Fluidized beds are used for a variety of processes such as food, pharmaceutical, petrochemical and energy production. Supersonic gas injection nozzles are used to grind particles in fluidized beds. For example, in the Fluid Coking process, which uses thermal cracking reactions to upgrade heavy oil, supersonic nozzles inject steam to control coke particle size. Maintaining a high attrition rate with a lower steam flowrate would reduce energy consumption, increase reactor throughput. and reduce sour wastewater production. The purpose of the present research is to study particle attrition with supersonic convergent-divergent nozzles in a fluidized bed at high temperatures, under conditions such as those encountered in the Fluid Coking process. According to the experimental results, the grinding efficiency is significantly improved by increasing fluidized bed temperature, attrition gas properties, or nozzle size. The experimental data further suggest that particle fragmentation is the dominant attrition process when using supersonic nozzles in a hot fluidized bed. (C) 2012 Elsevier B.V. All rights reserved.