Investigation Of The Synergetic Effect And Co-thermochemical Conversion Of Lignite Blended With Biomass

The low carbon transition of energy has slowed the growth of fossil energy consumption to a certain extent,but the demand for fossil energy still accounts for a large proportion of the global energy market.Coal still plays a dominant role in the energy structure of our country,and the shortage of high-quality coal forces our country to develop the low-rank coal represented by lignite on a large scale.However,the direct combustion of lignite leads to the increase in exhaust heat loss and equipment corrosion,low thermal efficiency and high CO₂ emission.The co-thermochemical conversion of biomass and lignite can effectively reduce the emission of coal and improve the combustion characteristics and overcome the handicaps of biofuels.Therefore,the co-combustion experiment of lignite and biomass and the reactivity of co-pyrolysis char were studied in this paper.The effect of biomass on the thermal conversion characteristics of Shengli lignite was investigated.The development and application of clean utilization technology provides theoretical basis and reference.Firstly,the combustion experiments of Shengli lignite and pine-needle humus blend with different blending ratios were carried out by thermogravimetric analysis,and the combustion characteristics and the synergistic effect of co-combustion process were studied.A new synergetic index is proposed to quantify the synergistic effect of co-combustion process.The activation energy is calculated by Flynn-Wall-Ozawa?FWO?and Kissinger-Akahira-Sunose?KAS?methods,and a more accurate kinetic model is obtained by master-plots method.The results show that there is a proper blending ratio which enhances dramatically synergistic effect during the co-combustion process,and thus the combustion characteristics of the blended samples are improved.The kinetic results show that the combustion activation energy of the blended fuel is lower than that of lignite and pine-needle humus,which indicates that the pine-needle humus can reduce the energy barrier overcome by the blended fuel reaction.The catalytic and non-catalytic effects of humus on lignite were quantifed by the synergy index.The results showed that the coupling of catalytic effect and non-catalytic effect contributed to significant synergistic effect.At the lower humus ratio,the non-catalytic action is dominant in co-combustion,and the catalytic action is more obvious at higher humus ratio.The surface structure,pore structure and microcrystalline structure of co-pyrolysis char with different blending ratios were studied.The surface morphology and functional evolution of the co-pyrolysis char were observed by SEM,FT-IR,and the pore structure of the co-pyrolysis char was studied by BET and fractal theory.The effect of humus on the pore structure of co-pyrolysis char was quantitatively analyzed by calculating the fractal dimension of pyrolysis char.The carbon structure and microcrystalline structure of co-pyrolysis char were studied by Raman spectroscopy and XRD analysis and deconvolution method.The results show that there is a linear correlation between specific surface area and fractal dimension.With the increase of humus ratio,the order degree of carbon microstructure and graphitization degree of the co-pyrolytic char decrease.The reaction characteristics and kinetics of co-pyrolysis char in O₂ and CO₂atmosphere were studied by non-isothermal thermogravimetric analysis,and the relationship between gasification activity index and pore structure and microcrystalline structure parameters was investigated.The results show that the reaction activity of pyrolysis char could be improved by increasing the proportion of humus in mixed char in O2 atmosphere.In CO2 atmosphere,the time required to achieve the same conversion rate is shortened with the increase of humus content in pyrolysis char at low temperature,while the law of blended char at high temperature is contrary.The positive synergistic effect of kinetic parameters is observed in the process of co-pyrolysis char gasification.The results show that there is a linear relationship between the pore structure parameters and the reaction activity index,and the exponential equations of the reaction activity and the microcrystalline structure parameters are obtained.