Equipment design and costs for separating homogeneous mixtures
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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

Equipment Design and Costs for Separating Homogeneous Mixtures



Design procedures for columns with sieve trays
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


Design procedures for columns with sieve trays cont d
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)


Design procedures for columns with sieve trays cont d1
Design Procedures for Columns with Sieve Trays (cont’d)

  • Selection of column internals


Design procedures for columns with sieve trays cont d2
Design Procedures for Columns with Sieve Trays(cont’d)

  • Determination of column diameter


Design procedures for columns with sieve trays cont d3
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


Design procedures for columns with sieve trays cont d4
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


Design procedures for columns with random packing
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


Design procedures for columns with random packing cont d
Design Procedures for Columns with Random Packing (cont’d)

  • Heights of columns

    • HTU method




Design procedures for columns with structured packing cont d
Design Procedures for Columns with Structured Packing (cont’d)

  • Diameter

  • Height

    • HETP: Rule of thumb


Other distillation processes
Other Distillation Processes

  • Batch distillation:

    • Food, pharmaceuticals and biotechnolgy industries

    • Rayleigh equation


Other distillation processes cont d
Other Distillation Processes (cont’d)

  • Azeotropic distillation



Cost estimation cont d
Cost Estimation (cont’d)

  • Costs of distillation column

25 trays

50 trays


Cost estimation cont d1
Cost Estimation (cont’d)

  • Costs of sieve tray


Cost estimation cont d2
Cost Estimation (cont’d)


Cost estimation cont d3
Cost Estimation (cont’d)


Cost estimation cont d4
Cost Estimation (cont’d)


Cost estimation cont d5
Cost Estimation (cont’d)




Design procedures
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


Design procedures cont d
Design Procedures (cont’d)

  • Stage efficiency and column height

    • Overall efficiency

    • Column height: Tray spacing/HTU/HETP



Selection of membranes
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)



Design parameter
Design Parameter

  • Permeance: porosity, solubility or partition coefficient

  • Separation factor/selectivity

  • Purity and yield




Selection of adsorbent
Selection of Adsorbent

  • Activated Carbon

  • Molecular Sieve Zeolites

  • Silica gel

  • Activated Alumina


Basic adsorption cycles
Basic Adsorption Cycles

  • Temperature Swing cycle

    • Cycle time: few hours

    • Capacity: 1 kg per 100 kg

      of adsorbent


Basic adsorption cycles cont d
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


Basic adsorption cycles cont d1
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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