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Equipment Design and Costs for Separating Homogeneous Mixtures

Equipment Design and Costs for Separating Homogeneous Mixtures. 1. Distillation. Design Procedures for Columns with Sieve Trays. Designation of design bases Composition and physical properties of feed and product

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Equipment Design and Costs for Separating Homogeneous Mixtures

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  1. Equipment Design and Costs for Separating Homogeneous Mixtures

  2. 1. Distillation

  3. Design Procedures for Columns with Sieve Trays • Designation of design bases • Composition and physical properties of feed and product • Special limitations: maximum temperature and pressure drop restrictions, presence of reactive materials or toxic components etc • Selection of design variables: operating pressure, reflux ratio, feed condition • Establishment of physical equilibria data • data for binary pairs are combined with a model (Wilson, NRTL and UNIQUAC) to predict multi-component behavior; UNIFAC model is used for prediction based on functional group

  4. Design Procedures for Columns with Sieve Trays (cont’d) • Determination of number of equilibrium stages • Underwoodequation for minimum reflux • Minimum number of stages from Fenske equation • Number of equilibrium stages, N as a function of and (Gilliand equation)

  5. Design Procedures for Columns with Sieve Trays (cont’d) • Selection of column internals

  6. Design Procedures for Columns with Sieve Trays(cont’d) • Determination of column diameter

  7. Design Procedures for Columns with Sieve Trays (cont’d) • Efficiency: • Tray Spacing: 0.46 to 0.61 m (0.3 and 0.91 m are also used) • Column height

  8. Design Procedures for Columns with Sieve Trays (cont’d) • Sieve Tray Geometry • Hole dia: 0.005-0.025 m • Fractional free area: 0.06-0.16 m2 • Fractional downcomer area: 0.05-0.3 m2 • Pitch/hole dia ratio: 2.5-4.0 • Tray spacing: 0.305-0.915 m • Weir height: 0.025-0.075 m

  9. Design Procedures for Columns with Random Packing • Determination of diameter • Vapor velocity is 70 to 90 % of flooding velocity • Recommended pressure drop • 400 to 600 Pa/m for atmospheric and high-pressure separation • 4 to 50 Pa/m for vacuum operations • 200 to 400 Pa/m for absorption and stripping column

  10. Design Procedures for Columns with Random Packing (cont’d) • Heights of columns • HTU method

  11. Design Procedures for Columns with Random Packing (cont’d) • HETP method

  12. Design Procedures for Columns with Structured Packing

  13. Design Procedures for Columns with Structured Packing (cont’d) • Diameter • Height • HETP: Rule of thumb

  14. Other Distillation Processes • Batch distillation: • Food, pharmaceuticals and biotechnolgy industries • Rayleigh equation

  15. Other Distillation Processes (cont’d) • Azeotropic distillation

  16. Cost Estimation

  17. Cost Estimation (cont’d) • Costs of distillation column 25 trays 50 trays

  18. Cost Estimation (cont’d) • Costs of sieve tray

  19. Cost Estimation (cont’d)

  20. Cost Estimation (cont’d)

  21. Cost Estimation (cont’d)

  22. Cost Estimation (cont’d)

  23. 2. Absorption and Stripping

  24. Gas Treatment with Solvent Recovery

  25. Design Procedures • Column diameter: 70 to 90% of the flooding velocity, Larger of the top or bottom diameter is used • Number of equilibrium stages: Modified Kremser equation Solute fraction absorbed Solute fraction stripped

  26. Design Procedures (cont’d) • Stage efficiency and column height • Overall efficiency • Column height: Tray spacing/HTU/HETP

  27. 3. Membrane Separation

  28. Selection of Membranes • Fabricated from natural and synthetic polymers • Membrane modules • Plate and Frame ($250-400/m2) • Spiral-wound ($25-100/m2) • Hollow fiber ($10-20/m2) • Tubular ($250-400/m2) • Capillary ($25-100/m2) • Ceramic ($1000-1600/m2)

  29. Concentration Profile across Membranes

  30. Design Parameter • Permeance: porosity, solubility or partition coefficient • Separation factor/selectivity • Purity and yield

  31. Flow Patterns

  32. 4. Adsorption

  33. Selection of Adsorbent • Activated Carbon • Molecular Sieve Zeolites • Silica gel • Activated Alumina

  34. Basic Adsorption Cycles • Temperature Swing cycle • Cycle time: few hours • Capacity: 1 kg per 100 kg of adsorbent

  35. Basic Adsorption Cycles (cont’d) • Inert Purge cycle • Regeneration is done by purging inert gas and lowering the partial pressure of the adsorbate • Cycle times are only a few minutes • Capacity 1 to 2 kg adsorbate per 100 kg adsorbent

  36. Basic Adsorption Cycles (cont’d) • Pressure Swing cycle • Cycle time: few minutes • Capacity: 1 to 2 kg per 100 kg adsorbent

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