Ca- and Mg-rich waste as high active carrier for chemical looping gasification of biomass

Abstract

Chemical looping gasification (CLG) is a promising technology for high-quality syngas production. One key issue to successful CLG is the selection of high-performance oxygen carrier. In this study, several Ca- and Mg-rich steelmaking wastes from steel industry, such as blast furnace slag (BF slag), blast furnace dust (BF dust) and Linz-Donawitz converter slag (LD slag), were used as oxygen carriers in chemical looping gasification of biomass. The results showed that the reducibility of Ca- and Mg-rich waste, especially LD slag and BF dust, was superior to that of hematite. Considering long-term operation, the cyclic stability of steelmaking waste was tested. BF dust showed a poor stability, while the other carrier (hematite, BF slag or LD slag) presented an excellent stability during multiple redox cycles in spite of partial sintering and agglomeration. Moreover, the effects of supply oxygen coefficient (O/B ratio) and reaction temperature on CLG of biomass were investigated. The results revealed that Ca- and Mg-rich waste exhibited a higher syngas production compared to hematite. The higher performance could be attributed to the improved reduction rate of Fe2O3 and gasification rate of biomass by Ca or Mg in steelmaking waste. In addition, LD slag exhibited the higher gas value at the O/B ratio of 1 at 900 °C. As a consequence, LD slag was an appropriate oxygen carrier for CLG of biomass in terms of perfect reducibility, superior cyclic stability and high reactivity.