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 are not used for CWM because their high inherent moisture contents produce a lower energy density slurry fuel.
However, low rank coals still 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 decreasing of pore volume occur.
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 contact angle were measured to know the surface properties of HWD treated low rank coals. The analysis of FT-IR spectra and the value of contact angle of HWD treated low rank coal surface showed that the hydrophilic carboxyl group was dissolved and the inherent moisture was removed. So the hydrophobicity of coals was increased by HWD treatments. The ultimate analysis says that the oxygen consisting of hydrophilic functional group(carboxyl, hydroxyl group) was decreased. Also, the reduction of pore volume and pore area was resistant to moisture reabsorption. As the process temperature was increased, the extent of improvement of surface properties was increased.
