Bed-to-surface heat transfer in conical spouted beds of biomass–sand mixtures

• Wall-to-bed and bed-to-spout heat transfer rates have been determined.
• Effects of superficial velocity on bed-to-surface heat transfer have been studied.
• Experiments were carried out at three superficial velocities with sawdust and sand.
• The heat transfer coefficient values are favorable enough for attaining high heating rates in combustion.

The effects of superficial gas velocity, bed composition and other operating parameters on bed hydrodynamics and bed-to-surface heat transfer were investigated the influence of bed height and gas velocity sawdust, sand and 30–70, 40–60 and 50–50 mixtures of biomass and sand in a conical spouted bed. Experiments were performed at minimum spouting velocity and 10 and 20% above this. At each superficial velocity, experiments were conducted at three heights, 0.1, 0.2 and 0.3 m above the inlet. A specially designed heat transfer probe measured the bed-to-surface heat transfer coefficient. The heat transfer coefficient increased from the wall to the spout, and also was observed to increase with increasing percentage of biomass in the blend. The experimental results are compared with published results, showing good agreement with the influence of height of the bed and gas velocity.

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