5.1.1. Effect of Varying Reforming Temperature

The variation of H2 molar flow rate at the outlet of the steam methane and steam methanol reformers in thermodynamic equilibrium with varying reforming temperature and S/C ratio was derived to understand the system behavior. As can be observed in Figure 10a, the methane steam reformer shows the tendency that at S/C ratios below 3.5, the hydrogen flow rate increases when the reforming temperature increases up to 750 ◦C. After then, the H2 molar flow rate decreases as the reforming temperature increases. At S/C ratios above 3.5, the H2 molar flow rate continuously decreases as the reforming temperature increases. The steam methanol reformer shows a trend that as the reforming temperature increases from 180 to 260 ◦C, the molar flow rate of H2 continuously decreases, although the decrease rates are different, as shown in Figure 10b. Figure 10a,b represent the behavior of each reformer and can be used for interpretation of each system in the next section. The effects of varying the reforming temperature on the efficiencies and molar flow rate of CO2 in the methane-based and methanol-based systems were studied and illustrated in Figure 11.

As can be observed in Figure 11a, for the methane-based system, as the reforming temperature increases from 700 to 950 ◦C, the electrical, cogeneration, and exergy efficiency continuously decrease, from 39.53%, 63%, and 41.14% to 37.92%, 58.03%, and 38.47%, respectively. This trend occurs because as the reforming temperature increases, the amount of additional fuel needed for the reformer and combustor increases by 5.8% and leads to a decrease in efficiencies of the system. It can be noticed that the slope of the efficiency curves between 700 and 750 ◦C is less steep than that at other temperature ranges. The reason for this is that the amount of hydrogen produced increases when the temperature is increased from 700 to 750 ◦C; after then, the amount of hydrogen produced starts to decrease, as shown in Figure 10a. In addition, the slope of the cogeneration efficiency curve is a little steeper than that of the electrical and exergy efficiencies as the amount of the produced CO2 increases; accordingly, the heat required to capture CO2 in the CCU increases. The methanol-based system shows a similar behavior to that of the methane-based system, as shown in Figure 11b. As the reforming temperature increases from 180 to 260 ◦C, the electrical and exergy efficiencies decrease from 47.85% and 43.25% to 46.27% and 42.23%, respectively, whereas the cogeneration efficiency stays almost constant. Noteworthy, unlike the methane-based system, as the reforming temperature increases above 200 ◦C, the amount of produced CO2 decreases. This happens because an increase in the reforming temperature above 200 ◦C will favor the CO formation and the increase in CO content will decrease the production of H2 and CO2. Therefore, the heat required for CO2 capture increases and this results in a slight increase in cogeneration efficiency as the reforming temperature increases.

(**a**) Steam methane reformer: Methane supply of 1 kmole/h.

(**b**) Steam methanol reformer: Methanol supply of 1 kmole/h.

**Figure 10.** Variation of H2 molar flow rates of the exit gases from the reformer as a function of the S/C ratio and reforming temperature.

**Figure 11.** Influence of reforming temperature on system efficiencies and variation of molar flow rates of CO2 and fuel.
