Intensification of hydrodynamics and heat transfer characteristics of coal-char-gas flow in a high solids-flux downer with swirling blade nozzle

Abstract

Achieving high-density particle operation and obtaining uniform inlet particle distribution in the downer is the key to improving pyrolysis yield. In this work, a multifluid framework was developed to systematically study the hydrodynamics and heat transfer characteristics of a downer with swirling blade nozzle (DSBN). A heat transfer model that considers gas-solid convective, solid-solid collision, and thermal radiation was established. And a swirling blade enhancement factor (β) was defined to quantify the flow mechanism and heat transfer characteristics of coal-char particles. Results indicate that SBN can shorten the time for flow to reach stability by 33.3%. The βCV on coal and char can reach a maximum of 87.6%, enhancing the uniformity of particles velocity flow field. Regarding heat transfer characteristics, the stable temperature of coal in DSBN is higher than conventional downer (CD), βU on coal and char can reach 6.64% and 1.69%, respectively. The optimal strengthening effect of SBN on the char-coal mixing is concentrated at the inlet, with a maximum βIM of 70.17%. Also, compared to the CD, coal-gas and char-gas heat transfer coefficients in the DSBN have increased by 147.3% and 31.5%, respectively, and the coal-char thermal conductivity coefficient has increased by 77.8%.