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 multicomponent 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 N min x LK x HK ln x HK D x LK B ln LK / HK av LK / HK av LK / HK D LK / HK B 1/ 2 Number of equilibrium stages, N as a function of Nmin and R min(Gilliand equation) R Rmin 0.566 N N min 0.751 N 1 R 1 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 Vnf Csb 20 0.2 L v v Vn 50 90%Vnf m"v An Vn AC A n Ad 1/ 2 4A c D 0.5 Design Procedures for Columns with Sieve Trays (cont’d) Efficiency: Eo 0.492L LK / HK av 0.245 Tray Spacing: Hs 0.46 to 0.61 m (0.3 and 0.91 m are also used) Column height N act N Eo H c N act 1Hs H 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 Z (HTU )( NTU ) m"v HTU K G a e Ac NTU y1 dy y y y* 2 Vv VL HTU HTU v HTU L k va e k La e mV L Design Procedures for Columns with Random Packing (cont’d) HETP method ln HETP HTU 1 Z HETP N Design Procedures for Columns with Structured Packing Design Procedures for Columns with Structured Packing (cont’d) Diameter Height HETP: Rule of thumb HETP 9.29 10 ap Other Distillation Processes Batch distillation: Food, pharmaceuticals and biotechnolgy industries Rayleigh equation W ln F xi2 x i1 dx i yi x i 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 A iN 1 A i N 1 Ai 1 Solute fraction absorbed SiN 1 Si Solute fraction stripped N 1 Si 1 L Ai KiV Si KiV L Design Procedures (cont’d) Stage efficiency and column height Overall efficiency Eo 19.2 57.8 log L 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