Vol 27高等學(xué)?；瘜W(xué)學(xué)報(bào)No. 22006年2月CHEMICAL JOURNAL OF CHINESE UNIVERSITIES熱重分析法研究貝殼固硫反應(yīng)動(dòng)力學(xué)韓奎華,路春美,程世慶,王永征,趙建立〔山東大學(xué)能源與動(dòng)力工程學(xué)院,濟(jì)南250061)摘要采用熱分析法研究了貝殼和石灰石固硫反應(yīng)過程,用等效粒子模型對(duì)固硫反應(yīng)過程進(jìn)行了表征,計(jì)算分析了其固硫反應(yīng)動(dòng)力學(xué)參數(shù).結(jié)果表明,貝殼比石灰石含有較多的堿金屬鹽,其作用是提高了貝殼固硫反應(yīng)速率常數(shù)和有效擴(kuò)散系數(shù).貝殼固硫反應(yīng)中存在補(bǔ)償效應(yīng).根據(jù)等動(dòng)力學(xué)溫度判別固硫劑活性適用于不同反應(yīng)控制區(qū)的活性判斷.堿金屬成分對(duì)鈣基固硫劑活性有正負(fù)兩個(gè)方面的影響,含量過大或過小都會(huì)削弱固硫劑活性,因而存在最適含量.在1073-1273K溫區(qū)固硫時(shí),鈣基固硫劑中堿金屬離子與鈣離子摩爾比為1:50左右時(shí)固硫活性較高.關(guān)鍵詞固硫;動(dòng)力學(xué);鈣基固硫劑;補(bǔ)償效應(yīng);貝殼中圖分類號(hào)0643文獻(xiàn)標(biāo)識(shí)碼A文章編號(hào)0251-079020060240327405煤是我囯蘊(yùn)藏最豐富和利用極廣的化石能源,其直接燃燒產(chǎn)生的SO2是污染空氣和形成酸雨的主要物質(zhì)之一.石灰石資源豐富,廉價(jià)易得,已成為控制燃煤S∽排放的主要鈣基材料,但在高溫固硫時(shí)利用率普遍較低.在最新研究3中新型的鈣基固硫劑貝殼顯示出良好的高溫固硫性能,相同試驗(yàn)條件下其氧化鈣最大轉(zhuǎn)化率高出石灰石10%~30%本文研究二者的固硫反應(yīng)過程和動(dòng)力學(xué)特性,期望為改善石灰石固硫性能、制備復(fù)合鈣基固硫劑提供了一定的理論支持.1實(shí)驗(yàn)部分1.1試劑采集山東半島沿海的4種貝殼和一種石灰石,經(jīng)烘干、曆制和篩分制成實(shí)驗(yàn)用樣品,按GB3286《石灰石、白云石化學(xué)分析方法》對(duì)樣品進(jìn)行化學(xué)成分分析,結(jié)果見表1Table 1 The main chemical composition of test samples mass fraction %o)]Test sampleAl,O3K ONa, OCaoMgfScallop shell0.0.040.400.040.4954.530.27Trumpet shell0.000.040.070.060.00Ark shell0.02Clam shell0.1653.371.2實(shí)驗(yàn)過程固硫反應(yīng)動(dòng)力學(xué)實(shí)驗(yàn)在北京光學(xué)儀器廠生產(chǎn)的LCT2型差熱天平中進(jìn)行,實(shí)驗(yàn)所用樣品質(zhì)量為10±0.2)ms以排除粒間內(nèi)擴(kuò)散的影響),粒徑范圍為0.105~0.3mm,實(shí)驗(yàn)用模擬煙氣各組分的體積含量為κCO2)=15%,以O(shè)2)=5%和κ(SO2)=0.296%,N2氣為平衡氣.模擬煙氣流速0.931.19m/(以排除氣膜擴(kuò)散影響),實(shí)驗(yàn)終止溫度800中國煤化工:/min.固硫劑中氧化鈣的轉(zhuǎn)化率的計(jì)算公式為CNMHGx=△m· M Cao{mo·WCa0)[ M CasO4)-MCa0)](1)枚稿日期:200501-14基金項(xiàng)科學(xué)基金批準(zhǔn)號(hào):59976019)和山東省自然科學(xué)基金批準(zhǔn)號(hào):Y2003F07)資助聯(lián)系人11958年岀生),女,教授,博士生導(dǎo)師,主要從事清潔燃燒與污染物防治研究.E-mail:cml@su.edu.328高等學(xué)?；瘜W(xué)學(xué)報(bào)VoL 2式中,x為固硫劑中CaO的轉(zhuǎn)化率;m為固硫劑的初始質(zhì)量;Δπ為反應(yīng)后固硫劑增重;κCaSO)為CaSO4摩爾質(zhì)量;Ca0)為CaO摩爾質(zhì)量;WCaO)為固硫劑中CaO的質(zhì)量分?jǐn)?shù)2結(jié)果與討論2.1時(shí)間和溫度對(duì)固硫劑鈣轉(zhuǎn)化率的影響貝殼和石灰石在不同溫度下固硫反應(yīng)的Ca0轉(zhuǎn)化率(x)與時(shí)間(t)的關(guān)系曲線見圖1.在相同實(shí)驗(yàn)溫度下貝殼CaO轉(zhuǎn)化率明顯大于石灰石飪圖A)B)]在1273K時(shí),扇貝殼、海螺殼、毛蚶殼、花蛤殼和石灰石的CaO最大轉(zhuǎn)化率分別為94.40%,80.85%,79.68%,79.27%和62.32%(A)(c)1073KO0-G-D-D-1173KH401073Kt shell1223K1273K一1223K1273K20AClam shellFlinstone80100/minFig 1 Sulfation of different samples at 1 273 K(A )Trumpet shell B limestone C) five samples2.2固硫反應(yīng)動(dòng)力學(xué)表征研究采用等效粒子模型←6處理實(shí)驗(yàn)數(shù)據(jù).氣固反應(yīng)在產(chǎn)物和反應(yīng)物之間的界面進(jìn)行,固體產(chǎn)物層厚度隨時(shí)間延長(zhǎng)而增加,反應(yīng)初期,粒子表面產(chǎn)物層較薄,反應(yīng)處于化學(xué)反應(yīng)控制階段;隨時(shí)間增長(zhǎng),產(chǎn)物層厚度增加,反應(yīng)處于擴(kuò)散控制階段.模型的積分表達(dá)式如下表面化學(xué)反應(yīng)控制階段A,+ AG(x)產(chǎn)物層固體擴(kuò)散控制階段BI BPio(3)其中r,/(kcao2(6bD.c)(5)(6)x)=1-3(1-x)+2(1-x)式中動(dòng)力學(xué)參數(shù)分別用 Arrhenius方程表示為E(R7)e-E(Rgr)(9)式中,t為反應(yīng)時(shí)間min):cM為SO2氣體濃度(mo/mL);cs為固硫劑中CaO的濃度(momL):R,為顆粒原始半徑(cm);C(x)為表面反應(yīng)控制階段轉(zhuǎn)化率對(duì)應(yīng)函數(shù);P(x)為固體擴(kuò)散控制階段轉(zhuǎn)化率對(duì)應(yīng)函數(shù);k為表面反應(yīng)速率常數(shù)cm/min);k為指前因子(cm/min);E為反應(yīng)活化能(kJ/mol);A1和B為時(shí)間校正因子(mn):b為反應(yīng)計(jì)量系數(shù);D為有H中國煤化工D為與D對(duì)應(yīng)的指前因子(cm3/min):E為擴(kuò)散活化能W/ml):R為摩爾氣CNMHG根據(jù)等效粒子模型,固體轉(zhuǎn)化率(x)時(shí)間t)變化的動(dòng)力學(xué)曲線上存在兩個(gè)特征轉(zhuǎn)化率5].一是對(duì)應(yīng)于反應(yīng)控制結(jié)束時(shí)的轉(zhuǎn)化率x,二是對(duì)應(yīng)于由過渡區(qū)正式進(jìn)入粒子固體擴(kuò)散控制區(qū)時(shí)的轉(zhuǎn)化率x對(duì)x~t曲線求導(dǎo),根據(jù)微分曲線的變化與轉(zhuǎn)折點(diǎn)(即反應(yīng)速率的變化)確定兩個(gè)特征轉(zhuǎn)化率對(duì)應(yīng)的時(shí)間萬和據(jù)以區(qū)分反應(yīng)過程中的控制區(qū)No. 2韓奎華等:熱重分析法研究貝殼固硫反應(yīng)動(dòng)力學(xué)3292.2.1表面化學(xué)反應(yīng)控制階段根據(jù)式(6)對(duì)t內(nèi)轉(zhuǎn)化率κ進(jìn)行處理,再按式(2)得固硫劑的G(x)-t關(guān)系圖圖2)由圖2可看出,G(x)與t呈現(xiàn)良好的線性關(guān)系R=0.9664~0.999等效粒子模型能較好地描述石灰石、不同種類貝殼的固硫過程.0201073K1073K0.15015122xK·1123K05}◆127301o}·273X◆1273K0.100.050.050.0500000t/t/minFig 2 Gr(x)vs. t of desulphurization reaction(A)Trumpet shell (B) clam shell ( C)limestone.2.2.2產(chǎn)物層固體擴(kuò)散控制階段根據(jù)式7)對(duì)后轉(zhuǎn)化率x進(jìn)行處理,再按式3擬合得固硫劑的Px)~t關(guān)系圖圖3)由圖3可看出,P(x)與t呈現(xiàn)良好的線性關(guān)系R=0.9176~0.9985),對(duì)于仼何固硫劑,隨著反應(yīng)溫度的增加,斜率眀顯增大,說眀溫度對(duì)產(chǎn)物層固體擴(kuò)散的影響較大.由于貝殼的孔結(jié)構(gòu)有利于反應(yīng)氣體的擴(kuò)散23,使得反應(yīng)中孔擴(kuò)散和產(chǎn)物層擴(kuò)散同時(shí)控制區(qū)較石灰石的明顯反應(yīng)推遲進(jìn)入產(chǎn)物層固體擴(kuò)散控制階段,CaO轉(zhuǎn)化率進(jìn)一步提高.0.40(B)0.25(C)0.35}1073K1073K1073K▲1173K0.30123K0.250.25·1273K2330.20123￥◆1273A0150.15b0.100.1030Fig 3 P(x)vs. t of desulphurization reaction2.2.3動(dòng)力學(xué)參數(shù)計(jì)算分別對(duì)式4)和(5)式兩邊取對(duì)數(shù),分別以l(1/A),(1/B)對(duì)1/T作圖,由直線的斜率和截距分別求得E,k。,E和D(表2)由表2可看出,在表面化學(xué)反應(yīng)控制階段,貝殼的E比石灰石的小,而E遠(yuǎn)比石灰石的5979k/mol),對(duì)于貝殼固硫反應(yīng),E減小,指前因子k也相應(yīng)減小;E增大,指前因子D也相應(yīng)增大,說明E和k。,E和D存在補(bǔ)償效應(yīng)Table 2 Kinetic parameters of So, removal process by Ca-basedsorbent in different control regionsE(kJ·mol-1)1)fkJ·mol-1)Do/(cm2Trumpet shell17.024824.5Ark shell16.32324.8814275.Clam shell15.22230.22中國煤化工147529.8019.42359.01CNMHG郭漢賢等η從理論上解釋了ZnO和CaO脫硫/固硫過程的補(bǔ)償效應(yīng),指出該補(bǔ)償效應(yīng)既存在于表面化學(xué)反應(yīng),也存在于粒子固體擴(kuò)散反應(yīng).貝殼固硫動(dòng)力學(xué)中補(bǔ)償效應(yīng)回歸結(jié)果lmo=2.9181+0.1700E(R=0.9573)(10)D0=-2.5662+0.09267E(R=0.9980)(11)330高等學(xué)?；瘜W(xué)學(xué)報(bào)VoL 22.3固硫劑活性判別標(biāo)準(zhǔn)補(bǔ)償效應(yīng)使 Arrhenius方程中慣用的活化能概念不能準(zhǔn)確衡量固硫劑活性,根據(jù)式8)式(9)和表2中數(shù)據(jù)分別計(jì)算出各溫度下的k和D值,二者可直觀地反映出固硫劑反應(yīng)活性(表3).分析表3中的數(shù)據(jù),反應(yīng)速率常數(shù)k和產(chǎn)物層固體有效擴(kuò)散系數(shù)D與圖1中CaO的轉(zhuǎn)化率曲線相符Table 3 Kinetic parameters k and Ds at different temperaturesT/Kcm. min-1)10D./cm2) SampleT/kk cm. min-1)10 D,(cm2. min-1)Scallop shell 1 07351.78Ark shell69.5252.1381173Clam shell 1 0734.23527318612Trumpet she236.743127321.281Limestone 1 0734840964.8256.528Ark shell0730542127318.711117360.9517.931根據(jù)等動(dòng)力學(xué)溫度判別活性的方法3,溫度TT時(shí),活化能E越大,速率常數(shù)k越大通過計(jì)算,貝殼固硫化學(xué)反應(yīng)控制區(qū)與固體擴(kuò)散控制區(qū)等動(dòng)力學(xué)溫度T分別為708和1298K.而實(shí)驗(yàn)溫度為1073~1273K,對(duì)于化學(xué)反應(yīng)控制階段,溫度高于708K時(shí),對(duì)于化學(xué)反應(yīng)控制階段活化能越大,速率常數(shù)越大;而對(duì)于產(chǎn)物層固體擴(kuò)散控制階段,實(shí)驗(yàn)溫度低于1298K,則應(yīng)有E越小,有效擴(kuò)散系數(shù)D越大.這與實(shí)際計(jì)算的k和D值變化趨勢(shì)(表2和3)吻合.可見,采用等動(dòng)力學(xué)溫度判別固硫劑活性時(shí),適用于不同反應(yīng)控制區(qū)的活性判斷,如表面反應(yīng)控制區(qū)的反應(yīng)活化能與速率常數(shù)的變化關(guān)系,擴(kuò)散控制區(qū)的擴(kuò)散活化能與有效擴(kuò)散系數(shù)的變化關(guān)系.2.4貝殼中堿金屬離子對(duì)硫化活性的影響Hia等8指出,SO2與CaO所進(jìn)行的氣固兩相間的固硫反應(yīng)中,Ca2和02離子擴(kuò)散起著重要作用,這取決于固體晶格中點(diǎn)、面缺陷及異種離子的種類,而且外加雜質(zhì)和離子的大小對(duì)其有很大的影響. borgwardt等”研究指岀,堿金屬鹽促進(jìn)固硫的作用是其堿金屬離子的離子效應(yīng).已有研究結(jié)果山表明,有些堿金屬鹽按Li',Na'和K離子半徑增大的次序,促使CaO固硫反應(yīng)表面化學(xué)反應(yīng)控制階段的活化能E依次減小,但沒有分析堿金屬鹽摻雜量對(duì)固硫活性的影響.表1中4種貝殼的化學(xué)成分中K和Na的含量依次增加,堿金屬離子與鈣離子的摩爾比分別為0.017,0.024,0.0290.032,它們的表面化學(xué)反應(yīng)控制階段活化能依次降低.另外,在較低溫度下除扇貝殼外,其它貝殼與石灰石的產(chǎn)物層固體有效擴(kuò)散系數(shù)D相差不大.隨著反應(yīng)溫度增大,貝殼的D顯著增大,而石灰石的D略有增大.這主要是由于貝殼比石灰石含有更多的堿金屬鹽表1),低熔點(diǎn)的堿金屬化合物,不僅自身熔融成液相,而且與CaO和 CaSo形成低熔點(diǎn)的液相共熔物,因此不僅改變了固硫劑孔結(jié)構(gòu)的特性,而且也增加了固硫劑及產(chǎn)物層的晶格缺陷,促進(jìn)了后期的產(chǎn)物層擴(kuò)散反應(yīng)21綜上所述,堿金屬成分有著正負(fù)兩方面的影響,既增加晶粒結(jié)構(gòu)缺陷,提高了表面化學(xué)反應(yīng)速率常數(shù),又降低了固體熔點(diǎn),從而易導(dǎo)致燒結(jié),應(yīng)存在最適的含量范圍,含量過大或過小都會(huì)削弱固硫劑活性.分析比較貝殼與石灰石堿金屬含量(表1)和固硫活性(表2和3),忽略貝殼中堿金屬以外痕量雜質(zhì)的微弱影響,可以得岀在1073~1273K溫區(qū)固硫時(shí),固硫劑中堿金屬離子(主要為Naˉ,Kˉ)與Ca2摩爾分?jǐn)?shù)為2%左右時(shí)固硫活性較高.中國煤化工參考文HCNMHG[1] LU Chun-Me(路春美), ZHAO Jian-x趙建立), HAN Kui-Hu(韓奎華) Journal of Chemical Industry and Engineering化工學(xué)報(bào))[J],2003,54(2):273-276cy點(diǎn)數(shù)播mnCC],sah: Shanghai Scientific and Technical Pre,019 the International Conference on En2] HAN K韓奎華), LU Chun-Me(路春美), HAO Hai-Xid趙海霞)etal.No. 2韓奎華等:熱重分析法研究貝殼固硫反應(yīng)動(dòng)力學(xué)331[3]LUN(劉妮), CHENG Le-Ming(程樂鳴), LUO Zhong-Yang(駱仲泱)ea. 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Acta scientiae circumstantiae環(huán)境科學(xué)學(xué)報(bào)J]1997,17(3):284-288Studies on the desulfurization Kinetics of shell sorbentUsing Thermogravimetric Analysis MethodHAN Kui-Hua LU Chun-Mei, CHENG Shi-Qing, WANG Yong-Zheng ZHAO Jian-LiSchool of Energy and Power Engineering Shandong University, Jinan 250061, ChinaAbstract The general desulfurization sorbent, limestone is limited in sulfation temperature range and suffersfrom rapid loss of reactivity and incomplete utilization. However, plentiful shells are generally abandoned asarbage especially in coastal area which consist of CaCO, similar to limestone. Desulfurization with shelshows a higher calcium utilization and better sulfation property than limestone under various experimental con-litions. The desulfurization reaction process of calcium-based sorbent including four species of shell and a sortof limestone were investigated by thermogravimetric analysis method. The kinetic behavior was expressed bythe modified grain model. The activation energy(en) and the pre-exponential factor( ho )of surface reactionthe activation energy(e,)and the pre-exponential factor( Do )of product layer diffusion reaction were calculated and explained according to the model. It is shown that the modified grain model can describe the desulfurrization course of shells and limestone. Additions of alkali metal salts may improve microstructure and productdiffusion of sorbent during high temperature sulfation and enhance the initial reaction rate and the final Caoconversion of sorbents. The kinetic parameters of shell desulfurization show a compensation effect. There arelinear relationships between logarithms of the pre-exponential factor Inko InDo and activation energies Ea ,Erespectively. The method based on the isokinetic temperature T, to estimate sorbent activity is applied to different control stage. Alkali metal salts can enhance the initial reaction rate at the same time can accelerate thehigh temperature sintering of sorbent so there is optimal content in sorbent. The advisable molar ratio of alkalimetal cations( mainly Na and k) to Ca in the sorbent is best kept to 2% approximately at the desulfurrization temperature range of 1 073-1 273 KYH中國煤化工Keywords Desulfurization Kinetics Calcium-based sortCNMHGhell(Ed.: S, I)