氣相溫度脈動(dòng)對(duì)非球形生物質(zhì)顆粒焦炭燃燒的影響

李 捷，張 健

氣相溫度脈動(dòng)對(duì)非球形生物質(zhì)顆粒焦炭燃燒的影響

李 捷，張 健

（清華大學(xué)航天航空學(xué)院工程力學(xué)系，北京 100084）

將生物質(zhì)顆粒與煤粉混合燃燒，可以有效地利用生物質(zhì)能。生物質(zhì)顆粒通常形狀很不規(guī)則，有著較大的長(zhǎng)徑比，非球形特性較為明顯。對(duì)于在燃燒室內(nèi)運(yùn)動(dòng)與燃燒的生物質(zhì)顆粒，氣相湍流脈動(dòng)是否會(huì)對(duì)非球形生物質(zhì)顆粒的燃燒反應(yīng)過(guò)程產(chǎn)生作用有待探討。該文研究了氣相溫度脈動(dòng)對(duì)熱氣流中非球形生物質(zhì)顆粒瞬時(shí)焦炭燃燒的影響，給出了不同氣相平均溫度和顆粒長(zhǎng)徑比下生物質(zhì)顆粒瞬時(shí)質(zhì)量和瞬時(shí)焦炭燃燒速率隨時(shí)間的變化。研究表明氣相溫度脈動(dòng)對(duì)不同長(zhǎng)徑比的生物質(zhì)顆粒的焦炭燃燒過(guò)程均有明顯的影響，導(dǎo)致顆粒質(zhì)量下降變快，焦炭燃盡時(shí)間變短。氣相溫度脈動(dòng)幅度的增加進(jìn)一步加快了不同長(zhǎng)徑比顆粒瞬時(shí)質(zhì)量的下降。該文的研究揭示了氣相溫度的湍流脈動(dòng)對(duì)非球形生物質(zhì)顆粒瞬時(shí)焦炭燃燒過(guò)程的作用，這種作用并不會(huì)因?yàn)轭w粒長(zhǎng)徑比的變化而發(fā)生改變。

生物質(zhì)；燃燒；排放控制；非球形顆粒；焦炭；氣相溫度脈動(dòng)

0 引 言

生物質(zhì)能作為清潔的可再生能源，具有良好的經(jīng)濟(jì)、生態(tài)和社會(huì)效益。生物質(zhì)的熱化學(xué)轉(zhuǎn)化，如生物質(zhì)顆粒與煤粉的混合燃燒，不僅可以有效地利用生物質(zhì)能，而且可以減少燃燒污染物和溫室氣體的排放[1-3]。

與煤粉混合燃燒的生物質(zhì)顆粒在燃燒室內(nèi)同時(shí)受到氣相湍流、顆粒非球形性、顆?；瘜W(xué)反應(yīng)、對(duì)流傳熱傳質(zhì)等多種因素的共同作用和制約[4]。生物質(zhì)顆粒通常形狀很不規(guī)則，有著較大的長(zhǎng)徑比，非球形特性較為明顯。非球形性會(huì)影響顆粒的表面積和氣相對(duì)顆粒的動(dòng)量、能量和質(zhì)量傳遞，因此生物質(zhì)顆粒與球形顆粒的空氣動(dòng)力學(xué)和傳熱傳質(zhì)特性有較大的不同，這給對(duì)生物質(zhì)顆粒運(yùn)動(dòng)、傳熱傳質(zhì)和燃燒的理論描述帶來(lái)了難度。

另一方面，由于氣相湍流燃燒的作用，與煤粉混燃的生物質(zhì)顆粒在燃燒室內(nèi)的運(yùn)動(dòng)與燃燒始終處于有速度和溫度湍流脈動(dòng)的熱氣流中。氣相速度的湍流脈動(dòng)對(duì)生物質(zhì)顆粒的運(yùn)動(dòng)具有不容忽視的影響[5]，而氣相溫度的脈動(dòng)是否會(huì)對(duì)非球形生物質(zhì)顆粒的焦炭燃燒過(guò)程產(chǎn)生影響則有待探討。生物質(zhì)顆粒與混燃的煤粉顆粒相比，除非球形狀更為明顯外，還有許多其他不同的性質(zhì)，如尺寸相對(duì)較大、密度較低、反應(yīng)活性較高等。因此，生物質(zhì)顆粒對(duì)氣相溫度湍流脈動(dòng)的瞬時(shí)響應(yīng)與煤粉顆粒不同，生物質(zhì)顆粒焦炭燃燒受氣相溫度脈動(dòng)的作用也與煤粉顆粒不同。目前國(guó)內(nèi)外在對(duì)燃燒室內(nèi)生物質(zhì)顆粒與煤粉混燃的數(shù)值模擬中，均未考慮到氣相溫度的湍流脈動(dòng)對(duì)生物質(zhì)顆粒焦炭燃燒的影響[6-9]。

生物質(zhì)顆粒呈現(xiàn)出不同的非球形狀，本文選取扁長(zhǎng)橢球形狀的顆粒[10]作為非球形生物質(zhì)顆粒的代表。扁長(zhǎng)橢球顆粒具有變化范圍較大的長(zhǎng)徑比或球形度，其形狀還可用作柱狀顆粒的一種近似。通過(guò)求解顆粒的瞬時(shí)控制方程組，研究了在高溫氣流環(huán)境中不同的平均溫度下，氣相溫度脈動(dòng)對(duì)生物質(zhì)顆粒焦炭燃燒的影響。

1 非球形生物質(zhì)顆粒焦炭燃燒的瞬時(shí)控制方程組

假設(shè)生物質(zhì)顆粒的水分和揮發(fā)分已經(jīng)釋放完畢，顆粒中僅包含焦炭和灰分?？紤]氣體-顆粒的對(duì)流傳熱、顆粒與燃燒室壁面的輻射傳熱以及焦炭燃燒放熱反應(yīng)，生物質(zhì)顆粒的瞬時(shí)能量方程可寫為

式中T為顆粒瞬時(shí)溫度，K；m為顆粒瞬時(shí)質(zhì)量，kg；C為顆粒比熱，J/(kg·K)；為時(shí)間，s；ck、rk和Q分別為氣相對(duì)顆粒的對(duì)流傳熱量、燃燒室壁面對(duì)顆粒的輻射傳熱量及焦炭燃燒放熱量，W。

考慮到生物質(zhì)顆粒的橢球形狀，顆粒瞬時(shí)質(zhì)量可表示為

式中和分別為橢球顆粒的長(zhǎng)半軸和短半軸尺寸，m；pk為顆粒材料密度，kg/m3。

氣相對(duì)顆粒的對(duì)流傳熱量為

式中為氣相導(dǎo)熱系數(shù)，W/(m·K)。

顆粒與燃燒室壁面的輻射傳熱量可以表示為

式中ε為顆粒表面發(fā)射率；σ為Stefan-Boltzmann常數(shù)，5.67′10-8W/(m2·K4)。

焦炭燃燒放熱量可以表示為

按氧氣向橢球顆粒表面擴(kuò)散得到的焦炭氧化反應(yīng)瞬時(shí)速率為

式中為焦炭氧化反應(yīng)的化學(xué)當(dāng)量比系數(shù)，此處僅考慮焦炭氧化反應(yīng)生成CO的單一反應(yīng)，即=1.332，ox,s和ox,∞分別為顆粒表面和環(huán)境中的氧氣質(zhì)量分?jǐn)?shù)，和分別為氣相密度（kg/m3）和組分?jǐn)U散系數(shù)（m2/s），Sh為顆粒Sherwood數(shù)?？紤]到顆粒的非球形性，上述各式中顆粒Nusselt數(shù)和Sherwood數(shù)的計(jì)算式分別取為[11]

式中Re為顆粒相對(duì)于氣體運(yùn)動(dòng)的Reynolds數(shù)，按與顆粒等體積球的直徑計(jì)算。Pr和Sc分別為氣體的Prandtl數(shù)和Schmidt數(shù)，en為非球形顆粒增強(qiáng)因子。非球形增強(qiáng)因子可由關(guān)于顆粒長(zhǎng)徑比的代數(shù)式表示為[12-13]

式（12）與文獻(xiàn)[14]和[11]得到的扁長(zhǎng)橢球顆粒非球形增強(qiáng)因子的積分表達(dá)式是一致的，而代數(shù)表達(dá)式比積分表達(dá)式更便于應(yīng)用。式（10）和（11）是將顆粒Nusselt數(shù)和Sherwood數(shù)分別表示成了球形顆粒Nusselt數(shù)和Sherwood數(shù)與非球形增強(qiáng)因子的乘積。

通過(guò)異相化學(xué)動(dòng)力學(xué)得到的顆粒焦炭反應(yīng)瞬時(shí)速率為[15]

式中s、s、ox、B、E和分別為顆粒表面的氣體壓力（Pa）與分子量（kg/mol）、氧氣分子量（kg/mol）、焦炭反應(yīng)指前因子（kg/(m2·s·Pa)）與活化能（J/mol）和通用氣體常數(shù)（J/(mol·K)）。

將式（2）與式（6）～（8）代入式（1）中，得到顆粒的瞬時(shí)能量方程為

顆粒的瞬時(shí)質(zhì)量方程為

設(shè)焦炭燃燒過(guò)程中，顆粒的材料密度不變，長(zhǎng)徑比=/也保持不變[16]，得到顆粒的瞬時(shí)短半軸尺寸為

扁長(zhǎng)橢球顆粒的瞬時(shí)表面積為

由式（17）可求出與顆粒等表面積球的瞬時(shí)半徑。

將生物質(zhì)顆粒置于瞬時(shí)溫度空間分布均勻但隨時(shí)間呈正弦方式脈動(dòng)的熱氣流中，氣相瞬時(shí)溫度按式（18）給出

2 數(shù)值求解與工況參數(shù)

對(duì)顆粒瞬時(shí)控制方程組使用有限差分法進(jìn)行離散，得到它們的差分方程，進(jìn)而數(shù)值求解得到生物質(zhì)顆粒瞬時(shí)溫度、質(zhì)量、尺寸和質(zhì)量變化率等隨時(shí)間變化的歷程。采用一種草本生物質(zhì)燃料（薊）作為研究對(duì)象。其焦炭燃燒的指前因子與活化能分別為[15]：B=0.46 g/(m2·s·Pa)，E=63 kJ/mol。工業(yè)分析成分為：水分12.26%，揮發(fā)分61.92%，固定碳19.25%，灰分6.57%。焦炭燃燒過(guò)程中顆粒材料密度、比熱和表面發(fā)射率均為定值，分別取為[17]：pk=90.4 kg/m3，pk=1 600 J/(kg·K)，ε=0.8。氣相導(dǎo)熱系數(shù)和比熱通過(guò)經(jīng)驗(yàn)關(guān)系式，由氣相溫度和組分濃度計(jì)算得到[18]。

此外，還計(jì)算并分析了松木顆粒的瞬時(shí)焦炭燃燒過(guò)程。松木顆粒瞬時(shí)焦炭反應(yīng)的動(dòng)力學(xué)速率為[19]

式中的動(dòng)力學(xué)參數(shù)為：B=0.65Tm/s，E=63 kJ/mol；s為顆粒表面的氣體密度，kg/m3。松木的工業(yè)分析成分為：水分12.38%，揮發(fā)分69.41%，固定碳17.40%，灰分0.81%。松木焦炭顆粒的材料密度為63.7 kg/m3。

為了考察氣相溫度脈動(dòng)對(duì)生物質(zhì)顆粒瞬時(shí)質(zhì)量變化和瞬時(shí)焦炭燃燒速率的影響，對(duì)2種生物質(zhì)顆粒的瞬時(shí)焦炭燃燒過(guò)程在不同的工況條件下進(jìn)行了計(jì)算。計(jì)算中氣相平均溫度分別取為1 000和1 100 K。生物質(zhì)顆粒焦炭反應(yīng)的活性較強(qiáng)，在更高的氣相平均溫度下，氣相溫度脈動(dòng)對(duì)生物質(zhì)顆粒焦炭燃燒仍有影響，由于生物質(zhì)焦炭顆粒的燃盡時(shí)間變短，這種影響會(huì)有所削弱。顆粒初始的等體積球直徑取為200m，顆粒Reynolds數(shù)取為0，壁面溫度和顆粒初始溫度均取為300 K。數(shù)值求解的時(shí)間步長(zhǎng)均取為10-5s。氣相環(huán)境中的組分僅考慮氮?dú)夂脱鯕?，它們的質(zhì)量分?jǐn)?shù)分別為0.9和0.1。氣相溫度脈動(dòng)頻率取為100 Hz，氣相溫度脈動(dòng)幅度分別取為0、0.1和0.2，試驗(yàn)測(cè)得的燃燒室內(nèi)氣相溫度脈動(dòng)均方根值與氣相平均溫度之比為0.1～0.2[20]。文獻(xiàn)[21]對(duì)生物質(zhì)顆粒的形狀進(jìn)行了測(cè)量，得到扁長(zhǎng)橢球顆粒的最大長(zhǎng)徑比為10。因此對(duì)草本生物質(zhì)顆粒的長(zhǎng)徑比分別取為1.4、4和7，松木顆粒的長(zhǎng)徑比分別取為5和10。圖1顯示了扁長(zhǎng)橢球顆粒在1.4、4和7共3種長(zhǎng)徑比下的初始形狀。

注：M為生物質(zhì)扁長(zhǎng)橢球顆粒的長(zhǎng)徑比，下同。

3 結(jié)果與討論

圖2a給出氣相溫度脈動(dòng)對(duì)長(zhǎng)徑比為1.4的草本生物質(zhì)顆粒焦炭燃燒瞬時(shí)質(zhì)量變化的影響。當(dāng)氣相平均溫度為1 000 K時(shí)，在焦炭燃燒過(guò)程中，與不考慮氣相溫度脈動(dòng)相比，考慮氣相溫度脈動(dòng)的橢球顆粒瞬時(shí)質(zhì)量的下降變快，焦炭燃盡時(shí)間變短。增大氣相溫度脈動(dòng)幅度，顆粒瞬時(shí)質(zhì)量的下降得到進(jìn)一步加快，焦炭燃盡時(shí)間也得到進(jìn)一步的縮短。當(dāng)氣相平均溫度從1 000 K上升到1 100 K時(shí)，氣相平均溫度的提高顯著地加快了顆粒瞬時(shí)質(zhì)量的下降，縮短了焦炭燃盡時(shí)間。當(dāng)氣相平均溫度為1 100 K時(shí)，氣相溫度脈動(dòng)對(duì)長(zhǎng)徑比為1.4的生物質(zhì)顆粒焦炭燃燒的瞬時(shí)質(zhì)量變化仍有較明顯的影響，氣相溫度脈動(dòng)幅度的增大使顆粒瞬時(shí)質(zhì)量的下降加快。但與氣相平均溫度為1 000 K時(shí)相比，氣相溫度脈動(dòng)對(duì)顆粒瞬時(shí)質(zhì)量下降和焦炭燃盡時(shí)間的影響有所減弱。

圖2b給出了氣相平均溫度為1 000和1 100 K時(shí)，氣相溫度脈動(dòng)對(duì)長(zhǎng)徑比為4的草本生物質(zhì)顆粒焦炭燃燒瞬時(shí)質(zhì)量變化的影響。由圖2b可見，氣相溫度脈動(dòng)導(dǎo)致長(zhǎng)徑比為4的顆粒的瞬時(shí)質(zhì)量下降和焦炭燃盡時(shí)間明顯變快。圖2c分別給出了氣相平均溫度為1 000和1 100 K時(shí)，氣相溫度脈動(dòng)對(duì)長(zhǎng)徑比為7的草本生物質(zhì)顆粒焦炭燃燒瞬時(shí)質(zhì)量變化的影響。盡管長(zhǎng)徑比增加較多，但顆粒瞬時(shí)質(zhì)量的下降仍受到氣相溫度脈動(dòng)的明顯作用。氣相溫度脈動(dòng)使顆粒質(zhì)量下降變快和焦炭燃盡時(shí)間變短。

注：為氣相平均溫度，K，余同。mk0為生物質(zhì)顆粒的原始質(zhì)量，kg。

圖3a給出氣相溫度脈動(dòng)對(duì)長(zhǎng)徑比為1.4的草本生物質(zhì)顆粒瞬時(shí)焦炭燃燒速率的影響。在氣相平均溫度為1 000和1 100 K時(shí)，不考慮氣相溫度脈動(dòng)與考慮氣相溫度脈動(dòng)得到的長(zhǎng)徑比為1.4的顆粒的瞬時(shí)焦炭燃燒速率有較大的差別。不考慮氣相溫度脈動(dòng)時(shí)得到的顆粒瞬時(shí)焦炭燃燒速率隨著反應(yīng)的進(jìn)行平穩(wěn)地變化。而考慮氣相溫度脈動(dòng)時(shí)得到的瞬時(shí)焦炭燃燒速率則隨時(shí)間脈動(dòng)式地變化，且隨著氣相溫度脈動(dòng)幅度的增加，脈動(dòng)的幅度增大。這是因?yàn)闅庀鄿囟让}動(dòng)導(dǎo)致顆粒溫度的脈動(dòng)，而顆粒溫度的脈動(dòng)進(jìn)一步影響到焦炭燃燒速率的變化。同時(shí)還可以看到，在焦炭燃燒過(guò)程中，由于焦炭燃燒反應(yīng)動(dòng)力學(xué)速率與顆粒溫度之間的指數(shù)函數(shù)關(guān)系，與不考慮溫度脈動(dòng)時(shí)相比，考慮溫度脈動(dòng)時(shí)的焦炭燃燒速率峰值增加的幅度略大于谷值減少的幅度。而氣相溫度脈動(dòng)幅度的增加進(jìn)一步拉大了峰值增加幅度和谷值減少幅度的差距。因此，考慮氣相溫度脈動(dòng)時(shí)要快于不考慮氣相溫度脈動(dòng)時(shí)顆粒焦炭的質(zhì)量損失，且氣相溫度脈動(dòng)幅度越大，焦炭的質(zhì)量損失越快。

圖3 氣相溫度脈動(dòng)對(duì)不同長(zhǎng)徑比的草本生物質(zhì)顆粒瞬時(shí)焦炭燃燒速率的影響

圖3b分別給出了氣相平均溫度為1 000和1 100 K時(shí)，氣相溫度脈動(dòng)對(duì)長(zhǎng)徑比為4的草本生物質(zhì)顆粒瞬時(shí)焦炭燃燒速率的影響。由圖3b可見，受氣相溫度脈動(dòng)的作用，長(zhǎng)徑比為4的顆粒的瞬時(shí)焦炭反應(yīng)速率呈現(xiàn)出明顯的脈動(dòng)，且脈動(dòng)幅度隨氣相溫度脈動(dòng)幅度的增加而增大。與不考慮氣相溫度脈動(dòng)時(shí)相比，考慮氣相溫度脈動(dòng)時(shí)的瞬時(shí)焦炭反應(yīng)速率峰值增加的幅度超過(guò)了谷值減少的幅度。圖3c分別給出了氣相平均溫度為1 000和1 100 K時(shí)，氣相溫度脈動(dòng)對(duì)長(zhǎng)徑比為7的草本生物質(zhì)顆粒瞬時(shí)焦炭燃燒速率的影響。長(zhǎng)徑比為7的顆粒瞬時(shí)焦炭燃燒速率依然受到氣相溫度脈動(dòng)的顯著影響，隨時(shí)間脈動(dòng)式地變化?？紤]與不考慮氣相溫度脈動(dòng)相比，瞬時(shí)焦炭燃燒速率峰值增加的幅度超過(guò)了谷值降低的幅度。

圖4給出了氣相平均溫度為1 000 K時(shí)，氣相溫度脈動(dòng)對(duì)長(zhǎng)徑比為5和10的松木顆粒焦炭燃燒過(guò)程中瞬時(shí)質(zhì)量變化的影響。如圖4a所示，長(zhǎng)徑比為5的松木顆粒的瞬時(shí)質(zhì)量變化受到氣相溫度脈動(dòng)的影響，氣相溫度脈動(dòng)使顆粒瞬時(shí)質(zhì)量下降得更快。氣相溫度脈動(dòng)幅度的增大進(jìn)一步加快了顆粒的質(zhì)量損失。對(duì)比圖4b與圖4a可以看到，隨著長(zhǎng)徑比的增大，具有相同初始等體積球直徑顆粒的焦炭燃盡時(shí)間縮短。盡管如此，長(zhǎng)徑比為10的松木顆粒的瞬時(shí)質(zhì)量變化也受到了氣相溫度脈動(dòng)的影響，顆粒瞬時(shí)質(zhì)量以比不考慮氣相溫度脈動(dòng)時(shí)相對(duì)更快的速率下降。隨氣相溫度脈動(dòng)幅度增大，這一影響變得更加明顯。

圖4 氣相溫度脈動(dòng)對(duì)不同長(zhǎng)徑比的松木顆粒焦炭燃燒瞬時(shí)質(zhì)量變化的影響

4 結(jié) 論

本文考慮到生物質(zhì)顆粒的非球形狀，對(duì)顆粒在有溫度脈動(dòng)的熱氣流環(huán)境中的瞬時(shí)焦炭燃燒過(guò)程進(jìn)行了計(jì)算，得到如下結(jié)論：

1）在不同氣相平均溫度下，氣相溫度脈動(dòng)對(duì)生物質(zhì)橢球顆粒的瞬時(shí)焦炭燃燒過(guò)程均有明顯的影響，導(dǎo)致顆粒瞬時(shí)質(zhì)量下降變快。氣相溫度脈動(dòng)幅度的提高進(jìn)一步加快顆粒瞬時(shí)質(zhì)量的下降，進(jìn)而減少焦炭燃盡時(shí)間。當(dāng)氣相平均溫度升高時(shí)，氣相溫度脈動(dòng)對(duì)顆粒瞬時(shí)質(zhì)量下降和焦炭燃盡時(shí)間的影響有所減弱。

2）在長(zhǎng)徑比大于1的條件下，氣相溫度脈動(dòng)對(duì)具有不同長(zhǎng)徑比或球形度的生物質(zhì)顆粒的瞬時(shí)焦炭燃燒過(guò)程均有較明顯的影響，加快了顆粒瞬時(shí)質(zhì)量的下降和焦炭的燃盡。

3）不考慮氣相溫度脈動(dòng)時(shí)不同長(zhǎng)徑比顆粒的焦炭燃燒速率隨時(shí)間平穩(wěn)地變化，而考慮氣相溫度脈動(dòng)時(shí)顆粒的瞬時(shí)焦炭燃燒速率隨時(shí)間脈動(dòng)式地變化。隨著氣相溫度脈動(dòng)幅度的增加，焦炭燃燒速率脈動(dòng)的幅度增大。

4）本文的研究揭示了氣相溫度的湍流脈動(dòng)對(duì)非球形生物質(zhì)顆粒瞬時(shí)焦炭燃燒過(guò)程的影響，在生物質(zhì)與煤粉混燃的湍流多相燃燒理論模型中應(yīng)當(dāng)考慮到這一影響。

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Effects of gas temperature fluctuation on char combustion of non-spherical biomass particle

Li Jie, Zhang Jian

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Biomass energy is a renewable energy. It is abundant in resources, and has net zero emission of CO2and relatively low nitrogen and sulfur contents, and is widely found in the world. More attention has been paid to its utilization. Co-firing biomass with pulverized coal particles provides an effective manner to utilize biomass energy. Biomass particles are generally much irregular-shaped. They have large aspect ratios and exhibit obvious non-spherical characteristics. For biomass particles moving and burning in a combustor, the turbulent fluctuation of gas velocity has evident effects on the particle motion. But whether the gas turbulent fluctuation imposes influences on the reaction processes of non-spherical biomass particles needs to be studied. The effects of gas temperature fluctuation on the instantaneous char combustion of non-spherical biomass particles in a hot gas were explored in the present paper. Biomass particles with prolate spheroidal shapes were studied. The theoretical expressions for both mass transfer and heat transfer enhancement factors of prolate spheroidal particles were employed in algebraic forms. They are functions of particle aspect ratio. The Sherwood number or Nusselt number for the prolate spheroidal particles can be expressed as the product of the enhancement factor and the Sherwood number or Nusselt number for the spherical particles.Thistle and pine are 2 types of biomass fuel. Their instantaneous char reaction processes were calculated.The thistle particles have aspect ratios of 1.4, 4, and 7. The aspect ratios for the pine particle are 5 and 10. The gas flow has a time-averaged temperature of 1 000 and 1 100 K.The fluctuation amplitude of the gas temperature was chosen to be 0, 0.1 and 0.2. Both thistle and pin particles have the same initial diameter of the equal-volume sphere. Its magnitude is 200m. The instantaneous variations of particle mass and char combustion rates with time were provided under different time-averaged gas temperature and particle aspect ratios. The results showed that the gas temperature fluctuation had evident influences on the instantaneous char combustion processes of biomass particles with different aspect ratios. It leaded to faster mass loss of the particles andshortened time for the char combustion. The increase in the fluctuation amplitude of the gas temperature would further enhance the instantaneous mass loss of the particles with different aspect ratios. The instantaneous char reaction processes of both thistle and pine particles were affected by the gas temperature fluctuation. As a result of gas temperature fluctuation, the particles lost their mass and the char burns out at faster rates.The instantaneous char combustion rates of the biomass particles with different aspect ratios exhibited smooth variations with time when the gas temperature fluctuation was not considered. While fluctuating variations with time were found for the instantaneous char combustion rates of the biomass particles obtained with the gas temperature fluctuation. The present study reveals the effects of turbulent fluctuation of gas temperature on the instantaneous char combustion processes of non-spherical biomass particles. The influences will not change when the particle aspect ratio experiences variations.

biomass; combustion; emission control; non-spherical particle; char; gas temperature fluctuation

10.11975/j.issn.1002-6819.2019.15.030

TK16

A

1002-6819(2019)-15-0241-05

2019-01-21

2019-07-15

國(guó)家自然科學(xué)基金資助項(xiàng)目（51376106）

李 捷，博士，主要從事多相燃燒的研究。Email：leejay1986@163.com

張 健，教授，博士，主要從事湍流多相流動(dòng)與燃燒的研究。Email：jianzhang@mail.tsinghua.edu.cn

李 捷，張 健. 氣相溫度脈動(dòng)對(duì)非球形生物質(zhì)顆粒焦炭燃燒的影響[J]. 農(nóng)業(yè)工程學(xué)報(bào)，2019，35(15)：241－245. doi：10.11975/j.issn.1002-6819.2019.15.030 http://www.tcsae.org

Li Jie, Zhang Jian. Effects of gas temperature fluctuation on char combustion of non-spherical biomass particle[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2019, 35(15): 241－245. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.2019.15.030 http://www.tcsae.org