摘要:【目的】現(xiàn)有微球形材料磨損指數(shù)的測(cè)試方法均在氣固兩相中進(jìn)行,建立一種在三相流化條件下評(píng)價(jià)微球形材料耐磨性的方法,以更準(zhǔn)確測(cè)定微球形材料在氣液固三相流化時(shí)的磨損指數(shù)?!痉椒ā吭趥鹘y(tǒng)氣固兩相耐磨性測(cè)試基礎(chǔ)上,在體系中引入去離子水作為液相,提出并建立一種在氣液固三相體系中的微球形材料耐磨性測(cè)試方法;系統(tǒng)研究了樣品預(yù)篩分、氣體流量、樣品量、加水量和測(cè)試時(shí)間等對(duì)耐磨性測(cè)定結(jié)果的影響,探索微球形材料在氣液固三相中的磨損時(shí)變規(guī)律。【結(jié)果】氣體流量對(duì)耐磨性測(cè)試結(jié)果影響最為顯著,提高氣體流量會(huì)使測(cè)得的磨損指數(shù)增大,且直徑小于20 μm的細(xì)顆粒會(huì)干擾耐磨性測(cè)試結(jié)果的準(zhǔn)確性,應(yīng)在測(cè)試前篩除。使用3批樣品開展耐磨性重復(fù)測(cè)試,相對(duì)標(biāo)準(zhǔn)偏差均小于5%。采用Gwyn模型對(duì)測(cè)試數(shù)據(jù)進(jìn)行擬合,實(shí)測(cè)值與模型的吻合程度良好?!窘Y(jié)論】建立的耐磨性測(cè)試方法具有較優(yōu)的準(zhǔn)確性和重復(fù)性,能夠更真實(shí)地預(yù)測(cè)微球形材料在氣液固三相流化床中的耐磨性優(yōu)劣。
關(guān)鍵詞:微球形材料;耐磨性;氣液固三相流化
中圖分類號(hào):TB4;TQ016.1文獻(xiàn)標(biāo)志碼:A
引用格式:
張哲,肖瑋婷,賀宇飛,等.微球形材料在三相流化時(shí)磨損指數(shù)的測(cè)試方法[J].中國(guó)粉體技術(shù),2024,30(4):94-103.
ZHANG Zhe,XIAOWeiting,HEYufei,etal.An attrition index test method for microspherical materials in gas-liquid-solidthree-phase fluidization[J].China Powder Science and Technology,2024,30(4):94-103.
流化床是常用的反應(yīng)裝置之一,所用催化劑多為粒徑數(shù)十至數(shù)百微米的微球形顆粒。流化床在運(yùn)行過程中,催化劑顆粒之間以及顆粒與設(shè)備和管道內(nèi)壁之間存在劇烈碰撞和摩擦,因此為了維持裝置運(yùn)轉(zhuǎn)穩(wěn)定,要求催化劑具備良好的耐磨性[1-2],耐磨性的測(cè)試方法也至關(guān)重要。
目前耐磨性的常規(guī)檢測(cè)手段有直管噴吹法、噴杯法以及彈性模量測(cè)試等。由于直管噴吹法所用測(cè)試設(shè)備與工業(yè)氣固兩相流化床裝置最為接近,因此應(yīng)用最為廣泛。目前已發(fā)布實(shí)施的耐磨性測(cè)試標(biāo)準(zhǔn)均采用直管噴吹的方法,如流化催化裂化催化劑磨損指數(shù)測(cè)試標(biāo)準(zhǔn)、甲醇制低碳烯烴催化劑磨損指數(shù)測(cè)試標(biāo)準(zhǔn)、以及氧化鋁的磨損指數(shù)測(cè)試標(biāo)準(zhǔn),這些標(biāo)準(zhǔn)均是在氣固兩相流化床中進(jìn)行測(cè)試的。氣液固三相流化床也有著重要工業(yè)應(yīng)用,如蒽醌法制過氧化氫流化床工藝、煤的直接液化等[14-15]。目前在三相流化狀態(tài)下測(cè)試微球形材料耐磨性的研究還比較少。為了更準(zhǔn)確地測(cè)試微球形材料在三相流化床中的耐磨性,本文中結(jié)合氣固相磨損指數(shù)測(cè)試方法,提出了適用于氣液固三相體系的微球形顆粒磨損指數(shù)測(cè)試方法,并研究了不同因素對(duì)磨損指數(shù)測(cè)量準(zhǔn)確性的影響。
1材料與方法
1.1試劑材料和儀器設(shè)備
試劑材料:Pd-Al?O?微球形催化劑(其中Pd的質(zhì)量分?jǐn)?shù)為2%,Al?O?的質(zhì)量分?jǐn)?shù)大于97%,英國(guó)Johnson Matthey公司,簡(jiǎn)稱JM樣品);微球形Al?O?(其中Al?O?的質(zhì)量分?jǐn)?shù)大于99%,自制樣品),采用專利中公開的方法制備16;由于待測(cè)樣品在去離子水中不溶,分散性好,且去離子水無毒不會(huì)產(chǎn)生二次環(huán)境污染,因此本文中選擇去離子水作為液相。
儀器設(shè)備:Mastersizer 2000型激光粒度儀(英國(guó)Malvern公司);Sigma 300型掃描電子顯微鏡(德國(guó)ZEISS公司);ALF-1型磨損指數(shù)測(cè)試儀(北京中儀勵(lì)朗科技有限公司),裝置流程簡(jiǎn)圖如圖1所示。主要組成元件包括石英管柱、氣體流量測(cè)量和控制設(shè)備、外接壓縮氮?dú)怃撈?、集塵器和不銹鋼試樣桶(內(nèi)徑為28 mm,高為125 mm,進(jìn)氣漏孔直徑為(0.381±0.002)mm)。
1.2方法
準(zhǔn)確稱量一定質(zhì)量的JM樣品或自制樣品,加入一定量的去離子水,分散均勻后轉(zhuǎn)移至磨損指數(shù)測(cè)試儀器底部的試樣桶中,并將試樣桶與石英管連接固定。使用壓縮氮?dú)庾鳛闅庠矗ㄟ^調(diào)節(jié)壓力控制流量至設(shè)定值,噴吹一定時(shí)間后收集漿液。收集的漿液自然靜置過夜使固體顆粒完全沉降,傾去上層水相后使用無水乙醇置換2次,待樣品自然晾干后轉(zhuǎn)移至烘箱內(nèi)110°℃干燥恒重。使用孔徑為20 μm標(biāo)準(zhǔn)篩篩分干燥后的樣品,得到粒徑小于20 μm的篩下粉體和大于20 μm的篩上粉體,分別稱重。
根據(jù)GB/T 6609.33—2009《氧化鋁化學(xué)分析方法和物理性能測(cè)定方法第33部分:磨損指數(shù)的測(cè)定》13中使用的磨損指數(shù)計(jì)算公式
式中:IA為磨損指數(shù);w,為磨損前的粒徑大于45 μm顆粒的質(zhì)量分?jǐn)?shù);w.為磨損后的粒徑大于45 μm顆粒的質(zhì)量分?jǐn)?shù)。
國(guó)標(biāo)測(cè)試的樣品主要是電解鋁生產(chǎn)所用的砂狀氧化鋁,采用粒徑為45 μm的砂狀氧化鋁主要是為了衡量氧化鋁的起塵性。本方法的測(cè)試對(duì)象之一是蒽醌法制過氧化氫流化床工藝所用的微球形材料,其粒徑為2~200 μm,為盡量減小樣品預(yù)處理對(duì)原顆粒群的影響,本方法采用20 μm作為基準(zhǔn)。因此國(guó)標(biāo)中的w,在本文中對(duì)應(yīng)磨損前粒徑大于20 μm顆粒的質(zhì)量分?jǐn)?shù)(由于磨損前樣品中不含有粒徑小于20 μm的顆粒,因此w,=100%)、而wa對(duì)應(yīng)磨損后粒徑大于20 μm顆粒的百分含量,據(jù)此可從國(guó)標(biāo)的公式推導(dǎo)出本文中的摩擦指數(shù)計(jì)算公式如下
式中:wA為磨損后的粒徑小于20 μm顆粒的質(zhì)量分?jǐn)?shù);m?為磨損后的粒徑小于20 μm顆粒的質(zhì)量;m?為磨損后的粒徑大于20 μm顆粒的質(zhì)量;平行測(cè)試兩次,結(jié)果取算術(shù)平均值。
2結(jié)果與分析
2.1氣固噴吹測(cè)試
首先使用JM樣品,采用GB/T 6609.33—2009《氧化鋁化學(xué)分析方法和物理性能測(cè)定方法第33部分:磨損指數(shù)的測(cè)定》13測(cè)試樣品在氣固兩相耐磨性實(shí)驗(yàn)中的性能,原始樣品、測(cè)試后樣品以及紙濾筒內(nèi)收集的細(xì)粉體的粒度分布如表1和圖2所示。經(jīng)耐磨測(cè)試后,樣品的粒徑明顯變小,質(zhì)量矩體積平均粒徑d?,3由87.2 μm減小至61.8 μm,但索太爾平均粒徑d?,2卻由41.2 μm增加至46.2 μm。這是因?yàn)闇y(cè)試過程中較細(xì)顆粒更容易被氣體夾帶進(jìn)入紙濾筒,使得測(cè)試后樣品中粒徑小于15 μm的細(xì)顆粒占比大幅減小,其中粒徑小于4 μm的極細(xì)顆粒甚至完全消失。由于索太爾平均粒徑對(duì)細(xì)顆粒的變化更為靈敏,因此造成測(cè)試后樣品的索太爾平均粒徑增大。紙濾筒中細(xì)粉的粒度呈雙峰分布,且其d,0為42.2 μm,說明被氣體噴吹至紙濾筒內(nèi)的細(xì)粉中可能存在部分粒徑較大的顆粒。測(cè)試后濾筒內(nèi)樣品的SEM圖像如圖3所示。由圖3可觀察到顆粒完整、且粒徑大于20 μm的較粗顆粒,這些顆粒并非磨損產(chǎn)生的,而是樣品自身存在、由氣流夾帶進(jìn)入紙濾筒中的,它們會(huì)導(dǎo)致測(cè)試結(jié)果偏大;此外,樣品測(cè)試后仍殘留有粒徑為4~15 μm的細(xì)顆粒未進(jìn)入紙濾筒中,又會(huì)引起測(cè)試結(jié)果偏小。以上結(jié)果說明,顆粒夾帶現(xiàn)象會(huì)導(dǎo)致測(cè)試結(jié)果失真,因此本文提出引入去離子水予以解決。
2.2樣品中細(xì)顆粒的影響
為了研究樣品中細(xì)顆粒對(duì)測(cè)試結(jié)果的影響,分別使用孔徑為20 μm標(biāo)準(zhǔn)篩和孔徑為45 μm標(biāo)準(zhǔn)篩對(duì)JM樣品進(jìn)行預(yù)篩分,得到的篩上粉體分別命名為JM?o+和JM45+。采用1.2中所述方法測(cè)試未篩分的JM原樣和上述2種篩后樣品的耐磨性,具體測(cè)試條件為:樣品質(zhì)量20.0 g,加水量60.0 mL,氣體流量7.0 L/min,測(cè)試時(shí)間30 min,不同樣品的磨損指數(shù)見表2,測(cè)試前后的粒度分布如表2和圖4所示。
測(cè)試結(jié)果表明,3組樣品經(jīng)耐磨測(cè)試后顆粒粒徑均明顯減小,但磨損指數(shù)卻差別明顯,JM原始樣品的磨損指數(shù)為7.42%,顯著大于JM?0-原始樣品和JM?5+原始樣品的(分別為3.46%和2.73%)。結(jié)合不同樣品的粒度分布,推測(cè)這可能是由于原始樣品中存在較多的小于20 μm的顆粒,這部分顆粒在測(cè)試后也會(huì)穿透篩網(wǎng)成為篩下粉體,從而引起磨損指數(shù)增大。使用掃描電子顯微鏡觀察不同樣品的篩下粉體進(jìn)行驗(yàn)證,如圖5所示,JM測(cè)試后樣品的篩下粉體中包括很多粒徑小于20 μm、且外形完整的顆粒,JM?0+測(cè)試后樣品的篩下粉體中這類顆粒占比明顯減少,說明這些顆粒是樣品中本來存在的,而非磨損過程中產(chǎn)生的,這是因?yàn)椴糠诸w粒并不是完美的球形且粒度與孔徑為20 μm的標(biāo)準(zhǔn)篩的篩孔接近,因此預(yù)篩分時(shí)沒有被除去。將這部分顆粒的質(zhì)量計(jì)入磨損指數(shù)的計(jì)算勢(shì)必會(huì)引起計(jì)算結(jié)果偏大;而JM?5測(cè)試后樣品的篩下粉體中幾乎沒有形貌完整的球形顆粒,完全由磨損過程產(chǎn)生的不規(guī)則碎屑組成,說明使用孔徑為45 μm的標(biāo)準(zhǔn)篩可消除樣品中粒徑較小的顆粒對(duì)測(cè)試結(jié)果的影響,從而提高測(cè)試結(jié)果的準(zhǔn)確性。
盡管預(yù)篩分消除了粒徑小于20 μm的顆粒對(duì)測(cè)試結(jié)果的干擾,但還需驗(yàn)證其對(duì)原顆粒群耐磨性的影響。分別選取3批自制樣品,開展對(duì)比實(shí)驗(yàn)考察預(yù)篩分對(duì)耐磨性的影響。
對(duì)比實(shí)驗(yàn)1:使用孔徑為45 μm的標(biāo)準(zhǔn)篩對(duì)樣品進(jìn)行預(yù)篩分,隨后按本節(jié)的測(cè)試條件測(cè)試耐磨性,最后根據(jù)式(2)計(jì)算磨損指數(shù),結(jié)果如表3所示。
對(duì)比實(shí)驗(yàn)2:使用原始樣品,在對(duì)比實(shí)驗(yàn)1的條件下測(cè)試耐磨性,最后使用激光粒度儀測(cè)定磨后樣品的粒度分布,并計(jì)算因磨損產(chǎn)生的細(xì)顆粒的體積分?jǐn)?shù)。對(duì)比實(shí)驗(yàn)2中樣品耐磨測(cè)試前后的粒徑分布如圖6所示,3個(gè)樣品的原樣中均沒有直徑小于20 μm的顆粒,但測(cè)試后均檢測(cè)到了粒徑小于10 μm的顆粒,可認(rèn)為這些顆粒是磨損產(chǎn)生的。使用激光粒度儀測(cè)定這部分顆粒的體積分?jǐn)?shù),以表示原始樣品的磨損程度,結(jié)果如表3所示。在對(duì)比實(shí)驗(yàn)1中測(cè)得的樣品1、樣品2和樣品3的磨損指數(shù)分別為2.17%、1.58%和0.77%,而在對(duì)比實(shí)驗(yàn)2中對(duì)應(yīng)樣品測(cè)試后產(chǎn)生的細(xì)顆粒的體積分?jǐn)?shù)分別為3.77%、3.26%和1.21%,相對(duì)大小趨勢(shì)一致,因此本方法能夠表征原顆粒系的磨損指數(shù)。
綜上可知,預(yù)篩分不僅可以避免小顆粒對(duì)測(cè)試結(jié)果的干擾,而且還能夠真實(shí)反映原顆粒系的耐磨性能。
2.3操作條件的影響
為考察操作條件對(duì)磨損指數(shù)的影響,設(shè)計(jì)正交實(shí)驗(yàn)。取樣品質(zhì)量、水量和氣體流量3個(gè)因素,每個(gè)因素設(shè)置3個(gè)水平,實(shí)驗(yàn)時(shí)間均為0.5h。用四因素三水平L?(34)正交表安排實(shí)驗(yàn),使用自制樣品1,實(shí)驗(yàn)方案、磨損指數(shù)結(jié)果如表4所示。相同實(shí)驗(yàn)條件平行測(cè)試2次,取算數(shù)平均值。極差分析如表5所示。
由實(shí)驗(yàn)結(jié)果可知,不同因素對(duì)磨損指數(shù)的影響程度由大到小為氣體流量、加水量、樣品質(zhì)量。磨損指數(shù)隨氣體流量的增加而增大,隨加水量的增加而減小,而隨著樣品質(zhì)量增加,磨損指數(shù)先減小再增大,但該因素的k值極差與空列接近,說明其影響與隨機(jī)誤差接近。根據(jù)以上分析,當(dāng)樣品質(zhì)量為20.0 g、加水量為100.0 mL、氣體體積流量為8.0 L/min時(shí)磨損指數(shù)最大,根據(jù)此條件測(cè)得磨損指數(shù)為2.29%,大于設(shè)計(jì)正交實(shí)驗(yàn)中結(jié)果的最大值2.22%。由于該條件下樣品磨損程度最為劇烈,更便于對(duì)比不同樣品的耐磨性優(yōu)劣,因此將其作為最終的測(cè)試條件。
2.4重復(fù)性
使用3批不同樣品在上述條件下開展重復(fù)性實(shí)驗(yàn),每批樣品平行測(cè)試5次,結(jié)果如表6所示,不同樣品的磨損指數(shù)的相對(duì)標(biāo)準(zhǔn)偏差為3.45%~4.46%,均小于5.00%,說明本方法的重復(fù)性較好[17-18]
2.5時(shí)變規(guī)律
為了研究樣品在氣液固三相磨損測(cè)試中的時(shí)變規(guī)律,采用與2.4相同的測(cè)試條件,分別測(cè)試了在磨損實(shí)驗(yàn)時(shí)間為0.5、1.0、1.5、2.0、2.5h時(shí)樣品的磨損指數(shù),結(jié)果如圖7所示。顆粒在氣固流化床中的磨損模型中,比較有代表性的是Gwyn1提出的Gwyn模型和Klett等20提出的分段模型。二者的主要區(qū)別在于,后者認(rèn)為由于原始樣品顆粒表面粗糙,存在較多棱角與裂紋,因此初期的磨損速率較高,而運(yùn)行一段時(shí)間顆粒表面逐漸變光滑,此時(shí)磨損速率趨于穩(wěn)定且大幅降低2~3個(gè)數(shù)量級(jí)。此外,不同模型所用的實(shí)驗(yàn)設(shè)備不完全相同,Gwyn使用的磨損設(shè)備是傳統(tǒng)的氣固流化床,而Klett使用的則是循環(huán)流化床。由于本文使用的設(shè)備與Gwyn更為接近,且自制樣品表面較為光滑,幾乎不存在棱角與裂紋,因此0.5h時(shí)測(cè)得的磨損速率與之后的并沒有數(shù)量級(jí)上的差別。綜上,本文采用Gwyn模型對(duì)測(cè)試數(shù)據(jù)進(jìn)行擬合,圖7為不同時(shí)間的磨損指數(shù)及Gwyn模型擬合圖。由圖7可見,磨損指數(shù)實(shí)測(cè)值(以實(shí)心數(shù)據(jù)點(diǎn)表示)與擬合曲線(以虛線表示)吻合程度均較好,這說明在本方法采用的測(cè)試條件下,顆粒的磨損規(guī)律與氣固兩相中的相似。
3結(jié)論
1)建立了一種在氣液固三相條件下測(cè)試微球形顆粒磨損指數(shù)的方法,提出了應(yīng)預(yù)先篩除待測(cè)樣品中直徑小于20 μm的細(xì)顆粒以更真實(shí)地反映樣品的耐磨性。
2)設(shè)計(jì)正交實(shí)驗(yàn)考察了操作條件對(duì)磨損指數(shù)的影響,發(fā)現(xiàn)氣體流量的影響最為顯著,將磨損指數(shù)最大時(shí)的條件確定為最終條件以便對(duì)比不同樣品的耐磨性。對(duì)本方法進(jìn)行了重復(fù)性驗(yàn)證,相對(duì)標(biāo)準(zhǔn)偏差均小于5%,重復(fù)性較好。
3)采用本方法研究了微球形材料的磨損時(shí)變規(guī)律,發(fā)現(xiàn)與Gwyn模型擬合程度較好。
4)本文建立的測(cè)試方法與實(shí)際的氣液固三相流化過程更為接近,因此能夠更好地預(yù)測(cè)微球形材料在三相流化床中的耐磨性能,具有重要應(yīng)用價(jià)值。
利益沖突聲明(Conflict of Interests)
所有作者聲明不存在利益沖突。
All authors disclose no relevant conflict of interests.
作者貢獻(xiàn)(Authors'Contributions)
張哲、賀宇飛和閆子涵進(jìn)行了方案設(shè)計(jì),張哲、肖瑋婷和趙曉東參與了論文的寫作和修改,賀宇飛和李殿卿作為指導(dǎo)教師對(duì)論文進(jìn)行了修改。所有作者均閱讀并同意了最終稿件的提交。
The study was designed by ZHANG Zhe,HEYufei,and YAN Zihan.The manuscript was written and revisedby ZHANG Zhe,XIAOWeiting,and ZHAO Xiaodong.HE Yufei and LI Dianqing revised the paper asinstructors.All authors have read the final version of the paper and consented to its submission.
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An attrition index test method for microspherical materials in gas-liquid-solid three-phase fluidization
ZHANG Zhe1,2,XIAO Weiting2,HE Yufei1,3*,YAN Zihan?,LI Dianqing1,3,ZHAO Xiaodong2
1.State Key Laboratory of Chemical Resource Engineering,College of Chemistry,Beiing University of Chemical Technology,Beiing100029,China;
2.Liming Research amp;Design Institute of Chemical Industry Co.,Ltd.,Luoyang 471000,China;
3.Quzhou Institute for Innovation in Resource Chemical Engineering,Quzhou 324000,China;
4.State Key Laboratory of Heavy Oil Processing,College of Chemical Engineering and Environment,China University of Petroleum(Beijing),Beijing 102249,China
Abstract
Objective The three-phase fluidized bed is extensively employed in chemical industry due to its low mass transfer resistance,uniform temperature distribution,and maximized contact between catalysts and reactants.Theatrition resistance of catalysts isa crucial parameter due to the severe collisions between catalyst particles and the inner walls of reactors,as well as among theparticlesthemselves.However,existing attrition resistance tests are typically conducted in gas-solid two-phase environments,and the catalysts are also applied in the similar system.Therefore,designing a new method which simulates a three-phase fluid-ized bed is both academically and practically significant.
Methods In this paper,deionized water was introduced as the liquid phase to transform the traditional gas-solid two-phase attri-tion test into a gas-liquid-solid three-phase test.Atrition tests were conducted on pristine samples and samples that were pre-screened to remove fines under 20 μm or 45 μm to determine the influence of sample pre-screening on test results.Anorthogo-nal test was designed to evaluate the contributions of gas flow volume(6 to 8 L/min),sample mass(20.0 to 30.0g),and watervolume(100 to 140 mL)to the attrition index.The combination of levels that resulted in the highest attrition index from theorthogonal test was proposed as the optimal test condition for the new method,and its repeatability was evaluated.Attritiontestswith durations ranging from 0.5 to 2.5 h were conducted to study the time-profile characteristics of microspherical materials ingas-liquid-solid three-phase fluidization.
Results and Discussion In traditional tests,fines collected in the fltering flask often contain intact microparticles,whicharemistakenly calculated as attritedfines,leading to systematical bias.Additionally,fines with diameter below 20 μm in thesample can interfere with attrition test results for the same reason and should therefore be pre-screened.With these improve-ments,the fines collected in the novel method were solely those generated during the attitiontest.The orthogonal test showedthe relative significance of different factors in the following order:gas flow volumegt;sample massgt;water volume,with the firstfactor positively correlated with the result and the last two negatively.The highest attrition index was observed when using 20.0gof the sample,100 mL of water,and a gas flow volume of 8.0 L/min.To evaluate the repeatability of the new attrition testmethod,three batches of samples were tested,with five parallel experiments for each sample.The relative standard deviationranged from 3.48%to 4.46%,indicating good reliability.Atrition test results over time corresponded well with the Gwynmodel,indicating that the attrition mechanism in the three-phase fluidized bed was similar to that in the gas-solid two-phasesystem.
Conclusion A novel method for evaluating atrition resistance of microspherical materials used in three-phase fluidized beds wasestablished.To more precisely reflect attrition resistance in real three-phase reactors,fines with diameter below 20 μmshouldberemoved.The orthogonal test showed that gas flow volume had the most significant influence on attrition.The repeatability ofthe test was confirmed,with a relative standard deviation of less than 5%,indicating good reliability.The new method can beused to determine the attrition resistance of different materials used in three-phase reactors,which has important practicalapplications.
Keywords:microsphericalmaterial;attritionresistance;gas-liquid-solid three-phase fluidization
(責(zé)任編輯:孫媛媛)