Chemical-looping combustion of solid fuels in a 100 kW dual circulating fluidized bed system using iron ore as oxygen carrier

Journal article, 2016

Chemical-looping combustion (CLC) is an innovative carbon-capture technology with potential to drastically reduce the cost of capture. By using a circulating bed material to transfer oxygen from the combustion air to the fuel, air and fuel are never mixed and the CO2 can be obtained as a separate flue gas stream, undiluted by N2. In other words, carbon capture is inherent to the CLC process. Here, we present findings from a 100 kW chemical-looping combustor for solid fuels. The oxygen carrier used in the present tests was an iron ore from Tierga, Spain. In total, 26 h of operation using bituminous coal and wood char as fuel was achieved. The highest gas conversion with bituminous coal was 87%, and the highest gas conversion using wood char as fuel was 93%. The carbon capture efficiency with bituminous coal was 94-98%, which is lower than what has been observed with ilmenite. For the wood char, the carbon capture was even lower. The fate of nitrogen and sulfur was investigated. It was found that 84 wt% of the S-containing gas was SO2, and only 16 wt% was H2S. The nitrogen analysis indicates that the fuel-N converted to gas was distributed as 10 wt% NO, 37 wt% NH3, and 53 wt% N2. It was found that the oxygen-carrier particles retained their high reactivity throughout the operational period. Furthermore, the expected lifetime of the iron ore was found to be approximately 300 h.