台灣六種主要焙燒竹材燃料性質之研究

Abstract

近年來能源短缺與環境問題日漸受到各界關注，因此開發新技術與發展再生能源已成為全球潮流。竹類為大型木質草本植物，其生命週期相較一般樹木為短，具有發展生質能源的潛力。但未處理之竹材卻有高含水率、低熱值、運送及儲存不易等缺點，故須經過焙燒處理以改善缺點，並提高熱值，增加能源密度。 本研究以能源化的角度探討竹材作為生質煤的可行性，探討焙燒後的熱化學性質，以提供作為燃料使用時依據。實驗針對6種竹材進行250、270及290 oC的焙燒處理和TGA焙燒模擬，並給予60、75及90 min的持溫時間，接著進行近似分析、元素分析與熱值分析探討生質物於焙燒前後之基本性質差異，亦會透過TGA分析，探討生質物的熱重特性及其組成分變化。 實驗結果顯示出，隨著焙燒溫度的上升，色澤會由淺色轉至深褐色。竹類生質物具有低N及S的特性，而其C含量會隨焙燒溫度的上升而增加，而H與O的含量反之下降，成分漸漸趨於煤類，尤以夏季綠竹與夏季刺竹成分最接近泥煤。近似分析結果中發現，竹類生質物具低灰分與高揮發分之特性，而經過焙燒後，其含水率與揮發分會降低，相對固定碳則會提高，含水率降低對於燃料之運輸及儲存上具有正面價值。在熱值部分，秋季竹類熱值約在4,200-4,500kcal/kg，夏季材之熱值則普遍較秋季材為高，介於4,501-4,810 kcal/kg之間，且經過焙燒後可有6-16%之提升。其中秋季竹材以綠竹、麻竹與刺竹的能量密度最高；夏季竹材之能量密度則是除了麻竹外皆有良好的提升(約提高12%)。值得注意的是，秋季竹材以麻竹焙燒效果最佳，孟宗竹最差；而夏季竹材則剛好相反，以孟宗竹效果最佳，麻竹最差。 綜合上述，可發現竹材為一具有能源價值之生質物資源，且焙燒處理確實會提升竹類生質物的燃料性質，如可燃分、熱值、能量密度…等，而研究中各項試驗分析之結果，相信對台灣往後的竹材焙燒技術發展具有正面的幫助。

Torrefaction is a kind of thermal treatment process that carried out at temperatures ranging from 200 to 300 oC to improve its heat value and grindability for substitution of coal. In this process the biomass hemicellulose is degraded, maintaining its cellulose and lignin content. Six kind of major bamboos including Moso bamboo, Makino bamboo, Ma bamboo, Green bamboo, Thorny bamboo, and Long shoot bamboo were torrefied in the study. All bamboos were felled at fall of 2010 and summer of 2011. After cutting, bamboos were dried and heated to 250, 270, and 290 oC with 60, 75, and 90 minutes duration. Then the torrefied mass was carried basic property testing including proximate analysis, ultimate analysis, TGA, and heat value in order to understand the difference among raw material and its torrefied products. Results show that the color of biomass will turn to brown or dark brown as increasing of torrefied temperature and time duration. Ultimate analysis shows that oxygen element was reduction while hydrogen and carbon content increased with the temperature increasing. Therefore torrefaction process results in reduction in O/C ratio which essentially contributes to increase in heat value. The results of the proximate analysis also shown as increasing of terrified temperature, volatile fraction was reduced while fixed carbon was increased. Raw bamboos were higher volatiles and lower Ash content, however, volatiles reduced and fixed carbon increased after torrefaction process. Both heat value of fall bamboos and summer bamboos are about 4,200-4,500kcal/kg and 4,501-4,810 kcal/kg, respectively. Heat value of torrefied bamboos are 6-16% higher than that of raw material except fall Moso bamboo and summer Ma bamboo. All fall Green, Ma and Thorny bamboos are higher energy density after torrefaction and most of summer bamboos increase 12% energy density after torrefaction. Among all fall torrified bamboos, Ma shown the highest heat value while Moso was the lowest. However, summer torrified bamboo shown the reversed results. These indicates that bamboo is a suitable biomass source for torrefaction process.