圓柱形生質材料的熱分解

Pyrolysis Behavior of Biomass with Cylindrical Shape

林正亮(Jeng-Liang Lin)

《農業機械學刊》 3卷1期 (1994/03) Pp. 47-56

https://doi.org/10.30062/JAM.199403.0004

摘要

一個圓柱形生質材料的熱分解模式，以考量熱傳遞和化學分解反應爲控制因素推導而得，其中化學分解假設爲一階單一反應。模式的分析結果將可用於描述圓柱形生質材料的熱分解過程。參數分析結果顯示化學反應參數中的活化能對熱分解速率影響比頻率因素大，而且祇要生質原的熱性質對溫度的上升有提昇的效果，都能增加熱分解速率。從重量損失和顆粒溫度的關係中可得熱分解的開始溫度約爲500K，而結束溫度約爲800K。
對於特定長度的圓柱體祇要當其直徑小於1×10^(-3)mm時，熱分解所需時間均爲3毫秒，這結果表示較小顆粒的熱分解過程由化學反應所控制。當直徑大於1×10^(-3)mm時，熱分解所需時問隨著直徑的增加而快速的增長，然而最後將趨緩，因爲在直徑非常大時，圓柱體將成爲一個厚度固定的無限大之平板，其熱分解時間將趨近於一常數，所以熱分解時間和直徑的對數並無成比例的關係。以熱對流係數爲常數的熱傳遞模式，分析特定5個不同直徑長度比之圓柱體的熱分解所需時間，而得到熱分解時間和直徑1.2-1.5次方成比例，此結果非常接近於文獻報告中實驗的結果。

關鍵字

熱分解 ； 生質材料 ； 圓柱體 ； 熱傳遞

並列摘要

A pyrolysis model of biomass was developed by considering heat transfer rand kinetics of decomposition as the limiting steps. The kinetics of decomposition was assumed to be a single first-order reaction. Solutions of the model were derived to describe the pyrolysis behavior of biomass with cylindrical shape. Parametric studies show that variation of activation energy has larger effect on pyrolysis than that of frequency factor, and thermophysical parameters having an effect on increase in particle temperature will increase pyrolysis processes. From the results of variation of weight loss with particle temperature, pyrolysis starts around 500 K and is complete around 800 K.
For a cylinder with a certain length, pyrolysis time is always 3 ms for diameter smaller than 1×10^(-3)mm, this result indicates that chemical kinetics limit pyrolysis behavior for smaller particles. For diameter greater than 1×10^(-3)mm, pyrolysis time increases rapidly with increase in diameter, then pyrolysis time will level off even increase in diameter furthermore. A straight line correlation between pyrolysis time and logarithm of diameter can not be obatined since cylinder will become an infinit slab with a finite thickness as diameter to be very large, hence pyrolysis time will converge to a certain value. Variations of diameter with pyrolysis time for 5 different diameter/length ratios of cylinder are obtained by heat transfer model with constant heat convection coefficient; the results, which show pyrolysis time being proportional to the diameter to the 1.2-1.5 power, give a very good agreement with experimental results in literatures.

並列關鍵字

Pyrolysis ； Biomass ； Cylinder ； Heat transfer