An investigation into the moisture absorption properties of thermally dried South African fine coal

摘要

The aim of this research was to study the absorption characteristics of thermally dried fine coal from South African collieries. After milling to -150 mu m and pressure filtration, the samples were subjected to either air drying or thermal drying at 150 deg C. The samples were then put into a climate box at 28 deg C and at three different relative humidity levels, namely 30, 60 and 94 per cent. It was found that the equilibrium moisture content of thermally dried coal at a specific relative humidity was lower than that of air dried coal. The relationship between the equilibrium moisture content and relative humidity is described by 1-RH=exp (-KTM_e~n). There was no relationship between the volatile matter content and equilibrium moisture content, but there was an increase in the equilibrium moisture content of the coal with an increase in mineral content. The moisture uptake rate increased with an increase in temperature and a decrease in particle size. A model is discussed that fitted the experimental data and gave a good prediction for changes in the conditions. There was no evidence of greater moisture absorption by thermally dried coal.