下抽式木質燃料空氣氣化爐操作條件對產氣狀況之影響研究

Influences of Operating Conditions on Quality of Producer Gas of Downdraft Wood Gasifier

蔡尚貿(Shang-Mau Tsai)

指導教授 ： 郭景宗

國立臺灣大學/工學院/機械工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.00816

摘要

生質是一種重要永續能源，它的主要來源為廢竹木及收成後之農作物根莖與蓬蓱M水生植物等。使用生質當燃料來發電可減少地球溫室氣體的排放。然而生質能的運用應該從傳統低效率的直接產熱運用轉變成用來結合熱電共生的高效率運用。生質能的氣化過程是將固態燃料轉換成氣體燃料，再將氣體燃料用於可燃氣渦輪機或引擎等現代轉換裝置來產生電和熱。以下抽式氣化爐可製造出低焦油量與低粒子之乾淨產氣，非常適合小型之熱電共生系統來使用。因此，本研究以一小型下抽式氣化爐（高度750mm與直徑150mm）來探討操作條件對產氣狀況之影響研究。
氣化反應爐可於起爐後之九十分鐘內達到穩定狀態，且能夠連續輸出可燃氣體。由氣化反應爐中可發現生質之乾燥、熱解、燃燒與焦炭之氣化等各種不同反應區。氣化爐內之反應區分佈狀況不但會對產氣熱值與產氣率產生影響，同時也會影響焦油與粒子之生成量。而影響反應區分佈狀況之因素包括有：生質燃料種類、生質含水份、燃料供給率、燃燒溫度與輸配空氣量等之差異。
本氣化爐之最佳操作範圍已經由實驗找出。當燃料供給率之範圍為2.55至2.81 Kg/hr時，其最佳空燃比之範圍為2.79 至3.79之間；此時可輸出最佳之產氣熱值範圍為3.81至4.40 MJ/Nm3，且其產氣率範圍為8.8-12.4 Nm3/hr。實驗結果顯示產氣成份、熱值與產氣率皆會於燃料供給時降低而使得範圍變化太大。建議可藉由減少燃料進料量與縮短燃料供給間隔來改善產氣輸出並使變化幅度縮小。

關鍵字

熱解 ； 生質 ； 氣化爐 ； 氣化

並列摘要

Biomass is an important renewable energy resource produced from trees, agriculture crops, and aquatic plants. Using biomass as fuel for power generation is carbon neutral and helps to lower the emission of global warming gases. However, the application of biomass should be shifted from its traditional low-efficiency applications for heating to high-efficiency applications for combined heat and power generation. The gasification process for biomass converts renewable substances to fuel gas that can be used in a modern conversion device, such as gas turbine or engine, for the production of electricity and heat. Downdraft stratified gasifier is suitable for small scale heat and power production due to the fact that its producer gas contains low tar and low particulates. Therefore, a laboratory scale downdraft gasifier with 750mm height and 150 mm diameter is used in this study to investigate the relations between quality of producer gas and operation conditions.
Steady state condition is reached within ninety minutes after start-up, then the producer gas is generated continuously. Different reaction zones including heating and drying, pyrolysis, gasification, combustion and char reduction, can be identified inside the gasifier reactor. Distribution of reaction zones affects the heating value of producer gas and the rate of gas generation, as well as tar content and particulates. Factors influence the distribution of reaction zones including fuel type, fuel load, moisture content, combustion temperature and air staging.
Optimum operation condition of the gasifier varies in the range of 2.79 to 3.79 Kg-air/Kg-fuel at the feeding rate between 2.55 and 2.81 Kg/hr. HHV of producer gas is 3.81-4.40 MJ/Nm3 at a volumetric flow rate of 8.8-12.4 Nm3/hr. The producer gas composition, heating value, and generation rates vary in a wide range more less in synchronization of the fuel feeding cycles. Improvement is suggested by shortening the feeding intervals with lower charge to even out the fluctuations in output.

並列關鍵字

biomass ； pyrolysis ； gasification ； gasifier

參考文獻

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