本文選題：固定床鼓泡反應器 + 微氣泡�。� 參考：《浙江大學》2017年碩士論文

【摘要】：固定床鼓泡反應器是一種特殊的鼓泡反應器,其中固體顆粒固定不動,氣液兩相并流向上,液相是連續(xù)相,氣相是分散相,氣相以氣泡的形式分散于液相中。氣泡尺寸對相間傳質(zhì)至關重要,傳統(tǒng)固定床鼓泡反應器中氣體分布器產(chǎn)生的氣泡尺寸都在毫米級以上,特別是在低氣液比條件下不利于氣液相間傳質(zhì)。本文提出了一種新型的固定床鼓泡反應器,使用文丘里型氣液分布器產(chǎn)生微米級的氣泡,利用微氣泡比表面積大、上升速度慢和溶解速度快的特點來強化傳質(zhì)。圍繞固定床鼓泡反應器中微氣泡的形成演化規(guī)律這一關搖科學問題,通過研究單個文丘里氣泡發(fā)生器和文丘里型氣液分布器的微氣泡發(fā)生性能,闡明了微氣泡的形成機制和調(diào)控方法;通過研究氣泡在液相床層和規(guī)整填料中的運動規(guī)律以及聚并破碎行為,揭示微氣泡的演化機制。主要工作和研究結(jié)果如下:1.綜合使用高速攝像機測量氣泡尺寸分布和CFD模擬,研究了單個文丘里氣泡發(fā)生器和文丘里型氣液分布器的微氣泡發(fā)生性能,提出了文丘里氣泡發(fā)生器和文丘里型氣液分布器的設計原則,獲得了優(yōu)選的結(jié)構參數(shù)和操作參數(shù)。首先,研究了氣速、液速等操作條件和喉管直徑等結(jié)構參數(shù)對氣泡Sauter平均直徑的影響規(guī)律,建立了氣泡Sauter平均直徑與液相雷諾數(shù)、氣相雷諾數(shù)的經(jīng)驗關聯(lián)式,發(fā)現(xiàn)了低氣液比條件下通氣量小于抽吸量導致的氣泡Sauter平均直徑隨時間周期性波動的現(xiàn)象。其次,在驗證CFD模型準確性的基礎上,探討了操作條件對文丘里氣泡發(fā)生器內(nèi)速度分布和壓力分布的影響規(guī)律,發(fā)現(xiàn)提高液速或降低氣速使得壓力軸向分布變陡,液體對氣體的剪切破碎作用增強,有利于生成微氣泡。模擬還發(fā)現(xiàn),在低氣液比條件下,擴大段內(nèi)液體出現(xiàn)偏流現(xiàn)象,與實驗結(jié)果一致,且隨著氣液比的增大,偏流現(xiàn)象逐漸消失。最后,考察了床型、文丘里氣泡發(fā)生器間距、氣液分布器傾斜角度對文丘里型氣液分布器出口氣泡尺寸的影響。研究發(fā)現(xiàn),增大管間距有利于減少氣泡間的聚并,推薦的管間距不小于78mm,且文丘里型氣液分布器具有較好的抗塔板傾斜性能。2.在對液相床層中不同尺寸的氣泡進行受力分析的基礎上,綜合使用高速相機和粒子軌跡測速法(PTV),實驗揭示了液相床層中不同尺寸氣泡的運動規(guī)律以及不同液相高度床層內(nèi)氣泡的運動規(guī)律和分布規(guī)律。研究發(fā)現(xiàn),氣泡在液相床層中的運動軌跡按照氣泡尺寸可以分為三類:對于直徑小于1 mm的微米級氣泡,其運動軌跡為一條直線;對于直徑為1.0～5.5mm的氣泡,其運動軌跡是一條周期性振蕩的S型或者"之"字型曲線;對于直徑大于5.5mm的氣泡,其運動軌跡是一條偶爾出現(xiàn)擺動的曲線。文丘里氣泡發(fā)生器產(chǎn)生的氣泡以氣泡束的形式進入液相床層,且氣泡束的寬度隨著床層高度、氣量和液量的增加而增大。在靠近文丘里氣泡發(fā)生器的區(qū)域,氣泡運動主要受液體的運動狀態(tài)控制,不同尺寸的氣泡表現(xiàn)出相似的運動行為;在遠離文丘里氣泡發(fā)生器的區(qū)域,氣泡行為主要由氣泡自身控制。3.利用高速相機研究發(fā)現(xiàn)了氣泡在規(guī)整填料床層內(nèi)具有的3種主要聚并機制和4種主要破碎機制,以及微氣泡和常規(guī)氣泡在規(guī)整填料床層內(nèi)行為的差異性。其中,氣泡在規(guī)整填料床層聚并機制主要有:降速聚并、壓縮聚并、粘壁聚并,破碎機制主要有:剪切破碎、撞擊破碎、加速破碎、拉伸破碎。而且,隨著填料間距的增大,氣泡表現(xiàn)出的聚并機制和破碎機制種類逐漸增多。在間距為3mm的規(guī)整填料床層內(nèi),與填料間距尺寸相當?shù)某Ｒ?guī)氣泡表現(xiàn)出聚并、破碎、形變和自由運動等多種行為,而微氣泡以聚并和自由運動為主,很難發(fā)生破碎和形變。此外,催化劑類型和尺寸對氣泡的破碎聚并行為具有重要影響。與空床時相比,裝填催化劑以后,床層內(nèi)氣泡Sauter平均直徑顯著增大,床層對微氣泡具有明顯的聚并作用。隨著球形顆粒粒徑的增大,氣泡Sauter平均直徑先增大后減小,當球形顆粒粒徑為3 mm時床層內(nèi)形成的氣泡Sauter平均直徑最大。選擇較大粒徑的球形顆粒有助于保持微鼓泡狀態(tài)。
[Abstract]:A fixed bed bubbling reactor is a special bubbling reactor in which solid particles are fixed, gas-liquid two phase and flow up, liquid phase is continuous phase, gas phase is dispersed phase and gas phase is dispersed in liquid phase in the form of bubbles. Bubble size is vital to mass transfer in the gas distributor in a traditional fixed bed bubble reactor. The size is above the millimeter level, especially under the condition of low gas and liquid ratio. This paper presents a new type of fixed bed bubbling reactor, which uses the Venturi type gas distributor to produce micrometer scale bubbles. The mass transfer is strengthened by the characteristics of microbubbles, which are larger than the surface area, slow rising speed and fast dissolution rate. The formation and evolution of microbubbles in a fixed bed bubbling reactor is a scientific problem. The formation mechanism and regulation methods of microbubbles are clarified by studying the microbubbles in the single Venturi bubble generator and the Venturi gas distributor, and the motion laws of bubbles in the liquid bed layer and the regular packing are studied. The evolution mechanism of microbubbles is revealed and the evolution mechanism of microbubbles is revealed. The main work and research results are as follows: 1. the bubble size distribution and CFD simulation are used to measure the bubble size distribution and the performance of the microbubbles in the single Venturi bubble generator and the Venturi gas distributor. The Venturi bubble generator and Venturi type gas are proposed. The optimum structure parameters and operating parameters are obtained. First, the influence of the structure parameters, such as gas velocity, liquid speed, and other structural parameters on the average diameter of the bubble Sauter, is studied. The empirical correlation of the average diameter of the bubble Sauter, the Reynolds number of the liquid phase and the Reynolds number of the gas phase is established, and the low gas ratio is found. On the basis of verifying the accuracy of the CFD model, the effect of operating conditions on the velocity distribution and pressure distribution in the Venturi bubble generator is discussed, and the axial distribution of the pressure distribution in the Venturi bubble generator is discussed. The shear breaking effect of the liquid on the gas is enhanced and it is beneficial to the formation of microbubbles. It is also found that the phenomenon of partial flow occurs in the expanded section under the condition of the ratio of low gas to liquid, which is in accordance with the experimental results, and the phenomenon of partial flow gradually disappears with the increase of the gas and liquid ratio. Finally, the bed type, the spacing of Venturi bubble generator, and the gas and liquid distributor are examined. The influence of the tilt angle on the outlet bubble size of the Venturi gas distributor is found. It is found that the increase of the tube spacing is beneficial to reducing the coalescence between the bubbles and the recommended tube spacing is not less than 78mm, and the Venturi gas distributor has a good anti tray tilt performance.2. in the basis of the force analysis of different sizes of bubbles in the liquid bed layer. On the base of the high speed camera and particle trajectory velocimetry (PTV), the motion law of different sizes of bubbles in the liquid bed and the law of movement and distribution of bubbles in the high bed layer of liquid phase are revealed. It is found that the movement track of bubbles in the liquid bed can be divided into three types according to the size of the bubbles: for the small diameter, the size of the bubbles can be divided into small diameter. The trajectory of a micro bubble at 1 mm is a straight line; for a bubble with a diameter of 1 to 5.5mm, its trajectory is a periodic oscillating S or "" type curve; for a bubble with a diameter greater than 5.5mm, its trajectory is an occasional swing curve. The bubbles generated by the Venturi bubble generator are a bubble beam. In the form of the liquid bed layer, the width of the bubble beam increases with the height of the bed, the amount of gas and the amount of liquid. In the area near the Venturi bubble generator, the bubble movement is mainly controlled by the motion state of the liquid, and the bubbles of different sizes show similar motion behavior; in the area far away from the Venturi bubble generator, the bubble row 3 main mechanisms of coalescence and 4 main breakup mechanisms in a structured packing bed, and the differences in behavior of microbubbles and conventional bubbles in a structured packing bed, were found to be mainly controlled by a high speed camera.3. using a high speed camera. The mechanisms of polycondensation and adhesion are mainly: shear breaking, impact crushing, accelerated breaking, and tensile breaking. Moreover, as the spacing of packing increases, the coalescence mechanism and breaking mechanism of bubbles increase gradually. In the regular packing bed with spacing of 3mm, the conventional bubbles with the same spacing between the packing show and break. In addition, the type and size of the catalyst have an important effect on the fragmentation and aggregation of the bubbles. Compared with the empty bed, the average diameter of the bubble Sauter in the bed layer is significantly increased and the bed layer is microbubbles compared with the empty bed. With the increase of the particle size of spherical particles, the average diameter of the bubble Sauter increases first and then decreases. When the spherical particle size is 3 mm, the average diameter of the bubble Sauter in the bed layer is the largest.
【學位授予單位】：浙江大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ051.14

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