Coalification model

A series of low-rank materials, ranging from biomass waste to subbituminous coal, were subjected to hydrothermal coalification, i.e. heat treatment in an autoclave with water. The results, together with relevant literature data, cover a wide range of reaction conditions: temperatures from 120° to 390° and residence periods from 1 min to 6 months. Using overall kinetics, the progress of hydrothermal coalification in terms of the evolution of carbon dioxide as a function of the conditions has been expressed in a simple model. Low-rank materials can be described in terms of properties that can be gathered into general relations which hold over wide ranges. Over the range from biomass to subbituminous coal, where coalification mainly implies the evolution of water and carbon dioxide, the conversion model allows the prediction of the enrichment of a material on the basis of feedstock properties and the conditions applied.