塞流式反應器中一氧化氮之均相反應及異相催化反應

Homogeneous and Heterogeneous Catalytic Reactions of Nitric Oxide in a Plug-Flow Reactor

陳俊甫(Jiun-Fu Chen)

指導教授 ： 錢建嵩

中原大學/工學院/化學工程研究所/碩士(2001年)

https://doi.org/10.6840/cycu200100377

摘要

燃燒爐內預防氮氧化物之生成主要可由燃料預先處理、燃燒過程之改善及後段煙道氣處理三方面著手。無論採用何種方式，要有效控制氮氧化物之排放，首要之務就是要了解氮氧化物之生成與還原機制。本研究係針對NO之均相(homogeneous)及異相催化(heterogeneous catalytic)反應進行探討，以石英玻璃及316不鏽鋼製之塞流式反應器(plug flow reactor, PFR)模擬流體化床乾舷區中不同之溫度(600~1000℃)、氧濃度(3.7~9.58 vol %)及停滯時間(1.56~3.76 sec)對NO轉化率之影響。

在均相反應系統NO/N2/O2中，NO藉由反應NO+O+M=NO2+M轉化為NO2，而反應速率常數k值隨著溫度升高而降低，故NO之轉化率隨溫度升高而降低；氧濃度增加，受熱分解所產生之氧原子增加，故較高氧濃度時有較高之NO 轉化率。停滯時間增加，NO之轉化率亦隨之增加。

在316不鏽鋼管非均相反應系統NO/N2中，700℃時NO藉由異相催化反應(heterogeneous catalytic reaction)還原，NO轉化率隨溫度增加而增加；隨停滯時間增加而有先增加後持平之趨勢。316不鏽鋼管內之非均相反應系統NO/N2/O2中，反應以均相反應為主；NO之轉化率會隨溫度升高而降低，隨氧濃度增加而增加。異相反應中NO轉化之程度亦隨氧濃度增加而增加。

在含氧狀況下將不鏽鋼網狀物置入石英玻璃管中，則NO之轉化率隨不鏽鋼網狀物之表面積增加而增加。

關鍵字

一氧化氮 ； 異相催化反應 ； 均相反應

並列摘要

The chemical reactions in the system NO/N2/O2 have been studied in a plug-flow reactor (PFR) to simulate the reaction within the freeboard of the fluidized-bed combustor. Experiments were carried out over wide ranges of temperature (600~1000 ℃), residence time (1.56~3.76 sec) and concentration of oxygen (0~9.58 vol %). The homogeneous reactions were performed in a quartz-glass reactor. The heterogeneous catalytic reactions on stainless steel were performed in a 316 stainless-steel reactor and a quartz glass reactor with stainless-steel meshes.

The major homogeneous reaction of the NO/N2/O2 systems is NO+O+M=NO2+M. The rate constant of this reaction decreased with temperature and the conversion of NO decreased as the temperature increased. On the other hand, the conversion of NO increased with residence time and the concentration of oxygen. It is suggested that the free radicals of oxygen that formed during thermal homolysis played an important role in this homogeneous reaction.

NO can be reduced by the heterogeneous catalytic reaction of the mixture of NO/N2 on the stainless steel. This reaction started at 700℃ and NO was almost reduced entirely at 1000℃. In this situation, the reduction rate of NO increased with increasing residence time. In the presence of oxygen, the conversion of NO decreased with the concentration of oxygen. The conversion of NO in the stainless-steel reactor is higher than that in the quartz-glass reactor in the same operating condition. It is showed that the conversion of NO increased with surface area of stainless steel.

並列關鍵字

nitric oxide ； heterogeneous reaction ； homogeneous reaction

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