Senior Capstone Design 2015-2016
Senior Capstone Design 2015-2016
LYONDELL BASELL:ADDING PACKING TO DISTILLATION COLUMN
AND DESIGNING CONDENSER
Submitted by:
An Tran – Chemical Engineering Janica Daniels – Chemical Engineering Josh Jagneaux – Chemical Engineering Julian Johnson – Chemical Engineering
Submitted to: Dr. Borden – Chemical Engineering
Department of Engineering
McNeese State University
Lake Charles, LA 70609Date Submitted: April 20, 2016
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Table of Contents : Table of Contents…………………………………………………………………………………2
A. Executive Summary…………………………………………………………………….3-4
B. Body of Report………………………………………………………………………...4-32
1. Introduction……………………………………………………………………………4
a. Background…………………………………………………………………....4
b. Flowsheet Diagram……………………………………………………………6
c. Summary of Sections in Project Report……………………………………….6
2. Background Information………………………………………………………………6
a. Confirm the Amount of all Components in Column by Mass Balance……….6
b. Determine Number of Stages and Feed Point Location……………………….7
Equation……………………………………………………………….7
1) Determine Minimum Number of Stages...........…………………...7
2) Determine Minimum Reflux Ratio………………………………..7
3) Determine Number of Stages……………………………………...8
4) Determine Feed Point Location…………………………………...8
Result………………………………………………………………….9
3. Project Design…………………………………………………………………………9
a. Section 1: Adding 10-ft packing to Distillation Column………………...9
b. Section 2: Designing Overhead Condenser……………………………14
c. Section 3: Process Economics…………………………………………25
d. Section 4: Safety and Hazard………………………………………………...28
C. Conclusion……………………………………………………………………………31-32
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A. Executive Summary
An evaluation of the process economics was completed in order to determine if the
project should push forward. In this project, the cash flow was based on savings from
reliability issues based on the design of the condenser. If the amount of ethylene is increased
in the overhead stream, plugging issues, which typically occur one-two times a month would
be eliminated. The value for the savings is based on the assumption that plugging of the
equipment occurs once a month. The value for the savings yearly is $207 K. For this project,
a new condenser and 10-ft of additional packing had to be purchased, the cost of the
equipment is about $50 K. The NPV and IRR values were calculated based on a 7% interest
rate and a 10 year period. The NPV value is about $700 K and the IRR is 38%. Being that
both of the NPV is positive, LyondellBasell could move forward with the project and save
hundreds of thousands dollars a year if the project was successful.
The flowrate of Ethylene coming out of Condenser after adding 10-ft of packing at
the temperature is T = 42oF and P = 300 psig is find base on Pro II model. Because Pro II
allow user to work with number of stage only, not work with height of packing, number of
height equivalent to theoretical plates needs to figure out. Then, the mole and mass fraction
of Ethylene in Condenser is gotten from Pro II. Adding 10-ft of packing is result to increase
2.5 lb/h of Ethylene. It means that the flowrate of Ethylene is increased 60 lb/day,
21900lb/year.
A new overhead condenser to replace to current stab-in one was designed. The new
condenser is a two tube-pass exchanger, and will achieve an overall heat transfer coefficient
of about 275 W/m2-K. The required surface area is around 75 square meters, which will be
used to find an initial estimate for the heat exchanger’s cost. 1/8-inch schedule 40 piping will
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be used for the tubes inside the exchanger. These tubes will have a length of 6 meters, and be
arranged in a triangular pitch. A standard shell clearance of 56 millimeters was selected, as
well as 30% baffle spacing for the shell. All the design specifications were chosen and
optimized with the intention of maximizing the heat transfer coefficient while minimizing
pressure drop across the condenser, which should offer the lowest cost while still performing
the required work.
B. Body of Report
1. Introduction:
a. Background
LyondellBasell is the third largest chemical manufacturer in the United States.
LyondellBasell’s Lake Charles plant produces polypropylene. The polymers produced by the
Lake Charles plant is used to make clothing, CD covers, building materials, and food packaging
just to name a few. Lyondell assigned a specific task to the group. They believed that one of their
systems are running at a subpar level. The system in place involves a distillation column with a
stab-in condenser that produces about 62% ethylene in the top of the column, and about 93 % of
propylene at the bottom of the column. The feed entering the distillation column consist of
mainly propylene and ethylene, at a flow rate of 10000 lb/h and a temperature of 90°F. It consist
of two packed beds, one is 9-ft, and the other is 19 ft. The flow rate leaving the stab-in condenser
is 4000 lb/h, and the flowrate leaving the bottom of the column is 6000 lb/h. Chilled water enters
the stab-in condenser at a rate of 350 GPM and 32°F, and exits at 40°F. The height of the column
is 53-ft, with a diameter of 22in. The packing is dumped, 1-in, metal intalox rings. The stab-in
condenser is 13.5 in in length. The reflux leaving the condenser is 100 %. The column operates
at a total pressure of 300 psig. The feed and the overhead stream is vapor, and the bottoms
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stream is liquid. Lyondell’s main objective is to increase overhead separation by obtaining a
richer ethylene stream in the overhead, and a richer propylene stream in the bottoms. The team of
engineers at Lyondell believe that this may be achieved by removing the stab-in condenser and
adding at least 10 ft of packing to the column. The problem for LyondellBasell lies within a
surplus of propylene in the overhead stream. An increase of propylene in the overhead stream
can prompt quality control issues and lead to plugging of the equipment downstream. This
project consisted of first, designing a base case for our system, or designing the system as is.
Next, the problem and the source of value was identified, which for this system, is quality
control and reliability issues due to a surplus of propylene in the overhead stream. Research,
calculations, and trial and error experiments that would lead us in a direction of achieving better
separation were conducted. Options were then developed in order to improve the system and
obtain better separation. An economic analysis was done for each option in order to narrow down
the choices for the selection process. Based on our work, the removal of the stab-in condenser
replaced with a horizontal condenser and adding more packing could lead to a 5 ° change
entering the condenser which could slightly increase the purity of ethylene in the overhead
stream.
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b. Flowsheet Diagram
c. Summary of Sections in the Project Report
1. Section 1: Adding 10-ft of packing to distillation column
2. Section 2: Designing overhead condenser
3. Section 3: Process Economics
4. Section 4: Safety and Hazard
2. Background Information:
a. Confirm the Amount of all Components in Column by Mass Balance
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The mass fraction and mass flowrate of all components (propylene, ethylene, propane, and
ethane) is given in table below.
Table 1.
b. Determine Number of Stages and Feed Point Location:
Equation:
From the data that is given in Table 1, number of stages, reflux ratio and feed point location is
calculated following by these equation:
1) Determine Minimum Number of Stages (Chapter 17 – Chemical Engineering Design
∝LK (top)=PC 2H 4
¿
PC 3H 6¿ at Tc(C ) ∝LK (bott )=
PC 2H 4¿
PC 3 H6¿ at Tb (C)
∝lk (mean)=∝LK (top)+∝LK (bott )
2
Nmin=log [ xlkxhk ]d [ xhk
x lk ]blog (∝lk )mean
∝i :RelativeVolatiity of Component i withrespect ¿ some ReferenceComponent
T c , T b:Temperature of Condenser∧Reboiler (℃ )
Nmin :MinimumNumber of Stages
2) Determine Minimum Reflux Ratio (Chapter 17 – Chemical Engineering Design)
∑ ∝i x i, f
∝i−Ѳ=1−q ∑ ∝i x i , d
∝i−Ѳ=1+¿ Rmin¿ q=−C p , vap¿¿
Rmin :minimumRefluxRatio
x i ,d :Concentrationof Component i∈theDistillate at minimumReflux
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θ :Root of the Equation
x i ,f :Concentration of Component i∈the Feed
3) Determine Number of Stages (Assume Plate Efficiency is 1)
N−Nmin
N+1=3
4×[1−( R−Rmin
R+1 )0.566 ] N :Number of Stages
R :Reflux Ratio
4) Determine the Feed Point Location
l og [ N r
N s]=0.206 log [( BD )( x f ,hk
x f ,lk)( xb , lk
xd , hk )2]
N r :Number of Stages above the Feed ,including any∂Condenser
N s :Number of Stages below the Feed ,including any∂ Reboiler
x f , HK :Concentrationof Heavy Key∈the Feed
x f , LK :Concentrationof Light Key∈the Feed
xd ,HK :Concentrationof Heavy Key∈the topProduct
xb , LK :Concentrationof Light Key∈thebottomProduct
Result:
From those above equations at Tf =80F and Pf = 300 psig, the relation between number of stages
and reflux ratio are shown in the below graph:
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Figure 1.
So:
Figure 2.
Therefore, 26ft of IMTP#25 is equal 19 stages and the feed is send to tray 4th.
3. Project Design:
a) Section 1: Adding 10-ft packing to Distillation Column
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I. T-xy Diagram and Concentration of Ethylene at Equilibrium
Figure 3.
From the graph below, for condenser, at Tc = 42 F and Pc = 300 psig, the mole fraction
of Ethylene at equilibrium is 0.72
However, the mole fraction of ethylene coming out of condenser now is 70.94; therefore,
adding more packing will help to increase the mole fraction of Ethylene at condenser; and can
increase the purity of product.
II. Find Number of Height Equivalent to a Theoretical Plate (HETP):
For the Condenser with T = 42F and P = 300 psia, with the mass flowrate of condenser D = 4000
lb/h; the vapor velocity is equal 0.3 ft/s and density of vapor is equal 2.296 lb/ft3.
F-factor is calculate by: F s=v √ρG = 0.5 (ft/s(lb/ft3)0.5)
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The relation between F-factor and HETP is given following the graph below:
Figure 4.
Therefore, # HETP for IMTP #25 is equal 1.25 ft. It means with 10ft of packing is added, the
maximum number of stages that can have in the column is equal 28 stages.
III. Relation between Number of Stages to Mass Flowrate, Mole Flowrate, and Mole
Fraction of Ethylene coming out of Condenser:
Because the system is not getting to equilibrium, adding more packing will help to
increase the mole fraction of Ethylene at condenser; therefore can increase the purity of product.
The relation between number of stages to mass flowrate, mole flowrate, and mole
fraction of ethylene coming out of condenser is shown in the below table:
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Figure 5.
For the Condenser with Tc = 42 F. Pc = 300 psig, Heat Duty = 1.5 MM BTU/h, adding
10-ft of packing (or increase 9 stages more), the flowrate of Ethylene coming out of Condenser is
increased 2.5 lb/h. It means that the flowrate of Ethylene is increased 60 lb/day, 21900lb/year.
IV. Other options to increase mass fraction/mole fraction of Ethylene in Condenser
1) Decrease temperature of Condenser by changing cooling system:
The table and graph below are present how the temperature of condenser effects to mass fraction/
mole fraction of Ethylene in product.
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The lower temperature, the better separation the system can get.
2) Increase pressure by adding compressor:
The higher pressure, the better separation
However, because of high expense, both options CANNOT be chosen.
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b) Section 2: Designing Overhead Condenser
Design Specifications:
Transferring heat to and from process fluids is an essential part of most chemical
processes. The most common equipment used to accomplish this, is shell and tube heat
exchangers. Shell and tube heat exchangers pump one fluid through a bundle of tubes. The
bundle of tubes is contained in a shell, where another fluid flows to transfer heat from the hot
fluid into the cold fluid. In this case, the cooling fluid, water, flows through a bundle of tubes,
while a hot mixture of ethylene and propylene flows across the cold tube bundle to cool and
condense the ethylene/propylene mixture.
Currently, LyondellBasell uses a stab-in condenser inside their distillation column.
LyondellBasell wants to know if it would offer any financial benefit to remove the current stab-
in condenser from the column, replacing it with an additional bed of packing, and installing an
overhead, horizontal condenser in the stab-in’s place.
Removing the current stab-in condenser from the distillation column would free up about
12 feet of space inside it. That 12 feet of extra space would be used as room to add an additional
bed of packing with a depth of about 10 feet. As more packing is added, more pressure drop
across the column occurs, which in-turn, drops the outlet temperature of the fluid. This decrease
in temperature can incrementally increase the separation of the product fluid. As packing is
added more of the propylene in the mixture would drop to the bottom’s product, therefore
increasing the purity of the desired product, ethylene, out of the top of the column.
The scope of this project is to design an overhead condenser to replace the current stab-in
one, to make room to add another bed of packing to the distillation column. The increased
packing could increase the purity of the distillation column’s product, which could then be sold
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for an increased profit. So, if the cost of purchasing and installing a new overhead condenser is
less than the additional income that would be made from selling a purer product, then that option
will be chosen. If, however, the increased profit is not enough to cover the cost of a new
condenser, then the system will be kept as is, instead.
Before a new, overhead condenser is designed, it is a good idea to analyze
LyondellBasell’s current, stab-in condenser first. This involves fully defining the overall heat
transfer coefficient to calculate a theoretical value for it, and compare that theoretical value to the
actual value that the stab-in condenser is operating with. If the theoretical and actual Uo values
are different, that will help determine any errors or fouling or potential problems that will occur
in the design of the new condenser. If, however, the theoretical and actual heat transfer
coefficient values are the same, then basing the design of the overhead condenser on the data
from the stab-in condenser will be a good assumption.
First, Uo, is broken down into its components, which is done in the design textbook by equation
(19.2):
Fouling can, first, be assumed to be zero to ease the calculation. If there is a discrepancy
between the theoretical and actual Uo value, then fouling may need to be accounted for later,
however. The do and di variables are the outside and inside diameters of the tubes, and kw is the
thermal conductivity of the tube material. That leaves only the outside and inside heat transfer
coefficients, ho and hi, respectively, that need to be calculated. Because water is used as the
cooling, or tube-side, fluid, a special correlation can be used, that makes hi easy to calculate. It is
calculated using the following equation: hi=4200 (1.35+.02 t )ut.8 /d i
2
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The last value needed to calculate the theoretical Uo value for the stab-in condenser is the
outside heat transfer coefficient, ho. This shell side heat transfer coefficient is calculated using
Kern’s method from the design book. First, Reynolds and Prandtl numbers are needed, and
calculated from the equations:
ℜ= ρ×u×diμ
Pr ¿C p∗μ /k
Where ρ is the density of the fluid, u is the tube-side velocity, di is the inside diameter of
the tube, Cp is the heat capacity, k is the thermal conductivity, and μ is the fluid’s viscosity.
These values are then used to find the shell side heat transfer coefficient by the Nusselt number:
Nu=hs∗de
k= jh∗ℜ∗Pr .33
After that calculation, and ho and hi have been found, the overall heat transfer coefficient,
Uo, can be calculated. This, theoretical, value for Uo for the current, stab-in condenser was found
to be between 270-300 W/m2-K. This value was then compared to the condenser’s actual Uo
value, found to be around 270 W/m2-K using the equation:
Q=U∗A∗ΔT
These two values are almost identical, which suggests that the stab-in condenser is
working as expected, according to fundamental equations, with little or no fouling. This
discovery means that basing the design for the new condenser on the data from the current stab-
in condenser is a good option. The next step of the project is to complete a design for an
overhead condenser using the design process for shell and tube heat exchangers found in the
design book.
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The first step of the design process for shell and tube heat exchangers is to define the
required duty and make any assumptions needed. The condenser’s required duty is first
calculated using the equation:
Q=m×Cp×∆T
Where m is the mass flow rate, calculated from the volumetric flow rate which is given,
Cp is the heat capacity of water, and the change in temperature is also given. Then, a Uo value of
300 W/(m2*K), from the stab-in condenser, is assumed, and a required surface area is found.
The required number of tubes to handle the condenser’s duty is then calculated using an
assumed pipe size. Then, the number of tubes is used with the volumetric flow rate of the cooling
water, which is given, to find a tube-side velocity of the fluid. This tube side velocity will be
important later, when determining the cost of pump power required. Then, the correlation for
water as the tube side fluid is used to calculate the tube-side heat transfer coefficient.
The next step in condenser design is to use the Kern’s method to find the shell side heat
transfer coefficient, as described above in the analysis of the stab-in condenser. Reynolds,
Prandtl, and Nusselt numbers are all needed to calculate the shell side coefficient. Most of that is
calculated from simple physical properties of the shell side fluid. However, one thing that must
be chosen, and eventually optimized, is baffle spacing.
A baffle is the shell that contains the tube bundle. The size of the baffle spacing controls
the shell side fluid’s velocity. A high shell side velocity gives good heat transfer coefficient, but
at the cost of increased pressure drop. Later, these two options will be weighed, to finish the
design of the condenser.
Once the shell side and tube side heat transfer coefficients have been calculated, the only thing
left is to optimize the design of the condenser. This means choosing the specifications of the
condenser that handle the condenser’s duty, but at the lowest possible price. Optimization was
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done on the outside diameter of the tubes first, followed by optimizing the pipe thickness. After
tube sizing is optimized, the length of the tubes is chosen as well. These three optimizations are
each done by finding the effect of the different choices on Uo and pressure drop, and then
choosing whichever option creates the highest heat transfer coefficient while also minimizing
pressure drop.
The cost of the condenser can be broken down into two main components, the cost of the
exchanger equipment and the cost of the pump required to push the cooling fluid through the
tubes. The cost of the exchanger equipment is just the cost of equipment calculated from
equation (7.9) in the design book:
C=a+b∗Sn
Where C is the cost of the heat exchanger, S is the sizing parameter for the equipment,
surface area in m2 for heat exchangers, and a, b and n are parameters for each type of equipment,
given in table 7.2. The second component is the cost of pumping power. The power draw for a
pump is calculated by the equation:
Power=Vol. Flow∗ΔP
To get the total cost for the condenser and pump, the cost of equipment is added to the
cost of the power that the pump must deal with. This cost analysis is done for each different
option, and the option with the lowest price is chosen as the optimum value.
Table 2.
The graph above shows the effect of pipe diameter on overall cost of the heat exchanger.
This graph shows that the cost of the condenser and pump drops as the size of the piping drops.
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So, for this system the price is lowest at 1/8-inch schedule 40 piping. The numerical data for the
information shown in the graph above is found in the following two tables.
Size (in) Do (m) Di-40 (m) TSV (m/s) SSV (m/s) Uo [W/m2-K] ΔP (bar) Cost
1/8 0.405 0.269 2.41 2.56 375 1.500 $ 36,060.89
1/4 0.540 0.364 1.64 1.86 258 0.540 $ 39,619.39
3/8 0.675 0.493 1.20 1.58 204 0.218 $ 43,124.78
1/2 0.840 0.622 0.90 1.24 152 0.123 $ 49,425.22
3/4 1.050 0.824 0.64 0.99 113 0.050 $ 58,510.55
1 1.320 1.049 0.53 0.83 88.0 0.028 $ 69,165.42
Table 3
Size (in) Do (m) Di-80 (m) TSV (m/s) SSV (m/s) Uo [W/m2-K] ΔP (bar) Cost
1/8 0.405 0.215 3.77 2.56 395 4.50 $ 37,293.45
1/4 0.540 0.302 2.39 1.86 273 1.33 $ 39,316.85
3/8 0.675 0.423 1.62 1.58 216 0.51 $ 42,291.56
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 $35,000
$40,000
$45,000
$50,000
$55,000
$60,000
$65,000
$70,000
Pipe Diameter Selection
Schedule 40Schedule 80
Outside Diameter of Tubes (m)
Cost
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1/2 0.840 0.546 1.17 1.24 161 0.23 $ 48,060.82
3/4 1.050 0.742 0.79 0.99 119 0.08 $ 56,693.45
1 1.320 0.957 0.63 0.83 93.0 0.04 $ 66,533.58
Table 4.
Tables 3 and 4 show an option for pipe sizing in each row. Each column in the table
shows how changing only tube diameter effects the rest of the system. As pipe diameter changes,
it either lowers or raises the cross sectional area of flow, which changes tube and shell side
velocities. This, in turn, changes the pressure drop and overall heat transfer coefficient. As heat
transfer coefficient goes up, the required surface area of the condenser goes down, which drops
the price. However, as heat transfer rates go up, pressure drop rises as well, which leads to a
greater power requirement for the pump, which increases price. So, to optimize the design, the
Uo value for each option is used to calculate that options required surface area, and a cost for the
exchanger equipment is calculated. The pressure drop for that option, is then used to calculate
the cost of electricity to run the pump. These two costs are added together, and the lowest total
price is the best option.
After tube size and scheduling is optimized and chosen, a pipe length is optimized using
the same method. By first seeing how changing pipe length effects overall heat transfer
coefficient, and therefore surface area and price, and then by using the pressure drop from that
option to calculate the required electricity for the pump.
The graph above plots how pipe length effects total cost of the condenser and pump. This
graph shows that at a tube length of 6 meters, the price is lowest, around $37,000. The numerical
data shown in that graph is also tabulated in the table here:
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Tubing Length (m) # of Tubes TSV (m/s) SSV (m/s) Uo [W/m2-K] ΔP (bar) Cost
1/8 in. (40) 1 2300 0.52 0.75 160 0.03 $ 48,098.18
1/8 in. (40) 2 1200 1 1.28 233 0.17 $ 40,884.26
1/8 in. (40) 3 800 1.51 1.77 292 0.49 $ 38,031.58
1/8 in. (40) 4 600 2.01 2.22 325 1.04 $ 37,161.15
1/8 in. (40) 5 500 2.41 2.56 345 1.84 $ 36,912.53
1 2 3 4 5 6 7 8 9 10 $36,000
$38,000
$40,000
$42,000
$44,000
$46,000
$48,000
Pipe Length Selection
Pipe Length (m)
Cost
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1/8 in. (40) 6 400 3.01 3.04 385 3.09 $ 36,722.63
1/8 in. (40) 7 350 3.44 3.36 399 4.47 $ 37,194.92
1/8 in. (40) 8 300 4.01 3.77 431 6.74 $ 37,867.49
1/8 in. (40) 9 260 4.63 4.19 479 9.81 $ 38,844.69
1/8 in. (40) 10 240 5.02 4.45 498 12.42 $ 40,055.20
Table 6
Table 6 shows that as pipe length increases, overall heat transfer coefficient does, as well.
A length increases, less tubes are needed to give the same amount of surface area. Less tubes
means that to push the same amount of fluid through the exchanger, the velocity must be higher.
And as velocity increases, so does pressure drop. This is similar to tube diameter, in that as the
length increases so does heat transfer coefficient, which lowers price, but pressure drop is also
increasing which raises the required price. The point of the optimization is to find where the
balance in cost is, finding the maximum heat transfer coefficient, while also minimizing pressure
drop.
Using the same Cost of equipment equation from earlier, combined with the required
electricity to power the pump, a length of 6 meters for the tubes was found to have the lowest
total cost, around 36-37 thousand dollars. This optimization is then combined with the first to
specify the tubing that will be used in the new overhead condenser. Schedule 40 1/8-inch pipes
with a length of 6 meters offer the highest heat transfer coefficient while still having a
manageable pressure drop.
After tube sizing and length have been chosen, baffle spacing is the last optimization to
do. Baffle spacing optimization is done similarly to pipe size and length, in that how it effects
overall heat transfer coefficient is the most important. However, instead of tube side pressure
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drop being the other value to optimize around, with baffle spacing it is shell side pressure drop
that is affected. This is because increasing or decreasing baffle spacing is only changing the size
of the shell around the tube bundle, which effects shell side velocity, not tube side velocity.
Shell side pressure drop is different from the tube side pressure drop, however, in that the
required power of the pump is not the dominant factor, it is the change in vapor-liquid
equilibrium data with pressure drop that matters. As the pressure drops, separation decreases
because more propylene will lift into the top product, which decreases purity.
The graph above shows the effect of baffle spacing on overall heat transfer coefficient as
well as shell side pressure drop. The main point of optimization for baffle spacing is pressure
drop because as pressure drop increases, separation decreases, and the purity of the product is the
most important factor in this project.
Spacing SSV (m/s) Uo [W/(m2*K)] ΔP (bar) ΔP (psi)
15% 4.05 481 5.86 85.00
15% 20% 25% 30% 35% 40% 45% 50%150
200
250
300
350
400
450
500
0.00
1.00
2.00
3.00
4.00
5.00
6.00
Baffle Space Selection
Uo ValueΔP (Bar)
Baffle Spacing %
Uo (W
/m2*
K)
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20% 3.04 385 2.29 33.22
25% 2.43 322 1.04 15.07
30% 2.03 276 0.54 7.83
35% 1.74 242 0.31 4.51
40% 1.52 215 0.19 2.74
45% 1.35 186 0.12 1.79
50% 1.22 170 0.08 1.16
Table 7
A pressure drop of 15 psi can alter the VLE data to lower the purity of the product by 1-
2%, which is not acceptable for LyondellBasell. However, a pressure drop of below 8 psi did not
show a large drop in separation, and the overall heat transfer coefficient is 276 W/(m2*K) which
falls within the 270-300 range that would be expected from the analysis of the stab in condenser.
Because of this, a baffle spacing of 30% was chosen. Once baffle space is chosen, the
optimization of the condenser design is complete, and all values for specifying the design are set.
So, the new overhead condenser will be a shell and tube heat exchanger with water as the
cooling fluid, on the tube side, and the ethylene/propylene mixture on the shell side. The tubing
is chosen as 1/8-inch schedule 40 piping with a tube length of 6 meters. The baffle spacing was
picked as 30% to maximize heat transfer coefficient while maintaining separation of the
products. These values produce an overall heat transfer coefficient of 275 W/(m2*K), a tube side
pressure drop of around 3 bar, with a shell side pressure drop of just over half a bar. The
condenser will be made with carbon steel because the temperature and pressure of the system
isn’t extreme enough to require a more expensive metallurgy.
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c) Section 3: Process Economics
An evaluation of the process economics was completed in order to determine if the
project should push forward. In this project, the cash flow was based on savings from reliability
issues based on the design of the condenser. If the amount of ethylene is increased in the
overhead stream, plugging issues, which typically occur one-two times a month would be
eliminated. The value for the savings is based on the assumption that plugging of the equipment
occurs once a month. The value for the savings yearly is $207 K. For this project, a new
condenser and 10 ft of additional packing had to be purchased, the cost of the equipment is about
$50 K as displayed in Table 11.
Equipment List Units for Size S a b n Estimated Cost of Equipment Heat Exchanger, Shell and Tube, E-407 m2 74 28000 54 1.2 37,451$
Table 7.2: Purchased Equipment Cost for Common Plant, Ce=a+bSn
Table 8
Table 8 displays the cost of the condenser without taking into account the type of
material that the condenser is made out of. The area for the horizontal condenser is 74 m2, which
gives a +/- 50 % estimate of about $40 K. These values and equations were obtained from the
Chemical Engineering Design Book written by Towler and Sinnot.
Equipment Type Installation FactorsDistillation Columns 4Pressure Vessels 4Heat Exchangers 3.5Miscellaneous Equipment 2.5
Installation Factors (Hand Method Table 7.4)
Table 9
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Diamter of the Column 1.83 ftArea 2.630219909 ft2
3.28 ft3Height 1.247044016 min order, ftNumber of Orders 8.0Price per Order 600.00$ Cost of Packing 4,811.38$ Packing + Installation 12,028.44$
IMTP 1-in. Metal Packing, Beihai Kaite Chemical Packing
Table 10
Table 10 displays the cost of packing. These values were found on a website that sells
IMTP metal packing. The price of the packing is $600/m3. These values were used because there
was no book values that correlated with metal IMTP packing in the Chemical Engineering
Design book. A value for the number of orders of packing needed were obtained by finding the
height of the packing in meters by dividing 1 m3 by the area of the packing required. Then take
that 10 ft of packing required and divide by the height found in order to find out how many
orders are needed. This project needed 8 orders of packing which would cost about $5 K. This
value was multiplied by an installation factor, shown in Table to get a total cost of $12 K for
packing.
Carbon Steel 1
49,479.32$
Material Factors
Equipment Cost x Material Factor
Table 11
Being that our horizontal condenser is made of carbon steel, and the basis for the cost
was stainless steel, a material factor had to be used. Based on the material factor for carbon steel,
displayed in Table 11, the total cost of the equipment is about $50K.
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ISBL 143,106$ OSBL: ISBL x .3 42,932$ Contingency 14,311$ Design and Engineering 42,932$ Offsite 42,932$ Total Fixed Capital Cost 286,213$
Total Fixed Capital Cost
Table 12
Table 12, displays the ISBL which is the total cost of the equipment and installation for
the process. The OSBL was calculated by multiplying the ISBL by a factor of .3. Contingency
was accounted for by multiplying the ISBL by a factor of .1. Offsite estimates were obtained by
multiplying the ISBL by a factor of .3, and the same goes for design and engineering. These
values added together yields an estimate of the total fixed capital cost, which is $300 K.
Period 10 yrsInterest 7%
Period Cash Flow Depreciation Taxable Income Taxes Cash Flow After Tax Income NPV0 0 -$ 0 0 (286,212.98)$ (286,213)$ 1 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 126976.18632 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 118669.3333 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 110905.91874 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 103650.39135 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 96869.52466 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 90532.265987 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 84609.594388 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 79074.387279 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 73901.29651
10 207,360.00$ 28,621.30$ 178,738.70$ 71,495.48$ 135,864.52$ 69066.63226668,043$
IRR 38%
Table 13
The total fixed capital investment was used in order to calculate the net present value and
the IRR. The net present value is about $700 K, +/-50 %. The IRR is 38 %. These values
28
conclude that the project can proceed to completion being that the NPV is positive and the IRR is
38% over a 10 year period and an interest rate of 7%.
d) Section 4: Safety and Hazard
Toxicity Data LC50Hazardous Classification (ppm/min) Lower Limit Upper Limit Autoignition Temp. (°F) Flash Point (°F)
Propylene Extremely Flammable 500 658 yes 2 11.1 851 -162Ethylene Extremely Flammable 200 96 yes 2.7 36 914 -213
Safety Analysis
Material Exposure Limit (PEL, ppm)
LDAR required? Flammability/Explosion Range in air (vol% in air) Explosivity Properties
These two compounds are extremely flammable. The distillation column has to be
designed with caution to prevent fires and explosions. Heating can also cause a rise in pressure
with a risk of bursting. Open flames, sparks, and smoking must be avoided in order to prevent
fires. If a fire does occur the ethylene/propylene stream must be shut off immediately. If not
possible and no risk to surroundings, let the fire burn itself out. In other cases, extinguish the fire
with powder.
Vapor/air mixtures are explosive. Some of the ways to prevent explosions are: closed
systems, ventilation, and explosion-proof electrical equipment. In case of explosion, cool fire
down by spraying water from a sheltered position.
Exposure to ethylene/propylene can cause major damage to the human body. Inhalation
of these substances can cause a sore throat and coughing. If exposed to skin or eyes, redness can
occur. Proper PPE will help prevent these damages.
If a spill occurs of either ethylene/propylene the area must be evacuated immediately.
The liquid should be collected in sealable containers. The rest should be absorbed with either
sand or inert absorbent. The collected spill should be stored properly. Storage should be fireproof
and kept away from acids and bases.
29
Incident Effects Recommendations Likelihood Severity Detection Overall risk
1 Reverse flowNo damage to this particular equipment
Check valves to prevent backflow 1 1 3 3
2 No flowIf exposed to heat source it could expand and over pressured the vessel Temp alarms 7 5 5 175
3 More flow Over pressured and cause rupture Flow meters 5 3 1 15
4 As well as flow It will affect downstream Gas chromotography 5 7 10 350
5 Less flow No damage N/a 0
6 High temp/Low tempHigh temp could combust or over pressure. Low temp could condense Temp transmitter 3 7 3 63
7 High pressure/Low pressure Rupture tubes or shell Pressure transmitter 3 7 3 63
8 Reverse flow No damage Check valves 1 1 7 7
9 No flow Ethylene could over heatTemp transmitter on inlet and outlet side 7 7 3 147
10 More flow Over cool the ethylene Flow meters 3 1 3 9
11 As well as flow Temp water would increase Treat water 3 3 3 27
12 Less flow Ethylene could over heat Flow meters 7 7 3 147
13 High temp/Low tempHigh temp will not cool it down. Low temp is prefered Temp transmitter 5 5 1 25
14 High pressure/Low pressure No damage N/a 0
Ethylene side
Water side
The HAZARD above is on the overhead condenser that was designed. There are several
outcomes that could lead to personal injury or equipment design failure. There are four possible
failures that stand out according to the overall risk of this condenser.
The first incident is no flow from the ethylene side. This is the second highest risk
because if the condenser is exposed to heat, an increase of pressure can occur causing the tubes
to rupture. The highest risk is on the ethylene side also. If impurities occur in the stream, that
30
will affect the product downstream and will ultimately decrease the profit. No flow/less flow in
the water side is the third worse circumstance with the overhead condenser. If water flow is
decrease, the ethylene will over heat and the product will not be as pure as it needs to be.
The Boston Square below depicts the HAZARD chart. The numbers on the graph
correspond to the number on the left side of the incident.
0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
7
8
9
10
1
2
3 4
66, 7
1,8
9
10 11
13
Overhead Condenser
Severity
Like
lihoo
d
C. Conclusion
The overall decision of this project has been to proceed with it and remove the stab-in
condenser. According to the VLE graph, the system is almost, but not quite in equilibrium. The
removal of the stab-condenser will give the system ten more feet of packing. This will allow for
31
1-2% more ethylene out the top stream because the system will get a temperature drop of about
five degrees. The overhead condenser that has been optimized based on overall heat transfer
coefficient and pressure drop. The overall heat transfer coefficient is 275 W/m2K and the tube
side pressure drop is 3 bar. The overhead condenser will be made out of carbon steel since it is
the best price selection that matches the needs of the system. The equipment cost of the overhead
condenser and the additional packing totals to roughly $50,000. The total fixed capital cost of
this project amounts to about $287,000. The economics of this project were based on assuming
that the additional 1-2% more ethylene coming out the top stream, will decrease the plugging to
once a month instead of twice a month. The net present value of this project is $668,000. The
internal rate of return for this project is 38% and the cost of capital is at 7%. According to these
calculations and assumptions the project is one that will be successful and worth the investment.
