Fluor Daniel Lectureship Award                  Flour Daniel Lectureship Award                  AIChE 2001 Annual Meeting,...
1. Fluidization processes      previous developments and fundamental researches2. Significance of agglomerating fluidizati...
coal, wastes,                    biomass                                           FCC                          coal      ...
Enos, J.L.,(1964)Capacity in world total [%]                                             FCC                              ...
COMMERCIAL                    Cat Reactors        FCC              Incinera-                                              ...
Advantages, particularly1. high yield by uniform & stable temperature field      that cannot be obtained by any other     ...
Disadvantages  However, the advantages listed are closely related to the disadvantages of fluidization such as,1. High bac...
In the case of     Municipal Waste Incineration 1. The frequent and unpredictable variation of calorific value of waste fe...
MSFB                                           1974 BattelleWaste plastic                              Columbus Lab.pretre...
Expanded                                        Horizon of       New Technical                    Fluidization           H...
Nature and Art             Natural Science and             Engineering Science    The presence of column wall made    the ...
‘Turbulent’                               ‘ Turbulent ’      Dense      Dense                                             ...
Fluidization, matured ?• Once only few professional peoples business.• Trough national projects since the 70s including CC...
Still exist high hurdles for higher selectivity, lower              emissions and safer scale-up.   New applications once ...
2. SIGNIFICANT ASPECTS OF      AGGLOMERATING       FLUIDIZATIONFor a long period, phenomena associated with agglomeratingf...
Defluidization velocity [m/s]        Polyolefin Process                                                                   ...
Puzzling Umf                                     increase for                                    fine powders u [cm/sec] [...
Chronology                        Green letters: fundamentals1961 Davidson’s Bubble1966 Jimbo, Sugihara’s umf issue left a...
Spray granulation    moisture content of bed[%]                                                                           ...
①FluidizationBag filter                       interval                                                       15s          ...
① bubbling period:                pulse (in reverse flow period)  Bed expansion de-     ①                        ②  agglom...
Potential of binderless     granulation •Particle strength: how much is needed ? •Weak granules help easy tabletting, hige...
#30-2         #30-2           #16-2           #16-2       #30-1          #30-1           #16-1           #16-1ZnO       #3...
original                                                            PSG                                                   ...
1mm           1mm            1mm  No. 2         No. 3          No. 4                                                      ...
Lactose                      3                                 Granule size: 0.355~0.5mm                                  ...
Applications•Hard metal cutting tool manufacturingand other PM materials•Ceramic and other materials•Pharmaceutical agglom...
feed compositions                                            powd. dp(WC) WC Co wax*                                      ...
Transverse rupture strength [N/mm2]                                                                                   PSG ...
500mm                      L : E=1 : 1                                                            500mm   Co-agglomeration...
100Concentration of Ethenzamide                                          1000mm                                     Granul...
Size Determining Mechanismin Agglomerating Fluidization          2.1 Background    2.2 Potential of Binderless            ...
difference, P                                              difference, P                          B           D         ...
Comparison of previous model concepts  Authors             Model               External force/energy                   Coh...
4                                                              4                          expansion                       ...
agglomerating                                         fluidization unstable point                                         ...
Two difficulties in I-H model       1. particle-particle attraction force ?       2. agglomerates grow while bubbles      ...
3                            Ff                2.5   Load [mPa]                 2                1.5                      ...
1E-3                                                                            1E-3                     No. 4            ...
500Median diameter [10-6m] Median diameter [10-                                                                  600    ...
3. Further discussions on the size      determining mechanism  3.1 DEM simulation      3.2 Comparison of Major Forces in t...
The DEM simulation stands in between the two-fluid model (TFM) andthe direct Navier-Stokes simulation (DNS). DEM takes car...
COMBUSTION                  Spray                         Agglomerating      AGGLOMERATION                            Gran...
dp=100mm, rp=3700kg/m3                                u0=0.1m/s, Ha=1.0×10-19J0.411s     0.430s      0.450s       0.469s  ...
dp=100mm, rp=3700kg/m3                        u0=0.1m/s, Ha=1.0×10-19J 0.460s     0.462s      0.464s        0.467s        ...
Agglomerate: Fcoh>Frep, max                       Collision: Fcoh<Frep, max           *Non-cohesive Ha=0.4x10-19J Ha=1.0x1...
High voltage DC power source (0-9kV)                                                                                      ...
r1                 From Kelvin’s theory                   r2         r2=[-3+(9+8brp)]/2b   rp                         b=(...
mm,                     ZnO 0.57 u0=0.351m/s, column diam.=0.3m               0.1             1E-3                        ...
Liquid bridge curvature from bridge              volume VLVL/(pda3)=1.5(r1a/ra)2[1- (r1a/ra)(1+2/ (r1a/ra))1/2sin-1[1/(1+ ...
T=870 ーC, d p  =900 mm, Surface                           tension=0.4N/m, Ha=1410-20 J/                    Db,p=10atm   ...
2D DEM results: dp=200mm,                                  T=1273K, u0=0.26m/s3 micro contact points   smooth surface     ...
CONCLUDING REMARKS1. Secrets of Fluidization have been unveiled almost by the 60 yrsendeavor and fluidization should now b...
DEM: problems to be Solved The problems of DEM in view of its future application to real large scalecomputation are coming...
REMAINING MOUNTAINS IN DEM               SIMULATIONCollision formulation: particle shape, surface roughness, plasticdeform...
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New Developments Through Microscopic Reconstruction of the Nature of Fluidized Suspensions 011106 AIChE FlourDaniel lectureship award lecture

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Presentation was made at AIChE Particle Technology Forum as an Award Lecture.
After a brief review of achievements of fluidization engineering over decades, a discussion is made on one of the latest issues for applications in material industries as well as for the improvements in reliability of many fluidization processes, i.e., granulation and defluidization issues.
2.1 Background
For a long period, phenomena associated with agglomerating fluidization have been treated with complete empiricism and scientific lights were shed seldom on them. It was, however, natural because the basic intention of fluidization has long been the better gas and solid contacting and, accordingly, agglomeration has been only one of unwanted side effects, which, once technically avoided, tend to be forgotten. At the same time, knowledge on elementary processes that should be relevant to agglomerating fluidization, e.g., bubble characteristics, forces acting among fluidized particles, surface characteristics of solids etc., was only gradually established during the last decades.
Defluidization/agglomeration issues are, however, quite significant in a majority of fluidization processes probably except for gas-to-gas catalytic processes. In polyolefin processes agglomeration due to softening of plastic particles in local hot spots should be avoided. In a polyolefin reactor it has been confirmed by a DEM simulation of Kaneko et al. (1998) that a stable solid circulation does not help removing the heat of polymerization. Instead, a solid motion induced by the always-fluctuating bubbling action is necessary as shown in Fig. 3.
Ash melting and agglomeration, which finally causes defluidization, limits the operating temperature and pressure of pressurized fluidized bed combustion (PFBC) or gasification (PFBG). Figure 4 shows the so-called "sinter eggs" formed in a FBC boiler that is close to those found in AEP Tidd PFBC. Sinter egg/grain formation is again experienced recently in a commercial scale PFBC in Japan.

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New Developments Through Microscopic Reconstruction of the Nature of Fluidized Suspensions 011106 AIChE FlourDaniel lectureship award lecture

  1. 1. Fluor Daniel Lectureship Award Flour Daniel Lectureship Award AIChE 2001 Annual Meeting, AIChE 2001 Annual Meeting Particle Technology Forum November 2001 November 6, 2001, Reno, NV New Developments through New Developments throughMicroscopic Reconstruction of theMicroscopic Reconstruction of the Nature of Fluidized SuspensionsNature of Fluidized Suspensions Masayuki Horio Tokyo U. A & T Koganei, Tokyo
  2. 2. 1. Fluidization processes previous developments and fundamental researches2. Significance of agglomerating fluidization 2.1 Background 2.2 Potential of Binderless granulation 2.3 Size Determining Mechanism in Agglomerating Fluidization3. Further discussions on the size determining mechanism 3.1 DEM simulation 3.2 Comparison of Major Forces in the context of I-H model 3.2.1 A case study on ZnO 3.2.2 Ash agglomeration in FBC 3.2.3 Additional remarks4. Concluding remarks
  3. 3. coal, wastes, biomass FCC coal biomass catalytic catalytic wastes cracking and bio Gasificat- reactionsde-SOx,H2S,HCl ion PP, PE FBC olefin power Applications polymeri gen. zation of waste Fluidization iron ore hardening, manage- reduction, annealing, patenting, ment Powd. M OTHER: Portland Cement, mixing, Si Ferrite, Ceramics, mixing, Nanoparticles separation, drying, amusement, chlorina healthcare agglom tion & -eration, CVD coatin’ food, pharmaceutical
  4. 4. Enos, J.L.,(1964)Capacity in world total [%] FCC yearThe first dramatic success of fluid catalytic cracking (FCC).See how desruptive the FCC technology that time was to all other technology options.
  5. 5. COMMERCIAL Cat Reactors FCC Incinera- CFBC tors PP, CVD PFBC PE; R Si; AFBC & Spray D Granu lators 1930 1940 1950 1960 1970 1980 1990 2000Major Fluidized Bed Process Developments
  6. 6. Advantages, particularly1. high yield by uniform & stable temperature field that cannot be obtained by any other contact modes.2. high heat transfer rate when solids or surface are immersed.3. good solid mixing and potential of handling solids continuously4. High energy efficiency and resources utilization capability
  7. 7. Disadvantages However, the advantages listed are closely related to the disadvantages of fluidization such as,1. High back mixing, then low yields.2. Poor gas-gas contact efficiency without high surfacearea catalysts.3. Highly erosive conditions to immersed surfaces andhigh attrition conditions to bed particles because of highparticle collision frequency (essential for high heattransfer rate).4. High defluidization potential at high load conditions dueto agglomeration or clinkering.5. Short residence time of fine particles and gas speciesemitted from solids.6. Low mixing intensity in the freeboard.
  8. 8. In the case of Municipal Waste Incineration 1. The frequent and unpredictable variation of calorific value of waste feed as well as the rapid preheating and incineration rates make it difficult to adjust the air-to-fuel ratio at a stoichiometric air ratio as low as 1.2 of coal combustion. To avoid high PCDD/PCDF formation the air ratio has to be as high as 2.0~2.5.  fuel pretreatment (RDF), slow pyrolysis at low temperatures 2. Remaining volatiles have to be combusted in the freeboard but the turbulent mixing in the freeboard is still not sufficient.  circulating fluidized bed 3. The presence of chlorine makes it difficult to control the bed temperature by in-bed tubes. Furthermore, the water spray method from the top of the freeboard adopted sometimes brought high DXN emission.  de-chlorination by CaCO3. 4. Alkali and chlorine compounds formed in the bed help to form agglomerates.  de-chlorination, strict material balance
  9. 9. MSFB 1974 BattelleWaste plastic Columbus Lab.pretreatment 1970’s: Conoco plant troubled Sand 1980’s: Kurarey & Idemitsu plants RDF troubled. machiie Limestone Spec. of MSFB at Kraray Co. steam: 70t/h 8.92 MPa, 513C fuel: coal plastics waste AC MSFB born again etc. as a flexible energy recovery process
  10. 10. Expanded Horizon of New Technical Fluidization High Demand Challenges Processes but High Risk due to the lack New Scientific of Knowledge Challenges Expanded Knowledge on Fluidization Phenomena Fluidization research has been aiming at new designs and newprocess developments as other chemical engineering principles have. However, it has to develop phenomenological understanding of thenature of fluidized suspensions because no other disciplines evermore seriously encountered it. Good Heritage of Fluidization Research
  11. 11. Nature and Art Natural Science and Engineering Science The presence of column wall made the analysis much easier volcanic cloud plateauartificialplant hail
  12. 12. ‘Turbulent’ ‘ Turbulent ’ Dense Dense Dilute and suspension suspension ‘ Fast ’ suspension suspension Fluidization turbulent fast bed bed pnewmatic transport A phase diagram of a FCC powder. (Horio and Ito (1997); data: Hirama et al.)For analogy with matters: gas velocity u0 should correspond to temperature, solid circulation flux Gs to pressure, and particle volume flux p to density
  13. 13. Fluidization, matured ?• Once only few professional peoples business.• Trough national projects since the 70s including CCTand by the spread of fluidized bed sludge/wasteincinerators, fluidization has become popular in amuch wider professions.• Unfortunately in Japan, the serious DXNs emissionfrom furnaces with poor temperature control by waterspraying made the term "fluidized bed" a little morepopular to people.• Its application is widening even coming closer toeveryday life. A bed for a burned patient is an alreadyclassical invention but recently a dry bathing systemfor nursing an aged person (Yokogawa (1998)) hasbeen invented.
  14. 14. Still exist high hurdles for higher selectivity, lower emissions and safer scale-up. New applications once expected promising in the field of materials processing have not yet achieved muchbreakthrough except for pharmaceutical granulation and small applications.After the enthusiasm of circulating fluidization research inthe 80s, the most interesting, essential and highlyinterdisciplinary research topics lie in1) new contacting concept development including co-currentdown-flowing suspensions in the downer to provide lessback mixing conditions in catalytic reactors and porous BMfor incineration and other gas-solid systems.2) agglomerating fluidization including granulation and the3) numerical simulation by DEM, DNS.In today’s talk the agglomerating fluidization issues arediscussed with a wide perspective.
  15. 15. 2. SIGNIFICANT ASPECTS OF AGGLOMERATING FLUIDIZATIONFor a long period, phenomena associated with agglomeratingfluidization have been treated completely empirically andscientific lights were shed seldom on them.It was, however, natural because the basic intention offluidization has long been the better gas and solid contactingand, accordingly, agglomeration has been only one ofunwanted side effects, which, once avoided, tend to beforgotten.At the same time, knowledge on elementary processes thatshould be relevant to agglomerating fluidization, e.g., bubblecharacteristics, forces acting among fluidized particles,surface characteristics of solids etc., was only graduallyestablished during the last decades.
  16. 16. Defluidization velocity [m/s] Polyolefin Process CoalUniform gas feeding Nonuniform gas feeding Gasification particle temp. particle velocity particle temp. particle velocity vector vector t=9.1 sec t=8.2 sec Fig. 5. Defluidization curves for different coal 3umf 3umf 3umf 2umf 2umf species in a pilot scale fluidized bed gasifier 15.7umf Circulation eddies (Fujioka and Nagai (1988)) : Upward motion : Downward motion Starting cast shot FB Fines taken up Combustion 1500F 87% reduction 1600F 87% reduction Iron-oxide Experimental data from self nucleation tests Wt pct Wt pct Wt pct Reduction Size, mesh US std Starter bed first cycle Final bed Final bed less Starter beda second cycle Final bed Final bed less Starter bedb third cycle Final bed Final bed less oversize oversize oversize +20 32.1 42.3 44.6 -20+30 18.2 33.6 49.4 55.6 38.1 66.0 67.0 36.2 65.4 -30+40 45.1 18.3 27.0 30.0 12.5 21.7 22.0 10.1 18.2 -40 36.7 16.0 23.6 14.4 7.1 12.3 11.0 9.1 16.4 Significance of Agglomerating Fluidization in almost all fluidized bed processes
  17. 17. Puzzling Umf increase for fine powders u [cm/sec] [cm/sec] Data by Sugihara(1966) andumfmf correlation by Jimbo (1966) g(rp -rff) 2 n2aF umf= dp + 3pbm dp 18bm [ Along with their efforts for establishing Soc. Powder CaCO3 Tech. Japan] dp [mm]
  18. 18. Chronology Green letters: fundamentals1961 Davidson’s Bubble1966 Jimbo, Sugihara’s umf issue left a question at least to Japanese1973 Geldart’s Powder classification and ‘Group C’ for cohesive ones197X Donsi-Massimila(75), Masters-Rietema(77): Cohesion force and fluidized bed behavior1985 Chaouki et al., Group C fluidization and agglomerate size (da) prediction1987 Kono et al.: Measurement of force acting on particles1988 Morooka et al.: Energy balance model for da1990 Pacek-Nienow: Fine & dense hardmetal powder fluidization1991 Campbell-Wang: Particle pressure in a FB1992 Nishii et al.: Pressure Swing Granulation1993 Tsuji, Kawaguchi & Tanaka: DEM for Fluidized Bed1998 Mikami, Kamiya & Horio: Numerical simulation of agglomerating FB (SAFIRE) Iwadate-Horio: Particle pressure / Force balance model to predict da
  19. 19. Spray granulation moisture content of bed[%] F RD A: acetoaminophen E: ethensamide gas vel. yield d50 bulk density VC: ascorbic acid A E VC timeFig. 8. Typical moisture content curves in spray granulation. Fig. 9. Effect of drug types on product size distribution of fluidized bed(Aoki (1997)) spray granulation (Sunada et al. (1997)( F: free bubbling type, RD: rotating distributor type)
  20. 20. ①FluidizationBag filter interval 15s ②Compaction 1s interval 0 time[s] 7200 Gas tank Compressor 0.41m f0.108m Compressor ①Fluidization ②Compaction interval interval (a) apparatus (b) operation Pressure Swing Granulation Nishii et al., U.S. Patent No. 5124100 (1992) Nishii, Itoh, Kawakami,Horio, Powd. Tech., 74, 1 (1993)
  21. 21. ① bubbling period: pulse (in reverse flow period) Bed expansion de- ① ② agglomerates and compaction, attrition and solids revolution make grains spherical. cake Fines are separated and re compacted on the filter. fines‘ entrainement ② filter cleaning & bed expansion reverse flow period: Cakes and fines are bubbling returned to the bed cleaning-up the filter, and bed is compacted distributor promoting compaction agglomerates’ growth and attrition and consolidation. air (in bubbling period) What happens in PSG?
  22. 22. Potential of binderless granulation •Particle strength: how much is needed ? •Weak granules help easy tabletting, higer green density, potential application to DPI •Attrition reagglomeration mechanism helps achieving content uniformity
  23. 23. #30-2 #30-2 #16-2 #16-2 #30-1 #30-1 #16-1 #16-1ZnO #30-2 #30-1 #16-2 #16-1 500mm Structure of PSG granules Granules split by a needle show a core/shell structure. (Horio et al., Fluidization X (2001))
  24. 24. original PSG granules Cumulative weight [%] PSG granules slide 500mm from ZnO gate dp=0.57mm after 1st fall 2nd fall 3rd fall Particle size [10-6m]PSG granules: weak but strong enough!Change in PSD of PSG granules in realistic conditions
  25. 25. 1mm 1mm 1mm No. 2 No. 3 No. 4 100 Cumulative size distribution [v%] 80 d p,sv [mm] No. 2 7.48 60 No. 3 4.95 No. 4 4.79 40 No. 5 4.141mm 1mm 1mm No. 6 3.71 20 No. 7 2.58 No. 5 No. 6 No. 7 0 0 10 20 30 40 50 Product Powders Primary particle size [mm] Original Powders Fig. 4 Size distributions of primary particles PSG Microphotographs of PSG granules offound possible for Fig. 6 from lactose lactose dp<3mm Tkakno et al. (1998)
  26. 26. Lactose 3 Granule size: 0.355~0.5mm 0.01 Ethensamide Lactose Load[gf] 2 force [N] 1E-3 1 Lactose 1E-4 0 40 80 120 160 200 1 10 displacement [mm] 100 Displacement[μm](a) photo image (b) particle compression (c) close-up of test elastic behavior Characteristics of PSG granules
  27. 27. Applications•Hard metal cutting tool manufacturingand other PM materials•Ceramic and other materials•Pharmaceutical agglomeration andDPI (dry powder inhalation) etc.
  28. 28. feed compositions powd. dp(WC) WC Co wax* x10-6m %wt %wt %wt 1 1.5 93.0 7.0 0.5 2 6.0 85.0 15.0 0.5 Powder 1 Powder 2 Powder 3 3 9.0 77.0 23.0 0.5 dp(cobalt)=1.3-1.5x10-6m *) Tmp(wax)=330K preparation: 1. grinding 2.5hr 2. vacuum drying PSG:Agglomerate 1 Agglomerate 2 Agglomerate 3 Dt=44mm charge=150g u0=0.548 m/s Hard Metal Application P(TANK)=0.157 MPa SEM images of feeds and product granules total cylces=64 Nishii et al., JJSocPPM(1994)
  29. 29. Transverse rupture strength [N/mm2] PSG method PSG method convent- ional method Co content [wt%] Co content [wt%]Application to hard metal industry (Nishii et al., JJSPPM(1994)) Improved strength of sintered bodies
  30. 30. 500mm L : E=1 : 1 500mm Co-agglomeration L : E=0 : 1 of lactose and ethensamide CH2OH O H O H C-NH2 CH2OH H OH H OCHCH3 2 OH O O OH H H OH OH H H H H OH ・H2O10mm 10mm Lactose Ethenzamide
  31. 31. 100Concentration of Ethenzamide 1000mm Granule Sample : 10mg in Product Granules [%] 80 500mm 60 250mm 40 UV 20 absorbance: 300nm 0 0 20 40 60 80 100 Average Mass Concentration of Ethenzamide in Feed [%] Chemical Uniformity of PSG granules
  32. 32. Size Determining Mechanismin Agglomerating Fluidization 2.1 Background 2.2 Potential of Binderless granulation 2.3 Size Determining Mechanism in Agglomerating Fluidization
  33. 33. difference, P difference, P B D B’ C’ D’ C A A’ pressure pressure E’ mf,a u superficial gas velocity, u0 superficial gas velocity, u0 A B C A B’ C’ D’ E’ Dleft: a completely uniform and rigid bed; right: a realistic bed A thought experiment of fluidization of cohesive powders
  34. 34. Comparison of previous model concepts Authors Model External force/energy Cohesion force/energy Comments FGa Fpp Chaouki [ ] FGa = Fpp No bubble FGa = p d a3 hwd p hw et al. Fpp = 2 1+ 8 2 3 hydrodynamic r ag 6 16 p effects included. Force balance Hr van der Waals force gravity force ≒drag force between primary particles No bubble v=u mf Etotal =(Ekin+Elam ) Esplit hydrodynamic Etotal=(Ekin+Elam ) h w (1- a)d a2 Morooka Elaminer =3pmu mfd a2 Esplit = effects included. =Esplit shear 322 If 3m umf <hw (1-a) et al. Ekinetic =mu mf 2/2 Etotal  ad p /(32pd p  a), Energy balance energy required to negative d a is laminar shear + kinetic force break an agglomerate obtained. expansion Fcoh,rup Fexp = Fcoh,rup exp = - Ps Bed expansion force caused by p Db rag(-Ps)d a2 Had a(1- a) bubble Fexp = Fcoh,rup = bubbles isIwadate-Horio 2n k 242 equated with Force balance cohesive rupture force. bed expansion force cohesive rupture force
  35. 35. 4 4 expansion expansion 3 2Ps 3 Ps Ps 2Ps rp(1-)gD b rp(1-)gDb 2 2 Ps =-1/4=2p/3 -1/2 =0.639p -1/4 bubble A 1 -3/4 -1/8 1 -1/2 -1/8 2,000 -3/4 Ps = -1/20 b -1 -1/20 -0.843 a c 0 0 -4 dp/dz=1.31×10 [Pa/m] b 0 1,500 b 0 3/2 1,306z/R 1/20 z/R -1 -1 P[Pa] 5/4 1/20 5/4 1 1,000 gas pressure 3/4 1 1/2 1/8 1/8 3 -2 1/2 3/4 -2 1/4 dp/dt=-5.44×10 [Pa/s] 1/4 500 particle pressure -3 -3 d compaction compaction -4 -4 0 0 1 2 3 4 0 1 2 3 4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 x/Rb x/Rb time[s] (a) two dimensional bed (b) three dimensional bedFig. 17 Normal stress distribution around a bubble; left: theoretical predictionfor 2D and 3D single isolated bubble; right: experimentalverification (Horio, Sugaya and Iwadate. (1998)) Particle pressure around a Davidson’s bubble
  36. 36. agglomerating fluidization unstable point The critical condition 1E-4 stable point B Hada(1- a) 1E-5 Fcoh,rup= 24 2 A C log F[N] 1E-6log F[N] saddle point 1E-7 fluidized 1E-8 pDbra g da2  is reduced to Fexp= 2 nk 1E-9 modify Fexp 3E-5 1E-4 3E-4 1E-10 1E-6 3E-6 1E-5 3E-5 1E-4 3E-4 1E-3 3E-3 3E-6 1E-5 1E-3 3E-3 log d a[m] log d [m] a Ps* defluidization ( u0=umfa) (a) Force balance and two solutions (b) Critical agglomerate size Force balance to determine agglomerate size I-H model (Powder Technol., 1998)
  37. 37. Two difficulties in I-H model 1. particle-particle attraction force ? 2. agglomerates grow while bubbles are absent ? 4 expansion agglomerating 3 fluidization unstable point The critical condition 2Ps Ps rp(1-)gDb 1E-4 2 stable point B  1E-5=0.639p -1/4 Fcoh,rup H ad a(1- a) = 1 -1/2 -1/8 24  e2 A C  da 1 E-6 log F[N] forc log F[N] -3/4 Ps = -1/20 ture F coh,ru p -0.843 rup on 1 E-7 0 esi e fluidized saddle point coh rc b 0 2 fo on da 1 E-8 3/2 ns i  pDbra g d a2   is reduced toz/R -1 1/20 pa Fexp= p ex F ex modify Fexp 1 E-9 5/4 - 2- nk - 1 1/2 5 - - 1 - - 3 - 1/8 3/4 -2 1/4 3 -6 E 15 E- 3E5 3E-5 1 -4 E4 E 3E4 3E-4 1 E-3 3E-3 1 10 E- 1E6 1E-6 3E6 3E-6 1 E-5 3 -5 E5 E 1 -4 E4 E 3E E-4 1 E3 E-3 3E-3 log d a[m] log d a[m] Ps* defluidization ( u0=umfa) -3 compaction (a) Force balance and two solutions (b) Critical agglomerate size -4 0 1 2 3 4 x/R b ( b) three dimensional bed
  38. 38. 3 Ff 2.5 Load [mPa] 2 1.5 Grain compression test and 1 0.5 typical force displacement 0 0 50 100 150 Displacement [mm] 200 responses(a) Example of fr actur e tensile str ength mesur ement A : Elastic and plastic deformation Ff B : Elastic brittle fracture Ff CCD C :Plastic deformation Ff Then,particle-to-particle cohesion force was (b) Types of mesur ements determined by Rumph Eq.
  39. 39. 1E-3 1E-3 No. 4 No. 5 F exp 1.4E-3 1 1E-4 1E-4 F exp = F coh,rup F coh,rup Lactose F[N] F[N] 77 1.2E-3 1 .05 2 = 1E-5 1E-5 ZnO .15 al =0 al =0 L:E=7:3 ti c ti c cri 1E-6 1E-6 1E-3 cri   dobs=677mm dobs=788mm L:E=1:1 dcalc=621mm dcalc=723mm [m] 1E-7 1E-7 1 10 100 1000 10000 1 10 100 1000 10000 L:E=3:7 a,calc d a [ m m] d a [ m m] 8E-4 1E-3 1E-3 No. 6 No. 7 6E-4 d 1E-4 F exp F exp F coh,rup 1E-4 F coh,rupF[N] 1 1 = = 4E-4 08 F[N] 1E-5 2 .08 .15 1E-5 al =0 al =0 ti c ti c 1E-6 2E-4 cri 1E-6 cri   dobs=607mm dobs=373mm dcalc=726mm dcalc=667mm 1E-7 1 10 100 1000 10000 1E-7 d a [ m m] 1 10 100 d a [ m m] 1000 10000 0E+0 0E+0 4E-4 8E-4 1.2E-3 2E-4 d a,obs [m] 1E-3 6E-4 1.4E-3 Comparison of model predictions with observed data Agglomerate size determination by I-H Fig. 13 Agglomerate size determination (PSG:2hr, pre-sieving by 16mesh) model (Takano et al. Powd. Tech.,accepted,2001; Lactose; PSG:2hrs, presieving by 16 mesh)
  40. 40. 500Median diameter [10-6m] Median diameter [10- 600 Median diameter [10- adsorption at: 293K, 293K, p(adsorbate): 4kPa 4kPa 400 500 No effect: desorbed during PSG 6m] 6m] 300 400 0 3 6 9 12 0 3 6 9 12 Notes: At 573K all Absorption time [h] Absorption time [h] hydroxyl groups Median diameter [10-6m] 500 on TiO2 are 500 eliminated 573K, 573K, (Morimoto, et al., 13.3kPa 13.3kPa Bull. Chem. Soc. 400 JPN, 21, 41(1988). 400 Highest heat of immersion at 573K 300 (Wade & No effect ?? Hackerman, Adv. Chem. Ser., 43, 222, 200 300 (1964)) 0 3 6 9 12 0 3 6 9 12 Absorption time Absorption time [h] (a) C2H5OH [h] (b) NH4OH heat treatment:at p<13.3Pa 523K, for 6 hrs adsorption: bed= f150x10mm Further possibility of size modification of PSG in a 0.03m3 vacuum dryer granules (from TiO2 (0.27x10 m) ) by heat and -6 PSG: charge=0.0333 kg surface treatment 50% u0=0.55 m/s RH: 40- fluidiz.:15 s comp.: 1 s Nishii & Horio (Fluidization VIII, 1996) total cycles=450
  41. 41. 3. Further discussions on the size determining mechanism 3.1 DEM simulation 3.2 Comparison of Major Forces in the context of I-H model 3.2.1 A case study on ZnO 3.2.2 Ash agglomeration in FBC 3.2.3 Additional remarks
  42. 42. The DEM simulation stands in between the two-fluid model (TFM) andthe direct Navier-Stokes simulation (DNS). DEM takes care of all distinctparticles and collisions. In the TFM particles are treated as a continuumhaving a constitutive characteristics, which is derived based on stochasticmechanics. In the DNS each particle should be surrounded by quite a fewfiner grids to simulate fluid motion, as precisely as the particle scale, basedon the first principle.Initiated by Candall and Struck (1979) DEM is now widely utilized inmany researchers of particulate materials. However, the concept ofDEM was applied to fluidized bed only recently by Tshuji et al. (1993).Since it has been the authors belief that a simulation model has to beable to deal with trouble making phenomena such as agglomeration,where particle deformation may be maintained by bond formation, thesoft sphere model that allows multiple collisions and agglomerateformation with reasonable complication was thought to be the right wayto go.We have been developing models to take care of realistic situations inchemical engineering. We also organized a research consortium with R-Flow corporation, a software company in Japan, for a three year project(1997-2000) to study the industrial needs and theoretical investigation.Now we can be sure about the present limitation of DEM.
  43. 43. COMBUSTION Spray Agglomerating AGGLOMERATION Granulation/Coating Fluidization FB w/ Immersed Ash Tubes : Melting FB of Particles w/Pressure Effect I-H Solid Bridging van der Waals Rong-Horio 1998 Tangential 2000 FB w/ Interaction Kuwagi-Horio Lubrication Immersed Iwadate-Horio Effect 1999Coal/Waste Tubes 1998 Kuwagi-HorioCombustion Parmanently Rong-Horio 2000 in FBC Wet FB 1999 Mikami,Kamiya, SAFIRE Horio DEM forAgglomerating FBs 1998 Particle-Particle Mikami-Horio 1996 Single Char Heat Transfer Dry-Noncohesive Bed Combustion Rong-Horio Tsuji et al. 1993 Natural Phenomena in FBC 1999 Rong-Horio OTHER 1999 Olefine Scaling Law Polymerization Structure of for DEM PP, PE Emulsion Phase Computation Low Reynolds Kajikawa-Horio Simulation Kaneko et al. 1999 Kajikawa-Horio 2000~ 2001 Catalytic Reactions LARGE SCALECHEMICAL REACTIONS FUNDAMENTAL SIMULATION
  44. 44. dp=100mm, rp=3700kg/m3 u0=0.1m/s, Ha=1.0×10-19J0.411s 0.430s 0.450s 0.469s 0.489s High particle normal stress right below a bubble (Kuwagi-Horio(2001))
  45. 45. dp=100mm, rp=3700kg/m3 u0=0.1m/s, Ha=1.0×10-19J 0.460s 0.462s 0.464s 0.467s 0.469s 0.472s 0.474sClose look at agglomerates (blue ones) in the region above a bubble
  46. 46. Agglomerate: Fcoh>Frep, max Collision: Fcoh<Frep, max *Non-cohesive Ha=0.4x10-19J Ha=1.0x10-19J Ha=2.0x10-19J Kuwagi-Horio(2001) Numerically determined agglomerates
  47. 47. High voltage DC power source (0-9kV) 100 static bed height: 200mm fluidizing velocity: 0.4m/s Filter % collection [wt%] 80 voltage: ±0~9kV fluidization time: 5min 175 60 Ground electrodeAluminiumelectrode 40 entrained Positive electrode particles 150 10 20 Bag filter 200 490mm 0 0 2 4 6 8 10 )( )( Positive voltage [kV] 2D Fluidized bed(a) Appaaratus (b) Results for ZnO agglomerate entrained from the bed (dp=0.78mm, da=337mm)Fig. 22 qa=2.310-15C for a 50mm granule, and 1.610-11C/kg Determination of particle charge by parallel electrode method
  48. 48. r1 From Kelvin’s theory r2 r2=[-3+(9+8brp)]/2b rp b=(RTrL/M)ln(1/RH)For primary particles: Flb,pp=pr2(1+r2/r1)For agglomerates:Flb,aa=pr2a(1+r2a/r1a) r1a r2a ra Liquid bridge force
  49. 49. mm, ZnO 0.57 u0=0.351m/s, column diam.=0.3m 0.1 1E-3 F FvW (with deformation) exp 1E-5 FvW0 Force [N] 1E-7 1E-9 Fgravity 1E-11 Fcapillary;RH=0.6 1E-13 Fstatic electric. 1E-15 1E-17 1E-6 1E-5 1E-4 1E-3 0.01 da [m]Force comparison for ZnO
  50. 50. Liquid bridge curvature from bridge volume VLVL/(pda3)=1.5(r1a/ra)2[1- (r1a/ra)(1+2/ (r1a/ra))1/2sin-1[1/(1+ (r1a/ra))] Karita PFBC 10bar 870C sinter grain: a=0.2 bed height: 3.3m bed width: 11.3m =0.35 N/m (Novok et al. (1995)), =0.0515
  51. 51. T=870 ーC, d p  =900 mm, Surface tension=0.4N/m, Ha=1410-20 J/ Db,p=10atm 10 0.1 Db,p=1atmForce [N], Db [m] 1E-3 Flb,pp 1E-5 Flb,a 1E-7 FvdW 1E-9 1E-11 FG Fexp,p=10atm 1E-13 Fexp,p=1atm 1E-15 1E-17 1E-6 1E-5 1E-4 1E-3 0.01 Solids size [m] Force comparison for a PFBC/AFBC conditions
  52. 52. 2D DEM results: dp=200mm, T=1273K, u0=0.26m/s3 micro contact points smooth surface 9 micro contact points Case of Metal Sintering steel shots deposit growth vs. surface roughness Kuwagi-Horio 2000
  53. 53. CONCLUDING REMARKS1. Secrets of Fluidization have been unveiled almost by the 60 yrsendeavor and fluidization should now be no more a riskytechnology.2. We are coming close to the comprehensive knowledge offluidization: Bubbling, turbulent, fast to pneumatic; Adhesioneffects and agglomerating fluidization; Scaling law and Numericalsimulation.3. More challenge to invent a new reactor concept that provides alonger but uniform gas species residence time and equal eventsfor all particles.4. Challenge for materials process developments based on thethermal uniformity of fluidized beds, but guaranteeing theuniformity of events for individual particles in the mass. Thedevelopment should be from its beginning.5. More emphasis on education / continuing education needed; inaddition to fundamental research and high-tech developments,social/everyday applications should be encouraged.
  54. 54. DEM: problems to be Solved The problems of DEM in view of its future application to real large scalecomputation are coming out from its essential intermediate naturebetween TFM and DNS. At this moment millions of particles of uniformsizes can be dealt with a fast machine by say a week of computation but ifwe are simulating a bed of f2m and 4m high containing say 1mm particleswe have roughly 10 billion particles. Accordingly, it is necessary to inventa new method that allows us to bypass the tedious collision computations.Another difficulty is relevant to how to overcome the assumption ofuniform particles. If we introduce particle size distribution, we are forcedto do 3D computation although 3D computation itself was already done byMikami (1998). In the computation of distributed particle size systems,however, we are facing the limitation of the simple fluid cell treatment andtend to introduce subgrids to take care, for instance, the segregation ofparticles in a cell, small particle motion around a large article surface etc.The third difficulty originates from the present formulation of collisionwith the assumption of spherical smooth surface particles. The surfacecharacteristics are found very much significant even in our simple modelof surface roughness in iron particle sintering (Kuwagi et al. (1999)). Morerealistic look into the collision, lubrication and friction phenomena isneeded.
  55. 55. REMAINING MOUNTAINS IN DEM SIMULATIONCollision formulation: particle shape, surface roughness, plasticdeformation, attrition, lubrication force, attraction and repulsion forcesEffect of particle distribution in a gas cell: local clusteringeffect on pressure gradientParticle size distribution: shielding effect of particles in the up-stream; Local clustering and adhesionGas boundary layer and wake around a particle: Boundarylayer during a collision; Gas wake shedding behind a particle; Gas-gasreaction modeling; freeboard modelingParticle-to-particle heat transfer: Boundary layer modificationduring collision; transient effects etc.Long distance interaction forces: Collision and static electricitycharging;Large scale computation: minimum 100million particlesRealistic process modeling: heat & mass transfer, erosion,attrition, agglomeration, gas-solid reaction, gas-gas reaction

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