Minimum fluidization velocity and reduction behavior of combusted iron powder in a fluidized bed

The fluidization and reduction behavior of micron-sized iron oxide powder, produced by iron combustion, is studied in a lab-scale cylindrical fluidized bed. The minimum fluidization velocity umf is found to stabilize above normalized static bed heights of 0.5 H/D (static bed height divided by the bed diameter). umf is measured as a function of temperature between 280 and 860 K for both H2 and N2 as fluidizing gas. The experimental results start to deviate from the Ergun correlation at temperatures above 560 K, both for N2 and H2. A new correlation, taking the cohesive inter-particle solid bridge force into account, is proposed in this work to predict the minimum fluidization velocity at high temperature. Reduction experiments are carried out for a total time of 5 h at constant excess velocity with 50, 75 and 100 vol% of H2 and temperatures between 623 and 823 K. Gradual defluidization occurs when the operating temperature exceeds 800 K. A maximum reduction degree of 61% is obtained at 807 K and 100 vol% H2.

Automated summary

In this study, the fluidization and reduction behavior of micron-sized iron oxide powder produced by iron combustion were investigated in a lab-scale cylindrical fluidized bed. The minimum fluidization velocity (umf) was found to stabilize above a normalized static bed height of 0.5 H/D. Experimental results deviated from the Ergun correlation at temperatures above 560 K, prompting the proposal of a new correlation that takes cohesive inter-particle solid bridge force into account. Reduction experiments revealed gradual defluidization at temperatures exceeding 800 K, with a maximum reduction degree of 61% achieved at 807 K and 100 vol% H2.