Sticking Behavior of Pellets During Direct Reduction Based on Hydrogen Metallurgy: An Optimization Approach Using Response Surface Methodology

Sticking of pellets occurs in the direct reduction process of gas-based shaft furnace. This phenomenon has negative effects on the smooth flow of raw materials and continuous operation of production, leading to lower product quality and productivity. The objective of this study is to determine the optimal process conditions for direct reduction process with minimized sticking index (SI) and maximized metallization rate (MR) based on response surface method (RSM), through studying the effects of single and multiple factors during the reduction process on SI and MR of pellets. Based on the single factor of reduction experiment, the RSM and central composite design (CCD) were used to optimize SI and MR, and the experimental parameters included TiO2 addition, reduction temperature, reduction time, and load. The analysis of variance ( ANOVA) evaluation technique was used to analyze the fitted quadratic regression model and the significance of each item in the model, which clearly revealed the linear, interaction, and squared effects of each parameter. The optimum process parameters were as follows: the TiO2 addition was 3.28%, the reduction temperature was 1027.53 degrees C, the reduction time was 68.91 min, and the load was 0.40 kg/cm(2). The optimum responses corresponding to these optimized operating conditions were found as 19.57% (< 20%) and 90.26% (> 90%) for SI and MR, respectively. The optimized responses were validated experimentally at optimum experimental parameters and found to be within acceptable error levels.