Study on the drying characteristics of green pellets of ultrafine iron ore concentrate

Abstract

Ultrafine iron ore concentrate pose challenges like poor pellets formation performance, low-bursting temperature, and a complex drying thermal regime. To examine the drying characteristics of green pellets of ultrafine iron ore concentrate, we employed Weibull distribution function and Dincer model to fit and analyze the corresponding drying curve. The effects of drying temperature and air speed on the strength of dried pellets were also studied. Our findings reveal that the drying process of green pellets of ultrafine iron ore concentrate involves three stages: ascending speed, constant speed, and descending speed. As the drying temperature and air speed increase, the drying time decreases. The coefficient of determination R2 for the fitted Weibull distribution function model ranged from 0.995 to 0.998, while the R2 value for the Dincer model ranged from 0.990 to 0.996. Both fitted models align with experimental data and prove to be effective. According to the Bi values obtained through the Dincer model, raising the drying air speed in the initial stage and the drying air temperature in the subsequent stage of the drying system can efficiently remove moisture, reduce green pellets rupture risk, and maintain productivity. The moisture diffusion coefficient and convective mass transfer coefficient increase with rising temperature and air velocity, following the order of Deff > Dcal > D*eff as determined by the Weibull distribution function, Dincer model, and Fick's second law. Additionally, the activation energy value of ultrafine iron ore concentrate for drying derived from the Arrhenius formula is 4515.60 J/(mol?K). Notably, increasing drying temperature increases the strength of dried particles due to their more compact and dense internal structure. This study offers theoretical support for simulating the drying of green ultrafine iron ore concentrate pellets and provides guidelines for selecting diverse drying conditions and designing drying equipment.