Hydrothermal Carbonisation as Treatment for Effective Moisture Removal from Digestate-Mechanical Dewatering, Flashing-Off, and Condensates' Processing

One of the processes that can serve to valorise low-quality biomass and organic waste is hydrothermal carbonization (HTC). It is a thermochemical process that transpires in the presence of water and uses heat to convert wet feedstocks into hydrochar (the solid product of hydrothermal carbonization). In the present experimental study, an improvement consisting of an increased hydrophobic character of HTC-treated biomass is demonstrated through the presentation of enhanced mechanical dewatering at different pressures due to HTC valorisation. As part of this work's scope, flashing-off of low-quality steam is additionally explored, allowing for the recovery of the physical enthalpy of hot hydrochar slurry. The flashing-off vapours, apart from steam, contain condensable hydrocarbons. Accordingly, a membrane system that purifies such effluent and the subsequent recovery of chemical energy from the retentate are taken into account. Moreover, the biomethane potential is calculated for the condensates, presenting the possibility for the chemical energy recovery of the condensates.

Automated summary

Hydrothermal carbonization (HTC) is a thermochemical process that converts low-quality biomass and organic waste into hydrochar. Improved mechanical dewatering of HTC-treated biomass is demonstrated, along with the recovery of physical enthalpy and condensable hydrocarbons through flashing-off of steam. A membrane system is considered for purifying the effluent and recovering chemical energy from the retentate, with the biomethane potential of condensates calculated for further energy recovery.