Concentration profile of jet gas in the feed injection zone of a FCC riser

Availableonlineatwww.sciencedirect.comScience DirectProgress inNatural scienceLSEVIERProgress in Natural Science 18(2008)1285-1291www.elsevier.com/locate/Concentration profile of jet gas in the feed injection zone of a FCC riserChenglin E, Yiping Fan, Kai Zhang,, Hu Zhang bState Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, Chinainstitute of Science and Technology in Medicine, Keele University Medical School, Thornburrow Drice, Hartshill, ST4 70B, UKReceived 16 January 2008; received in revised form 28 January 2008; accepted 30 January 2008AbstractThe concentration profiles of jet gas are investigated in the feed injection zone of a cold- model FCC riser by using a hydrogen tracetechnique. Experimental results demonstrate that four types of jet gas concentration profiles can be used to describe the mixing betweenthe jet gas and pre- lift gas in the feed injection zone. The four types are a distinct M-shaped profile for weak mixing, an indistinct Mshaped profile for medium mixing, a sharp profile for strong mixing, and a parabolic profile for full mixing. the heights for regions ofinitial and full mixing reduce when decreasing the jet gas velocity or increasing the pre-lift gas velocity. Furthermore, the momentumratio, M Mr(where M; is the momentum of jet gas, Mr is the mixture momentum of pre -lift gas and solid particles)is introduced todescribe the effects of gas-solid physical properties, operating conditions, and equipment configuration on the jet gas concentration dis.tribution. The heights for regions of initial and full mixing between jet gas and pre-lift gas are found to be 0-0.375 and 0.375-0.675 mwhen M /Mr<0.29,0.375-0675 and 1.075-1 375 m when M/M,>0.54, and 0-0. 375 and 0.675-1.075 m when M;M between 0. 29 and0.54, respectively@2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by elsevier Limited and Science inChina Press. All rights reserved.eywords: FCC riser; Feed injection zone; Jet gas concentration; Momentum ratio1. IntroductionIn the past two decades, Werther et al. [2] Amos et al.[3] Gayfin et al. [4] and Sterneus et al. [5]experimentallyA riser reactor is one of the most important units in fluid investigated gas mixing behavior in the riser based on thecatalytic cracking(FCC) process, which has been widely radial profiles of gas concentration, while Thelogs et alused in the modern petroleum refinery industry [1] In this [6] Subramanya et al. [7] Gupta and Rao [8, 9), and gaoFCC unit, catalysts enter the bottom of the riser from the et al [10] numerically simulated the atomization efect ofregenerator. These catalyst particles are then conveyed by a feed oil gas in the feed injection zone on FCC riser perforpre-lift gas steam to the feed injection zone, where catalysts mance. There are few reports on the analysis of complexmeet the feed oil gas injected through atomizing nozzles three-phase flow of feed oil gas, pre- lift gas and catalystand a rapid chemical reaction between jet gas and catalyst particles in the feed injection zone of the riser. To ourparticles occurs [1]. Atomization of feed oil gas, concentra- knowledge, only Fan et al. [11-14] investigated the oiltion distribution of feed oil gas, mixing between feed oil gas gas concentration profiles in the feed injection zone andand pre-lift gas, as well as mixing between feed oil gas and proposed two types of feedstock injection structures bycatalyst particles have a great impact on this chemical using the relative oil gas concentration distributionreaction.[13, 14]. However, actual feed oil gas concentration distribution in the feed injection zone has advantages over itsCorresponding author. Tel. +86 10 89733939: fax: +86 10 69724721中国煤化工 type of FCC reactorsE-mailaddress:kaizhang@cup.edu.cn(K.zhang)CNMHG1002-0071/S- see front matter e 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limitedand Science in China Press. All nights reserveddoi:l0.016 pnsc.008.01038C. Eet al. Progress in Natural Science 18(2008)1285-1291Actual feed oil gas phase concentration is adopted in concentration obtained directly from samples is the hydro-this study rather than relative concentration when using a gen concentration in the gas phase, but it does not reprehydrogen tracer technique. The radial profiles of actual sent the concentration in gas-solid two-phase flow. Basedfeed oil gas concentration are investigated at different axial on the concept of eigenconcentration, Fan et al. [11-14]positions in the feed injection zone of a riser at different jet calculated the relative concentration of the jet gas asgas velocities and pre-lift gas velocities. Furthermore, a followsew parameter, defined as the ratio of the momentum offeed oil gas to the mixture momentum of pre-lift gas and C-csolid particles, is proposed to describe the effects of physi-al properties of gas and solid, operating conditions, and where Max Ci is the maximum value of Cp.equipment configuration on the feed oil gas concentration In this study, a new parameter is proposed to describedistributionthe actual concentration distribution of the jet gas, i. e, feedoil gas, in a riser feed injection zone, which is expressed as2. Measurement method and experimental set-upQecHeCi= CnE=(3)2. Measurement method2(g+Q)Gas tracer technique, an effective method for measuringwhere is the dimensionless radial position, =r/R; e; isthe local voidage, and a is the averaged cross-section voi-the gas concentration profiles and mixing behavior in the dage obtained from integration of e, along the cross-sec-gas-solid fluidized bed [2-5, 11-16, was employed in this tion. In the above equation, Ca represents the actual jetstudy to investigate the concentration distribution of thegas concentration in gas phase, and Ci represents the ac-as a gas tracer was injected into the nozzles in pulse method tual jet gas concentration in gas and solid phasesFig. I keep(a)and(b)shows the radial profiles of Coand then the nozzle jet gas brought hydrogen into the riser from Eq (2) and Cn from Eq (3), respectively, at a height[1-14] Because hydrogen injection time was quite short of H=0.675 m when the pre-lift gas velocity ranges fromand the flux of tracer was far less than that of pre- lift gas 2.25 to 4.30 m/s. It can be seen that Co keeps a constantor jet gas, it is difficult to measure accurately hydrogen con- of 1 at the riser center(r=0) for all three differentcentration. In order to systemically reduce measurementerrors and noises due to intensive turbulence in the feed pre-lift gas velocities. A slight increase in the relative jetzone, an eigenconcentration of jet gas, i.e., feed oil gas, gas concentration can be seen at r/r of less than 0.75, whenwas introduced by Fan et al. [11-14] as followsthe pre-lift gas velocity increases from 2. 25 to 4.30 m/s inFig. I keep(a). In contrast, the actual jet gas concentration=oQ iin the gas and solid phases, Cn, gradually decreases at alle+er(1) radial positions with the increasing pre-lift gas velocity,when the jet gas velocity keeps constant as shown inwhere Ci stands for the eigenconcentration of the jet gas at The average cross-sectional jet gas concentration, Ca,isthe ith radial position, c; for the sampling tracer concentra- obtained by integrating jet gas relative(Co) and actualtion,g; and @r for the volume flow rates of the jet gas and (Cn) concentration along the radial distribution, and thepre-lift gas, respectively. It is noted that the sampling tracer calculation results at a height of H=0.675 m are shown50.806互0000000003中国煤化工100-0.75-0.50-0.25250.500751.000.751.00CNMHGFig..The radial profiles of the jet gas concentration for different pre-lift gas velocities(the axial height above the nozzles H is 0.675 m, the jet gas velocityis 41.7 m/s ). Curves 1-3 represent jet gas concentration at the pre-lift gas velocity U, of 2. 25, 3. 28, and 4.30 m/s, respectively. (a) The relative jet gasoncentration from Eq (2 ),(b)actual jet gas concentration from Eq (3)C. Eet al Progress in Natural Science 18(2008)1285-1291in Fig. 2. When the jet gas velocity increases from 41.7 to proposed by Fan et al. [ 12-15). In contrast, the maximum83. 3 m/s while the pre-lift gas velocity keeps constant as and average relative errors decrease to 4.2% and 2.6%,shown in Fig. 2 keep(a), the average cross-section jet gas respectively, by the modified method in this studyconcentration increases by using parameter Cil. The aver- The above comparisons of the radial distribution of jetage concentration obtained from parameter Cio, however gas concentration, average cross-section jet gas concentra-gives a contrary tendency. Similar phenomena cantion,and average cross-section jet gas volume flux indicateobserved from Fig. 2 keep(b), when the pre-lift gas velocity that Cn suggested in this study is more reasonable than Codecreases but jet gas velocity keeps constant. The average in the Refs. [11-14] to describe the jet gas concentration incross-section jet gas concentration from Ca increases while the feed injection zone of a FCC riser.decreases from the parameter Co-Furthermore, the average cross-section jet gas volumeflux, @o, can be calculated by the average cross-section 2. 2. Experimental set-upjet gas concentration and the average interstitial gas vol-ume flux asA schematic diagram of the experimentald inthis study is shown in Fig 3. The riser vessel consists of a(g+Q)(4) series of 186 mm I.D. flanged plexiglass pipes with a heightof 12 m. Four nozzles equivalent to the atomizing nozzles inThe calculated average cross-section jet gas volume the FCC unit are located at a height of 4.5 m above the pre-fluxes( @ol from relative jet gas concentration and @o2 lift gas distributor and installed with an angle of 30 relativefrom actual jet gas concentration) are summarized in Table to the riser axis. The hydrogen tracer technique is employed1. The experimentally measured jet gas volume flux is com- to measure the concentration distribution of the jet gas inpared to the two calculated values, Lol and Qo2. It can be the feed injection zone of the riser. FCc catalysts are usedfound that the maximum relative error is up to 94.3% and as solid particles. Both jet gas and pre-lift gas are air. Allthe average relative error is 30.0%o by using the method the experiments are carried out at atmospheric pressure0800780.55互0500.30Fig. 2. The average cross-section jet gas concentration by varying the jet gas velocity and pre-lift gas velocity. Curve I represents the average jet gasconcentration from Eq (2); curve 2 is for the average jet gas concentration from Eq (3).(a) The average concentration versus jet gas velocities whilekeeping pre-lift gas velocity constant(H=0.675 m, U,=4.30 m/s). (b)the average concentration versus pre- lift gas velocities while keep jet gas velocityconstant(H=0.675 m, U=41.7 m/s)e mparison between the measured and calculated jet gas volume fluxv(m/)Refs.[11-14This study(m3/h)28.53.5479.843].1390.7中国煤化工451.324CNMHG4666247.1370.562417.2489.520C. Eet al I Progress in Natural Science 18 (20Mixing between jet gas and pre lift gas is quite weak at thisaxial position. At heightsH=1075 m, on the other hand, a sharp profile of the jetgas concentration, a sharp increase in the center(/r=o)and a gradual decrease in the middle region(r/R=0.32-0.54)indicate that mixing between the two gas phasesbecomes gradually intensive. Up to the height ofH=1. 375 m, a parabolic profile of the jettion means full mixing of jet gas with pre- lift gas, becausethis profile is similar to the voidage profile before the jetgas is introduced into the riser.of 3. 28 m/s and Uj of 41.7 m/s10Fig. 4b, an indistinct M-shaped profile of jet gas concentra-tion can be seen at a height of H=0.375 m, where the concentration of jet gas increases at the center(r/R=O)anddecreases in the middle region(r/R=0.32-0.54), comparedwith that at the same section in Fig. 4a. This profile indi-Fig. 3. Schematic diagram of the experimental apparatus (1)Inlet of cates that jet gas partially enters into the center region(r/xiliary fluidizing gas,(2)inlet of pre-lift gas, (3)pre-lift section,(4) R=O) of the riser and the mixing of jet gas with pre-liftgas at both given jet gas velocity and pre- lift gas velocityincomer, (il) dipleg of secondary stage cyclone, (12) dipleg of first becomes stronger under this operating condition. At astage cyclone, and(13)inlet of fluidizing gas.height of H=0.675 m, the concentration profile of jetand a room temperature of approximately 25C. The oper- gas is similar to that in Fig 4a at the same height. Mixingbetween the two gas phases becomes gradually stronger asating conditions for pre-lift gas velocity, nozzle jet gas the height increases. above a height of H=1075 m, fullvelocity, and solid fux are in the range of 2.234. m/s, mixing has been realized but this mixing pattern can onlybe seen at a height of 1. 375 m in Fig. 4aIt is apparent that there exist four types of jet gas con-3. Results and discussioncentration profiles as shown in Fig. 4 to describe diferentmixing intensities between jet3. 1. Jet gas concentration profiles at different axial positions feed injection zone of a riser. a distinct M-shaped profilestands for very weak mixing, an indistinct M-shaped profileFig 4 shows the radial profiles of the jet gas concentra- for medium mixing a sharp profile for strong mixing, and ation at different axial heights for two sets of the jet gas parabolic profile for full mixingelocity and pre-lift gas velocity. At Ur of 2.25 m/s andUj of 62.5 m/s, as shown in Fig. 4a, a distinct M-shapedprofile of the jet gas concentration is observed at a height 3. 2. Efects of jet gas velocityof H=0.375 m. This indicates that the majority of the jetgas passes in the middle region(r/R=0.32-0.54)of the The jet gas concentration is described in Fig 4 at two dif-riser, while the majority of the pre-lift gas flows in the cen- ferent sets of jet gas velocity and pre-lift gas velocity. Theter regions(r/R=0-0.32)and close to the wall (r/R20.95). change of jet gas velocity and pre-lift gas velocity is investi-09}a中国煤化工01000750.50-0.250.250.500.751.00CNMH GO75 100Fig 4. Radial profiles of jet gas concentration at diferent axial heights. curves 1-4 represent the jet gas concentration at H=0.375, 0.675, 1.075, 1.375 mrespectively; curve 5 is for the voidage at H=1. 375 m before jet gas enters the riser. (a)U=62.5 m/s, Ur =2.25 m/s, (b)U=41.7 m/s, U,=3. 28 m/s.C. Eef al/ Progress in Natural Science 18(2008 )1285-1291gated in this and the following sections. When pre- lift gas gas velocity of about 41.7 m/s is found to be a transitionalvelocity is fixed at 4.30 m/s and jet gas velocity increases from point, which can account for different mixing characteristics41.7 to 83.3 m/s, the radial profiles of jet gas concentration at between jet gas and pre- lift gas at different heightsdifferent heights are shown in Fig. 5. At the section ofH=0.375 m as shown in Fig 5a, as jet gas velocity reduces 3. 3. Efects of pre-lift gas velocityfrom 83.3 to 41.7 m/s, the concentration of jet gas decreasesin the regions of r/R from 0.32 to 0.95, while increases at the By varying pre-lift gas velocity from 2.25 to 4.30 m/scenter of r/R=0. Changes in the concentration profiles of jet while keeping a constant jet gas velocity of 41.7 m/s,thegas from a distinct M-shape(poor mixing) to an indistinct effect of pre-lift gas velocitradial profiles of jetM-shape( medium mixing) with decreasing jet gas velocity concentration is shown in Fig. 6. At a height ofindicate that slow jet gas velocity can improve mixing in this H=0.375 m, when pre-lift gas velocity increases,section. At a height of H=1075 m, a decrease of jet gas decrease of jet gas concentration in the radial region of r/velocity results in reduction of jet gas concentration at all R=0.32-0.95 and an increase at the center(/R=O)canradial positions, and changes from a sharp profile for strong be observed in Fig 6a. This observation suggests the trans-mixing to a parabolic profile for full mixing( Fig 5b). It can formation of jet gas concentration profile from a distinctbe seen from Fig. 5 that the jet gas velocity has a great impact M-shape for very weak mixing to an indistinct M-shapeon mixing intensity at different heights. When the jet gas for medium mixing, which is found at a transitional pre-liftvelocity is smaller than 41.7 m/s, initial and full mixing gas velocity of about 3. 28 m/s. In contrast, at a height ofbetween jet gas and pre- lift gas occur in the feed injection H=1075 m, as shown in Fig. 6b, the jet gas concentrationzone of a riser at a height of 0-0.375 m and 0.675-1.075 m, profile changes from a sharp profile for strong mixing to arespectively. However, when the jet gas velocity is greater parabolic profile for full mixing with increasing pre-lift gathan 41.7 m/s, the heights for initial and full mixing change velocity, which is similar to that with decreasing jet gasto 0.375-0.675 m and 1.075-1.375 m, respectively. The jet velocity in Fig 5b. A similar conclusion can be drawn thatb八入0.00-0.75-050-0250250500751.0000-0.75-0.50-0250250500.75100Fig. 5. Efects of jet gas velocity on jet gas concentration profiles. Curves 1-3 represent jet gas concentration at Uj=41. 7, 62.5, and 83.3 m/s, respectively(a)H=0.375mU=4.30m/s,(b)H=1.075m,U1=4.30m/s.中国煤化工9.75256023075109CNMHGO7S L00P/RFig. 6. Effects of pre-lift gas velocity on jet gas concentration profiles. Curves 1-3 represent jet gas concentration at Ur=2. 25, 3. 28, and 4.30 m/s,respectively. (a)H=0.375 m, Uj=41.7 m/s,(b)H=1075 m, U=41.7 m/s.1290C. Eet al Progress in Natural Science 18(2008)1285-1291the transitional pre-lift gas velocity is around 3. 28 m/s the effects of the momentum ratio on jet gas concentra-under this operating condition.tion at different heights in a riser are shown in Fig. 7. At aThe heights for initial and full mixing between jet gas height of H=0.375 m, jet gas concentration decreases innd pre-lift gas are about 0-0.375 m and 0.675-1.075 m, the riser except at the center(/r=0)with a decrease ofrespectively in the feed injection zone of a riser when the the momentum ratio as shown in Fig. 7 keep(a). The con-pre-lift gas velocity is greater than 3. 28 m/s, while they centration of jet gas is a distinct M-shaped distribution forare.375-0675 and 1.075-1.375 m when pre- lift gas veloc- very weak mixing when the momentum ratio is greater thanity is smaller than 3. 28 m/s0.54, while it becomes an indistinct M-shaped distributionfor medium mixing when the momentum ratio is smaller3. 4. Ejects of momentum ratiothan 0.54. Therefore, the transitional momentum ratcan be found to be about 0.54. At the heights ofBesides jet gas velocity and pre- lift gas velocity discussed H=0.675 m and H=1075 m, the jet gas concentratioabove, other parameters, such as solid phase flux, solid changes from a sharp distribution for strong mixing to aphase velocity, cross-section areas of the nozzle and the parabolic profile for full mixing with a decrease of theriser, and number of nozzles, have an effect on jet gas con- momentum ratio as illustrated in Fig. 7 keep(b)and keepcentration in the feed injection zone of a riser. In order to (c). The transitional momentum ratio is about 0. 29 atinvestigate the influences of these parameters, a momentum H=0.675 m, while it is 0. 54 at H=1075 m. Up to theratio, defined as the ratio of the momentum of jet gas, Mi, height of H =1.375 m, as shown in Fig. 7 keep(d), the con-to the mixture momentum of pre- lift gas and solid parti- centration profiles of jet gas are all parabolic for full mixingcles, Mr, is proposed as followsfor the momentum ratio ranging from 0. 29 to 4.21MNA: UFAIn Fig. 7, the regions for initial and full mixing betweenMr P, U2Ar +G,UpA5)jet gas and pre-lift gas are dependent on the momentumratio. The regions inside a riser for initial and full mixingwhere A and A, are the cross-section areas of each noz. are: (i)about 0-0.375 and 0.375-0.675 m, respectively,and a riser, respectively, N is the number of nozzles, e i when the momentum ratio is smaller than 0.29and Pr are the densities of jet gas, and pre-lift gas respec- 0-0.375 and 0.675-1.075 m, respectively, when the momen-tively, G, is solid phase flux, and Up is solid phase velocity. tum ratio ranges from 0. 29 to 0. 54; and (ii )about 0.375.ab0.6-1.00-0.75-050-0.2500.2-100-0.75-050-02500.250.500.751.00r/R08}d中国煤化工-1.00-0.75-050-25CNMHG07S TOOFig.7. Radial profiles of jet gas concentration at different values of M/Mr. Curves 1-7 represent jet gas concentration at My/M=0.29, 0.54, 0.66, 1.05,215237,and4.2l, respectively.(a)H=0.375m,(b)H=0.675m,(c)H=1.075m(d)H=1.375C. Eet aL I Progress in Natural Science 18(2008)1285-12910.675 and 1.075-1.375 m, respectively, when the momen- Referencestum ratio is greater than 0.54.[I] Chen YM. Recent advances in FCC technology. Powder Technology206;163(l)2-8.4. Conclusions[2] Werther J, Hartge EU, Kruse M. Radial gas mixing in the upperdilute core of a circulating fluidized bed. Powder Technology992;703):293-30lA new method has been proposed to investigate the jet [3] Amos G, Rhodes MJ, Mineo H. Gas mixing in gas-solids risersChemical Engineering Science 1993: 48(5): 943-9nique. The maximum relative error between the calculated (4) Gayfin P. Diego LF, Adfinez J Radial gas mixing in a fast fuidizedand measured jet gas volume flux is 4.2% and the average[5] SteGas mixingin circulaterror is about 2.6%, which suggests that this method canfluidized-bed risers. Chemical Engineering Science 2000: 55(1): 129-48precisely calculate the actual concentration of jet gas in a [6] Theologos KN, Lygeros Al, Markatos NC. Feedstock atomizationFCC risereffects on FCC riser reactors selectivity. Chemical Engineeringfound to represent four different mIxing beham. profiles areFour types of the jetgas concentratiocience199954(22):5617-25.[7] Subramanya V, Saket L, Vivek V, et al. Modeling of vaporizationand cracking of liquid oil injected in a gas-solid riser. Chemicaljet gas and pre-lift gas. The distinct M-shaped profileEngineering Science 2005: 60(22): 6049-66stands for very weak mixing, the indistinct M-shaped pro- [8] Gupta A, Rao DS. Efect of feed atomization on FCC performancefile for medium mixing, the sharp profile for strong mixing,simulation of entire unit. Chemical Engineering Science2003:5820}4567-79The effects of jet gas velocity and pre-lift gas velocity on (9) Gupta A, Rao Ds. Model for the performance of a fuid catal.the mixing characteristics between jet gas and pre-lift gasEngineering Science 2001: 56(15): 4489-50are investigated in the feed injection zone of the riser. [10] Gao JS, Xu CM, Lin SX, et al. Simulation of gas-liquid-solid 3 phaseThe heights for regions of initial and full mixing decreaseatywhen reducing the jet gas velociting the pre-lift200147(4)“677-92gas velocity[ll] Fan YP, Ye S, Chao Zx, et al. Gas-solid two-phase flow in FCCriser, AIChE Journal 2002: 48(9): 1869-87A momentum ratio has been introduced to describe the (12) Fan YP, Ye S, Lu CX, et al. Gas-solid two phase flow in feedfects of the physical properties of gas and solid, operatinginjection zone of FCC riser reactor. Journal of Chemical Industryconditions, and equipment configuration on the jet gaand Engineering 2002: 53(10): 1003-8, [in Chineseconcentration distribution. Experimental results have [13]Fan YP, Cai FP, Shi MX, et al. The gas-solid two-phase flow and theshown that the heights for regions of initial and full mixingimprovement in the feedstock injection-mixing zone of FCC riserActa Petrolei Sinica 2004: 20(5): 13-9, [in Chinese]decrease with the decreasing momentum ratio[14] Fan YP, Cai FP, Shi MX, et al. Two types of novel feedstockinjection structures of the FCC riser reactor. Chinese Journal ofChemical Engineering 2004: 12(1 ): 42-8Acknowledgement[15]Li JH, Weinstein H. An experimental comparison of gas backmixingThis work was supported by National Natural Sci[16] Patience G, Chaouki J. Gas phase hydrodynamics in the riser of aFoundation of China (Grant Nos. 20576076irculating fluidized bed. Chemical Engineering Science20476057)99348(18):3195-20中国煤化工CNMHG