A system for producing glass spheres in which the combustion air introduced into the furnace is preheated. The furnace has a shroud enclosing at least a portion of its outer surface, and ambient air is introduced to the space between the outer surface and the shroud by means of a fan generating a slight...http://www.google.se/patents/US4046548?utm_source=gb-gplus-sharePatent US4046548 - Apparatus for producing spherical particles
