DESIGN OF PACKED TOWER

FOR LIQUID-LIQUID EXTRACTION

VIVEK J. PINGALE 641497

A PROJECT REPORT ON

GUIDED BY : Dr. Shashank G. Gaikwad Scientist, NCL , Pune

Liquid -Liquid ExtractionThe separation of the components of a liquid mixture by treatment with a solvent in whichone or more of the desired components is preferentially soluble is known as liquid–liquidExtraction.In all extraction processes, the important feature is the selective nature of the solvent,in that the separation of compounds is based on differences in solubility's, rather thandifferences in volatilities as in distillation.

Extraction is in many ways complementary to distillation

and is preferable in thefollowing cases

1. Where distillation would require excessive amounts of heat, such as, for example, when the relative volatility is near unity.

2. When the formation of azeotrope’s limits the degree of separation obtainable in distillation.

3. When heating must be avoided.4. When the components to be separated are quite

different in nature.

Three stages are involved

1. Bringing the feed mixture and the solvent into intimate contact.

2. Separation of the resulting two phases.3. Removal and recovery of the solvent from

each phase.

IN THE SINGLE-STAGE BATCH PROCESS ILLUSTRATED IN FIGURE

THE SOLVENT AND SOLUTION

ACETIC ACID+ WATER+ TOLUENE SYSTEM

•Composition Formation•Mixing•Stabilizing•Separating•Analyzing•Calculation

BATCH NO. Water in

gm

Acetic acid in

gm

Toluene in

gm

Batch-1 23 28 24

Batch-2 22 30 23

Batch-3 24 25 26

Batch-4 21 34 20

Batch-5 20 37 18

Batch-6 19 40 16

Batch-7 30 10 35

Batch-8 29 13 33

Batch-9 28 15 32

Batch-10 27 18 30

Batch-11 26 20 29

Batch-12 25 22 28

Batch-13 30 10 35

the toluene and acetic acid solution are mixed together and then allowed to separate into the two phases—the extract E containing the required solute in the added solvent and the raffinate R, the weaker solution with some associated solvent. With this simple arrangement, mixing and separation occurin the same vessel.

GENERAL SEPARATION PROCESS

APPLICATION OF LIQUID-LIQUID EXTRACTION

In the processing of coal tar liquids.In the production of fuels in the nuclear industry.To the separation of hydrocarbons in the petroleum industry.The separation of aromaticsfrom kerosene-based fuel oils to improve their burning quality.The separation of aromatics from paraffin and naphthenic compounds to improve the temperature-viscosity characteristics of lubricating oils.

It may also be used to obtain relativelypure compounds such as toluene from catalytically produced reformatesin the oil industry, in the production of anhydrous acetic acid, in the extraction ofphenol from coal tar liquors, and in the metallurgical and biotechnology industries.

PACKED TOWER

A packed tower is a hollow tube, pipe, or other vessel that is filled with packing material.

Two liquid phase are always present with contact.

Packing can randomly filled with small objects

The packing increases the interfacial area and increases mass transfer rates

Steady state mass transfer process

BASIC DATA FOR DESIGN Function Process material Steps involve for design of packed column Selection of packing Operating and design temperature and

pressure Material of construction Tower dimensions Opening and connections required Specification of internal fitting

FUNCTION Liquid-liquid, Liquid-vapor, Liquid-gas , Contact

Operations

STEPS INVOLVE FOR DESIGN OF PACKED COLUMN

Selection of packing Determine the column height Determine the column diameter packing support liquid distributor Check for pressure drop, liquid holdup,

and flooding.

SELECTION OF PACKING1) The Compounds are Temperature Sensitive2) Pressure Drop Is Important (Vacuum

Service)3) Liquid Loads are Low4) Towers are Small In Diameter5) Highly Corrosive Service (Use Plastic Or

Carbon)6) The System Is Foaming7) The Ratio of Tower Diameter To Random

Packing Is Greater Than 10.

TYPES OF PACKING MATERIAL

Raschig ring Lessing ring

Partition ring

Berl saddle

Intalox saddle

Tellerette Pall ring

PACKING MATERIALS

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.450

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

f(x) = 0.488204525774549 x − 0.0229504189507744R² = 0.995132253223116

Acetic Acid in Raffinate Phase

AA ORG.Linear (AA ORG.)Linear (AA ORG.)

GRAPH OF MOLE FRACTION OF ACETIC ACID IN EXTRACT PHASE VS. MOLE FRACTION OF ACETIC ACID IN ORGANIC PHASE

EXPERIMENTAL HTU DETERMINATON

The height of a transfer unit (HTU) is a measure of the separation effectiveness of the particular packing for a particular separation process.

Height of overall Transfer Unit, HTU is 3.396562707 m calculated by using slope m= 1.1965

EXPERIMENTAL NTU DETERMINATON

The number of transfer units (NTU) required is a measure of the difficulty of the separation

Number of a transfer unit (NTU) is 0.96122 calculated by using slope m= 1.1965

EXPERIMENTAL HEIGHT OF PACKING

Packing Height (Z) = Height of a Transfer Unit (HTU) X Number of a transfer unit (NTU)

 Z = 3.396562707 m X 0.96122 =3.2648 m

0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.20

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

f(x) = 1.055724552825 x − 0.0009970299391

NRTL

NRTL

Linear (NRTL)

NRTL graph for acetic acid

HTU DETERMINATON USING NRTL

The height of a transfer unit (HTU) is a measure of the separation effectiveness of the particular packing for a particular separation process.

Height of overall Transfer Unit, HTU is 1.430722756 m calculated by using slope m= 1.055

NTU DETERMINATON FOR NRTL

The number of transfer units (NTU) required is a measure of the difficulty of the separation.

Number of overall Transfer Unit, NTU is 3.01 calculated by using slope m= 1.055

NRTL HEIGHT OF PACKING

Packing Height (Z) = Height of a Transfer Unit (HTU) X Number of a transfer unit (NTU)

 Z = 1.430722756 m X 3.01 =4.3077 m

DETERMINE THE COLUMN HEIGHT

Column height is calculated from HETP (Height Equivalent to Theoretical Plate)

Kx = liquid phase mass transfercoefficient

(X1*-X1) = driving force for MT of

raffinate phase

a= Interfacial area of packing

DETERMINE PACKING HEIGHTZ = N × H

where.,Z= packing heightN= number of transfer unit (NTU) -

dimensionlessH= height of transfer unit (HTU) – dimension

of length

COLUMN DIAMETER To handle the liquid and vapour flow Ratio of tower diameter to packing

diameter should usually be at least 15 Packed diameter is less 1/8th column

diameter. Use too large size in a small column can cause poor liquid distribution.

LIQUID DISTRIBUTOR

Perfect liquid distribution is defined asproviding equal liquid per unit area of thepacked bed surface.

• Orifice flow variation random, ± 5% to 6%• Head at minimum capacity, 2 inches• Light liquid risers have a 1 inch freeboard above max pool depth• Quiet liquid pool• Low horizontal liquid velocity, <1.25ft/s• Feed pipe discharge does not disrupt orifice flow• Orifice as large as possible

SUMMARY OF GOOD LIQUID DISTRIBUTOR DESIGN

PRESSURE DROP, LIQUID HOLDUP

& FLOODING. Packed towers almost always have

lower pressure drop compared to tray towers.

Generally packed towers are designed for 50% -- 85% flooding. If flooding is to be reduced,

Select larger packing size and repeat the above steps. OR

Increase the column diameter and repeat the above steps.

TOWER DIMENSIONS

Height Of Tower Was Estimated To be 3.26 m With Diameter of 0.163 m, Thickness of Tower Material 50 mm

Height Equivalent to Theoretical Stage (HETS) for liquid - liquid contacting is 0.4 - 0.56 m for in Bialechi rings.

Conclusion The final design includes significant

predicted improvements over the batch performance done in the lab. The design is based upon sound correlations as verified by the literature data consulted but still suffers from the cumulative propagation of small but significant error. While this was minimized by the careful selection of the correlations chosen, we have confidence in the numbers produced is cautiously estimated as ±20% and guessed to be as low as ±10%.

ACTUAL EXPERIMENTAL DESIGN OF PACKED COLUMN

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