Power-to-X processes for the abatement of industrial steelwork emissions: a study in demonstration, optimization and pre-industrialization

The decarbonization of hard-to-abate sectors such as steel is imperative to curb anthropogenic greenhouse gas (GHG) emissions and mitigate their consequences. Point source carbon capture is a mature technology acknowledged by the IEA as a crucial instrument in achieving global targets, though the increased energy demands of capture and utilization systems further increase the requirements of flexibility, efficiency, and durability on nascent technologies. CO₂ absorption via hollow fiber membrane contactors (HFMCs) and H₂O/CO₂ electrolysis via planar solid oxide stacks (SOESs) show such potential but face considerable challenges at industrial scale, particularly with system integration and feedstock impurities. The research manuscript hereafter probes the pre-industrial viability of said technologies, demonstrating key performance indicators in relevant operating conditions while identifying optimized process designs that improve techno-economic feasibility.‎ Chapter 1 begins with a status report on the rate of anthropogenic greenhouse gas emissions by sector following the COVID-19 pandemic, along with an overview of global targets and midterm projections. The timeframe of decarbonization for hard-to-abate sectors is addressed, followed by the potential that Power-to-X (Power-to-X) technologies promise contrasted with the techno-economic barriers currently delaying industrialization. Finally, the key research challenges addressed by this manuscript are contextualized through the C2FUEL concept within industrial zone of the Dunkerque harbor in northern France for the production of dimethyl ether (DME) as a maritime fuel.‎ Chapter 2 aims to demonstrate with brute blast furnace gas (BFG) from an industrial source the long-term performance of CO₂ capture with hollow fiber membrane contactors, whose process intensification potential has been theoretically demonstrated in lab but seldom tested with actual industrial gas containing dust and corrosive sulfur impurities at dew point conditions. The technical specifications regarding BFG, the main off-gas from blast furnaces producing pig iron, are discussed, including the main impurities to be considered in the pre-pilot design. The kinetic theory establishing the intensification potential of hollow fiber membrane contactors is presented, with which a simplified model validated on lab-scale tests is reconfirmed with brute BFG using a benchmark aqueous amine solvent (30 wt%MEA). Duplicate durability campaigns exceeding 2 000 h of total operation are then reported, demonstrating the pretreatment design and HFMC durability for BFG whilst also determining the performance and purity of the regenerated CO₂ anticipated for a pre-industrial CO₂ capture and utilization (CCU) pilot. A proprietary solvent is also tested for the second durability campaign and compared to the benchmark tested during the first durability campaign. Chapter 3 aims to characterize the performance and durability of proprietary solid oxide cells under relevant operating conditions for Power-to-X processes, providing a basis for further studies related to system integration and optimization. Special attention is afforded to the co-electrolysis mode with variable H₂ content, with analysis of the outlet vapor composition to explore the reactive extent of side reactions (i.e. water gas shift / methanation) and determine whether the assumption of thermodynamic equilibrium is valid. A ½D steady-state model is then proposed, with nonlinear regression of key kinetic parameters for CO₂ electrolysis and side reactions utilizing data obtained within the scopes of the C2FUEL project and this chapter. ‎Chapter 4 aims to simulate and identify the optimal operating configuration for the production of DME utilizing HFMCs and SOESs along with packed bed membrane reactors (PBMRs) equipped with a bifunctional catalyst for CO₂/CO hydrogenation and methanol (MeOH) dehydration. The chapter explores six feasible and innovative process designs afforded to the C2FUEL concept and proposes a system model developed in Aspen Plus v14 with integrated 0D isothermal Fortran subroutines simulating the three key technologies. Permutations of the stack mode (steam-/co-electrolysis) and reactor configuration (without/with membranes) establish baseline performances of key criteria (specific energy, conversion, and make-up) for the target product DME and the main byproduct MeOH. As elaborated in ‎Chapter 3, special consideration is given to the degradation of the stack to study the balance-of-plant strategies that operators may employ during key points in the unit’s lifetime. Finally, a novel process design (Patent No. PCT/NL2023/050410) coupling the stack with the reactor in a synergistic manner is presented and modeled, improving performance across all performance criteria while also promoting favorable gas matrices that in principle promote electrode/catalyst longevity. Chapter 5 aims to refine the technical analysis presented previously to account for key economic and environmental indicators related to the commodification of sustainable fuel within Europe. The chapter investigates further the six process configurations explored in ‎Chapter 4 now incorporated into a comparative discounted cash flow analysis and life cycle impact assessment to identify the optimal process configuration. A cradle-to-grave techno-economic assessment of the C2FUEL concept then explores the limitations of the business model for maritime offtakers within the Dunkerque harbor, conducting a sensitivity analysis on relevant input parameters.‎ Chapter 6 culminates the work conducted within the scope of WP5 of the C2FUEL project to demonstrate at TRL6 pre-industrial pilots for CO₂ capture and utilization (CCU) and high temperature electrolysis (HTE). The diverse safety norms and key challenges faced during the project are reviewed, followed by the field results obtained for the CCU with industrial BFG in France and for the HTE with purified steam in Finland. Experimental results are compared with modelling efforts in ‎Chapter 2 and ‎Chapter 3. Chapter 7 concludes the manuscript by summarizing the results, establishing a holistic techno-economic assessment on the current state of three (3) key Power-to-X technologies in the context of decarbonization.