Effect of pellet reduction swelling on burden movement in shaft furnace by DEM simulation

Compared with the traditional blast furnace, the direct reduction shaft furnace boasts distinct advantages such as a short process flow, low energy consumption, and low carbon emissions, thus showing broad prospects against the background of the "dual carbon" goals. In this study, a scaled-down simulation model with a ratio of 1:5 was established based on a domestically developed hydrogen-based shaft furnace independently designed by an enterprise. Key input parameters like particle flow velocity in the model were determined in accordance with the Froude number, aiming to investigate the influence of the reduction swelling behavior of pellet ores inside the gasbased shaft furnace on particle flow. This research is intended to provide a theoretical basis for optimizing shaft furnace operation, suppressing abnormal swelling, and improving reduction efficiency. By analyzing the changes in particle flow pattern, velocity distribution, contact force chain, and void fraction distribution, the influence mechanism of pellet reduction swelling on the particle movement behavior inside the furnace was revealed. The results indicate that the reduction swelling of pellets does not alter the overall "V" shape flow pattern, but significantly enhances the aggregation effect of particles in the central region, and this enhancement becomes more pronounced with the increase in swelling rate. Under the condition of similar flow velocities, the particle movement exhibits a distinct vertical stratification characteristic, with the flow velocity in the bottom cone region showing a particularly prominent increase. Contact force analysis demonstrates that the stress distribution inside the furnace is extremely uneven under the pellet swelling condition, and high stress concentration occurs in the conical region, which is likely to aggravate equipment wear. The void fraction decreases along the height direction of the bed; under the working conditions where the pellet swelling rates are 6% and 12%, the average voidage at the bottom decrease to 35% and 37%, respectively, which may affect the gas flow resistance and the uniformity of reducing gas distribution. This study clarifies the key influence of pellet reduction swelling on the movement characteristics of pellets and provides guidance for the process optimization and design of shaft furnaces.