Evaluation of low-cost oxygen carriers for biomass chemical looping gasification

Biomass Chemical Looping Gasification (BCLG) is a cost-effective and efficient alternative to conventional gasification. The selection of appropriate oxygen carriers (OCs) is crucial for stable BCLG performance. These OCs need to possess high reactivity, selectivity, material strength, and resistance to sintering. The study investigated various OC materials, including industrial wastes (copper, nickel slag, desulphurization, LD, and ladle slags), residential waste (sewage sludge ash), and natural ore (manganese). The evaluation of OCs focused on reactivity, H2-selectivity, mechanical strength and sintering behaviour. Except for ladle slag, all OC samples exhibited favourable reactivity due to the presence of Fe- and Mn-oxides possessing high oxygen transport capacity (10-17.6%). Nickel slag, manganese ore, and desulphurisation slag displayed notable H2-selectivity (8.7 to 10.4). It can be attributed to the presence of less-active (lattice) oxygen, limiting strong oxygen agents such as Fe2O3, Fe3O4, and Mn2O3. Moreover, desulphurization slag contained highly selective Ca2Fe2O5, which falls within the partial oxidation zone of the Ellingham diagram. Furthermore, all OC samples exhibited desirable material strength (>20 MPa), suitable for fluidised bed reactors. However, nickel, LD, and ladle slags demonstrated limited sintering with sintering onset temperatures exceeding 963 degrees C. This limited sintering may be attributed to the absence of iron silicates, iron-bearing aluminium silicates, manganese silicates, and potassium that contributed to the low thermal stability observed in the remaining OCs. Altogether, nickel slag calcined at 1100 degrees C was identified as the most promising OC material with optimal reactivity, selectivity, material strength, and minimal sintering for BCLG. Overall, this study provides a detailed and scientific methodology for OC selection and can aid future OC development.