本文選題：生物三相內循環(huán)流化床　切入點：CFD　出處：《湖南大學》2015年碩士論文

【摘要】：生物三相內循環(huán)流化床具有優(yōu)越的流體力學性能、良好的傳質效果等特征。然而,目前其工程放大設計主要依靠經驗參數(shù),還未形成一套以數(shù)值分析、結構量化表達為基礎的設計理論。利用計算流體力學(CFD)探討操作參數(shù)、結構參數(shù)對生物三相內循環(huán)流化床性能的影響,對其放大設計具有較重要的意義。本研究借助計算流體力學,利用歐拉模型建立能夠有效地描述生物三相內循環(huán)流化床反應器內部氣液固三相復雜流動的數(shù)學模型,并用實例證明CFD模型能夠有效地反映生物三相內循環(huán)流化床反應器內部氣、液、固三相復雜的流體特征。以此為基礎探討操作參數(shù)、結構參數(shù)對生物三相內循環(huán)流化床性能的影響。操作參數(shù)的影響探討結果顯示:隨著固體裝載率的增大,氣含率先增大后減小,在13%處取得最大值。當表觀氣速在0~0.05m/s的范圍內時,氣含率隨著表觀氣速的增大而增大,在0.05m/s處達到最大值,表觀速度大于0.05m/s時,氣含率不再隨著表觀氣速的增大而增大,而是基本保持不變。液體循環(huán)速率隨著固體裝載率的增大而減小,隨著表觀氣速的增大而增大。在以氣含率、液體循環(huán)速率作為約束條件的情況下,本流化床反應器的最佳固體裝載速率為13%,最佳表觀氣速為0.05m/s。粒徑大的固體顆粒更加有利于破碎氣泡,同時也使得相界面積增大,所以氣含率隨著固體顆粒粒徑增大而增大;粒徑大的固體顆粒對液體循環(huán)程度的影響比較大,當實際操作中要求液體循環(huán)速率比較大時,宜采用粒徑比較小的固體顆粒,對提高液體循環(huán)速率有利。結構參數(shù)的影響探討結果顯示:導流筒與反應器的直徑比(Dr/D)主要影響液體的循環(huán)程度,從液體循環(huán)速率分布的均勻化以及液體循環(huán)速率峰值考慮,Dr/D取0.7時最優(yōu);高徑比(H/D)主要影響氣液固的流動型態(tài),H/D比較小時應特別注重對氣體分布裝置進行優(yōu)化設計;導流筒距液面高度(H1)主要影響上升區(qū)與液面之間的區(qū)域內的流場結構,對于高1.0m的流化床來說H1取100 mm時能達到較優(yōu)的流場結構以及液速分布;導流筒距底部高度(H2)主要影響流化床反應器內底部混合區(qū)域內流體的運動以及液體對底部區(qū)域顆粒的卷帶速度的大小和方向,該高度最小應該達到下降區(qū)的縫隙長度,但繼續(xù)增大后液體對下降區(qū)底部區(qū)域污泥顆粒的卷帶作用急劇減弱,容易導致水力死區(qū)的出現(xiàn)。
[Abstract]:Biological three-phase internal circulating fluidized bed has excellent hydrodynamic performance and good mass transfer effect. However, at present, the design of biological three-phase internal circulating fluidized bed mainly depends on empirical parameters and has not yet formed a set of numerical analysis. Based on the design theory of quantitative expression of structure, the effects of operating parameters and structural parameters on the performance of biological three-phase internal circulating fluidized bed are discussed by using computational fluid dynamics (CFD). In this study, with the aid of computational fluid dynamics and Euler model, a mathematical model of gas-liquid-solid complex flow in a biological three-phase internal circulating fluidized bed reactor was established. An example is given to prove that CFD model can effectively reflect the complex fluid characteristics of gas, liquid and solid in a biological three-phase internal circulating fluidized bed reactor, on the basis of which the operating parameters are discussed. The effect of structure parameters on the performance of a biological three-phase internal circulating fluidized bed. The results show that with the increase of solid loading ratio, the gas content increases first and then decreases. When the apparent gas velocity is in the range of 0~0.05m/s, the gas holdup increases with the increase of the apparent gas velocity. When the apparent gas velocity is greater than 0.05m/s, the gas holdup increases with the increase of the apparent gas velocity. The liquid circulation rate decreases with the increase of the solid loading rate and increases with the increase of the apparent gas velocity. When the gas holdup and the liquid circulation rate are taken as the constraint conditions, the liquid circulation rate decreases with the increase of the solid loading rate, and increases with the increase of the apparent gas velocity. The optimum solid loading rate of the fluidized bed reactor is 13 and the best apparent gas velocity is 0.05 m / s. The larger particle size is more favorable for the broken bubble and the larger the phase boundary area is, so the gas holdup increases with the increase of the particle size. Solid particles with large particle size have great influence on liquid circulation degree. When the liquid circulation rate is large in practical operation, solid particles with smaller particle size should be used. The effect of structural parameters on the liquid circulation rate is favorable. The results show that the diameter ratio of the diversion tube to the reactor (Dr / D) mainly affects the circulating degree of the liquid. Considering the homogenization of liquid circulation rate distribution and the peak value of liquid circulation rate, the optimum value of Dr / D is 0.7, the ratio of height to diameter (H / D) mainly affects the flow pattern of gas-liquid-solid and the optimum design of gas distribution device should be paid special attention to when the ratio of H / D is small. The flow field structure in the area between the rising area and the liquid surface is mainly affected by the height of the diversion tube from the liquid level. For the fluidized bed with a height of 1.0 m, the flow field structure and the liquid velocity distribution can be better when H _ 1 is taken at 100 mm. The height of the diversion tube from the bottom to the bottom mainly affects the movement of the fluid in the mixing zone at the bottom of the fluidized bed reactor and the size and direction of the velocity of the liquid to the particle in the bottom area. The minimum height should be the gap length of the descending zone. However, the effect of the liquid on the sludge particles in the bottom of the descending zone decreases sharply after further increasing, which leads to the emergence of the hydrodynamic dead zone.
【學位授予單位】：湖南大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：X703

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