Natural Gas Processing Gas Quality from reservoir to market

Dr. Stathis Skouras, Gas Processing and LNG

RDI Centre Trondheim, Statoil, Norway

Schedule

Tuesday 09.12.2014: 09:45 12:30

Lecture: Natural Gas Processing

Thursday 11.12.2014: 11:45 14:30

Lecture: Distillation of azeotropic mixtures

Tuesday 16.12.2014: 09:45 11:30

PC-lab / HYSYS exercises

o Dew Point Control Unit (DPCU)

o Extractive Distillation (Acetone-methanol with water as entrainer)

2

Outline

Introduction

Statoil

Natural Gas

Gas Value Chain

Gas Quality

Natural Gas Processing

Water dew point processes

Acid and sour gas removal

H2S and mercury removal (trace components)

Hydrocarbon dew point processes

Examples of real process plants

3

4

Statoils natural gas business

A major gas player the second largest supplier to Europe

Supplying gas to UK, Germany, The Netherlands, Belgium, France, Italy and Spain

Developing international gas value chains in the US and the Caspian region

Holds a 20% share in the Trans Adriatic Pipeline (TAP) project. TAP will start in

Greece, cross Albania and the Adriatic Sea and come ashore in southern Italy

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What is natural gas? Components

Mainly methane, ethane, propane and

butanes

Small amounts of pentane (C5) and heavier

components (C6+)

Acid/sour gases such as CO2 and H2S

Inerts such as nitrogen (N2)

Trace components such as mercury (Hg)

and sulphur compounds (S)

Water (vapour)

6

1 Sm3 = 1 m3 @ 15C and 1 atm

1 kmol = 23.64 Sm3

1 Sm3 770 gr and gives 11 kWh of heat

Price 0.30 /Sm3 (EU) and 0.15 /Sm3 (US)

Natural gas compositions (typical values)

7

Natural Gas Terminology

Rich Gas: Rich in heavy components.

Further processing required

Sales gas (dry gas): Ready for sale to

the market

Liquified Natural Gas (LNG): -162C @

1 bar

Natural Gas Liquids (NGL): Ethane and

heavier HC (C2+)

Naphtha: Rest of the NGL (C5+)

Condensate: Heavier liquids from

integrated gas/oil production (C6+)

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Liquefied Natural Gas (LNG) Pipeline gas

Natural gas transport

Pressure: 250 - 50 bar

Temperature: ambient temperature

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Pressure: atmospheric

Temperature: -162C (at boiling point)

1. Production fields (offshore Norway)

2. Transportation pipelines

Rich gas

Sales gas

Oil/Condensate

3. Gas processing plants (onshore Norway)

4. Receiving terminals (continental Europe)

Norwegian Gas Transport Network

Complex system

8 000km of pipelines

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Gas Value Chain

Offshore processes Subsurface

(reservoir,

drilling and well, flow

assurance)

Gas Processing

(extracting high added value products) Downstream

Onshore processes

Subsea and wells

Receiving terminals

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Topsite facilities

(prepare for transport) Midstream

Upstream

Upstream

Storage, Metering and Distribution

Gas Quality

Scientific field dealing with the compositions,

the physical properties and the

specifications of natural gas

Why gas quality?

Ensure unproblematic transport of gas

Ensure unproblematic processing of gas

Prevent corrosion and erosion of equipment

Prevent ice and gas hydrates

Prevent condensation of hydrocarbon liquids

Ensure safe use of gas

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Gas quality specs along the value chain (1/2)

Specifications for rich gas transport Offshore processes

Ric

h g

as

Onshore processes

Designation and unit Specification

Max operating pressure (barg) 210

Min operating pressure (barg) 112

Max operating temperature (C) 60

Min operating temperature (C) -10

Max cricondenbar pressure (barg) 105

Max cricondentherm temperature (C) 40

Max water dew point (C at 69barg) -18

Max carbon dioxide (mole%) 2

Max hydrogen sulphide and COS (ppmv) 2

Max O2 (ppmv) 2

Max daily average methanol content (ppmv) 2.5

Max peak methanol content (ppmv) 20

Max daily average glycol content (litres/MSm3) 8

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Specifications for sales (dry) gas transport

Gas quality specs along the value chain (2/2)

Sa

les

(d

ry)

ga

s

Onshore processes

Receiving terminals

Designation and unit Specification

Hydrocarbon dew point (C at 50 barg) -10

Water dew point (C at 69 barg) -18

Maximum carbon dioxide (mole%) 2.50

Maximum oxygen (ppmv) 2

Maximum hydrogen sulphide incl. COS (mg/Nm3) 5

Maximum mercaptans (mg/Nm3) 6.0

Maximum sulphur (mg/Nm3) 30

Gross Calorific Value (MJ/Sm3) 38.1 43.7

Gross Calorific Value (MJ/Nm3) 40.2 46.0

Gross Calorific Value (kWh/Nm3) 11.17 12.78

Wobbe Index (MJ/Sm3) 48.3 52.8

Wobbe Index (MJ/Nm3) 51.0 55.7

Wobbe Index (kWh/Nm3) 14.17 15.47

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Natural Gas Processing

Water occurs naturally in the reservoir

Free water phase is removed in 3-phase separators

Water (vapour) is naturally dissolved in the natural gas

Water must be removed from the gas to avoid:

Free water in gas pipelines (corrosion)

Ice/hydrate formation (plugging of equipment and pipes)

Water removal processes:

Condensation (cooling and separation)

Absorption by glycol processes (moderate dew-pointing)

Adsorption on solids (severe dew-pointing)

Water dew point

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Water dew point

Transport

specification:

-18C at 69 barg

(20-30 ppm)

Process needed:

Glycol absorption

process

Offshore processes Onshore processes

Process

specification:

0.1 to 1 ppmv

Process needed:

Adsorption on

solids

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Glycol

Contactor

Cooler

Filters

Glycol

Regenerator

Surge drum Pump

Filter

Glycol/condensate

separator

Wet natural

gas

Dry natural gas

Rich TEG

Lean TEG

LT HX HT HX

Water

vapour

Flash drum P=70 bar

T=30C

P=1bar

T=200C

Counter-current mixing of tri-ethylene glycol (TEG) and natural gas

Meets pipeline water dew point specifications (-18C at 69 barg)

Water removal offshore - Glycol absorption (physical)

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Water removal onshore - Adsorption on solids

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Adsorption in to a solid material

Used in deep gas processing at low temperatures

Removal of smaller amounts of water

Extreme dryness, down to 0.1 ppm water

Porous structures with high internal surface area (200 800 m2/g)

Strong affinity for water, 5 25 % by weight

Solids like

Molecular sieve (3A or 4A type) (Zeolite)

Activated alumina (Al2O3)

Silica gel (SiO2)

Activated carbon

Regenerative processes

Water removal by adsorption

Source: UOP

Acid/sour gas removal (CO2 and H2S)

Most natural gas contains acid gas

CO2 (acid)

H2S and other sulfur compounds (sour)

Why remove acid gas:

Corrosion induced by acid gas (+ free water)

Freezing of acid gas in process equipment

Sales specifications

Toxicity and reactivity (H2S)

Typical specification for sweetened gas:

CO2 in pipeline gas:

Acid gas removal (CO2 and H2S) by absorption (physico-chemical) in amines

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H2S (traces) removal on metal oxide

Upstream precautions:

No liquids (free water / condensate)

Minimise glycols, amines and particles

Downstream effects:

Water

Dust particles

Acid gas content

Mercury in natural gas

Mercury is the only metal to be liquid at room T&P (20C, 1atm)

Mercury occurs naturally in oil & gas reservoirs

Mercury concentration vary from one field to another, and also

through one fields lifetime

Mercury compounds are highly toxic

Mercury must be removed prior to gas processing to avoid severe

corrosion of aluminium equipment

Mercury removal process:

Adsorption on solids

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//upload.wikimedia.org/wikipedia/commons/9/99/Pouring_liquid_mercury_bionerd.jpg

Mercury removal by adsorption on solids

Main methods

Sulfur impregnated activated carbon

Hg + S HgS

Reaction between Hg and a metal sulfide

(typically alumina) forming HgS (Chemisorption)

Hg + MSx MS(X-1) + HgS

Molecular sieve technology

Amalgamation with silver

Hydrocarbon dew point - Phase envelope of natural gas

C Critical point

N Cricondenbar

M Cricondentherm

Vapor + liquid

Gas

Liquid

Dense phase

The phase envelope is ONLY

a function of COMPOSITION

Cricondenbar

Cricondentherm

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Effect of composition on phase envelopes

Source: A. M. Elsharkawy / Fluid Phase Equilibria 193 (2002) 147-165

Effect of heavy ends (C7+)

Manipulate phase envelope by

removing NGL or heavy ends (C7+)

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Sales gas pipeline (ab): - Cricondentherm spec

- Transport at intermediate/low

pressures

- No liquid formation above

cricondentherm (gas phase)

- Manipulate phase envelope by

removing NGL to reach a

cricondentherm spec.

Practical importance of phase envelopes

Rich gas pipeline (ab) - Cricondenbar specification

- Transport in high pressures

- No liquid formation above

cricondenbar (dense phase)

- Manipulate phase envelope

by removing NGL to reach a

cricondenbar spec.

a

b

a

b

Gas transport in pipelines

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Manipulation of phase envelopes along the Value Chain- HC dew point control

Source: A.O. Fredheim, E. Solbraa, Compendium Industrial Processes, TEP4185 NTNU

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NGL recovery processes / HC dew point control

FEED-FLASH

PRODUCT-FLAS

EX1

FEED

GAS

LIQUID

S1

S2

S3

FEED-FLASH

VALVEPRODUCT-FLAS

FEED

GAS

LIQUID

S1

S2

S3

Joule-Thompson valve Expander process

JT-valve (isenthalpic)

Expander process (isentropic) creates shaft work -

achieves lower temperatures (deeper NGL extraction)

Expander combined with a compressor (energy recovery)

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FEED-FLASH

PRODUCT-FLAS

EX1

E1

FEED

GAS

LIQUID

S1

S2

S3

S4

S5

Heat integration between feed and

product (gas/gas HX)

FEED-FLASH

PRODUCT-FLAS

EX1

E1E2

FEED

GAS

LIQUID

S1

S2

S3

S4S5

S7

Precooling with sea

water or extra cooling

(refrigeration cycle)

Deeper NGL extraction

More robust scheme

Pre-cooling and expansion

NGL recovery processes / HC dew point control

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NGL fractionation

C2

C3

iC4

nC4

C5+

De-etanizer

De-propanizer

De-butanizer

Butane

splitter

Propane

1 2

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Steam

Steam

Steam

Steam

Sea

water

Sea

water

Sea

water

Feed

5

6

5

8

7

NGL fractionation in series of distillation columns

Make high added value products (C2, C3, C4, C5+) C2+ from

NGL recovery

Real Process Plants

Offshore processing: sgard B

Nyhamna

Europipe II

Europipe I

Norpipe

Emden

TS

Norne

sgard

Haltenpipe

Heidrun

Franpipe

Zeebrugge

Zeepipe I

St Fergus

Vesterled

Frigg

Statfjord

Krst

Kollsnes

Melkya

Snhvit

Ormen Lange

Easington

Langeled

Ekofisk

Sleipner

Troll

Dunkerque

Kristin

Tjeldbergodden

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sgard B Process

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Inlet separation (3-phase)

CO2/H2S

removal Water dew point HC dew point

STABILISED

OIL

FEED

RICH GAS

EXPORT

Oil stabilization

Example onshore processing:

Krst plant

Nyhamna

Europipe II

Europipe I

Norpipe

Emden

TS

Norne

sgard

Haltenpipe

Heidrun

Franpipe

Zeebrugge

Zeepipe I

St Fergus

Vesterled

Frigg

Statfjord

Krst

Kollsnes

Melkya

Snhvit

Ormen Lange

Easington

Langeled

Ekofisk

Sleipner

Troll

Dunkerque

Kristin

Tjeldbergodden

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Krst plant: Feed pretreatment

Mercury

removal

H2S

removal

Water dew point

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Krst plant: HC dew point control unit (DPCU) COOLING

Expansion/compression

NGL RECOVERY

C2+ to NGL

fractionation

Gas/Gas HX LT separator De-C1

column JT-

valves

Turbo-expander

Future Oil & Gas Production The Statoil Subsea Factory

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Oil storage

Gas compression

Gas, oil, produced

water separation

Power distribution

and control

Manifold

Sea water injection

template with pumping

Produced water

injection template

Production

template Produced water

injection pump Production

template

ROV

intervention

Oil pump

Oil export

Gas export

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Presenters name: Dr. Stathis Skouras

Presenters title: Principal Researcher, RDI Centre Trondheim, Statoil, Norway

efss@statoil.com, tel: +47 97 69 59 62

www.statoil.com

Thank you

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General block diagram for an off-shore process

MEG

WELL STREAM RICH GAS

DRYING SOUR

GASES

CONDENSATE/

WATER

SEPARATING

STABILIZING

CONDENSATE H2S and

CO2

WATER

MEG WATER

TREATING

DESTILLATION

COMPRESSION