A cold model study was carried out of an internally circulating fluidized bed membrane reactor for hydrogen production by steam reforming. This configuration facilitates a novel process in which air is introduced for autothermal operation, while avoiding diluting the hydrogen in the gas stream by nitrogen. A column of diameter 230 mm and height 2.4 m contained a membrane box of square cross-section. Gas circulation was investigated by injecting helium tracer into the top of the bed above the membrane box and detecting its concentration in the annulus and lower membrane box by a thermal conductivity detector. Solids circulation was determined from the downward velocity of particles in the annulus. The major resistance to solids circulation was found to be at the passage connecting the outer downflow to the inner upflow compartment. A ring distributor helped overcome this resistance. (C) 2009 Elsevier Ltd. All rights reserved.