orig./HP)