(135e) Continuous Large-Scale Production of Red Mud Oxygen Carriers with a Rotary Kiln for Chemical Looping Combustion

Chemical looping combustion (CLC) has the feature of inherently enriching CO₂ concentration by circulating solid metal oxides (called oxygen carrier or OC) between an air reactor and fuel reactor. The durability and cost of OC directly impacts the economy and competitiveness of the CLC technology. Unfortunately, current available OC production techniques require a series of fabrication steps in order to obtain necessary properties, particularly mechanical strength and reactivity. The complicated production process significantly increases the cost of OC preparation and makes it difficult to scale up, one of the biggest challenges for CLC. Looking for a cost-effective production technique for large-scale OC production is very meaningful for the development of CLC. In this work, red mud, byproduct from the alumina industry, was used as raw OC material. An electrical, lab-scale rotary kiln was adopted for continuously producing red mud-based OC. Different fabrication parameters, including firing temperature, feeding rate, rotation speed and kiln angle, were investigated for the purpose of optimizing the resulting clinker properties. Clinker product was evaluated based on its mechanical strength, density and reactivity. The product obtained at 1250°C from the rotary kiln showed a higher strength (2.7 N) than, but similar reactivity (3.86%/min from Fe₂O₃ to Fe₃O₄) to, the OC prepared by the lab-scale freeze granulation method (2.3 N, 3.87%/min from Fe₂O₃ to Fe₃O₄). Repeatability of OC fabrication with the rotary kiln was verified as well. The mineral phase formations at different firing temperatures were analyzed. Fe₃Al₂(SiO₄)₃ and Fe₃(Al_0.2Fe_1.8)(SiO₄)₃, almandines, which contribute to the hardness of the clinker, were detected when firing at 1250°C and 1300°C, respectively. Fabrication costs associated with the rotary kiln was estimated to be around $346/ton, or two orders less than conventional preparation methods.