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Distillation Column design basics -3.pptx
- 1. 1 Separation Process-II (ChE-306) Design ofSieve Plate Column
- 2. 2 McCabe & Smith,Unit Operation of Chemical Engineering, CH # Distillation MTO-CHT-301-KSK-MS-JAVED
- 3. 3 Condenser & Top Plate •Construction of top plate depends on the condenser. • The simplest arrangement to obtain reflux and liquid product is single total condenser. SINGLE TOTAL CONDENSER abc= top plate MTO-CHT-301-KSK-MS-JAVED
- 4. 4 PARTIAL CONDENSER PARTIAL CONDENSER a'b’c’=additional theoretical stage 𝒙𝑪 ≠ 𝒙𝑫 MTO-CHT-301-KSK-MS-JAVED
- 5. 5 Bottom plate and re-boiler 𝐱𝐦 =𝐱 𝐰 If; Then ; 𝒚𝒎+𝟏=? ?? cde= reboiler plate MTO-CHT-301-KSK-MS-JAVED
- 6. 6 Invariant Zone Recall minreflux ratio • At min. reflux ratio an acute angle is formed. • It contains an infinite no of plates. • At this point, there is no change in liquid and vapor concentration. • The term “Invariant Zone” is used to describe these infinite no of plates. • It is also known as “PINCH POINT”. MTO-CHT-301-KSK-MS-JAVED
- 7. 7 Design of SievePlate Column
- 8. 8 General Characteristics ofDistillation Tower • Tower Dia ( 0.3 to 9)m • No. of plates (up to hundred) • Plate Spacing (up to 6 in.) • Plate type (Bubble Cap/Sieve plate/Valve plates)
- 9. 9 Sieve Tray • Vaporbubbles up through simple holes in the tray through flowing liquid. • Liquid is maintained on tray by the kinetic energy of vapors. • Vapor area is in the range of (5-15)% of tray area.
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- 11. 11 Valve Tray • Itis the modification of sieve tray. • Perforations are covered by liftable caps. • Vapor flows lifts the caps, thus self creating a flow area for the passage of vapor. • It inhibits liquid leakage. • It can also operate at low vapor rates. • Cost= 20% Sieve tray
- 12. 12 Bubble Cap Tray •Vapor rises through opening in the tray into bubble caps. • Vapor flows through slots in the periphery of each cap and bubbles upward through flowing liquid. • Cost= 2*(Sieve tray)
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- 14. 14 Packings versus Trays •A tray column that is facing throughput problems may be de- bottlenecked by replacing a section of trays with packings. Advantages of packings • packings provide extra inter-facial area for liquid-vapour contact • efficiency of separation is increased for the same column height • packed columns are shorter than trayed columns
- 15. 15 Addressing Factors ForSieve Plate Design • Number of Plates • Correction for plate efficiency • Type of Plate • Holes in Trays • Down-comer Size • Weir Height • Column Diameter • Pressure drop per tray • Vapor rate
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- 17. 17 Sieve Plate Operation Liquidflows across the plate & passes over weir to a down-comer leading to bottom below. Liquid flows pattern is cross flow on each plate. But, overall flow pattern in column is countercurrent.
- 18. 18 Weir • A weiron the tray ensures that there is always some liquid (holdup) on the tray. • Holdup should be at a suitable height.
- 19. 19 Downcomer • Itis usually a pipe, welded to the plate. • It is used to transport fluid in downward direction. • It covers (10-15)% of column X-section area.
- 20. 20 Under flow Weir •To improve liquid distribution. • To prevent the entry of bubbles in the down-comer.
- 21. 21 Vapor Flow • Flowof vapor in upward direction is occurred through holes. • Holes are arranged in triangular pattern • Hole size ( 5-12) mm.
- 22. 22 Vapor Velocity • Velocityof upward moving vapors should be high enough that can create frothy mixture of liquid and vapors . • It can provide large surface area for mass transfer. • Froth density = 0.2* liquid density • Froth height should be several times high than liquid height on plate.
- 23. 23 Vapor Pressure Drop •is needed; 1. to make flow of vapors through perforated regions 2. to make liquid flow on the plate. Pressure drop across a single plate is 50-70 mm H2O.
- 24. 24 How to Develop •Pressure drop is developed automatically by the reboiler during generation of vapors.
- 25. 25 Orifice Coefficient • Itshows the “fraction of the open area”. • It depends on plate thickness. • Co= • Mostly Co= 0.66-0.72
- 26. 26 Factors affecting liquidHoldup Francis Equation Correlation Factor
- 27. 27 Downcomer Level • Levelin downcomer must be greater or less than level on plate? Liquid volume fraction Height of aerated liquid
- 28. 28 Assignment (Deadline: ___________) •Example 18.2, 18.3 and 18.6 McCabe & Smith, Unit Operation of Chemical Engineering, 6th ed., CH # Distillation
- 29. 29 Operational Problem inDistillation
- 30. 30 Flooding • Flooding Occurswhen; “height of aerated liquid becomes greater than plate spacing”. Flooding >>> due to excessive vapor flow What is the consequence of flooding??? Flow to next plate is hindered
- 31. 31 Weeping • Weeping occursat >>> Low Vapor Velocities • is not enough and liquid flow down through holes. • Weeping decreases plate efficiency. ∆ 𝑷
- 32. 32 Entrainment • A phenomenonwhere small portion of liquor undergoes vaporization which is carried out by vapors as a droplet in a condenser. • Results in contamination of condensate
- 33. 33 Vapor Velocity Surface tensionfor organic liquids
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Editor's Notes
- #37 Factors determining Column Performance Liquid and Vapor velocities Physical properties of liquid and vapor Extent of entrainment of liquid by rising vapor streams The hydraulics of the flow of liquid and vapor across and through tray