渦旋式流體化床燃燒爐中一氧化碳與氮氧化物排放關係之探討

The Study of the Relationship between CO and NOx Emission in the Vortexing Fluidized Bed Combustor

林宜盛(Yi-Sheng Lin)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/碩士(2010年)

https://doi.org/10.6840/cycu201000808

摘要

流體化床燃燒爐之操作溫度較低(750-850℃)，故爐內生成之氮氧化物以燃料式氮氧化物(Fuel-NOx)為主。氮氧化物之生成受到不同操作條件所影響，各操作條件下所形成的燃燒環境亦不同，進而影響爐內氮氧化物之生成與還原反應。燃燒不完全則會產生大量CO，導致燃燒效率降低，而CO常被作為判斷爐內燃燒狀況優劣之指標之一，因此有效控制其排放濃度顯得相當重要。
本研究係建置實驗室規模之渦旋式流體化床燃燒爐，其乾舷區內徑為0.154m高為4m，燃燒室截面積為0.22 m × 0.11 m之矩形。二次空氣由乾舷區底部以切線方向送入爐內，其注入點位於分配板上方0.796 m高。本研究以2.8 mm ~ 3.6 mm之煤炭為燃料，矽砂為床質，利用回應曲面法進行實驗設計並分析實驗數據，探討各操作條件如床溫、床內計量氧比及過量氧率對於旋風分離器入出口之CO及NOx排放濃度之影響並探討CO與NOx之間的關聯性。
研究結果顯示，操作參數對於旋風分離器入出口CO排放濃度之影響，以過量氧率之效應最大，其次為床內計量氧比，床溫之效應則最不顯著。旋風分離器入出口CO排放濃度達到最低之操作條件為床溫800℃、床內計量氧比70%與過量氧率100%。操作參數對於旋風分離器入出口NOx排放濃度之影響，以過量氧率之效應較大，床溫之效應為次之，床內計量氧比之影響為三個參數中最小。旋風分離器入出口NOx排放濃度達到最低之操作條件為床溫900℃、床內計量氧比100%與過量氧率60%。旋風分離器對於煙氣中之CO與NOx之影響並不明顯。最後，由本研究可發現到CO與NOx之關聯性呈指數衰退之現象。

關鍵字

流體化床燃燒爐 ； 旋風分離器 ； 氮氧化物 ； 一氧化碳

並列摘要

The operating temperature is lower in the vortexing fluidized bed combustor than the other type combustors, the major source of NOx originate from fuel-NOx in the combustor. The formation of NOx is deeply influenced with different operating conditions. The different operating conditions form with different combustion circumstances, and then affect the reaction of formation and reduction with NOx. Incomplete combustion produces a large amount of CO so that the combustion efficiency decreases, CO is considered one of the indices to determine that the combustion circumstance is good or not. So it is important to control the gaseous pollutant emission effectively.
A bench-scale vortexing fluidized bed combustor (VFBC) was set up in the present study. The combustor cross area is 0.22 × 0.11 m2, and the freeboard is in 0.154 m I.D. and 4 m height. The secondary air injected nozzles were installed tangentially at the bottom of freeboard. The particle size of 2.8 mm to 3.6 mm coal was used as the fuel. Silica sand was employed as the bed material. The effects of various operating parameters, such as bed temperature, stoichiometric oxygen in the combustion chamber and the excess oxygen ratio were investigated. These operating conditions were determined by means of response surface methodology. The effects of operating conditions on NOx and CO emissions at the cyclone inlet and outlet and the relationship between concentration of NOx and CO were investigated.
The results of CO emissions at the cyclone inlet and outlet show that the effect of the excess oxygen ratio is more important than stoichiometric oxygen in the combustion chamber, and the effect of bed temperature is not obvious. The optimum operating condition for the minimum CO emissions at the cyclone inlet or outlet are at bed temperature=800℃, stoichiometric oxygen in the combustion chamber=70% and excess oxygen ratio=100%。
The results of NOx emissions at the cyclone inlet and outlet show that the effect of excess oxygen ratio is more important than bed temperature, and the effect of stoichiometric oxygen in the combustion chamber is the lowest of the three parameters. The optimum operating condition for the minimum NOx emissions at the cyclone inlet and outlet are at bed temperature=900℃, stoichiometric oxygen in the combustion chamber=100% and excess oxygen ratio=60%. With regard to the CO and NOx emissions, the effect of the structure of the cyclone is not so obvious. Finally, the relationship between concentration of CO and NOx indicates the phenomenon of the exponential decay in the study.

並列關鍵字

CO ； cyclone ； fluidized bed combustor ； NOx

參考文獻

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