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Distillation Column Design

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Distillation

• Distillation is defined as a process in which liquid or vapor mixture of two or more substances is separated into its component fractions of desired purity, by the application and removal of heat.

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Types of Distillation

• Batch distillation• Continuous distillation• Steam distillation• Azeotropic distillation• Extractive distillation

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Open Steam Distillation

Live steam is in direct contact with fluids being distilled.

Mostly used in petroleum and petrochemical industries.

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Why Open Steam Distillation?

• Aqueous solution is distilled to give non-aqueous solute as distillate and water is removed as bottom product.

• Heat required for this process is provided by the use of open steam.

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Continued…….

• Use of open steam for these process is more economical.

• No need of reboiler at the bottom of the column which reduces cost.

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Column selection

Two types of columns• Plate column• Packed column

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Plate Columns

• Handle large liquid rates.• Less chances of flooding.• More reliable design.• High liquid holdup.• Suitable for fouling services.• Low cost.• Predictable hydraulic and mass

transfer behavior.

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Packed Column

• Low pressure drop/ smaller diameter.• Low to moderate cost for random

packing, high cost for structured packing.• Not suitable for fouling services.• Suitable for foaming fluids.• Liquid holdup is less.• Less pressure drop .

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Selection Criteria of Column

• Liquid flowrate is high.• steam is corrosive.• Liquid is non-foaming.

So I selected plate column for my process

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Design Steps

• Designation of design basis• Selection of operating conditions.• Selection of key components• Feed Bubble point and dew point calculations.• Top Tray Temp Calculation .• Bottom product temperature calculation.

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Continue…

• Calculation of steam flowrate.• Calculation of Rmin and optimum reflux ratio.• Calculation of Nmin and theoratical no of plates.• Location of feed point.• Calculation of column diameter.• Calculation of column efficiency.• Calculation of column height.

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Feed and Product Specifications

Components Feed Bottom product Top product

Ethyl Chloride 6.75 0.75 6

Water 3007 3007

Acetaldehyde 1002.40 1000 2.5

Acetic Acid 9.83 9.8

Crotonaldehyde 5.7 5.7

Chloro Ethanol 16.8599 16.8

Total(kg/hr) 4048.588 4040.05 8.5

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Design Variables

Operating Pressure• High pressure reflects an increase in condenser

and reboiler duties and decrease in latent heat of vapourization.

• Lower limit is set to avoid vaccum distillation.• Operating pressure should be selected so that the

buble point of top product is 5 to 10 C above ⁰summer cooling water temperature.

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Continued…

• So I select operating pressure of column

3 Atmosphere. The steam entering in the column is saturated

At pressure 60 kgf/cm2

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Key components

Light key ( Ethyl Chloride)

Most volatile component in bottom product. Heavy key (Acetaldehyde)

Least volatile component in top product

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Feed Bubble Point And Dew Point

Calculated by iterative procedure by this formula

• Bubble point Σyi= Σ (ki* xi)=1• Dew point Σxi= Σ (yi / ki)=1• Bubble point is 372 K• Dew point is 400 K

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• Top tray temperature = 313 k• Bottom product temperature = 380 k

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Steam flowrate

• Steam flowrate is calculated from this formula

• By putting all above values steam flowrate rae is calculated as

ssf mmTcpmQ 11

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Minimum reflux ratio

• For this q and θ should be calculated first.

• Using underwood’s equation

)1(Tcp

q

i

ifi xq1

12.1q

4.1

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Actual Reflux Ratio

• Using equation of minimum reflux

• Actual reflux ratio is 1.2 - 1.5 of minimum reflux ratio so

i

iDixR 1min

14.1min R

372.1

2.1 min

R

RR

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Minimum no of stages

• According to fenske’s equation

• αLK,avg is volatility of light key in top and bottom product and calculated from the formula

avgLK

WLK

WHK

DHK

DLK

xx

xx

N,

,

,

,

,

logmin

LWLDavgLK ,

13min N

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Theoratical no of stages

• Using Gilliland’s correlation

• From Graph

09.01min

R

RR

37.1

14.1min

R

R

4.01min

N

NN13min N

22N

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Column Efficiency

• O’Connell’s correlation gives

• αLK is average relative volatility of light key.

• μavg is molar average liquid viscosity (mNs/m2)

• Calculated value is

)log(5.3251 avgLKOE

377.0

8.1

avg

LK

95.55OE

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Actual no of stages

• Actaul no of stgaes are related to column efficiency as

• Efficiency is 55.95% , and theoratical stages are 13 so

Oact E

NN

36actN

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Location Of Feed Tray

• kirkbide correlation gives approximate method for estimating feed plate location.

• Ne is number of stages above feed plate and Ns is number of stages below feed plate.

• Above equation gives

HW

LW

LF

HF

x

x

D

W

x

x

Ns

Nelog206.0log

36

779.0

actse

s

e

NNN

NN

16

20

s

e

N

N

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Column Diameter

• Flow parameter

• Assuming tray spacing = 18 inch from graph

č = .28

• UVN is flooding velocity.

5.

L

VLV V

LF

5.

VL

VVNU

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Actual no of stages

• Actaul no of stgaes are related to column efficiency as

• Efficiency is 55.95% , and theoratical stages are 13 so

Oact E

NN

36actN

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Actual no of stages

• Actaul no of stgaes are related to column efficiency as

• Efficiency is 55.95% , and theoratical stages are 13 so

Oact E

NN

36actN

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Actual no of stages

• Actaul no of stgaes are related to column efficiency as

• Efficiency is 55.95% , and theoratical stages are 13 so

Oact E

NN

36actN

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Actual no of stages

• Actaul no of stgaes are related to column efficiency as

• Efficiency is 55.95% , and theoratical stages are 13 so

Oact E

NN

36actN

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Actual no of stages

• Actaul no of stgaes are related to column efficiency as

• Efficiency is 55.95% , and theoratical stages are 13 so

Oact E

NN

36actN

www.company.com

Actual no of stages

• Actaul no of stgaes are related to column efficiency as

• Efficiency is 55.95% , and theoratical stages are 13 so

Oact E

NN

36actN

www.company.com

Actual no of stages

• Actaul no of stgaes are related to column efficiency as

• Efficiency is 55.95% , and theoratical stages are 13 so

Oact E

NN

36actN