## 3 Results
### Smr vs. SE-SMR: Sensitivity Analysis  
Moving to the results of the sensitivity studies, these are reported in terms of contour maps, each of which shows varying temperature and S/C. Nine maps were produced for each performance variable, for the three pressures investigated (1, 10 and 20 bar), and for three different CaO/CH\({}_{4}\) molar ratios (0, 0.5, 1). Figures 2-4 show all the maps for the indicators H\({}_{2}\) dry concentration (y\({}_{\rm H2}\)), CH\({}_{4}\) conversion (X\({}_{\rm CH4}\)), and H\({}_{2}\) yield (\(\eta_{\rm H2}\)), respectively. The maps on the left refer to a CaO/CH\({}_{4}\) molar ratio equal to 0, which corresponds to the traditional SMR case. Figure 2: \(y_{H2}\) (dry) as a function of temperature and S/C ratio for CaO/CH\({}_{4}\) from 0 to 1 (from left to right) at three different pressures: 1 bar (upper maps), 10 bar (center maps), and 20 bar (bottom maps). When considering SMR, for all the monitored performance variables (Figures 2-4), an increasing trend is observed as temperature or S/C ratio increase. The temperature dependence is expected due to the high endothermicity of the reforming reactions. The S/C ratio also plays a significant influence on the equilibrium conditions, as already mentioned; a high excess of steam shifts the chemical equilibrium towards product formation, in accordance with [PERSON]'s principle, leading to higher H\({}_{2}\) yields. Under the best operating conditions in the ranges considered, 725 \({}^{\circ}\)C and S/C = 5, namely the highest temperature and S/C ratio simulated, a dry hydrogen concentration of 78%, a methane conversion of over 99%, and a hydrogen yield of around 89% are achieved at 1 bar. As  
Figure 3: \(X_{CH_{4}}\) as a function of temperature and S/C ratio for CaO/CH\({}_{4}\) from 0 to 1 (from left to right) at three different pressures: 1 bar (upper maps), 10 bar (center maps), and 20 bar (bottom maps). for the effect of increased pressure, i.e., moving downwards on the maps at CaO/CH\({}_{4}\) = 0 for each performance variable, the effect on the indicators is detrimental, as reforming reactions occur with an increase in the number of moles. For example, given, again, T = 725 \({}^{\circ}\)C and S/C = 5, the maximum values achieved by the performance variables are, at 10 and 20 bar, respectively:  
\[y_{H_{2}}^{dry}\cong 74\%,\ X_{\text{CH4}}\cong 0.78,\ \eta_{\text{1H4}}\cong 0.71 \ (\text{@10 bar});\]  
\[y_{H_{2}}^{dry}\cong 70\%,\ X_{\text{CH4}}\cong 0.63,\ \eta_{\text{1H4}}\cong 0.58 \ (\text{@20 bar}).\]  
Figure 4: \(\eta\) as a function of temperature and S/C ratio for CaO/CH\({}_{4}\) from 0 to 1 (from left to right) at three different pressures: 1 bar (upper maps), 10 bar (center maps), and 20 bar (bottom maps). These results agree with those presented in the literature [14; 32]. Overall, to give an idea of the strong negative effect of pressure, calculating the average decrease of the performance indicators when moving from traditional SMR at 1 bar to SMR at 10 bar, a reduction for yH2, X and \(\eta\) by 16%, 44%, and 41%, respectively, was recorded. Moving to the SE-SMR conditions, firstly, it can be stated that increasing the S/C feed ratio always has a positive effect on the three performance indicators, and this effect is emphasized by sorption-enhanced conditions. On the contrary, since the effect of the other parameters is not so straightforward, a more in-depth discussion is presented below, considering temperature variation at different pressures and CaO/CH4 ratios. By starting from the pressure effect, thus fixing the CaO/CH4 ratio, for example to 0.5 (the maps in the middle of each figure), and moving downwards, in Figure 2 a worsening of the H2 purity, with the pressure increase from 1 to 10 to 20 bar, can be observed. The reason is clear, as high pressures disadvantage reforming reactions, leading to higher concentrations of unconverted methane.