流體化床燃燒爐中醋酸對氮氧化物排放之效應

The Effect of Acetic Acid on NOx Emission from a Vortexing Fluidized Bed Combustor

顏維生(Wei-Sheng Yen)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/碩士(2008年)

https://doi.org/10.6840/cycu200900219

摘要

近年來對於燃燒產生之煙氣中氮氧化物排放減量技術有快速的發展，主要分為燃料預先處理、燃燒過程改善及煙道氣處理三方面，其中以煙道氣處理之選擇性非觸媒還原法的設備與操作較為簡易，一般選用尿素或氨等含氨基化合物做為還原劑，將其注入高溫煙道氣中直接與氮氧化物進行還原反應。
本研究係於一高度4.6 m之渦旋式流體化床燃燒爐中進行，燃燒室底面積為0.8 m × 0.4 m，乾舷區內徑為0.75 m，二次空氣由乾舷區底部以切線方向進入爐內，注入點距分配板2.05 m。以煤炭做為燃料，矽砂為床質，醋酸為還原劑，並使用回應曲面法分析實驗數據，藉以探討不同操作條件對燃燒爐中氮氧化物出口排放濃度之影響。主要操作參數為：床內計量比氧量、床溫及醋酸注入位置。
研究結果顯示，出口NOx排放濃度隨著床內計量比氧量的增加而上升；隨著床溫的增加而明顯上升。醋酸對於爐出口NOx排放濃度確有減量之效果，推測其原因為醋酸(CH3COOH)中之羧基(-COOH)與CHi於高溫中游離出的自由基與NOx進行還原反應，且於醋酸注入點為二次風入口下方時有一較低之NOx排放濃度。出口NOx排放濃度減量百分比隨著醋酸注入點高度的上升而增加；隨著床內計量比氧量的增加而增加。NOx排放濃度減量百分比隨床溫上升有一先升後降的趨勢，且於850℃時有一較高之減量效果，判斷其原因為當溫度介於810～850℃，還原反應效果大於床溫上升所產生之NOx濃度增加，於床溫850℃時兩者產生之效果達一平衡抵消狀態，而當溫度繼續上升介於850～890℃，此時床溫上升產生之NOx濃度增加大於NOx還原反應效果，故減量效果有一先升後降的趨勢。

關鍵字

渦旋式流體化床 ； 氮氧化物 ； 回應曲面法 ； 醋酸

並列摘要

In recent years there has been a great development in flue gas control technologies of de-NOx. It is usually divided into three fields: pre-combustion fuel treatment, combustion modification and post combustion flue gas treatment. Selective non-catalytic reduction is an uncomplex post combustion flue gas treatment. NOx in the flue gas was reduced to N2 by reaction with NH3 or urea, CO(NH2)2, at a high temperature.
The effects of operating conditions on NOx emissions were investigated experimentally in a pilot scale vortexing fluidized bed combustor with 0.75 m I.D. and 4.6 m in height. The secondary air injected nozzles were installed tangentially at the bottom of freeboard. Coal was used as the fuels and silica sand was employed as the bed material. Acetic acid was applied to be reductant. The effects of various operating parameters, such as the stoichiometric oxygen in the combustion chamber, the bed temperature and the injecting location of acetic acid were investigated. These operating conditions were determined by means of response surface methodology.
The experimental results show that the NOx emission increased with the stoichiometric oxygen in the combustion chamber and the bed temperature. NOx emission can be decreased by the injection of acetic acid at high temperature. The NOx emission decreases with an increase in the injecting location of acetic acid. The NOx removal increased with the stoichiometric oxygen in the combustion chamber and the injecting location of acetic acid. It should be noted that the NOx removal ratio increases with the bed temperature at first, when the bed temperature is above 850℃, the NOx removal ratio decreases with the bed temperature. Therefore, the optimum temperature for NOx removal is 850℃ or so.

並列關鍵字

VFBC ； NOx ； Acetic Acid ； RSM

參考文獻

黃煜翔, “木屑於渦旋式流體化床燃燒爐中氣態污染物排放之研究,” 私立中原大學化學工程學系碩士論文(2006)。

楊宗翰, “廢液於渦旋式流體化床焚化爐中氧化亞氮排放之研究,” 私立中原大學化學工程學系碩士論文(2003)。

Aho, M. J., J. P. Hamalainen and J. L. Tummavuori, “Conversion of Peat and Coal Nitrogen through NCN and NH3 to Nitrogen Oxides at 800℃,” Fuel, 72, 837-841 (1993).

Aho, M. J., J. P. Hämäläinen and J. L. Tummavuori, “Conversion of Peat and Coal Nitrogen through NCN and NH3 to Nitrogen Oxides at 800℃,” Fuel 72, 837-841 (1993a).

Aho, M. J., J. P. Hämäläinen and J. L. Tummavuori, “Importance of Solid Fuel Properties to Nitrogen Oxide Formation Through HCN and NH3 in Small Particle Combustion,” Combust. Flame 95, 22-30 (1993b).