On the basis of the physical and chemical performance of Huadian oil shale and the design experience of Huadian 65 t/h oil shale-fired circulating fluidized bed (CFB) boiler operation, this paper introduces several main characteristics of oil shale, such as platy structure, high volatile and Ca/S content, and low ignition temperature, which are relevant to the design of CFB boiler, and analyses key design technologies of large-scale oil shale-fired circulating fluidized bed boiler. The design principles of large-scale oil shale-fired CFB boiler are suggested: (1) to adopt a II-shape configuration natural circulation mode with medium-temperature cyclone with downward gas exhaust, reliable antiwear technology and self-desulfurization technology; (2) to determine a circulating ratio of 6, hot state superficial air velocity of 5-6 m/s. combustion portion of about 0.5-0.6 in dense phase zone, and air velocity at the nozzle hole of air cap of 50-60 m/s; (3) to adopt an igniting system with hot gas generator below distributor plate and oil guns as auxiliary ignition device above distributor plate, and fluidized bed ash cooler retrieving the heat taken by hot slag. Lastly, the design scheme of 420 t/h superhigh pressure oil shale-fired CFB boiler is put forward and the general configuration and technical data are given at the end of this paper. (c) 2005 Elsevier B.V. All rights reserved.