Coupling of CaO-dried sewage sludge with two-stage sorption-enhanced steam gasification for inherent separation of high-purity hydrogen and carbon monoxide

This paper integrated alkai-dried sewage sludge (SS) using calcium oxide (CaO) and bagasse (BA) with a two-stage sorption-enhanced steam gasification (SESG) process to separately generate high-purity H 2 and CO at different temperature regions, while exploring optimal conditions and coupling mechanism. Response surface experiment revealed that SS and BA exerted opposing effects on H 2 and CO production, highlighting the importance of balancing their mass ratio. Increasing CaO dosage and H 2 and CO-generation stages temperatures enhanced H 2 and CO production. The optimal conditions were identified as a CaO dosage of 1.2, with temperatures of 600 °C and 750 °C for H 2 and CO-generation stages, considering cost and energy efficiency. With the optimal CaO and BA dosage, the moisture of SS reduced from 80 % to below 40 % within 3h, enabling low-energy dewatering. During H 2 -generation stage (600 °C), residual moisture and Ca(OH) 2 in the dried SS generated in-situ steam promoting steam reforming reactions, and Ca(OH) 2 has more CO 2 sorption capacity than CaO and catalytic effect of cyclization and dehydrogenation of generated tar, to boost H 2 production. During CO-generation stage (750 °C), CaCO 3 released CO 2 to gasify char, improving CO production. The process produced 113.5 mL/g dry biomass of H 2 with 74.1 vol% purity during H 2 -generation stage and 113.3 mL/g dry biomass of CO with 59.8 vol% purity during CO-generation stage. This paper proposed a new approach for drying and resource utilization of SS for inherently separated generation of high-purity H 2 and CO, providing a more sustainable and resource-efficient process.