Effect of scale-up of lower and middle splash region on heat transfer characteristics of circulating fluidized bed risers

摘要

In the present work, a comparative study of steady-state wall-to-bed heat transfer was conducted along the lower and middle splash region located in the riser of height 2.85 m of three different circulating fluidized beds (CFBs) with bed cross-sections of 0.15 m x 0.15 m, 0.20 m × 0.20 m, and 0.25 m × 0.25 m. Experiments were conducted under similar operating conditions on above-mentioned three CFB set-ups using the same weight of sand per unit area of the distributor plate, non-dimensional superficial velocity (U*), heat flux, and sand particle size. Further, experiments were conducted on all the three CFB set-ups for five different non-dimensional air velocities (U* = 5,5.5,6,6.6, and 8) and two different weights of sand inventory per unit area of the distributor plate with average particle size of 460 μm. Bed temperature distributions across the lower and middle splash regions were measured and compared for the three bed cross-sections. Axial distributions of heat transfer coefficient along the height of lower and middle splash region of risers were evaluated and compared for the three bed cross-sections. The effect of superficial velocity, sand inventory, and bed cross-section on temperature and heat transfer coefficient was investigated. Based on the present study, correlations were developed for the bed Nusselt number as a function of various non-dimensional numbers for lower and middle splash regions of the riser. The non-dimensional area parameter (A*) was found to be a significant number. Predictions of these correlations are in agreement (±16 per cent) with experimental data.