Influence Mechanism Study Of Biomass Particles Accumulation On Pyrolysis Char Structure And Reactivity

With the depletion of fossil energy and increasingly serious environmental pollution,utilization of biomass energy has been widely concerned at home and abroad.Agricultural waste is the main biomass resource in China.The development and utilization of c lean and efficient conversion technology is of great significance for the development of diversified energy structure,promotion of economic development and improvement of ecological environment.Based on the lack of research on biomass particle accumulati on pyrolysis at home and abroad,this paper takes typical agricultural waste rice husk as the research object,the in-depth study of the evolutionary behavior of rice husk char stuctures prepared with different particle bulk densities,characteristics of pyrolysis and oxidation reactions,and release rule of gas products,this has significant significance for deeply revealing the mechanism of biomass pyrolysis.In this paper,pyrolysis of rice husk/rice husk char was studied by TG-FTIR.Firstly,rice husk/Al ₂O₃ was mixed into two bulk density samples,and char with different residence times were prepared in a 600oC fixed-bed pyrolysis reactor.Fourier transform infrared spectroscopy?FTIR?,X-ray diffraction pattern?XRD?and fully automatic specific surface a rea and pore size analyzer?BET?were used to analyze the structure of rice husk char.The results show that the bulk density of the particles significantly affects the conversion rate of pyrolyzed char and has a particularly significant effect on the volatile release stage.In comparison,low bulk density pyrolysis carbonization reaction progresses faster.Analysis of char production during the volatile release phase found that low bulk density thermal conditions caused the content of O and H containing fu nctional groups in rice husk chars to rapidly decrease and aromatic structure to increase slowly;analysis of char production during the initial stages of carbonization revealed that the aromatic structure gradually reached peak,it is gradually reduced in the subsequent char pyrolysis stage.In the presence of Al ₂O₃,the growth of the stack thickness of aromatic sheet was suppressed,but high bulk density accelerated aromatization rate during carbonization process.The lamellar distance of char decreases w ith the increase of residence time,char gradually tends to graphitization,and low bulk density is favorable for the graphitization of char.Change of bulk density has a small effect on the pore diameter of char produced in the initial stage of volatile release,and the specific surface area and pore volume of char produced in the later stage of carbonization are significantly increased.Low bulk density promotes increased surface area and expanded pore volume of char.Change of char structure has an influence on pyrolysis and oxidation reaction characteristics and release rule of gas products.Based on analysis of the structure of rice husk char prepared at two particle bulk densities,TG-FTIR technology was used to study the pyrolysis and oxidation r eaction characteristics and gas release of rice husk char in anaerobic and aerobic atmospheres.Under the same experimental conditions,pyrolysis experiments of rice husk samples prepared with three bulk densities were also studied.The results show that high bulk density leads to a lower peak value of the maximum weight loss rate of rice husks during pyrolysis,and TG pyrolysis curve shifts to the high temperature region.The larger the particle bulk density will hinder gas release rate and affected product d istribution,2D FTIR spectrum of rice husk pyrolysis under high bulk density did not show a significant release peak of organic matter containing C=O.Under an oxygen-free atmosphere,pyrolysis volatility of coke prepared with high bulk density has a large characteristic index,and activation energy required for the pyrolysis reaction is lower.The peak absorption peaks of the gas products of char pyrolysis gradually decrease,and the release amount of H ₂O,CO₂,CO,CO₄ and organic components containing C=O gradually decreases with the increase of the residence time of pyrolysis.However,high bulk density char pyrolysis produced higher releases amounts of gas products.In an aerobic atmosphere,high bulk density char is easier to catch fire,the burnout rate is higher and activation energy required for the oxidation reaction is lower.Release amount of H ₂O and CO₂ increased first and then decreased during char pyrolysis,and release amount of CO,CO ₄and organic components containing C=O gradually decreased.However,release amount of gas products from high bulk density char oxidative pyrolysis is higher.The difference in structure of pyrolysis char of two kinds of particle density affects the char's oxidation reactivity.The results sh ow that the bulk density has a significant effect on the oxidative reactivity of char produced in the volatile release stage,and the influence on the reactivity of char produced in carbonization stage is weakened.Char oxidation reactivity at both bulk densities tends to decrease first and then increase.In comparison,high bulk density char oxidation reactivity is strong.