Light expanded clay and slate aggregates mfr. - in which surplus hot air from the cooling drum is fed directly to the pre-heater

A light expanded clay or slate aggregates and similar blown materials are mfd. in a plant consisting of three rotary drums arranged in sequence for pre-heating expanding and cooling of the initial granulate in counter current to gases flowing in the reverse direction, i.e. from the cooler to the furnace and then to the pre-heater. A gas pipe is used which projects into the cooler. The gas pipe (for air) pref. extends through more than half the length of the cooling drum and is used either directly or indirectly to supply air heated by the cooling aggregate via a pipe which by-passes the furnace and carries the hot air into the pre-heating drum. Maximum thermal efficiency is obtd. by using all the heat in the cooling aggregate. Normally, the amt. of air used in the cooler is far greater than the air needed in the furnace; in this invention, the surplus hot air is fed to the preheater via a by-pass.