Evolution of carbon and nitrogen during chemical looping gasification of rapeseed cake with Ca-Fe oxygen carrier

Abstract

• Higher OC/RC ratio is beneficial to the transformation of carbon. • NH 3 and HCN are the major N species in CLG of rapeseed cake. • Fe and Ca in CaFe 2 O 5 can increase the yields of NH 3 and HCN. • The reaction pathways of nitrogen in CLG are summarized. • CLG is promising process for the sustainable production of NH 3 . Rapeseed cake (RC) is an attractive fuel for its high caloricity, but the high-nitrogen content seriously hinders its utilization. Meanwhile, chemical looping gasification (CLG) is a promising technology for the production of N 2 free high-quality syngas. Inspired by using RC as a source of C for syngas production, it also can be a possible source of N and H for the sustainable production of NH 3 . Hence, recycling N and H from RC via CLG was proposed for NH 3 production. This paper evaluates the effects of oxygen carrier (CaFe 2 O 5 (CaFe) and 60% Fe 2 O 3 /Al 2 O 3 (FeAl)) on kinetic parameters, as well as the evolutions of carbon and nitrogen during CLG of rapeseed cake using TG-FTIR. Results show that the gasification behavior is remarkably influenced by oxygen carrier at both devolatilization and char reaction stages. CaFe shows a remarkably higher reduction activity compared to FeAl, especially at char reaction stage. The superior activity of CaFe can be also reflected in the lower activation energy compared to FeAl. As regards to nitrogen emission, NH 3 and HCN are the dominant nitrogen species, whereas HNCO is minor. Meanwhile, the migration of nitrogen includes catalytic pyrolysis and oxidation by lattice oxygen (O*). It is feasible to control the migration path of nitrogen by adjusting the operating conditions. Thus, CLG is an attractive pathway for efficiently utilizing rapeseed cake, which can not only produce tunable syngas, but also possibly make the most use of nitrogen as valuable chemicals.