Improving the Energy-Related Aspects of Biowaste Treatment in an Experimental Hydrothermal Carbonization Reactor

摘要

AbstractHydrothermal carbonization (HTC) is a thermochemical conversion process with the potential to treat the prevalent wet urban biowaste in low- and middle-income countries. The generated hydrochar solids are a hygienic, homogenized, carbon rich and energy dense product with economic value that can be used as an alternative to wood-based charcoal or fossil fuel. Obtaining a satisfactory energy efficiency of the process is, however, one of the prerequisites for the possible breakthrough of this technology. In an experimental HTC reactor, a model kitchen/market waste feedstock (17.8 MJ/kgdb) was hydrothermally carbonized with varying loading rates (TS 20 and 25 %) under mild operational conditions with peak temperatures of 160–190 °C and process times of 2–10 h above 160 °C. The aim was to evaluate the energy ratio of the process under these conditions while examining the impact on the hydrochar quality. Results show that the chemical properties of the produced hydrochar and its heating value were of moderate quality (21.1–24.4 MJ/kgdb), showing similar characteristics like torrefied products. HTC of a 25 % TS-load during 2 h at 180 °C and maximum pressure of 18.3 bar resulted in a char chemical output energy that is twice as high as the electrical energy consumed in the process. If considering the theoretical methane potential of the process water, the energy ratio could be increased to 2.6; while reactor insulation could further enhance this ratio to 3. This article reveals the merits of mild HTC and provides relevant knowledge for attaining an optimized, energy efficient HTC system.