第34卷第1期燃料化學(xué)學(xué)報(bào)Vol 34 No. I2006年2月Journal of Fuel Chemistry and TechnolFeb.2006文章編號(hào):0253-24092006)01-0123403玉米秸熱解動(dòng)力學(xué)研究張曉東,許敏,孫榮峰,孫立山東省科學(xué)院能源研究所,山東濟(jì)南250014)關(guān)鍵詞:生物質(zhì);熱解;動(dòng)力學(xué);活化能中圖分類號(hào):TK6文獻(xiàn)標(biāo)識(shí)碼:AStudy on the kinetics of corn stalk pyrolysis by TG-DTG analysisZHANG Xiao-dong, XUSUn Rong-feng sun liEnergy Research Institute of Shandong Academy of Sciences Jinan 250014, ChinaAbstract: The pyrolysis kinetics is very important for the development of biomass thermal chemical conversiontechnology, By means of the TG-DTG analysis the pyrolysis behavior and kinetics of corn stalk were investigated with the heating rate from 5 C/min to 100 C/min. The experimental data reveal that the kinetic parametersare much influenced by the operating conditions. And the activation energy of pyrolysis reaction increases withheating rates. Through the kinetics compensation processing the apparent kinetic parameters of pyrolysis are ob-tained with the activation energy of 66. 5 kJ/ mol and the frequency factor of 3 165s. A kinetic model is validated for the corn stalk pyrolysis, which can well fit the experimental results. Moreover, some fundamental data ofpyrolysis is provided which is much valuable for the understanding of process mechanismKey words: biomass pyrolysis i kinetics activation energy生物質(zhì)能具有低硫和二氧化碳零排放的特點(diǎn),工藝的研究開發(fā)提供重要的基礎(chǔ)數(shù)據(jù)。國外對(duì)纖維其在能源結(jié)構(gòu)中的地位越來越重要。作為一種高效素?zé)峤鈩?dòng)力學(xué)已進(jìn)行了一些研究56但生物質(zhì)作生物質(zhì)能轉(zhuǎn)化途徑熱化學(xué)轉(zhuǎn)化可獲得氣、液和固態(tài)為纖維素、半纖維素、木質(zhì)素等的復(fù)雜聚合物其熱多種能源產(chǎn)物2。其中熱解是熱化學(xué)轉(zhuǎn)化中最解行為與單純纖維素差別較大67。因此本文的熱為基本的過程是氣化、液化及燃燒過程的初始和伴解研究集中在玉米秸這種常見的軟質(zhì)秸稈類生物質(zhì)生反應(yīng)對(duì)熱解的分析有助于熱化學(xué)轉(zhuǎn)化過程控制原料。及高效轉(zhuǎn)化工藝的開發(fā)3熱解動(dòng)力學(xué)是表征熱1實(shí)驗(yàn)部分解過程中反應(yīng)過程參數(shù)對(duì)原料轉(zhuǎn)化率影響的重要手段41通過動(dòng)力學(xué)分析可深入了解反應(yīng)過程和機(jī)實(shí)驗(yàn)采用的玉米秸元素分析、工業(yè)分析和化學(xué)理預(yù)測(cè)反應(yīng)速率及難易程度為生物質(zhì)熱化學(xué)轉(zhuǎn)化學(xué)轉(zhuǎn)化組成分析見表1。熱重分析之前原料試樣均需磨細(xì)為200μm并混合均勻表1生物質(zhì)原料的元素分析、工業(yè)分析及化學(xué)組成分析Table 1 Analysis data of biomass feedstockProximate analysis 1 /%Ultimate analysis w, /Biochemical analysis we, /As/kf kg) cellulose hemi-cellulose lignin80.946.805.7441,400.660.1116849實(shí)驗(yàn)儀器為TGυTA6200型熱重差熱分析儀。2熱解動(dòng)力學(xué)模型的構(gòu)建采用高純N2為載氣流量10m/min。升溫速率為2.1熱重?cái)?shù)據(jù)的動(dòng)力學(xué)處理圖1為玉米秸在不5℃/min、10℃/min、20℃/min、30℃/min、50℃/同升溫速率下的熱重(TG)和微分失重DrG)曲線。min、100℃/min反應(yīng)終溫1000℃。由圖1可見不同升溫速率的失重曲線基本類似只收稿日期:2005403408;修回日期:200508-21。燃料化學(xué)學(xué)報(bào)第34卷是反應(yīng)的起始溫度、終止溫度、失重速率、失重峰值點(diǎn)E等略有差異。由TG曲線可看出熱解過程可分為三dns AexdRtxi-xy(3)個(gè)階段第一階段為脫除表面水的過程到120℃左對(duì)上式兩邊取對(duì)數(shù)有右結(jié)束該階段原料內(nèi)部發(fā)生少量解聚及玻璃化轉(zhuǎn)E變”現(xiàn)象3。第二階段為生物質(zhì)熱解的主反應(yīng)段,aT)h(1x)=1(B)Rr(4)發(fā)生80%-90%的失重到300℃400℃結(jié)束不即上式左邊ln()nl(1-x)與1/7呈線性關(guān)系同升溫速率下該階段的結(jié)束溫度不一致。第三階段為殘余物的緩慢分解過程失重越來越小殘余物質(zhì)Y=aX+b形式直線斜率(-B),截距為H()量接近恒定熱解最終產(chǎn)物為部分炭和灰。通常動(dòng)對(duì)同一種生物質(zhì)原料在一定溫度范圍內(nèi)假定其熱力學(xué)分析都是針對(duì)失重最為劇烈的熱解過程主反應(yīng)解反應(yīng)的活化能E和頻率因子A為定值。反應(yīng)級(jí)數(shù)區(qū)進(jìn)行的。的確定需在保持(式4)為線性關(guān)系的前提下通過編程數(shù)值計(jì)算來求取也可以采用試算法即對(duì)n取多4.000個(gè)值通過對(duì)實(shí)驗(yàn)數(shù)據(jù)的擬合考察數(shù)據(jù)點(diǎn)對(duì)直線關(guān)系的符合程度后比較確定。本文采用了試算法對(duì)多3000個(gè)升溫速率下的熱重實(shí)驗(yàn)數(shù)據(jù)進(jìn)行處理數(shù)據(jù)的線性相關(guān)性采用最小二乘法計(jì)算擬合殘差來描述。對(duì)于升溫速率5℃/min熱重?cái)?shù)據(jù)進(jìn)行試算的部分結(jié)果見表2。由表2可知反應(yīng)級(jí)數(shù)n取值接近于1即玉米秸原料熱解反應(yīng)可近似為一級(jí)反應(yīng)這與大部分emperature I/c研究者所認(rèn)為的纖維素類原料熱分解反應(yīng)近似為一圖1玉米秸熱解過程的TG和DTG曲線級(jí)反應(yīng)是一致的本文數(shù)據(jù)處理中采用n=1,該Figure 1 TG and DtG curves of pyrolysis of corn stalk處理方式對(duì)實(shí)驗(yàn)結(jié)果準(zhǔn)確度影響不大。(1)5K/min;(2)10K/r表2反應(yīng)級(jí)數(shù)n的取值對(duì)實(shí)驗(yàn)數(shù)據(jù)線性度的影響(3)50K/min;(4)100K/minTable 2 Effect of reaction order on the linearity of初始質(zhì)量為m的樣品在程序升溫下發(fā)生分解nalysis data反應(yīng)在某一時(shí)間t,質(zhì)量變?yōu)閙測(cè)其分解速率可Reaction order, nLinearity coefficient, R 0.880 1 0. 90280.9835 0 929 9以表示為d=6x),(1)2.2熱解動(dòng)力學(xué)參數(shù)的確定利用(式4)對(duì)玉米秸熱解主反應(yīng)段進(jìn)行分析。不同升溫速率進(jìn)行熱重x為反應(yīng)物轉(zhuǎn)化率,定義為xmm,其中分析所獲得的動(dòng)力學(xué)參數(shù)見表3m。為不能分解的殘余物質(zhì)量。k為反應(yīng)的速率常表3不同升溫速率下玉米秸熱解反應(yīng)動(dòng)力學(xué)參數(shù)Table 3 Kinetic parameters of corn stalk pyrolysi數(shù)根據(jù) Arrhenius關(guān)系式,k可以表示為k=Aexinder different heating rates代7)其中E為反應(yīng)活化能A為頻率因子R為氣體 Heating rate Activation energy Frequency factorEEkJ·mol常數(shù)T為反應(yīng)溫度。63.952812.8人x)為轉(zhuǎn)化率x的函數(shù)其函數(shù)形式取決于反3086.9應(yīng)類型或反應(yīng)機(jī)制。對(duì)簡(jiǎn)單反應(yīng)可取(x)=317967.573352.11-x)n為反應(yīng)級(jí)數(shù)。69.97dtAexp- Dmx 1-x)(2)由表3可見不同升溫速率下得到的活化能和同時(shí)根據(jù)TG分析的升溫程序有升溫速率B=d頻率因子存在著差異。排除實(shí)驗(yàn)分析誤差的影響張曉東等:玉米秸熱解動(dòng)力學(xué)研究所需能級(jí)就越高。同時(shí)活化能的增大伴隨著頻率數(shù)據(jù)點(diǎn)進(jìn)行線性擬合結(jié)果見圖2得動(dòng)力學(xué)補(bǔ)償效因子的增大這主要是由于熱重法中熱重曲線的形應(yīng)表達(dá)式:lnA=0.0324E+5.9049。狀與升溫速率等實(shí)驗(yàn)條件相關(guān)的緣故反應(yīng)器內(nèi)傳從而確定熱解主反應(yīng)段的動(dòng)力學(xué)參數(shù),并建立熱傳質(zhì)情況的變化引起動(dòng)力學(xué)參數(shù)的變化。對(duì)此需玉米秸熱解的表觀反應(yīng)動(dòng)力學(xué)表達(dá)式為引入相應(yīng)的動(dòng)力學(xué)補(bǔ)償效應(yīng):lnA=aE+b451。dx3165.58.314×7X1x)(5)66518這樣頻率因子對(duì)活化能變化的效應(yīng)就能得到部分補(bǔ)償經(jīng)補(bǔ)償處理后所得動(dòng)力學(xué)參數(shù)受實(shí)驗(yàn)條件的宋春財(cái)?shù)炔捎枚喾N數(shù)學(xué)處理方法進(jìn)行玉米影響要小的多。秸熱解動(dòng)力學(xué)分析其利用 Coats- Redfern微分處理將玉米秸數(shù)據(jù)標(biāo)示于mA~E坐標(biāo)系中并對(duì)后得到的活化能為68kJ/mol左右但其發(fā)現(xiàn)不同處理方法所得動(dòng)力學(xué)參數(shù)相差很大。賴艷華等得8.15到不同升溫速率下玉米秸熱解活化能在58kJ/mol~64kJ/mol與本文結(jié)果接近但頻率因子值變化范圍較大3結(jié)語800在對(duì)玉米秸進(jìn)行熱重分析的基礎(chǔ)上從動(dòng)力學(xué)角度對(duì)其熱解過程進(jìn)行了研究。不同熱解條件下所得反應(yīng)動(dòng)力學(xué)參數(shù)不同,且活化能隨升溫速率的增6364656667686970Activation energy E/(W.mol加而增大。引入動(dòng)力學(xué)補(bǔ)償效應(yīng)荻得玉米秸熱解表觀反應(yīng)活化能6.5k/mol,頻率因子3165s-1圖2不同升溫速率下的動(dòng)力學(xué)補(bǔ)償效應(yīng)Figure 2 Kinetic compensation effect of corn stalk pyrolysis從而建立了玉米秸熱解過程動(dòng)力學(xué)表達(dá)式。參考文獻(xiàn)[1]吳創(chuàng)之,馬隆龍.生物質(zhì)能現(xiàn)代化利用技M]北京北學(xué)工業(yè)出版社,2003.211WU Chuang-zhi, MA Long-long. 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