A self-designed internally circulating fluidized bed cold test apparatus was built to investigate the gas-solid flow characteristics in a new kind of internally circulating fluidized bed furnace. The test material was circulating ash from a power plant CFB boiler. Optical fiber probes and differential pressure transmitters were employed for the measurements. The particle internal circulation rate and the solids holdup in the upper space of the furnace were studied by changing the fluidization air velocity in the main chamber, the height of partition wall and the initial static bed height. The results showed that with the increase of fluidization air velocity in the main chamber, the particle internal circulation rate increased at first then decreased. Meanwhile, the particle internal circulation rate decreased with the increase of the partition wall height and increased with the increase of initial static bed height in the main chamber. The solids holdup in the upper space of the internally CFB cold test apparatus was 1-4% of that in the normal CFB cold test apparatus. The proportion of particle external circulation rate was relatively low in the circulating system. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.