Blast cap is the key component of air distributor in circulating fluidized bed (CFB) boilers. Its configuration and performance affects the fluidization quality of the bed, as well as the boiler performance. With the advantage of controlling the jet penetration characteristics and the resistance coefficient individually, bell type blast cap has been widely applied in big-scale utility CFB boilers. Moreover, the inner circuitous gas pass of the bell-type blast cap is able to prevent the bed material from flowing backward into the air chamber effectively, and its tube shield is also convenient to be maintained and replaced. Consequently, the bell-type blast cap is also fit for the small scale industrial CFB boilers with lower operation and maintenance levels in spite of higher manufacturing cost. At present, bell type blast cap is mainly applied in the large scale utility CFB boilers, seldom employed in the small scale industrial CFB boilers with lower bed pressure drop. In the study, aim to acquire favorable fluidization quality and reasonable pressure drop of the bed of small scale industrial CFB boiler, the air jet penetration characteristics of the bell type blast cap were investigated in static beds composed of two typical solids in CFB individually, and the impacts of the inner configuration on blast cap's resistance characteristics were studied via numerical simulation. The detailed design principle and approach of bell type blast cap was proposed finally based on the study results. (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.