Investigation of reusability of process water in the hydrothermal carbonization of biomass

In this thesis, the effects of process water reuse during hydrothermal carbonization of grape pomace, orange pomace and poultry litter were investigated. For this purpose, process water reuse was exercised in the hydrothermal carbonization (HTC) of this biomass at a temperature of 225 °C, three times. Results showed that mass yields of hydrochars increased in the first cycles and but only slightly in further steps. By reuse of spent liquor, the energy content of hydrochars was found to be from 75% to 87% for grape pomace, from 69% to 78% for orange pomace and from 68% to 77% for poultry litter, which are higher than that of lignite and close to that of typical bituminous coals. Total organic carbon content and inorganic content of the spent liquor increased. pH values of spent liquors of all biomasses were in the acidic range and remained unchanged with increasing cycle number. The highest conductivity values were obtained in HTC of grape pomace. The highest conductivity values were obtained in case of grape pomace due to the high degree of dissolution of biomass ash during hydrothermal carbonization process. As a result, recirculation of spent liquor, hydrochar having similar properties was successfully obtained.