Chemical-looping combustion with natural gas using spray-dried NiO-based oxygen carriers

The work presented in this chapter demonstrates the economical feasibility of making a good oxygen carrier from commercial raw materials using a commercial production method, i.e. spray-drying. A batch fluidized-bed reactor was used for an extensive screening of many NiO-based oxygen carriers. This screening process led to the production of two major particle batches, which were used in continuous chemical-looping experiments. High-temperature experiments in a batch-fluidized bed verified the thermal durability of the particles. The most important result presented here concerns long-term operation (> 1000 h) of a 10-kWth chemical-looping combustor using spray-dried NiO-based oxygen carriers. Conversion of the fuel was good, and increased with (a) decreased circulation, and (b) increased fuel-reactor temperature. Combustion efficiency close to 99% was accomplished using these spray-dried particles. At the end of the test series, the continuous loss of fine material was 0.003%/h, which corresponds to a particle life time of 33000 h. No decrease in reactivity was seen during these long-term tests. The fuel used in the experiments was natural gas and methane.