本文關鍵詞：氯化鎂調質煙氣促進汞催化氧化的試驗與機理研究　出處：《山東大學》2015年碩士論文　論文類型：學位論文

  更多相關文章： 汞 SCR催化劑 氯化鎂 氧化 活性氯

【摘要】：汞具有劇毒性、高揮發性和生物富集性,是一種全球性污染元素。燃煤汞排放被認為是大氣中汞污染的主要來源,對環境造成的污染問題越來越受到世界各國的廣泛關注。煙氣中的汞主要有3種形態：單質汞(Hg0)、氧化態汞(Hg2+)和顆粒態汞(Hgp),Hg2+易溶于水,絕大部分可通過濕法脫硫設備得到脫除,Hgp易于被除塵設備所捕獲,單質汞由于具有極大的化學穩定性和較差的水溶性而不易被現有污染物控制設備所脫除。利用SCR催化劑對汞的催化氧化作用,結合濕法脫硫設備聯合脫汞投資及運行成本低、適合現有電廠的改造,是一種經濟可行且極具競爭力的燃煤電廠汞污染控制方法。利用常規污染物控制設備聯合脫汞的關鍵在于提高SCR催化劑對單質汞的氧化效率。由于SCR催化劑對單質汞的氧化效率受煙氣中氯含量的制約,煤中氯含量高,煙氣中HCl含量就越高,SCR催化劑對汞的氧化效率越高,因而對于低氯煤,SCR催化劑對汞的氧化受到限制。脫硫廢水中富含氯化鎂,氯化鎂在高溫下可分解產生氯化氫(HCl)氣體,本文提出將脫硫廢水中的主要成分氯化鎂噴射在SCR脫硝裝置的前置煙道中,利用高溫煙氣促進氯化鎂分解,產生氯化氫,從而促進SCR催化劑對單質汞的氧化。首先,研究了商業釩鈦基SCR催化劑對單質汞的氧化性能,進而對SCR催化劑氧化單質汞的機理進行了探討。試驗結果表明,HCl可以明顯提高SCR催化劑對單質汞的氧化作用,汞的氧化效率隨著溫度的升高而升高,350℃時氧化效率可達到80%左右,繼續升高溫度,氧化效率變化不大,可見催化劑對脫汞和脫硝的溫度窗口相一致。O2可以顯著提高SCR催化劑對單質汞的吸附能力,HCl和Hg0都可以吸附在催化劑表面,但HCl的吸附弱于單質汞的吸附,SCR催化劑催化Hg0氧化的反應機理主要是Eley-Rideal機理,即催化劑表面吸附態的Hg與氣相中的HCl或弱吸附態的HCl反應,實現汞的氧化。其次,在固定床試驗臺上研究了商業SCR催化劑添加氯化鎂對單質汞形態轉化的影響,主要考察氯化鎂添加量、溫度以及氣氛對汞形態轉化的影響。試驗結果表明,氯化鎂在高溫下分解產生HCl和活性氯,可以促進單質汞的均相氧化。用氯化鎂調質SCR催化劑可以大幅度提高其對單質汞的氧化效率,在350℃,基本煙氣條件下,氯化鎂添加量從0wt%到1wt%范圍內,汞的氧化效率隨添加量增加從22.3%迅速提高至83.4%。溫度升高有利于單質汞向氧化態汞轉化,其中在350℃達到峰值,是汞催化氧化的最佳溫度。O2和NO可以促進添加氯化鎂后催化劑對單質汞的氧化,SO2和H2O抑制單質汞的氧化,添加氯化鎂后對催化劑的脫硝效率沒有明顯的影響。機理試驗表明氯化鎂分解產生HCl和活性氯,在催化劑的作用下可以達到對汞的高效氧化。最后,量子化學密度泛函理論是計算晶體結構和表面反應機理的精確方法,本文利用密度泛函理論結合周期性平板模型研究氯化鎂產生的活性氯促進SCR催化劑氧化單質汞的機理。模擬結果表明,Cl在V2O5(001)表面為化學吸附,Cl與V2O5表面的O有強烈的成鍵作用,對V2O5起到改性的作用,增加了催化劑表面的活性位。Hg0在吸附Cl后的V2O5(001)表面可以穩定地生成HgCl,一部分HgCl吸附在催化劑表面,一部分HgCl從催化劑表面脫附,兩種情況都有利于單質汞的氧化。
[Abstract]:Mercury is a global pollution element, which is highly toxic, highly volatile and bioenriched. Mercury emission from coal burning is considered to be the main source of mercury pollution in the atmosphere, and the pollution problem caused by the environment has attracted more and more attention from all over the world. Mercury in flue gas mainly has 3 forms: elemental mercury (Hg0), oxidized mercury (Hg2+) and particulate mercury (Hgp), Hg2+ soluble in water, most can be removed by wet desulfurization equipment, Hgp can easily be captured by the elemental mercury removal equipment, because of its great chemical stability and the poor water solubility and not easy to be the removal of existing pollutant control equipment. Using SCR catalyst to catalyze the oxidation of mercury, combined with the combined mercury removal from wet desulphurization equipment and low cost of operation, is suitable for the transformation of existing power plants. It is an economically viable and competitive way of mercury pollution control in coal-fired power plants. The key of combined dehhl removal by conventional pollutant control equipment is to improve the oxidation efficiency of SCR catalyst for Hg. Because the oxidation efficiency of SCR catalyst to elemental mercury is restricted by chlorine content in flue gas, the content of chlorine in coal is high, the content of HCl in flue gas is higher, and the oxidation efficiency of SCR catalyst to Hg is higher. Therefore, for SCR of low chlorine coal, the oxidation of Hg is limited. Rich in magnesium chloride desulfurization wastewater, magnesium chloride can be decomposed to produce hydrogen chloride at high temperature (HCl) gas, this paper put forward the main components of magnesium chloride injection in SCR desulfurization wastewater in flue pre denitrification device, promote the decomposition of magnesium chloride by high temperature flue gas, hydrogen chloride is produced, so as to promote the oxidation of elemental mercury catalyst SCR the. First, the oxidation performance of commercial vanadium and titanium based SCR catalyst for the oxidation of Hg was studied, and the mechanism of SCR catalyst for the oxidation of Hg was discussed. The test results show that HCl can significantly improve the oxidation effect of SCR catalyst on elemental mercury, mercury oxidation efficiency increases with the increase of temperature at 350 DEG C, the oxidation efficiency can reach about 80%, with increasing of temperature, the oxidation efficiency changed little, visible catalyst on the temperature window for mercury removal and denitrification are consistent. O2 can significantly improve the adsorption ability of SCR catalyst for the mercury, HCl and Hg0 can be adsorbed on the catalyst surface, but the adsorption of HCl on the weak adsorption of elemental mercury, the reaction mechanism of Hg0 catalytic oxidation of SCR catalyst is the main mechanism of Eley-Rideal, Hg and HCl reaction gas adsorption state phase HCl or weak adsorption state, realize the oxidation of mercury. Secondly, the influence of commercial SCR catalyst added with magnesium chloride on the transformation of elemental mercury was studied on a fixed bed test bench. The effects of magnesium chloride addition, temperature and atmosphere on mercury transformation were investigated. The results show that the decomposition of magnesium chloride at high temperature produces HCl and active chlorine, which can promote the homogeneous phase oxidation of the elemental mercury. The SCR catalyst with magnesium chloride quenched and tempered can significantly improve the oxidation efficiency of elemental mercury. At 350, the oxidation efficiency of mercury increased from 22.3% to 83.4% when the amount of magnesium chloride increased from 0wt% to 1wt%. The increase of temperature is beneficial to the conversion of the elemental mercury to the oxidized mercury, which reaches the peak at 350, which is the best temperature for the catalytic oxidation of mercury. O2 and NO can promote the oxidation of elemental mercury after adding magnesium chloride, and SO2 and H2O inhibit the oxidation of elemental mercury. The addition of magnesium chloride has no obvious effect on the denitration efficiency of the catalysts. The mechanism test shows that magnesium chloride is decomposed to produce HCl and active chlorine, and the high efficient oxidation of mercury can be achieved under the action of the catalyst. Finally, quantum chemical density functional theory is an accurate method to calculate crystal structure and surface reaction mechanism. In this paper, the theory of density functional theory combined with periodic slab model is used to study the active chlorine produced by magnesium chloride to promote the mechanism of SCR catalyst to oxidize elemental mercury. The simulation results show that Cl is chemisorbed on the surface of V2O5 (001), and Cl has strong bonding effect with O on the surface of V2O5, which plays a modified role in V2O5 and increases the active site on the catalyst surface. Hg0 can stably generate HgCl on the V2O5 (001) surface after Cl adsorption. A part of HgCl adsorbed on the surface of the catalyst. A part of HgCl is adsorbed on the catalyst surface. The two conditions are beneficial to the oxidation of elemental mercury.
【學位授予單位】：山東大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TQ132.2;X773

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