Natural minerals as oxygen carriers for chemical looping combustion in a dual circulating fluidized bed system

A first experimental campaign has been conducted at a 120 kW fuel power dual circulating fluidized bed installation for chemical looping combustion of gaseous fuels. In these test runs natural ilmenite (FeTiO3) has been used as oxygen carrier material. The plant consists of two interconnected circulating fluidized bed reactors (stainless steel construction, inner diameter: 0.15 m, height: air reactor 4.1 m, fuel reactor 3 m). Variations of fuel composition (natural gas, synthetic gas mixtures of H2 and CO), load, temperature and solids circulation rate have been performed for the bulk bed material. Further, natural olivine, (Fe,Mg)2SiO4, has been studied as an additive to increase hydrocarbon conversion. Despite the limited height of the risers, the results show reasonable fuel conversion for CO and H2 at 950 ∘C. The conversion of natural gas, i:e. CH4, on the other hand, is relatively low for the pure ilmenite material at about 30–40%. A certain dependency of fuel conversion on load is found especially for CH4. Addition of natural olivine results in a moderate increase of CH4 conversion.