Fluent Simulation

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 ?

Presentation of FLUENT • Program for Fluids simulations in any geometry (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 • Geometry definition

FLUENT strategy • meshing

FLUENT WHAT ARE THE OBJECTIVES AND INTERESTS ?

FLUENT objectives Objectives: 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 any parameters (optimization)

FLUENT objectives NUMERICAL 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 Loocking for :

– 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

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 with 1 or 2 impellers

FLUENT simulations Impellers 4 PPR30° N

H

Hag1 Dag1 D

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

Single impeller Poor agitation on upper zone

NOT OPTIMAL FLOW FIELD

OK

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…

FLUENT simulations Impellers 4 PPR30° N

Hag2

H Dag2

Hag1 Dag1 D

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

Multi impellers • Baffles effect

• Second impeller action

Multi impellers 2 impellers could improve the mixing, BUT…

Multi impellers • Poor mixing at tank bottom

OK

BAD

Multi impellers

Multi impellers • Incorrect distribution of fluid velocity

OK

• Danger if solids BAD

Multi impellers • No cleaning effect at the bottom

• Not down pumping action

FLUENT simulations Impellers 4 PPR30° N

Hag2

H Dag2

Hag1 Dag1 D

Case B (change of position) • N=55 rpm • D=6600 mm • H=7200 mm • Dag1=2500 mm • Hag1=1.6 m • Dag2 =2500 mm • Hag2 = 5.1 m

Multi impellers • Better fluid motion and mixing at the bottom OK

Multi impellers • Good agitation at the bottom

Multi impellers • Correct velocity field OK

Multi impellers •Cleaning effect on the bottom

FLUENT simulations Influence 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 solids suspension

Solids suspension Initial situation (solids deposit at bottom) Case B

Case A liquid

solids

Solids suspension Case A

37 sec

Case B

6 sec

Solids suspension Case A

115 sec

Case B

20 sec

Solids suspension Case B

Case A

720 sec

2317 sec

Very slow suspension

quicker suspension

FLUENT simulations Influence of impellers…number

Impact on the Blending time

Blending time What is the target ?

What What isis itit ?? • Required time for uniformity • Based on pulse of tracer • Monitoring over time of concentration at # locations top mid bottom cone

• • • •

To be minimized To have good mixing To avoid over-concentration To avoid loss of recovery as P2O5 UN and CO

Blending time Case A

Case B 1 impeller

2 impellers

+/- 80 sec

+/- 60 sec

FLUENT simulations

EXCITING DYNAMIC VIDEOS

FLUENT simulations

CONCLUSIONS ON 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