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Separations

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Separations ChEN 4253 Design I Chapter 19 Terry A. Ring University of Utah Simple Separation Units Flash Quench Liquid-liquid decantation Liquid-liquid Flash ... – PowerPoint PPT presentation

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Title: Separations


1
Separations
  • ChEN 4253 Design I
  • Chapter 19
  • Terry A. Ring
  • University of Utah

2
Simple Separation Units
  • Flash
  • Quench
  • Liquid-liquid decantation
  • Liquid-liquid Flash
  • Sublimation
  • Solid/Vapor Flash
  • Crystallization
  • Filtration

3
Use of Separation Units
4
Separation ReactionHydrodealkylation of
TolueneTH2??BCH4side reaction2B??
BiphenylH2
Reactor Effluent T1,350F P 500 psia
5
Reactor Effluent
Reaction Conditions T1,350F P 500 psia
6
After Flash to 100F _at_ 500 psia
Recycled Reactants
7
Separation
  • Vapor Separation
  • CH4 from H2
  • Liquid Separation

8
Further SeparationWhat separation units should
be used?
  • Liquid Separation
  • Toluene, BP110.6ºC
  • Benzene, BP80.1ºC
  • What happens to the Methane (BP -161.5ºC) and
    Biphenyl (BP255.9ºC) impurities?
  • Gas Separation
  • Hydrogen
  • Methane
  • what happens to the Toluene and Benzene
    impurities?

9
(No Transcript)
10
Direct Distillation Sequence
11
Criteria 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
  • Cost

Phases I and II, Components 1 and 2 (light key
and heavy key)
12
Distillation
13
Distillation
14
Plate Types
  • Bubble Cap Tray
  • Sieve Tray

15
Packed Towers
  • Random Packing
  • Structured Packing

Note Importance of Distributor plate
16
Distillation
aKL/KH
  • Relative Volatility
  • Equilibrium Line

17
Distillation
  • Rectifying Section
  • R reflux ratio
  • Vvapor flow rate
  • Stripping Section
  • VB Boil-up ratio
  • Feed Line

18
Minimum Reflux Ratio
19
McCabe-Thiele
20
Step Off Equilibrium Trays
21
Marginal Vapor Rate
  • Marginal Annualized Cost Marginal Vapor Rate
  • Marginal 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 above

22
Short cut to Selecting a Column 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 _at_ N/Nmin2 or see Fig 19.1
  • VD (R1)
  • V Vapor Flow Rate
  • D Distillate Flow Rate (Production Rate)
  • RReflux Ratio

23
Figure 19.1
24
How To Determine the Column Pressure given coolant
  • Cooling Water Available at 90ºF
  • Distillate Can be cooled to 120ºF min.
  • Calculate the Bubble Pt. Pressure of Distillate
    Composition at 120ºF
  • equals Distillate Pressure
  • Bottoms Pressure Distillate Pressure 10 psia
    delta P
  • Compute the Bubble Pt. Temp for an estimate of
    the Bottoms Composition at Distillate Pressure
  • Give Bottoms Temperature
  • Not Near Critical Point for mixture

25
Design Issues
  • Packing vs Trays
  • Column Diameter from flooding consideration
  • Trays, DT(4G)/((f Uflood p(1-Adown/AT)?G)1/2 e
    q. 19.11
  • Uflood f(dimensionless density difference), f
    0.75-0.85 eq. 19.12
  • Packed, DT (4G)/((f Uflood p?G)1/2 eq. 19.14
  • Uflood f(flow ratio), f 0.75-0.85 eq. 19.15
  • Column Height
  • Nminlog(dLK/bLK)(bHK/dHK)/logaLK,HK
    Fenske eq.19.1
  • NNmin/e (or 2 Nmin/ e)
  • Column Height NHtray
  • Tray Height typically 1 ft (or larger), 2 inch
    weir height
  • Packed Height NeqHETP (or 2 NeqHETP)
  • HETP(height equivalent of theoretical plate)
  • HETPrandom 1.5 ft/inDp Rule of thumb eq.
    19.9
  • Tray Efficiency, e f(viscosityliquid aLK,HK)
    Fig 19.3
  • Pressure Drop
  • Tray, ?P?Lg hL-wier N
  • Packed, ?PPacked bed (weeping)

26
Tray Efficiency
19.3
µL aLK,HK
27
Costing
28
Column Costs
  • Column Material of Construction gives ?metal
  • Pressure Vessel Cp FMCv(W)CPlatform
  • Height may include the reboiler accumulator tank
  • Tray Cost NCtray(DT)
  • Packing Cost VpackingCpacking Cdistributors
  • Reboiler CB a AreaHX
  • Condenser CB a AreaHX
  • Pumping Costs feed, reflux, reboiler
  • Work Q?P
  • Tanks
  • Surge tank before column, reboiler accumulator,
    condensate accumulator
  • Pressure Vessel Cp FMCv(W)CPlatform

29
CPI
30
Distillation Problems
  • Multi-component Distillation
  • Selection of Column Sequences
  • Azeotropy
  • Overcoming it to get pure products
  • Heat Integration
  • Decreasing the cost of separations

31
Problem
  • Methanol-Water Distillation
  • Feed
  • 10 gal/min
  • 50/50 (mole) mixture
  • Desired to get
  • High Purity MeOH in D
  • Pure Water in B

32
Simulator Methods - Aspen
  • Start with simple distillation method
  • DSDTW or Distil
  • Then go to more complicated one for sizing
    purposes
  • RadFrac
  • Sizing in RadFrac
  • Costing

33
Simulation Methods- ProMax
  • Start with 10 trays (you may need up to 100 for
    some difficult separations)
  • set ?P on column, reboiler, condenser and
    separator
  • set ?T on condenser
  • Create a component recovery for HK in bottom with
    large
  • Set Reflux ratio 0.1 (increase to get
    simulation to run w/o errors).
  • May need pump around loop estimate.
  • Determine aLK,HK, viscosity
  • (use Plots Tab to determine extra trays)
    determine Nmin and feed tray
  • Use Fig. 19.1 to determine Rmin from R, N from
    Nmin
  • Redo calc with tray efficiency defined see Figure
    19.3 correlation.
  • Recommendations for final design
  • Use N/Nmin2 (above and below feed tray)
  • R/Rmin1.2

34
Figure 19.1
35
Tray Efficiency
µL aLK,HK
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