son to other technologies. Experiences with a
sawdust ®lter after a concurrent gasi®er showed
that cleaning intervals are in the range of 200 h
of operation. The cleaning requires very rigid
safety precautions since the tar-laden sawdust is
extremely toxic. The sawdust must be treated as
hazardous waste. Sand bed ®lter cleaning is
regarded less critical than sawdust ®lter cleaning.