A triple-bed combined circulating fluidized bed (TBCFB) system, which is composed of a downer, a bubbling fluidized bed (BFB), and a riser, is proposed for the pyrolysis and gasification of coal and biomass. In order to effectively utilize the heat energy produced by the combustion of the char in the riser for the pyrolysis of coal/biomass in the downer and/or gasification of char in the BFB, a high solids mass flux and a large solids holdup are necessary. An analysis of the overall pressure balance around the TBCFB was presented for predicting the maximum achievable solid mass flux under given experimental conditions. The effects of solids inventory, particle physical properties, and gas seal structures on the solids mass flux and the solids holdup were discussed. A correlation for the prediction of solids mass flux in the range of 200-400 kg/m(2) s in the riser under operating conditions was developed based on experimental data from the literature and our laboratory. (C) 2010 Elsevier B.V. All rights reserved.