Application to the cement sector and Optimization of the overall process

Remi CHAUVY
Thermodynamics and Mathematical Physics Unit

Supervisors: Prof. Guy DE WEIRELD and Prof. Diane THOMAS

The mitigation of CO2 emissions to remedy the global climate change is of major interest. Carbon Capture Utilization and Storage (CCUS) technologies aim therefore to extract CO2 either from concentrated sources such as power stations, steel mills or cement factories, and then use it as a raw material for carbon-based products, including fuels, chemicals, and building materials.
To this extent, this work, carried out in the framework of the ECRA (European Cement Research Academy) academic Chair at UMONS, aimed to identify the most promising CO2 conversion alternatives, and developed process models to determine costs and environmental impacts. An original multistep method was therefore proposed to identify and then select the best emerging options to be implemented in short- to mid-term via multi-criteria assessment, including technical, economic, energetic, environmental, and market considerations. Several multi-criteria decision analysis methods were considered, enhancing the robustness of the results and limiting the interpretation of biases. A ranking of viable alternatives was discussed, involving the production of compounds that have a relative low unit price, but significant market volume, including methanol, methane, calcium carbonates, microalgae, sodium carbonates, urea, syngas and ethanol, and compounds that have a high unit price but low market volume, such as dimethyl carbonates, polycarbonates, formic acid and salicylic acid. In particular, methanol and methane were identified as two of the most promising alternative products for CO2 utilization among examined cases in sensitivity analysis. As a result, the hydrogenation of CO2 to methanol and methane, the latter in the form of synthetic natural gas (SNG), were deeply assessed. The entire CCUS chain was investigated, from industrial CO2 capture applied to cement plant flue gas, to its conversion together with renewable hydrogen and purification of the final product, through simulation and process-to-process integration. It allowed to get relevant techno-economic parameters and perform life cycle analyzes, identifying hotspots contribution and quantifying most significant environmental impacts.
Simulation and LCA results highlighted that both methanol and SNG are good candidates for climate change mitigation, even though highly depending on assumptions and system boundaries. In both cases, CO2-based process pathways are costlier than conventional production technologies. Their economic breakthrough is strongly related to high capital investments and electricity costs required for the production of hydrogen, which is nevertheless expected to decrease in the upcoming years.
From a more global perspective, the benefits of CO2 utilization for climate change mitigation appear to be then potentially significant when the CO2 storage option is not available and/or not accepted, and when it is deployed as an alternative to fossil carbon sources. Beyond climate mitigation, CO2 utilization provides services, such as the reuse of industrial wastes to produce CO2-based products, materials and chemicals, and the storage of variable renewable energy including the use of existing distribution infrastructures, as illustrated in the study of the two aforementioned CO2-based alternatives.