渦旋式流體化床燃燒爐中以煙氣迴流燃燒花生殼之研究

Combustion of Peanut Shell in a Vortexing Fluidized Bed Combustor with Flue Gas Recirculation

王源杰(Yuan-Jie Wang)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/碩士(2013年)

https://doi.org/10.6840/cycu201300905

摘要

花生殼是台灣常見農業廢棄物，年產1.6萬噸，其熱值高適合當做生質燃料應用於流體化床燃燒爐中。本研究係於一渦旋式流體化床燃燒爐中，以矽砂為床質，進行花生殼之燃燒實驗。爐體總高度4.6m，燃燒室面積0.8m × 0.4m之矩形，乾舷區內徑0.75m之圓柱形，二次風由乾舷區下端，距氣體分佈器2.05m高，以切線注入。
本研究將破碎後之花生殼及顆粒狀花生殼分別於固定釋熱量130,000 kcal/hr，一次風總風量3 Nm3/min，二次風總風量2 Nm3/min，並在煙氣迴流模式下，改變過量氧率、床下計量氧比、粒徑大小，探討操作條件對爐內溫度、污染物排放、燃燒份額、燃燒效率等影響。於進料時發現破碎花生殼容易架橋，故對架橋現象進行的深入探討。此外為了解其渦旋效應，於爐內總氧量0.8175 Nm3/min下，固定一次風總風量3 Nm3/min，二次風量由1.56 Nm3/min，逐漸加入0、0.44、0.75及1 Nm3/min之氮氣，以探討軸向、徑向溫度分佈，飛灰收集量、污染物排放、燃燒份額、燃燒效率之影響。
實驗結果顯示，當過量氧率增加時，出口CO減少，NOx增加，燃燒室燃燒份額下降，乾舷區燃燒份額上升，燃燒效率上升；床下計量氧比增加，破碎花生殼出口CO排放濃度增加，NOx減少，燃燒效率下降；而顆粒花生殼於床下計量氧比效應下，其結論與破碎花生殼相反；在本研究條件下，粒徑越大，燃燒效率越高，CO排放減少，NOx增加；二次風流量越大，渦旋效應越強，使燃料於爐內滯留時間增加，CO排放減少，燃燒效率增加。經本研究得知花生殼適合於流體化床中燃燒，其CO及NOx之排放濃度皆低於法規標準，燃燒效率可達99%以上。

關鍵字

花生殼 ； 流體化床 ； 燃燒

並列摘要

Peanut shell is common agricultural waste in Taiwan, and its high calorific value is suitable to be used as biomass fuel for fluidized bed combustion. In this study, the experiments are conducted in a vortexing fluidized bed combustor (VFBC) using silica sand as bed materials. The combustor has a height of 4.6 m. The combustion chamber is 0.8 m × 0.4 m in area and freeboard has an ID of 0.75 m. The secondary gas is introduced into the freeboard tangentially at 2.05 m above the air distributor plate.
Different operating conditions, including excess oxygen ratio, stoichiometric oxygen ratio in the bed, and particle sizes, are used to investigate their effects on the axial temperature profile, pollutant emissions, combustion efficiency, and combustion fractions. Furthermore, in order to understand the vortexing effect, with a fixed total oxygen rate of 0.8175 Nm3/min and primary gas rate of 3 Nm3/min in the furnace, nitrogen is added to secondary gas in 4 separate runs with the rate of (0, 0.44, 0.75 and 1 Nm3/min), respectively.
The results showed that crushed peanut shell can cause bridging in the hopper during the feeding process; therefore, compressed shell pellets is the best way to solve the feeding problem. As excess oxygen ratio increases, both of crushed and pelletized peanut shell have higher bed temperature and combustion efficiency. As stoichiometric oxygen ratio increases, different results for crushed and pelletized peanut shell are observed. This is due to the different major combustion locations from different particle densities of the two fuels. Axial CO and NOx profiles indicate there are two specific regions inside the reactor, i.e. formation and decomposition. The CO emission from the vortexing FBC is found to be in the range of 55-73 ppm for crushed peanut shell and of 45-60 ppm for pelletized peanut shell, with excess oxygen ratio of 40-60%. In every experiment, combustion efficiency of peanut shell is always over 99%.

並列關鍵字

combustion ； Fluidized Bed ； Peanut shell

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