Prediction of self-heating in detergent powders for application to spray dryer wall accumulations

Abstract

During the spray drying of detergent formulations, powder can accumulate on the inner walls of the spray drying tower. Under certain conditions, when the accumulations are large enough, self-heating can occur. This leads to unwanted charring and in severe cases to thermal runaway. In this study, basket heating methods, namely the steady-state approach and cross-point temperature method, were used to estimate the zero-order kinetics of the self-heating reaction of a typical detergent formulation. It was found that the resulting kinetics of these two methods were not in agreement, with this being attributed to the cross-point temperature method’s sensitivity to errors. The estimated kinetics were used in a 2D-axisymmetric transient model of heat transfer within an oven heated basket of detergent powder. Temperature-time profiles, and critical ambient temperatures, predicted by the model agreed well with experimental measurements. The model was also used to explore the value of using nth-order kinetics that were estimated using a thermogravimetric measurement technique. Theses kinetic showed no benefit over the zero-order kinetics and introduced unnecessary complexity. Future work will see this model and the insights gained applied to the problem of modeling self-heating in spray dryer wall accumulations.