【摘要】：湍動(dòng)流化床反應(yīng)器因其氣固接觸充分、熱質(zhì)傳遞效率高、處理量大等優(yōu)點(diǎn),已廣泛應(yīng)用于化學(xué)和石油工業(yè)等諸多領(lǐng)域。目前,湍動(dòng)流化床的研究多集中在流動(dòng)行為方面,傳質(zhì)行為的研究相對(duì)較少,傳質(zhì)行為的計(jì)算流體力學(xué)(Computational Fluid Dynamics,CFD)模擬更是鮮有報(bào)道。針對(duì)湍動(dòng)流化床稀密兩相均為半連續(xù)相的特性,本論文將其氣固流動(dòng)結(jié)構(gòu)分為擬離散的氣穴相和擬離散的聚團(tuán)相,并使用Cc,Cd,Csc,Csd,Cf和Csf六個(gè)濃度參數(shù)描述湍動(dòng)流化床的傳質(zhì)過(guò)程,從而根據(jù)質(zhì)量守恒等原理建立基于結(jié)構(gòu)的氣固傳質(zhì)模型,最后通過(guò)CFD模擬驗(yàn)證氣固傳質(zhì)模型的可靠性,并對(duì)湍動(dòng)流化床的氣固傳質(zhì)行為進(jìn)行分析研究。提出將湍動(dòng)流化床的流動(dòng)結(jié)構(gòu)分為擬均勻的稀密兩相,根據(jù)兩相間質(zhì)量守恒建立基于湍動(dòng)流化床非均勻結(jié)構(gòu)的氣固傳質(zhì)模型的新思路。首先,通過(guò)推導(dǎo)獲得每一相的傳質(zhì)速率方程,將各相傳質(zhì)速率進(jìn)行加和即可得總體傳質(zhì)速率,再結(jié)合平均傳質(zhì)速率定義,即可獲得基于結(jié)構(gòu)的湍動(dòng)流化床傳質(zhì)系數(shù)的表達(dá)式,用于描述非均勻結(jié)構(gòu)對(duì)湍動(dòng)流化床氣固傳質(zhì)的影響;其次,結(jié)合傳質(zhì)平衡原理、傳質(zhì)與反應(yīng)的平衡關(guān)系等可得到一維和二維的組分輸送方程,并實(shí)現(xiàn)傳質(zhì)方程所需六個(gè)濃度參數(shù)的封閉求解。氣固流動(dòng)參數(shù)由基于結(jié)構(gòu)的湍動(dòng)流化床曳力模型求解,傳質(zhì)模型的數(shù)值模擬由商業(yè)軟件Fluent實(shí)現(xiàn),以甲烷燃燒和臭氧分解實(shí)驗(yàn)結(jié)果對(duì)模擬結(jié)果進(jìn)行校驗(yàn),結(jié)果表明模擬結(jié)果與實(shí)驗(yàn)數(shù)據(jù)吻合較好,證明該傳質(zhì)模型具有較高的準(zhǔn)確性。通過(guò)模擬研究還發(fā)現(xiàn),雖然甲烷濃度在催化劑濃度較高的位置會(huì)因化學(xué)反應(yīng)消耗而降低,但組分流動(dòng)以及擴(kuò)散的影響使甲烷濃度與催化劑濃度之間不存在絕對(duì)的大小對(duì)應(yīng)關(guān)系。隨著氣速的增加,由于組分流入速率增加和停留時(shí)間變短,臭氧濃度有所增加,但因?yàn)闅夤虃髻|(zhì)得到強(qiáng)化,反應(yīng)消耗的臭氧總量是增加的。此外,稀密兩相間的組分交換過(guò)程是臭氧分解反應(yīng)的控制步驟。本工作利用臭氧分解作為模型反應(yīng),通過(guò)以上的湍動(dòng)流化床傳質(zhì)模型分析了傳質(zhì)模擬結(jié)果與相間傳質(zhì)系數(shù)求解關(guān)聯(lián)式、氣速的關(guān)系。結(jié)果表明,采用以聚團(tuán)為基礎(chǔ)的Foka關(guān)聯(lián)式計(jì)算相間傳質(zhì)系數(shù)時(shí),基于結(jié)構(gòu)的湍動(dòng)流化床傳質(zhì)模型的模擬結(jié)果最好。本文還進(jìn)一步分析了顆粒含量、聚團(tuán)當(dāng)量直徑對(duì)組分濃度的影響。
[Abstract]:Turbulent fluidized bed reactor has been widely used in many fields such as chemistry and petroleum industry because of its advantages of sufficient gas-solid contact high heat and mass transfer efficiency and large treatment capacity. At present, the study of turbulent fluidized bed is mostly focused on the flow behavior, but the study of mass transfer behavior is relatively few, and the computational fluid dynamics (Computational Fluid Dynamics,CFD) simulation of mass transfer behavior is rarely reported. In this paper, the gas-solid flow structure of turbulent fluidized bed is divided into quasi-discrete cavitation phase and quasi-discrete cluster phase, and Cc,Cd,Csc,Csd, is used to analyze the gas-solid flow structure of turbulent fluidized bed. The mass transfer process of turbulent fluidized bed is described by six concentration parameters of Cf and Csf. According to the principle of mass conservation, the gas-solid mass transfer model based on structure is established. Finally, the reliability of gas-solid mass transfer model is verified by CFD simulation. The gas-solid mass transfer behavior of turbulent fluidized bed was studied. The flow structure of turbulent fluidized bed is divided into quasi-uniform dense two-phase and a new idea of gas-solid mass transfer model based on non-uniform structure of turbulent fluidized bed is proposed according to the conservation of mass between two phases. Firstly, the mass transfer rate equation of each phase is derived, and the total mass transfer rate can be obtained by adding the mass transfer rate of each phase, and then the expression of mass transfer coefficient of turbulent fluidized bed based on structure can be obtained by combining the definition of average mass transfer rate. It is used to describe the effect of non-uniform structure on gas-solid mass transfer in turbulent fluidized bed. Secondly, according to the principle of mass transfer equilibrium and the equilibrium relation between mass transfer and reaction, the one-dimensional and two-dimensional component transport equations can be obtained, and the closed solution of six concentration parameters required for the mass transfer equation can be realized. The parameters of gas-solid flow are solved by a structure-based turbulent fluidized bed drag model. The numerical simulation of the mass transfer model is implemented by commercial software Fluent. The simulation results are verified by the experimental results of methane combustion and ozone decomposition. The results show that the simulation results are in good agreement with the experimental data, and it is proved that the mass transfer model has high accuracy. The simulation results also show that the concentration of methane decreases with the consumption of chemical reaction when the catalyst concentration is high, but there is no absolute relationship between the concentration of methane and the concentration of catalyst due to the effect of component flow and diffusion. With the increase of gas velocity, the ozone concentration increases due to the increase of component inflow rate and shorter residence time, but the total ozone depletion is increased due to the enhancement of gas-solid mass transfer. In addition, the component exchange process between two phases is the control step of ozone decomposition reaction. In this work, ozone decomposition is used as a model reaction, and the relationship between mass transfer simulation results and interphase mass transfer coefficient is analyzed by using the above turbulent fluidized bed mass transfer model. The results show that the structure-based turbulent fluidized bed mass transfer model has the best simulation results when the mass transfer coefficient between phases is calculated by using the Foka correlation formula based on clusters. The effects of particle content and cluster equivalent diameter on the component concentration were also analyzed.
【學(xué)位授予單位】：中國(guó)科學(xué)院大學(xué)(中國(guó)科學(xué)院過(guò)程工程研究所)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ051.13

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