Regeneration of iron fuel in fluidized beds, Part I: Defluidization experiments and theoretical prediction model

Hydrogen-based direct reduction of iron oxide powder in gas-fluidized beds has become an emerging technology. Agglomeration of fine powder at elevated temperatures is however one key issue hindering the technological development. To obtain better knowledge of the high-temperature agglomeration mechanism, the (de-)fluidization behavior of micron-sized combusted iron particles is experimentally studied in this Part I. Effects of various operating and material variables (temperature, gas flow rate, and particle size) on the fluidization and agglomeration behavior are investigated. Different fluidization regimes (e.g. stable fluidization, agglomerating fluidization, fast defluidization) are categorized based on the experimental results. A theoretical model based on the force balance is developed to predict the regime boundaries of fluidization. The obtained knowledge is applied for experimental design of the hydrogen-based iron direct reduction process in Part II.