納米添加劑對燃燒固硫影響特性研究

第42卷第7期熱力發(fā)電Vol. 42 No. 72013年7月THERMAL POWER GENERATION .Jul. 2013納米添加劑對燃燒固硫影響特性研究王淑勤,張曉潔華北電力大學(xué)環(huán)境科學(xué)與工程學(xué)院,河北保定071003[摘要]采用自制的納米TiO2作為燃燒固硫添加劑，對納米TiO2催化CaCO3的分解過(guò)程進(jìn)行了熱重試驗研究,對固硫后氣體吸收液和固體產(chǎn)物分別進(jìn)行了離子色譜和紅外光譜分析,并采用Coats and Redfern模型對CaCO3分解反應的動(dòng)力學(xué)過(guò)程進(jìn)行了計算。結果表明,納米TiO2對CaCO,的分解有明顯的促進(jìn)作用，可使分解溫度降.低、反應活化能E下降;納米TiO2會(huì )導致CaCO3晶格扭曲，減小微晶的晶格能,促進(jìn)CaCO3分解成反應活性高的CaO分子;納米TiO2會(huì )加快O2的吸附速度,使添加劑周?chē)旱姆磻俣燃涌?，同時(shí)促進(jìn)SO2轉化成SO3,以及SO2向CaO的內部擴散,完全燃燒產(chǎn)物還會(huì )抑制CaSO3的分解,從而提高CaCO3的固硫效果。[關(guān)鍵詞]納米二氧化鈦;催化;燃燒固硫;添加劑;碳酸鈣分解[中圖分類(lèi)號] X511 [文獻標識碼]A [文章編號] 1002-3364(2013)07 -038-06[DOI編號] 10. 3969/j. issn. 1002 3364.2013. 07. 038Effect of nano- additive on desulfurization during combustionW ANG Shuqin, ZHANG XiaojieSchool of Environmental Science and Engineering ,North China Electric Power University ,Baoding 071003, Hebei Province,ChinaAbstract: By using the self-prepared nano-TiO2 as sulfur retention additive during combustion, .thermogravimetric experiment on nano TiO2 catalyzing the CaCO3 decomposition was performed.Moreover , the gas absorption liquid and solid products after desulfurization were analyzed by ionchromatography and infrared spectrum method, respectively. Furthermore,the Coats and Redfemmodel was employed to conduct calculation for the kinetic process of CaCO3 decomposition. Theresults showed that, the nano- TiO2 enhanced the CaCO3 decomposition obviously , namely the re-action activation energy E decreased with the reaction temperature;in the presence of nano TiO2，the CaCO3 crystal lattice was distorted and the crystal lattice energy decreased, improving theCaCO3 decomposing to CaO with high reactivity ;on the other hand, the nano TiOz can acceleratethe absorption rate of O2 to speed up the reaction rate of coal particles around the additive, im-prove the SO2 converting to SO3 and promote the SOr dispersing into the inner CaO,at the sametime, the complete combustion products can inhibit the CaSO3 decomposition so as to improve thedesulfurization effect.Key words: nano TiO2 ;catalysis;sulfur retention additive;CaCO3 decomposition在燃煤中加入助燃固硫添加劑，能提高煤中揮燒,縮短燃燒時(shí)間,提高煤的燃燒固硫效率，節能減發(fā)分的析出速率,降低煤的著(zhù)火溫度,加速焦碳燃排效果顯著(zhù)[+41。煤高溫燃燒固硫反應的化學(xué)反應收稿日期: 2012-07-27中國煤化工基金項目:華北電力大學(xué)基金資助項目(2005/4002)作者簡(jiǎn)介:王淑勤(1965-),女,河北定州人,博士,教授,從事大氣污染控制技術(shù)的教.MYHCNMHGE-mail: wsqhg@ 163. com40熱力發(fā)電2013年于0.057mm的顆粒。在通氧量為40mL/min的條15141312|J10件下,固硫率計算結果如圖4所示。00rost90f8s+34后480-1-石灰溶液2- 吸收瓶3- 管式爐4- 燃燒管5-瓷舟75F6一流量計7- 洗氣瓶8一貯氣瓶 9一干燥塔10-T 型管70-11-推棒 12-溫度控制器 13-翻膠帽 14-橡膠寨15-熱電偶.750 800 850900 950 1000圖3燃燒固硫試驗裝置反應溫度/心Fig.3 Experimental apparatus for combustion and圍4納米TiO2對CaCO3煅燒后固硫率的影響sulfur retentionFig. 4 Effeet of nano-TiO2 on desulfurization efficiency of2結果與討論calcinated CaCO32.1反應溫度對固硫率的影響由圖4可見(jiàn),采用方式a煅燒時(shí)最高固硫效率固硫率η為:對應的反應溫度為900 C,方式b則為800 C,可見(jiàn)本體煙氣中sO.含量一樣品煙氣中SO,含量X 100%在納米TiO2的作用下,CaCO3在較低溫度下就能夠本體煙氣中SO2含量(1)分解成CaO,且最佳固硫效率達到了93. 7%。對比表1數據可以看出,新煅燒的CaO固硫率高于分析式中,本體煙氣中SO2含量指原煤在同等試驗條件純CaO。下燃燒時(shí)煙氣中的SO2含量,mg/m3。為了模擬燃燒脫硫的實(shí)際工況，反應溫度選2.3納米 TiO2對CaCO3煅燒分解效果的影響800~950 C。添加等量納米TiO2時(shí),反應溫度對利用熱重分析試驗考察納米TiO2對CaCO3分CaCO3和CaO固硫率的影響見(jiàn)表1。由表1可見(jiàn)，解效果的影響1011。添加納米TiO2對CaCO3熱分CaCO,和CaO的最佳反應溫度分別為950.850C,解的影響如圖5所示。且CaO固硫率明顯高于CaCO3.這是因為高溫下16CaCO3須先煅燒分解成CaO才能有效地與SO2反12CaCO,應,所以升高反應溫度可以提高固硫率。CaCO,+TiO,表1不同反應溫 度下的固硫率Table 1 Desulfurization efficiencies at450500550600650700750800850900different temperatures反應溫度/C項目(a)TG800850900950CaCO3固硫率/%46.4 47.447.957.5CaO固硫率/%79.887.884.969.72.2納米TiO2對CaCO3煅燒后固硫率的影響試驗納米TiO2添加量為煤樣重量的8%,反應CaCO,+TiO2溫度分別為750、 800、850、900、950 C,采用a.b2種不同的煅燒方式，研究納米TiO2對CaCO3固硫率的影響。方式a是分別在上述5種溫度條件下溫度/C .將CaCO3恒溫煅燒25 min,然后與煤、定量納米(b)DTATiO2混合研磨至粒徑小于0. 057 mm的顆粒;方式中國煤化工曲線(xiàn)b是先將CaCO3和納米TiO2混合,然后分別在5種Fig.5CNMHG/es of CaCO,溫度下恒溫煅燒25 min,再與煤混合研磨至粒徑小wiun ana witnout nanor 1 IU2 aoditionhttp: // www. rlfd. com. cn http: // rlfd. periodicals. net. cn第7期王淑勤等納米添加劑對燃燒固硫影響特性研究4:2.5.2燃燒后氣體產(chǎn)物2.4 CaCO, 分解動(dòng)力學(xué)分析根據熱重分析的試驗數據對CaCO3分解進(jìn)行試樣燃燒生成的氣體由裝有高純水的吸收瓶串動(dòng)力學(xué)分析。CaCO, 分解的化學(xué)反應為零級[01，聯(lián)二級吸收 燃燒結束后對吸收液進(jìn)行離子色譜分析,結果見(jiàn)表2。Coats and Redfern方程可簡(jiǎn)化為:RT(2)表2煙氣吸收液離子色譜 分析結果In[號]=1n[能(1-智)]最Table 2 lon chromatography analysis results ofa = (mo一m,)Mco/ mo (Ma.co, - Mco)flue gas absorption liquiduS/cm式中:a為反應程度;mo為樣品初始質(zhì)量,g;m,為t吸收液離子組分時(shí)刻樣品的質(zhì)量,g;Mco為CaO的摩爾質(zhì)量;Mcco,項目SO3- SO,2為CaCO,的摩爾質(zhì)量;A為頻率因子,min-';E為褐煤吸收液離子電導率30.926 0. 694活化能,kJ/mol;β為升溫速率,K/min;T為絕對溫褐煤和CaCO3吸收液離子電導率2.208 23. 927度,K;R為氣體常數,J/(mol. K)。RT/E在升溫褐煤CaCOs和TiOr吸收液離子電導率1.268 3. 147過(guò)程中可視為常數,故ln[a/T°]對1/T的斜率即為離子電導率越高,其含量越高。由表2可見(jiàn),煤CaCO3分解的化學(xué)反應活化能。根據CaCO,熱重分析試驗數據擬合,得到線(xiàn)性.燃燒后的煙氣吸收液中SO3-含量較多,表明煙氣相關(guān)系數R大于0.99,進(jìn)而求得樣品A、B的化學(xué)中SO2的含量較大,添加碳酸鈣后其煙氣吸收液中反應活化能分別為126. 57.101. 43 kJ/mol?？梢?jiàn)，SO32-含量減少,證明碳酸鈣可有效脫除SOr ;未添添加納米TiO2使得CaCO。分解的活化能降低了加納米TiO2的煙氣吸收液中SO,?-含量較高,說(shuō)明25. 14 kJ/ mol。SO3脫除效果不高，且部分SO2被氧化成SO, ;舔加納米TiO2后其煙氣吸收液中SO3-和SO,.-的含2.5產(chǎn)物分析和表征量均明顯減少,尤其SO.2-約減少至1/8, 即煙氣中2.5.1煅燒分 解后的固體產(chǎn)物通過(guò)X射線(xiàn)衍射分析CaCO3+TiO2樣品完全的SO2和SO3均減少。燃燒過(guò)程的主要反應如下:煅燒分解后的固體產(chǎn)物,結果如圖6所示。由圖6CaCO3- > CaO+ CO2(3)可見(jiàn),CaCO3 + TiO2樣品的煅燒產(chǎn)物中主要為2SO2+O2- > 2SO3CaO,含有少量鈣鈦礦,沒(méi)有CaCO3、銳鈦礦或者金SO3 +CaO+ TiO2-◆CaSO. + TiO2 (5)紅石晶型的TiO2.這證明試驗條件下CaCO3 已完CaO+SO2 +一O2- CaSO,(6)全分解,分解過(guò)程中納米TiO2與少量CaO反應形成了鈣鈦礦。這是因為納米TiO2的加入,增加了CaO+SO2->CaSO3(7)CaCO3微晶的內部畸變和應力,使微晶的晶格有不CaSO3 + 1/2O2 + TiO2催化、氧化. CaSO, + TiO2同程度的減小，最終使得CaCO3顆粒的熱分解更加(8)易于進(jìn)行。CaO+ SO2 +1/2 O2 + TiO2催化、氧化。600 r-CaOCaSO, + TiO2b-鈣鉆礦perovskite00 t促進(jìn)固硫反應產(chǎn)物層擴散是提高固硫效率的關(guān)400鍵,隨著(zhù)固硫反應的進(jìn)行產(chǎn)物層不斷加厚,不含添加; 300-劑的顆粒形成的致密產(chǎn)物層不利于SO2繼續擴散，承200-而含有添加劑的顆粒形成結構疏松的產(chǎn)物層有利于JhLbbSO2的擴散。納米TiO2的吸附作用促進(jìn)了SO,參10 20)40506(70與脫硫反應,同時(shí)又催化了SO2參與脫硫反應,從20/(")而提高了SO2和SO3脫除效果。圖6 CaCO, +TiO2樣品煅燒產(chǎn)物XRD分析Fig. 6 The XRD spectrum of calcinated CaCO32.5.3 脫硫后固體產(chǎn)物with nano-TiO2 addition通過(guò)紅中國煤化工北鈣與SO2反MHCNMHG應固體產(chǎn)物的脫制，知不對國I所小。http: // www. rlid. com. cn http: // rlfd. periodicals. net. cn_42熱力發(fā)電2013年1003結論0(1)自制的混晶型納米TiO2的顆粒和孔徑分Dz 60布較均勻,具有較強的催化性能。米40(2)作為過(guò)渡金屬氧化物的TiO2由于存在空塑201余雜化軌道,具有活化性質(zhì),能夠進(jìn)人CaCO3的晶ii||CaO Caso, Casq, Cas格內部促進(jìn)其分解，降低CaCO,的分解活化能,減__. 111少由于碳酸鈣高溫分解吸熱對煤燃燒的不利影響。3500 3000 2500 2000 1500 1000 500(3)固硫產(chǎn)物以CaSO3和CaSO,為主。納米波數/cm'圉7樣品C(無(wú)添加劑)與樣品D(有添加劑)的紅外TiO2作為氧的活性載體,將氧富集在添加劑表面，促進(jìn)SO2氧化成SO,增加CaO與SO2、SO3的反光譜分析(850 C )Fig. 7 The infrared spectra of desulfurization products of應進(jìn)程,最終形成固體產(chǎn)物硫酸鈣。煤完全燃燒可CaO with and without nan-TiO2 addition at 850 C以抑制固硫產(chǎn)物CaSO,發(fā)生分解,從而提高固硫效結合文獻[11]從所得樣品的紅外光譜圖(圖7)率?？梢钥闯龈魑镔|(zhì)的吸收峰位置、有氧條件。添加納[參考文獻]米TiO2后,CaSO3和CaSO,的吸收峰相對增高,無(wú)[1]周?chē)?鄔麗群.稀土鈣鈦礦型燃煤催化劑的催化機理論是否有添加劑,固體產(chǎn)物中都有CaS.可見(jiàn),有氰研究[J].潔凈煤技術(shù),2007 ,13(2):62-65.條件下存在CaSO3歧化反應:ZHOU Guojiang, WU Liqun. 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