玉米秸秆及其发酵沼渣热解动力学研究

摘要

The pyrolysis characteristics of fermentation residue of corn stover was analyzed.The pyrolysis kinetics were studied with FWO and Starink methods.The most probable mechanism function of pyrolysis also was evaluated by Malek method.The effect of anaerobic digestion on corn stover was deduced by comparing with the untreated corn stover.The results of proximate and ultimate analysis showed that the volatile content of fermentation residue was decreased by 19.48％ compared with the untreated corn stover and the fixed carbon content was increased by 27.87％.The oxygen content was decreased by 24.25％,which was an advantage for pyrolysis.The analysis of lignocellulose illustrated that cellulose and hemicellulose were decreased by 39.94％ and 30.96％,respectively,while the lignin was increased by 109.14％,which contributed to the maximum weight loss rate of fermentation residue decreasing and the carbon yield was much higher after pyrolysis.The results of pyrolysis kinetics showed the activation energy of fermentation residue was 91 ～ 130 kJ/mol,which was lower than that of corn stover.The mechanism function curve of two samples had similar trends,which can be divided into two parts.When the conversion ratio (α) was less than 0.6,they can be illustrated by order of reaction (n =2) mechanism model.When the conversion ratio (α) was more than 0.6,the pyrolysis of corn stover was in accord with the cylindrical symmetric three-dimensional diffusion mechanism (D4),while fermentation residue was more inclined to the spherical symmetric three-dimensional diffusion mechanism (D3).The research result can provide a theoretical basis for optimization of process conditions and industrial application of fermentation residue turning to bio-fuel.%为研究厌氧发酵过程对秸秆类生物质热解特性及动力学的影响,以玉米秸秆及其厌氧发酵沼渣为研究对象,分析了二者热解特性,分别采用Flynn-Wall-Ozawa(FWO)法和Starink法对热解活化能分布进行研究,并结合Malek法对其主要热解阶段的最概然机理函数进行了探讨.原料基本特性分析结果表明,玉米秸秆经过厌氧发酵后,挥发分含量减少19.48％,固定碳含量增加27.87％,半纤维素与纤维素相对含量分别降低了39.94％与30.96％,木质素相对含量增加了109.14％.热重试验结果表明,与玉米秸秆相比,发酵沼渣最大失重速率减小,且残炭率较高.对二者热解动力学分析结果表明,发酵沼渣的活化能主要分布于91 ～ 130 kJ/mol之间,低于玉米秸秆原样;二者机理函数可采用两阶段理论描述,当转化率小于0.6时可由反应级数n=2机理模型进行描述;当转化率大于0.6时,玉米秸秆更符合圆柱形对称三维扩散机理(D4),发酵沼渣更符合球形对称三维扩散机理(D3).本研究为发酵沼渣热解制备生物燃料工艺条件优化和工业化应用提供了理论依据.