生質顆粒在恒溫流場中的乾燥和熱分解

Drying and Pyrolysis of Biomass Particles in a Constant Temperature Flow Field

林正亮(Jeng-Liang Lin)

《農業機械學刊》 6卷4期 (1997/12) Pp. 1-12

https://doi.org/10.30062/JAM.199712.0001

摘要

乾生質顆粒為基礎所建立的燃燒模式，可能無法精確的描述高濕農產廢棄物的整個燃燒過程，因為含水率的高低與燃燒過程之影響並不清楚，因此為能以燃燒方式順利處理高濕農產廢棄物，應先探討乾燥與其後續過程之關係。生質顆粒在高溫流場中，以一考慮熱傳遞和化學分解反應的模式，描述顆粒在燃燒過程中乾燥和熱分解的現象，其中乾燥過程是以暫態熱傳遞具有移動邊界條件描述之，並假設水份蒸發是在一移動球面進行而且向顆粒中心移動，而熱分解則以一階單一反應表示之。分析結果顯示出大顆粒的燃燒過程中，乾燥和熱分解有極大部份是同時發生，但對於小顆粒而言，乾燥和熱分解的過程就有明顯的先後順序；流場溫度愈高，乾燥和熱分解同時進行的比例愈高，而在較低溫度下，乾燥和熱分解的過程，有先後順序的傾向愈明顯。此外，顆粒含水率的高低對於乾燥和熱分解所需時間，就如預期般，含水率愈高，乾燥所需時間愈長，而且與顆粒直徑平方成正比。分析顆粒與流場間的熱傳遞特性對於乾燥和熱分解影響，其結果並不顯著，原因為顆粒溫升主要是由顆粒內的熱傳導所控制。

關鍵字

乾燥 ； 熱分解 ； 熱傳遞

並列摘要

Combustion model based on dry biomass particles might not be applied to describe whole combustion behavior precisely for agricultural wastes with high moisture content. Since the effect of moisture on combustion is not well understood, it is necessary to study the relationship among drying and its following procedures in order to dispose high moisture agricultural waste effectively by combustion. A model with heat transfer and chemical decomposition was developed to describe drying and pyrolysis behaviors during combustion as biomass particles heating in a furnace. A transient heat transfer with moving boundary condition and a drying front moving toward center of a burning particle were used to simulate drying process. Pyrolysis was assumed to be an one-step first order reaction. Analytical results indicate that drying and pyrolysis occur mostly simultaneously for larger particles and sequentially for smaller particles. For temperature effect, drying and pyrolysis occur likely to be simultaneous as burning at a higher temperature; however, drying and pyrolysis can be distinguished as burning at a lower temperature. In addition, time required for drying and pyrolysis would be longer for particles with higher moisture content as expected. The effects of thermal properties between particles and surroundings on drying and pyrolysis processes were found to be minimal, the reason of the results is that increase of particles temperature to be controlled by heat conduction inside particles.

並列關鍵字

Drying ； Pyrolysis ； Heat transfer