Fuel Nitrogen Conversion in Chemical Looping with Oxygen Uncoupling of Coal with a CuO-Based Oxygen Carrier

The interest in chemical looping with oxygen uncoupling (CLOU) of coal as a method for CO2 enrichment has increased drastically during recent years. The objective of this work was to experimentally investigate fuel nitrogen conversion in the CLOU process of coal with a CuO-based oxygen carrier in a batch fluidized-bed unit. Three coals of different rank (anthracite, sub-bituminous, and bituminous) and their corresponding chars were used as fuels. Furthermore, experiments of coal combustion under air-fired conditions were performed to recognize the unique pathway of fuel nitrogen conversion in CLOU. Experimental results indicated that NO was formed in the largest amount of total NOx. For the Shenhua bituminous coal that was used, most of the NO, NO2, and N2O from fuel nitrogen was formed during the devolatilization stage of the coal. However, with Xuzhou sub-bituminous coal or Huaibei anthracite as fuels, a certain portion of NO was derived from char-N. Under the current experimental conditions (temperature of >900 degrees C), N2O formation was much less, because of its highly sensitive reactivity with temperature. Meanwhile, in the CLOU process, NO2 derived from fuel nitrogen accounted for a relatively large proportion, although it was lower than NO. The unique NO2 formation supported the occurrence of the heterogeneous reactions between gases and solid oxygen carrier particles in the reactor, where the oxygen carrier and coal were intensively mixed. Also, the gaseous oxygen from CuO particles participated in the reactions. Furthermore, with char as fuels, lower NOx formation was found, and the char nitrogen conversion to NOx was almost proportional to carbon conversion.