Flow Characteristics in an External-Loop Airlift Slurry Reactor

China Petroleum Processing and Petrochemical TechnologyModeling and Simulation2012,Vol. 14, No.1, pp 46-49March 30, 2012Flow Characteristics in an External-LoopAirlift Slurry ReactorTang Xiaojin(Research Institute of Petroleum Processing, SINOPEC, Beijing 100083)Abstract: The local flow characteristics in an extemal-loop airlift slury reactor were investigated. The axial profiles of thelocal gas holdup, the Sauter mean diameter and the rise velocity were obtained. It was found that the bubble size and risevelocity were infuenced by the solid holdup, and the bubble coalescence was enhanced by the increase of the solid holdup.A new correlation was used to predict the slip velocity between the gas phase and the slurry phase by taking into account thelocal gas holdup, the bubble size, and the physical properties of the experimental system. By using this correlation, the localdrag cofficient can be calculated in the bubble swarm.Key words: slury reator; bubbl; gas holdup; slip velocity; drag coficient1 IntroductionGas outlet.... GasGas-liquid-solid slurry bubble reactor is widely used inBubbleenergy and chemical industries'. The uniform axial dis-Phase interfacetribution and radial distribution of the dispersed phases,Gas- slurry separatorsuch as bubbles and catalyst particles, are very importantto the reaction process. Then, external-loop airlft slurryDowncomer- Riserreactors are developed to obtain the uniform distributionof the dispersed phael-31. In this study, the flow char-Gas distributoracteristics in an external-loop airlift slurry reactor wereinvestigated. A new correlation was used to predict the- - Plenum regionslip velocity. By means of this correlation, the local drag. Gas inletcoefficient can be calculated in the bubble swarm.Figure 1 Experimental sel-up2 Experimentalthe nickel particles are mixed to form slurry. The slurryThe cold model extermal-loop airlift slurry bubble reac-leaves the gas-slurry separator of the riser, then enters thetor is shown in Figure 1. The riser is 3 m in height anddowncomer and finally returns back to the riser. The local280 mm in diameter, and the downcomer is 80 mm ingas holdup, bubble diameter and bubble velocity are mea-diameter. A perforated plate is used as the gas distributorsured by the conducting probe method.with 55 orifices. The diameter of each orifice is 2 mm. Thecompressed air, water and nickel particles were used as3 Flow Characteristicsthe gas phase, the liquid phase and the solid phase, respec-The axial profile of the local gas holdup εg is shown intively. The mean diameter of the nickel particle is 58 umFigure 2. In the radial direction, E。at the centre position isand the packing density is 2100 kg/m'.higher than at the wall position. In the axial direction, 6g in-As shown in Figure I, the compressed air enters the re-actor from the bottom and exits from the top. The air isCorrr中国煤化工iaojin, Email: tangxj.dispersed into bubbles by the distributor. The water andrpp@s:fYHCNMHG46Tang Xiaojin. Flow Characteristics in an Extermal-Loop Airlif Slurry Reactor27r6.524-21f昌5.518吾5.015 tg,-0.05g.-=0.05u=0.122 m/s14g-0.122 m/suyj-0.047 m/sug-0.047 m/s1 -23-1/01/323 1-1-2/3 -1/1/:2/1r/Br/(a(a)30r2724 -21-8t8s,-0.10s=0.10 .5tug-0.122 m's"g0.122 m/s2tuj-0.039 m/s14g-0.039 m/s-I-2/3-2/3 -1/3 01/32/31r/RrIR(b)Figure 2 Axrial profile of local gas holdupFigure3 Axial profile of d2■- 0.5m;●- -0.8m;▲-1.2m; ▼-1.6m;◆2.0 m■- 0.5m;●- -0.8m;▲-1.2m;▼ - 1.6m:◆2.0m .creases with an increase in the height. Because the decrease value is 0.1, the radial distribution of ds2 is a zigzag distri-of the pressure with an increasing height leads to the break-bution instead of a cup-type distribution at an ε, value ofage of bubbles, e。is higher at the top than at the bottom.0.05. Under the similar operating conditions, da is larger ataThe axial profile of Sauter mean diameter ds2 is shown in higher c, value than at a lower &, value. This indicates that anFigure 3. It can be found that ds is strongly infuenced byincrease of ε, can enhance the coalescence of the bubbles.the solid holdup e, When the 8, value is 0.05, dsz is small-The axial profile of the bubble mean rising velocity Um iser at the centre position than at the wall position, andshown in Figure 4. Similar to Figure 3, E, strongly influ-d2 decreases with an increase in the height. When the E。ences the distribution of Umw When the &, value is 0.05, um.1.2 r6.-0.101=0.122 m/s.0usj-0.039 m/s09管0.9-首是0.8!0.8-6-0.05.70.71ug2=0.122 m/s.6 .uy-0.047 m/s0.6-1 -2/3 -1/3 01/3 2/3 1rRFigure4 Profile of bubble ri中国煤化工■0.5m;●- 0.8m;▲- -1.2m; 1FYHCNMHG47●China Petroleum Processing and Petrochemical Technology2012,14(1):46-49is larger at the centre position than at the wall position.1.25The Um value increases with an increase in the height..00When the e, value is 0.1, the radial distribution ofum is azigzag distribution.冒0.754 Slip velocity and drag coefficient言0.50For carrying out the fluid dynamics computation of the0.25-20%slurry bubble reactor, it is very important to obtain thedrag force exerted on the bubbles by the slurry, so the0.25 0.500.751.00 1.25drag coefficient Cp should be expressed by Eq. 14. In Eq.uslip.exp m/:1, ds2 and E。can be obtained by experiments, and the slipFigure 5 Comparison between the calculated usiep and thevelocity Isp between the gas phase and the slurry phaseexperimental datacan be calculated by Eq. 2. Richardson and Zaki sug-gested to correlate Ustp andεg by Eq.359. In Eq. 3, u。canConclusionsbe derived from Eq. 410. The viscosity of the slurry μ canIn an external-loop airlift slurry bubble reactor, the localbe calculated by Eq. 5m]. By using Eqs. 1 to 5, Cp in the :flow characteristics were investigated. The experimentalbubble swarm can be calculated.results show that the solid holdup infuences strongly onc= 42P)gd,.!(1-g2)(1)the bubble diameter and rising velocity. High solid holdupD3~ Pau面can enhance bubble coalescence. A modified equation(2) was developed to calculate the slip velocity between dif-6 1-ferent phases. In this way, the local drag coefficient canUuip=u(1-e)"(3)be obtained in the bubble swarm.u6p1u6b21u弓+u62.Symbols used_. 1 Pa-Pg34% +34。Cp- drag cofficient;gd;z， 21a+3p%(4)dx- Sauter mean diameter, mm;u-velocity, m/s;u62=,um- rising velocity, m/s;~Vdr(a.+p) 2us- -slip velocity, m/s;_ 11+0.5(1-s)4(5) 8- -phase holdup;It can be seen from Eq.3 that the deformation and coales-μ - viscosity, Pars;cence of bubbles are not considered, but the existence ofρ density, kg/m';the solid particles can actually enhance the bubble coales-σ- surface tension, N/m.cence as shown in Figure 3. Thus, Eq.3 is modified to Eq.Subscripts6 in order to take into account the bubble coalescence.g- -gas phase;Uusp=u(1-e)(1+16e2)(6) 1-liquid phaseFigure 5 is a comparison between the calculated Usip ass- -solid phaseindicated by Eq. 6 and the experimental usip as indicated sI- -slurryby Eq. 2. As shown in Figures, Eq. 6 can be used to∞- isolated bubble in an ifinite mediumcalculate Usip with its average deviation less than +20%.By using Eqs. 1, 2, 4, and 6, C can be obtained. In thisstudy, the values of ds and eg are local values, so the local [I] Fa中国煤化工tion Eneering [M.Cp in the bubble swarm can be obtained.:MYHCNMHG●48●Tang Xiaojin. Flow Characteristics in an External-Loop Airlift Slurry Reactor[2] Freitas C, Fialova M, Zahradnik J, et al. Hydrodynamics of[5] Richardson JF, Zaki W. Sedimentation and fuidization: parta three -phasc extermal-loop airlift bioreactor [J]. ChemicalI [0]. Chermical Engineering Research and Design, 1954, 32Engineering Science, 2000, s5 (21): 4961- 4972(1):35-53[3] Young M A, Carbonell R G, Ollis D F. Airlift bioreactors:[6] Jamialahmadi M, Branch C, Moller Steinhagen H. Terminalanalysis of local two-phase hydrodynamics []. AIChE J,bubble rise velocity in liquids[J]. Chemical Engineering Re-1991, 37 (3): 403- 428search and Design, 1994, 72(1): 119 1224] Simonnet M, Gentric C, Olmos E, et al. Experimental deter-[7] Ma D, Kan D, Luo B, et al, Chermical Engineering Hand-mination of the drag coficient in a swarm of bubbles小book: Vol. 1 [M]. 2nd Edition. Beijing: Chemical IndustryChemical Engineering Science, 2007, 62 (3): 858 -866Press. 1996: 136-141 (in Chinese)Projects "Technology for Manufacturing Environmentally FriendlyType Aromatic Hydrocarbon Rubber Filling Oil" and“Technologyfor Manufacturing Environmentally Friendly Type Rubber FillingOil from Intermediate Base Lube Oil Extract" Passed Appraisaland Assessment ReviewThe projects“Technology for manufacturing environmen-the foremost position of lube oil processing flow diagram,tally friendly type aromatic hydrocarbon rubber flling oiland the lube oil extract is called the normal order lube(ARE solvent extraction technology)" and“Technologyoil extract. 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