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Monday, 17 October 2016
An experimental study of rheological properties and stability characteristics of biochar-glycerol-water slurry fuels
Centre for Energy (M473), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
Received 21 May 2016. Revised 26 July 2016. Accepted 26 July 2016. Available online 5 August 2016.
Biochar-glycerol-water slurries with desirable rheological properties were prepared.
Yield stress and viscosity increased as glycerol content increased.
Slurry fuels became more shear-thinning with higher glycerol content.
Slurry fuels became more stable with higher glycerol content.
The rheological behaviour and stability characteristics of biochar-glycerol-water slurry fuels were experimentally investigated, emphasising the effect of glycerol addition. A pine sawdust biochar with a size fraction of < 32 μm and a median particle size (D50) of approximately 12 μm was used. A biochar-glycerol-water slurry fuel was prepared by dispersing biochar particles in a premixed glycerol/water solution as the suspending medium with glycerol content varying from 0 to 100 wt%. 2 wt% lignosulfonic acid sodium salt (LASS) (on the basis of dry weight of biochar) was added to the suspending medium as a dispersant. The effect of glycerol content on the rheological properties and stability characteristics of the slurry fuels were studied. The yield stress was measured with a Brookfield vane viscometer and the dependence of apparent viscosity and shear stress on the shear rate was characterised using a Haake VT550 cone and plate viscometer. The stability characteristics of the slurry fuels were characterised by using a “drop rod” method. As glycerol content increased, the maximum biochar loading decreased from 50 to 10 wt% while the calorific values of the slurry fuels first increased and then decreased, reaching a maximum of 21 MJ kg− 1at 90 wt% glycerol content. For a given biochar loading, increasing glycerol content increased the viscosity of the suspending medium and therefore the viscosity of the slurry fuels, displaying higher yield stress, more apparent shear-thinning behaviour and higher stability due to the enhanced flocculation of biochar particles.