Rapid co-pyrolysis of lignite and biomass blends: Analysis of synergy and gasification reactivity of residue char

This work investigated the structural evolution of rapid co-pyrolysis char and its influence on co-gasification characteristics. The chars were prepared in a high frequency furnace at 900 degrees C with the heating rate of 300 degrees C/min, using Xinjiang lignite and cotton straw as raw materials. Blends of coal and biomass were prepared in proportions of 25:75, 50:50 and 75:25 wt.%. Compared to the individual pyrolysis, co-pyrolysis enhanced the transformation of ion-exchanged alkali and alkaline-earth metals (AAEMs). Moreover, the surface area of copyrolysis chars were enhanced, and the carbon structure of biomass char in mixtures became more ordered. The gasification reactivity of co-pyrolysis char was evaluated by thermogravimetric analyzer (TGA), including isothermal (800, 850 and 900 degrees C) and non-isothermal (5 degrees C/min) gasification using CO2 as agent. For isothermal gasification, the synergistic effect of reactivity changed from inhibition to promotion with the increasing conversion. The synergy index changed obviously at 800 degrees C. For non-isothermal gasification, the maximum reaction rate was increased. The blends with 75% biomass had the minimum activation energy. The co-gasification reactivity varied with the temperatures, biomass blending ratios and conversions, which were well related to the char structural evolution caused by rapid co-pyrolysis.