Kinetics of solid-solid reaction between cotton char and Ni/olivine in chemical looping gasification

Direct solid-solid reaction characteristics of cotton stalk char (CSC) and nickel loaded olivine (Ni/olivine) were studied using micro-fluidized bed reaction analyzer (MFBRA). Model fitting method was used to fit 29 model functions under isothermal conditions. Three optimal models were selected to calculate kinetics of the solid-solid reaction of cotton char and oxygen carries. The results show that CO and CO₂ are main gas products of CSC and Ni/olivine. CO is first and then CO₂ is evolved during the reaction. CSC does not completely convert into CO₂, and concentration of CO is higher than that of CO₂. With increasing reaction temperature, concentration and yield of CO and CO₂ in the product gas increase obviously. The average activation energies for CO, CO₂ and CSC are 27.5, 46.4 and 69.8 kJ/mol, respectively. The non-isothermal reaction characteristics and kinetics of CSC and Ni/olivine were studied by thermogravimetric analyzer (TGA). The results show that reaction of CSC and Ni/olivine starts at 750 ℃, and reached the peak at 890 ℃. The activation energy of non-isothermal reaction is 72.05 kJ/mol, which is in accordance with the result of MFBRA. It indicates that the solid-solid reaction between char and nickel-based oxygen carrier easily occurs in during chemical looping gasification of biomass.