.Since the high amount of steam can react with CH4 via the endothermic SMR reaction (Eq. (3.1)) and some amount of heat was used to heat up the steam, the heat demand in the FR was high when the process was operated at high SFR/CH4 molar ratios. By contrast, when the process was operated at high Fe3O4/CH4 molar ratios, the large amount of the high-temperature circulating solid could supply heat to the FR; thus, the heat demand in the FR was decreased. Figure 5.21 shows the effect of the SFR/CH4 and Fe3O4/CH4 molar ratios on the total energy demand for each FR temperature. The results showed that increasing the SFR/CH4 molar ratio increased the total heat demand, while the effect of the Fe3O4/CH4 molar ratio on the total heat demand was insignificant. This was due to the total heat demand mainly depending on the heat duty of the calcinator, which increased when the amount of CaCO3 increased by increasing the SFR/CH4 molar ratio.