Thermodynamic analysis and kinetic investigations on biomass char chemical looping gasification using Fe-Ni bimetallic oxygen carrier

Chemical looping gasification (CLG) is viewed as a novel and promising gasification technology because it can produce high quality syngas with low cost. In this work, a highly active Fe-Ni bimetallic oxide (NiFe2O4) was used as an oxygen carrier (OC) to promote biomass char conversion and the kinetic model of char reacting with OC was focused on to guide the active design of OC. A suitable ratio of OC to char is determined at 0.30 for obtaining the maximum gasification efficiency according to the thermodynamic analysis. NiFe2O4 produced by sol-gel method shows the highest reactivity among the four OC candidates that prepared with different methods through thermogravimetric-mass spectrum (TG-MS) analysis. Non-isothermal experiments were carried out to obtain the kinetic model of OC reduction by char, founding that the activation energy of redox reaction gradually increases with conversion ratio (α) and the kinetic mechanism can be described by the random nucleation and subsequent growth model and chemical reaction model respectively before and after α passes 0.5. The α value is generally less than 0.5 to avoid excessive reduction of OC, indicating that the redox reaction should conform to the random nucleation and subsequent growth model to avoid the sintering and agglomeration of OC.