Synthesis gas production from chemical looping gasification of lignite by using hematite as oxygen carrier

Abstract

Chemical looping gasification (CLG) of lignite by using hematite oxygen carrier is performed to achieve high purity synthesis gas. The oxygen carrier reaction performance as well as the effects of temperature and lignite/oxygen carrier ratio on the syngas evaluation are investigated by TG and fixed bed reactor coupling with various analytical methods. The experimental results reveal that the hematite oxygen carrier consisting primarily of Fe2O3, SiO2 and Al2O3 presents three H2 reduced peaks at 472.59 °C, 634.17 °C and 849.01 °C respectively, corresponding to the crystal form transition from Fe2O3 to Fe. Lignite pyrolyzes preferentially to generate intermediates then further reacts with oxygen carrier to produce synthesis gas in CLG process, following the oxygen carrier reaction path of Fe2O3 → Fe0.963O → Fe2O3. Oxygen carrier plays a key role in promoting lignite conversion to synthesis gas in CLG process owing to the lattice oxygen shifting reactions equilibrium to the direction of syngas production. Excessive lattice oxygen is beneficial to CLG reaction until the L/O ratio reaches to 4/6 with the limitation of heat and mass transfer in reaction system. However, the minimum value of O/L is 2/8, which ensures the oxygen carrier makes obvious promotion effect in reaction process. High temperature improves synthesis gas yield and carbon conversion by enhancing endothermic reactions in CLG process. The hematite oxygen carrier recovers main crystalline phase after the CLG process without serious sintering.