Effect of temperature on the fuel properties of food waste and coal blend treated under co-hydrothermal carbonization

Abstract

A blended feedstock containing food waste and coal was used to perform co-hydrothermal carbonization (Co-HTC) at different temperatures to observe the effect of temperature on the solid fuel properties of different hydrochars. Moreover, these hydrochars were mixed with molasses which act as a binder to prepare high mechanical strength pellets. A range of techniques was used to characterise the hydrochars and pellets. Food waste and coal hydrochars produced at 300 °C exhibited high heating value (HHV) of 31.1 and 31.4 MJ/kg respectively, however, high heating value of the Co-HTC 300 °C hydrochar decreased to 28.6 MJ/kg. The ash content of hydrochar obtained via the Co-HTC at 300 °C, was 53% less than the ash content of raw coal. Combustion results showed that the Co-HTC of food waste and coal is thermally more suitable than HTC of food waste and coal. During pelletization molasses played an important role in making solid bridge between the hydrochars. The tensile strength of all the hydrochars ranged between 2 and 4.5 MPa. The blend treated at 300 °C showed the highest tensile strength of 4.5 MPa. The mass density of food waste and blend increased as the temperature was increased, however, the mass density of the coal sample showed a decreasing trend. The energy densities of all the hydrochars ranged between 22.2 and 39 GJ/m³ and the energy density of the blends were higher than the coal and food waste hydrochar.

Keywords: Co-Hydrothermal carbonization; Coal; Food waste; Hydrochar; Pellet; Tensile strength.