Pyrolysis/Gasification Mechanism And Synergistic Effect Of Biomass And Bituminous Coal

Pyrolysis and gasification clean energy conversion technology is the frontier technology of energy research.The clean utilization of biomass energy can effectively alleviate the severe energy challenges in today’s world.In this paper,wheat straw,peach wood,and bamboo were pyrolyzed in a quartz tube furnace at different temperatures.The composition of pyrolysis gas and the physical and chemical properties of char products were analyzed.Furthermore,CO₂was used as the gasification agent for char gasification,and char gasification experiment was carried out.Conventional thermogravimetric analysis and a new congruent–mass thermogravimetric analysis were used to study the reaction mechanism of co–pyrolysis of coal and biomass.Meanwhile,the influence of experimental conditions on co–pyrolysis was studied,and the kinetic analysis of main pyrolysis stages was conducted to explore whether there was synergistic effect in the co–pyrolysis process.The surface morphology of pyrolytic char was evaluated by scanning electron microscopy（SEM）and fractal dimension.The results showed that pyrolysis temperature had a significant effect on the properties of char.High pyrolysis temperature was beneficial to accelerate the gas release rate and improved the final gas production.As the pyrolysis temperature increased,the quality of char decreased.The content of element C in three kinds of char increased,while the content of element O and element H in peach and bamboo char decreased,while the content of element O in wheat straw char changed little,the O/C and H/C molar ratio of biomass char decreased gradually.Char calorific value was also affected by temperature obviously.SEM images showed that pyrolysis temperature increased,pore development expanded,and a large number of folds appeared on the surface.Fractal box dimension increased first and then decreased.In the gasification experiment,it was found that the peach wood char and wheat straw char prepared by pyrolysis at 600°C had the highest gasification activity,and the bamboo char prepared at 700°C had the highest gasification activity.Pore structure can affect the activity of gasification reaction.Well developed pore structure is helpful to improve gasification reactivity.With the change of pyrolysis temperature,the specific surface area and micropore volume of char increased first and then decreased,but the temperature at which the peak value occurred was slightly different.The peach wood char produced by pyrolysis at 600°C has better gas adsorption characteristics,and the adsorption desorption curve lags obviously,while the bamboo char has poor gas adsorption characteristics.The gasification effect of peach wood char is better than that of wheat straw char and bamboo char.Biomass with lower ash content,higher O/C molar ratio,and more developed pore structure had superior gasification performance.The conclusion of this paper has important reference value for large–scale clean and efficient utilization of biomass resources.Congruent–mass thermogravimetric analysis can compare the interactions in the co–pyrolysis process more intuitively and reduce the influence of initial mass on the determination of interaction relationship.The TG curve and final char yield of co–pyrolysis of coal and biomass are lower than that of single pyrolysis of coal and biomass.Synergistic effect appears in co–pyrolysis of coal and biomass.With the increase of heating rate,the thermogravimetric hysteresis appeared and the thermogravimetric curve gradually moved to the high temperature region.With the increase of carrier gas flow rate,the synergistic effect weakens.The kinetics of different reaction stages was analyzed by Coats–Redfern method,the results show that the activation energy required in the main co–pyrolysis stage of the mixture is lower than that in the pyrolysis stage alone.The micromorphology shows that biomass char has a more developed pore structure than coal,and the box dimension indicates that co–pyrolysis increases the surface irregularity of char.The conclusion of this study has important reference value for large–scale clean and efficient utilization of biomass resources,and it is of great significance to judge the interaction mechanism of two or even multiple mixed samples in the process of co–pyrolysis.