- 學位論文
選擇性非觸媒還原法於一氧化碳鍋爐脫硝過程應用之數值解析
Numerical Analysis of the SNCR Method for NOx Reduction in a Carbon Monoxide Boiler
摘要
本文探討選擇性非觸媒還原(SNCR)法對於一氧化碳鍋爐脫硝效果之影響，研究中探討還原劑(NH3)之注入位置、注入量與孔徑等之影響，本研究測試了5個不同的NH3注入位置、5種不同的還原劑注入孔徑、以及5種不同的還原劑注入量，由研究結果發現NOx主要是由鍋爐入口附近高溫區產生；還原劑噴注位置對於NOx去除效果有密切影響，必須選擇可使還原劑通過SNCR法合適反應溫度區的噴注位置，例如鍋爐入口或氧化段下方軸向迴流區後半部位置，方可使還原劑發揮降低NOx的功能；當還原劑由鍋爐入口噴入時，隨著還原劑的噴入量增加，NO的降低效率提升，但效率逐漸緩和並趨向於定值，當還原劑噴入量達到設計量的2.5倍(NSR=26.2)時，鍋爐內部NO平均生成量由46.2ppm降低至21.7ppm，效率達53%，比還原劑噴入量為設計值時之NO去除率還低2%，在另一方面，當還原劑由鍋爐入口下游3.6m處噴入時，還原劑噴入量對於NO濃度的影響並不明顯；當還原劑由鍋爐入口噴入時，當噴注孔徑最小時(DNH3=3mm)，NO濃度降低最多，但在相同的還原劑噴入量情況下，還原劑噴注孔徑大小對於NO濃度分佈、溫度分佈與流線軌跡等之影響並不明顯， SNCR法之脫硝效率主要仍是與還原劑在流場中之合適反應溫度區有關，若無法達到合適反應溫度區，則還原劑噴注孔徑再小，或者還原劑噴入深度再深，脫硝效果仍是難以改善。
並列摘要
This study investigates numerically the NOx reduction by SNCR in a CO boiler. The combustion and fluid flow in the FPC CO boiler is examined with emphasis on the effect of SNCR on NOx reduction. Parametric studies which include the influences of the injection position, amount, and hole size of the reducing agent were performed. Simulation results indicate that NOx is formed mainly in the high temperature region near the boiler inlet where the mixing caused by swirler is strong. Among the reducing agent injection positions investigated, the boiler inlet has the best NOx reduction efficiency, while 0.5m downstream the boiler inlet has the worst NOx reduction efficiency. When the reducing agent is injected from the boiler inlet, a NOx reduction efficiency of 51% is achieved if designed amount of reducing agent is injected. When reducing agent is injected from 3.6m downstream the boiler inlet, the NOx reduction efficiency is 14% for designed amount of reducing agent. The injection position of reducing agent has a siginificant influence on the NOx reduction efficiency. Positions of better NOx reduction should be where reducing agent can pass through a region suitable for SNCR reaction or the residence time of reducing agent in a suitable reaction region can be longer, e.g., the boiler inlet or the lower portion of the oxidizer downstream section. When reducing agent is injected from the boiler inlet, NOx reduction efficiency increases with the amount of reducing agent but gradually levels off. When the amount of reducing agent is increased to 2.5 times the designed value, NOx reduction efficiency is 53%. On the other hand, when reducing agent is injected from 3.6m downstream the boiler inlet, the NOx concentration is not significantly influenced by the amount of reducing agent injected. Finally, when reducing agent is injected from the boiler inlet, the best NOx reduction efficiency is achieved when the size of reducing agent injection hole is the smallest. However, on the condition of fixed amount of reducing agent injected, the NOx concentration, temperature and streamtraces inside the boiler are not significantly influenced by the size of reducing agent injection hole. On the other hand, when reducing agent is injected from 3.6m downstream the boiler inlet, the NOx concentration, temperature and streamtraces inside the boiler are not significantly influenced by the size of reducing agent injection hole.