Investigation of LD-slag as oxygen carrier for CLC and OCAC in a 10 kW unit using high-volatile biomass

Other conference contribution, 2022

A steel slag from the Linz-Donawitz process, called LD-slag and having significant calcium and iron-fractions, was investigated as an oxygen carrier in a 10 kWth chemical-looping combustor with three high-volatile biomass fuels. In order to improve operability, the LD-slag was found to require heat-treatment under high temperature before using in the unit. In total, operation with the biomasses was conducted for more than 26 hours at the temperatures of 870-980°C. The fuel thermal power was in the range of 3.4-10 kWth. The operation involved chemical looping combustion (CLC), chemical looping gasification (CLG) and oxygen carrier aided combustion (OCAC). Around 12 h was in CLC operation, 13.3 h was conducted under CLG-conditions, while the remaining 0.7 hour was OCAC. Here, the focus is on the results obtained during the CLC and OCAC parts of the campaign. The increase of temperature in the fuel reactor and air flow to the air reactor leads to better performance, with the oxygen demand reduced to 10% while the carbon capture was always higher than 95%. Steam concentration in the fuel reactor has little effect on the performance. In OCAC, a higher oxygen ratio promotes the combustion a lot, with the normalized CO2 concentration >95%, indicating almost full combustion. The circulating oxygen carrier can also contribute to OCAC, while more study is needed. Bed agglomeration was found in OCAC tests, whereas this is absent in CLC/CLG.