玉米穗軸於渦旋式流體化床燃燒爐中燃燒之研究

Combustion of corncob in a vortexing fluidized bed combustor

林士閔(Shih-Min Lin)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/碩士(2011年)

https://doi.org/10.6840/cycu201100807

摘要

本研究係在一渦旋式流體化床燃燒爐中，進行玉米穗軸之燃燒實驗。實驗所用之設備，爐體總高度4.6m，燃燒室為面積0.8m × 0.4m之矩形，乾舷區為內徑0.75m之圓柱形，二次空氣從乾舷區下端，距氣體分佈器2.05m高，以切線方式通入。以破碎後之玉米穗軸為研究對象，燃料顆粒大小在5mm以下，針對不同操作模式：(1)只通一次空氣 (2)階段燃燒 (3)煙氣迴流，以及各種不同操作條件，包括床溫、配風比、床下計量氧比，來探討軸向溫度分佈、CO、NOx排放濃度、燃燒效率、燃燒份額、床下以熱傳管移除之熱量，共13組實驗，另外加做1組以切塊方式準備之大顆粒燃料，長度與直徑皆30mm左右之圓柱狀，探討燃料顆粒大小之影響。
實驗結果顯示，最佳之操作模式為煙氣迴流，有最低之CO及NOx排放濃度，燃燒效率有85%~90%左右，床溫操作於700℃、過量空氣量46%及床下計量氧比100%為最佳。另外，燃料大小以大顆粒較佳，有助於NOx降低及燃燒效率之提升，而CO只有些微上升。若以熱能回收角度來看，採用只通一次空氣，可得到較高之燃燒效率，床區之燃燒份額較高，床下熱傳管回收之熱量也最多，床溫操作在700℃、過量空氣量83%、使用小顆粒燃料，床內之熱能回收就可達燃料燃燒產生之熱量的四分之一，且污染物排放濃度皆在法規標準之下，若使用大顆粒燃料，不僅可再提升燃燒效率及床區燃燒份額，還能降低NOx之排放濃度。

關鍵字

煙氣迴流 ； 階段燃燒 ； 玉米穗軸 ； 流體化床

並列摘要

In this study, combustion of corncob was investigated in a vortexing fluidized bed combustor. The combustor has a 4.6m height, an area of 0.8m × 0.4m of combustion chamber and a 0.75 inner diameter of freeboard. The second air was inducted into the freeboard tangentially at 2.05m height above the air distributor. Corncob was shattered into particles of 5mm under. Use different operating modes (only with 1st air, stage combustion and flue gas recirculation (FGR)) and different operating conditions (bed temperature, air ratio, stoichiometric oxygen percentage in the bed) to discuss the axial temperature distribution, CO and NOx emissions, combustion efficiency, combustion proportion and heat removed from the bed. These were carried out 13 experiments. Besides, there was an additional experiment that corncob was cut into cylinders with about 30mm both in length and diameter to discuss the fuel particle size effect.
The results show that the optimum operating mode in this study is FGR. Use FGR to operate at 700℃, with 46% excess air and 100% stoichiometric oxygen percentage in the bed is optimum condition and with combustion efficiency of 85%~90%. Additionally, large particle size is better than small particle size. Use large particle size as fuel can improve combustion efficiency, decrease NOx emission and only increase CO emission slightly. If taking energy recovery into consideration, operating mode of only with 1st air can be the first choice. It gets higher combustion efficiency and more combustion proportion in bed zone, so heat removed by heat transfer tube from the bed was much higher. Heat energy in the bed can recover one-quarter of the heat generated from fuel combustion when operating condition is at 700℃ and with 83% excess air and using small fuel particle size. The pollutant emissions are all conformed to EPA regulations. Furthermore, combustion efficiency and combustion proportion in bed zone can be higher and NOx emission can be lower, if large particle size of corncob was taken as fuel.

並列關鍵字

fluidized bed ； corncob ； stage combustion ； flue gas recirculation

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