Heat recirculation in syngas production from apple wood waste via hybrid filtration combustion: Quantitative assessment and mechanisms under varying flow rates

Heat recirculation is a key feature of hybrid filtration combustion gasification systems. However, quantifying the heat recirculation effect and analyzing its mechanism remain key challenges that hinder system optimization. An experimental investigation was combined with a theoretical energy distribution model to quantify heat recirculation in an hybrid filtration combustion gasification reactor. Coupling this model with experiments, we then clarified how heat recirculation influences chemical reactions under apple wood conditions. The main conclusions are as follows: when inlet flow rate was below 52.1 L/min, variation in the heat recirculation was insignificant. When the inlet flow rate was further increased from 52.1 to 72.1 L/min, the heat recirculation increased by 16.36%. The heat recirculation effect is derived from two components: fresh air preheating and flue gas waste heat recovery. The preheated air first promotes char pyrolysis and combustion before the reaction zone reaches its peak temperature. After the unburned mixture absorbs the waste heat from flue gas, heat recirculation further breaks the intermolecular hydrogen bonds between hemicellulose and cellulose in unburned apple wood. As moisture is carried away by high-temperature flue gas, the recovered heat may accelerates the breaking of glycosidic bonds and side chains in hemicellulose, thereby significantly enhancing the pyrolysis reaction.