Novel Renewable Double-Energy System for Activated Biochar Production and Thermoelectric Generation from Waste Heat

In this study, a novel renewable double-energy system, coupling activated biochar production and thermoelectric generation, is conducted and demonstrated. In the installed 13 thermoelectric modules (TEMs), they are partitioned into three groups of 3, 4, and 6 TEMs. The temperature difference across the TEMs depends upon the number of TEMs and is ranked as 3 TEMs > 4 TEMs > 6 TEMs. By harvesting the waste heat from the carbonization of water chestnuts, the greatest mean output power of single TEMs is 14.1 W and the mean output power of the installed 13 TEMs at the carbonization time of 10–30 min is 8.8 W. The higher heating value of produced activated biochar is 28.17 MJ kg–1, accounting for 42.7% improvement in the calorific value when compared to its untreated counterpart. The analysis also suggests that heavy metals contained in this coal-like renewable solid fuel are fairly low. The activated biochar possesses high hydrophilicity and specific surface area (430 m2 g–1), and a large portion of pore sizes is smaller than 2 nm. The analyses of attenuated total reflectance spectrometry, X-ray diffractometry, and thermogravimetry also clearly indicate the impact of carbonization on the biomass structure. Overall, the produced activated biochar is suitable for an alternative fuel, absorbent, and soil amendment.