蔗渣的热解与燃烧动力学特性研究

Study on the kinetic characteristics of bagasse pyrolysis and combustion

利用热重分析仪对蔗渣在不同升温速率下的热解、燃烧失重特性进行了研究。采用Friedman法对反应过程中可能存在的反应机理进行初步判断,蔗渣热解过程由其主要组分半纤维素、纤维素和木质素热解的三个独立的平行反应来描述,相应的反应活化能分别为203.92kJ·mol1、238.50kJ·mol1和77.11kJ·mol1;蔗渣燃烧过程分为两段,第一段类似于其热解过程,第二段由木质素热解和残焦燃烧共同组成的连续反应,反应活化能为255.57kJ·mol1和159.11kJ·mol1。通过非线性回归法拟合获得的曲线与实验曲线基本一致,证实了蔗渣的热解、燃烧过程中存在着上述假定的反应机理。

As a primary energy source, bagasse has huge potential to steam or power generation in sugarcane industry. Due to its high moisture content, bagasse can cause problem of instable combustion in traditional boiler. Some new techniques have been developed to improve thermal conversion efficiency, such as gasification or co-firing with coal. The mechanism of bagasse degradation is very complex and has not been fully elucidated. This work is to describe the thermal decompose behavior of bagasse in different thermochemical processes. Non-isothermal kinetics has been proposed as an alternative to the classical determination of activation energy parameters. The dynamic thermal analysis was carried out in a Netzsch STA409 thermobalance. The pyrolysis and combustion characteristics of bagasse were obtained at different heating rates. With the Friedman method, some latent reaction mechanisms can be derived from the data analysis of non-isothermal experiments. A mechanism based on three independent parallel reactions have been used to model the pyrolysis process of hemicellulose, cellulose and lignin, with activation energy of 203.92 kJ·mol-1, 238.50 kJ·mol-1 and 77.11 kJ·mol-1 respectively. Combustion process can be divided into two distinct stages, with first stage coinciding with pyrolysis process and the second one concerning a consecutive reaction of lignin pyrolysis and char combustion with activation energy of 255.57 kJ·mol-1 and 159.11 kJ·mol-1, respectively. The fitting curve of TG obtained from nonlinear regression method is coincident with experiment curves. Based on this study, it is suggested that the three major components of bagasse appear to be pyrolyzed independently with little interactions. Comparing their thermal stability, lignin is found to be most stable, the next is cellulose, while hemicellulose appears to be least stable. The results can also provide useful data for the design of a thermochemical conversion processes for bagasse utilization.