In the present study, a novel fluidized bed with the internal separator was developed to achieve the self-sustained preheating of pulverized coal. In the developed internal fluidized bed combustor (IFBC), the pulverized coal could be heated up to 850 degrees C-950 degrees C by its partial combustion. The hot pulverized coal was fed into the furnace of pulverized coal (PC) boiler for complete combustion. Combining PC boiler with the IFBC could achieve easer ignition and reduce nitrogen oxides emission for the low-rank coal. To verify the feasibility and optimize the design and operation of the IFBC system, the cold experiments were performed in a small-scale IFBC for continuous feeding with Group A particles. The effect of superficial air velocity on the operational performance and gas-solid flow characteristics in the IFBC was investigated by electrical capacitance tomography, pressure measurement as well as visual observation. The experiments showed that, the IFBC could operate stably in the case of continuous feeding when superficial air velocity ranged from 1.5 m/s to 2.25 m/s, in which the material output rate was steady, nearly equal to the material input rate. With the increase in the superficial air velocity, more solids remained in the standpipe and the discharge pattern of standpipe shifted from the continuous discharge to the intermittent discharge, thereby resulting in the unstable operation. The solids intermittent dump referred to a typical feature of the intermittent discharge, characterized by a sawtooth function. (C) 2019 Elsevier B.V. All rights reserved.