Heat Transfer Modeling and Self-Sustained Thermal Operation of a Pilot-Scale Rotary Kiln for Slow Pyrolysis of Poultry Litter

Abstract This study evaluated the slow pyrolysis of poultry litter in a pilot-scale continuous rotary kiln (350–400 kg/h input, 140–180 kg/h biochar output) operated in Asfan, Saudi Arabia. Phenomenological mathematical modeling, simulation, and sensitivity analysis were used, with the model solved numerically in Python and compared to operational monitoring data from the pilot plant. The results showed that the model successfully captured key thermal phenomena, including heat regeneration in the reactor's final section, predicting a peak wall temperature of 815 K, close to the experimental average of 835 K. However, the simulated biochar yield (30%) was lower than the experimental value (39.4%), primarily due to the use of kinetic parameters derived from wood pyrolysis, which do not account for the complex composition and catalytic minerals present in poultry litter. Parametric sensitivity analysis identified the supplied heat, inlet solids mass flowrate, and activation energy for char formation as the most influential parameters on temperature profiles and biochar yield. The study underscores the need for poultry litter-specific kinetic models, experimental validation with additional thermocouples, and implementation of multicomponent models to improve predictive accuracy, while also supporting the feasibility of using pyrolysis gases as an internal heat source.