Hydrothermal carbonization coupled with gasification for collaborative disposal of kitchen waste and yard waste

Abstract

Kitchen waste and yard waste are typical components of municipal solid waste. In this paper, two schemes for collaborative disposal of these two wastes by hydrothermal carbonization (HTC) coupled with gasification were proposed and compared: Scheme 1: co-gasification of poplar with hydrochar derived from food waste; Scheme 2: direct gasification of hydrochar derived from co-HTC process of food waste and poplar. HTC was the pretreatment to regulate the composition and structure of raw materials. After HTC, the H/C and O/C of food waste decreased to the minimum of 1.06 and 0.14, respectively, and the coalification degree was increased close to lignite. Most of K and Na would be removed but Ca was enriched during HTC process, in which hydrochar derived from food waste at 260 °C contained the highest Ca content of 3752.30 mg/kg. The C=C and C=O functional groups of hydrochar were richer than the raw materials indicating the aromatization degree was improved. In Scheme 1, the gasification feedstock had relatively higher alkali and alkaline earth metals and volatile, resulting in a rapid gasification and the H2/CO ratio was between 1.6 and 1.8. In Scheme 2, the co-HTC hydrochar had high content of fixed carbon which can reach the maximum of 48.62 wt.% when the temperature was 260 °C. Due to the richer surface functional group structure, especially C=O, the hydrochar was easy to crack into CO during the initial gasification stage, and H2/CO ratios of the syngas were all less than 1. HTC coupled with gasification could broad the waste usage to meet the different industrial process needs, which can achieve waste disposal and energy conversion efficiently.