FLUENT SIMULATIONS

Clearwater AIChE - June 2006

SCOPE

• What is FLUENT ?• What are objectives and interests ?• Focus on Agitation operation• Some general examples of agitation

results• Conclusions

FLUENT

WHAT IS FLUENT ?WHAT IS FLUENT ?

Presentation of FLUENT

• Program for Fluids simulations in anygeometry (standard and not standard)

• Based on Computational Fluid Dynamics• Based on resolution of equations for

conserved properties:– Heat transfer– Mass transfer– Momentum transfer

FLUENT strategy

• Modelisation of the geometric system• Meshing of this geometry: discretization

in small cells• Resolution of continuity equations by

successive calculations in each cell

FLUENT strategy

• Geometrydefinition

• meshing

FLUENT strategy

FLUENT

WHAT ARE THE OBJECTIVES WHAT ARE THE OBJECTIVES AND INTERESTS ?AND INTERESTS ?

FLUENT objectivesObjectives: to be able

– To study and visualize the fluid motion in any size tank

– To improve process performances by simulating alternative designs

– To have flexiblity for changing quickly anyparameters (optimization)

FLUENT objectivesNUMERICAL SIMULATIONS allow:

⇒To create a large potential of investigation⇒To obtain prediction of fluid motion⇒To favour development, optimization and innovation⇒To save time, money and man power

FLUENT activities

Main FLUENT interests for chemical process:

– Chemical reactions– Heat and mass transfer– Sedimentation of solids particles– Multi-phasis systems (absorption, separation, …)– Agitation operation– Etc….

FLUENT simulations

FOCUS ON AGITATION

Agitation with FLUENT

How to design a good agitator ?

Stirred tank

Agitation with FLUENT

– Quick dispersion and homogeneization– Adequate pumping flow– Efficient solids suspension– Efficient mixing and chemical reaction– Minimum of dead zone and by-pass

flows– Optimization of power consumption

Loocking for :

FLUENT simulations

AGITATION PARAMETERS

• type of impeller (axial or radial)• type of tank• Number of impeller• position of impeller(s)• Standard or not standard geometry

Type of impeller

Types of tank

Number of impeller

FLUENT simulations

SOME GENERAL EXAMPLES...

- flow patterns- blending time- solids suspension- some ‘’sexy’’ video

FLUENT simulations

Tank fitted with1 or 2 impellers

Case 0• N=55 rpm• D=6600 mm• H=7200 mm• Dag1=2500 mm• Hag1=1600 mm• Down pumping

FLUENT simulations

H

D

Dag1Hag1

N

Impellers 4 PPR30°

Single impellerPoor agitation on upper zone

OK

NOT OPTIMAL

FLOW FIELD

single vs multi impeller(s)

Position of single impeller:• To avoid solids sedimentation• Risk to create poor agitation on surface

Solution:• Increase rotation speed? No (danger abrasion)• Install a second impeller? Yes but…

Case A• N=55 rpm• D=6600 mm• H=7200 mm• Dag1=2500 mm• Hag1=2.5 m• Dag2 =2500 mm• Hag2 = 5.5 m

FLUENT simulations

H

D

Dag1Hag1

N

Dag2

Hag2

Impellers 4 PPR30°

Multi impellers• Baffles effect

• Second impelleraction

Multi impellers2 impellers could

improve the mixing,

BUT…

Multi impellers

• Poormixing attank bottom

OK

BAD

Multi impellers

Multi impellers

• Incorrect distribution of fluidvelocity

• Danger if solids

BAD

OK

Multi impellers

• No cleaningeffect atthe bottom

• Not down pumpingaction

Case B (change ofposition)

• N=55 rpm• D=6600 mm• H=7200 mm• Dag1=2500 mm• Hag1=1.6 m• Dag2 =2500 mm• Hag2 = 5.1 m

FLUENT simulations

H

D

Dag1Hag1

N

Dag2

Hag2

Impellers 4 PPR30°

Multi impellers

• Better fluidmotion andmixing atthe bottom

OK

Multi impellers

• Goodagitation atthe bottom

Multi impellers

• Correct velocityfield

OK

Multi impellers•Cleaningeffect on thebottom

FLUENT simulationsInfluence of impellers position

and number:

Impact on flow patterns

Impact on agitation efficiency

Impact on blending time

Impact on solids suspension

FLUENT simulations

Influence of impellers position

Impact on solidssuspension

Solids suspension

Case A Case B

Initial situation (solids deposit at bottom)

solids

liquid

Case A Case B

Solids suspension

37 sec 6 sec

Case A Case B

Solids suspension

115 sec 20 sec

Case A Case BSolids suspension

Very slow suspension

quickersuspension

2317 sec 720 sec

FLUENT simulations

Impact on theBlending time

Influence of impellers…number

Blending timeWhat is the

target ?What is it ?What is it ?

• Required time for uniformity• Based on pulse of tracer• Monitoring over time of

concentration at # locations• To be minimized• To have good mixing• To avoid over-concentration• To avoid loss of recovery

as P2O5 UN and CO

top

mid

bottomcone

Blending timeCase BCase A

2 impellers1 impeller

+/- 80 sec +/- 60 sec

FLUENT simulations

EXCITING DYNAMIC VIDEOS

FLUENT simulations

CONCLUSIONSON FLUENT

Conclusions• Large potential of utilities• Development and improvement of designs• Save time and $$• PRAYON uses CFD to optimize its technologies

Thank you

Have a good day