ENGINEERING. UAEU. United Arab Emirates University College of Engineering Industrial Training and Graduation Project Unit. Design and optimization of a fractionation unit. Mariam Ali Albraiki Hanaa Saeed Al-Shamsi Lamya Lari Fatima Al-shehhi . Advisor: Dr. Rachid Chebbi.
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United Arab Emirates University
College of Engineering
Industrial Training and Graduation Project Unit
Design and optimization of a fractionation unit
Mariam Ali Albraiki
Hanaa Saeed Al-Shamsi
Advisor: Dr. Rachid Chebbi
The project is about designing and optimizing fractionating plant in Al-Ruwais Fractionation Unit. Our target from the fractionation unit is to design and optimize a unit in order to separate the liquid components from natural gas into DEO, C3, butanes and C5+.
Separation process operates basically on the principle of pressure reduction to achieve the separation of gas from a liquid inlet stream.
Definition of Compressor
Compressors are described as mechanical device that takes in a gas and increases its pressure by squeezing volume of it into a smaller volume
Types of Compressor
The vapor area of the holes varies between 5 to 15% of the tray area
In the sieve plate, vapor bubbles up through simple holes in the tray through the flowing liquid
Hole sizes range from 3 to 12 mm in diameter, with 5 mm a common size
vapor or gas rises through the opening in the tray into bubble caps
This type has been used over 100 years
The gas flows through slots in the periphery of each cap and bubbles upward through the flowing liquid.
modification of the sieve tray, they are essentially sieve plate with large diameter holes.
stage efficiency is the performance of a practical contacting stage to the theoretical equilibrium stage. Murphree plate efficiency is the ratio of the actual separation achieved to that which would be achieved in an equilibrium stage
Check the weeping rate.
Check the pressure drop.
Check downcomer back up.
Recalculate the percentage flooding Check entrainment.
The liquid- vapor flow factor was determined for the top and bottom part using the following equation:
Flv ( Top) = 0.359
Flv ( Bot) = 0.394
Lw = Liquid mass flow rate in Kg/s
Vw = Vapour mass flow rate in Kg/s
Ρv = is the vapor mass density in Kg/m3
Ρl = is the liquid mass density in Kg/m3
From the graph ,it the KTop and KBotwere found as 8*10-2 and 7.6*10-2 respectively.
Next step was to correct the surface tension for top either bottom as shown below , from HYSYS simulator the surface tension are
S Top = 2.771 *10-3 N/m
S Bot = 2.155 *10-3 N/m
K'Top = 0.0538
By using the equation
K’Bot = 0.0486
u f is the flooding vapor velocity in m/s
K' is the correction value for the surface tension in top and bottom part
u fTop=0.1387 m/s
With 85 % flooding
u fBot=0.1387 m/s
u’ fBot=0.097 m/s
In order to find the Maximum volumetric flow rate , the following equation was used
V top =0.074 m3/s
V bot=0.077 m3/s
Vw = Vapour mass flow rate in Kg/s
Ρv = is the vapor mass density in Kg/m3
In this step , the net area was calculated using the following equation
Top = 0.628 m2
Bot = 0.802 m2
In this part, it was assumed that the downcomer area is 12% from the total as a trial step , the column cross –sectional area are
= 0.713 m2
= 0.911 m2
Finally , the column diameter column at top and bottom
D top =0.952 m
D is the column diameter in m
A is the net area
D bot =1.01 m
Weir height = 50 mm
Hole diameter = 5 mm
Plate thickness = 5 mm
Total pressure drop
ht = hd +( hw+ how)+ hr
100 mm liquid
Actual minimum vapor velocity =
= 0.709 m/s
Downcomer liquid back up
Back –up in downcomer was estimated by
hb = (hw + how) + ht + hdc
= 178 mm
= 0.0875 m/s
Number of holes
Area one hole = 1.964 *10-5 m2
Number of holes =
= 3869.6 = 3870
Device that facilitate the exchange of heat between two fluids that are at different temperature without allowing them to mix
Most heat exchangers are classified in one of several categories on the basis of configuration of the fluid flow path through heat exchanger.
The most common types of flow path configuration are:
The advantage of this type are:
The configuration gives a large surface area in small volume
Can be constructed from a wide range of materials
Fluid location: shell or tube
Corrosive fluid Tube
Fouling fluid Tube
Higher temperature Tube
Higher pressure Tube
More viscous Shell
Low Flow rate Shell
For Tube (1-2) m/s
For Shell (0.3-1) m/s
The closer the approach temperature used, the larger will be the heat transfer area required.
Minimum approach temperature = 20oC
Selection of pressure drop depends on the economical analysis that gives the lowest operating cost.
Heat Exchanger Design
Step 2 : Selecting Number of shell and tube passes
Ft : Temperature correction factor
Step 4: Selecting a trial value for the overall heat transfer coefficient U
Step 5 : Calculating the heat transfer area A
Q : The heat load, was taken from ASPEN PLUS simulation result
Step 7: Calculating shell side heat transfer coefficient ho
Trial and error is used if the computed Uo is different than the assumed U
Total head loss:
Gas pressure drop:
If FR0 ≥ 0.5 that means weeping is not a problem.
Entrainment mass flow rate :
What happens to hydrogen sulfide when it enters the environment ?
for about 18 hours.
Breathing very high Concentrations:
Death within just a few breaths
Loss of consciousness after one or more breaths
Breathing Low Concentrations:
Sore throat and cough
Shortness of breath
Long-term, low-level exposure:
Loss of appetite
Occupational Safety and Health Administration (OSHA):
Acceptable concentration of (20 ppm) in the workplace.
National Institute of Occupational Safety and Health (NIOSH(
recommends a maximum exposure level of 10 ppm.
The characteristics, sources, and hazards of Hydrogen
Proper use of the Hydrogen Sulfide detection methods
used on the site.
warnings at the workplace.
Symptoms of Hydrogen Sulfide exposure
Proper rescue techniques and first-aid
procedures to be used in a Hydrogen Sulfide exposure.
Worker awareness of workplace practices
and maintenance procedures to protect
personnel from exposure to hydrogen sulfide.
General consideration in finding the cost for equipments as the following steps ( example : depropanzier column)
Using the process engineering index in Figure as :
Value of index at 1998 = 390
Value of index at 2003 = 395
Purchase cost, $ for vessel = (bare cost from Figure) x (material factor) x (pressure factor ).
Purchase cost, $ for vessel = (bare cost from Figure 5.1.3)x(material factor)x (pressure factor ).
With 1.5% inflation from 2003 to 2004 it will become as:
Purchased and installation cost for depropanizer column = $87312
Total physical plant cost (PPC) = PCE (1+ f1 + f2 + f3+ f6)
= (377,028) (1+ 0.7+0.7+0.2+0.5)
= 11,168,786.8 x (1+ 0.3+0.05+0.1)
Three units were studied in this project. Simulation was done for the two units using two different simulators. GASCO specifications were met. In sweetening unit, hydrogen sulfide concentration was reduced to 4ppm. Process equipment design, sizing and cost estimation were done in this project. Fixed capital cost for the whole plant is found to be $6,556,844.