Chapter 3 - THE WATER IN BROWN COAL

Abstract

This chapter discusses the nature of water in brown coal. The coalification of brown coal process is accompanied by the elimination of water because of both the chemical changes associated with coalification and the physical consolidation of the deposit. This high moisture content critically impacts on virtually every facet of brown coal utilization. Thechapter discusses the problems associated with the determination of moisture content and moisture holding capacity, the factors influencing the variability of moisture content in Victorian brown coals, and the methods of moisture removal (drying). Early studies in Victoria on the brown coal-water system concentrated on the determination of the moisture content of the coal, the variation of moisture content through the Latrobe Valley deposits, and processes for the removal of the moisture. As the severity of drying increases, there is a continuum in the evolution of water from the coal, ranging from initially normal evaporation of free surface water to eventually the release of water formed during the thermal decomposition of oxygen-containing functional groups in the coal and water from the dehydration of the adventitious minerals in the coal. The equilibrium moisture content of brown coal at ambient humidity is in the relatively flat multilayer sorption section of the isotherm. Large variations in humidity are required to produce significant changes in the moisture content of the coal. The increase in the moisture content raises the temperature, due to the exothermic heat of condensation, and accelerates the rate of oxidation.