FLUENT SIMULATIONS

							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°         Case 0
                   N
                           • N=55 rpm
                           • D=6600 mm
                           • H=7200 mm
                       H
                           • Dag1=2500 mm
                           • Hag1=1600 mm
Hag1
            Dag1           • Down pumping
          D
                 Single impeller
Poor agitation                       NOT
on upper zone                      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°         Case A
                   N
                           • N=55 rpm
                           • D=6600 mm
                           • H=7200 mm
Hag2
                       H
              Dag2
                           • Dag1=2500 mm
                           • Hag1=2.5 m
Hag1                       • Dag2 =2500 mm
            Dag1
                           • Hag2 = 5.5 m
          D
                   Multi impellers
• Baffles effect



• Second
  impeller
  action
 Multi impellers
 2 impellers could
improve the mixing,

      BUT…
              Multi impellers
• Poor
  mixing at
                                OK
  tank
  bottom




                                BAD
Multi impellers
                 Multi impellers
• Incorrect
  distribution
                                   OK
  of fluid
  velocity



• Danger if
  solids
                                   BAD
               Multi impellers
• No
  cleaning
  effect at
  the bottom



• Not down
  pumping
  action
        FLUENT simulations
Impellers 4 PPR30°
                           Case B (change of
                             position)
                   N       • N=55 rpm
                           • D=6600 mm
Hag2                       • H=7200 mm
                       H
              Dag2         • Dag1=2500 mm
                           • Hag1=1.6 m
Hag1                       • Dag2 =2500 mm
            Dag1
                           • Hag2 = 5.1 m
          D
                 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 A                              Case B
liquid




            solids
         Solids suspension
Case A                       Case B




     37 sec              6 sec
         Solids suspension
Case A                       Case B




     115 sec             20 sec
             Solids suspension
  Case A                               Case B




               2317 sec                         720 sec
Very slow                  quicker
suspension                suspension
  FLUENT simulations
Influence of impellers…number


        Impact on the
        Blending time
                          Blending time
        What is it ?
        What is it ?                   What is the
                                        target ?

• Required time for uniformity
• Based on pulse of tracer
• Monitoring over time of          •    To be minimized
  concentration at # locations     •    To have good mixing
                                   •    To avoid over-concentration
                    top
                                   •    To avoid loss of recovery
                                        as P2O5 UN and CO
                    mid

                   bottom
                       cone
            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