Heat convection and radiation in flighted rotary kilns: A minimal model

TL;DR

This paper introduces a minimal, yet effective, model for heat transfer in flighted rotary kilns, capturing key experimental behaviors and enabling optimization of kiln length through a new efficiency criterion.

Contribution

The study presents a simplified heat transfer model that accurately describes temperature variations and includes radiation effects, offering a new approach for kiln design optimization.

Findings

Model predicts exponential temperature variations without radiation.

With radiation, temperature profiles fit stretched exponentials.

Proposes an efficiency criterion for system length optimization.

Abstract

We propose a minimal model aiming to describe heat transfer between particles (i.e. grains) and gases in a model of flighted rotary kilns. It considers a channel in which a convective gas interacts with a granular suspension and a granular bed. Despite its simplicity it captures the main experimental findings in the case of dilute suspension of heavy grains typical of what can be observed in many industrial rotary kilns. Energy balance between each phase takes into account the main heat transfer mechanisms between the transverse granular motion and the convective gas. In the absence of radiation heat transfer, the model predicts exponential variations of the temperatures characterized by a length which depends on the granular and gas heat flow rates as well as on the exchange areas. When radiation is taken into account, the model can be solved numerically. For this case, the temperature variations can be fitted by stretched exponentials whose parameters are found to be independent of the studied phases. Finally, an efficiency criterion is proposed to optimize the length of the system.