英译汉

Fluidization of extremely large and widely sized coal particles as well as its application in an advanced chain grate boilerXinhua Liu,Guangwen Xu ⁎,Shiqiu GaoState Key Laboratory of Multi-Phase Complex System,Institute of Process Engineering,Chinese Academy of Sciences,P.O.Box 353,Beijing 100080,ChinaA B S T R A C TA R T I C L E I N F O Article history:Received 24October 2007Received in revised form 20March 2008Accepted 22March 2008Available online 8April 2008Keywords:Steam coalFluidized-bed pyrolyzer Chain grate boiler Fluidization SegregationA pyrolysis combustion technology (PCT)was developed for high-ef ficiency and environment-friendly chain grate boilers (CGBs).The realization of the PCT in a CGB requires that extremely large and widely sized coal particles should be first pyrolyzed in a semi-fluidized state before being transported into the combustion chamber of the boiler.This article was devoted first to investigating the fluidization of 0–40mm coal particles in order to demonstrate the technical feasibility of the PCT.In succession,through mixing 0–10mm and 10–20mm coal particles in different proportions,multiple pseudo binary mixtures were prepared and then fluidized to clarify the effect of particle size distribution.With raw steam coal used as the feedstock,the super ficial gas velocity of about 2.0m/s may be suitable for stable operation of the fluidized-bed pyrolyzer in the CGB with the PCT.In the fluidization of widely sized coal particles,approximately half of the coal mass is segregated into the bottom section of the bed,though about 15%of 10–20mm large particles are broken into 0–10mm small particles because of particle attrition.The experimental results illustrate that an advanced CGB with the PCT has a high adaptability for various coals with different size distributions.©2008Elsevier B.V.All rights reserved.1.IntroductionA grate firing technology (GFT)has been widely adopted in most of the coal-fired chain grate boilers (CGBs)in China.A conventional CGB generally has the advantage of a simple design,but the disadvantages of a large excess air coef ficient and serious fuel leakage.Especially,there always exists a low-temperature chain grate zone in the feeding side of the conventional CGB,where a slow drying rate of coal may lead to incomplete combustion of the fuel.All these disadvantages of the conventional CGB must lead to low combustion and thermal ef ficiency.On the other hand,a high combustion temperature of about 1600K in the conventional CGB may not only increase the formation rate of thermal-nitrogen oxides,but also decrease the desulfurization ef ficiency of Ca-based sulfur absorbent.The SO x emitted from small-scale coal-fired industrial boilers in China has accounted for one third of the nation's total sulfur emission.Consequently,it is important for the nation to improve the existing or develop a new GFT in order to achieve the target of energy saving and emission reduction.A decoupling combustion technology (DCT)is featured with decoupling the general combustion process of coal into fuel pyrolysis and char combustion [1].Through burning pyrolysis gas both inside the char bed and in the combustion chamber,a boiler with the DCT has low smoke and NO x emissions,but a high thermal ef ficiency.The DCThas been implemented successfully in the grate boilers with the capacity smaller than 1.0MW.Although the capacities of these grate boilers are very dif ficult to increase to meet industrial use standards because they are generally based on fixed-bed combustion,the successful application of the DCT in the small-scale grate boilers demonstrates that the DCT has a potential to be utilized to overcome the above-mentioned disadvantages of the GFT.In response to the need for the implementation of the DCT in the CGBs with greater capacities,a so-called pyrolysis combustion tech-nology (PCT)was recently proposed [2].As sketched in Fig.1,a semi-fluidized pyrolyzer is introduced into the low-temperature grate zone of a conventional CGB.The pyrolysis and the combustion region of the CGB are connected via an over flow passage at the top of the pyrolyzer and a slot between the chain grate and the pyrolyzer distributor.With coal as well as desulfurizer being loaded into the pyrolyzer,the air flow fed into the pyrolyzer is controlled to only fluidize small particles in the feedstock so that the other non fluidized large particles segregate into the bottom.The pyrolysis gas and the fluidized small/char particles formed in the pyrolyzer over flow into the combustion chamber and onto the chain grate of the boiler,respectively.Those non fluidized and high-temperature char particles drop onto the chain grate beneath the pyrolyzer through the gas distributor and are in turn transported into the grate-firing zone with the turn of the chain grate.In this design,the reduction of NO x emissions is likely realized with reburning of the pyrolysis gas in the combustion chamber,while desulfurization inside the boilers hopes to be achieved via absorptions of sul fide in the pyrolyzer and of SO 2in grate firing of the char.Powder Technology 188(2008)23–29⁎Corresponding author.Tel./fax:+861062550075.E-mail address:gwxu@ (G.Xu).0032-5910/$–see front matter ©2008Elsevier B.V.All rights reserved.doi:10.1016/j.powtec.2008.03.008Contents lists available at ScienceDirectPowder Technologyj o u r n a l h o me p a g e :w w w.e l sev i e r.c o m /l oc a t e /pow t e cMoreover,the absorption of SO 2may be enhanced by low-tempera-ture combustion of the char in the absence of volatiles.The large char particles deployed on the bottom of the fuel bed minimize fuel leakage loss through the chain grate,thereby increasing combustion ef ficiency of the advanced boiler with the PCT.In order to directly utilize the same feedstock of the conventional CGBs in an advanced CGB with the PCT,the coal particles of 0–40mm in the pyrolyzer should be maintained in a semi-fluidized state since the sizes of steam coal fed into the conventional CGBs generally range from zero to about 40mm.When a portion of small coal or char particles are fluidized stably in the top section of the pyrolyzer,despite possible carryover of some fines,the other large particles should be concentrated in the bottom section.A number of published literatures focused on the fluidization of large particles [3–8],but the average diameters of those so-called large particles were generally smaller than several millimeters.Therefore,it may not be reliable to directly extrapolate the experimental data reported in these literatures to the fluidization of 0–40mm steam coal.So,this article was devoted first to investigating the fluidization of extremely large and widely sized coal particles (e.g.0–40mm)in order to illustrate the technical feasibility of the PCT.In succession,three types of pseudo binary mixtures prepared by mixing 0–10mm and 10–20mm coal particles in different proportions were tested to clarify the effect of particle size distribution and to provide some quantitative data for the design of the advanced CGB with the PCT.2.ExperimentalAs shown in Fig.2,a square Plexiglas bed with a cross-section area A t of 0.15×0.15m 2and a height H t of 0.9m was used to perform all experiments.Nine bubble cap tuyeres constitute a gas distributor with an opening area ratio of about 5%.The pressure drop Δp 0across the gas distributor measured in empty bed can be correlated to super ficial gas velocity U g as:D p 0¼0:425U 2gþ0:282U g À0:032ð1Þwith con fidence degree of up to 0.9998at 0.1m/s ≤U g ≤4.0m/s.The pressure drop across the whole fluidized bed including the gas distributor was monitored with a differential pressure transducer and recorded at a given sampling frequency of 100Hz.By subtracting Δp 0from the total pressure drop across the whole fluidized bed,one can easily determine the pressure drop Δp b across the particle bed.The flow rate of the fluidizing air provided by a forced draft fun was measured with a rotameter.Gas –solids separation was effected in turn by a cyclone and a dust filter wherefrom the gas was exhausted into the air.The tested particles were steam coal of 0–40mm,a kind ofbituminite usually used in industrial CGBs.The coal was sieved into three components denoted as A of 0b d p b 10mm,B of 10≤d p b 20mm and S of 20≤d p b 40mm.Both the components A and B were further subsieved into different narrow cuts shown as Ci in Table 1,where i =0to 9with a larger i for a larger cut.Three types of pseudo binary mixtures tested in the article were all prepared by mixing the com-ponents A and B in different proportions.The notation A x B y means that the mass proportions of A and B in the binary mixtures are x and y ,respectively.Fig.3shows differential size distributions of the fluidizing materials as well as the components A and B from sieve analysis.The surface mean diameters d p ,as listed in Table 2,of the components A,B,their mixtures A x B y and steam coal calculated withd p ¼1=X n i ¼1x cid pci ð2Þwere adopted in the article,where d pci refers to the arithmetical mean value of the smallest and largest particle sizes in cut Ci or the component S,x ci is the mass fraction of the cut characterized with d pci ,and n is the number of narrow cuts constituting a material.Supposing the density ρs of coal particles is 1340kg/m 3,the minimum fluid-ization velocity U mf,cal of each material can thus be estimated from d p using the equation of Wen and Yu [9],as summarized in Table 2.In order to reproduce the feeding manner of the fuel in an actual fluidized-bed pyrolyzer,a weighed amount of steam coalwasFig.1.Principle of a chain grate boiler with pyrolysis combustiontechnology.Fig.2.Schematic of experimental setup.Table 1Sieving data of coal particles Component Narrow cut d pc ,mm AC00–2C12–4C24–6C36–8C48–10BC510–12C612–13C713–15C815–16C916–20S20–4024X.Liu et al./Powder Technology 188(2008)23–29gradually introduced into a bed running at a given U g within abouttwo minutes through a hopper fixed at the top side of the bed.After further fluidizing the coal bed for about 10min and then shutting off the fluidizing air supply abruptly,the coal bed obviously appeared two different regions because of particle segregation:the top section composed of small particles and the bottom section made up of large particles.The coal particles in the top and the bottom section were in turn removed layer-by-layer using a suction pipe connected to a vacuum line via a discharge filter.The particles from different layers were further sieved to determine the amounts of the narrow cuts speci fied in Table 1.When a pseudo binary mixture of the components A and B was tested,a premixed and weighed amount of the mixture was loaded into the bed at first.Experiment was started with gradually increasing U g to about 2U mf,cal of the tested particles at somehow small intervals within about 20min.After maintaining the maximum gas velocity for another five minutes,decreasing U g back to zero was performed in about 10min.The particle bed at rest was in turn divided into four layers of the same height,and each layer was suctioned out of the bed and then sieved to the cuts C0to C9as done after the test with the steam coal.A static bed height H s of about 0.4m was chosen in this study according to possibly actual fuel bed height of the pyrolyzer in an advanced CGB with the PCT.This required about 7.0kg coal to be loaded into the bed as the fluidizing material.3.Results and discussionIn order to compare different sets of experimental results,all pressure drop data across the coal bed Δp b and super ficial gas ve-locities U g were converted respectively into normalized terms denotedas Δp b⁎and U g ⁎by D p b T ¼A t ÂD p b =mg ðÞð3ÞandU gT ¼U g =U mf ;cal :ð4ÞThe so-called flotsam and jetsam proposed by Wu and Baeyens [8]were adopted to represent small and large component respectively when testing multiple pseudo binary mixtures.Consequently,the mixing index M ¼x j ;top =x j ;overall ;ð5Þa traditional quantitative measure of segregation of a binary system [6]can be introduced to quantify the mixing characteristics of the tested coal particles.Generally,x j ,top in Eq.(5)is jetsam mass fraction in the top of the bed when the bed at rest was divided into two ormore layers,and x j ,overall is the overall mass fraction of jetsam in the entire bed.So,M equals zero and 1.0corresponding to complete segregation and perfect mixing respectively.Similarly,all jetsam mass fraction data x j were also converted into normalized values x j ⁎viax j T ¼x j =x j ;bottom :ð6ÞHere,x j ,bottom is jetsam mass fraction in the bottom layer.3.1.Fluidization and segregation of raw steam coalAbout 7.4kg of 0–40mm raw steam coal was fluidized at a fixedU g ⁎=2.63.As shown in Fig.4a,the coal bed at fluidization clearly took on two different regions:the top and the bottom section,which were characterized with homogeneous fluidization and non fluidized state,respectively.Fig.4b shows the stationary bed after the fluidization lasted for ten minutes and in succession was stopped by cutting off the fluidization gas supply abruptly.The bed material was segregated into distinctive two layers,and the height of the bottom large-particle section is almost the same as that of the non fluidized section in Fig.4a.These verify further that the bottom section of the bed in the fluid-ization test was in fact in a fixed-bed state.Fig.5a shows that the dimensionless pressure drop Δp b⁎across the coal bed gradually increased with the loading of coal into the bed until reached a maximum of about 0.7at the end of feeding.Then,ittendedFig.3.Size distributions of steam coal,components A,B and their mixtures.Table 2Properties of coal particles Material d p ,mm U mf,cal ,m/s A 2.060.74B13.62 2.45A 0.75B 0.25 2.610.90A 0.49B 0.51 3.63 1.14A 0.33B 0.67 4.78 1.36Steam coal3.351.08Fig.4.Typical fluidization and segregation pattern of steam coal:(a)fluidization at U g⁎=2.63(U g =2.84m/s);(b)segregated bed after 10-minute fluidization at U g ⁎=2.63(U g =2.84m/s).25X.Liu et al./Powder Technology 188(2008)23–29to decrease a little,as an indication of particle elutriation,and finally stagnated at about 0.6.Due to the bottom section in non fluidized statein the test,the dimensionless pressure drop Δp b⁎in Fig.5a is con-stantly below 1.0.On the other hand,the carryover of fine particles viathe elutriation would also decrease Δp b⁎,but this effect was sub-ordinate at U g⁎=2.63(U g =2.84m/s).Fig.5b shows the mass fraction distributions of all narrow cuts,including the component S,in the fluidized and the non fluidized layer.For comparison,the data for raw steam coal were also included.It can be seen that the mass fractions of the smallest cut C0in both the layers are smaller than its initial mass fraction in the raw steam coal be-cause of the elutriation.The mass fraction of the component S in the non fluidized layer is much greater than that in the fluidized layer,indicating quantitatively severe segregation of fluidized steam coal.During the steam coal was continuously fed onto the bed surface,the small coal particles in the feedstock were soon either fluidized or elutriated in the top section of the bed,whereas the other large coal particles sank into the bottom section because of the pull of gravity.It is out of question that this phenomenon actually helps to prevent the fine fuel particles leaking into the plenum of the boiler through the chain grate at the bottom of the pyrolyzer.Since the segregation surely happened to the fluidization of steam coal,the coal may also be treated as a kind of pseudo binary mixture made up of 0–10mm flotsam and 10–40mm jetsam.Based on the experimental data on the jetsam concentrations in the top fluidized and the bottom non fluidized section,the normalized concentration x j ⁎of 10–40mm coal particles was figured out to be subject to an axial pro file conceptualized in Fig.5c with dashed line.According to Eq.(5),the corresponding M for the coal bed after fluidization is 0.318,of-fering another quantitative measure of the segregation degree.In fact,the mass percentage of non fluidized large particles in the bottom section was found to be about 45%,while the fluidized and the elutriated coal particles accounted approximately for 27%and 28%oftotal mass of the fed coal respectively at U g =2.84m/s or U g⁎=2.63. 3.2.Fluidization and segregation of binary coal particlesThe size distribution of coal for industrial boilers may vary within a certain range.Several pseudo binary mixtures of the components A and B at different fractions were thus investigated to clarify how the coal size distribution affects the fluidization and segregation char-acteristics of the materials.According to Noordergraaf et al.[4],slugging must be expected for large particles in fluidized beds of small diameter and with a large aspect ratio.The fluidization of the mixture A 0.75B 0.25was found tobelong to this type at U g ≈U mf,cal (i.e.,U g⁎≈1.0).However,slugging behavior was seldom observed for the other two mixtures with agreater mass fraction of the component B during U g⁎varying from zero to about 2.0.These experimental phenomena can be explained by the fact that the inter-space among large and anomalous coal particles existing in the bed with a greater mass fraction of the component B makes the gas easy to pass through the bed and thus inhibits the formation of gas bubbles in bed size.Visual observation of the experiments shows that the fluidization of the mixtures was in fact a progressive process controlled by the interaction between gas velocity and particle size.With increasing U g gradually,small particles inside the coal bed were dragged up to the surface and fluidized at first.When U g increased to about 2.0U mf,cal and was maintained at this value for a few minutes,the coal bed reached a dynamical equilibrium and was clearly segregated into the top and the bottom layer.As shown in Fig.6a,the top and the bottom section of the A 0.75B 0.25bed were rather like turbulent and bubbling fluidization,respectively.For the material A 0.33B 0.67(Fig.6c),the top fluidized section was featured with slow and large bubbles,while the bottom section was more like an expanded bed.The fluidization pattern of the material A 0.49B 0.51shown in Fig.6b was rather in between,showing many small gas cavities in the bottom section but some large bubbles in the turbulent top section.As discussed before,the implementation of the PCT in a CGB relies on the pyrolysis of coal in advance of the grate firing andsuccessfulFig.5.Characterization of fluidization of steam coal:(a)variation of Δp b⁎with time;(b)mass faction distributions of narrow size cuts;(c)axial concentration pro file of 10–40mmparticles.Fig.6.Fluidization patterns of multiple pseudo binary mixtures at U g⁎≈2.0:(a)A 0.75B 0.25,U g⁎=2.33,U g =1.85m/s;(b)A 0.49B 0.51,U g ⁎=2.27,U g =2.46m/s;(c)A 0.33B 0.67,U g ⁎=2.18,U g =2.73m/s.26X.Liu et al./Powder Technology 188(2008)23–29segregation of small coal/char particles from large ones.The control ofthe quantity of small-size coal particles over flowing into the combustion chamber from the pyrolyzer is of signi ficance for the operation of the coal pyrolyzer illustrated in Fig.1.For different binary mixtures of the components A and B,the mass ratios of the elutriated,the fluidized and the non fluidized coal particles to total bed materialsat U g⁎≈2.0were shown in Fig.7.The mass percentage of the non-fluidized particles decreased slightly with increasing the mass fraction of the component A,re flecting that large coal particles were more dif ficult to be fluidized at the same normalized super ficial gas velocity.But the difference of about 10%(from 60%to 50%)in the mass percentage of the non fluidized particles for differently sized coals suggests surely a less variation in volume of the non fluidized section,which implies actually a relatively stable operation of the pyrolyzer and a high adaptability of the advanced CGB with the PCT to various coals with different size distributions.Above all,a relatively con-stant elutriation of 12–15%of the fine particles shown in Fig.7means a stable combustion temperature of the advanced CGB,which would promote the control and reduction of NO x emissions in actual operation.Fig.8a shows that with increasing U g⁎from zero the normalized pressure drop Δp b⁎increased gradually and finally approached a transition point wherefrom it tended to keep constant.Dislike usual fluidization processes,so-called pressure drop overshot [10]did not appear during ascending the gas velocity,but the transition pointoccurred at U g⁎greater than 1.0due to the wide-size distribution of the tested coal particles.The dimensionless transition velocity U tran⁎in-creased with increasing the mass fraction of the component A,but the absolute gas velocity corresponding to the transition point did not change much actually because theoretical the minimum fluidization velocity of the mixture decreased correspondingly.The absolute transition gas velocity was also found to be greater than theoretical the minimum fluidization velocity of the component A,but to be still much smaller than that of the component B.As a result,increasing thegas velocity beyond U tran⁎must lead to an increase of the pressure drop across the bottom non fluidized bed of large particles because ofincreasing the gas –solid friction there.But overall Δp b⁎may exhibit very little change within some range because the pressure drop across the top fluidized section of the coal bed decreases with increasing the gas velocity due to the elutriation of the fine particles.Contrarily,at a given super ficial gas velocity,increasing the mass ratio of the component A in the mixture may lower the pressure drop from the bottom non fluidized bed,but increase the pressure drop across the top fluidized section.Therefore,the dimensionless pressure drop Δp b ⁎beyond U tran⁎had almost the same value smaller than unity for all the three binary mixtures tested.These indicate that for arbitrarily sized steam coals the dimensionless gas velocity suitable for the pyrolyzerof the advanced CGB with the PCT should be just beyond U tran⁎so that the pyrolyzer has relatively stable pressure drop to facilitate thecombustor control.According to Fig.8a,this velocity might be U g⁎between 1.5and 2.0or U g of about 2.0m/s.Under this condition,the fluidized and the non fluidized layer in different beds were demar-cated at a very similar bed level,as shown in Fig.6,showing further that the pyrolyzer in an advanced CGB with the PCT may run at similar U g⁎for different coal particles.As can be seen from Fig.8b,the dimensionless height h b /H s of the particle bed increased with elevating the gas velocity,but the increaseof h b /H s ,like the variation of Δp b⁎,seemed to take on a different trend beyond the transition point for each binary mixture.Before thetransition velocity U tran⁎,an increase of the particle bed height can be attributed to uniform expansion of the entire coal bed,while after the transition point to the formation of gas bubbles in the top fluidized section since the bottom non fluidized layer does not expand again under this condition.Fig.8c plots the standard deviation σp of pressure fluctuation determined fromr p ¼1k À1X k i ¼1D p bi Àh D p b i ðÞ"#0:5;ð7Þwhere,i and k are the index and total number of data points,b Δp b N isthe time-averaged pressure drop across the particle bed.Once U g⁎was beyond about 1.5,the standard deviation σp began to increase continuously with increasing the gas velocity in response to the formation of obvious bubbles in the bed.Therefore,we suggest that the minimum bubbling velocity U mb of the binary mixtures should be equal to about 1.5U mf,cal [11].The result con firms essentially that the tested coal similar to group D particles [12]was very likely to form gas bubbles in fluidization,and in agreement with the conclusionfromFig.7.Mass ratios of the elutriated,the fluidized and the non fluidized particles to total bedmaterials.Fig.8.Characterization of fluidization of pseudo binary mixtures:(a)variation of Δp b⁎in ascending U g ;(b)variation of normalized particle bed height h b /H s in ascending U g ;(c)variation of pressure standard deviation σp in ascending U g ;(d)variation of Δp b ⁎with descending U g .27X.Liu et al./Powder Technology 188(2008)23–29Fig.8a,the normalized superficial gas velocity U g⁎should be greater than about1.5U mf,cal in actual operation of the advanced CGB.The minimumfluidization velocity of a type of particles is gen-erally defined with the pressure drop measured during descending gas velocity[13].Fig.8d then shows that it may be difficult to determine the minimumfluidization velocity of the tested large and wide-size particles using the method.This is again related to the fact that in the tested case large coal particles in the bottom section of the bed was notfluidized at all,making the pressure dropΔp b⁎gradually decrease with descending U g⁎due to continuously decreasing the gas–solid friction from the bottom nonfluidized section.In fact,there might be no single the minimumfluidization velocity for the wide-size coal particles tested here,because somefines,for example,the narrow cut C0of0–2mm particles,may be completely carried over when the larger ones of over10mm become to be fullyfluidized.According to the experimental method specified in the Section2, the particle bed afterfluidization was divided into four layers of the same height.Fig.9shows the mass fractions of the narrow cuts C0toC9in the four layers and the mixtures.The mass fractions of the narrow cuts C5to C9with a greater diameter generally increased from the bed top to the bottom(i.e.,from the1st to the4th layer).While,the mass fractions of the narrow cuts C0to C4with a smaller diameter commonly followed a reverse variation tendency.The mass fractions of the cut C0in all the layers were lower than that in the feedstock due to the elutriation.The narrow cuts C2to C4accounted for most part of thefluidizable particles.All of these results demonstrate actually the segregation of the binary mixtures in thefluidization since all of them were premixed completely before being loaded into the bed.If the components A and B were taken asflotsam and jetsam respectively in this case,axial profile of jetsam concentration de-termined after stopping thefluidization illustrated further the feature of the segregation.As shown in Fig.10,with decreasing the mass fraction of the component B from0.67to0.25,axial profile of jetsam concentration x j⁎became more and more nonuniform.Correspond-ingly,the mixing index M for three pseudo binary mixtures de-termined by dividing the jetsam concentration in thefirst(top)layer by that in the fourth(bottom)layer was found to decline from0.836to 0.259,indicating severe segregation of the mixture containing more flotsam particles under the similar operating conditions.Geldart et al.[3]reported that the segregation by size difference became smaller under a premise of fullfluidization as the mean size of the solids decreased.Theirfindings is essentially consistent with the above experimental results,because in this study the premixedfine powder in the bed moved upwards only through the voids among large non-fluidized particles,rather than through either the entrainment within the channels or the bulk movement driven by gas bubbles as in a fully fluidized bed.Thereby,contrary to the mass ratio of the elutriated particles in thefluidization of the binary mixtures,the segregation, the mixing degree of the binary mixtures depends strongly upon the coal size distribution.Another worth noting phenomenon in thefluidization of extre-mely large coal particles is particle attrition,which has close relation with thefluidizing material and the maximumfluidization gas ve-locity in this study.As shown in Fig.11,compared with the initial mass of the narrow cuts C0to C1respectively,their residual mass in the bed afterfluidization decreased even more than50%,which might be mainly attributed to the elutriation of thefines.But,afterfluidization the quantities of the narrow cuts C2to C4increased to be greater than their initial mass in the feedstock respectively.The increase extent of the cut mass increased with increasing the mass fraction of the component B and the maximumfluidization gas velocity adopted in the tests.Since the narrow cuts C6to C8must not be blown out of the bed at the superficial gas velocity tested,the particle attrition resulted in the above experimental phenomena,because afterfluidization the residual quantities of these large cuts in the bed appeared anobviousFig.11.Mass change of narrow cuts in the bed before and afterfluidization of three binarymixtures.Fig.10.Axial profile of jetsam concentration for three types of binarymixtures.Fig.9.Mass fraction distributions of narrow cuts in each layer and the initial bedmaterial:(a)A0.75B0.25;(b)A0.49B0.51;(c)A0.33B0.67(initial mixture;1stlayer;2nd layer;3rd layer;4th layer).28X.Liu et al./Powder Technology188(2008)23–29。