A novel route to utilize waste engine oil by blending it with water and coal

•A novel and feasible utilization of WEO is proposed.•COWS can be prepared by 15wt.% WEO with water and coal successfully.•COWS has better static stability than that of CWS with the same coal content.•COWS of 48wt.% coal content has the same LHV with CWS of 67.88wt.% coal content. Coal–oil–water slurry (COWS) synfuel can be prepared successfully by waste engine oil (WEO), water and coal in the existence of Tween 80 and SL. The effects of coal type, coal particle size distribution, and WEO blending proportion (α) on the slurryability of COWS were investigated, and certain essential properties, such as slurryability, rheology, thixotropy, and stability of COWS were examined. The results show that the maximum coal content of COWS decreases with an increment in α, ranging from 60wt.% at α=0 to 48wt.% at α=15wt.%. The apparent viscosity of COWS becomes high when the amount of WEO is increased for the same coal content. The lower heating value (19.15kJ/g) of 48wt.% COWS (α=15wt.%) is equivalent to that of CWS with 67.88wt.% coal. The mass ratio of separated supernatant to oil–water emulsion for COWS with 49wt.% coal decreases by 1.12% while the amount of WEO is increased to 15wt.% from 10wt.%. COWS exhibits the non-Newtonian pseudoplastic fluid behavior. Its pseudoplasticity and thixotropy are also promoted as the coal content of COWS is increased. And the dispersion and stabilization mechanism of COWS is discussed.