Challenges in Spray Dryer Modeling Alfred Jongsma, Tetra Pak CPS - PowerPoint PPT Presentation

Challenges in Spray Dryer Modeling Alfred Jongsma, Tetra Pak CPS March 2012

CHALLENGES IN SPRAY DRYER MODELING Content Spray Drying ► Technology Modeling ► Motivation ► Characteristics Droplet Drying ► Modeling ► Parametric Study Validation Conclusions March 2012

Challenges in Spray Dryer Modeling Spray Drying

SPRAY DRYING Technology Hot Air Inlet Cyclone “Fines” Spray Spray Return Chamber ”Fines” Fluid Bed Powder March 2012

SPRAY DRYING Technology March 2012

SPRAY DRYING Typical numbers 5 Ton/hr Whole Milk Dryer ► Volume 700m3 20 m ► Energy consumption 5 MW ► Efficiency 40-65% 8.5 m March 2012

SPRAY DRYING A ‘Small’ Dryer (1000 kg/hr) March 2012

Challenges in Spray Dryer Modeling Characteristics of Spray Drying

MODELING Characteristic Spray Drying Process Continuous Phase (Air) ► Confined Jet = Transient! ► Jet Reynolds Number  10 6 Dispersed Phase (Droplets / Particles) : no collisions ( α p < 10 -3 ) ► Dilute ►  p /  air >> 1 : only drag and gravity Lagrangian approach favoured over 2 Fluid model: ► Easier closures ► Easier incorporation of additional Particle Models, e.g. drying March 2012

Challenges in Spray Dryer Modeling Incorporation of Droplet Drying

DROPLET DRYING Inter-Phase Transfer MILK HEAT MASS DROPLET CONCENTRATION GAS FILM FILM GAS TEMPERATURE R 0 R March 2012

DROPLET DRYING Heat Transfer Assumptions ► No internal gradient Biot << 1 MILK HEAT DROPLET ► Schiller Nauman ► Spherical Particles GAS FILM TEMPERATURE ► Ideal Shrinkage ► At Particle Surface T particle = T gas R 0 March 2012

DROPLET DRYING Mass Transfer Assumptions ► Internal gradient Biot > 1 MILK MASS DROPLET ► Transfer limited by internal gradient  “CDRC” ► Spherical Particles CONCENTRATION FILM GAS ► Ideal Shrinkage ► At Particle Surface, Sorption Equilibrium: X particle = f(X gas ) 0 R March 2012

DROPLET DRYING CDRC: Critical Drying Rate Curve    1 Y dm M    w , b w   f d DSh log  p *   dt M 1 Y a w X w Y w,b Y w * 1.0 0.8 X c 0.6 f n    X e e  X X    0.4 f     X X c e 0.2 0 Best fit n = 2 0 0.2 0.4 0.6 0.8 1.0 X March 2012

DROPLET DRYING Implementation Field functions ► Correction Mass Transfer Coefficient (X c & n are constants) n    e  X X    f     X X c e ► Sorption Isotherm Ckm a  0 w X    e ( 1 ka )( 1 ka Cka ) w w w p w  H O a 2 p ( T ) H O , Sat 2 March 2012

CFD Model Spray Drying Parametric Study

PARAMETRIC STUDY Simplified Geometry Air Inlet Base ► T = 200°C ►  m = 2.9 kg/s ► Y w = 0.01 Hollow Cone Skim milk ► T = 70°C ►  m = 0.34 kg/s 35° ► X w = 0.5 15° ► 1 Nozzle: ► v = 194 m/s Air Outlet ► T = 75°C ► Y w = 0.064 March 2012

PARAMETRIC STUDY Parameter Variations Parameter Base Case Variations Air ► Velocity (Diameter) d=base small & large ► Velocity profile Normal Swirl ► Turbulence intensity Medium High & low Droplets ► Inlet Velocity v = 194m/s 100 & 250 44, 102 & 160 m m ► Size PSD Atomisation ► Cone angle 35° 25º & 45º ► Spray pattern Hollow cone Full cone ► Nozzle Position Medium High & low March 2012

PARAMETRIC STUDY Results Base Case March 2012

PARAMETRIC STUDY Results Base Case March 2012

PARAMETRIC STUDY Results Base Case Particle Tracks d p < 60 m m & d p > 100 m m Observations: ► Small particles concentrate in Jet centre ► Large particles concentrate on Jet edges March 2012

PARAMETRIC STUDY Results Base Case Particle Tracks: Temperature Observations ► Initial stage: wet bulb temperature ► Highest temperatures near Jet centre ► Final stage: uniform temperature March 2012

PARAMETRIC STUDY Results Base Case Particle Tracks d p < 60 m m & d p > 100 m m March 2012

Challenges in Spray Dryer Modeling Validation

VALIDATION Drying in reality Mechanism Depends on: ► Chemical composition ► Initial concentration ► Air temperature ► Mixing of droplets and air ► Trajectory ► Agglomeration March 2012

VALIDATION Drying, even more Real Powder Morphology: External Structure SEM Images “Regular” Whole Milk Powder Cone (Product) Cyclone (Fines) March 2012

VALIDATION Drying, even more Real Powder Morphology: Internal Structure FIB SEM Images “Regular” Whole Milk Powder Cone (Product) Cyclone (Fines) March 2012

Challenges in Spray Dryer Modeling Conclusions

CHALLENGES IN SPRAY DRYER MODELING Conclusions Spray Dryer Modeling ► Prohibitively Expensive to build Pilot Plants ► CFD Model Development ► Validation & Refinement Needed Droplet Drying ► Simple approach already reveals important phenomena ► Real drying much more complicated Planned refinements ► Account for Morphology ► Influence on Drag / Drying Rate etc. ► Collisions & Agglomeration March 2012