Abstract
The paper reports the effects of surface fractal structures on the rheological behavior and combustion kinetics of raw brown coal and three modified coal water slurries (CWSs). The results show that the fractal structures and physicochemical properties of samples are dependent on various modification processes. The apparent viscosities of the coal water slurries increase with increasing surface fractal dimensions (D), especially with decreasing shear rates. Furthermore, it has been proved that the ignition temperatures and apparent activation energies of modified CWSs are lower than that of raw coal water slurry. Compared with the traditional qualitative analysis of the effect of pore structures on CWSs properties, D can more efficiently indicate the quantificational effect of pore structures on the rheological behavior and combustion kinetics of CWSs.
Highlights
With more than 60 wt% solid in small particle size (\50 lm) and low apparent viscosities (1200 MPa s), coal water slurry (CWS) has been extensively developed as a coal-based clean fuel in many countries (Phuoc et al 2014)
The other reason is that the volume–average particle size decreases with increasing D, which can increase free water among coal particles and volumetric particle amount, and this is beneficial to decreasing the apparent viscosities of the modified CWSs
The combustion dynamics of the four CWSs can be determined on the differential thermo gravimetric (DTG) curves obtained at different heating rates
Summary
With more than 60 wt% solid in small particle size (\50 lm) and low apparent viscosities (1200 MPa s), coal water slurry (CWS) has been extensively developed as a coal-based clean fuel in many countries (Phuoc et al 2014). The complex pore structures of solid particles have important effects on CWS preparation and combustion properties of modified coals, the present researchers mostly focused on qualitative analysis of pore structures (Yavuz et al 1998; Burdukov et al 2002; Tahmasebi et al 2012). The effects of pore fractal structures on the rheological behavior and combustion kinetics of modified brown coal water slurries (CWSs) were seldom reported. Based on the fractal theory, it is valuable to quantitatively evaluate the complicated and nonlinear porosity of coal particles, and clarify the impacts of surface fractal dimensions (D) on modified CWSs properties. The results are helpful for expanding application range of the modified brown coals
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