## 1 Introduction
SE-SMR is still transitioning to TRL 6; three pilot scale projects exist with configurations involving single or two interconnected bubbling fluidized bed (BFB) reactors [2; 18; 20; 19]. Two pilot plants are already operated at low pressure (1-3 bar), with ongoing tests showing hydrogen concentrations higher than 80% up to around 95% and about 90% carbon capture rate [18; 19]. Finally, a 1.5 MWth pilot plant is currently being developed to produce blue hydrogen under high pressure conditions (up to 30 bar); the HyPER project is focused on unlocking technical challenges and scaling up hydrogen-enabled aviation to meet net zero emissions targets [20]. The main experimental efforts, at all levels of technological development, involved the mitigation of catalyst deactivation and sorbent sintering, demonstrating that research on catalyst substrates and sorbents can significantly improve the materials' endurance. Among the possible CO2 sorbents for SE-SMR, the most attractive are the CaO-based ones due to their abundance, low cost, high theoretical sorption capacity, and fast carbonation kinetics [7]. When these materials are applied in the reformer/carbonator the following reaction occurs:  
\[\text{CaO(s)}+\text{CO}_{2}(\text{g})\leftrightarrow\text{CaCO}_{3}(\text{s}) \qquad\qquad\Delta\text{H}_{298\text{K}}=-\,178\text{ kJmol}^{-1} \tag{4}\]  
The combined reforming/carbonation reaction may be thermally neutral, with the exothermic carbonation reaction providing enough heat for the endothermic reforming reaction and producing CaCO\({}_{3}\) that is then regenerated in a calciner operated at around 900 \({}^{\circ}\)C with directly or indirectly provided heat [2]. Different works in the literature deal with the improvement of the initial sorbent capacity and its durability over multiple cycles, involving thermal pre-treatments, acid treatments, and water/steam reactivation. Furthermore, studies involved the incorporation of different inert refractory materials or the preparation of entirely synthetic CaO with different precursors and using different methods [7, 21, 22]. In addition to calcium oxide, other sorbent materials of interest for this type of high-temperature (>600 \({}^{\circ}\)C) application are sodium and lithium silicates/zirconates [8]. More recently, bi-functional materials combining catalytic and CO\({}_{2}\) sorption properties on the same structure are receiving interest since they could compact and integrate the process and lead to significant cost reductions. However, further advances are still needed so that such materials can effectively maintain high performance over several cycles [7, 23, 24]. With regard to process models and optimization studies, most of them merely simulate and apply equilibrium reactors. In this work, Aspen Plus was used, including fluidization regimes and kinetic limitations by means of its \"Fluidbed\" block, to simulate the process in a fluidized bed reactor, with the aim of providing a preliminary characterization before completing the study in a chemical looping configuration based on dual interconnected fluidized bed reactors. A mapping of the possible favorable operating conditions to carry out the process, based on the various and diverse hydrogen uses, was provided.