Comprehensive experimental study on energy conversion of household kitchen waste via integrated hydrothermal carbonization and supercritical water gasification

In China, huge amount of household kitchen waste (HKW) is generated, and it is difficult to be treated due to its complex organic composition and high moisture. Hydrothermal technique can directly convert organic matters into hydrochar or syngas based on the operating conditions. In this study, a two-stage energy recovery process by integrating hydrothermal carbonization (HTC) and supercritical water gasification (SCWG) was used for HKW treatment. Firstly, HKW was processed by HTC at various temperatures (200–300 °C), producing hydrochar and HTC derived liquid. Energy densified hydrochar (20.63 MJ/kg), highest fixed carbon, and lowest volatile matter was obtained at 300 °C and 75 min residence time of HTC. HTC derived liquid containing rich organic content was sequentially converted to H₂-rich syngas by SCWG. Highest H₂ yield of 3.94 mol/kg_HKW was produced at optimal condition (300 °C, 75 min HT – 480 °C, 20 min SCWG). The comparison of integrated process (HTC + SCWG) with direct SCWG were discussed, the lowest energy efficiency (8.99%) and return on energy investment (25.55%)) was obtained in direct SCWG. Cost benefit ratio of 1.86 implied that integrated process is an economically feasible. Therefore, energy recovery process can be a promising method for disposal and utilization of HKW.