二次氧量對分級氣化爐氣化特性影響的分析和比較

第63卷第2期化工學(xué)報Vol. 63 No. 2CirsIour20122012年2月CIESC JournalFebruary研 究論文資二次氧量對分級氣化爐氣化特性 影響的分析和比較吳玉新，蔡春榮，張建勝，岳光溪，呂俊復(清華大學(xué)熱能工程系，熱科學(xué)與動(dòng)力工程教育部重點(diǎn)實(shí)驗室，北京100084)摘要:分級給氧氣流床氣化爐具有爐內混合過(guò)程強烈、噴嘴附近溫度較低等優(yōu)點(diǎn)。采用CFD數值方法研究了二次氧量變化對氣化爐運行特性的影響，分析比較了不同二次給氧量下相交射流火焰特性的變化。當二次給氧量較低時(shí)，二次火焰在回流區的作用下明顯向上偏斜，其射流動(dòng)量不足以影晌主射流產(chǎn)生的宏觀(guān)流場(chǎng)。二次氧量大于總氧量的8%時(shí)，回流區在二次射流的卷吸作用下收縮，但顆粒停留時(shí)間有所增加。二次氧量為16%時(shí)，與二次氧量為2%的工況相比，氣化爐上游的平均溫度降低約20C，二次射流高度處的平均溫度提高約300C.由于總的氧煤質(zhì)量比不變，二次氧量的變化對氣化爐下游的影響并不顯著(zhù)。關(guān)鍵詞:數值模擬;分級氣流床氣化爐;二次給氧;氣化爐流場(chǎng)DOI: 10. 3969/j. issn. 0438-1157. 2012.02. 005中圖分類(lèi)號: TQ171.6+ 25; TQ 54文獻標志碼: A文章編號: 0438- 1157 (2012) 02- -0369 - -06Numerical investigation of effects of secondary oxygen ratio onperformance of staged-entrained flow coal gasifierWU Yuxin, CAI Chunrong, ZHANG Jiansheng, YUE Guangxi, LU Junfu(Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department ofThermal Engineering , Tsinghua University, Beijing 100084, China)Abstract: The staged oxygen entrained flow coal-slurry gasifier has such advantages as higher carbonconversion rate, stronger turbulent mixing inside gasifier and lower temperature near coal slurry nozzle. Inthis paper, the effects of secondary oxygen mass flow rate (SOMFR) on gasification performance werenumerically investigated through CFD simulation. The CFD model was based on the Euler-Lagrangianmethod. Realizable ke model was used to acquire the turbulent information in the gasifier. Presumed PDFmethod was adopted to consider interactions between turbulence and homogeneous reactions. Thecharacteristics of the gasification flames were analyzed as well as the flow field under different SOMFR inthe staged gasifier. As SOMFR decreased, the secondary gasification flame curved up with backflow nearthe wall. At the same time, dome wall temperature increased as well. When SOMFR was less than 8% ofthe total oxygen mass flow rate, the momentum flux of the secondary oxidizer is too low to change themacro flow field. When SOMFR was larger than 8% of the total oxygen mass flow rate, the recirculationregion shrank due to the entrainment of secondary flow. However, particle residence time increased, sincethe velocity in back-flow region increased. Particle gasification process would be benefited from thischange. As SOMFR increased, the down-flow flame length decreased as well as the average temperature inthe top furnace region. The result showed that the average temperature decreased by 20C when SOMFR2011- 08-03收到初稿.2011- 10- 10收到修改稿.Receved date; 2011-08- 03.聯(lián)系人及第一作者，吳玉新(1979-). 男，博士.著(zhù)金項目:國家重點(diǎn)基礎研究發(fā)展計劃項目(2010C227006).Foundation item:_ supported by the National Basic ResearchProgram of China (20中國煤化工MHCNMH G .●370●化工學(xué)報第63卷increased from 2% to 16% of the total oxygen mass flow rate. At the height where secondary oxygen wasintroduced, the average temperature increased by 300C as well. In all cases, the temperature flow field atthe down-section of the gasifier did not change, since the oxygen coal mass ratio was kept constant.Key words: numerical simulation; staged-entrained flow coal gasifier; secondary oxygen; flow field ingasifier引言1研究對象及數值模型煤的氣化是煤清潔利用的重要過(guò)程之一，在該1.1研究對象描述過(guò)程中，煤被轉化為易于處理的氣體并被分離凈化模擬對象為一臺水煤漿分級給氧氣化爐[23],后直接用作氣體燃料或者化工原料[1。分級氣流床氣化爐主噴嘴內環(huán)和外環(huán)分別通人12. 5%和75%煤氣化爐采用分級給氧技術(shù)，將大部分氧氣和水煤的O2和CO2氣體混合物，在保證霧化效果同時(shí)降漿從主噴嘴送入爐體，而將剩余氧氣在爐體側壁以低主噴嘴氧煤比和主噴嘴附近溫度，延長(cháng)主噴嘴使對沖形式給人[2。該技術(shù)主噴嘴氧煤比低，氣化火用壽命。剩余氧化劑從距爐頂約為1/3爐高的對沖焰溫度不高，對主氣化噴嘴形成有效的保護作.噴嘴引人，二次氧提高了該區域的氣化溫度，進(jìn)而用;二次氧氣的給人在提高氣化溫度同時(shí)增強了彌補了主火焰區溫度降低帶來(lái)的不利因素.爐內湍流混合過(guò)程，因此該氣化爐具有穩定運行時(shí)本文中，氣化爐水煤漿濃度為59. 1%，氧煤間長(cháng)、碳轉化率高等特點(diǎn)[4]。質(zhì)量比為0.92 [約合0.64 m'O2●(kg煤)-'],氣在分級氣化爐中，一次給氧量和二次給氧量間化用煤為神府煤，其工業(yè)分析及元素分析見(jiàn)表1.的配比是- -個(gè)重要參數，合理優(yōu)化兩者的配比，能煤顆粒粒徑分為30、60、 110、175 μm四檔，其夠得到最佳運行工況。二次氧是通過(guò)射流的方式在質(zhì)量分數分別為50%、15%、30%、5%。氣化爐側壁面橫向給人，類(lèi)似于煤粉鍋爐中的二次表1水煤漿 原料煤的工業(yè)分析和元素分析風(fēng)。這種給氧方式屬于典型的橫向湍流射流，在達Table 1 Primary and ultimate analysis of coal for slurry到一定的剛度條件下，會(huì )對局部流場(chǎng)產(chǎn)生重要影Primary analysis(D)/%Ultimate analysis(DAF)/%響。高偉等[5]研究了橫向射流火焰的特性，發(fā)現隨V FC A QHv/MJ.kg-iC HO N S33.3957.97 6.74 26. 16374.394.36 13.08 0.92 0.51著(zhù)射流動(dòng)量降低，橫向火焰沿主流方向彎曲明顯，穿透深度逐漸減小。吳海玲等[0]采用數值模擬方法為分析二次氧氣體流量變化對二次火焰以及整比較了二維橫向射流的平均流動(dòng)和湍流特性，并分體氣化效果的影響，分別取二次氧份額為總氣體流析了二次射流回流區對下游壁面換熱特性的影響。量的16%、13%、8%、4%和2%進(jìn)行比較，相應郭婷婷等[']對湍流橫向射流的流動(dòng)特性進(jìn)行數值模地，通過(guò)調整主噴嘴中心給氧量以保證各工況下的擬，發(fā)現橫向射流與主氣流速度是影響橫向射流特氣化爐氧煤質(zhì)量比保持恒定。性的重要參數。1.2模型假設和數值模擬方法這些學(xué)者的成果對氣化爐二次給氧的火焰特性基于簡(jiǎn)化PDF模型建立的三維CFD模型已對研究有很好的參考價(jià)值，但一方面，橫向射流氣化分級給氧氣化爐進(jìn)行了數值模擬[34),并與實(shí)驗結火焰在氣化爐壁面回流以及主射流的共同影響下，果進(jìn)行了詳細比較，證明了該三維模型的準確性。其形態(tài)不同于典型的橫向射流[1;另一方面，氧氣詳細的CFD模型介紹和驗證見(jiàn)文獻[4, 10]， 在射人氣化合成氣氛圍將產(chǎn)生反擴散湍流火焰，這一這 里僅對主要模型方法做簡(jiǎn)單介紹?；鹧嫣匦耘c傳統的擴散火焰也存在明顯差異[89]。本文采用EulerLagrangian方法描述氣固湍流為掌握二次氧流量變化對氣化過(guò)程的影響，本文對反應過(guò)程。對氣相分別求解連續方程、動(dòng)量方程和.一臺 分級氣流床氣化爐進(jìn)行三維數值模擬，在不同能量方程，采用Realizablek-e模型預測氣化爐的二次給氧量條件下分別預測氣化爐運行特性，并詳湍流特性1;為:中國煤化工考慮湍細比較爐內流場(chǎng)以及氣化火焰的變化趨勢.流脈動(dòng)對化學(xué)反應MHCNMHG化PDF374●化工學(xué)報第63卷47: 3119-3129 .References[9] Wu Kuang-Tsai， Robert T Essenhigh Mapping anstructure ofof inverse diffusion flames of methane//20thInverse .m ”Symposium ( International) on Combustion [C]. 1984:New York; John Wiley & Sons Inc，19811925-1932F)。Y。[2] Zhang jiansheng (張建勝)，Wu Yuxin[10] Wu Yuxin (吳玉新), Zhang Jiansheng (張建勝)，WangGuangxi (岳光溪), et al. 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