Understanding Heat Transfer and the Role of Bed Hydrodynamics in High-Temperature Fluidized Beds

Abstract

A comprehensive understanding of heat transfer between the bed and immersed surfaces is critical for successfully designing and operating high-temperature gas–solid fluidized bed reactors. However, the impact of temperature on heat transfer, particularly in beds operating above 1000 °C, remains underexplored. This study investigates heat transfer between a fluidized bed and an immersed vertical surface over a temperature range of 300–1500 °C, with a focus on the relationship between heat transfer and bed hydrodynamics. The results indicate that below 1200 °C, the heat transfer coefficient (h₀) increases gradually with temperature, with radiative heat transfer contributing less than 18% to h₀. Above 1200 °C, h₀ exhibits an exponential increase for Al₂O₃ and ZrO₂ particles, while it decreases for MgO particles due to enhanced interparticle forces from particle softening and agglomeration. At 1500 °C, radiative heat transfer accounts for up to 30% of the total heat transfer. Additionally, smaller particles demonstrate higher h₀ but lower radiative contributions than larger particles. Increasing superficial gas velocity significantly reduces h₀ below 1200 °C but has minimal impact at higher temperatures. Larger beds reduce wall confinement effects, enhancing particle mixing and subsequently increasing h₀. A comparison of the experimental data with predictions from existing correlations reveals their inadequacy across the studied temperature range. To address this, a new empirical correlation is proposed to improve accuracy for predicting heat transfer in high-temperature fluidized beds.