Experimental Study On Chemical Looping Gasification Of Modified Iron-Nickel Oxygen Carrier To Produce Hydrogen-Rich Synthesis Gas

Biomass energy is a low-carbon energy source which is abundant,environmentally friendly,and renewable.Biomass pyrolysis gasification technology is to convert biomass energy into high-quality fuel gas.At present,the traditional gasification methods have the disadvantages of low energy efficiency,high gas production cost,and complex systems.In order to improve gas quality and reduce production costs,biomass chemical looping gasification technology is proposed.Biomass chemical looping gasification technology is to replace the traditional oxygen-enriched gas with the lattice oxygen in the oxygen carrier to provide oxygen for the gasification process.By controlling the ratio of oxygen carrier to biomass in the gasification reaction,the synthesis gas produced after the reaction can be rich in H₂ and CO,and the utilization rate of biomass energy can be improved.Therefore,the biomass chemical looping gasification technology has high energy efficiency and low cost.In this paper,the iron-based oxygen carrier was doped with active metal nickel to prepare the iron-nickel oxygen carrier,and then the oxygen carrier was modified with alkali metal and inert carrier for the chemical looping gasification reaction of pine wood chips to find the best reaction conditions to prepare hydrogen-rich synthesis gas with a low Ni O loading ratio.First of all,we prepared Fe/Ni oxygen carrier by mechanical impregnation method,and performed chemical looping gasification reaction with pine sawdust on a fixed bed.The reaction time,Ni O load to mass ratio,reaction temperature,water vapor to biomass ratio,and peroxygen coefficient were investigated influence on the reaction,in order to judge the best reaction conditions.The experimental results showed that the iron based oxygen carrier had a load to mass ratio of 3%Ni O,reacted at a reaction temperature of800?,a peroxidation coefficient of 0.2,and a ratio of water vapor to biomass of 1.25for 50 minutes,in the synthesis gas prepared after the gasification reaction,the volume concentration of H₂ reached 43.06%,the carbon conversion rate was 78.22%,the calorific value of syngas reached 7.49MJ/Nm³,and the gas production rate was1.25Nm³/kg.Then,the alkali metal was introduced to modify the Fe/Ni oxygen carrier,and the optimal loading ratio and cycle performance of the alkali metal were investigated.The experimental results showed that the optimal load to mass ratio of alkali metals was 5%,the volume concentration of H₂ in the synthesis gas after the gasification reaction was47.83%,the carbon conversion rate was 85.44%,and the corresponding calorific value of the synthesis gas was 7.97MJ/Nm³,the output of synthesis gas was 1.49Nm³/kg.After 15 cycles of experiments on a fixed bed,the reactivity of the alkali metal modified Fe/Ni oxygen carriers decreased,but the reactivity remained high.Characterization results showed that as the number of cycles increases,alkali metals would be lost,some Fe/Ni spinel structures would be damaged,and the pores on the surface of the oxygen carrier would shrink.Finally,the inert carrier?-Al₂O₃ was used to modify the Fe/Ni oxygen carrier.The experimental results showed that the optimal loading mass ratio of the inert carrier?-Al₂O₃ was 40%,and the reactivity of the oxygen carrier was improved after the inert carrier was supported.We could learn that the specific surface area of the oxygen carrier was significantly improved from the BET characterization results.After 10 cycles of experiments on a fixed bed,we could learn that the oxygen carrier maintains a good reactivity,the quality of the synthesis gas was good,and the relative volume concentration of H₂ in the synthesis gas remained above 45%.We could learn that after10 cycles of the oxygen carrier loaded with the inert carrier,the surface morphology didn't form a dense surface,and the pore distribution was still obvious fron the characterization results.