Calibration and Extension of a Coal char Annealing Model

Researchers have proposed various models for coal char thermal deactivation over the past 25 years. Thermal deactivation is an umbrella term to describe the numerous physical and chemical changes that alter coal reactivity as it transitions from raw coal to young char to annealed char. This collection of changes (especially altered char surface area, ash fusion, and carbon graphitization) is profoundly influenced by factors such as particle heating rate, peak particle temperature, and coal type. Current annealing models essentially collect the entire umbrella of changes in a distributed activation energy, and compute a reduced char activity based on the temperature history of the particle. Since the heating rate, peak temperature, and coal type heavily influence char morphology and chemical structure, the distribution of the activation energies for various deactivation processes will change with these three factors. The current work proposes deactivation model extensions to incorporate effects of coal type, heating rate, and peak particle temperature into the form of the distributed activation energy curve. Each proposed new form will be calibrated with a broad selection of data from the literature, and the uncertainty in the calibrated model will be calculated using the Gaussian Process Models for Simulation Analysis (GPMSA) package developed at Los Alamos National Laboratory. This package uses a Bayesian framework to create posterior probability distributions on the deactivation model predictions.