Abstract: A method and system of converting biomass to biochar in a hydrothermal carbonization apparatus wherein subcritical water at a temperature of 230-350° C. and 500-3000 psi is reacted with the biomass to form biochar, biocrude and gases. The method and system include recycling the biocrude back to the hydrothermal carbonization apparatus which improves biochar yield and provides water for the biomass reaction to occur.

Abstract: The present invention relates to a method for conversion of biomass to biochar in subcritical water at 230-350° C. and 500-3000 psi. Under subcritical water conditions, biomass readily converts into biochar, biocrude, and some gases. In this invention, yield of biochar is significantly improved by recycling of biocrude. The process can produce hydrophobic biochar that has at least 70 wt % (dry basis) carbon as opposed to ˜25 wt % carbon in hydrophilic biomass, and has a heating value of about 29 MJ/kg (HHV-dry basis) which is comparable to good quality coals. More than 90% energy of biomass is retained in the biochar. The invention provides an effective means to convert biomass into a high energy density fuel for use in a variety of applications.