97079632 effect-of-mixing-in-stirred-tank-reactor-1

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97079632 effect-of-mixing-in-stirred-tank-reactor-1

  1. 1. EFFECT OF MIXING IN ASTIRRED TANK REACTOR
  2. 2. ESSENSE OF THE PROJECT To study the performance of a Stirred Tank Reactor using different parameters. To design a better and a controlled mixing process that utilizes raw materials and avoids pollution. To cut down the mixing expenditure.
  3. 3. MIXING• Mixing isdefined as the reduction of in-homogeneity in order to achieve a desired process result.• The primary objective of the mixing is to achieve a homogeneous mixture, generally this means, attaining a nearly uniform distribution of the ingredients.• The in-homogeneity can be one of concentration, phase, or temperature. Secondary effects, such as mass transfer, reaction, and product properties are usually the critical objectives.
  4. 4. A horse-driven mixer is a pug mill preparing clay for brick making……………
  5. 5. MIXING TANKAgitated mixer are increasingly used to perform a variety of mixing tasks in chemical products Food Biochemical Pharmaceutical Medicine Energy, Environment protection, dealing with fining, homogenizing, dissolution, gas dispersion, solid suspension, heat transfer and diffusive transport of multiple raw materials.
  6. 6. GEOMETRY OF MIXING TANK A conventional stirred tank consists of a vessel equipped with a rotating mixer. The vessel is generally a vertical cylindrical tank. Nonstandard vessels such as those with square or rectangular cross-section, or horizontal cylinder vessels are sometimes used. The rotating mixer has several components: an impeller, shaft, shaft seal, gearbox, and a motor drive. Wall baffles are generally installed for transitional and turbulent mixing to prevent solid body rotation (sometimes called fluid swirl ) and cause axial mixing between the top and bottom of the tank . .
  7. 7. Schematic of a mixing tank
  8. 8. MIXING MECHANISMS Dispersion or diffusion is the act of spreading out. Molecular diffusion is diffusion caused by relative molecular motion and is characterized by the molecular diffusivity. Eddy diffusion or turbulent diffusion is dispersion in turbulent flows caused by the motions of large groups of molecules called eddies; this motion is measured as the turbulent velocity fluctuations. Convection (or bulk diffusion) is dispersion caused by bulk motion. Taylor dispersion is a special case of convection, where the dispersion is caused by a mean velocity gradient. It is most often referred to in the case of laminar pipe flow, where axial dispersion arises due to the parabolic velocity gradient in the pipe.
  9. 9. MEASURES OF MIXEDNESS Scale of segregation is a measure of the large scale breakup process (bulk and eddy diffusivity) without the action of diffusion. It is the size of the packets of B that can be distinguished from the surrounding fluid A. Intensity of segregation is a measure of the difference in concentration between the purest concentration of B and the purest concentration of A in the surrounding fluid. Molecular diffusion is needed to reduce the intensity of segregation, as even the smallest turbulent eddies have a very large diameter relative to the size of a molecule.
  10. 10. RESIDENCE TIME DISTRIBUTION Residence time distributions represent the first generation of mixing models. The residence time distribution measures features of ideal or non ideal flows associated with the bulk flow patterns or macro mixing in a reactor or other process vessel. In RTD analysis, a tracer is injected into the flow and the concentration of tracer in the outlet line is recorded over time. When the mixing is ideal or close to ideal and the reaction kinetics are known, the RTD can be used to obtain explicit solutions for the reactor yield . The chief weakness of RTD analysis is that from the diagnostic perspective, an RTD study can identify whether the mixing is ideal or non ideal, but it is not able to uniquely determine the nature of the non ideality. contd……
  11. 11. RESIDENCE TIME DISTRIBUTION Residence time distributions are the first characteristic of mixing. The characteristic time scale for a residence time distribution is the mean residence time of the vessel. The characteristic length scale is the vessel diameter, or volume. The conclusion is that improvements in CFD codes and still faster computers are needed for accurate design calculations in complex geometries. Residence time calculations will be a useful tool for their validation
  12. 12. PARAMETERS CONSIDERED Type of mixing process Lateral mixing Axial mixing Type of flow Laminar Flow Turbulent Flow Type of reactor Batch reactor Type of mixers to be used Mechanical Agitators Materials taken for the mixing process
  13. 13. KEY PROCESS VARIABLES Residence time (τ) Volume (V) Temperature (T) Pressure (P)
  14. 14. TYPES OF IMPELLERSThree blade marine type Double flight ribbon type:.  A high efficiency turbulent flow  It is the most efficient blender of impeller used on our smallest all existing close clearance turbine agitators at direct drive agitators motor speeds.  . Generally used for applications  The high solidity permits where viscosities are ordinarily operation nearer the boiling greater than 30,000 MPa. point without cavitations.
  15. 15. TYPES OF IMPELLERSAxial impeller : Straight Blade Impeller :  A reasonably cost effective impeller  A cost effective impeller in both turbulent and laminar flow.  Good impeller for applications where for operation very near the the viscosity changes over a wide floor of a tank for agitating range causing the flow regime to the heel in solids vary between turbulent and laminar flow. suspension applications.  A reasonably cost effective impeller for solids suspension.
  16. 16. CASE STUDYPROCEDURE:1. Fill the overhead tanks with NaOH and Ethyl Acetate.2. Adjust the flow rates of NaOH and Ethyl Acetate until the flow reaches steady state.3. Switch on the stirrer.4. Add 10 ml of Glacial Acetic Acid to the reactor5. Collect the samples from outlet for every 30 seconds of time interval.6. Take 10ml from each sample and transfer it to the conical flask which contains 10ml HCl.7. Titrate the sample with NaOH by adding phenolphthalein indicator, till colorless solution turns to pink.8. Note down the volume of NaOH rundown.9. Repeat the same procedure for different flow rates.
  17. 17. FORMULAE QNaOH * NNaOHCAO = QNaOH + QETHYL ACETATE VETHYL ACETATE *ᵨSETHYL ACETATE = M.W.(1+VETHYL ACETATE )
  18. 18. CBO = QETHYL ACETATE *SETHYL ACETATE QNaOH + QETHYL ACETATE M = CBO CAO CA = GNaOH VSAMPLEXA = 1 - CA CAOτ = V QNaOH + QETHYL ACETATE
  19. 19. OBSERVATIONS AND CALCULATIONS
  20. 20. EFFECT OF MIXING WITHOUT STIRRER S.NO QNaOH QETHYL ACETATE V NaOH (LPH) (LPH) RUNDOWN ml 1 12.5 15 6.5 2 10 12.5 4.7 3 7.5 10 3.3 4 5 7.5 3.0 5 2.5 5 2.0
  21. 21. S NO τ XA sec 1 0.03709 0.0001 2 0.0453 0.010 3 0.0582 0.0109 4 0.0816 0.112 5 0.136 0.119
  22. 22. RESIDENCE TIME Vs CONVERSION 0.14 0.12 0.1A 0.08 0.06onXevcsri 0.04 0.02 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 Residence time, τ (sec)
  23. 23. CONVERSION BY VARYING RPMsS.No XA AT 400 RPM XA AT 600 RPM XA AT 1000 RPM τ sec 1 0.0512 0.0841 0.112 0.03709 2 0.0740 0.099 0.344 0.045 3 0.0911 0.156 0.499 0.058 4 0.202 0.331 0.546 0.0816 5 0.335 0.584 0.844 0.136
  24. 24. RESIDENCE TIME Vs CONVERSION 0.9 XA @ 0.8 400 RPM 0.7 0.6A XA @ 0.5 600 RPM 0.4 0.3 XA @onXevcsri 0.2 1000 0.1 RPM 0 0 0.025 0.05 0.075 0.1 0.125 0.15 Residence time, τ (sec)
  25. 25. CONVERSION WITH A THREE BLADE MARINE TYPE IMPELLER S.No QNaOH QETHYL ACETATE Volume of NaOH (LPH) rundown (LPH) ml 1 12.5 15 6.9 2 10 12.5 6.5 3 7.5 10 6.3 4 5 7.5 6.1 5 2.5 5 6.0
  26. 26. S.No XA τ Sec 1 O.O114 0.037 2 0.02021 0.045 3 0.02117 0.058 4 0.19905 0.0816 5 0.20704 0.136
  27. 27. RESIDENCE TIME Vs CONVERSION 0.25 0.2A 0.15 0.1onXevcsri 0.05 0 0 0.025 0.05 0.075 0.1 0.125 0.15 Residence time, τ (sec)
  28. 28. CONVERSION WITH A STRAIGHT BLADE TYPE IMPELLER S NO QNaOH QETHYL ACETATE V NaOH RUNDOWN (LPH) (LPH) ml 1 12.5 15 7.5 2 10 12.5 6.9 3 7.5 10 6.5 4 5 7.5 6.3 5 2.5 5 6.1
  29. 29. S NO XA τ Sec 1 0.0321 0.0370 2 0.05705 0.045 3 0.06774 0.058 4 0.18905 0.0816 5 0.33903 0.136
  30. 30. RESIDENCE TIME Vs CONVERSION 0.4 0.35 0.3A 0.25 0.2 0.15onXevcsri 0.1 0.05 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 Residence time, τ (sec)
  31. 31. CONVERSION WITH AN AXIAL HIGH EFFICIENCY IMPELLER S NO QNaOH QETHYL ACETATE V NaOH RUNDOWN (LPH) (LPH) ml 1 12.5 15 9.0 2 10 12.5 8.5 3 7.5 10 7.0 4 5 7.5 6.9 5 2.5 5 6.5
  32. 32. S NO XA τ Sec 1 0.045 0.037 2 0.101 0.045 3 0.194 0.058 4 0.310 0.0816 5 0.381 0.136
  33. 33. RESIDENCE TIME Vs CONVERSION 0.45 0.4 0.35 0.3A 0.25 0.2 0.15onXevcsri 0.1 0.05 0 0 0.025 0.05 0.075 0.1 0.125 0.15 Residence time, τ (sec)
  34. 34. CONVERSION WITH A DOUBLE FLIGHT RIBBON IMPELLER S NO QNaOH QETHYL ACETATE VOLUME OF NaOH (LPH) (LPH) RUNDOWN ml 1 12.5 15 8.4 2 10 12.5 7.5 3 7.5 10 6.7 4 5 7.5 6.5 5 2.5 5 6.4
  35. 35. S NO XA τ Sec 1 0.0421 0.037 2 0.0631 0.045 3 0.082 0.058 4 0.210 0.0816 5 0.348 0.136
  36. 36. RESIDENCE TIME Vs CONVERSION 0.4 0.35 0.3A 0.25 0.2 0.15onXevcsri 0.1 0.05 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 Residence time, τ (sec)
  37. 37. COMPARISION OF VARIOUS TYPES OF IMPELLERS BY TAKING CONVERSION AS FACTOR 0.45 0.4 with out impeller 0.35 three blade marine 0.3 type impeller A 0.25 flat 4-blade type 0.2 impeller o n X e v c s 0.15 r i double flight ribbon impeller 0.1 0.05 axial impeller 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 Residence time, τ (sec)
  38. 38. APPLICATIONS Stirred tank reactors are frequently used in the chemical and biochemical industry to accomplish mixing tasks. Stirred tank reactors are used for the mixing of various types of polymerizations, precipitations and fermentations. A better designed and controlled mixing process leads to significant pollution prevention, better usage of raw materials and avoids expensive separation costs downstream in the process.
  39. 39. CONCLUSION• From our project we were able to study the following: – Inefficient mixing has large negative effects on the yield and selectivity of a broad range of chemical reactions, because slow mixing can retard desired reactions. – The speed of the agitators and its involvement in the effect of mixing using a Tachometer and a Dimmerstat. – We have taken different stirrers and achieved maximum conversion and studied the effect of mixing varying RPM and found out the properties of different impellers and their rate of mixing using different liquids. – The best conversion we have achieved for axial impeller because of the twisted blade structure when compared with other three impellers.
  40. 40. SCOPE FOR FUTURE WORKThis study can be extended by varying different reactors , agitators and solutionsThe study can be done in closed type vessels where different fluids can be taken.
  41. 41. REFERENCESSchmidt, Lanny, The Engineering Of Chemical Reactions. NY Oxford Press, 1998.Octave Levenspiel, The Chemical Omnibook,Oregon St Univ Bookstores 1993.Effect Of Mixing in a Stirred Tank Reactor- Chemical Engineering Journal.Warren L.McCabe, Julian Smith, Peter Harriot. Unit Operations Of Chemical Engineering-2005.Bakker R A, “Micro mixing in Chemical Reactors” Thesis ,Delft University,1996.
  42. 42. THANK YOU

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