Stable operating range and solids residence time of fine fluorite particles in the two-stage fluidized bed

[Display omitted] •The stable operation range of fine fluorite particles in two-stage fluidized bed.•The mean solids residence time of fine fluorite particles in two-stage fluidized bed.•The influence of particle elutriation rate in two-stage fludized bed.•the difference between straight downcomer and orifice downcomer in two-stage fluidized bed. Solids transmission behavior is essential for the design and optimization of the multi-stage fluidized bed. This work investigated the stable operation range and solids residence time of fine fluorite particles in a cold-model two-stage fluidized bed to reveal the transmission behavior of fine particles, and compared effects of different downcomers on orifice downcomer and straight downcomer. Results showed that fine cohesive particles were transferred as slugs for different the downcomer configuration. The operating limit increased with the increased feeding rate and the stable operating range in the bed with orifice downcomer was wider. Moreover, we evaluated the partial performance of the multistage fluidized bed as a reactor by calculating the average residence time of the particles (bed holdup/ solid mass flow rate). The average solid residence time changed exponentially or linearly under different operating conditions and is larger for orifice downcomer. The fitting models for prediction of solids residence time were established and the relative deviations were below 25%. The orifice downcomer was more suitable for the fluidization of fine cohesive particles in the multi-stage fluidized bed, because it can increase the residence time of the fluidized bed and has better operating flexibility.