Effect of H_2S on Chemical Looping Combustion of Coal-Derived Synthesis Gas over Fe-Mn Oxides Supported on Sepiolite, ZrO_2,and Al_2O_3

摘要

The performance of Fe-Mn oxide oxygen carriers supported on sepiolite, ZrO_2, and Al_2O_3 with simulated synthesis gas/air in a novel combustion technology known as chemical looping combustion (CLC) was evaluated. Thermogravimetric analyses (TGAs) and bench-scale low-pressure (10 psi) flow reactor tests were conducted to evaluate the performance. Multicycle tests were conducted in atmospheric TGA with oxygen carriers using simulated synthesis gas with and without H_2S. The effect of H_2S impurities on both stability and oxygen transport capacity was also evaluated. Multicycle CLC tests were conducted in the bench-scale flow reactor at 800 ℃ with selected samples as well. Chemical-phase composition was investigated by the X-ray diffraction (XRD) technique. Five-cycle TGA tests at 800-900 ℃ indicated that all oxygen carriers exhibited stable performance. It was interesting to note that there was complete reduction-oxidation of the oxygen carrier during the five-cycle test. Fractional reduction, fractional oxidation, and global reaction rates were calculated from the data. It was found that the support-type had a significant effect on both fractional reduction-oxidation and reaction rate. The oxidation reaction was significantly faster than the reduction reaction for all oxygen carriers. The presence of H_2S in the synthesis gas resulted in a positive effect on the reaction rate. Bench-scale low-pressure flow reactor data indicate stable reactivity, full consumption of oxygen from the oxygen carrier, and complete combustion of H_2 and CO. XRD data of samples showed stable crystalline phases without the formation of sulfides or sulfites/sulfates and complete regeneration of the oxygen carrier.