The fate of sulphur in the Cu-based Chemical Looping with Oxygen Uncoupling (CLOU) Process

The Chemical Looping with Oxygen Uncoupling (CLOU) process is a type of Chemical Looping Combustion (CLC) technology that allows the combustion of solid fuels with air, as with conventional combustion, through the use of oxygen carriers that release gaseous oxygen inside the fuel reactor. The aim of this work was to study the behaviour of the sulphur present in fuel during CLOU combustion. Experiments using lignite as fuel were carried out in a continuously operated 1.5 kWth CLOU unit during more than 15 h. Particles containing 60 wt.% CuO on MgAl2O4, prepared by spray drying, were used as the oxygen carrier in the CLOU process. The temperature in the fuel reactor varied between 900 and 935 °C. CO2 capture, combustion efficiency and the sulphur split between fuel and air reactor streams in the process were analysed. Complete combustion of the fuel to CO2 and H2O was found in all experiments. Most of the sulphur introduced with the fuel exited as SO2 at the fuel reactor outlet, although a small amount of SO2 was measured at the air reactor outlet. The SO2 concentration in the air reactor exit flow decreased as the temperature in the fuel reactor increased. A carbon capture efficiency of 97.6% was achieved at 935 °C, with 87.9 wt.% of the total sulphur exiting as SO2 in the fuel reactor. Both the reactivity and oxygen transport capacity of the oxygen carrier were unaffected during operation with a high sulphur content fuel, and agglomeration problems did not occur. Predictions were calculated regarding the use of a carbon separation system in the CLOU process in order to reduce sulphur emissions. Coals with high sulphur content, such as lignite and anthracite, would require a carbon separation system in order to comply with legislation governing sulphur-limits. In conclusion, coals with a high sulphur content can be burnt in a CLOU process using Cu-based material to obtain high carbon capture efficiencies.