本文選題：氮氧化物 + 選擇性催化還原　； 參考：《上海電力學(xué)院》2017年碩士論文

【摘要】：氮氧化物(NO_x)是最主要的大氣污染物之一,隨著世界環(huán)境形勢日益嚴(yán)峻,我國的環(huán)保標(biāo)準(zhǔn)也日益嚴(yán)格。近年來,我國環(huán)保部門對火電機(jī)組NO_x排放要求不斷提高,火電廠的環(huán)保壓力不斷增加。因此開發(fā)出高效、安全、經(jīng)濟(jì)的脫硝技術(shù)已成為火電行業(yè)迫在眉睫的問題。選擇性催化還原(SCR)煙氣脫硝技術(shù)因其具有較高的脫硝效率(最高可達(dá)90%)、對機(jī)組安全運(yùn)行影響較小、系統(tǒng)組成簡單的特點(diǎn)成為火電機(jī)組降低NO_x排放的首要選擇。主要從微觀反應(yīng)機(jī)理入手建立微觀反應(yīng)模型,分析影響脫硝效率的主要因素,其中反應(yīng)溫度、流場均勻性、氨氮摩爾比等對脫硝效率有重要影響;然后以山西某廠600MW超臨界燃煤機(jī)組SCR脫硝系統(tǒng)為研究對象建立宏觀模型,通過FLUENT6.3軟件對某600MW超臨界燃煤機(jī)組的SCR煙氣脫硝反應(yīng)器內(nèi)速度分布場、壓力分布場、氨氣濃度分布場、NO_x脫除效果、NH_3逃逸率及不同粒徑的飛灰顆粒運(yùn)動特點(diǎn)進(jìn)行數(shù)值模擬。首先,主要針對優(yōu)化前反應(yīng)器內(nèi)出現(xiàn)的低速三角區(qū)、高速沖刷區(qū)和低速回流區(qū)采用不同形狀的導(dǎo)流板進(jìn)行優(yōu)化。模擬結(jié)果顯示,“圓弧”型、“平直—圓弧—平直”型、“圓弧—平直”和“平直”型導(dǎo)流板可以有效抑制煙道彎頭和變截面處煙氣速度分離的現(xiàn)象。最終將AIG下游標(biāo)準(zhǔn)速度偏差從優(yōu)化前的56.90%降到9.43%,小于設(shè)計(jì)標(biāo)準(zhǔn)要求的15%;首層催化劑入口標(biāo)準(zhǔn)速度偏差從優(yōu)化前的67.34%降低到8.60%,小于設(shè)計(jì)標(biāo)準(zhǔn)要求的15%。其次,通過噴氨模擬對反應(yīng)器內(nèi)NH_3濃度分布進(jìn)行模擬,模擬結(jié)果表明,由于NH_3濃度較低,受流場均勻性影響較大,微弱的流場偏差對NH_3的濃度分布都有較大的影響。采用等速噴氨時(shí),由于近壁面煙氣流速較低、擾動較小,所以,近壁面NH_3濃度偏高,首層催化劑入口 NH_3濃度分布并不理想,標(biāo)準(zhǔn)濃度偏差Cn達(dá)23.45%,遠(yuǎn)高于設(shè)計(jì)標(biāo)準(zhǔn)要求的5%,脫硝效率僅為80.90%,NH_3逃逸率為23.44uL/L。為降低NH_3濃度分布偏差提高脫硝效率,對噴氨格柵進(jìn)行分區(qū),將噴氨格柵分為三個(gè)區(qū)域,通過4種噴氨方案對氨氣濃度偏差進(jìn)行調(diào)整,最終將首層催化劑入口 NH_3濃度分布偏差由等速噴氨時(shí)的23.45%降低到4.73%,反應(yīng)器出口 NH_3逃逸率由優(yōu)化前的23.44uL/L降低到4.57uL/L,脫硝效率由等速噴氨時(shí)的80.90%提高到86.77%,優(yōu)化效果顯著。最后,對不同粒徑下飛灰顆粒的運(yùn)動特征及濃度分布進(jìn)行了模擬,對合理布置灰斗,加裝吹灰器的具體位置具有一定的指導(dǎo)意義。
[Abstract]:Nitrogen oxide (NO_x) is one of the most important atmospheric pollutants. With the increasingly severe environmental situation in the world, the environmental standards of our country are increasingly strict. In recent years, the environmental protection departments of our country have continuously improved the NO_x emission requirements of thermal power units, and the environmental pressure of thermal power plants has been increasing. The selective catalytic reduction (SCR) flue gas denitrification technology has a high efficiency of denitrification (up to 90%), which has little influence on the safe operation of the unit, and the simple composition of the system becomes the primary choice for the thermal power unit to reduce the NO_x emission. The main factors affecting the denitrification efficiency are analyzed, in which the reaction temperature, the uniformity of the flow field, the mole ratio of ammonia and nitrogen have an important influence on the denitrification efficiency. Then the macro model is established for the SCR denitrification system of 600MW supercritical coal-fired unit in a factory of Shanxi and the SCR flue gas denitrification reaction of a 600MW supercritical coal-fired unit through FLUENT6.3 software. The velocity distribution field, the pressure distribution field, the distribution field of ammonia gas concentration, the effect of NO_x removal, the escape rate of NH_3 and the movement characteristics of fly ash particles with different particle sizes are numerically simulated. Firstly, the low velocity triangle area in the pre optimized reactor, the high speed scour area and the low velocity reflux area are optimized with different shapes of diversion plates. The results show that the "circular arc" type, "flat straight arc straight" type, "circular arc straight" and "flat" type diversion plate can effectively restrain the phenomenon of flue gas velocity separation at the pipe elbow and the variable section. Finally, the standard velocity deviation of the downstream AIG is reduced from 56.90% before the optimization to 9.43%, less than the design standard, 15%; the first layer catalyst. The standard velocity deviation of the inlet is reduced from 67.34% before the optimization to 8.60%, which is less than the 15%. required by the design standard. The simulation of the concentration distribution of NH_3 in the reactor is carried out by the simulation of the ammonia injection simulation. The simulation results show that the uniformity of the flow field is greatly influenced by the low concentration of NH_3, and the weak flow field deviation has a great influence on the concentration distribution of the NH_3. When the constant velocity of ammonia is used, the near wall flue gas velocity is low and the disturbance is smaller, so the NH_3 concentration in the near wall is high, the concentration distribution of the initial catalyst inlet NH_3 is not ideal, the standard deviation is Cn up to 23.45%, which is far higher than the design standard 5%, the denitrification efficiency is only 80.90%, the NH_3 escape rate is 23.44uL/L. to reduce the NH_3 concentration distribution deviation. In order to improve the denitrification efficiency, the ammonia grille is divided into three regions, and the ammonia concentration deviation is adjusted by 4 kinds of ammonia spraying schemes. The NH_3 concentration distribution deviation of the first layer catalyst inlet is reduced from 23.45% to 4.73% at the constant velocity of ammonia injection, and the escape rate of the reactor outlet is reduced from the 23.44uL/L to 4.57u before the optimization. L/L, the efficiency of denitrification increased from 80.90% to 86.77% at the constant speed of ammonia injection. The optimization effect was significant. Finally, the movement characteristics and concentration distribution of fly ash particles under different particle sizes were simulated. It was of certain guiding significance for the rational layout of the ash hopper and the specific position of the soot blower.

【學(xué)位授予單位】：上海電力學(xué)院
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：X773

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