Assessing the Effectiveness of the Hydrothermal Carbonization Method to Produce Bio-Coal from Wet Organic Wastes

Abstract

The study is devoted to the assessment of the thermodynamic efficiency of the hydrothermal carbonization (HTC) method to produce bio-coal from wet organic waste (biomass). The HTC method is a process of thermochemical conversion of biomass into solid biofuel (bio-coal) as a result of its heating up to 150–280°С in the presence of water. The competitive advantages of the HTC method and the properties of bio-coal produced by this method from various organic waste are analyzed. The energy consumption values for implementation of the HTC process and the conventional torrefaction method are compared. It is demonstrated that the energy consumption in the production of bio-coal by the HTC method is several times lower than in the torrefaction process since water heated at a high pressure remains a liquid. This, in turn, offers a high potential for recovery of thermal energy (approximately 87%) in the HTC process. The heating value of the produce bio-coal is as high as 27 MJ/kg, which is comparable with that of commercial power coals. An analysis of the properties of biochar produced in the HTC process suggests that, in principle, it may be burned at coal-fired power stations together with conventional coal (if proper gas treatment equipment is available). The HTC method can be used for pretreatment of water-rich organic wastes and biomass to produce a quality fuel and a water solution that can be used as a base for production of fertilizers.