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Technische Universität Hamburg-Harburg Institute of Solids Process Engineering and Particle Technology Fluidization - Fundamentals and Applications - A Tutorial Joachim Werther Institute of Solids Engineering and Particle Technology Hamburg University of Technology D 21071 Hamburg, Germany 5th World Congress on Particle Technology, April 23-27, 2006 Orlando, Florida, USA

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  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

    Fluidization- Fundamentals and Applications -

    A TutorialJoachim Werther

    Institute of Solids Engineering and Particle TechnologyHamburg University of Technology

    D 21071 Hamburg, Germany

    5th World Congress on Particle Technology, April 23-27, 2006Orlando, Florida, USA

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

    2

    Contents1. Introduction

    1.1 Definitions1.2 Forms of fluidized beds1.3 Advantages and disadvantages of the fluidized bed as a reactor1.4 Comparison of the fluidized bed reactor with other types of gas-

    solid reactors2. Typical fluidized bed applications

    2.1 Historical development of the fluidization technique2.2. Technical applications of the fluidized bed

    2.21 Physical processes2.2.11 Mechanical processes2.2.12 Processes with heat and mass transfer

    2.22 Chemical processes2.2.21 Heterogeneous catalytic reactions2.2.22 Polymerizations reactions2.2.23 Solids as heat carriers2.2.24 Processes with reacting solids

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

    3

    3. Fluid-mechanical principles3.1 Minimum fluidization velocity

    3.11 Experimental determination of the minimum fluidization velocity3.12 Prediction of the minimum fluidization velocity

    3.2 Fluidization properties of typical solids (Geldarts classification)3.3. The state diagram of fluidized beds according to Reh3.4 Gas distribution

    3.4.1 Devices for gas distribution3.4.2 Minimum pressure drop3.4.3 Design of perforated plates

    4. Local fluid mechanics of gas-solid fluidization4.1 Isolated bubbles in fluidized beds4.2 Bubble coalescence and splitting

    5. Circulating fluidized beds5.1 Fluid mechanical characteristics5.2 Design characteristics

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    6. Entrainment6.1 Mechanisms6.2 Definitions and correlations

    7. Solids mixing in fluidized beds7.1 Mechanisms7.2 Solids dispersion coefficients

    8. Literature

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

    5

    What is fluidization?

    Definition:A fixed bed may be brought into a liquid-like (fluidized) state by an upward flowing fluid once the flow exceeds a minimum value. In the fluidized state the fluid experiences a pressure drop which is equal to the weight of the particle bed minus its buoyancy divided by the beds cross-sectional area.

    At = cross-sectional area of column = voidage of the bed

    t s ffb

    t

    A H (1- ) ( ) gp A

    =

    p

    p

    V.

    pfb

    V.

    Packed bed Fluidized bed

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

    6

    Forms of gas-solid fluidized beds

    state of minimumfluidization

    bubblingfluidized bed

    circulatingfluidized bed

    turbulentfluidization

    slugging fluidized bed

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

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    Some properties of the fluidized bed

    specific lighter objects are floating on the bed surface

    upon tilting a horizontal adjustment of the bed surface occurs

    through a hole in the wall the bed will flow out like a liquid

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

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    Advantages and disadvantages of gas-solid fluidized beds

    Advantages:- intense solids mixing by rising bubbles causes uniform temperature

    distribution, even with highly exothermal reactions no hot spots- large transfer area between gas and solids- excellent heat transfer between fluidized bed and walls or internals- liquid-like behavior of fluidized bed makes solids handling easy

    Disadvantages:- existence of bubbles causes bypass of reactant gas- intense solids mixing causes backmixing of reactant gas- intense movement of particles is responsible for particle attrition

    ( catalyst costs) and erosion of walls and bed internals- scale-up of fluidized bed processes is more difficult than for fixed beds

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

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    Comparison of gas-solid reaction systems

    Fine (0.02-0.5mm), with narrow particle-size distribution

    Broad particle-size distribution (ca. 0.02-6mm); high fines content acceptable

    Medium size (ca. 2-6mm) and uniform; no fines

    Large pellets (ca. 8-20mm), as uniform as possible; no fines

    Particle size

    Properties intermediate between fluidized bed and moving bed

    Very efficient exchange, good heat transport by solids

    Poor heat exchange; due to high heat capacity of solids transport of large quantities of heat by way of circulating solids

    Poor heat exchange; heat transport limits scale-up

    Heat supply and removal, heat exchange

    Axial temperature gradients can be held within limits by high solids circulation

    High solids mixing ensures uniform temperature distribution in bed; temperature control by heat exchangers immersed in bed or by admission and removal of solids

    Temperature gradients can be held within limits by virtue of high solids circulation and high gas throughput

    Danger of hot spots with exothermic reactions

    Temperature distribution

    Possible for fast reactions; recycle of unreacted fines often difficult

    No special requirements for feed particle-size distribution; high fines content also possible; continuous operation yields uniform product

    For uniform feed particle size with low fines content; large reactor capacities possible

    Unsuitable for continuous processes; batchwise operation yields nonuniformproduct

    Suitability for gas-solid reactions

    Gas in virtually plug flow; high conversion possible

    Backmixing of gas due to mixing motion of solids and bubble-gas bypass lead to lower conversion

    Plug flow gas ensures high gas conversion

    Catalyst attrition may be critical, depending on operating conditionsCatalyst attrition negligible

    can also be used with catalyst that is rapidly deactivatedonly for catalyst that is deactivated very slowly

    Suitability for heterogeneous catalytic gas-phase reactions

    Entrained flowFluidized bedMoving bedFixed bedCharacteristics

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidized bed - applications

    The first patent was issued in 1922 to BASF in Germany for a fluidized-bed gasifier for lignite.Inventor: Fritz Winkler

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

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    Winklers gasifier

    airoxygen

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

    and Particle Technology

    12

    FCCFluid Catalytic Cracking - the most successful fluid bed process

    The problem: carbon deposition from cracking deactivates catalyst

    The solution: cycling a fluidized catalyst between reactor and regenerator, use hot regenerated catalyst as heat carrier for supplying heat to endothermalcracking reaction.

    1940 development work by Essoand MIT

    1942 13,000 barrels/day plant in Baton Rouge

    C CH H

    H HC CH H

    H HC CH H

    H HCH

    H

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Reactor: oil vapors react in presence of catalyst

    Regenerator: coke is burned off to regenerate the catalyst

    FCC process: Kellogg-Orthoflow system

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    The riser cracking process: the UOP system

    reactor

    stripper regenerator

    air gridriser

    slidevalve

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidization technology: physical processes

    air slide conveyorfor the transport of solids

    elutriatorfines are elutriated fromcoarse particle fluidized bed

    solid-liquid suspension

    classification watercoarse

    fluidized bed

    fines

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidization technology: processes with heat and mass transfer

    fluidized bed cooler

    for alumina particles

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidization technology: processes with heat and mass transfer

    fluidized-bed drying fluidized-bed spray granulationSprhflssigkeit

    gas gas

    product product

    solution

    solution

    bottom spray top spray

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidization technology: processes with heat and mass transfer

    Coating of glass beads with paraffin in the supercritical fluidized bed

    fluidizing medium: CO2fluidized bed 80 bar, 40C

    supercritical solution before

    expansion: 160bar, 70C

    20 m

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidized bed chemical processes solid is a catalyst

    Example 1: Phtalic anhydride from naphtalene (Badger/Sherwin-Williams process)

    problem:highly exothermal reaction,explosion risk limits inletconcentration with fixed bed reactors

    solution:-naphtalin is injected in the liquid form mixing occurs in the fluidized bed, no explosion possible, no separate evaporator-temperature homogeneity avoids hot spots-in-bed heat exchanger extracts heat of reaction

    naphtalene

    product gas

    filter

    steam

    air

    Dowtherm

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidized bed chemical processes solid is a catalyst

    3 6 3 2 2 23C H NH O CH CH CN 3H O2

    + + = +

    Example 2: Synthesis of acrylonitrile(Sohio process)Ammoxidation of propylene

    - precise adjustment of reaction temperature leads to optimum yield

    - mixing of reactants inside the fluidized bed avoids risk of explosion

    - steam raising via in-bed heat exchanger tubes

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidized-bed chemical processes solid is the product in a catalytic process

    reactor

    cooler

    catalyst

    separator

    compressor

    Gas-phase polymerization of ethylene (Unipol process)

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidized-bed chemical processes: solid particles act as heat carriers

    Fluid Coking Process

    for the thermal cracking of heavy residues,

    cracking leads to coke

    deposition on bed particles (petroleum coke)

    coke is partially burned and heated in the heater hot, particles supply heat to the reactor

    a) Slurry recycle; b) Stripper; c) Scrubber;d) Reactor; e) Heater; f) Quench elutriator

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluidized-bed chemical processes: solid particles are reactants

    Calcination of aluminiumhydroxide (Lurgi process)

    - endothermal reaction- countercurrent flow

    of gas and solids through the process saves energy

    a) Venturi fluidized bedb) Cyclonec) Fluidized-bed furnaced) Fluidized-bed coolere) Recycle cyclonef) Electrostatic precipitator

  • - low NOx by staged combustion

    - in-situ desulphurization with limestone dosing:CaCO3 CaO + CO2CaO + SO2 + 1/2O2CaSO4

    Coal combustion in the (circulating) fluidized bed

    a) Circulating fluidized-bed reactor

    b) Recycle cyclonec) Siphond) Fluidized-bed heat

    exchangere) Convective passf) Dust filterg) Turbineh) Stack

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Fluid-mechanical principles the minimum fluidization velocity

    Measurement in the laboratory:

    At : cross-sectionalarea of column

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    0

    250

    0 300

    p

    u

    Minimum fluidization velocity evaluation of measurement

    - segregation occurs around umf avoid measuring here!

    - just take measurements in the fully fluidized state and in the fixed bed state

    - umf is then determined by extrapolation

    - a reproducible fixed bed is obtained by shutting the gas supply suddenly off in the fully fluidized state

    pfb

    umf

    pfb

    bed +distributor

    bed

    distributor

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Minimum fluidizing velocity - calculation

    fluidized bed pressure drop: pfb(uumf) = (1-)(s-f)gHfixed bed pressure drop: pfix(uumf) = function of u, dp, , gas conditions

    (e.g. Erguns equation)

    umf from pfb = pfix (u=umf)Good approximation: Remf=33.7 {(1+3.610-5Ar)0.5-1} (Wen + Yu, 1966)

    If a sample of the bed solids is available, the following procedure is recommended:

    1. Measure umf with air under ambient conditions in the lab2. Calculate the Sauter diameter of the bed solids from Erguns equation3. Convert umf (air, ambient conditions) to umf (gas at process

    conditions) by using Erguns equation (Werther, Chem.-Ing.-Techn., 1976)

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Minimum fluidization velocity Calculation of umf under process conditions

    Measured and calculated minimum fluidization velocities as function of pressure and temperature. (Measurements by Knowlton, 1974 with nitrogen (T=293K) and by Janssen, 1973 with air (p= 1bar)).

    Comparison between measured and calculated minimum fluidization velocities for different gases (Measurements by Singh, Rigby and Callcott, 1973).

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Geldart (1973): The existence of types of powders with characteristic behaviors

    Group C:fine, cohesive materials, difficult to fluidize, particles are sticking to each other, rat holes are formed, mechanically stirring of the bed may be needed

    Group A:typical is FCC catalyst, good fluidization, above umf first homogeneous fluidization which breaks down at umb, upon shutting off the gas supply the bed is slowly collapsing.

    Group B:typical is sand of 0.1-0.3mm, bubbling occurs immediately above umf, upon shutting off the gas supply the bed is rapidly collapsing.Group D: large particles, typical are wheat grains, formation of very large bubbles.

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    purpose:to characterize the state of fluidization for a given system by an (average) voidage

    abscissa:particle Reynolds number

    ordinate:

    auxiliary grid with

    Fluid-mechanical principles- Rehs status diagram

    pudRe

    =

    2f

    s f p

    3 uFr with Fr4 gd

    =

    3 3p s f f2

    f s f

    gd uAr , Mg

    = =

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Rehs status diagram

    - its backbone is the force balance on a single particle ( o)

    - the lines = const for gas-solid (bubbling, aggregative) fluidization are based on experiments

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Rehs status diagram

    may be used to locate different fluidized bed (and even fixed bed) processes

    a) Circulating fluidized bed

    b) Fluidized-Bed roaster

    c) Bubbling fluidized bed

    d) Shaft furnace

    e) Moving bed

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Rehs status diagram

    can answer a number of practical questions:

    - which voidage is expected for given solids (dp,s), gas (,,g) and gas velocity u? calculate Ar, Re status S

    - particles of which size will be elutriated? use M = const S1

    - if particle agglomeration occurs: for which size fluidization will break down? use M = const S2

    - find the minimum fluidization velocity use Ar = const S3

    - where is a (theoretical) upper limit of fluidization? use Ar = const S4

    S

    S1 S4

    S2

    S3

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    The role of the gas distributor in the fluidized bed

    The distributor shall- ensure uniform fluidization over the entire cross-section of the bed- provide complete fluidization of the bed without dead spots

    (where, for example, deposits can form)- maintain a constant pressure drop over long operation periods

    (outlet holes must not become clogged)- prevent solids from raining through the grid both during operation

    and after the bed has been shut off

    Distributor types:- porous plates in the laboratory- perforated plates, nozzles, bubble caps, spargers in technical units

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Gas distribution devices in large-scale fluidized bed combustors

    1 Nozzle7 bubble cap2-6 and 8combined types with mixed characteristics of bubble caps and nozzles,10 sparger9,11,12, special designs (after VGB_MerkblattM218 H)

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Gas distributor design

    distributor

    bed

    p 0.1 ... 0.3p

    Basic requirement:

    Design procedure:

    - (index o relates to conditions in orifice, drag coefficient CD from measurement)

    - with uo calculate number no of orifices from continuity

    2o d D 0p C u2

    =

    Problems with gas distributor:

    - open jets will cause attrition of bed solids- pressure fluctuations may cause backflow of solids into the windbox

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    37Local fluid mechanics: Bubble formation

    Gas-solid fluidized beds are characterized by the presence of bubbles bubbles are responsible for the temperature homogeneity of fluidized-bed reactors

    (bubbles are stirring the bed) and for the excellent heat transfer between bed and walls or intervals (bubbles account for surface renewal at the heat transfer surfaces)

    but: bubbles are also responsible for drawbacks of the fluidized-bed reactor:- bubbles cause a bypass of reaction gas which limits the conversion of a catalytic

    gas-phase reaction- bubble-induced solids movement leads to attrition of the bed particles and

    erosion of walls and internals the ultimate cause of bubble formation is the universal tendency of gas-solid flows

    to segregate.Stability theories (Jackson, Molerus etc.) indicate that disturbances induced in an initially homogenous gas-solid suspension do not decay but always lead to the formation of macroscopic voids

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    Local fluid mechanics: Gas flow in and around a rising bubble

    pressure outside bubble is higher than inside gas will flow into the bubble

    Davidsonss bubble model:

    streamlines of fluid (broken lines) and particles (solid lines) around a spherical bubble

    p

    h

    ( )( )s f mfdp 1 gdh = pressure insidebubble is constant

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Visualization of bubble fluid dynamics

    Injection of an NO2 bubble into an incipiently fluidized 2 D bedDavidson and Harrison, 1971)

    X-ray photo of a 3 D bubble(Rowc, 1971)

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    40Coalescence and splitting of bubbles

    Coalescence of bubbles from Toei et al. (1965)(X-ray photo anddimensionless correlation)

    Splitting of a single bubble (X-ray sequence, Rowe, 1971)

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    Calculation of bubble growth

    b

    v/

    bvud

    dhdd

    =

    392 31

    1/ 3b

    0.2v,o 20

    0

    0.008 porous plated

    industrial gas distributor withVm 1.3g V volumetric gas flow through a single orifice

    =

    =

    &&

    for Geldart group A and B solids (Hilligardt and Werther, 1987)

    dv = diameter of volume-equivalent sphere

    h = height above distributorb = bubble volume fractionub = bubble rise velocitycoalescence splitting

    = mean bubble lifetime

    mfu 280 (typically 0.05 ... 0.15 s)g

    =

    at h=h0:

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Gas jets in fluidized beds

    (after Karri and Werther, 2003)correlations suggested by Merry(1974):

    ( )

    0.3 0.2 2

    up f o o

    o s p p

    0.4 0.22phor o 0 f

    o s p s o

    L d u 5.2 1.3 1d d gd

    dL u 5.25 4.5d 1 gd d

    =

    =

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Circulating fluidized beds

    most important applications:catalytic cracking (FCC process) fluidized-bed combustion

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    Operating characteristics of FCC risers and CFB combustors

    1 %(1-10 %)

    mean solids volume concentration in upper dilute zone of riser

    approx. 20-40 sapprox. 4saverage solids residence time per single pass

    5-8 m/s>300 kg/m2s(external) solids circulation rate Gs

    5-8 m/sbetween 4.5 6 m/s

    (min. velocity at bottom) and 15-20 m/s (at riser exit)

    operating characteristics:superficial gas velocity

    approx. 0.2 mm broad size distribution

    approx. 0.06 mmbed particle size distribution:Sauter diameter dps

    membrane walls(vertical tubes/fins)

    flatwalls of riser

    20height-to-diameter ratio

    4-8m (hydraulic diameter)0.7 1.5 mriser diameter

    mostly rectangular or square

    circulargeometry:cross-section of riser

    CFB combustorFCC riser

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    CFB fluid mechanics

    Q3 = cumulative mass distribution, ut = single particle terminal velocity

    circulating fluidized beds are operated well above the single particlesterminal velocities!

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    CFB fluid mechanics

    CFB is characterized by very high slip velocity!

    cv,mf

    pneumatic conveying

    CFB bubbling (stationary) fluidized bed

    usl = slip velocityGs = solids circulation

    rate kg/m2s

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    CFB local fluid mechanics (combustion systems)

    Flensburg combustor 105 MWth, 100 % load, u = 6.3 m/ss = thickness of hydrodynamical boundary layer

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Pressure distribution in the CFB system

    a = fluidized bed, b = return leg

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    CFB: Design options for the pressure seal

    Siphon L-valve

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    Entrainment from fluidized beds

    - bubble eruptions shed particles into the freeboard

    - entrained particles disengage in the freeboard: coarser particles sink back into the bed, finer particles are elutriated

    - the disengagement process is finished after TDH(= transport disengaging height)

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    Calculation of entrainment

    the specific mass flow rate of solids leaving the CFB at the trop (above TDH) is

    xi = mass fraction of the (entrainable) particle size fraction in the bed material

    i* = elutriation rate constant for this size fraction, kg/m2sobtainable from various empirical correlations

    =i

    iis xG

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    52Estimation of TDH for FCC catalyst type particles

    (after Zenz and Othmer,1960; the parameter is the bed diameter)

    0,1 1

    0,1

    1

    10

    0.3 m7.5 m

    3 m

    1.5 m0.6 m

    0.15 m

    0.075 m

    D = 0.025 m

    t

    r

    a

    n

    s

    p

    o

    r

    t

    d

    i

    s

    e

    n

    g

    a

    g

    i

    n

    g

    h

    e

    i

    g

    h

    t

    T

    D

    H

    ,

    m

    U - Umf, m/s

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Solids mixing in fluidized beds

    Solids are displaced by rising bubbles

    particle drift effect causes

    particle mixing dispersion process

    Solids are carried upward in the wakes of rising bubbles

    convective transport

    The consequence: mixing in the vertical direction is much better than in thehorizontal direction!

    The mechanism:

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Solids circulation in fluidized beds

    radial distribution of the visible bubble flow

    bubble-induced solids circulation pattern

    (Werther, 1974)

  • Technische Universitt Hamburg-HarburgInstitute of Solids Process Engineering

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    Lateral solids mixing in a bubbling fluidized bed

    Measurements by Bellgardt and Werther (1986)

    Solid CO2 (dry ice) was injected through the side wall of the bed.Sublimation cooling led to a steady-state temperature distribution in the bed with a distinct temperature gradient in the horizontal direction

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    Vertical dispersion of solids in fine-particle fluidized beds

    better mixing with increasing fluidizing velocity and in beds of larger diameters horizontal dispersion coefficients are two orders of magnitude lower!

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    Heat transfer to internals / walls in fluidized beds

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    Bed-to-wall heat transfer depends on particle size

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    Maximum heat transfer coefficient as a function of particle size

    max decreases because heat capacity of small particles is rapidly exhausted

    heat conduction in the gas-filled gap between particle and wall is limiting

    gas convection is increasingly contributing

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    Literature:

    [1] D. Kunii and O. Levenspiel:Fluidization Engineering Second Edition.Butterworth-Heinemann, Boston 1991

    [2] J.R. Grace, A.A. Avidan, T.M. Knowlton (Eds): Circulating fluidized bedsBlackie Academic and Professional, London 1997

    [3] W.C. Yang (Ed.):Handbook of Fluidization and Fluid-Particle Systems.Marcel Dekker, New York 2003.

    The current state of the art is documented in the proceedings of three conference series:

    Fluidization (Engineering Foundation Conference, 11th was 2004)International Conference on Circulating Fluidized Beds (8th was 2005)Fluidized Bed Combustion Conference (18th was 2005)