Performance of calcium manganate as oxygen carrier in chemical looping combustion of biochar in a 10 kW pilot

Journal article, 2016

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are carbon capture technologies which achieve gas separation by means of cycling oxidation and reduction of a solid oxygen carrier. In this study, the performance and CLOU properties of an oxygen carrier with perovskite structure, CaMn0.9Mg0.1O3-δ, were investigated in a 10 kW pilot. The fuel consisted of biochar with very low sulphur content. Around 37 h of operation with fuel were carried out in the 10 kW chemical looping combustor. Previous operational experience in this unit has been achieved using different natural minerals as oxygen carrier – mainly ilmenite and manganese ore. Parametric studies performed in this work included variation of fuel flow, solids circulation rate, temperature and fluidization gas in the fuel reactor. The oxygen carrier was exposed to a total 73 h of hot fluidization (T > 600 °C). No hard particle agglomerations were formed during the experiments. An oxygen demand as low as 2.1% could be reached under stable operating conditions, with a carbon capture efficiency of up to 98%. CLOU properties were observed at all fuel reactor temperatures, ensuring stable operation even without steam as gasification agent present in the fuel reactor. The results suggest that CaMn0.9Mg0.1O3-δ, is suitable for the use as oxygen carrier in chemical looping combustion of solid biochar and offers higher gas conversion than previously tested materials without CLOU properties such as ilmenite. The experiments constitute the first successful operation using a non-copper CLOU oxygen carrier in combustion of solid fuel.