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

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

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 random packing cont d1

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


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

Cost Estimation


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)


Equipment design and costs for separating homogeneous mixtures

2. Absorption and Stripping


Gas treatment with solvent recovery

Gas Treatment with Solvent Recovery


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


Equipment design and costs for separating homogeneous mixtures

3. Membrane Separation


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)


Concentration profile across membranes

Concentration Profile across Membranes


Design parameter

Design Parameter

  • Permeance: porosity, solubility or partition coefficient

  • Separation factor/selectivity

  • Purity and yield


Flow patterns

Flow Patterns


Equipment design and costs for separating homogeneous mixtures

4. Adsorption


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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