The Effect of Fly Ash from Different Coal Sources on the Reactivity of an Iron-based Oxygen Carrier for Chemical Looping Combustion

摘要

The University of Kentucky, Center for Applied Energy Research is investigating oxygen carriers (OC) for chemical looping combustion (CLC) with the goal of developing a pressurized chemical looping combustion/gasification process for generating electricity from coal. An important issue in the application of CLC to a solid fuel is the effect of ash on the performance of the OC. A previous study using a bituminous coal ash obtained from an electric utility suggested that the ash. was not detrimental to the capacity and reactivity of two iron based OCs and iron, oxide already present in the ash may have contributed additional OC activity~1. With the wide variety of coals used to generate electricity worldwide, it is unlikely that all ashes will have the same effect on OCs. Recently four ashes obtained from bituminous, sub-bituminous, and lignite coals were used in a comparative study of their effect on the reactivity of an iron based OC to combust a high carbon beneficiated coal char under dry inert gas (argon) conditions in a TGA~2. As expected the ash effect on the OC varied with the different ashes. The lignite ash did not affect the performance of the OC up to the highest concentration (75%) tested. The Bulgarian subbituminous which had a Fe_2O_3 concentration of nearly 14% caused a 20% reduction in the performance of the OC which was contrary to anticipated results. The Powder River Basin (PRB) ash produced a slight reduction in carbon removal ability as did the China bituminous ash. However, the results for the China ash which had 8.5% residual carbon indicated that the OC at the right carbon to OC ratio could also combust the residual carbon in the ash as well as the carbon in the fuel char. This study was undertaken to further investigate the impact on an iron based OC of these four different fly ashes in the presence of water vapor (WV) consistent with conditions which would exist during CLC in comparison to dry gas results.