Pressures in a circulation loop under various conditions were measured in a cold mode (a riser of 35 mm I.D. x 5450 mm high and a fluidized reactor of 160 mm I.D. x 1250 mm high) with particles of mean diameter of 78 mum, and bulk, and particle densities of 1.03, and 1.90 g/cm(3), respectively, Solid circulation rates were measured with a load cell hopper. The particle hold-ups at various sections were analyzed from differential pressure data. The voidage in the riser reactor increases with the increase in gas velocity, even though the solid circulation rate increases with gas velocity. The solid circulation rate increases to a maximum with gas velocity at the riser, and levels off because the non-mechanical valve adopts the role of solid rate determining step in the circulation loop of the system. Particle hold-up in the riser reaction zone increases by using an underflow standpipe loopseal below the fluidized reactor instead of an overflow standpipe loopseal.