Process simulation study using CHEMCAD software for the separation columns for linear alkyl benzene (LAB) plant

103 Pages·3.419 MB·English

by  Lateef Omar Saaed.

PROCESS SIMULATION STUDY USING
®
CHEMCAD SOFTWARE FOR THE
SEPARATION COLUMNS FOR LINEAR ALKYL
BENZENE (LAB) PLANT

A THESIS
Submitted to the Chemical Engineering Department,
College of Engineering,
University of Tikrit
In Partial Fulfillment of the Requirements for the
Degree of Master of Science in Chemical Engineering

By:
Omar Saaed Lateef
(B.Sc. Chem. Eng.)

Supervisor:
Dr. Zaid A. Abdel Rahman

2006 A.D 1427 A.H
CERTIFICATE OF SUPERVISOR

I certify that this thesis has been prepared under my supervision as a
partial fulfillment of the requirements for the degree of Master of Science in
Chemical Engineering at the chemical engineering , College of Engineering,
University of Tikrit.

Signature:

Name: Dr. Zaid A. Abdel-Rahman
Supervisor

In view of that available recommendation I forward this thesis for
debate by the Examining Committee.

Signature:
Name: Dr. Ahmed S. Othman
Assistant professor
Head of Chemical engineering Department
Date: / / 2006
EXAMINERS CERTIFICATE

We certify that we have read this thesis and as Examining Committee
examined the student in its contents and that in our opinion, it meets the
standard of a thesis for the degree of Master Science in Chemical
Engineering.

Signature: Signature:

N ame: Dr.Riadh H. Hasan Name: Dr. Duraid F. Ahmed
Member Member

Signature: Signature:

Name: Dr. Zaid A. Abdel-Rahman Name: Dr.Abdul Mun'em A. Karim

Member (Supervisor) Chairman

Approve by the council of the college of engineering

Signature:
Name: Dr. Farouk M. Mahdi
Assist Professor
Dean of Engineering College
Date: / / 2006
ACKNOWLEDGMENTS

In the name of ‘Allah’ most gracious most merciful
Before anything, I profusely thank ‘Allah’ who enabled me to complete this
humble work.
I would like to express my sincere appreciation and deep gratitude to my
supervisor Dr. Zaid A. Abdel Rahman for his continuous help, active
encouragement, invaluable advice and suggestions.
Special thanks for the Chemical Engineering Department of the College of
Engineering in Tikrit University.
Special appreciation is expressed to the teaching staff during the courses of the
first year of M.Sc. study, especially Dr. Abdul Mun'em A. Karim, and Dr. Ameer M.
Hameed, for their continual encouragement in the Chemical Engineering
Department.
Deep appreciation and gratitude expressed to all friends who helped me,
especially my colleague Lateef A. Ibraheem, for their valuable and continual help
during the study.
Deep appreciation and gratitude expressed to engineering staff in
Arab Company for Detergent Chemicals (ARADET),
Finally special thanks for Iraqi Youth & Student Organization.

i
SUMMARY

CHEMCAD process simulation software was used for the analysis of the
existing linear alkyl benzene (LAB) production plant (Arab Detergent Company,
Beiji-Iraq), especially the major separation columns which are; HF-stripper,
Benzene column, Paraffin column, & Rerun column.
Simulated columns performance curves were constructed. The variables
considered in this study are the thermodynamic model option, top and bottom
temperatures, feed temperature, feed composition & reflux ratio.
Also simulated columns profiles, temperature, vapor & liquid composition, were
constructed, using different thermodynamic models options.
Four different thermodynamic models options (SRK, TSRK, PR, and ESSO
equation of states) were used, affecting the results within 1-25% variation for the
most cases.
For HF-stripper (21 real stages, feed stage 1), the simulated results show that
about 5% of paraffin (C10 & C11) presents at the top stream which may cause a
problem in the LAB production plant. The major variation was noticed for the total
top vapor flow rate with bottom temperature(from about 7000 kg/hr to 19000 kg/hr
with the 30 oC difference of bottom temperature) and with feed composition(from
10000 kg/hr to 4500 kg/hr). The column profiles maintain fairly constants from tray
5 (immediately below feed) through tray 18 (immediately above reboiler). These
trays can be removed without severely affecting the column profile.
For Benzene Column (32 real stages, feed stage 14), the simulated results
show that bottom temperature above 200 oC the weight fractions of top
components, except benzene, increases sharply, whereas benzene top weight
fraction decreasing sharply. Also, feed temperature above 180 oC shows same
trends. The column profiles remain fairly constant from tray 3 (immediately below
condenser) to tray 10 (immediately above feed) and from tray 15 (immediately
below feed) to tray 25 (immediately above reboiler).
ii
For paraffin column (38 real stages, feed stage 16), the simulated results show
that bottom temperature above 240 oC is not recommended because the total
bottom flow rate decreases sharply, whereas the weight fractions of paraffins
decrease slightly.
For rerun column (two packing sections, feed 2nd section) the simulated results
show that critical change of bottom temperature effect was noticed for the bottom
flow rate decrease from about 2500 kg/hr to 150 kg/hr for bottom temperature
increase from 185 oC to 195 oC.
Simulation of the four columns in LAB production plant using CHEMCAD
simulator, confirms the real plant operations data, specially with the top
temperature and total top and bottom flowrate (with in 10% variation). High
deviation of simulated top and bottom components weight fractions with plant
values were noticed.

iii
NOMENCLATURE

a p.s: Interfacial area, packing surface, (m2/m3)
B: Bottom product (kg/hr)
BL: Liquid product from reboiler (kg/hr)
BV : Vapor product from reboiler (kg/hr)
do: Hole diameter of tray, (mm)
D : Top product (kg/hr)
DL: Liquid product from condenser (kg/hr)
D rec.: Rectifying section diameter, (mm)
D str.: Stripper section diameter, (mm)
DV : Vapor product from condenser (kg/hr)
F
j
: Feed flowrate on stage no. (j) (kg/hr)
HF
j: Feed enthalpy (MJ/hr)
H : Total liquid enthalpy of bottom product (MJ/hr)
lB
H : Total liquid enthalpy of top product (MJ/hr)
lD
H
lj: Liquid enthalpy on stage no. (j) (MJ/hr)
H : Total liquid enthalpy on bottom stage (MJ/hr)
l,N−1
H : Total vapor enthalpy on condenser (MJ/hr)
v,1
H : Total vapor enthalpy of bottom product (MJ/hr)
vB
H : Total vapor enthalpy of top product (MJ/hr)
vD
H
vj: Vapor enthalpy on stage no. (j) (MJ/hr)
K : Constant of thermodynamic option on reboiler
iB
K : Constant of thermodynamic option on condenser
iD
K : Constant of thermodynamic option over any stages
ij
L : Total liquid flowrate refluxed to top stage (kg/hr)
0
L
j−1: Total liquid flowrate out put from stage no. (j-1) (kg/hr)
L : Total liquid flowrate out put from stage no. (j) (kg/hr)
j
L : Total liquid flowrate to reboiler (kg/hr)
N−1
L p1: 1st section packing height, (mm)
L p2: 2nd section packing height, (mm)
L str.: Stripper section length, (mm)
iv
n: Number of component
N
min.: Minimum number of stages
P: Pressure, (Kpa)
PL : Liquid product from stage (j)
j
PV : Vapor product from stage (j)
j
Q : Condensed duty, (MJ/hr)
C
Q : Reboiler duty, (MJ/hr)
R
R
: Reflux Ratio (ratio of liquid refluxed to the distillate rate)
R
min.: Minimum Reflux Ratio
vf
: Vapor fraction
V : Total vapor flowrate input to condenser (kg/hr)
1
V : Total vapor flowrate input to stage no. (j) (kg/hr)
j
V
j+1 : Total vapor flowrate input to stage no. (j+1) (kg/hr)
x
Bhk: Weight fraction of heavy key in bottom product
x
Blk: Weight fraction of light key in bottom product
x : Weight fraction of heavy key in top product
Dhk
x
Dlk: Weight fraction of light key in top product
x : Liquid mole fraction of component (i) in bottom product
iB
x : Liquid mole fraction of component (i) in top product
iD
x
i.F: Liquid mole fraction of component (i) in feed
x
i,j−1: Liquid mole fraction of component (i) in stage (j-1)
x : Liquid mole fraction of component (i) in stage (j)
ij
x : Liquid mole fraction of component (i) in bottom stage
i,N−1
y : Vapor mole fraction of component (i) in condenser
i,1
y : Vapor mole fraction of component (i) in bottom product
iB
y : Vapor mole fraction of component (i) in top product
iD
y : Vapor mole fraction of component (i) in stage (j)
ij
y : Vapor mole fraction of component (i) in stage (j+1)
i,j+1
z
ij : Mole fraction of feed components
v
Greek Symbols
λ
ij : Activity Coefficient
α
lk,hk
: Relative volatility between the light key component and heavy key component
θ
: Root of equation (2-3), whereα ≤θ≤α., α are the relative volatilities of the key components
hk lk hk
(light and heavy) in the calculation

Subscripts
i
: Number of components
lk: Light key
hk: Heavy key
j
: Number of stages

Abbreviations

ESSO: Maxwell-Bonnell Vapor Pressure Equation of state
FUG
: Fenske-Underwood-Gilliand method
LAB: Linear Alkyl Benzene
LHSV: Liquid Hourly Space Velocity, hr-1
LLE: Liquid-Liquid Equilibrium
MESH
: Material, Energy, Summation of composition and Heat balance equations
Pacol: Paraffin Converted to Olefin Unit
SRK: Soave-Redlich Kwong equation of state
P.R: Peng Robinson equation of state
TSRK: Extended Soave-Redlich-Kwong equation of state
VLE: Vapor-Liquid Equilibrium

vi
Chapter “1”:

Introduction