Waste heat recovery analysis in a vertical riser with air–sand: hydrodynamics and heat transfer

Abstract

In the current global endeavor of energy conservation, waste heat recovery is a key contributor and deserves more focused attention. Process industries demand high energy inputs and often generate high-temperature exit gases, which can potentially be considered as secondary energy sources. If such waste heat is recovered, considerable savings in the net energy demand is possible. This report, based on this objective, details the outcome of an experimental study conducted in a vertical riser where solid particles, through a co-current contact with hot air, recover the energy content of the gas. Fabricated experimental setup is a prototype of suspension preheater (riser–cyclone combination) used in a modern-day cement industry. Data relevant to hydrodynamic and heat transfer patterns are collected as not much information is available in the literature on these aspects. Empirical correlations for acceleration length and heat transfer coefficient in dimensionless form, are reported and are recommended for not only cement but for diverse other industries, where waste heat recovery is possible.