【摘要】：氣固循環(huán)流化床反應(yīng)器是一個(gè)流動(dòng)、傳熱／傳質(zhì)和反應(yīng)多尺度時(shí)空耦合的復(fù)雜系統(tǒng),其中介尺度流動(dòng)結(jié)構(gòu)(如團(tuán)聚物或氣泡)起著關(guān)鍵性的作用�；诰鶆蚣僭O(shè),忽略了亞網(wǎng)格介尺度結(jié)構(gòu)影響的傳統(tǒng)雙流體模型(two-fluid model,TFM)對(duì)于模擬氣固非均勻流動(dòng)反應(yīng)體系是不合適的。需要在合理物理簡(jiǎn)化的基礎(chǔ)上建立介尺度模型,才可準(zhǔn)確描述流化床中的“三傳一反”行為。介尺度EMMS曳力模型在循環(huán)流化床流動(dòng)模擬中已經(jīng)得到了很好的應(yīng)用,但其網(wǎng)格無關(guān)性還需進(jìn)一步的驗(yàn)證。同時(shí),介尺度流動(dòng)結(jié)構(gòu)對(duì)于傳質(zhì)和反應(yīng)的影響也需進(jìn)行考察。鑒于此,論文第二章首先研究了不同固相體積分率下的雙周期微元區(qū)域內(nèi),應(yīng)用微元EMMS曳力和均勻曳力預(yù)測(cè)的滑移速度和傳質(zhì)系數(shù)隨網(wǎng)格分辨率的變化。對(duì)于A類顆粒,微元EMMS曳力在不同固相體積分率下都表現(xiàn)出了更好的網(wǎng)格無關(guān)性。兩種曳力模型預(yù)測(cè)的流動(dòng)結(jié)構(gòu)隨網(wǎng)格細(xì)化都捕捉到更合理的非均勻流動(dòng)結(jié)構(gòu),造成更大的傳質(zhì)阻力,使得有效傳質(zhì)系數(shù)下降,并在網(wǎng)格尺寸為10個(gè)顆粒直徑時(shí)趨于收斂。對(duì)于B類顆粒的傳質(zhì)研究也發(fā)現(xiàn)了類似現(xiàn)象。細(xì)網(wǎng)格預(yù)測(cè)的有效傳質(zhì)因子和基于EMMS結(jié)構(gòu)的傳質(zhì)非均勻因子隨固相體積分率的變化趨勢(shì)相同且在同一量級(jí)上。為了考慮介尺度非均勻結(jié)構(gòu)對(duì)于傳質(zhì)、反應(yīng)的影響,論文第三章和第四章提出了基于EMMS結(jié)構(gòu)的多流體傳質(zhì)和反應(yīng)模型,此模型在局部平衡或網(wǎng)格內(nèi)沒有非均勻結(jié)構(gòu)的假設(shè)時(shí),可以退化為TFM框架下的傳質(zhì)和反應(yīng)模型。應(yīng)用該模型分別在基于團(tuán)聚物或氣泡的流動(dòng)結(jié)構(gòu)下分析傳質(zhì)、反應(yīng)過程,定義了反應(yīng)和傳質(zhì)的非均勻因子,以修正TFM傳質(zhì)反應(yīng)模型。論文通過二維和三維構(gòu)體下的臭氧催化分解反應(yīng)模擬,對(duì)模型進(jìn)行了初步的驗(yàn)證,模擬結(jié)果與文獻(xiàn)結(jié)果相符。反應(yīng)速率越快,非均勻流動(dòng)結(jié)構(gòu)對(duì)于傳質(zhì)和反應(yīng)的影響越大。論文第五章通過虛擬實(shí)驗(yàn)來考察計(jì)算中在線調(diào)節(jié)機(jī)械閥門和改變提升管懸浮段長(zhǎng)度對(duì)于宏尺度非均勻流動(dòng)行為的影響。首次實(shí)現(xiàn)了帶可調(diào)節(jié)機(jī)械閥的、三維全循環(huán)的循環(huán)流化床模擬,模擬結(jié)果和實(shí)驗(yàn)描述相符。第六章對(duì)本論文進(jìn)行了總結(jié),提出了主要的結(jié)論和創(chuàng)新點(diǎn),并對(duì)未來的研究進(jìn)行了展望。
[Abstract]:Gas-solid circulating fluidized bed reactor (CFB) is a complex system with flow, heat / mass transfer and reaction multi-scale space-time coupling. Its mesoscale flow structure (such as agglomerates or bubbles) plays a key role. Based on the homogeneous hypothesis, the traditional two-fluid model (two-fluid model,TFM), which ignores the influence of mesoscale structure on subgrids, is not suitable for simulating gas-solid nonuniform flow systems. It is necessary to establish mesoscale model on the basis of reasonable physical simplification in order to accurately describe the behavior of "three to one inverse" in fluidized bed. Mesoscale EMMS drag model has been well applied in CFB flow simulation, but its mesh independence needs further verification. At the same time, the effect of mesoscale flow structure on mass transfer and reaction also needs to be investigated. In the second chapter, we first study the variation of slip velocity and mass transfer coefficient with grid resolution in the two-period microelement region with different volume fraction of solid phase, using differential EMMS drag and uniform drag force to predict slippage velocity and mass transfer coefficient. For A particles, the EMMS drag of microelement shows better mesh independence under different solid volume fraction. The flow structures predicted by the two drag models both capture more reasonable non-uniform flow structures with mesh refinement, resulting in greater mass transfer resistance, lower effective mass transfer coefficient, and convergence when the mesh size is 10 particle diameters. A similar phenomenon was found for the mass transfer of B particles. The effective mass transfer factor predicted by fine mesh and the non-uniform mass transfer factor based on EMMS structure have the same trend with solid volume fraction and are of the same order of magnitude. In order to consider the effect of mesoscale nonuniform structure on mass transfer and reaction, a multi-fluid mass transfer and reaction model based on EMMS structure is proposed in chapter 3 and chapter 4 in this paper. It can degenerate into mass transfer and reaction model under TFM framework. The model is used to analyze the mass transfer and reaction process under the flow structure of agglomerates or bubbles, and the heterogeneous factors of reaction and mass transfer are defined to modify the TFM mass transfer reaction model. In this paper, the ozone catalytic decomposition reaction is simulated under two and three dimensional structures, and the model is preliminarily verified. The simulation results are in agreement with the literature results. The faster the reaction rate, the greater the effect of heterogeneous flow structure on mass transfer and reaction. In the fifth chapter, the effect of on-line adjusting mechanical valve and changing the length of hoisting pipe on the macro-scale non-uniform flow behavior is investigated by virtual experiment. For the first time, a three-dimensional circulating fluidized bed simulation with adjustable mechanical valve is realized. The simulation results are in agreement with the experimental results. The sixth chapter summarizes the thesis, puts forward the main conclusions and innovations, and looks forward to the future research.
【學(xué)位授予單位】：中國(guó)科學(xué)院研究生院(過程工程研究所)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TQ031

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