Optimization and Design of Dehydration Unit and Ngl Process_2

8/13/2019 Optimization and Design of Dehydration Unit and Ngl Process_2

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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



Problem Definition



Problem Definition



Project Objective

Increasing NGL recovery Designing the unit



Summary of project I



Summary of Project I

HYSYS Simulator

Software used to simulate chemical processesdepending on the physical laws.



Expansion unit

Demethanizer

NGL Recovery Process

Compression unit

Refrigeration unit

Dehydration unit

The following units are used in NGL Recovery:



NGL Recovery Process



Graduation Project II



Graduation Project II

Designing NGL Process and Dehydration

Equipments

Estimating NGL Process and Dehydration

Cost

Studying Environmental Aspect



Designing NGL Process and DehydrationEquipments



Designing NGL Process Equipments

Separators

Air coolersHeat Exchangers

ChillersDemethaneizer



Heat Exchanger Description

Device that transfers heat from one fluid to

another without allowing them to mix



Heat Exchanger Types

Air-Cooled Exchangers

Shell-and-Tube Exchangers

Fired Heaters

Vaporizer

The exchanger are different in basic

geometrical configuration or types:



Shell & Tube Exchanger

Cold fluid

Hot fluid



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




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.




Shell & Tube Ex.

Fluid physical properties

Fluid physical properties required for design:Density

Viscosity

Thermal conductivityThe physical properties evaluated at the mean stream

temperature



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




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




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



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



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



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



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



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



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



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%



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 -



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]



Flow

•

• • • • •

• • • •

• •

• • •

• •

• • •

• • • •

• •

•

•

•

•

•

•

•

• •

• • •

• • • • •

•

•

•

•

•

• •

• • • •

•

•

•

•

Spray

Active area

Calming

zone

Downcomer

apron

Plate below

Plate above

Froth

Clear

liquid Liquid Flow

Dc

Dc

Ds



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



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



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



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



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



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



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



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 -




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 -



Environment Aspect



• 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



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 :



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



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:



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



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



Estimating NGL Process Cost



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



Total investment

Total investment required for project =

( 1+ 5%)Fixed capital

Plant attainment = 95%

Total investment required for project = $ 78,800,000



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 $



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

Documents

Optimization and Design of Dehydration Unit and Ngl Process_2