1. CL-304 (PED-II)
Instructor: Prof. Ashok Kumar Dasmahapatra
Group 8
PROCESS EQUIPMENT DESIGN
TERM PROJECT
Process & Mechanical Design of a Packed Bed Extractor
Group Members:
Namrata Das (130107034)
Nayan Gupta (130107035)
Nilesh Raj (130107036)
Niraj Chetry (130107037)
2. 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.
5. 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. 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 ф
o 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
7. 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
8. Mechanical Design: Specifications
Diameter of the tower, Di =1m
Height of the tower, H = 2.9m
Working Pressure = 1atm =10.1325 kg/cm2= 0.101325 MPa
Design Pressure, P = 1.13atm = 11.4497 kg/cm2= 0.114497 MPa
Shell Material: Plain Carbon Steel, Grade 2B (IS : 2002-1962)
Permissible Tensile Stress, ft = 950 kg/cm2 ~ 95 MPa
Insulation thickness = 100mm
Density of insulation = 770 kg/m3
Top disengaging space= 1m
Bottom separator space= 1m
Density of material of column = 7700 kg/m3
Wind Pressure = 130 kg/m2 ~ 1.275MPa
9. 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”
10. 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)
11. Results: Design Details
The design specifications based on the optimum choice of packing material are listed below:
13. 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.
