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Optimization & Designof a Gas Dehydration
& NGL Recovery Unit
Amal Omar
Atheeba Saeed
Huda Al-Mansouri
Noura Sulatn
Advisor: Coordinator:
Dr. Rachid Chebbi Dr. Mamdouh Ghannam
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Problem Definition
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Problem Definition
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Project Objective
Increasing NGL recovery Designing the unit
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Summary of project I
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Summary of Project I
HYSYS Simulator
Software used to simulate chemical processesdepending on the physical laws.
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Expansion unit
Demethanizer
NGL Recovery Process
Compression unit
Refrigeration unit
Dehydration unit
The following units are used in NGL Recovery:
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NGL Recovery Process
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Graduation Project II
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Graduation Project II
Designing NGL Process and Dehydration
Equipments
Estimating NGL Process and Dehydration
Cost
Studying Environmental Aspect
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Designing NGL Process and DehydrationEquipments
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Designing NGL Process Equipments
Separators
Air coolersHeat Exchangers
ChillersDemethaneizer
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Heat Exchanger Description
Device that transfers heat from one fluid to
another without allowing them to mix
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Heat Exchanger Types
Air-Cooled Exchangers
Shell-and-Tube Exchangers
Fired Heaters
Vaporizer
The exchanger are different in basic
geometrical configuration or types:
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Shell & Tube Exchanger
Cold fluid
Hot fluid
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Design Considerations
Shell & Tube Ex.
• Corrosive fluid
Fluid allocation: shell or tube
• High pressure fluid
• Viscous fluid
• Low flow rate
Shell SideTube Side
Shell & tube fluid velocity
Velocity used is depending on operating pressure.
For vapor high pressure (5-10) m/s
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Design Considerations
Shell & Tube Ex.
Stream temperature
The closer the approach temperature used, the larger
will be the heat transfer area required.
Minimum approach temperature = 20oC
Pressure drop
Selection of pressure drop depends on the economical
analysis that gives the lowest operating cost.
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Design Considerations
Shell & Tube Ex.
Fluid physical properties
Fluid physical properties required for design:Density
Viscosity
Thermal conductivityThe physical properties evaluated at the mean stream
temperature
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Heat Exchanger Design
Tube-side
T u b e Di am e t
e r
Shell-side
Shell-side
Tubes Length
S h e l l D i a m
e t e r
Tube-side
Baff le
T1 = 64 oC
t1 = 21 oC
t 2= 42
o
C
T2 = 50 oC
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Heat Exchanger Design
Physical properties needed for calculation:
Physical property NG inlet NGL product
Mass Flow Rate kg/s 51.6 32.5
Density kg/m3 32 537.56
Mass Heat Capacity
W/moC
2.21 2.63
Viscosity N.s/m2 1.32E-05 0.00012
Thermal conductivity
W/m.k
0.03465 0.089168
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Heat Exchanger Design
Basic assumption and constrains:
Outside diameter, do mm
Rang
16-50
Tube length Rang m 1.36 – 7.32
Baffle spacing 0.3-0.5
Baffle cut % 20-25
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Step 1: determining Number of shell and tube passes
)(
)(
12
21
t t
T T R
)(
)(
12
12
t T
t t S
Using FigureFt : Temperature
correction factor
Step 2 : calculate the ΔTlm and ΔTm :
)(
)(ln
)()(
12
21
1221
t T
t T
t T t T T lm
lmt m T F T
Heat Exchanger Design calculations
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Step 3 : Calculate the heat transfer area A by assuming
U (the overall heat transfer coefficient)
mT U
Q A
)( 21 T T cmQ p
Where,
Q : The heat load
m : mass flow rate
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Step 4 : calculate tube side and shell side coefficients
hi and hs:
w
r P e R jk
d hh
f
ii
14.0
33.0
w
r P e R jk
d hh
f
e s
14.0
33.0
Where,
d Ge R f
p
k
C r P
figure from jh
And,
di is the inside tube diameter
de equivalent diameter
k f is thermal conductivity of fluid
G is the mass velocity
μ is viscosity
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Step 5 : calculate Uo and compare it with the assumed
U :
ii
o
id i
o
w
i
oo
od oo hd
d
hd
d
k
d
d d
hhU
11
2
ln111
If the computed Uo is different
than the assumed U
Trail and error method is used by
repeating the calculations for
another assumed value for U
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Assumed U jh Tube jh shell Uo
270.00 1.80E-03 2.00E-03 337.13
337.13 1.70E-03 1.80E-03 367.17
367.17 1.70E-03 1.60E-03 367.95
Results
Outside tube Diameter 50 mmTube length m 3.66 m
Baffle spacing 0.2
Baffle cut 25%
For this design parameters
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Demethanizer
The raw liquid product is
separated into individualproducts in a series of
columns or towers in which
the top product is the most
volatile component in the
feed.
Description :
Feed
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Demethanizer
This Separation process is done by using mainly three
plates which shown below :
Type Bubble Cap Valve Sieve
Capacity Average High High
Flexibility Excellent Good Average
Pressure drop High Average Average
Cost High Moderate Low
Maintenance Fairly high Moderate Low
Plugging tendency High Moderate Low
Design Well known Well known
by supplier Well known
Market share
5%
70%
25%
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Demethanizer
Require Design Data:
For Top of Column For Bottom Column
Properties Liquid Gas Liquid Gas
ρ (kg/m3) 613.52 15.219 608.61 20.84
Mass flowrate (kg/h)
68670 56205 263686 47810
Volume flowrate(m3/h)
111 3693 433 2304
Viscosity Cp 0.142 - 0.154 -
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Design Procedure:
Number of theoretical plates(Assume) = [7 plate]
O’Connell correlation
E = 0.492(µL α)-0.245
@ T mean column Temperature=55%
E platecontactsmequilibriu plateactual of Number
= [13 PLATE]
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Flow
•
• • • • •
• • • •
• •
• • •
• •
• • •
• • • •
• •
•
•
•
•
•
•
•
• •
• • •
• • • • •
•
•
•
•
•
• •
• • • •
•
•
•
•
Spray
Active area
Calming
zone
Downcomer
apron
Plate below
Plate above
Froth
Clear
liquid Liquid Flow
Dc
Dc
Ds
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Design Procedure: 1.Diameter
For Design 85 percent flooding velocity was used
v
vl st K U
1
velocity Flooding
Vapor of rate f lowVolumitric
required area Net
4
Area Net Diameter Column
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Design Procedure: 2. Provisional plate design
Column diameter Dc 2.76 mColumn area Ac 5.97 m2
Downcomer area Ad= [Ac* 0.12] 0.72 m2
Net area An = Ac - Ad 5.25 m2
Active area Aa = Ac - 2Ad 4.54 m2
Depending on the ratio between Ad/Ac and by using Figure
Lw = 2.09 m
Hole diameter 5 mm
Plate thickness 5 mm
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Design Procedure: 3. Check weeping
Weeping The lower limit of the operating range occurs when
liquid leakage through the plate holes become excessive.
5.0
2 )4.25(9.0
v
hd K u
Minimum Velocity operating rate
h A
rateVapor Volumetric Minimum
velocityvapor imum Actual min
Greater than
d h hole diameter
Ah hole area
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Design Procedure: 4. Plate pressure drop
ht = hd +hw + how +hr
l
v
o
hd
C h
251
l
r h
310*5.12
3/2750
wl
wow
l Lh
1- Dry plate drop
2- Residual head
3- Maximum Weir crest
3/27.0750
wl
w
w
l
Lh
4- Minimum Weir crest
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Design Procedure: 5.Downcomer [back-up]
The downcomer area and plate spacing must be such that the level of liquid
and froth in the downcomer is well below the top of the outlet weir on theplate above to avoid flooding
Clear liquid downcomer Back-up is
Residence timewd
l bd
r
L
h At
It should be greater the 3 s
hap
how
hw
h b P l a t e
s p a c e
2
166
apl
wd dc
A
Lh
Aap
= hap
lw
hap = hw – 5
hb = hdc +(hw + how) + ht
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Design Procedure: 6.Entrainment flooding
Entrainment flooding is caused by an excessive
liquid flow rate generated by droplets carried out of
the gas-liquid dispersion on the tray and up to the
next tray by the gas stream.
velocity Flooding
Area Net
f lowvolumetric Maximum
Flooding Percentage
Fractional entrainment should be less than 1
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Demethaneizer Design Result:
Column Diameter (m) 2.8
Tray spacing (m) 0.4
Minimum operating rate velocity (m/s) 3.2
Actual minimum vapour veocity (m/s) 0.98
Total plate pressure drop 120.75
Residence time (s) 12.98
Fractional entrainment 0.0015
Dv (m) 0.003978
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Equipment Sizing Results
Equipment Diameter, m Length, m Heat transfer area m2
Separator V-100
1.4
4.3
-
Separator V-101 1.2 3.6 -
Separator V-102 1.1 3.2 -
Separator V-103 2.0 6.1 -
Separator V-104 1.1 3.4 -
Heat Exchanger LNG-106 - - 1,300
Heat Exchanger LNG-108 - - 6000
Heat Exchanger LNG-105 - - 11000
Chiller E-103 - - 140
Chiller E-104 - - 15
Air Cooler E-100 - - 6800
Air Cooler E-101 - - 24000
Air Cooler E-102 - - 28000
Demethanizer Column 2.8 12 -
Demethanizer (Separator) 3 9 -
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Environment Aspect
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• Release of sulfur oxide and Nox from emissions in
heater
• Disposal of Propane that used in refrigerants unit
• Composition of fuel used in compressors
• Dehydration Unit
Environmental Aspects : Sources of pollutants
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Dehydration is the removal of water from the
produced natural gas and is accomplished by
various methods:
Ethylene glycol.
Triethylene Glycol dehydration (TEG) and
diethylene glycol (DEG).
Dry-bed dehydrators using solid desiccants.
Dehydration Unit :
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Natural gas contains quantities of aromatic hydrocarbons.The main aromatic hydrocarbons are BTEX components(Benzene, Toluene, Ethyl Benzene, Xylene).
Type of desiccant used is Molecular sieves and theregeneration of desiccants is accomplished by application of hot
gas to vaporize water.
Solid desiccant dehydration using molecular sieve has a highattraction for aromatic hydrocarbons, which are also absorbed
from the natural gas with the water. Thus, a Solid Desiccant Dehydration Unit can be a majorsource of aromatic hydrocarbon emissions to the atmosphere.
Dry-bed dehydrators using solid desiccants
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BTEX and other hydrocarbons are best eliminated byincineration. The vapors from the still column of the heater areheated in the Incinerator and then separated from water bycooling.
Water are sent to waste water treatment while BTEX are sentto flare system or to other operations.
The wastes from this system are spent molecular sieve.
Solution for BETX problem:
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1. Volatile organic compound (VOC) emissions
VOCs may be released from the gas processing systems as freeloses emissions and by venting.
2. Mercury and mercury-contaminated soil
Mercury used in instrumentation and may be released due toimproper storage or maintenance and breakage.
3. Mercaptans
Any of a series of compounds of the general formula RSH,analogous to alcohols and phenols, but containing S in place ofO. Mercaptans are added to gas as an odorant.
Other Possible Sources of Waste
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4. Slop oil
May include any mixture of oil produced at various locations inthe gas processing plant which must be return or furtherprocessed to be suitable for use.
5. Plant wastewater
from:
Cooling tower.Boilers.
Separators.
Other Possible Sources of Waste
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Estimating NGL Process Cost
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Estimating NGL Process Cost
Total Purchased Cost of Equipment is: $ 2030000
$),1( 54321 f f f f f PCE PPC Cost Plant Physical Total
51800000$2.55)( PCE PPC Cost Plant Physical Total
75000000$(1.45)x51800000 capital Fixed
$),1( 121101 f f f PPC capital Fixed
%5 Capital Fixed capital Working
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Total investment
Total investment required for project =
( 1+ 5%)Fixed capital
Plant attainment = 95%
Total investment required for project = $ 78,800,000
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Operating Cost
Fixed operating cost: costs that do not vary with production
rate :Maintenance, take as 5% of fixed capital = $ 3750000
Operating labor, take as 100000 $ per year.Laboratory cost, take as 30% of operating labor = $ 30000
Plant overheads, take as 50% of operating labor = $ 50000
Capital charges, 10% of fixed capital = 7510000
Insurance, 1% of fixed capital = 751000
Supervision, , take as 20% of operating labor = $ 20000Licensed fees and royalty payments, 3% of fixed capital = 2250000
1. Fixed Cost
Total Fixed cost = 14,400,000 $
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Variable operating costs: costs that are dependent on the
amount of product that includes the cost of:
• Raw materials supplied from ADCO fields. Therefore,
raw material cost is not defined• Miscellaneous material ( 10% of maintenance cost) =
& 375000
• Maintenance ( 5% of fixed capital) = $ 3750000
• Utilities cost
Operating Cost
2. Variable Cost
Total Variable cost = 13,000,000 $
Total operating cost per year =$ 28,000,000