Chemical looping combustion of four different solid fuels using a manganese-silicon-titanium oxygen carrier

Journal article, 2018

In chemical looping combustion, solid metal oxide particles are utilized to transport oxygen from the air reactor to the fuel reactor. As fuel and air are never mixed, the energy penalty typically associated with gas separation in first-generation carbon capture and storage technologies can be avoided. To be considered as oxygen carrier for this process, a material should be reactive at relevant conditions, environmentally friendly, non-toxic, mechanically durable and have potential to be produced at low cost in large scale. Combined oxides of manganese and silicon have previously shown promise to meet these requirements. In this study, a spray-dried oxygen carrier based on a combined oxide of manganese, silicon and titanium was examined with respect to its performance in continuous chemical looping combustion of solid fuels. The experiments were carried out in a 10 kW chemical looping pilot unit which uses interconnected fluidized beds for oxygen carrier cycling. Prior to these experiments, the attrition rate was determined in a jet-cup rig. As the particles were comparably small and light, elutriation from the air reactor was high. The fuels used during a total experimental duration of 32 h were wood char, devolatilized hard coal, pet coke and lignite. In addition to varying fuels, the influence of fuel power, solids circulation and fuel reactor temperature were investigated. Gas conversion performance correlated clearly with the volatile content of the fuels, peaking at 97.8% for wood char and 94.6% for pet coke, which is the highest value ever reached for this particular fuel in this unit. Higher temperatures and solids circulation rates increased gas conversion. No decrease in performance over time, in particular no loss of reactivity due to sulphur accumulation, could be detected. The oxygen carrier released gaseous oxygen at relevant conditions. The particles were easily fluidized and fines production was low, suggesting a sufficient lifetime for the purpose.