Utilization of soybean dregs for solid fuel production through hydrothermal carbonization

Abstract

Hydrothermal carbonization is a thermochemical process used in converting biomass into a coal-like substance known as hydrochar. This is usually carried out at high temperature with water below the saturation pressure for a certain period known as holding time. The biomass used was soybean dregs, which is the residue obtained from processing soy sauce with low economic value. The aim of this study therefore, was to determine the calorific value of the hydrochar produced from soybean dregs at hydrothermal carbonization temperatures of 160?C, 190?C, and 220?C and at holding times of 30 and 60 minutes, also at a temperature of 190?C with the biomass and water ratio at 1:4 and 1:5. The results showed that the highest calorific value was produced a temperature of 220?C and a holding time of 60 minutes, which was 3.866 kcal/kg, the highest carbon content was 26.49%, the lowest moisture content was at 1.77%, the lowest volatile content was at 62.98%, while the lowest ash content was 8.64%. Considering biomass to water ratio with the holding time, the highest calorific value was at 3.546 kcal/kg, the highest carbon content was 20.32%, the lowest moisture content at 1.71%, the lowest volatile content was 68.58%, while the lowest ash content was at 8.37%. The highest calorific value of the hydrochar produced was similar to the calorific value standard of lignite coal which is around 3511-4611 kcal/kg according to the American standard testing and mineral.