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

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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

    • 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)

  • 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’d)

  • Selection of column internals


Design Procedures for Columns with Sieve Trays(cont’d)

  • Determination of column diameter


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’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

  • 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)

  • Heights of columns

    • HTU method


Design Procedures for Columns with Random Packing (cont’d)

  • HETP method


Design Procedures for Columns with Structured Packing


Design Procedures for Columns with Structured Packing (cont’d)

  • Diameter

  • Height

    • HETP: Rule of thumb


Other Distillation Processes

  • Batch distillation:

    • Food, pharmaceuticals and biotechnolgy industries

    • Rayleigh equation


Other Distillation Processes (cont’d)

  • Azeotropic distillation


Cost Estimation


Cost Estimation (cont’d)

  • Costs of distillation column

25 trays

50 trays


Cost Estimation (cont’d)

  • Costs of sieve tray


Cost Estimation (cont’d)


Cost Estimation (cont’d)


Cost Estimation (cont’d)


Cost Estimation (cont’d)


2. Absorption and Stripping


Gas Treatment with Solvent Recovery


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)

  • Stage efficiency and column height

    • Overall efficiency

    • Column height: Tray spacing/HTU/HETP


3. Membrane Separation


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)


Concentration Profile across Membranes


Design Parameter

  • Permeance: porosity, solubility or partition coefficient

  • Separation factor/selectivity

  • Purity and yield


Flow Patterns


4. Adsorption


Selection of Adsorbent

  • Activated Carbon

  • Molecular Sieve Zeolites

  • Silica gel

  • Activated Alumina


Basic Adsorption Cycles

  • Temperature Swing cycle

    • Cycle time: few hours

    • Capacity: 1 kg per 100 kg

      of adsorbent


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’d)

  • Pressure Swing cycle

    • Cycle time: few minutes

    • Capacity: 1 to 2 kg per

      100 kg adsorbent


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