Surface combustion

Abstract

Development of new energy-efficient high-temperature sintering furnaces is one of the key factors for cost reduction of refractory ceramic manufacturing. In this paper, a sintering furnace in which the volume of the furnace chamber is completely filled with a packed bed of ceramic spheres, and the energy source is the premixed combustion of natural gas with atmospheric air and oxygen has been experimentally studied. The furnace design allows the use of two combustion modes: (i) filtration combustion, when the narrow reaction front (combustion wave) freely propagates through the packed bed, (ii) jet-stabilized combustion when the reaction front is stabilized near gas inlet nozzles used for supplying the fresh mixture into the packed bed. Experimental analysis of both combustion modes was performed in the ranges of specific fuel flow rate from 7·10–3 to 107·10–3 Nm3·s–1/m2, firing rate from 244 to 3724 kW/m2, fuel-to-oxidizer ratio from 0.40 to 3.30, oxygen content in the oxidizer from 21 to 30 vol%. In these ranges, the temperature of the packed bed can be controlled within 1230–2220 K. Test sintering of samples pressed from powders of MgO and Al2O3 was carried out at 2170 K. It was found that the filtration combustion mode is effective for sintering parts with a characteristic size of up to 10 mm, and the packed bed can be completely formed of samples to be sintered. Jet-stabilized combustion mode is effective for sintering large pieces. In such a case, submerging samples within the packed bed enables double fuel saving compared to the stacking of samples in a furnace chamber of a conventional free-volume design. The new furnace based on the principles of premixed combustion in porous inert media can be in demand for small-scale production of ceramic parts.