Thermodynamic and kinetic analysis on the biomass syngas fueled chemical looping hydrogen generation process in fixed bed reactor

Abstract

Because of its simple structure and easy operation, the fixed bed reactor is widely used in the chemical looping process to assess the performance of oxygen carriers (OC) or to evaluate new chemical looping technologies. However, the systematic investigation of the redox behavior and temperature evolution during the chemical looping hydrogen generation (CLHG) process in the fixed bed reactor under different conditions, which is crucial for process optimization and reactor design, has received less attention. In the present work, the redox characteristics of the CLHG process with biomass syngas as the fuel in a fixed bed reactor were investigated and analyzed from a perspective of thermodynamics and kinetics. Results showed that high redox temperature (>800 °C) favors the fuel conversion due to the improved reaction kinetics and favorable thermodynamics. A space velocity in the range of 0.12–0.5 s−1 and superficial velocity of 0.008–0.075 m/s can provide enough reaction time meanwhile enhance the external diffusion of fuel gas, achieving high reduction degree of OC and further high H2 yield (3.4 mmol/g Fe2O3) and high H2 energy efficiency (45 %). Moreover, a violent OC bed temperature rise (100 °C) was observed in the air oxidization stage, which can be mitigated by diluting the Fe2O3 content and decreasing the air flow rate. Finally, the reaction front and flow front moving behavior were discussed in detail for a better understanding of the CLHG process.