Aker Solutions Presentation - Drying of Natural Gas

8/11/2019 Aker Solutions Presentation - Drying of Natural Gas

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part of Aker

2008 Aker Solutions

Drying of natural gas

Thomas Frde, October 21, 2010

Troll A


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Slide 2 2008 Aker Solutions part of Aker

Layout

1. Introduction/motivation

2. Industrial examples

3. Theory drying Dehydration

4. Summary


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BackgroundExplanations

Raw natural gas; gas produced

from the well

Sour natural gas; containshydrogen sulfide H2S or carbon

dioxide CO2

Sweet natural gas; contains little

sulfur and carbon dioxide Rich natural gas; contains larger

quantities of higher hydrocarbons

Wet natural gas; is saturated with

water vapor under natural

conditions

Petroleum technology volume 1-2 chapter 13 natural gas

Introduction

Krst Statoilhydro photo


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IntroductionGas specifications

Gas and liquid contracts usually contain the following basic considerations:

Gas

1. Minimum, maximum and nominal delivery pressure

2. Maximum water content (expressed as a dewpoint at a given pressure orconcentration)

3. Maximum condensable hydrocarbon content (expressed as ahydrocarbon dewpoint )

4. Allowable concentration of contaminants (H2S, carbon disulfide)

5. Minimum and maximum heating value

6. Cleanliness (allowable solids concentration)

Liquid

1. Quality of product (expressed as vapor pressure, relative or absolute

density)2. Specification (color, concentration of contaminants)

3. Maximum water content

Introduction


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Motivation

Treating

Water must be removed

Solid hydrates with hydrocarbons or hydrogen sulfide

Slugs in pipeline

Corrosive H2S and CO2

Petroleum technology volume 1-2 chapter 13 natural gas, Natural gas production processing transport A.Rojey et.al

Introduction

Hydrogen sulfide (H2S) must be

removed

Toxic and corrosive

Often done centralized treatment

plants Nitrogen

No heating value


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MotivationFlow configurations

Principal sketch natural gas, well to consumer

Well-stream from sub-sea/platform to shore (LNG; Snhvit, gas export; Troll and Ormen Lange)

Platform with full gas processing gas export (Sleipner)

Sleipner

snhvit

Troll, ormen lange

Troll

Introduction

Off shore platform

processing

Pipe line

Pipe line to europe

LNG

1: Off shore to land, pipe line demands2: Export pipe line, demands

3: LNG composition demands

Refinery and

petrochemicals

4: Condensate composition

demands


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Motivation

Typical north sea natural gas composit ion

Major components (mol percentage dry gas) in some north sea gas reservoirs

It can be seen from the table, that Troll produced very lean gas.

Other fields contains more CO2 and heavy components.

Introduction

1 Petroleum technology chapter 13 * hydrocarbons

A Well stream, B Pipeline stream

Saturated

Saturated

Saturated

Saturated

Saturated

H20

1-10

3

0.15

4.13

1.51

Propane

0-1

0.38

7.9

12.4

0.31

Other*

0-5

-

He

0-3

0.49

-

H2S

8.6833.421.6SleipnerB

0.4724.865.80.38South-east

asian field

8.7071.083.360.32KristinA

1-15

3.53

EthaneMethaneCO2N2

75-99

92.69

0-300-15Typical [1]

0.221.74TrollAA


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Industrial

examples


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Natural gas processing

Principal sketch natural gas processing route

Industrial


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Industrial examples

Troll, Kolsnes onshore plant

Industrial

Simplified flow sheet Troll onshore gas treatment plant Kolsnes


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Industrial examples

Principal sketch Troll, MEG*

System

Industrial

Background:

Troll is located in the north part of the North Sea, about 65 km west of Kolsnes

Ocean depth is above 300 meter

The field is divided into Troll east and Troll west

2/3 of the recoverable gas reserve is located in the east

* Monoethylene Glycol (MEG) also called ethylene glycol (EG)


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Troll

Dehydration system

Feed gas from

slug catchers

Inlet gasseparator

(Pressure, BARG)

(90)

(89.5)

(67)

(69.4)

Condensateand Glycol

(69)

(68.5)

(78.4)

Lean gas to pipelinecompressorsTurboexpander

Suction drum

Dewpointseparator

MEG


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Principal sketch KristinAll processing offshore

Kristin is a high pressure field (900 in the well, choke sea bottom to 350 bar)

Ocean depth is about 350 meters

Gas is transported to KrstEconomic choice of technology; takes advantage of high well pressure and existing single phase

pipe-line to Krst

Full processing offshore to meet existing pipe-line spec (105 cricondenbar) inlet pipeline pressure

211 bar and 50 degrees Celsius

Gas is delivered at Krst at 100 bar

Industrial

Q Q


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Kristin

Liquid separation system

Sketch of Kristins liquid separation system

Inlet

separator

2nd stage

separator

3rd stage

separator

1st stage

recompressor

2st stage

recompressor

3st stage

recompressor

To Dehydration system

(Pressure, BarA)

(87)

(26)

(2.15)

(1.7)

(7)

(25)

To condensate

storage

Inlet wet

gas

pressurereduc

tion

Pressureincreasing


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Kristin

Separation re-compressor package

From separator

To separator

Out of recompressorCompressor

separator

Sketch of Kristins separator recompression system


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Principal sketch KristinAll processing offshore

Kristin is a high pressure field (900 in the well, choke sea bottom to 350 bar)

Ocean depth is about 350 meters

Gas is transported to Krst

Economic choice of technology; takes advantage of high well pressure and existing single phase

pipe-line to Krst

Full processing offshore to meet existing pipe-line spec (105 cricondenbar) inlet pipeline pressure

211 bar and 50 degrees Celsius

Gas is delivered at Krst at 100 bar

Industrial

Q Q


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Kristin

De-hydration (TEG) system

Sketch of Kristins dehydration system

TEG: Triethylene glycol


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Snhvit

Principal sketch

Industrial

Slug

catcher

Inlet

separation

MEG

Recovery

Condensate

treatment

Feed from

pipeline CO2

Removal

CO2

De-

hydration

Mercury

Removal

Natural gas

liquefaction

To

pipeline LNG

storage

LPG

storage

Condensate

storageFractionation

First developed field in the Barents sea

Ocean depth of 300-350 meters

A gas field with condensate and an underlying thin oil zone

Choice of technology: Make LNG, no existing gas lines to Europe


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Snhvit dehydration system

Molecular sieve

Snhvits molecular sieve

Hot Oil

Regeneration

gas

Dry gas

(pressure, barA)

(64.9)

(63.0)

(64.0)

(63.7)

(63.2)

Wet gas

Regeneration gas

Example ofMolecular sieves


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Summary

Introduction, industrial examples and pipeline

These points have been discussed/explained:

General facts about natural gas

The dehydration system at: Troll (onshore), MEG injection and dehydration by cooling

(turboexpanders)

Kristin (offshore), dehydration by absorption (TEG system) Snhvit (onshore), dehydration by adsorption (molsieve)

Some of the issues related to transport of natural gas in pipelines


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Dehydration


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Natural gas processing

Principal sketch of a natural gas processing plant

Dehydration


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Dehydration

Natural gas is commerciallydehydrated in one of three ways

1. Absorption (Glycol dehydration)2. Adsorption (Mol sieve, silica gel, or activated

alumina)

3. Condensation (cooling) (Refrigerationwith glycol or methanol injection)

Four glycols are used for dehydrationand/or inhibition

1. Monoethylene Glycol (MEG) also

called ethylene glycol (EG)

2. Diethylene glycol (DEG)

3. Triethylene glycol (TEG)

4. Tetraetylhene glycol (T4EG)

Dehydration

Absorption and refrigeration with hydrate inhibition is the most common dehydration

process used to meet pipeline sales specifications

Adsorption processes are used to obtain very low water contents required in lowtemperature processes, for example LNG

TEG is most common in absorption systems

MEG is most common in glycol injection systems

Dehydration is the process of removing water from a gas and/or liquid


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AbsorptionDehydration


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Absorption

DehydrationNatural gas is dried by absorption,

often in a countercurrent scrubbing

unit

A liquid having a strong affinity forwater is used as an absorbent

A good absorbent should have:

1. Strong affinity for water

2. Low cost

3. Non corrosive

4. Low affinity for hydrocarbons andacid gases

5. Thermal stability

6. Easy regeneration

7. Low viscosity

8. Low vapor pressure at the contacttemperature

9. Low tendency to foam

Absorption

Dehydration

TEG

DEG

TEG

TEG

Vapor pressure25 C

Freezing point

C

Viscosity (25 C)

Molecularweight

T4EGDEGMEG

-13 - -7TEGT4EGMEG

17- 49T4EGDEGMEG

62 194T4EGDEGMEG

Increasing values

Basic glycol properties


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Basic glycol dehydration unit

Simplified flow diagram for a glycol dehydration unit. from the GPSA Engineering Data Book, 11th

ed.

Absorption

Dehydration


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The glycol dehydration unit

Wet gas (no liquid water) enter bottomof absorber and flowscountercurrent to the glycol. Leanglycol enters at the top

Absorber internal

Tray

Bubble cap

Valve

Sieve

Packing

Berl Saddle, Raschig Ring

ReactorOne, two pass trays

Bubble Cap

Bearl Saddle

Valve tray

Sieve trayBubble Cap tray

Absorption

Dehydration

Maximize

Contact area

and time

Gas/glycol


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Absorber design

Design parameters

Purity demand

Working temperatures

Working pressure

Choice of absorbent

Design procedure

Mass balance circulate enough glycol toabsorb the water in the gas

Gas rate tank diameter (flooding)

Equilibrium analysis number of equilibriumstages

Real analysis, have to take into account thereaction kinetic and contact time betweenglycol and gas. Gives number of actual trays

Dryer glycol higher concentrationdifferences higher reaction kinetichigher efficiency more expensive andheavier glycol regeneration system

Higher glycol circulation rate higherconcentration differences higher reactionkinetic higher efficiency higher pressure

drop

more expensive and heavier pumps

Principal sketch assuming:

Mass transfer are controlled by

resistance on the gas side

Straight operation and equilibrium

lines of mol fraction water in the gasphase

stagesactualofNo

stagesEQofNo

.

.

Absorption

Dehydration

Mol fraction water

in glycol

Molfractionwater

ingas

Bottom of

tower

Top of tower

Glycolflo

w

Gasflow

EQlineOP

line

Yb*

Yb

Yt*

Yt

Y mol frac. Watergas phase

Y* EQ mol frac.

Water gas phase


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Glycol regenerationAlternatives

A) Open stripping loop

B) Closed stripping loop

C) Cold finger

Increasedtemperature

A) Any inert gas is suitable. Theoretically best to insert

stripping gas between re boiler and surge tank

B) A closed stripping loop, isooctane can be used.

Vaporizes at re-boiler temperature and condenses and

can be separated from water in a three phase separator.

High stripping gas rates with little venting of

hydrocarbons. Glycol cons> 99.99% (w/w) has been

achieved.

C) A cold finger is inserted into a bucket in the

surge drum vapor space. A TEG mixture rich inwater condenses out. This mixture is taped off.

H2O partial pressure is lowered and lean glycol

concentration is increased. 99.5-99.9 % (w/w)

glycol has been achieved.

Absorption

Dehydration

Rich TEG

Re boilerHeat

Exchanger

A; Stripping gas

A; Wet strippinggas

Water

B; strippinggas

TEG unit

Cool

Heat

still

column


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Glycol regeneration

ComponentReboiler:

Temperature should not exceed 204 C (TEG) due to

degradation.

Some degradation of glycol in contact with heattransfer surface maximum heat flux rates.

Heat provided with direct fired fire tubes immersed in

the bath, hot oil, steam or electric resistance heating.

Stripping Colum:

Can be trayed or structural packed. Stripping gas

lowers the partial pressure of H2O in the gas phase,

and more water can be absorbed by the gas (Raoultslaw).

Surge drum:Retention time >20 min

Be able to hold all the re-boiler glycol, to allow repair

or inspection of the re-boiler heating coil.

Flash tank:

Used to remove light hydrocarbons,CO2, H2S. Operation pressure 15% of

the contactor operating pressure.

Filters:

Captures chemical impurities and solid

particles. Pressure drop is measured

and used as a replacing criteria.

Absorption

Dehydration


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Glycol absorptionPros and cons

Pros

Low initial cost

Low pressure drop across absorption towers

Recharging of towers present no problems

Materials that would cause fouling of somesolid adsorbents can be tolerated in thecontactor

Cons

Suspended matter, such as dirt, scale, and ironoxide may contaminate glycol solutions

Overheating of solutions may produce both lowand high boiling decomposition products

The resultant sludge may collect on heatingsurfaces, causing some loss in efficiency, or, insevere cases, complete flow stoppage

When both oxygen and hydrogen sulfide ispresent, corrosion may become a problembecause of the formation of acid material in the

glycol solution Liquids such as water, light hydrocarbons or

lubrication oils in inlet gas may requireinstallation of an efficient separator ahead ofthe absorber. Highly mineralized water enteringthe system with inlet gas may, over longperiods crystallize and fill the re-boiler with solid

salts Foaming of solution may occur with a resultant

carry-over of liquid. The addition of a smallquantity of antifoam compound usuallyremedies this problem

Absorption

Dehydration


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Dehydration by

cooling

D h d ti b


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Refrigeration system

A refrigeration system lowers thetemperature of a fluid or gas below thatpossible when using air or water atambient conditions.

Refrigeration systems are used for Removing of water Chilling natural gas for NGL

extraction

Chilling natural gas forhydrocarbon dew-point control

LPG product storage

Natural gas liquefaction (LNG)

Refrigeration processes: Mechanical refrigeration

Compression (uses energy in form of workto pump heat)

Absorption (use energy in form of heat topump heat, ammonia systems) Expansion refrigeration

Valve expansion (Joule Thompson)

Turbine expansion (Turbo expander)Natural gas liquid fractions as a function of

temperature at atmospheric pressure

Dehydration by

cooling NGL

recovery


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Refrigeration cyclePrincipal thermodynamic path

A-B,E cooled by heat exchange with the process gas.

B-C Natural gas is cooled by heat exchange with the refrigeration cycle. The gas temperature is lowered at

constant pressure.

E-F Natural gas is cooled by isentropic (constant entropy S) expansion through a turbine (turbo expander), EF

actual path.

B-D Natural gas is cooled by isenthalpic (constant enthalpy) expansion through a valve (Joule Thompson).

Dehydration by

cooling NGL

recovery

Thermodynamic pathLiquid recovery by refrigeration

D h d ti b


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Principal sketch of arefrigeration cycle

Refrigeration is achieved by vaporization at relatively low refrigerant pressure.

The refrigerant can be a propane or sometimes a halogen of the Freon type.

Dehydration by

cooling NGL

recovery

Natural

gas

Dehydration by


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Turbo expander cycle(Troll gas)

Dehydrated

gas

Condensate

and Glycol

Lean gas to pipeline

compressorsTurboexpander

Suction drum

Dewpointseparator

Turbo expander process for

NGL extraction

Phase envelope based Troll, dehydrated gas

1 Feed gas

1-2 Gas-gas heat exchanger

2-3 Suction drum

3-4 Turbine expander

4-5 Dewpoint separator


6-7 Compression

A hydrate inhibitor (MEG) is

often injected upstream of the

heat exchanger, if the gas is un-hydrated

y y

cool ing NGL

recovery

-10

10

30

50

70

90

110

-170 -140 -110 -80 -50 -20 10 40

Temperature [C]

Pressu

re

[Bar]

Path turbo expander

Feed gas phase envelope

Path joule thompson

1 2

3

45

67

Joule Thompson cycleDehydration by


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Joule Thompson cycle(Trol l gas)

Inlet gas

Condensateand Glycol

(69)

Lean gas to pipeline

compressorsTurboexpander

Suction drum

Dewpoint

separator

Phase envelope based on Troll, dehydrated

gas

Joule Thompson process

for NGL extraction

1 Feed gas


2-3 Suction drum

3-4 Valve expander

4-5 Dewpoint separator


A hydrate inhibitor (MEG) is

often injected upstream of the

heat exchanger, if the gas is un-

hydrated.

y y

cool ing NGL

recovery

-10

10

30

50

70

90

110

-170 -140 -110 -80 -50 -20 10 40

Temperature [C]

Pre

ssure

[Bar]

Path turbo expander

Feed gas phase envelope

Path joule thompson

1 2

3

45

6


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Dehydration


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Dehydration by adsorption

Adsorption describes any process where gas molecules are held onthe surface of a solid by surface forces. Adsorbents may bedivided into two classes.

Species is adsorbed due to physisorption and capillarycondensation

Species is adsorbed due to chemisorption (not much used innatural gas processing)

A sorbent must have the following properties:

1. High adsorption capacity at equilibrium

2. Large surface area

3. Easily and economically regenerated

4. Fast adsorption kinetics

5. Low pressure drop

6. High cyclic stability (kinetic and capacity)7. No significant volume change (swelling shrinking)

Dehydration

by sorption

Dehydration by adsorptionDehydration


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Dehydration by adsorption

The commercial available sorbents can be divided into three broad categories:1. Gel

A granular amorphous solid (silica gel (SiO2), alumina gel Al2O3)

2. AluminaHydrated form of aluminum oxide Al2O3, activated by drying off part of the hydrated water

adsorbed on the surface

3. Molecular sievesAlkali metal crystalline aluminosilicates, very similar to natural clays

Example of sorbents:

Silica gel (Gel type)Outlet gas water content down to 10 ppm (v/v) and dew point -60 C can be achieved

Regenerated between 120 and 200 C

It adsorbs hydrocarbons, which are desorbed during regeneration

Silica gel is destroyed by free water which causes the granules to burst, and react with bases

Activated alumina Al2O3Outlet gas water content


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Principal sketchAdsorbent system

http://www.uop.com/objects/96%20MolecularSieves.pdf

Flow sheet of a basic two tower adsorption system with regeneration

Molecular sieves

Dehydration

By sorption

Re

generation

Operation

Process gas

Regeneration gas

Regeneration gasProcess gas

Dehydration


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AdsorptionConcentration profiles

Active

Zone

Mass transfer

Zone

Equilibrium

Zone

Dry gas

Wet gas

Variation of adsorption zones with time and height Schematic view of reactor bed with adsorption zones

Equilibrium zone: Sorbent is saturated with water.

Mass transfer zone: All the mass transfer takes place in this zone.

Active zone: The sorbent has its full capacity for water, contains only residual

water left from regeneration cycle.

y

by sorption

Ad iDehydration


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AdsorptionGeneral point and re-generation

Design parameters

Number of adsorption unitsregeneration time

Gas velocity and allowablepressure drop diameter

Good internal flow distribution avoidchanneling

Proper pre-treating of the gas Degradation due to loss of

effective surface area Degradation due to blockage of

small capillary or latticeopenings

Proper heat loss management(insulation internal/external)

optimize regeneration Proper heat recovery

Possible to replace adsorbent

Principal sketch of reactor temperature duringregeneration

T0-TA heating of the reactor

TA-TB evaporation and breaking of surface

forces

TB-TC removing of heavy contaminants

and residual water

TC Cooling, heat recovery phase

Dehydration

by sorption

S d h d ti


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Summary dehydration

Different dehydration technologies have been discussed Absorption

Glycol system Trayed towers

Structural packing

Concentration profiles Design guide lines

System components

Cooling System

Compressor cooling Turbo expander Joule Thompson

Adsorption Concentration profiles

Design guide lines

System component/operation


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CO2 capturetechnology

CO capture from energy related sources


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CO2 capture from energy related sources

CombustionFossil fuel

Flue gas

Air

Energy

CO2separation

CO2

N2 ,O2

Gasification/

reforming

Fossil fuelH2, CO2

Air/O2 Steam

Energy

CO2separation

CO2

H2 Combustion

Air

N2 ,O2 , H2O

Energy

CO2 capture from large scale power plants is yet

to be implemented


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Selcetion of CO2 capture technology


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Selcetion of CO2 capture technology

http://www.uop.com/gasprocessing/6010.html

Typical CO2 absorption loop


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Typical CO2 absorption loop

Amine

AbsorberFeed

Gas

KO Drum

Product

Gas

KO Drum

Feedgas

Product gas

Lean-Rich

Exchanger

WaterMake Up

Water Wash

Pumps

Rich Solvent

Flash Drum

Flash gas

Lean Sol.

Cooler

(CW)

Carbon

Filter(Lean Sol)

Amine

Regen-

erator

HP Lean

Pump

LP Lean

Pump Regen.

Reboiler

(LPS)

Acid Gas

Condenser

(CW)

Regen.

Reflux

Drum

Reflux

Pump

Acid gas

Summary of presentation


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Summary of presentation

These points have been discussed/explained:

General facts about natural gas

Industrial dehydration examples The different mechanism in gas/liquid separation

Different dehydration technologies Absorption

Cooling

Adorption

Sour gas removal

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Aker Solutions Presentation - Drying of Natural Gas

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