CL-304 (PED-II) Instructor: Prof. Ashok Kumar DasmahapatraGroup 8

PROCESS EQUIPMENT DESIGNTERM PROJECT

Process & Mechanical Design of a Packed Bed Extractor

Group Members:Namrata Das (130107034)Nayan Gupta (130107035) Nilesh Raj (130107036)Niraj Chetry (130107037)

Problem Statement:

Extraction of Benzene is desired from a mixture of Benzene & 1-Hexene containing 78 mole% 1-Hexene and 22 mole% Benzene.

Flow rate of the feed solution is 6000 kg/hr.

Tetra-methylene Sulphone is to be used as the solvent for 96% extraction of benzene from the feed mixture.

Ternary equilibrium data:

Description:

Materials:Carrier : 1-Hexene (A)Solvent: Tetra-Methylene Sulphone (B) Solute : Benzene (C)

Continuous Phase Properties:Density (ρc) = 715.73 kg/m3 Viscosity (µc) = 4.7x10-4 Pa.sDiffusivity of Benzene (Dc) = 1.62x10-9 m2/s

Dispersed Phase Properties: Density (ρd) = 1261 kg/m3 Viscosity (µd) = 0.013 Pa.sDiffusivity of Benzene (Dd) = 4.1x10-9 m2/s Interfacial tension of dispersed phase (γ) = 0.00728 N/m

Solution Procedure: Process calculations

1. Equilibrium Curve:o Plot the right-angled ternary plot

2. Raffinate & Extract Phase Mass Flow Rates:o Use stoichiometric calculations to find these two

3. Minimum Solvent Rate:o Calculate the minimum solvent rate for extraction by locating Δm on the ternary plot

4. Equilibrium Solute Concentration in Extract:o Total material balance & solute balance gives => yE

5. Packing Material Specifications:o Using 3 different types of packing material- Raschig Rings- Lessing Rings- Berl Saddles

(Image Source: Google Image Search)

6. Flooding Velocity:o The flooding velocity for the dispersed phase & continuous phase is calculated using

the correlation:

(Ref: A.Suryanarayna, page:551, for correlation)

7. Column Diameter:o Using flooding velocity & mass flow rate, find the column diameter

8. Dispersed phase hold-up (ф):o Solve the cubic equation - UD + UC (ф/1- ф) = Vo ε ф(1-ф); where, Vo = C[aP ρC / ε3gΔρ]-0.5

to get the values of фo Select the root such as ф <0.52

9. Mass Transfer Coefficient (Koca):o Calculate Schmidt’s No. for both phases and use packing specifications and the above

value of ф along with the avg. coefficient distribution(m) from equilibrium data to calculate Koca

Solution Procedure: Process calculations

10. Height of Transfer Units (HtoC):o Using continuous phase velocity (UC) & mass transfer coefficient (Koca) to get HtoC

11. No. of Transfer Units (NtoC):o Using yE found from material balance and xF* found from the equilibrium curve, find

NtoC using the following: NtoC = xRʃxF dx/(x-x*) ~ (xF-xR)/(x-x*)M

where, (x-x*)M = [(xF-xF*)-(xR-xR*)]/[ln(xF-xF*)/(xR-xR*)]

12. Column Height:o Using the above two values of HtoC & NtoC , we get the column height: H = HtoC * NtoC

13. Comparison of Packing Materials:o We repeat the steps 1-11 for each of the packing material type and tabulate the results to compare all 3 types of material choice:

It is evident from the calculated results that “Lessing Rings” would be the optimum choice as a packing material for the desired extraction

Solution Procedure: Process calculations

Mechanical Design: Specifications

Diameter of the tower, Di =1mHeight of the tower, H = 2.9mWorking Pressure = 1atm =10.1325 kg/cm2= 0.101325 MPa Design Pressure, P = 1.13atm = 11.4497 kg/cm2= 0.114497 MPaShell Material: Plain Carbon Steel, Grade 2B (IS : 2002-1962)Permissible Tensile Stress, ft = 950 kg/cm2 ~ 95 MPaInsulation thickness = 100mmDensity of insulation = 770 kg/m3

Top disengaging space= 1mBottom separator space= 1mDensity of material of column = 7700 kg/m3

Wind Pressure = 130 kg/m2 ~ 1.275MPa

Mechanical Design: Calculations

1. Shell Thickness: o Using the formula: ts = PDi/(2fJ+P) + c , we get the shell thickness

2. Head Design:o Working Pressure Range: 0.1~1.5 MPa Choice of Head: Shallow dished & Torispherical We calculate the thickness of head by: t= PDoC/2fJ

3. Stress calculations: o Stress in the mechanical design due to various contributors are calculated: Axial Stress (compressive): fap= PD/4(ts-c) Compressive stress due to weight of shell upto a distance ‘x’ : fds=ρsgx Compressive stress due to weight of insulation: fd(ins)= ᴨDinstinsρins / ᴨDmt Compressive stress due to weight of liquid and tray: fdl= Wliq/ ᴨDm(ts-c) Stress due to weight of attachments: fd(att)= Wa/ᴨDmt Total compressive dead weight stress at height ‘x’: fdb= fap+fds+fd(ins)+fdl

Stress due to wind load at distance ‘x’: fws= 1.4Pwx2/ ᴨDot Stress in upwind side: fmax=fws+fap-fds

Stress in downwind side: fmax=fws+fap+fds

Calculating the failure location ‘x’ verifies the earlier calculated value of “Column Height”

Mechanical Design: Specifications

4. Internal Packing Support:o For column diameter upto 1.2m, we can use the GIS/EMS Random Packing Support

Grid in such small columns

(Ref: Internals for packed column, SULZER Chemtech)

5. Distributor:o For low interfacial tension value in LLX, Extraction Distributor VRX can be used.

(Ref: Internals for packed column, SULZER Chemtech)

Results: Design Details

The design specifications based on the optimum choice of packing material are listed below:

Graph:

Bibliography:

Mass Transfer Operations, 3e, Robert E. Treybal Mass Transfer Operations, A. Suryananarayana Mass Transfer Operations, B.K.Dutta Packed Tower Design & Applications, Ralph F. Strigle Perry’s Handbook, 8th Edition, Section-15, Mc Graw Hill Education Packed Column Design & Performance, L.Klemas & J.A.Bonilla Structured Packings: for Distillation, Absorption & Reactive Distillation, by SULZER Chemtech Ltd. Liquid-Liquid Extraction Technology, by SULZER Chemtech Ltd. Design Practice for Packed Liquid-Liquid Extraction Column, by SULZER

Chemtech Ltd. Internals for Packed Columns, by SULZER Chemtech Ltd.