Conical spouted bed combustor for clean valorization of sludge wastes from paper industry to generate energy

•Conical spouted bed combustor is suitable for clean valorization of sludge wastes.•Wide stable operating range of sludge wastes with inert material (sand).•Required spouting gas flow increases with particle size and inlet gas temperature.•Combustion with sand allows to operate at minimum temperature of 500°C.•Conical spouted bed combustor is highly efficient to obtain energy from sludge. Clean technology of spouted bed is applied to paper industry wastes for energy valorization of de-inking sludge by combustion in a temperature range from 500 to 700°C. The stable operating conditions for beds of different types of inert material (silica sand) have been tested in spouting regime over a wide range of operating conditions. The radial and axial temperature profiles of sand beds have been measured to improve the combustion efficiency of wastes. Thereafter, that sand providing the higher bed temperature has been applied as the fluidization material for combustion of papermaking sludge using a mass ratio of 2:1 (dry basis). The optimal conditions for the inlet air flow rate and temperature have been determined experimentally by maximizing the combustion efficiency and minimizing the amount of volatile compounds in the flue gas.