Development and Characterization of a Grape Marc Hydrochar Slurry Fuel

The development and characterization of a grape marc hydrochar slurry fuel are reported. The slurry fuel was prepared by mixing finely milled solid hydrochar, derived from the hydrothermal carbonization of grape marc, with water and dispersants. The rheological properties of the hydrochar slurry were measured using a cone and plate rheometer. The characterization of the radiatively heated hydrochar slurry was investigated by suspending a single fuel droplet in space using an acoustic levitator and irradiating it under radiation fluxes of 1.92 and 0.74 MW/m2. The higher heating value of solid hydrochar was found to be 26.0 MJ/kg, while 40 and 50 wt % hydrochar slurries had values of 10.4 and 13.0 MJ/kg, respectively. The flow behavior indexes of all slurry samples were less than unity. The temperature profiles of the suspended slurry droplets were temporally recorded. The maximum surface heating rate of the 50 wt % slurry droplet under radiation heating within the first 0.2 s was above 400 K/s. The maximum surface ignition time of suspended and irradiated hydrochar slurry droplets was measured at 0.37 ± 0.01 s, while the surface ignition temperature (Tig surf) was 375 ± 15 K, independent of heat flux. Employing the high-flux radiation system can efficiently heat the samples, and it is practical to simulate the heating behaviors of fuels in a real combustion environment. The attractive relatively low Tig surf highlights the newly developed hydrochar slurry having great potential application as a liquid biofuel.