Fate of sulfur in chemical looping combustion of gaseous fuels using a copper-based oxygen carrier

The development of the chemical looping combustion technology for gaseous fuels has reached a point where it has been demonstrated in several pilot units for several thousands of hours using a variety of oxygen carriers. So far, a lot of experimental work was focused on fuel conversion performance and life time of oxygen carrier particles. In addition to the general performance of an oxygen carrier regarding fuel conversion, it is of special interest how it interacts with fuel impurities or contaminants like sulfur. Here, it is not only of interest if and how impurities affect fuel conversion performance, but also in which composition and in which reactor stream (air reactor or fuel reactor) they leave the CLC system. This knowledge is of great importance when it comes to the requirements of exhaust gas treatment facilities in large scale units. In the present study, the fate of sulfur in chemical looping combustion has been investigated in a 120 kWth pilot unit consisting of two interconnected circulating fluidized beds using a copper based oxygen carrier prepared by impregnation on an inert alumina support. Natural gas from the grid, originally without sulfur, was used as fuel. To investigate the influence of sulfur, H2S has been added to the fuel stream up to a concentration of 2000 ppmv. In order to close the mass balance of sulfur, the exhaust gas streams of air and fuel reactor are analyzed against H2S and SO2. Further, solid samples of the oxygen carrier particles were taken on a regular basis to investigate potential interaction of sulfur with the particles. The contribution shows how sulfur affects the general fuel conversion performance of the oxygen carrier as well as how much H2S is converted to SO2 and in which exhaust gas stream it leaves the reactor system. Measurements were performed for several temperatures in the range of 800-850 degrees C.