A thermally efficient process for the expansion of perlite ore is described. The inlet port and burner of a perlite expansion chamber (preferably a vertical expander) are enclosed such that no ambient air can enter the chamber. Air and fuel are metered to the burner with the amount of air being controlled...http://www.google.se/patents/US4347155?utm_source=gb-gplus-sharePatent US4347155 - Energy efficient perlite expansion process
