玉米秸秆与市政污泥混合热解特性及动力学分析

    Pyrolysis characteristics and kinetic analysis of maize stovers mixed with municipal sludge

    • 摘要: 为探究玉米秸秆与市政污泥的混合热解特性,基于热重分析法,在不同升温速率(10、20和30 ℃/min)下对玉米秸秆、市政污泥及混样进行热重试验,同时采用Coats-Redfern积分法进行了动力学分析。结果表明:玉米秸秆与市政污泥相比热解特性差异大,残余率相差18.57%,综合热解指数相差35.73×10-5,活化能E相差35.31~46.88 kJ/mol。随市政污泥的从10%到90%,热解起始温度由277.7 ℃下降至256.1 ℃,残余率由33.69%增加至45.83%,最大失质量速率由7.88%/min下降至3.11%/min,综合热解指数由8.5×10-5下降至1.7×10-5。表明市政污泥虽改善了混样的热解起始温度,但同时也使残余率增加,失质量速率变缓,综合热解指数降低。混样综合热解指数显示二者共热解整体存在抑制作用。动力学参数显示,升温速率升高使活化能增加,玉米秸秆单独热解过程所需活化能E大于市政污泥,市政污泥的质量分数从10%提高到90%,热解活化能由66.01~46.16 kJ/mol降低至44.47~17.04 kJ/mol。该研究可为玉米秸秆和市政污泥的利用提供基础支撑。

       

      Abstract: Abstract: Pyrolysis technology is one of the main ways to treat biomass wastes. A typical agricultural and forestry waste, corn straw contains alkali metals and other catalytic components, showing the excellent pyrolysis behavior with high volatile matter while low ash content. Another typical municipal solid waste, the sludge contains a large amount of thermally degradable organic matter, pathogenic microorganisms, toxic and harmful organic matter. There are relatively high moisture and ash content in the sludge, compared with the corn straw. The co-pyrolysis of the sludge and the corn straw can be an effective way to improve energy efficiency, thereby enhancing the performance of the products. As such, it can fully realize the complementary advantages of two wastes. In this study, a ThermoGravimetric Analysis (TGA) test was performed on the mixed samples with the corn stalk and municipal sludge in the mass ratio of 9:1, 3:7, 5:5, 7:3, and 1:9 at different heating rates (10, 20, and 30 ℃/min), to explore the pyrolysis characteristics and the Degree of Synergy (DS) in the single and mixed samples. A Coats Redfern method was used to clarify the kinetic of weight loss curves. The results indicated that there were great differences in pyrolysis characteristics between corn stalks and municipal sludge, where the residual rate differed by 18.57 percentage points, the comprehensive pyrolysis index differed by 35.73×10-5, and the activation energy differed by 35.31 -46.88 kJ/mol. Specifically, the activation energy of sludge pyrolysis was lower than that of corn straw. Furthermore, the activation energy increased with the increase of heating rate, with a maximum of 30 ℃/min. The initial temperature of pyrolysis decreased from 360.3 ℃ to 440.3 ℃, with the content of municipal sludge varied from 10% to 90%, while the main pyrolysis interval of mixed samples became longer from 277.7-360.3 ℃, shifting to the high-temperature zone. The residual rate increased from 33.69% to 45.83%, whereas, the maximum weight loss rate decreased from 7.88 to 3.11%/min. There was a similar behavior in the comprehensive pyrolysis index, indicating a decrease from 8.5×10-5 to 1.7×10-5. The starting temperature of pyrolysis in the mixed samples was significantly improved by the municipal sludge, but some negative effects also occurred, including the longer interval time of pyrolysis, the higher residual rate, the slower weight loss rate, and the lower comprehensive pyrolysis index. The comprehensive pyrolysis index of mixed samples was lower than that of theoretical value, indicating an inhibitory effect in the co-pyrolysis of mixed samples. The activation energy required for the individual pyrolysis of corn stalks was greater than that of municipal sludge. The increase of activation energy varied at low and high temperatures in the mixed samples of corn stalks and municipal sludge, as the heating rate increased. The activation energy of pyrolysis in the mixed samples decreased from 66.01-46.16 kJ/mol to 44.47-17.04 kJ/mol, as the content of municipal sludge increased from 10% to 90%. The findings can provide insightful data support to the co-pyrolysis of corn straw and municipal sludge, and the further application of products in low-carbon agriculture.

       

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