The effect of hydrothermal carbonization (HTC) on entrained flow steam gasification of sewage sludge. Experimental validation of various gasification models

Proper sewage sludge management is challenging due to legal requirements, environmental concerns, and logistical complexities. Steam gasification offers a promising solution by producing high-quality syngas. While research has largely focused on fixed bed gasifiers, their scalability limitations restrict their economic viability. Entrained flow gasifiers, scalable to hundreds of megawatts as demonstrated in coal gasification, present a practical alternative for large-scale bioenergy with carbon capture and storage (BECCS) applications. However, designing such systems requires precise modeling approaches. This study experimentally validates equilibrium models and a computational fluid dynamics (CFD) approach for steam gasification of raw sewage sludge and hydrothermally carbonized (HTC) sludge. HTC pretreatment improved syngas quality by facilitating the use of CO2 as a feedstock carrier for entrained flow gasifiers. Among the models tested, the CFD approach and a tuned semi-equilibrium model closely matched experimental data, with average absolute errors of 4.5 % and 2.9 % in mole fraction, respectively. Using a 3-m drop tube furnace, entrained flow steam gasification demonstrated the production of high-quality syngas and offering practical scalability. This scalability enables the development of efficient BECCS power plants with negative CO2 emissions, showcasing the potential of entrained flow gasifiers for sustainable energy and environmental management.