Chemical looping combustion of solid biomass:Performance of ilmenite and braunite as oxygen carrier materials

Chemical looping combustion (CLC) is a novel technology, which is able to capture CO2 without an energy-demanding CO2 separation step, enabling lower energy requirements and much lower costs than conventional CO2 capture technologies. CLC using sustainable biomass as a fuel (bio-CLC) results in net-negative CO2 emissions, required to reach ambitious CO2 emission targets. Bio-CLC could be also demonstrated in larger scale at lower economic risk as a demonstration plant could be designed so that it would be possible to operate it also as an ordinary boiler after the demonstration period. Pilot scale bio-CLC process development tests were carried out using two types of wood pellets and wood char as fuels, and ilmenite and braunite - both natural ores with good availability, low cost and non-toxicity - oxygen carriers. Stable operation was achieved in totally 19 tests and performance of braunite was found to be better than ilmenite. High volatile content of biofuels was found to be the limiting factor of performance: in order to improve the performance, mixing and contact of volatiles with oxygen carrier material should be improved. Tests indicated that bio-CLC can reduce the risk of high temperature corrosion enabling the option to use higher steam values compared to conventional biomass combustion, improving the power generation efficiency.