Effective H2S control during chemical looping combustion by iron ore modified with alkaline earth metal oxides

Highlights: • The activity of the iron ore is improved by alkaline earth metals modification. • H₂S cannot adversely affect the performance of the modified iron ore in CLC. • BaO modified oxygen carrier can effectively remove H₂S during the CLC process. • Most of the input H₂S is released as SO₂ over the MgO and CaO modified iron ore. Iron ore (IO) modified with alkaline earth metal (AEM) oxides were developed as oxygen carriers (OCs) for the chemical looping combustion (CLC) of simulated municipal solid waste (MSW) syngas to simultaneously reduce the H₂S emission. The AEM oxides, especially BaO, were found to improve the CLC performance of IO greatly due to the formation of AEM ferrites, which promoted the lattice oxygen activity. When using the pristine IO, less than 10% of the input H₂S could be removed with the remaining being released from the reactor mainly in the form of SO₂. The loadings of CaO and MgO were also found to be ineffective in sulfur removal from the syngas, because the sulfur fixation reactions were kinetically and thermodynamically limited for CaO and MgO, respectively. By contrast, over 60% of the input H₂S was effectively retained on the BaO-loaded OC in the form of sulfates/sulfites because of the high reactivity between BaCO₃ and H₂S in the presence of Fe₂O₃. This study indicates that the IO loaded with BaO showed superior performance both in CLC of syngas and control of sulfur species, which can be used in the CLC of sulfur containing fuels to realize a cleaner combustion process.