Material balances of carbon, sulfur, nitrogen and ilmenite in a 100 kW CLC reactor system

Journal article, 2014

Chemical-looping combustion (CLC) is an unmixed combustion concept where fuel and combustion air are kept separate by means of an oxygen carrier, and the CO2 capture is inherently achieved. This work presents findings from a 100 kW chemical-looping combustor, which was operated with Colombian bituminous coal for 12 h, using ilmenite as oxygen carrier. The focus of the study is on a 4.7-h experiment with stable operating conditions, during which inbound and outbound gaseous, liquid, and solid flows of carbon, sulfur, nitrogen and ilmenite were carefully monitored and analyzed. The fuel power during this experiment was 71 kW. The gas conversion reached 83%, the carbon capture efficiency was 98-99%, and the solid fuel conversion based on carbon was 65%. The carbon balance confirms that a large fraction of the fuel escapes the reactor system unconverted. It also demonstrates that essentially all in- and outbound flows of carbon have been accounted for. The sulfur balance shows that the conversion in the fuel reactor of inbound sulfur is around 72%. Furthermore, it is found that 75% of the S-containing gas is SO2, and only 25% is H2S. The nitrogen analysis indicates that 62% of the nitrogen fed with the coal is converted to gas, and that the nitrogen in this gas is distributed as 1 wt-% HCN, 11 wt-% NO, 26 wt-% NH3, with the balance probably being N-2. In addition, the present work includes a comprehensive study on the structural integrity of ilmenite in circulating fluidized beds. It is found that the expected lifetime of ilmenite is approximately 700-800 h.