Several pilot-plant furnaces, the shaft and the rotary type, were designed, constructed and used to sinter a series of granulated charges (coal dust, ashes) containing 4-6 or 7-11% combustibles. In the rotary cocurrent furnace the yield was 60 kg/h, fuel consumption 1 and 1.5 L fuel oil/30 kg granulate at roasting losses 11 and 7%, resp. Flue gases contained neither CO nor furanes s nor dioxins. With a hybrid construction and tests run in a furnace 1 m long, 0 450 mm, full autothermicity was achieved with a 6.3% loss granulate layer 225 mm high, temp., 1100 K, and flue gases 900 K. With the 9% loss granulate, the temps. were 1200 and 1000 K, resp. With 12% loss granulate, the temp. in the layer was 1300 K and operation was correct. The resulting aggregates had d. < 850 kg/m(3), suitable for light concrete, the strength corresponding to the 25 mark.