A novel force balance model for predicting defluidization of ilmenite in a fluidized bed reactor

Ilmenite particles are readily defluidized when they are reduced in a fluidized bed reactor because nano-micro iron nuclei that precipitate on the particle surface are adhesive and tend to aggregate. We propose herein a novel force balance model with which to predict defluidization phenomena. This model is based on the particle cohesion force comprising the sum of the cohesion forces for surface asperities. As the surface coverage of iron particles increases with the extent of reduction, the cohesion forces of the particles gradually increase and eventually trigger defluidization. The surface coverage predicted by the model agrees well with experimental results for 88.4 - 154.7 mu m particles and the temperature range 700 - 850 degrees C. The new force balance model reveals that particle size, sphericity, and temperature play key roles in defluidization of ilmenite during reduction. Defluidization occurs readily for fine and irregular particles, especially at high temperatures. Our model combines asperity, surface coverage, and particle sphericity to make a more general prediction.