典型农作物秸秆组成及燃烧动力学分析

Composition and combustion dynamics analysis of typical crop straws

为了探讨我国典型区域典型农作物秸秆的组成及燃烧特性,在典型农作物种植区(河北省和吉林省)选择了三种典型秸秆(小麦秸秆、水稻秸秆和玉米秸秆),对其进行组分分析(工业分析、元素分析、纤维组成),借助差热-热重仪对其燃烧动力学特性进行研究。结果表明:三种秸秆中水稻秸秆灰分和综纤维素含量最高,小麦秸秆中S、Hg含量最高,其他工业分析(水分、挥发分、固定碳)和元素(C、H、O、N)组成均无明显差异。不同升温速率下,三种秸秆的TG和DTG曲线总体趋势相似,两个明显的失重峰分别对应挥发分的析出和燃烧阶段、固定碳燃烧阶段,且前者的失重率远高于后者;同一升温速率下,三种秸秆在低温燃烧区(挥发分析出和燃烧)的最大失重率由高到低依次为小麦秸秆>水稻秸秆>玉米秸秆,而高温燃烧区(固定碳的燃烧)玉米和水稻秸秆的最大失重率没有明显差别,均高于小麦秸秆。秸秆低温区燃烧和高温区燃烧动力学过程均符合二级燃烧动力学方程。研究表明,三种秸秆具有高挥发分、低灰分(水稻秸秆除外)、低硫的特点;秸秆的燃烧失重主要是挥发分的析出和燃烧,其次是固定碳的燃烧,而水分蒸发贡献量最少;快速失重峰形不仅与秸秆的组成有关,还与挥发分初析温度高低有关;双组分分阶段反应模型能够科学地描述农作物秸秆的燃烧动力学过程。

In order to discuss the composition and the combustion characteristics of typical crop straws from a typical region of China, three typical crop straws(wheat straw, rice straw, and corn straw)were chosen from typical crop straw planting areas(Hebei Province and Jilin Province). The compositions(industrial analysis, elemental analysis, and fiber composition)were analyzed and the combustion dynamics characteristics were studied using different heat and a thermogravimetric analyzer. The results showed that the contents of ash and synthetic cellulose of the rice straw were the highest among the three straws, and that the contents of S and Hg of the corn straw were the highest. Other industrial analyses(moisture, volatile matter, and fixed carbon)and element(C, H, O, and N)compositions showed no significant differences. At different heating rates, the overall trends of the TG and DTG curves of the three straws were similar. The two distinct weightlessness peaks corresponded to the precipitation and combustion stage of volatile matter and the combustion stage of fixed carbon, respectively;the weight loss rate of the former was much higher than that of the latter. At the same heating rates, the maximum weight loss rates of the three straws in the low temperature combustion zone(volatile matter precipitation and combustion stage)were from high to low in the order of wheat straw > rice straw > corn straw, while those of the rice straw and corn straw in the high temperature combustion zone(fixed carbon combustion stage)showed no significant difference, and both were higher than that of wheat straw. The combustion process of the straws in the low temperature zone and high temperature zone accorded with the two-stage combustion kinetics equation. The results indicated that the three straws had the characteristics of high volatile matter, low ash(except rice straw), and low sulfur contents. The weight loss of straw combustion was mainly due to volatile matter precipitation and combustion followed by fixed carbon combustion, while the contribution of water evaporation was the least. The peak shape of fast weightlessness was not only related to the composition of straw, but also to the initial precipitation temperature of volatile matter. The two-stage reaction model can scientifically describe the combustion kinetics of crop straws.