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 Underwood equation 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: m Fractional free area: m2 Fractional downcomer area: m2 Pitch/hole dia ratio: Tray spacing: m Weir height: 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 trays50 trays

Cost Estimation (cont’d) Costs of sieve tray

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 ($ /m2) Spiral-wound ($25-100/m2) Hollow fiber ($10-20/m2) Tubular ($ /m2) Capillary ($25-100/m2) Ceramic ($ /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