Kinetics analysis of cellulose chemical-looping gasification using Ca–Fe oxygen carrier

Abstract

Ca–Fe oxygen carrier (OC) is an effective material with high selectivity on H2 and CO to aid to the gasification of solid fuel materials such as organic solid waste or biomass in chemical-looping gasification (CLG). However, the reaction mechanism of raw materials with high volatiles such as cellulose remains unclear. Kinetics analysis is considered as the efficient method to investigate the reaction mode and mechanism. In this study, isothermal method was conducted and the tristate intermedia products were used as substrates to reveal the kinetics characteristic of cellulose conversion process in CLG. The results demonstrated that the reduction process of Ca–Fe OC could be divided into three stages, and the activation energies were 40.40 kJ/mol, 91.28 kJ/mol and 165.33 kJ/mol, respectively; this indicates that the lattice oxygen could be transferred easily in the first stage, but much more difficult in the later two stages. The weak oxidizing molecules such as CO2 could re-oxide the reduced OC quickly and the activation energy was 27.83 kJ/mol. The mechanism model on kinetic of tar cracking was similar to the reaction between H2 and OC, and the activation energy was 82.27 kJ/mol. The decomposition of char was recognized as the stochastic nuclear shrinkage process with an activation energy of 52.22 kJ/mol.