Agenda Fluid Mixing in Biotech and Pharmaceutical Applications • Mixing Theory What is Fluid Mixing? • Process Design of Agitators • Blending and Motion, Solids Suspension, Gas Dispersion • A combination of two or more species Kevin Eisert, Senior Application • Impellers -- Types and Styles Engineer through mechanical means to • Computational Fluid Mixing Susan Sargeant, Market Manager • Agitator Basics produce a desired result BPE • Gearbox/Agitator Types Eric Janz, Director-R&D • A rotating agitator produces high • Mounting Styles and Seals velocity liquid streams which come • Mechanical Design of Shafts into contact with stagnant or slower • Information Needed for Specifying an Agitator • Troubleshooting moving liquid, therefore momentum • Invited Comment transfer occurs.
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Dimensionless Groups - Nomenclature Reynolds Number Dimensionless Groups • A measure of the ratio of inertial forces D = Impeller Diameter • Mathematical models obeying the (those produced by the agitator) to viscous T = Tank Diameter laws of conservation of mass and forces N = Impeller Rotational Speed 2 momentum yields a few significant •NRe = 10.7 N D Sg/: groups applicable to fluid motion Z = Liquid Level Height (: = cp, D = inches, N = rpm) • Will not derive the groups from the : = Fluid Viscosity • Affects: Navier-Stokes equation, rather they Sg = Fluid Specific Gravity • Power Draw of Impellers • Pumping Capacity of Impellers will be presented and significance C = Impeller Off Bottom Clearance • Static Mixer Design explained S = Impeller Spacing • Surface Deformation • Number of Impellers • Baffle Design 4 5 6
Power Number -vs- Reynolds Number Froude Number Power Number -- Np
• A measure of the ratio of Inertial to • Dependent upon type/design of impeller and Gravitational Forces fluid properties •N= f ( N , N ) •N = N2 D/g = 7.2 x 10-7 N2 D p Re Fr Fr • Oftentimes N is not an effect and for high (N = rpm, D = inches) Fr NRe (Low Viscosity) the power number is • Used in Gas Dispersion and Solids Draw constant Down Applications • Experiments at different speeds, impeller • In many applications, gravitational effects are diameters, and fluid properties shows: unimportant and the Froude Number is not P % N3 P % D5 P % Sg significant • The ratio of Power to N,D, & Sg is the Power Number: 3 5 Np % P/(N D Sg) 7 8 9
1 What Affects Power Draw? Power Draw Calculation Pumping Number -- N • Fluid Properties such as Viscosity and q Specific Gravity and (if present) Gas • Dependent upon type/design of impeller • Impeller Type, Diameter, Pitch, and Width Hp = 6. 556 x 10-14 N3 D5 Sg Np and fluid properties • Impeller Rotational Speed • Flow of impeller is proportional to N & D3 • Geometric Effects such as Baffles, Coils, Q % N D3 Liquid Level, Pump Inlets, and Agitator Where: Mounting • The ratio of these two quantities is the N = Impeller Speed, rpm Pumping Number, Nq • Proximity Effects such as Impeller D = Impeller Diameter, inches 3 Nq = Q/ND Diameter to Tank Diameter Ratio and Off- Sg = Fluid Specific Gravity Q = N D3 N Bottom Clearance Np = Impeller Power Number q • Plus others to a lesser extent (blade •Nq = f (NRe) thickness)
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Pumping Number -vs- Reynolds Number What Affects Pumping Rate? Pumping Rate Calculation
• Fluid Properties: Viscosity, Presence of Gas, Specific Gravity -3 3 • Impeller Properties: Type of Impeller, Q (gpm) = 4.33 x 10 N D Nq Pitch, Width, Diameter, Clearance, etc. • Rotational Speed • Geometric Affects: Tank Diameter, Liquid Where: Levels, Draft Tubes, Baffles, etc. N = Impeller Rotation Speed, rpm D = Impeller Diameter, inches Nq = Impeller Pumping Number
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Blend Time Blend Time Blend Time -- Turbulent Flow •Tb = F(NRe)
•tu = -ln (1-U)/k
Where: tu = Blend Time for “u” uniformity U = % uniformity k = Mixing Rate Constant, time –1 (See Advanced Liq. Agitation)
• k = a N (D/T)b (T/Z)0.5 Where: a = Impeller Constant b = Impeller Constant N = Impeller Speed, rpm
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2 Blend Time Blend Time What determines Agitator Size?
• For 99% Uniformity • Blend times for higher viscosity fluids (NRe below turbulent) are corrected from a N • In simple terms, the size of the t99 = 4.605/k Re -vs- blend time chart agitator gearbox is rated on “Torque” Degree of Uniformity Relative Blend Time • Torque is proportional to Hp and 90 0.50 • Ways to improve Blend Time Speed 95 0.65 • Do not start from “Stratified” state 99 1.00 • Introduce additions near impeller J % Hp/N 99.9 1.50 • Pre-blend with Static Mixers (High Viscosity,Sg, • J (in-lbs.) = 63,025 Hp/N and Volume Ratios) 99.99 2.00 99.999 2.50
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Torque Impellers Impeller Styles • 3 hp at 68 rpm Î 2,780 in-lbs. • 10 hp at 100 rpm Î 6,302 in-lbs. • Turbine Style Impellers • The 10 hp at 100 rpm, would be a size • Axial Flow (High Efficiency) “3” and the 3 hp at 68 rpm unit would be • Radial Flow (Straight Blade/Disc) a size “1” agitator • Close Clearance Impellers • Relative cost difference is about 40% • Helix/Anchor • For the same type impellers: • High Shear Higher Torque = Higher Flow = Higher • Rotor/Stator Cost
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High Efficiency Impeller Commercial Impellers HE-3 Impeller Flow • Liquid Blending, Solids Suspension, Heat Transfer, • Following Impellers Show types of Upper Impeller in Gas Dispersion Impellers • Low Shear, High Pumping, Axial Flow • Reynolds Numbers $100 • Examples of the impellers are from • Turbulent Np = 0.28 (0.26 - 0.30) Chemineer • For a given agitator, the appropriate HE impeller is 20 percent larger than a pitched blade • Other Manufacturers Manufacture • Jet Foil Impellers will adhere to similar characteristics similar impeller styles
HE-3 Impeller
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3 High Efficiency/Hydrofoil Impeller High Efficiency High Solidity Impeller Np = 0.85 (0.8 to 0.95) •Liquid Blending, Heat Transfer, Solids Suspension •Low Shear, Axial Flow, High Pumping • Wide Blade hydrofoil impeller, axial flow •Similar in performance to HE-3 • Applications which require a high solidity axial •Np = 0.55 (0.5 to 0.6) flow impeller: three-phase systems, gas •Curved design of blade/hub results in higher strength: dispersion, abrasive solids, transitional flow lower weight (100>Nre<2,000) •Design requires cast impeller hubs
SC-3 Impeller
Maxflo W
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Pitched Plade Impeller P-4 Impeller Flow Straight Blade Impeller • Liquid Blending, Heat Transfer, Solids Suspension • Straight Blade Impeller with four blades • Especially good for drawing a vortex or for • Liquid blending, keep outlets clear from solids, material drawdown solids drawdown, tickler@ impeller, immiscible • Mixed Axial/Radial Flow fluid blending • Typical: 4-Blades, W/D = 0.20, 45 degree • Reynolds Number >1 • Turbulent Np = 1.3 (1.15 - 1.45) • Turbulent Np = 2.88 • Reynolds Number >10 • Simple flat blade design is often economical
P-4 Impeller S-4 Impeller
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Rushton Turbine High Efficiency Gas Dispersion Impellers Gassed Power Draw Comparison
• 6-Bladed Disc Style Impeller • 6-Bladed Curved Disc Impeller • Gas dispersion at low and intermediate • Gas Dispersion at all gas rates gas rates, liquid-liquid dispersion • Fermentations, Liquid/Liquid Dispersions • Turbulent Np = 5.0 CD-6 BT-6 • Dated Technology
D-6 Impeller
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4 Helical Ribbon Mass Transfer Coefficient Anchor Impeller
0.3
BT-6 • Close Clearance Agitator • Close Clearance Agitator 0.25 • Typical D/T Range: 0.95 - 0.98 • Typical D/T range: 0.95 - 0.98 CD-6 0.2 • Viscous Liquids (> 100,000 cp) • Viscous Liquids (> 100,000 cp)
0.15 • Blending and Heat Transfer • Blending and Heat Transfer D-6 • Less efficient but more cost effective than 0.1 Helical Ribbon
Mass Transfer Coefficient (1/s) 0.05 • Less surface area for cleaning than Helical Ribbon 0 0 0.02 0.04 0.06 0.08 0.1 Superficial Gas Velocity (m/s)
3 Retrofit comparison kla at Pu/V = 2.2 kW/m
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Choosing Impellers Impeller Performance - Example •Flow Controlled Processes: High Pumping/Low Shear System Geometry and Impellers •Blending Miscible Fluids, Heat Transfer, Solids Susp. HE-3 •High Efficiency/Pitched Blade/High Solidity JF3 •Dispersion Processes SC-3 •Gas Dispersion, Immiscible Fluids Maxflo W ® Impeller System •Radial Flow Impellers P-4 •Combination: Lower Radial (Disk)/Upper Axial S-4 BT-6 ® Baffle Recommendations CD-6 D-6 Rotor/Stator Low Pumping/High Shear 40 41 42
Impeller Performance Geometry Impeller Design Options •Buffer Tanks, Blend Tanks, Heat Transfer, Solids Susp. • All welded impellers • Number of impellers depends on • Type of impeller • High Efficiency Impellers • Threaded/sealed impellers • Reactors: • Viscosity/Reynolds Number of fluid • High Efficiency Impellers • Bolted (acorn nuts) blades • Liquid Level to Tank Diameter Ratio (Z/T) • Gas Dispersion Impellers • Set Screws, Keys, other options available • Impeller Diameter/Tank Diameter (D/T Ratio): • Pitched Blade Impellers • Affects Power Number of Impeller • Helix (High Viscosity) • Large D/T ratios not advised for Solids Susp. • Solids Drawdown • Location • Pitched Blade Impellers • For low level mixing, “tickler” impeller used
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5 Baffles Recommended Baffling Impeller Equations •Primary Pumping Capacity • Baffles are used to prevent swirling in lower viscosity Reynolds • Q (gpm) = 4.33 x 10-3 N D3 Nq applications and promote Atop to bottom@ mixing. Number Baffles • Impeller Horsepower Draw • Baffled Tanks produce the best mixing results •P = 6.556 x 10-14 N3 D5 Sg Np NRe > 1,000 T/12 width, T/72 offset • Impeller Reynold’s Number 500 < NRe < 1,000 T/24 width • Baffling not required in angled or vertical off center mixing 2 •NRe = 10.7 N D Sg / : NRe < 500 None • In certain situations, special baffle configurations may be Where: N = Rotational Speed, rpm used. Examples include vortex induction, baffles with internal • Number and spacing dependent upon impeller types D = Impeller Diameter, inches Nq = Impeller Pumping Number fluid flow for heat transfer capability Np = Impeller Power Number Where: T = Tank Diameter Sg = Fluid Specific Gravity : = Fluid Viscosity, cp
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Impeller Summary Blending and Motion •Many different impeller styles available Mixing Classifications •Agitator design starts with impeller selection • Blending and Motion • Liquid in contact with another liquid •Need to match impeller performance with process requirements as impeller efficiency can affect agitation. • Solids Suspension •Examples: • Liquid – Liquid Reactions •High efficiency impellers can improve agitation for a • Gas Dispersion given torque by generating a more uniform, axial flow • Blending of Miscible Liquids pattern • Heat Transfer Improvement •Special impellers such as the BT-6 improve gas • Blending out Dissimilarities handling. • Low Solids Slurries (< 2% Solids) •Wide blade hydrofoils (Maxflo W) are very good in 3- phase flow and as pumping impellers above a gas dispersion impeller. 49 50 51
Blending and Motion Problem Magnitude Determining Process Requirements •Size •Size • Equivalent Volume • How much flow is needed for the • Difficulty process? •Veq = Volume Sg • Process Result/Dynamic Result • Difficulty • Specific Blend Times • Batch Times • Fluid Viscosity • Heat Transfer Requirements • Process Result/Dynamic Response • Components being mixed • Process Results are related to Flow Rate
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6 Determining Process Requirements Blending and Motion Design Determining Process Requirements
• It is difficult to state the process result • Fundamental Dynamic Response for • Bulk Fluid Velocity Calculation: with precision. Such as how do you Blending and Motion is: • Bulk Fluid Velocity relate flow rate and blend time to: 3 2 • Characteristic of all velocities in the agitated v (ft/min) = Q (ft /min) / A (ft ) • Design of a pH adjustment tank? fluid • A Chemical Reaction? where: • Design logic starts with the selection of v = Bulk Fluid Velocity • Blend two very dissimilar components? a “Dynamic Response” Q = Flow Rate • Design Agitators to produce that A = Cross Sectional Area of response Tank
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Blending and Motion MILD AGITATION Agitation levels 1 and 2 are Determining Process Requirements characteristic of applications requiring minimum fluid velocities to achieve the process result. Bulk Fluid ChemScale Scale of Bulk fluid • Experience has shown the majority of Velocity Level agitation velocity, ft/min Description Blending and Motion problems are Agitators capable of level 1-2 will: solved with Bulk Fluid Velocities of 6 to 6 – 60 ft/min 1 to 10 16 Blend miscible fluids to uniformity if the 60 ft/min • The lower the intensity level, the lower specific gravity differences are less than • It is then possible to assign “Agitation the characteristic velocity, the lower the 0.1. Intensity Levels” to these Velocities flow rate, and the smaller the Agitator Blend miscible fluids to uniformity if the viscosity of the most viscous is less than • Chemineer calls these levels • ChemScale Levels can be used to 212 “ChemScale” 100 times that of the other. describe Process Results in more detail, Establish complete fluid-batch control. which is called a Dynamic Response Produce a flat, but moving surface.
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MEDIUM AGITATION Agitation levels 3-6 characteristic of fluid VIGOROUS/VIOLENT Agitation levels 7-10 characteristic of velocity in most chemical process industries AGITATION applications requiring high fluid velocity Scale of Bulk fluid for the process result, such as critical Example agitation velocity, ft\min Description reactors Scale of Bulk fluid Application ChemScale Blend miscible fluids to uniformity if specific agitation velocity, ft/min Description Media Prep Tank 1-2 3 18 gravity differences are less than 0.3 (Scale 3) Blend miscible fluids to uniformity if Resin Prep Tank 1-2 and 0.6 (Scale 6) Sg differences are less than 0.7 (Scale 742 Buffer Prep Tank 1-2 424Blend miscible fluids to uniformity if the 7) or 1.0 (Scale 10). viscosity of the most viscous is less than Blend miscible fluids to uniformity if pH Adjustment 1-3 5,000 (Scale 3) or 10,000 (Scale 6) times that 848 the viscosity of the most viscous is Reactor 6-10 530of the other. less than 70,000 (Scale 7) or 100,000 (Scale 10) times that of the other. Blend Tanks 4-7 Suspend trace solids (<2%) with settling rates 954 Solids Dissolving 3-5 of 2 to 4 ft/min. Suspend trace solids (<2%) with 636 settling rates of 4 to 6 ft/min. Produce surface rippling at lower viscosities. Provide surging surfaces at low 10 60 viscosities. 61 62 63
7 Agitator Selection Blending and Motion Blending and Motion • Process involves • Solving Blending and Motion problems also • Pick Impeller Type • For a particular Hp/Speed Combination requires the selection of the optimum impeller • Determine Size and Difficulty (Torque Level) the final steps are: type • Determine Dynamic Response (ChemScale Level) • Choose Impeller Diameter to draw the • Impellers will produce a combination of flow • Charts will provide Hp/Speed Combinations defined hp and shear (or head) which when loaded properly will provide the • Check geometric parameters D/T, C/T, Z/T • For Blending and Motion, increasing flow and Flow to produce desired Bulk Fluid Velocity and hence Agitation Level desired • Check other process parameters (Blend decreasing shear is typically most desirable Time, Heat Transfer Rate, etc.) • High Efficiency Impellers are used most often • Mechanical Design (Gearbox, Shaft, Seal, etc.)
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Blending and Motion Evaluating Agitation Mixing Classifications • Last step is Economic Evaluation • Motor hp does not correlate directly to mixing performance • Blending and Motion • Capital Cost Estimation • Torque correlates better with mixing intensity • Solids Suspension • Operation Cost Estimation (Chemscale) • Optimization • Why? For low horsepower and low speed • Gas Dispersion combinations, a large impeller is utilized. Flow is • Luckily, the calculations are proportional to N D3. computerized and a process and • Torque relates to capital cost. Motor hp relates mechanical design can be done quickly to operating cost. Consider both when considering agitator purchase!
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Solids Suspension Solids Suspension Solids Suspension
• Liquid in contact with Solids • Solids suspension applications, like Blending • Design Procedure •Examples: and Motion problems, are “Flow Controlled” •Size • This leads us to use “Flow” impellers rather • Catalytic Media Suspension • Difficulty than “Shear” (or head) impellers • Solids Incorporation • Process/Dynamic Response • High Efficiency Impellers are used most often • Resin / Buffer / Media Prep tanks • High Efficiency Impellers also reduce particle (depending on specific process) shearing
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8 Solids Suspension Difficulty Parameter Process Result/Dynamic Response
•Size • Design Settling Rate: • There are (4) levels of Suspension f (TSR, )Sg, SgL Fw) • No Solids Motion •Veq = V Sgsl • Solids Motion on Bottom Where: TSR = Terminal Settling Rate • Complete Suspension )Sg = ) Specific Gravity between solids and liquid • Complete and Uniform Suspension Fw = Weight Percent of Solids
SgL = Specific gravity of Liquid
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Design Procedure Design Procedure Design Procedure 0.28 • Parameters which Change Answers (ρ −ρ ) • Particle Size & Shape • Calculate settling velocity from solids and N =k s l u . *f(X)*f(D/T)*(T/T )−n js [[ ] t] o • Larger particles have higher settling velocities liquid properties or measure experimentally ρl and require more torque to suspend • Calculate Njs (Just-Suspended Speed) Where: • Icicle-Like or unusual shapes increase difficulty based on TSR, Impeller, Geometry --D/T, k = Impeller Constant = Solids Density • Liquid Viscosity etc. Ds Dl = Liquid Density • Higher Viscosity hinders settling and makes • If N > Njs => Complete Suspension ut = Terminal Settling Velocity suspension easier f(X) = Solids Loading (%) factor • Calculate Cloud Height or % T0 = Reference Tank Diameter • Problem of Particle Size “Unsuspended” T = Actual Tank Diameter D = Impeller Diameter • Particle size distribution is important n = Scale up exponent information to design optimum unit
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Related Topics Solids Suspension Summary Mixing Classifications • Makedown: System Specific. May Need High Chemscale and Upper Pitched Blade • (3) Levels of mixing • Blending and Motion Impeller for Fine, Difficult to Wet Solids. • Solids Motion • Solids Suspension • Resuspension: Ranges from Easy to • Complete Suspension Impossible • Gas Dispersion • Uniform Suspension • Solid Particle Shearing: • Calculate N , Cloud Height • High Efficiency Impellers are best js • High Efficiency Impellers are used
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9 Gas Dispersion Gas Dispersion Design Procedure • Gas Dispersion applications, unlike Blending • Liquid in contact with Gas & Motion and Solids Suspension, are “Shear •Size •Examples: Controlled” • Difficulty • This leads us to use “Shear” (or head) • Aeration Tanks impellers • Process Result/Dynamic Response • Fermentation • Disc Impellers are most often used (high gas • BioReactors flow). • Flow impellers can be used in low gas flow applications • Flow impellers are used as upper impellers in Gas Dispersion Applications
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Gas Dispersion Flow Patterns Gas Dispersion Flow Patterns Gas Dispersion
•Size
•Veq = SgL V • Difficulty • Actual Gas Flow Rate • Process Result/Dynamic Response • Mass Transfer, kla • Break gas into smaller bubbles to increase surface area
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Flow Regime Map Gas Dispersion Flow Patterns Gas Dispersion
• In Turbulent Regime the Flow Pattern • For a “Completely Dispersed” flow depends on: pattern: 0.5 0.5 • Aeration Number NA,CD = CCD (D/T) (NFR) N = Q /ND3 A g where: CCD is impeller dependent N = 1728 ACFM/(N D3) A (0.2 for D-6 and 0.4 for CD-6) • Froude Number Increasing speed above this point will N = N2D/g Fr not change the flow pattern, but will N = 7.2 x 10-7 N2 D Fr improve gas hold-up and mass transfer
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10 Gas Dispersion -- Pg/Po Curve Gas Dispersion -- Pg/Po Curve Gas Dispersion
• Power Requirements • Power draw will drop when impeller is “gassed” • Typically referred to as: Pg/Po • Designing agitator for the “gassed” state will yield better results, but need to account for low or no gas situations • ACVF Drives
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Gas Dispersion -- Hold-Up
•Gas Hold-Up Design Procedure Design Procedure • As gas is dispersed, the liquid level will rise to varying degrees. Must account for this in vessel design • Typically an increase in hold-up signifies smaller gas • First step is to design the agitator so the • Determine specific Mass Transfer Rate bubbles, thereby increasing surface area, and increasing impeller is not “Flooded” mass transfer based on process A B • Above flooding, increasing the gas rate " = C "(Pg/Vl) (vg) • Calculate economical combination of will increase kla (mass transfer Where: " = Gas Hold-Up power consumption and gas rate to v = Superficial Gas Velocity coefficient): g satisfy the process demands C , A, B = Constants a " kla % (P /V) g • Optimization in pilot plant and then • Increased power input will increase mass transfer in the system scale-up is often times used
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Gas Dispersion -- Impellers Computational Fluid Dynamics • A lower Dispersion Impeller is commonly Gas Dispersion Summary used to disperse gas and this impeller is “Concave” • Choosing the correct impeller system to avoid • Using Concave impellers improves the kla “flooding” important becaue it pumps more than flat blade disks, which helps minimize “Coalescence” • Higher P/V levels improve performance • The gas is often introduced through a sparge • Impeller “Unloading” in gassed –vs- ring located directly under the impeller ungassed state needs to be accounted for • Recent designs include upper “Flow” • Gas Sparge System Design is important to impellers particularly in biological systems to: performance of gas dispersion system • Maintain more uniform dissolved-oxygen • Computational Fluid Design (CFD) can aid in concentrations which is important in fermenters agitator design • Provide excellent overall tank blending
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11 CFD: Setting Expectations Computational Fluid Dynamics How CFD will help you What To Expect What Not To Expect • The fluid flow domain is subdivided into a large number of computational cells. This is called the mesh • Trends • Replacement for • CFD predicts the flow field that rules the process. or grid. good engineering • Visualization • CFD predicts performance in meeting the intended • Solve the mathematical conservation equations for: judgement • Complements physical task: blending time, mixing time scales, heat transfer •mass modeling. • Complete coefficients, etc. • momentum • Comprehensive data not replacement for •energy easily obtainable from testing • Many different impeller styles can and have been • turbulence experimental tests. • Accurate results analyzed. •chemical species • Answers for “what if…?” require •Results: questions. • Detailed models • detailed flow and shear fields • Knowledge of your • temperature fields • Highlights the cause not problem • chemical concentrations and productivity just the effect. • Knowledge of limitations • local mass fractions of additional phases
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The CFD Process • Determine agitator design you want to simulate CFD
• Boundary conditions are experimentally established for impeller (LDV, DPIV) • 2-D runs use a k-, model to solve equations in turbulent flow • k = Kinetic Energy of Turbulence • , = Rate of Dissipation of Turbulence • Results will produce a time averaged flow profile
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12 Blending Simulation Why look at flow patterns? • Flow patterns influence •Blend time • Level of solids suspension • Overall inside heat transfer coefficients
• Distribution of dissolved O2 in fermentations • Suspension of solids in the tank heel • Selectivity in competitive/competitive consecutive reactions • Flow patterns can be affected by: • Impeller style • Impeller to tank diameter ratio • Relative off-bottom distance • Viscosity (Reynolds number) • Impeller spacing Animation
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S-4 Impeller, Turbulent Flow, P-4 Impeller, Turbulent Flow, Constant Torque, D/T=1/3 Constant Torque, D/T=1/3
Flow Patterns at Different Max. Velocity = 97 ft/min Max. Velocity = 128 ft/min Max. Velocity = 91 ft/min Max. Velocity = 110 ft/min Max. Velocity = 110 ft/min Max. Velocity = 110 ft/min Impeller Off Bottom Clearances
C/T= 0.18 C/T= 0.35 C/T= 0.53 C/T= 0.18 C/T= 0.35 C/T= 0.53
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HE-3 Impeller, Turbulent Flow, Observations at Different Summary Constant Torque, D/T=1/3 Impeller Off Bottom Clearances Flow patterns can be affected by: • Radial Flow Impeller: S-4 • Characteristic 2 cell system at all clearances • Impeller style Max. Velocity = 268 ft/min Max. Velocity = 299 ft/min Max. Velocity = 299 ft/min • Proportionally more flow to lower cell at • Impeller to tank diameter intermediate clearances ratio • Mixed Flow Impeller: P-4 • Relative off-bottom • Set up large lower cell at high clearances distance • Flow in lower cells fraction of upper • Axial Flow Impeller: HE-3 • Viscosity (Reynolds • Conical area below impeller grows with clearance number) • Flow pattern hits bottom even at high clearances • Impeller spacing C/T= 0.18 C/T= 0.35 C/T= 0.53
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13 CFD Conclusion Agitator Drives Basic Components Types • CFD can be used to analyze: B Built by Agitator Manufacturer • Laminar blending B Buy-Out with Modifications PAgitator Drive B Speed Reducer • Turbulent blending B Buy-Out PPrime Mover B Motor • Stirred tank flow patterns Configuration Drive Mount/Shaft Seal • Optimize impeller designs P B Right-Angle B Parallel/Inline • Laminar and turbulent flow static mixers PMixer Shaft PImpeller(s) B Portable/Clamp • Heat transfer Gearing • Mass transfer B Spiral Bevel • And many other mixing applications such B Helical as fluidized beds, bubble columns, etc B Other (worm, planetary, etc.)
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High Torque Gear Drives Medium Torque Gear Drives Low Torque Drive Typical Features
GT Drive HT Drive < Right Angle or Parallel < Up to 1,000 hp < 1 to 30 hp < Various Gearing Options < Spiral Bevel & < 11 to 155 rpm < 1/4 to 5 hp Helical Gearing < Helical Gearing < 350 rpm standard < Tailored to large < Adaptable to wide < Customized speeds available applications application ranges < Equivalent to Chemineer < FDA White or < FDA White or DT, RBT, BT Steel-It Paint Steel-It Paint
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Basic Components Prime Mover Basic Components
Electric Motor - • Gear Drive B Speed Reducer PGear Drive B Speed Reducer Foot Mounted / C-Face Mounted PPrime Mover B Motor • Prime Mover B Motor PDrive Mount/Shaft Seal TEFC / FCXP • Drive Mount/Shaft Seal PMixer Shaft Standard / Chemical / Washdown Duty • Mixer Shaft • Impeller(s) PImpeller(s) ACVF Drives B Variable Speed Air Motors Other Drives - Hydraulic, Engines, etc.
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14 Mounting Configurations THINGS TO CONSIDER ABOUT Agitator Seals
AGITATOR MOUNTING Mechanical Seals • Pedestal Mounted • Weight • Lip Seal (Low Pressure B 2 to 3 psi) • Types • Mechanical Seals • Torque • Single/Double • Single Seals B Up to 150 psi • Bending Moment • Lubricated/Dry Running • Double Seals B Maximum pressure range • Manufacturers • Flange Options • Seal Requirements • Flowserve • Ferrule (tri-clamp) • Entry Point of Shaft • John Crane • ANSI • Chesterton • DIN
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Agitator Seals Agitator Seals Basic Components Double Mechanical Seals Single Mechanical Seals • Single Mechanical Seals • Leak Path is into vessel • Gear Drive B Speed Reducer • Leak path is to the atmosphere • Lowest Leakage Rate • Prime Mover B Motor • Lower leakage rates than stuffing boxes • Chemineer uses a Aback to back@ • Suitable to 150 psi arrangement (Pressurized Cartridge) • Drive Mount/Shaft Seal • Typically Dry Running • Mixer Shaft • Carbon -vs- Tungsten Carbide/Viton/316ss • Often requires liquid lubrication • Optional Materials • Carbon -vs- Tungsten Carbide/Viton/316ss • Impeller(s) • Silicon Carbide/Kalrez/EPDM/Teflon/Higher Alloys • Options: Silicon Carbide/ Kalrez/ EPDM/ Teflon/ Alloys
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Shaft Design DESIGN FOR SHAFT DIAMETER ALLOWABLE SHAFT STRESS
• FOLLOW PROCESS/IMPELLER DESIGN SHEAR STRESS= 6,000 PSI SF (TWISTING) • Shaft Stresses (Shear/Tensile) • SELECT SHAFT LENGTH • Shaft Critical Speed TENSILE STRESS= 10,000 PSI SF • Materials of Construction • DETERMINE THE MINIMUM REQUIRED SHAFT (ELONGATION) DIAMETER FOR STRESSES
SF = STRESS FACTOR (MATERIAL • CALCULATE SHAFT CRITICAL SPEED AND TEMPERATURE DEPENDENT) 316ss = 1.0 • COMPARE CRITICAL SPEED RATIO TO 304ss = 0.95 ALLOWABLE VALUE C276 = 1.33 • ITERATIVE PROCESS
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15 SHAFT CRITICAL SPEED CRITICAL SPEED CALCULATION CRITICAL SPEED RULES CRITERIA 6 2 • Critical Speed 0.394 10 d F NON-STABILIZED IMPELLER M •rotation speed corresponding to a natural frequency N = ------______Pitched/Straight Blade 65% c of a shaft/impeller system L pW p (L + S ) High Efficiency 80% e b • First Critical Speed •Most Important We = Equivalent Weight STABILIZED IMPELLER L = Shaft Length • Agitator Designs Operating Below the first critical Pitched/Straight Blade 80% S = Bearing Spacing speed (lowest) are optimal Well Designed HE NOT REQUIRED b •Low torque designs can be designed to run > critical d. = Shaft Diameter
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Critical Speed Options Materials of Construction Shaft Couplings • Carbon Steel • Non-Sanitary • Increase Shaft Diameter • Stainless Steels • Welded/Bolted • 304/304L • Sanitary • Shorten Shaft: A few inches has a • 316/316L • Welded/Acorn Nuts pronounced effect, but need to maintain • Duplex (Al6XN / Ferralium / Avesta 254) • Threaded process performance • High Nickel • Choose Lower Power/Lower Speed Agitator • Alloy 20 • Remove Weight • Alloy 200 •Step the Shaft • Alloy C276/B2 •Reduce blade thickness • Others • Monel 400 ---- Inconel 600/625/800 • Titanium
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Additional Design Considerations Basic Components Information for Agitator Design • Surface Finish Requirements • Rounded Edges / Smooth Welds • Gear Drive B Speed Reducer • USP Class VI or FDA elastomers • Type of Data • Prime Mover B Motor • Debris Well / Flush Ports • Vessel Data • Drive Mount/Shaft Seal • Beveled Washout • Process Data • Mixer Shaft • Mechanical Data • Impeller(s) • Previous Experience • Documentation Requirements • See Agitator Data Sheet for typical required data
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16 Process Data Vessel Data Process Data • Blending and Motion • Dimensions • Liquid Properties: Viscosity, Specific Gravity P Viscosity is most important for Blending • Diameter, Straight Side, Mounting Height, Top • Additions to be made and quantities and Bottom Depths, Agitator Mounting Flange • Heat Transfer properties (if required) and Motion and has greatest influence on Size, Access Way Sizes • Solids Suspension agitator sizing • Ratings • Liquid Properties: Viscosity, Specific Gravity P Solids(Size,%,Sg)/Liquid(Viscosity, Sg) • Pressure and Temperature • Solids Properties: Particle Size, Sg, Weight % Data is most important for Solids • Internals • Gas Dispersion Suspension • Baffles (Chemineer will recommend) • Temperature/Pressure of incoming gas P The more accurate the data, the more • Cooling/Heating Coils • Gas flow rates optimized the agitator • Other Obstructions • Liquid viscosity • Mass Transfer Requirements 145 146 147
Information for Agitator Sizing Conclusion Alternate Agitator Mechanical Data Designs
• Specifying/Describing the problem is critical P Materials of Construction for wetted • Accurate data = Accurate Designs Bellow Assembly parts • Viscosity is most important parameter on P Sealing Requirements agitator size for Blending & Motion Shaft P Mounting Requirements • Sealing, Materials, and other requirements P Other Special Requirements affect the mechanical design of the agitator Impeller 148 149 150 Impeller Style Sweeping Blade – New Approach Sweeping Blade Addresses: The impeller is designed to • Zero contamination from wearing parts convert the rocking motion Eliminates: • Easy to clean with few crevices. of the drive to flow with a • Complete Draining. circumferential component • Particle generation • Zero leakage through seals. Top view of impeller • Rotating mechanical seals & maintenance • Effective mixing (usually low shear) without • In-Tank bearings used with bottom entry baffles. O-ring mixers • 10:1 turndown w/out avoidance range. • Low center of gravity to avoid top heavy Hub • Tank damage associated w/ decoupling of tank/mixer configurations. End cap magnetic mixing impellers and/or bearing • Ability to produce very small batches. Sanitary removable failures • Small footprint. impeller design • Lower Cost of ownership could be an option. 151 152 153 17 Summary Questions? • The Sweeping blade configuration can effectively address the mixing and mechanical requirements of your systems • Total cost of ownership is lower than traditional rotating mixers • Design flexibility to match your needs • Can retrofit top or bottom entry mixers 154 155 18