The majority of today's coal-water mixture(CWM) technology has been developed to prepare a high energy density liquid fuel from bituminous coals. Low rank coals such as subbituminous coal and lignite, mostly because of their high inherent moisture contents, produce a lower energy density slurry fuel and cannot be economically utilized. However, low rank coals have advantages such as low sulfur, low ash and high volatile matter content. The hot water drying process is one method for preparing concentrated coal-water fuel slurries with reduction of a inherent moisture under high temperature and pressure. In this process, the physical and chemical changes such as decarboxylation, carbonization, and tar coating occur. These produce a coal product which is resistant to moisture reabsorption.
In this study, the rheological properties of HWD treated low rank coal-water mixture were investigated to observe the effect of HWD process. FT-IR spectrum and ζ-potential were measured to know the surface properties of HWD treated low rank coals. The analysis of FT-IR spectra and the value of ζ-potential of HWD treated low rank coal surface showed that the hydrophilic carboxyl group was dissolved and the anionic concentration of coal surface was increased. Also, as the process temperature was increased, the extent of improvement of surface properties was increased. This yields a product which has a lower viscosity and better stability.
