Chemical Process Simulation Distillation Riezqa Andika Department of Chemical Engineering Faculty of Engineering Universitas Indonesia Distillation Distillation is one of the oldest and most commonly used separation and purification methods (besides crystallization) and probably one of the most thoroughly investigated and understood. Jabir bin Hayyan described distillation, by using alembic in 8th Century. Tower/Column Absorber Tower / Column Peoples Refluxed Absorber According to condenser type: Reboiled Absorber Total Condenser Distillation Partial Full Reflux Current Industrial Distillation Zeotrope Distillation Azeotrope Minimum Boiling Maximum Boiling Can be done using: ▪ Pressure swing distillation ▪ Extractive distillation Distillation Internals Demister Liquid Distributor Packed Bed Support Plate Chevron (Vane)-Type Liquid Collector Liquid Distributor Corrugated Sheet Structured Packing Support Plate Liquid Collector Tray Liquid Collector Chimney Tray Liquid Collector Two-Pass Trays Tray Column Packed Column Trays vs Packings Tray Packing Random Packing Sieve Trays have Round Holes Punched or Drilled into the Tray Photograph of the Representatives of the First (Raschig Ring), Second (Pall Ring), Third (IMTP Saddle), and Fourth (Raschig Super Ring) Generations of Random (Dumped) Packings Structured Packing Structured Packing Photographs of the Top View of a 2.4 m Diameter Thormann Tray and a Cap Containing Vapor Directing Openings That Push the Liquid across the Tray Following the Pattern Shown in the Attached Drawing on the Middle Photograph Illustrating the Layout of a LargeDiameter Corrugated Sheet Structured Packing Bed Photograph of a Sheet of Raschig Super-Pak Trays vs Packings Trayed columns and packed columns have key advantages and disadvantages, including the following: ▪ Packed towers are more effective when used with corrosive liquids ▪ Packed towers handle foaming systems better than trays ▪ Packings provide extra interfacial area for liquid-vapor contact, so the efficiency of the separation is increased for the same column height ▪ Packed columns can be shorter and more cost-efficient than trayed columns ▪ Random packings are easier to install than trays and structured packing ▪ Optimal performance of packed columns require effective liquid distributors feeding the packed bed ▪ Tray towers offer better predictability than packed towers ▪ Tray towers are better at handling solids ▪ Tray towers are better at handling lower liquid rates Trays vs Packings Pressure drop When compared to trays, the biggest advantage associated with packings is lower pressure drops. This is particularly true with columns that are operating at pressures below atmospheric. Generally, the pressure drop across a bed of structured packing is about one-sixth of that across a stack of trays having the same total height. High pressure There are situations where packing is less applicable, such as high-pressure distillation columns, where pure products are being targeted. Trays perform better in those cases, and much more predictably, in such columns where the volumetric liquid-to-vapor ratios are high. Fouling Fouling is a challenge for all column types. With trays, parts can become plugged and lose the ability to pass liquid or vapor. With packings, liquid distributors can become plugged, making distribution suboptimal. Structured packings are much more prone to fouling than random packings, because the metal sheets of structured packings are tightly spaced. Revamps Over time, vendor companies developing new tray and packing geometries have improved the performance of these products. New generations of trays, random packings and structured packings have made it possible, at times, to substantially improve column performances with relatively easy column revamps. When trays replace packings, it is usually because the packing performance has been disappointing. When packing replaces trays, it is usually in pursuit of reduced pressure drops. Heuristics/Rule of Thumb Heuristics/Rule of Thumb Heuristics/Rule of Thumb Advanced Distillation (Single Column) Heat Integration Technology Heat Pump Technology Column in Unisim Design Component Splitter Short Cut Distillation Absorber Refluxed Absorber Reboiled Absorber Distillation Case Study - Component Splitter Design a distillation column to get propene in top stream with purity 96% (mole) and propane in bottom stream with purity 96% (mole). Components Mass Flow (kg/h) Ethane 4.1 Propene 10498.2 Propane 4000.4 n-Butane 131.8 Conditions Value Pressure (bar) 15.12 bar Fluid Package Peng-Robinson Component Splitter Component Splitter Note that the result is different with what we input. We can use this simulation result to estimate parameter e.g. mass flow on Top. Case Study - Distillation Design a distillation column to get propene in top stream with purity 96% (mole) and propane in bottom stream with purity 96% (mole). Components Mass Flow (kg/h) Ethane 4.1 Propene 10498.2 Propane 4000.4 n-Butane 131.8 Conditions Value Temperature (°C) 38 Fluid Package Peng-Robinson Design of Distillation Column Obtain: ▪ Operating pressure (if there is no known operating pressure) Obtain: ▪ Initial value of number of tray ▪ Initial value of feed stage Optimization Boiling Point C2H6 Molecular weight: 30.07 Boiling point: -88.60°C Components Mass Flow (kg/h) Ethane 4.1 Propene 10498.2 Propane 4000.4 n-Butane 131.8 Distillate C3H6 (propylene) Molecular weight: 42.08 Boiling point: -47.75°C C3H8 Molecular weight: 44.10 Boiling point: -42.10°C Bottom C4H10 Molecular weight: 58.12 Boiling point: -0.5020°C Separator The Vapour Fraction is set to be 0 (saturated liquid). Then, we will know vapor pressure at desired (certain) temperature. Short Cut Distillation propene in top stream with purity 96% (mole) propane in bottom stream with purity 96% (mole) pressure from separator simulation when vapor fraction = 0 See “Rule of Thumb” optimum (external) reflux ratio = 1.2-1.5 times minimum reflux ratio 1.5 * 9.013 = 13.5195 ≈ 13.520 Short Cut Distillation Remember this! Molar Flow Distillate: 256.4 kgmole/hr Remember this! Number of Trays: 86 Feed Stage: 34 Distillation From Short Cut simulation. Number of Trays: 86 Feed Stage: 34 Distillation Distillation From Short Cut simulation. Molar Flow Distillate: 256.4 kgmole/hr Distillation Not meeting the specification (0.96) Example of Advanced Distillation Simulation: Mechanical Vapor Recompression (MVR) Propane-Propylene Separation Shortcut Column MVR, >90% energy Conventional Column ΔT: 7.09℃ Reboiler Duty (MW) Conventional MVR 49.18 4.950 Example of Advanced Distillation Simulation: Dividing Wall Column (DWC) Benzene, Toluene, Xylene (BTX) Separation Direct Sequence DWC, 20-30% energy saving Indirect Sequence Reboiler Duty (kW) Direct Sequence Indirect Sequence DWC 1983.4 2279.2 1589 Assignment ▪ Simulate all the simulation. ▪ Make the last distillation column simulation meets all purity specification. ▪ Simulate MVR as in “4. MVR” file. Chemical Process Simulation Thank You
