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 °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 °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.

Biomass chemical looping gasification (BCLG) offers significant advantages over the conventional biomass gasification process in terms of enhanced gasification efficiency, inherent CO₂ capture, process circularity, and mitigated emissions of pollutants. This review discusses the prevailing status of research and development of BCLG in terms of production of high-quality syngas and negative carbon emissions based on the latest experimental and modelling studies. In particular, the design of the BCLG process and reactors is compared with conventional gasification. This review suggests that the BCLG process could be 10–25 % more efficient than the conventional combustion and gasification system in terms of economical H₂-production cost (3.37 USD/kg H₂-produced) and negative life cycle emissions of CO₂ (−14.58 kg-CO₂e/ kg-H₂ produced). This review has extensively considered the effects of process parameters and oxygen carriers (OCs) on gasification chemistry and reaction engineering during BCLG experiments. More specifically, the properties of OCs have been holistically analysed from technological, economic, and environmental perspectives to screen appropriate and affordable OCs for BCLG. In addition, the state-of-the-art modelling studies on BCLG are compared in terms of thermodynamic equilibrium, kinetics, and integrated processes. Technological challenges and research gaps in experiments and modelling have been highlighted in order to advance the BCLG process for industrial applications. In particular, further experimental work is needed to tackle issues related to stability and deactivation of OCs, fluidisation and circulation, the mechanical strength of OCs, the optimisation of feed conversion, and the integration and management of various thermal reactors. It is also desired to enhance the accuracy of models by incorporating optimisation of integrated processes and a more detailed reaction mechanism. Overall, BCLG is a promising negative emissions technology for renewable energy production, yet more innovative efforts in experimental and modelling studies are imperative to move towards more practical applications.

Globally, large amounts of biomass wastes such as cattle manure, fruit/vegetable waste, and cheese whey residual streams are disposed of from farming and food processing industries. A promising approach to convert such biogenic residues into valuable biofuels is Supercritical Water Gasification (SCWG). A detailed investigation on SCWG of the mentioned wet biomass wastes has been performed to assess the thermodynamic behavior of such a complicated system. This is conducted by combining advanced models with a supplementary experimental study, providing deep insight into the behavior of the SCWG system for different bio-waste sources. For the modelling part, different approaches including global, constrained and thermal quasi-thermodynamic equilibria have been pursued to analyze the influence of operating parameters on the produced biogas quality. Furthermore, SCWG experiments were conducted using biomass samples provided by our industrial partner. Reasonable agreements were observed between experimental results and predictions from constrained and thermal-quasi equilibrium models, showing significant improvements over the global thermodynamic equilibrium model. Results showed that superimposition of carbon conversion efficiency together with the use of a constant molar amount of specific compounds can improve the accuracy of the global equilibrium model. Furthermore, comparisons between different models revealed the advantage of the thermal quasi-equilibrium model, which uses the “approach temperature” concept, over the constrained equilibrium model, by reducing the complexities inherent in superimposing multiple constraints. Overall, the thermal-quasi equilibrium approach has its advantages of lumping all the additional constraints used in the constrained equilibrium model into an effective approach temperature, offering (i) a better reproducibility of the experimental data point and (ii) a rigorous basis for scale-up calculation. The results of this study provide a better understanding of the SCWG process for different types of wet biomass feedstocks as result of applying advanced analytical approaches and comparing with experiments.