Hydrothermal Treatment of Low Rank Coal for Making High Solid Loading and Stable Coal Water Slurries

Abstract

The objective of this research is to understand the effect of hydrothermal dewatering (HTD) on surface properties, stability and rheological behavior of lignite water slurry (LWS). The surface forces between coal particles are found to be attractive after HTD, which is proven by contact angle and zeta potential measurement, FTIR characterizations, and modeling using extended DLVO theory. The attractive particle network could be formed in highly concentrated slurry to increase LWS stability after HTD as shown by stability measurements. The rheological studies show that HTD treated LWS exhibits lower shear viscosity at 100 s-1 than raw LWS at the same mass fraction, which is probably attributed to the decrease of effective volume of HTD coal particle caused by the permanent reduction of both bound and non-freezable water in lignite. The maximum lignite concentration can reach 62 wt % by HTD at 300 °C and adding 1.0 w t% db (dry base) of polycarboxylate ether (PCE).