Distillation Presentation
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Transcript of Distillation Presentation
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Design Of Distillation Column
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Distillation Column
A Distillation Column is used to separate a multicomponent liquid mixture into distillates and bottoms due to differences in their boiling points.
They are of following two types based upon construction.
Tray Column Packed Column
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Choice b/w Tray & Packed Column
Plate column are designed to handle wide range of liquid flow rates without flooding.
For large column heights, weight of the packed column is more than plate column.
Man holes will be provided for cleaning in tray Columns. In packed columns packing must be removed before cleaning.
When large temperature changes are involved as in the distillation operations tray column are often preferred.
Random-Packed Column generally not designed with the diameter larger than 1.5 m and diameters of commercial tray column is seldom less than 0.67m.
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Selection Of Tray Type
Sieve trays are selected due to following main reasons.
High capacity. Less pressure drop. High Efficiency . Lowest Cost per unit area than all
other types with the downcomer. Good flexibility in
operation(Turndown ratio).
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Designing Steps Of Distillation Column
Calculation of Minimum Reflux Ratio Rm. Calculation of optimum reflux ratio. Calculation of theoretical number of stages. Calculation of actual number of stages. Calculation of diameter of the column. Calculation of weeping point. Calculation of pressure drop. Calculation of the height of the column. Calculation of thickness of the shell & Head.
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FEED COMPOSITION
ComponentFeed in Kgs/hr
Feed in Fraction
Feed in kmoles
TDA (LK) 85.4 0.035 0.700
PPG (HK) 2217.6 0.909 1.109
Water 128.66 0.053 7.148
Carbon diaoxide 1.32 0.001 0.030
Unconverted foam 6 0.002 0.001
total 2438.98 1.000 8.988
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TOP PRODUCT
ComponentTop prod. in Kgs/hr
Top product in Fraction
Top in kmoles
TDA (LK) 81.13 0.382 0.665
PPG (HK) 1 0.005 0.001
water 128.66 0.607 7.148
Carbon dioxide 1.32 0.006 0.030
total 212.11 1 7.843
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BOTTOM PRODUCT
Component
Bottom prod. in Kgs/hr
Bottom product in Fraction
Bottom in kmoles
TDA (LK) 4.27 0.002 0.035
PPG (HK) 2216.6 0.995 1.108
Unconverted foam 6 0.003 0.001
total 2226.87 1 1.144
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Ref:- www.cheric.org 10
DATACol. P (atm) 1Col. T ( C ) 190q (subcooled liquid) 1.3Average viscosity of feed (cp) 1.28V.P (atm) of TDA at 190oC 0.018volatility of TDA 0.018V.P (atm) of PPG at 190oC 0.004083volatility of PPG 0.004083Relative Volatility 4.41
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Ref:- Estimation of Polymer Properties
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viscosity calculations
TDA
Temperature ( C ) 190
viscosity (cp) 0.295
PPG
Temperature ( C ) 190
viscosity (cp) 1.395
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Ref:- Estimation 12
Nature Of Feed
q = 1 + Cpl(Tb – Tf) λ
q=1.3 (for subcooled liquid)
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Determination Of Reflux Ratio
Nmin = Ln [(X1/X2)D (X2/X1)B]
Ln (α12)av
By putting all values, we get
Nmin = 7
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Stage cut calculation
(α1xf1/α1-Θ)+(α1xf2/α2-Θ)=1-q
As q=1.3
So,
(α1xf1/α1-Θ)+(α2xf2/α2-Θ)= -0.3
By hit & trial we satisfy this eq. & get the value of “stage cut”
Θ=3.0
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Optimum reflux calculation
(α1xd1/α1-Θ)+(α2xd2/α2-Θ)=1+Rmin
Hence, Rmin=1.2
R =1.2*1.5
=2
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Feed stage location
Now by Eduljee relation (eq-15.4)No. of Theoritical stages=19
Tray Efficiency=Eo=0.492[µFavg(1 / 2)av ]Eo=57%No. of Actual Stages=33 By Kirkbride method,ND=23
NB=10So, feed enters the column 10 stages above
the bottom stage
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Ref:- Estimation of Polymer Properties
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FLOW RATESTop Flow RatesLn=D*Rmin kmol/hr 9.371Vn=Ln+D kmol/hr 17.214Bottom Flow Rates Lm=Ln+F kmol/hr 18.359Vm=Lm-B kmol/hr 17.214Vm m3/sec 1.817Vm kg/sec 7.23L/D 2V/D 3liquid density (kg/m3) 717.27M (g/gmole) 151.25R (atm.cm3/gmole.k) 82.06vapour density (kg/m3) 3.9809
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Mechanical Design
Vnf = CSb(/20)0.2(ρL-ρV/ρV)0.5
=0.559 m/s Vn = 0.80*Vnf
=0.447 m/s
mv = (V/D)*(D)*(M)/ρV
Vn
An= mv/Vn
= 3.72 m2
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Diameter calculations
Let 15% of the cross sectional area is occupied by the downcomer
Then, Cross sectional Area=Ac=
An/0.85
=4.38 m2
Dia of column=D= (4Ac/ π)1/2
=2.36m
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Height of Column
Tray spacing=Hs=1.5 ftAdditional height for phase
disengagement=▲H =2
ftHeight of Column=Hc= (Nact – 1) Hs +
▲H = 51 ft =15 meters
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PRESSURE DROP
Hd= 51 x (Uh)2 x ρv (Co)2 x ρL
Uh=velocity through holes =Vnf/0.1 = 5.56 m/secCo = 0.89 (from graph)So, we getHd=30.70 mm-liquidHr=Residual Head=12500/ρL=17.43 mm of liquidLength of weir=lw = 1.9 mHeight of weir=hw = .03 mHow Weir Crest= 750[mL/ρL*lw]2/3 = 23 mm-liqmL= liquid flow rateht (total pressure drop) = Hd+(Hw+ How)+Hrht = 98 mm-liq∆Pt= 9.81*10-3*(ht)*ρL =690Pa=0.15psi
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Ah total hole area i.e. 10% of Aa= 0.46 m2
Hole dia=3 mm (assumed)Area of one hole =7.06 (mm)2No. of holes= Ah/Area of one hole(m2)
=65100
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Ref:- chem engg design By:coulson Ed.3 vol:6
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CHECK WEEPING
Lw liquid flow rate kg/sec=7.71how weir crest (mm of liquid)=23.708how+hw (at minimum)=53.71K2=30Uh=K2-0.90(25.4-dh)
ρv
Uhmin vapour velocity m/sec=4.23Uh Velocity through holes (m/s)=5.56
As actual vap velocity is much higher than the Uh min so there will be no weeping
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CHECK ENTRAINMENT
Un =max vol vap flow rate/net area=1.02m/sec
FLV= mL/mv(ρv/ ρL)1/2
FLV=0.08K1=0.085Uf=K1[(ρL- ρv)/ ρv]1/2
Uf=1.14 m/sec
Percent flooding 90 Fractional Entrainment ψ = 0.03 well
below 0. 1 So Satisfactory
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Check Tray spacing
hap height of apron (mm) =20Aap clearance area under
downcomer=0.038m2hdc head loss in downcomer mm-liq=13.11hb=hw+how+ht+hdc (eq-11.91)hb Backup in Downcomer mm-liq=149
hb Backup in Downcomer =0.149 m1/2(tray spacing+weir ht.)=0.2436 mAs hb<1/2(tray spacing+weir ht.) so tray
spacing is acceptable
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Check Residence Time
tr = (Ad)*(hb)*(ρL)/mL
=9.10 sec
As tr > 3 sec. so, result is satisfactory
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Identification:
Item Distillation columnNo. required 1
Tray type Sieve tray
Function: Separation of polyols from TDA for further recycling Operation: Continuous
SPECIFICATION SHEETSPECIFICATION SHEET
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No. of tray=33Tray efficiency = 57%Pressure = 101.32 KPaHeight of column = 15 mDiameter of column=2.36 m Hole size = 3 mm Pressure drop per tray=0.15psi Tray thickness = 5 mm
Active holes = 65100 Weir height = 30 mmWeir length = 1.9 m Reflux ratio = 2:1 Tray spacing =0.457m Active area = 3.07 m2 Fractional Flooding = 0.03 No Entrainment
Design DataDesign Data
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