A Study of Selected Phenomena Observed During Rotary Kiln Incineration.

TLDR: In this article, a simulation of the Dow rotary kiln incinerator is used to predict the species, temperature, and flow field during baseline operation with no waste combustion, and a simple model is developed that correlates the mixing time constant to bed turnover rate.

Abstract: A comprehensive research program is underway at LSU with the ultimate goal of improved understanding and predictive capability for the performance of rotary kiln incinerators. In an extensive experimental study, packs containing toluene-contaminated clay sorbent are batch-fed into the field-scale rotary kiln incinerator of the Louisiana Division of Dow Chemical USA. Water cooled probes are used to obtain continuously gas temperatures and species concentrations within the kiln and afterburner, and existing facility instruments are also monitored. The kiln rotation rate is varied and turbulence air (air injected into the kiln to improve mixing) is added or turned off. Conditions at the kiln exit are found to be highly stratified. Species data from the afterburner and stack are used to determine the toluene evolution rate, which appears to be strongly influenced by bed motion regime but not kiln rotation rate or turbulence air. Mass balances are performed on the toluene, with good results. A numerical model of the Dow rotary kiln incinerator is formulated to predict the species, temperature, and flow field during baseline operation with no waste combustion. This simplified model shows the general features and trends at locations where experimental measurements are not feasible. The model is used in a parametric study to determine the influence of turbulence air addition and the importance o f buoyancy. The model is developed using the commercially available finite difference software, FLUENT, and solved on a 486 PC computer. The numerical results agree surprisingly well with the experimental data, offering a clearer picture of the buoyant flow field in the kiln. A pilot-scale rotary kiln simulator at The University of Utah is used to make experimental measurements of the thermal response of solids charged onto a preexisting bed of hot solids. Time constants for solids mixing are extracted from the measurements, and a simple model is developed that correlates the mixing time constant to bed turnover rate. The use of this correlation is then demonstrated in predicting the thermal history of a fresh charge of solids as it mixes with hot solids in a rotary kiln.