natural gas processing
DESCRIPTION
Statoil - Natural Gas Processing - Stathis Skouras - 2014TRANSCRIPT
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Natural Gas Processing Gas Quality from reservoir to market
Dr. Stathis Skouras, Gas Processing and LNG
RDI Centre Trondheim, Statoil, Norway
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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)
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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
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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)
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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)
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Natural gas compositions (typical values)
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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)
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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
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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
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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
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Water removal by adsorption
Source: UOP
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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:
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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
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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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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
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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
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6
5
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NGL fractionation in series of distillation columns
Make high added value products (C2, C3, C4, C5+) C2+ from
NGL recovery
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Real Process Plants
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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
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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
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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
[email protected], 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