烟粉和烟丝的热解燃烧特性及反应动力学分析

Investigation on pyrolysis/combustion characteristics and reaction kinetics of tobacco strands and tobacco powder

为了解尺寸对烟草原料热解燃烧动力学特性的影响,利用宏量型烟草高温热转化热重分析仪分析了不同切丝宽度烟丝及其粉碎后烟粉的热解燃烧特性,并使用Coats-Redfern法计算了样品在热解或燃烧过程中各失重阶段的动力学参数。结果表明:①烟粉的最大热解失重速率显著高于烟丝,而0.8~1.2mm范围内3种不同切丝宽度对烟丝的热解失重速率影响不明显;②烟粉在燃烧过程中,生物质三组分热转化导致的挥发分析出与燃烧反应失重峰在DTG曲线中合并为1个失重峰,而烟丝在该热转化过程表现为3个独立的失重阶段;③烟粉的起燃温度Ti高于烟丝、燃尽温度Tb显著低于烟丝,其综合燃烧特性指数S为4.75×10^-7%^2·min^-2·℃^-3,而3种切丝宽度烟丝的S值在2.63×10-7~2.99×10^-7%^2·min^-2·℃^-3范围内变化,且切丝宽度越小综合燃烧特性指数越高;④Coats-Redfern法热解动力学结果显示,在Zone2对应的小分子有机物热解温度范围内,烟粉的热解动力学主要由2级化学反应控制,而烟丝主要受三维扩散控制。烤烟尺寸越小其燃烧性越好,且与烟粉相比,烟丝在热转化过程中受到更加显著的传热传质阻力的影响。

In order to investigate the effects of tobacco size on its pyrolysis and combustion properties,tobacco strands of different widths and tobacco powder were tested by a macro-thermogravimetric analyzer.The kinetic parameters of the samples at different pyrolysis/combustion stages were calculated by Coats-Redfern method.The results showed that:1)The maximum weight loss rate of tobacco powder was significantly higher than that of tobacco strands.Within the test range of 0.8-1.2 mm,the strand widths did not affect weight loss rate obviously.2)The devolatilization and combustion of three biomass components(hemicellulose,cellulose and lignin)in tobacco powder combined into one peak in DTG curves,rather than three independent peaks in those of tobacco strands.3)Tobacco powder featured higher light-off temperature and significantly lower burn-out temperature than those of tobacco strands.The combustion characteristic indexes of tobacco powder was 4.75×10^-7%^2·min^-2·℃^-3,that of tobacco strands ranged from 2.63×10-7 to 2.99×10^-7%^2·min^-2·℃^-3,negatively correlated to cut width.4)The pyrolysis kinetic analysis of Coats-Redfern method indicated that the pyrolysis of tobacco powder was mainly controlled by a second-order chemical reaction in Zone 2 within the pyrolysis temperature range of small molecule organic matter,while the pyrolysis of tobacco strands was dominated by a three-dimensional diffusion.The samples of flue-cured tobacco of smaller size features better combustibility,and the thermal conversion reaction of tobacco strands was influenced more significantly by its resistance to heat and mass transfer.