Distillation_Lecture-1.ppt

Distillationin DesignTerry A. RingChEUniversity of Utahwww.che.utah.edu/ringUse of Separation UnitsCriteria for the Selection of a Separation Method Energy Separation Agent (ESA) Phase condition of feed Separation Factor Cost Mass Separation Agent (MSA) Phase condition of feed Choice of MSA Additive Separation Factor Regeneration of MSA CostPhases I and II, Components 1 and 2 (light key and heavy key)DistillationDistillationPlate Types Bubble Cap Tray Sieve TrayPacked Towers Random Packing Structured PackingNote: Importance of Distributor plateDistillation Relative Volatility Equilibrium Line=KL/KH Distillation Rectifying Section R= reflux ratio V=vapor flow rate Stripping Section VB= Boil-up ratio Feed LineMinimum Reflux RatioMcCabe-ThieleStep Off Equilibrium TraysWhat are you going to learn next year? Column sizing Diameter of Column Size of trays Height of packing Column Costing Optimization of column with respect to cost to run (capital cost and operating cost) How to develop a distillation train. How to set up side streams in multi-component distillation.Marginal Vapor Rate Annualized Cost Marginal Vapor Rate Annualized Cost proportional to Reboiler Duty (Operating Cost) Condenser Duty (Operating Cost) Reboiler Area (Capital Cost) Condenser Area (Capital Cost) Column Diameter (Capital Cost) Vapor Rate is proportional to all of the aboveDirect Distillation SequenceColumn Sequences No. of Columns Nc=P-1 P= No. of Products No. of Possible Column Sequences Ns=2(P-1)!/P!(P-1)! P= No. of Products P=3, Nc=2, Ns=2 P=4, Nc=3, Ns=5 P=5, Nc=4, Ns=14 P=6, Nc=5, Ns=42 P=7, Nc=6, Ns=132No. of Possible Column Sequences Blows up!How do I evaluate which is best sequence?Marginal Vapor Rate Annualized Cost Marginal Vapor Rate Annualized Cost proportional to Reboiler Duty (Operating Cost) Reboiler Area (Capital Cost) Condenser Duty (Operating Cost) Condenser Area (Capital Cost) Diameter of Column (Capital Cost) Vapor Rate is proportional to all of the aboveSelecting Multiple Column Separation Trains Minimum Cost for Separation Train will occur when you have a Minimum of Total Vapor Flow Rate for all columns R= 1.2 Rmin V=D (R+1) V= Vapor Flow Rate D= Distillate Flow Rate R=Recycle Ratio ProblemReactorFlashDistillation TrainAfter Flash to 100F 500 psiaRecycled ReactantsR assumed to be similar for all columnsVDSimplified Marginal Vapor Flow AnalysisColumn Design Minimum Cost for Distillation Column will occur when you have a Minimum of Total Vapor Flow Rate for column Occurs at R 1.2 Rmin N/Nmin=2 V=D (R+1) V= Vapor Flow Rate D= Distillate Flow Rate (=Production Rate) R=Reflux Ratio How To Determine the Column Pressure given coolantCooling Water Available at 90FDistillate Can be cooled to 120F min.Calculate the Bubble Pt. Pressure of Distillate Composition at 120F equals Distillate Pressure Bottoms Pressure = Distillate Pressure +10 psia delta PCompute the Bubble Pt. Temp for an estimate of the Bottoms Composition at Distillate Pressure Gives Bottoms TemperatureP Atm, Pressure generated by system.For Vacuum, how is it that generated?Not Near Critical Point for mixtureSteam Ejector Generates the Vacuum.High PressureHigh VelocitySteamVacuumBernoullis EquationVelocity Mach 1Design Issues Packing vs Trays Column Diameter from flooding consideration Trays, DT=(4G)/(f Uflood (1-Adown/AT)G)1/2eq. 14.11 Uflood= f(dimensionless density difference), f = 0.75-0.85 eq. 14.12 Packed, DT =(4G)/(f Uflood G)1/2eq. 14.14 Uflood= f(flow ratio), f = 0.75-0.85eq. 14.15 Column Height Nmin=log(dLK/bLK)(bHK/dHK)/logLK,HKeq. 14.1 N=Nmin/ Tray Height = N*Htray Packed Height = Neq*HETP HETP(height equivalent of theoretical plate) HETPrandom = 1.5 ft/in*Dpeq. 14.9 Tray Efficiency, = f(viscosityliquid * LK,HK)Fig 14.3 Pressure Drop Tray, P=Lg hL-wier N Packed, P=Packed bedTray EfficiencyL * LK,HKCostingColumn Costs Column Material of Construction gives metal Pressure Vessel Cp= FMCv(W)+CPlatform Reboiler CB AreaHX Condenser CB AreaHX Pumping Costs feed, reflux, reboiler Work = Q*P Tanks Surge tank before column, reboiler accumulator (sometimes longer (empty) tower), condensate accumulatorProblem Methanol-Water Distillation Feed 10 gal/min 50/50 (mole) mixture Desired to get High Purity MeOH in D Pure Water in BSimulator Methods - Aspen Start with simple distillation method DSTWU Winn-Underwood-Gilliland Method Min # stages, Rmin Fenske-Underwood Min # stages vs R - Gilliland Distil short cut Edmister Method Then go to more complicated one for sizing purposes RadFrac rigorous method Sizing in RadFracEric Carlsons RecommendationsE?R?P?PolarRealElectrolytePseudo & RealVacuumNon-electrolyteBraun K-10 or idealChao-Seader,Grayson-Streed or Braun K-10Peng-Robinson,Redlich-Kwong-Soave,Lee-Kesler-PlockerElectrolyte NRTLOr PizerSee Figure 2Figure 1PolarityR?Real or pseudocomponentsP?PressureE?ElectrolytesAll Non-polarP?ij?ij?LL?(See alsoFigure 3)P 10 barPSRKPR or SRK with MHV2Schwartentruber-RenonPR or SRK with WSPR or SRK with MHV2UNIFAC and its extensionsUNI。