A method of operating a fluidized bed deposition reactor to provide top removal of granular material, including production product is set forth. The vertical generally cylindrical reactor has at least one gas inlet at the lower end, at least one gas and solids outlet at the upper end and a gas/granular product separator connected to the gas and solids outlet. A heated reaction zone located in the lower portion of the reactor includes a fluidized bed; the bed being fluidized to establish a bubbling fluidized bed with a defined stable height. A disengaging space is provided above the stable bed height. A reaction gas is added to the bottom of the reactor, the reaction gas depositing a reaction product coating on the granular particles, the coating being abraded off the granules. The combined flow rate of the fluidizing gas and the reaction gas is adjusted so that a majority of the granular particles are retained in the reactor while maintaining bubbling. The height of the bed is increased and the disengaging height above the bed is decreased until the bursting of bubbles near the surface of the bed throws granular particles through the gas and solids outlet to the gas/granular product separator. The flow rates of the gases are controlled to maintain a balance between particles removed by the separator and the average rate of granular particle size increase as adjusted for attrition.