Optimization & Design

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Optimization Design of 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 processes
  depending on the physical laws.

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NGL Recovery Process
The following units are used in NGL Recovery

• Compression unit
• Refrigeration unit
• Dehydration unit

• Expansion unit
• Demethanizer

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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 Dehydration Equipments
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Designing NGL Process Equipments

• Separators
• Air coolers
• Heat Exchangers
• Chillers
• Demethaneizer

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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
The exchanger are different in basic geometrical
configuration or types

• Air-Cooled Exchangers
• Shell-and-Tube Exchangers
• Fired Heaters
• Vaporizer

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Shell Tube Exchanger
Cold fluid
Hot fluid
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Shell Tube Ex.
Design Considerations
Fluid allocation shell or tube
Tube Side
Shell Side

• Corrosive fluid

• Viscous fluid

• Low flow rate

• High pressure fluid

Shell tube fluid velocity
Velocity used is depending on operating pressure.
For vapor high pressure (5-10) m/s
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Shell Tube Ex.
Design Considerations
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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Shell Tube Ex.
Design Considerations
Fluid physical properties
Fluid physical properties required for
design Density Viscosity Thermal conductivity
The physical properties evaluated at the mean
stream temperature
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Heat Exchanger Design
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Heat Exchanger Design
Physical properties needed for calculation
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Heat Exchanger Design
Basic assumption and constrains
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Heat Exchanger Design calculations
Step 1 determining Number of shell and tube
passes
Using Figure
Ft Temperature correction factor
Step 2 calculate the ?Tlm and ?Tm
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Step 3 Calculate the heat transfer area A by
assuming U (the overall heat transfer coefficient)
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
Where,
And, di is the inside tube diameter de
equivalent diameter kf 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
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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For this design parameters
Results
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Demethanizer
Description
The raw liquid product is separated into
individual products in a series of columns or
towers in which the top product is the most
volatile component in the feed.
C1
NGL
Feed
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Demethanizer
This Separation process is done by using mainly
three plates which shown below
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Demethanizer
Require Design Data
For Top of Column
For Bottom Column
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Design Procedure
Number of theoretical plates (Assume) 7 plate
OConnell correlation E 0.492(µL a)-0.245 _at_ T
mean column Temperature55
13 PLATE
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Plate above

Spray
Froth

Flow
Clear liquid
Liquid Flow
Active area
Calming zone
Downcomer apron
Plate below
Dc
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Design Procedure 1.Diameter
For Design 85 percent flooding velocity was used
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Design Procedure 2. Provisional plate design
Depending on the ratio between Ad/Ac and by using
Figure
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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.
Minimum Velocity operating rate
dh hole diameter Ah hole area
Greater than
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Design Procedure 4. Plate pressure drop
ht hd hw how hr
1- Dry plate drop
3- Maximum Weir crest
2- Residual head
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 the plate above to avoid flooding
Clear liquid downcomer Back-up is
hb hdc (hw how) ht
Aap hap lw
hap hw 5
Residence time
It should be greater the 3 s
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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.
Fractional entrainment should be less than 1
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Demethaneizer Design Result
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Equipment Sizing Results
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Environment Aspect
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Environmental Aspects Sources of pollutants

• 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

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Dehydration Unit

• 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.

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Dry-bed dehydrators using solid desiccants

• 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
  the regeneration of desiccants is accomplished by
  application of hot gas to vaporize water.
• Solid desiccant dehydration using molecular
  sieve has a high attraction for aromatic
  hydrocarbons, which are also absorbed from the
  natural gas with the water.
• Thus, a Solid Desiccant Dehydration Unit can be
  a major source of aromatic hydrocarbon emissions
  to the atmosphere.

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Solution for BETX problem

• BTEX and other hydrocarbons are best eliminated
  by incineration. The vapors from the still column
  of the heater are heated in the Incinerator and
  then separated from water by cooling.
• Water are sent to waste water treatment while
  BTEX are sent to flare system or to other
  operations.
• The wastes from this system are spent molecular
  sieve.

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Other Possible Sources of Waste

• 1. Volatile organic compound (VOC) emissions
• VOCs may be released from the gas processing
  systems as free loses emissions and by venting.
• 2. Mercury and mercury-contaminated soil
• Mercury used in instrumentation and may be
  released due to improper 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 of O. Mercaptans are
  added to gas as an odorant.

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Other Possible Sources of Waste

• 4. Slop oil
• May include any mixture of oil produced at
  various locations in the gas processing plant
  which must be return or further processed to be
  suitable for use.
• 5. Plant wastewater
• from
• Cooling tower.
• Boilers.
• Separators.

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Estimating NGL Process Cost
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Estimating NGL Process Cost

• Total Purchased Cost of Equipment is 2030000

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Total investment
Total investment required for project ( 1
5)Fixed capital
Total investment required for project
78,800,000
Plant attainment 95
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Operating Cost
1. Fixed 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 20000 Licensed fees and royalty
payments, 3 of fixed capital 2250000
Total Fixed cost 14,400,000
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Operating Cost
2. Variable Cost

• 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

Total Variable cost 13,000,000
Total operating cost per year 28,000,000