18235156 Distillation Column (1)

Design Of Distillation Column By MUHAMMAD TARIQ 2005-Chem-89

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Synopsis • What is distillation? • Selection b/w Plate and Packed column • Selection of tray type • Design Calculations • Plate Hydraulic Design • Specification Sheet

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What is Distillation? “Process in which a liquid mixture of two or more substances is separated into its component fractions of desired purity on the basis of difference in relative volatility , by the application and removal of heat” 3

Column Internals Comparison b/w Tray & Packed Columns

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Choice b/w Tray & Packed Column The choice between these two for a given mass transfer operation is based on a detail cost analysis. However, The decision can be made on the basis of a qualitative analysis of relative advantages and disadvantages. 5

Tray & Packed Column Contd. • Non-foaming systems. • Liquid rates without flooding. • Periodic cleaning is easy in tray columns • Inter stage cooling • Design information • Height of the Column 6

Selection Of Tray Column I have selected the tray column for this particular system as; • • • •

As our system is non foaming. Height of the column is large. Temperature is high, i.e. 172.3oC Diameter is greater than 0.67m 7

Overview of Tray Column

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Plate Contactors • Cross-flow contactors are the most common type of plate contactors. • In a cross-flow plate the liquid flows across the plate and the vapour up through the plate. • The liquid move from plate to plate via down comer. • A certain level of liquid is maintained on the plates by weir. 9

Cross Flow Plate Contactors

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Plate Contactors Contd. Three principal types of cross flow trays are used classified according to the method used to contact the vapour and liquid. • Sieve Plates (Perforated Plate) • Bubble Cap Plates • Valve plates (floating cap plates) 11

Plate Contactors Contd.

Sieve Plate

Bubble Cap plate

Valve Plate

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Selection Of Sieve Plate I’ve selected the Sieve Plates because; • Pressure drop is lowest. • Their fundamentals are well established. • Sieve plates are the cheapest. • They are lighter in weight. • Maintenance cost is reduced due to the ease of cleaning

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Overview of Sieve Tray

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Factors affecting Distillation Column Operation Adverse Vapor Flow conditions can cause; • • • •

Weeping Coning Excessive Entertainment Flooding 15

Column Pressure And Type Of Condenser

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Distillation Column in PFD

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Simulation on HYSYS

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T=137o C P=110 KPa

Feed F= 2990 (kg/hr) T=161oC P=130KP a

3.864×106 KJ/hr

3.642×106 KJ/hr

Top Product D=490 (Kg /hr) T=117oC P=101K Pa

Bottom Product 2500 (Kg /hr) T=220oC P=160KPa 19

Material Balance

Heavy Key Component= Maleic Anhydride (MAN) 20

Design Calculations Of Distillation Column

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Data Required For Design

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Designing Steps of Distillation Column Calculation of • Minimum Reflux Ratio (R min). • Actual Reflux Ratio (R). • Minimum number of stages(N min). • Theoretical number of stages. • Actual number of stages. • Diameter of the column. • Weeping , entrainment, etc • Total Pressure drop. • Height of the column

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Minimum Reflux Ratio Using Underwood equation;

As feed is entering as Saturated Liquid, q = 1  = 24.8 Now, Rmin = 4.77 24

Actual Reflux Ratio There is no hard and fast rules for the selection of optimum reflux ratio, but for many systems the optimum will lie between 1.2 to 1.5 times the minimum reflux ratio; R = 1.25(R

min)

R =6 25

Minimum Number of Stages The minimum No. of Stages Nmin can be find from Fenske Equation which is,

N

= 20

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Theoretical Number of Stages Using Gilliland-Eduljee relation;

N = 39 Considering one stage achieved in Reboiler & Condenser N = 38 27

Location of Feed Plate Using Kirkbride relation;

& Hence, ND = 19

NB = 19 28

Overall Tray Efficiency A quick estimate of the overall column efficiency can be obtained from the correlation given by O, Connell which is shown below,

E o = 70.92%

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Actual Number of Stages As overall column efficiency is 70.92% So, N act= 38/0.709 N

act=

54

Now, Actual ND = 27 Actual NB = 27 30

Determination of Flooding Velocity Flow Parameter based on Rectifying Section;

FLV = 0.032 Assume ,Plate Spacing = 0.5m From Graph we get K1 = 0.07 Now Flooding velocity; 31

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Actual Operating Velocity Correction factor for surface tension, σ = 56.43 dyne/cm So, unf= 3.18 m/sec Assume , Actual operating velocity is the 85% of the flooding velocity, un= 2.71m/sec 33

Cross Sectional Area Of The Column

An

= 0.29m2

Taking Down-comer Area as 12% of total cross sectional area, Total Column cross sectional Area = Net Area/0.88 34

Diameter Of The Column Column Diameter D = 0.64m (based on Rectifying section) In the similarly way, D = 0.69m (based on Stripping section) As, Two Diameters are nearly same. So, the Diameters will be same for both the Sections.

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Plate Hydraulic Design

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Tray Design Down-Comer Area = 0.12(Ac) AD = .041m2 Active Area = Ac – 2AD Aa = 0.26m2 Hole Area = 0.1(Aa) = .026m2 Take weir height = 50mm 37

Weir Length As we have,

From Graph we get

So, Lw = 0.5m

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Weir Liquid Crest Using relation,

how = 23.69 mm For minimum Crest use 70% of maximum flow

how(min) = 18.68 mm Hence,

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Weeping Check Using relation;

From Graph U

K2 = 30.56

min

= 6.43 m/sec

Actual minimum Vapor velocity through holes;

V

act(min)

= 17.85 m/sec

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Weeping Phenomena

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Support Area Lw/Dc = 0.76 From graph; θ = 99o r = 0.33m Arc length = r×(п-θ) = .46 m As = 2×Arc. × .05 = 0.04 m2 43

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Calming Zone Area From Fig.

a = .25 m Az = 4a × 0.05 = 0.054m2 45

Perforated Area

Ap= Column Area – 2(Down-comer area) – Support area – Calming zone Area = 0.16 m2

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Number Of Holes Single hole Area = 1.96× 10-5 m2 No. of holes = Total hole area / single hole area = 1330 holes Hole Pitch;

From the graph, So, Lp = 11.5 mm

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Graph To Find The Hole Pitch

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Pressure Drop Calculation The pressure drop over the plates is an important design consideration, the total plate pressure drop is given below, Total head loss per plate = hd + hr + hw + how h d = Dry plate drop hr = Residual head

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Dry Plate Pressure Drop We know that,

We have: and Plate thickness / hole diameter = 1 From graph we get: Co = 0.91 Hence, h d = 30 mm-liquid

50

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Residual Head This is the head loss due to bubble formation and other losses. This is given by

hr = 11.41 mm-liq. 52

Total Pressure Drop Total head loss per plate = h + how

d

+ hr + hw

ht = 109.76 mm-liq. Pressure drop per plate = ΔPt = 925 Pa Total Pressure drop in the column; ΔP = No. of plates × ΔPt

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Down Comer Backup Assuming that down comer is 6 mm below the weir level; Then height of aperture thus formed is ; hap= hw- 6 =44mm Area under apron; A ap =h

ap×

L

= 0.02m2

w 54

Down Comer Backup

h

dc

=2.7mm

= 50+18.68+109+2.7 = 180.34mm 55

Residence Time Liquid residence time in down comer is given as

t r = 4.3 sec 56

Height of the Column Height of the distillation column can be find by the given below formula,

Where ΔH is the additional height required for the column operation. H c = 30 m

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Specification Sheet

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