Natural Gas Processing

Dr. Stathis Skouras, Gas Processing and LNG

RDI Centre Trondheim, Statoil, Norway

Schedule

Thursday 9/11/2017, 11:45 – 13:30

• Lecture 4

– Hydrocarbon dew point control (HCDP)

− Examples from offshore/onshore gas processing

• Lecture 5

– Low Carbon technologies and Future Value Chains (FVC)

– Kahoot quiz: Gas Processing

2

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

3

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

Specifications for “rich gas” transport Offshore processes

Prepares gas for

further transport

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 (LT/MSm3) 8

4

• Space and weight

limitations

• Expensive labour

• Expensive utilities

(cooling, water,

chemicals, electricity)

• Escape issues

Specifications for “sales (dry) gas” transport

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

• Prepares gas

for end user

• Recovers

valuable

NGL

products

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

5

• No space and

weight

limitations

• Access to

utilities

(cooling, water,

chemicals,

electricity)

• Easy escape

• ‘‘Sales gas’’ pipeline (a’b’):

- 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 at 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

6

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 and heavy ends (C7+)

7

8

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

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

Manipulate phase envelope by

removing NGL or heavy ends (C7+)

9

NGL recovery processes

• JT-valve (isenthalpic process) – moderate NGL recovery

• Expander (isentropic process) – achieves lower temperatures (deep NGL recovery)

• Expander creates shaft work – combination with compressor (energy recovery)

FEED-FLASH

VALVEPRODUCT-FLAS

FEED

GAS

LIQUID

S1

S2

S3

Joule-Thompson valve Sales gas

NGL

FEED-FLASH

PRODUCT-FLAS

EX1

FEED

GAS

LIQUID

S1

S2

S3

Expander processSales gas

NGL

10 -

Moderate NGL recovery - Thermodynamic path

11

• Heat integration between feed and

product (gas/gas HX)

• Lower temperatures achieved – deep NGL recovery

• More robust scheme wrt. feed disturbances

Pre-cooling and expansion

NGL recovery processes

FEED-FLASH

PRODUCT-FLAS

EX1

E1

FEED

GAS

LIQUID

S1

S2

S3

S4

S5

NGL

Sales gas FEED-FLASH

PRODUCT-FLAS

EX1

E1E2

FEED

GAS

LIQUID

S1

S2

S3

S4S5

S7

• Heat integration with cold

products and extra refrigeration

NGL

Sales gas

12 -

Deep NGL extraction processThermodynamic path

13

• Distillation column (de-methaniser) to increase NGL recovery

• Robust scheme to adjust C2 recovery according to market prices

Pre-cooling, expansion and fractionation

NGL recovery processes

Sales gasNGL

14

NGL fractionation

C2

C3

iC4

nC4

C5+

De-etanizer

De-propanizer

De-butanizer

Butane

splitter

Propane

1 2

34

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

Examples: Offshore and onshore processing

Offshore processing

Nyhamna

Europipe II

Europipe I

Norpipe

Emden

ÅTS

Norne

Åsgard

Haltenpipe

Heidrun

Franpipe

Zeebrugge

Zeepipe I

St Fergus

Vesterled

Frigg

Statfjord

Kårstø

Kollsnes

Melkøya

Snøhvit

Ormen Lange

Easington

Langeled

Ekofisk

Sleipner

Troll

Dunkerque

Kristin

Tjeldbergodden

16

17

Offshore processRich Gas

CricoP <105 barg

Su

bse

a

GT

Åsgard TransportMeter

H2S

Scavenger

Fuel Gas

26°C

31°C

25°C

Meter

TVP = 0.965 bar

Stabilised Oil26 bar

2 bar

30°C 30°C 30°C

121°C, 87 bar

Test

LP

Mod.

2nd stage separator

2nd stage separator 3rd stage separator 3rd stage separator

1st or 2nd stage separator

Mercury Removal Units

w/filters

1st stage

separator

2nd stage

separator

3rd stage

separator

Test-separator

Recompressor-train with 3 stages

Export gas compressor

HCDP control:

Cooling and

separation

WDP control:

TEG plant

Separation train

(3-phase)

Oil stabilization train

Feed

Gas train

Recompression train

Hg removal

Åsgard B Process

18

CO2/H2S

removal

STABILISED

OIL

FEED

RICH GAS

EXPORT

Oil stabilization train

Water

treatment

plant

Onshore processing: Kårstø plant

Nyhamna

Europipe II

Europipe I

Norpipe

Emden

ÅTS

Norne

Åsgard

Haltenpipe

Heidrun

Franpipe

Zeebrugge

Zeepipe I

St Fergus

Vesterled

Frigg

Statfjord

Kårstø

Kollsnes

Melkøya

Snøhvit

Ormen Lange

Easington

Langeled

Ekofisk

Sleipner

Troll

Dunkerque

Kristin

Tjeldbergodden

19

SnorreStatfjord Ø

GullfaksTordis

Sleipner Ø/VGudrunGungne Sigyn Volve

Åsgard Transport 42”

707 km

Sleipner 20”

light oil/condensate

245 km

NjordAlve

DraugenHeidrunNorneÅsgardMikkelKristin

Statpipe 30”

308 km

Europipe II 42”

650 km

Statpipe 28”

228 km

74 MSm3/d sales gas export

8 500 x 103 ton/yr liquid products

20

Kårstø gas processing plant

94 MSm3/d rich gas feed

72 x 106 ton/d feed gas

Kårstø: Feed pretreatment

Mercury

removal

H2S

removal

Water dew point

Driers

Cyclone

separator

Feed from

Åsgard Pig trap

LP steam

Filter

separator

Raw gas

filters

Feed pre-

heater Let-down

station

111 bar

5,8 °C

Crossover/

backflow

To warm turbo

expander

CoalescersMercury

Removal

H2S

filters

NET1

inlet

module

22

HCDP control unit (DPCU) – Cooling and expansionCOOLING

Expansion/compression

NGL RECOVERY

C2+ to NGL

fractionation

Gas/Gas HX LT separator De-C1

columnJT-

valves

Turbo-expander

23

Presenters name: Dr. Stathis Skouras

Presenters title: Principal Researcher

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

www.statoil.com

Thank you