Experimental study of microalgae chemical looping gasification with ilmenite, LD slag and iron sand in a 1.5 kWth unit

Chemical looping gasification (CLG) enables production of nitrogen-free syngas without need of air separation, thus offering a promising route for efficient biomass conversion. Microalgae, as a third-generation biofuel feedstock, present advantages in sustainability but pose challenges due to their high ash content. In this study, ilmenite, LD slag (a steelmaking byproduct from the Linz-Donawitz process), and iron sand were evaluated as oxygen carriers for microalgae CLG in a 1.5 kW th unit. The experiments were performed in various operating conditions and lasted 20–25 h with each oxygen carrier. Effects of key operational parameters including oxygen-to-biomass ratio (λ, 0.13–0.51), fuel reactor (FR) temperature (860–920 °C), and gasifying agent composition (H 2 O/CO 2 ratio, 100/0, 50/50 and 0/100) were investigated. The CLG performance was assessed with product gas composition, biomass conversion, carbon emitted from AR, syngas yield, cold gas efficiency, and tar formation that are essential for gasification processes. Oxygen carrier samples before and after the experimental campaigns were characterized with ICP-AES, XRD and SEM-EDX techniques to study changes in the physicochemical properties of the materials and their interactions with ash components of the microalgae. A TGA analysis was done to study the reactivity change of the materials during the campaign. Among the three materials, the LD slag exhibited the most promising overall performance. With this oxygen carrier, the syngas reached 1.5 Nm 3 /kg microalgae and the tar yield was suppressed to 0.5 g/kg. The outstanding performance with LD slag is deemed as a result of rich Ca content in the material, as calcium is a classical catalyst promoting gasification.