Simulation and Techno-Economic Analysis of Oxyfuel Combustion of Sewage Sludge Under Different Carbon Capture Conditions

Legal requirements are increasingly promoting the thermal treatment of sewage sludge in Germany, and alternative disposal methods are being investigated. Oxyfuel combustion is one promising thermal process for treating sewage sludge. However, the flue gas produced during the combustion process contains high levels of CO2, a greenhouse gas that poses environmental harm. To address this issue, this study analyzed oxyfuel combustion and various CO2 capture methods, aiming to utilize CO2 as a feedstock for methanol production. Energy and material balance simulations were carried out using Aspen Plus. Four distinct carbon capture methods: membrane carbon capture, cryogenic carbon capture, monoethanolamine carbon capture, and ionic liquid carbon capture were modeled. Three different oxygen configurations were tested: pure air, pure oxygen, and a 50/50 air–oxygen mixture. The oxygen separation systems, including air separation units and alkaline electrolyzers, were also studied and modeled. As a result, 14 different scenarios were created. The performances, energy efficiency, and economic results of each scenario were compared to one another and to existing literature, allowing for the identification of the most effective approaches. The oxyfuel combustion scenarios achieved the highest methanol output. MEA and ionic liquid capture combined with air combustion proved to be the most cost-effective options, while cryogenic capture incurred the highest costs due to its helium-based cooling requirements. Although ASU-based oxyfuel combustion achieved the lowest specific energy requirement for methanol production, electrolysis-integrated configurations remained economically disadvantageous, underscoring the critical influence of electricity prices on the overall feasibility of the system.