基于热重法的生物质工业分析及其发热量测定

Industrial analysis and determination of calorific value for biomass based on thermogravimetry

为了比较不同种类生物质的燃烧特性,丰富热重分析技术的应用方向,该文采用热重分析技术对农业剩余物、林业剩余物和工业加工废渣的代表性生物质进行了空气气氛下不同升温速率的燃烧特性试验研究。研究表明:3种类型生物质的燃烧过程均包括4个主要阶段:水分蒸发阶段、挥发分析出及燃烧阶段、固定碳燃烧阶段、燃尽阶段。该文提出1种确定样品工业分析值的方法,即热分析曲线法,并推荐应用20℃/min升温速率下的热分析曲线图来计算确定。同时还提出1种差热分析法,用以计算生物质样品发热量,分析发现,农业秸秆类剩余物适用于20℃/min的升温速率,木屑和甜高粱渣适用于5、10℃/min的升温速率。该文提出的计算工业分析值的热分析曲线法与计算发热量的差热分析法,为热重分析技术研究生物质的燃烧特性提供了新的应用方向,但2种新方法的建立,以及他们的有效性和适用性,仍需要大量试验数据的验证和进一步的试验研究。

The global energy crisis arouses growing interest in the field of renewable energy all over the world. Biomass is a world-recognized environmentally friendly renewable energy because of its lower contents of N and S element and the approximate zero net emissions of CO2. How to make full use of biomass energy has been an important direction of studies in the field of renewable energy. Biomass combustion is one of the most important technologies for large-scale efficient and clean utilization of biomass energy. The existing study on biomass combustion characteristics in China mostly focus on a kind of biomass, and little on different kinds of biomass. Thermal analysis curves （TGA- DTG- DTA） are commonly used in combustion characteristic analysis and dynamic analysis, but not in biomass combustion analysis. Therefore, this study investigated the combustion characteristics of biomass--agricultural residues （wheat straw, cotton straw, and cornstalk）, forestry residues （sawdust）, and industrial waste residues （sweet sorghum slag） at different heating rates （5, 10, 20, and 30℃/min） in air by thermo gravimetric analysis technology. Results showed that all the biomass combustion included four main phases：water evaporation stage, devolatilization and combustion stage, fixed carbon combustion stage, and burnout stage. The comprehensive combustion characteristic index S was ordered in wheat straw （XMJ）＆gt;cotton stalk （MHJ）＆gt; sweet sorghum slag （GLZ）＆gt; cornstalk（YMJ）＆gt; sawdust （MX）. The rise of heating rate could improve the combustion performance of biomass samples. Based on these results, a TGA-DTG-DTA method was proposed to determine the values of industrial analysis of samples. The weightlessness rate of A-B, B-C, and C-D was equal to moisture content, volatile content, fixed carbon content, respectively. The weightlessness rate of point D was the ash content of the sample. Thermal analysis curves under 20℃/min heating rate were recommended for industrial analysis. Meanwhile, a differential thermal analysis method was also proposed to determine calorific value of samples, which was the heat difference of peak area between RS （the heat discharged） and OP （the heat absorbed）. The other heat-related curves could be obtained from TA-60WS data processing software built in the instrument. Overall, the best combustion performance could be obtained at the heating rate of 20℃/min for agricultural residues, 5℃/min for sawdust and 10℃/min for sorghum slag. The differential thermal analysis and thermal analysis curve expanded the application of thermogravimetric analysis technology in studies on biomass combustion characteristic. However, their effectiveness and applicability required further verification of more experiments and data. It hoped that this study would provide valuable information for maturing biomass combustion technology in China.