Preparation and rheology of alcohol-water char and biochar slurry fuel

Ethanol and methanol were added to increase the volatile content of the aqueous low ash and low sulphur, lignite and mallee char slurry fuel. Lignite char slurries were prepared in aqueous solutions of ethanol with content ranging from 5 to 50wt% ethanol. The yield stress of the slurry was measured as function of solids concentration. A carboxylate acid dispersant was found to be effective in dispersing char particles in alcohol-water mixtures, especially those slurries with low alcohol content. This is indicated by the maximum solids loading achieved decreasing with alcohol content in the solution. This maximum loading is 65wt% for 100% water and reduced to 57wt% for 50:50% water-ethanol mixture. This trend was unchanged when the density difference between the solutions was taken into consideration by using volume fraction of solids as concentration in the plot. Without the dispersant, the maximum loading obtained is much lower. Viscometry results showed dilatant flow behaviour for the highest loaded slurry and Newtonian behaviour for dilute slurries. Lignite char slurries with of a top size of less than 32 micron were also prepared at concentration up to 60 wt% solids in 40wt% ethanol and methanol solution with the aid of 1wt% D102 dispersant. These slurries are close to meeting the specifications required as a diesel fuel replacement. A relatively low solids loading of less than 50wt% was obtained with fine Mallee char slurry prepared in 40wt% alcohol solution.