升溫速率對生物質(zhì)熱解的影響

第36卷第2期燃料化學(xué)學(xué)報Vol 36 No. 208年4月Joumal of Fuel Chemistry and Technol文章編號:0253-2409(2008)0223204升溫速率對生物質(zhì)熱解的影響任強強,趙長(cháng)遂(東南大學(xué)潔凈煤發(fā)電及燃燒技術(shù)教育部重點(diǎn)實(shí)驗室,江蘇南京2009%6)關(guān)鍵詞:生物質(zhì);熱解特性;升溫速率;氣體產(chǎn)物中圖分類(lèi)號:TK6文獻標識碼:AEffect of heating rate on biomass pyrolysisREN Qiang-qiang, ZHAO Chang-suiKey Laboratory of Clean Coal Power Generation and Combustion Technology of Ministry of Education, Southeast University,Nanjing 210096, China)Abstract: The pyrolysis behavior of three typical agricultural residues including rice husk, rice straw and wheatstraw, was studied at different heating rates(15 C/min, 40 C/min and 100 C/min)in a dynamic nitrogen flowof 80 mL/min by TG analysis coupled with Fourier Transform Infrared Spectroscopy( FT-IR). The variousgaseous products released during biomass pyrolysis were examined. The kinetic parameters under differentheating rates were acquired by kinetics analysis. The correlation coefficients are above 0. 99. The results showthat as heating rate increases the tG curve shifts to low temperature zone and the peak of dtg curve goes to lowtemperature area accordingly, but the total weight loss and activation energy of pyrolysis fluctuate little. Thereleasing behavior of gaseous products during pyrolysis of the three samples is similar. CO, CO2, H2O, CH, andorganics are the main gaseous products during biomass pyrolysis. When the heating rate increases, the yield ofgaseous products released increases, so does the releasing rateKey words: biomass; pyrolysis characteristic; heating rates; TGA-FTIR; gaseous products稻殼、稻稈及麥稈是中國主要的農業(yè)廢棄物,如力學(xué)及熱解氣體產(chǎn)物的析出規律進(jìn)行實(shí)時(shí)在線(xiàn)何綜合、有效地利用這些農業(yè)廢棄物進(jìn)行資源化研分析。究顯得十分必要。熱解是熱化學(xué)轉化中最為基本的實(shí)驗部分過(guò)程,是氣化、液化及燃燒過(guò)程的初始和伴生反應對熱解的分析有助于熱化學(xué)轉化過(guò)程控制及高效轉1.1實(shí)驗儀器實(shí)驗采用的儀器為法國TGA92型常壓熱重分析儀及德國 BRUKER公司 VECTOR化工藝的開(kāi)發(fā)。目前,國內外對生物質(zhì)及其組分的22型傅里葉變換紅外光譜儀。熱解已有大量的研究6,但對中國主要的農業(yè)廢1.2實(shí)驗條件實(shí)驗選用稻殼、稻稈及麥稈三種南棄物稻殼、稻稈及麥稈的研究較少。本研究利用熱京生物質(zhì),其基本性質(zhì)見(jiàn)表1。重和紅外聯(lián)用技術(shù)深入研究了升溫速率對三種典型生物質(zhì)熱解氣體產(chǎn)物的影響,并對生物質(zhì)的熱解動(dòng)表1生物質(zhì)的元素分析及工業(yè)分析Table 1 Proximate and ultimate analyses of biomassProximate analysis w,/%Ultimate analysis w,/%MAFCCHNS/Mkg-Rice husk9.8512.3663.39144038.244.1134.720.580.1414.28Rice straw6.8810.5878.544.0037.814.7834.630.710.0913.59Wheat straw8148:90n204109245721343480600251357每次實(shí)驗取樣品7mg粒徑小于0.2mm;高純?yōu)槭覝?800r停留10min采用三種升溫速率氮氣作為載氣流量為80mL/min;熱分析溫度范圍即15中國煤化工/min。實(shí)驗時(shí)熱CNMHG收稿日期:20070804;修回日期:2007-11-27聯(lián)系作者:趙長(cháng)遂,Tel:02583793453,Fax:02583793453,E-mail:rizhao@seu.edu.cn作者簡(jiǎn)介:任強強(1983-),男,江蘇宿遷人,碩士研究生,從事生物質(zhì)能利用研究。Emal:rengo2006@163.com第2期任強強等:升溫速率對生物質(zhì)熱解的影響天平自動(dòng)記錄質(zhì)量的變化信號。每個(gè)實(shí)驗完成后,及麥稈明顯失重,有大量氣體(包括焦油)析出,物做一個(gè)相同條件的空白實(shí)驗以消除系統誤差。TG料質(zhì)量急劇下降。研究表明3,此階段發(fā)生的熱的出囗氣體通過(guò)導管引人到FrR的氣體池中實(shí)解是纖維素、半纖維素及木質(zhì)素等生物質(zhì)有機組成時(shí)跟蹤檢測,并獲得失重時(shí)間(與溫度對應)-析出氣成分熱解疊加的結果。纖維素主要熱分解區域在體的紅外光譜分析結果,以期同時(shí)獲得樣品的熱失250℃~50℃,熱解后碳量較少,熱解速率很快;而重特性和析出特性木質(zhì)素較難熱解,熱解速率在400℃以后出現峰2結果與討論值。。在熱解溫度高于500℃,半纖維素和纖維素2.1生物質(zhì)TG.DTG分析的熱分解基本結束,此時(shí)以木質(zhì)素熱解為主。由于21.1熱解特性實(shí)驗圖1為三種生物質(zhì)在升溫木質(zhì)素熱解時(shí)形成較多的碳因此稻殼、稻稈及麥速率為15/m、40℃/mim及100m下的熱稈熱失重曲線(xiàn)和熱解速率曲線(xiàn)在高溫區趨于平緩。解曲線(xiàn)。由圖1可知,在200℃~500℃,稻殼、稻稈8至3Temperature n/C800Temperature t℃圖I不同升溫速率下生物質(zhì)熱解特性曲線(xiàn)Figure 1 TG-DTG curves of biomass pyrolysis at different heating rates,a:l5℃/mn;b:40℃/mn;c:100/min(a): rice husk;(b): rice husk;(c): rice straw:(d): wheat straw由圖1還可知隨著(zhù)升溫速率的升高,熱解速率曲線(xiàn)向低溫區偏移達到最高熱解速率(-dw/dr)所對應的溫度向低溫區偏移。不同升溫速率下三種式中:m為樣品初始質(zhì)量、mr為實(shí)驗結束時(shí)的質(zhì)量生物質(zhì)達到最大熱解速率時(shí)所對應的溫度有所不同,m為樣品任一時(shí)刻的質(zhì)量。根據質(zhì)量作用定律可以稻殼為320℃~350℃,稻稈為295℃-325℃,麥稈得到樣品熱解速率方程:為發(fā)生在300℃-35℃。這主要是由于三種生物質(zhì)心-Lf1(2)化學(xué)組成不同,導致熱解速率不同式中中國煤化工212熱解動(dòng)力學(xué)參數根據熱解曲線(xiàn),可以求解CNMHG生物質(zhì)熱解的反應動(dòng)力學(xué)參數。樣品在實(shí)驗中的總-E/RT質(zhì)量變化為式中:A為頻率因子、E為活化能R為氣體常數、T為燃料化學(xué)學(xué)報第36卷絕對溫度。EX則有研究表明”,秸稈類(lèi)生物質(zhì)的熱解反應可視為級反應。將式(3)代入式(2)積分并整理得(:Y=a+bx(5)-10)=141-2)-R()根據實(shí)驗結果,可以計算出樣品不同工況下XY值進(jìn)而求得a、b值,即可求得反應的表觀(guān)活化能E式中d為升溫速率,亦。令y=h[、l(1-g)和頻率因子A,計算結果見(jiàn)表2。各擬合方程的相關(guān)系數都大于0.99,說(shuō)明線(xiàn)性回歸比較合理表2生物質(zhì)的熱解動(dòng)力學(xué)參數Table 2 Kinetic parameters of biomass pyrolysisSample Heating rate/Cmin" t/CFitting equationE/kJ.mol-1A/minRice husk15238~366Y=3.4873-5878X-0.994248.883.60×10°242-375Y=3.3589-5988X-0.995749.795.91×10°236~361Y=1.9917-6649X0.998955.298.26×10°Rice straw234-346Y=2.5464-6292X-0.992142.751.48×10°239-352Y=4.3705-5142X0.990151.107.52×10°216-336Y=2.2939-6146X522.10×10236-358Y=1.5199-6935X-0.997749.635.72x103232~363Y=2.8370-6127X-0.997350.945.17×10°217~356Y=2.7531-5969X-0.9982.2生物質(zhì)熱解FTR分析體沒(méi)有紅外光譜吸收峰,因此,利用傅里葉紅外光譜熱解產(chǎn)物分析圖2分別為稻殼稻稈及麥不能檢測出這些氣體成分。但是H2是生物質(zhì)熱桿在40℃/mn升溫速率下熱解氣體產(chǎn)物的典型譜解的重要氣體組成作者將在以后利用質(zhì)譜檢測分圖。由圖2可知CO2CO0H2OCH及有機物是生析。下面以稻殼為例,深人了解升溫速率對生物質(zhì)熱物質(zhì)熱解主要氣體產(chǎn)物。有機物主要是烴類(lèi)、醛類(lèi)醇類(lèi)羧酸類(lèi)等大分子物質(zhì)。此外H2N2及O2等氣解氣體產(chǎn)物的影響。acids C=Oacids c-o alkanesCo月HHOCH, coW\40001000wavenumber dcmWavenumber a/cm-l圖2生物質(zhì)熱解產(chǎn)物譜圖Figure 2 Typical IR spectra of the products from three biomass pyrolysis at 40 C/min(a): rice husk(34℃);(b): nce straw(37℃);(e): wheat straw(323℃)222升溫速率對熱解氣體產(chǎn)物影響圖3為稻殼出值對應的溫度提高分別為350℃415℃及458℃在升溫速率l5℃/mn40℃/min及00℃/min下熱而在升溫速率15℃/mn40℃/min及100℃/min下解時(shí)主要氣體產(chǎn)物的析出過(guò)程。由圖3可知稻殼熱CH4達到最大析出值對應的溫度為437℃、600℃及解過(guò)程中,水的析出有兩個(gè)峰,CO2、CO及CH4的氣458℃,并不是隨著(zhù)升溫速率提高而相應增加,這與體釋放都為單峰曲線(xiàn)。1中國煤化工高于200℃時(shí),CO2的析出量隨著(zhù)熱解溫度的升CNMHGJ IR吸收曲線(xiàn)有高而明顯增加,達到最大值后迅速減小高于00相似的釋放規律,不同的是CO及有機物的釋放溫度時(shí)析出量很少。隨著(zhù)升溫速率升高,CO2達到最大析稍高大部分在300℃以上析出。第2期任強強等:升溫速率對生物質(zhì)熱解的影響0.30§025300405002005000意0004200400600800Temperature t/CTemperature t/℃Temperature t℃0040.1500300200l000配礦圖3稻殼熱解氣體產(chǎn)物的析出過(guò)程■:15℃/min;o:40℃/min;▲:100℃/min結語(yǔ)稻稈由于含有較高的揮發(fā)分熱解達到最大熱解速率生物質(zhì)熱解主要發(fā)生在200℃~500℃。隨著(zhù)升時(shí)所對應的溫度低于稻殼及麥稈。溫速率的升高樣品熱解的TG曲線(xiàn)向低溫區偏移,CO2、CO、H2OCH4及有機物是生物質(zhì)熱解的主DrG曲線(xiàn)峰值位置也相應地移向低溫區。稻殼、稻稈要氣體產(chǎn)物;隨著(zhù)升溫速率提高,氣體產(chǎn)物析出量增及麥稈熱解達到最大熱解速率時(shí)所對應的溫度分別加,釋放的速率加快;CO2及H2O的釋放溫度較低,為320℃~350℃、295℃~325℃、300℃~335℃。CO、CH4及有機物的釋放溫度稍高。參考文獻:[]楊海平陳漢平,晏蓉,張世紅,鄭楚光油棕廢棄物熱解的TGFR分析[].燃料化學(xué)學(xué)報,200,34(3):309314(YANG Hai-ping, CHEN Han-ping, YAN Rong, ZHANG Shi-hong, ZHENG Chu-guang. 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