Binderless fuel pellets from hydrothermal carbonization of municipal yard waste: Effect of severity factor on the hydrochar pellets properties

It has become crucial to understand the combined effect of temperature and time on hydrochar pellets quality if large scale pellets production is envisaged. This study investigated the effect of hydrothermal carbonization (HTC) of yard waste at different severity factor (SF) based on the Arrhenius equation on the fuel, mechanical, storage, transport and combustion characteristics of the hydrochar pellets. No additional binder was used. The increasing SF level during HTC has a direct effect on the calorific value and energy density of the hydrochar pellets. Tensile strength of the hydrochar pellets increased from 1.53 MPa to 4.80 MPa for lowest and highest SF level respectively. The natural length expansion of hydrochar pellets was maximum (21%) for lower SF, and was minimum (7%) for higher SF level pellets. Higher SF level increased the mass (1662 kg/m(3)) and energy (42 MJ/m(3)) density of pellets as compared to lower SF level (1473 kg/m(3) and 27 MJ/m(3) respectively). The result of hydrophobicity, impact resistance and length expansion revealed that the lower SF level hydrochar pellets has lower durability as compared to higher SF level hydrochar pellets. Higher SF level improved combustion performance of hydrochar pellets which was evident from the improved burnout and ignition temperature. The study revealed that densified, durable, energy-rich fuel pellets could be produced from municipal yard waste using HTC at a higher SF level without using any binders thus identifying itself as a valuable renewable energy source. (C) 2020 Elsevier Ltd. All rights reserved.