Hydrothermal carbonization of biomass: new experimental procedures for improving the industrial processes

This study aims to introduce new experimental methods, not yet described in the literature, to be adopted in hydrothermal carbonization processes. Silver fir was selected as model biomass in batch experiments in the range 200–300 °C, up to 120 min of reaction time, and at a 7:1 water to solid ratio. Simple equations were proposed for modeling the evolution of the process variables during the reaction, particularly the electrical conductivity of the liquid phase, correctly described by a simple two-step first order mechanism, regardless of the reaction temperature. At 200 °C, a perfect correspondence (R2 =0.9992) exists between liquid phase electrical conductivity and solid phase carbon content. The authors propose to monitor the industrial process withdrawing from the reactor the liquid and sampling its conductivity. The benefits of a flash expansion step between the reactor and the hydrochar drying units were discussed, and experiments demonstrated the usefulness of this process innovation.