7th Doha Natural Gas Conference
Qatargas 2, the Designs and Technologies for a
7.8 MTPA LNG Train
Author/Presenter:
Victor Perez, Qatargas 2, Process Commissioning Manager
Co-Authors:
Stephen Wright, Qatargas 2, Process Engineering Lead
Victor Chavez, Qatargas 2, Process Technical Lead
March 2009
1
TABLE OF CONTENTS
1.
INTRODUCTION ...................................................................................... 4
2.
QATARGAS OVERVIEW ........................................................................... 5
3.
ACID GAS TREATING SYSTEM ................................................................. 8
4. NGL EXTRACTION (ORTLOFF PROCESS)................................................... 8
5.
AIR PRODUCTS’ AP-XTM LIQUEFACTION TECHNOLOGY ........................... 9
6.
GE FRAME 9E GAS TURBINES FOR MECHANICAL DRIVES ...................... 11
7.
WASTE HEAT RECOVERY ..................................................................... 12
8.
SULFUR RECOVERY ............................................................................. 13
9.
CONCLUSION ....................................................................................... 14
10. REFERENCES ....................................................................................... 15
2
ABSTRACT
The Qatargas 2 LNG Project (QG2) is a “full supply chain” LNG joint venture set to
deliver reliable supplies of LNG from Qatar to customers in the United Kingdom and
around the world. The onshore QG2 liquefaction plant (QG2 Plant) is a critical element
of the overall QG2 full-value LNG chain development. Feed gas for the QG2 onshore
plant will be developed from Qatar’s North Field with over 900 proven TCF of nonassociated gas. The project will achieve a major advancement in the scale of LNG
production facilities through the incorporation of new advances in process technologies,
process integration and the use of key large scale equipment.
The QG2 onshore plant will extract LPGs (Propane and Butane), Condensate (C5+) and
Sulfur and will produce 7.8 million tons per annum of LNG from each of its two
production trains (Trains 4 & 5) for distribution predominantly to the UK national gas
transmission system.
This paper will provide a general overview of the onshore
facilities and review a few of the key technological advances developed by QG2 in this
first of a kind facility, including the application of the General Electric (GE) Frame 9E in
the mechanical drive application, the use of the Siemens variable frequency drives and
motor/generators in the compressor strings, the first application of the Air Products APX technology in the liquefaction of natural gas and the integration of power and steam
generation to achieve a highly efficient LNG plant design.
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1.
INTRODUCTION
The world demand for natural gas has renewed interest in the production and
transportation of liquefied natural gas (LNG) from resource rich areas in Africa
and the Middle East to customers in Europe and the Americas. Qatar has taken
the lead to meet this challenge with a vision of becoming the largest LNG
producer in the world (77 MTA by 2010) through the continued development of
the North Field, the largest non-associated gas reservoir in the world. This
vision will soon become a reality through the development of the world’s largest
LNG trains (Trains 4 & 5) which was initiated in a joint venture between Qatar
Petroleum and ExxonMobil. Ownership of this joint venture company, Qatargas
2, has recently been expanded to include a third partner, Total, in Train 5.
Economies of scale require the latest generation of LNG production facilities to
be larger than ever. These large plants are designed with facilities and
equipment that dwarf those in plants that are but a few years old. New designs
create new challenges for the people who must operate and maintain them. In
order to apply such large scale technologies and first of a kind equipment
applications, a rigorous technology development process has been followed to
critically assess the design of the key equipment and embark on a stringent
testing plan to ensure the facility will achieve a reliable operation. It has been a
challenging journey from the conception to the completion and start-up of the
QG2 onshore facilities, with the stage set to demonstrate the value of this world
class design.
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2.
QATARGAS OVERVIEW
The Qatargas 2 Project is located at Ras Laffan Industrial City on the northwest
coast of the State of Qatar. Ras Laffan has two LNG facilities: Qatargas and
RasGas. The existing Qatargas plant consists of three LNG trains, each with a
capacity of 3.2 MTA. The combined capacity of the existing plant is 9.6 MTA.
The Qatargas 2 onshore project is a two train expansion (Trains 4 & 5) to the
existing Qatargas plant (Trains 1, 2, & 3). The ownership in Train 4 is Qatar
Petroleum 70% and ExxonMobil 30% while the ownership in Train 5 is Qatar
Petroleum 65%, ExxonMobil 18.3% and Total 16.7%. Presently, the project is
well into the construction phase. Train 4 is scheduled to start LNG Production in
early 2009 and Train 5 will follow later in 2009. The EPC contractor is a joint
venture between Chiyoda Corporation of Japan and Technip France (CTJV).
The Qatargas 2 project is unique in the industry because of its large scale and
the agreed commercial scope between shareholders. Rather than developing a
plant for long-term, firm sales contracts, the QG2 venture is developing the full
supply chain for ex-terminal sales into an open market. The integrated projects
to produce, export, and sell LNG and LPG includes:




Offshore production platforms and pipelines
Onshore gas treating, LPG recovery and LNG facilities
Large LNG (LLNG) ships,
LNG re-gasification terminal at South Hook in Wales, UK
The LNG14 paper "QATARGAS 2: FULL SUPPLY CHAIN OVERVIEW" (Ref. 3)
provides an overview of the project, with particular focus on the large train
technologies that will be implemented.
The onshore facilities are depicted in the plot plan below by development phase
(Train 4/5 and associated facilities)
5
Trains 4 & 5
Process
Sulfur
Storage
Utilities
SW / CW
Flares
Effluent Treatment
Inlet Facilities
Slug Catcher
Qatargas 2 site on-plots development (blue/purple)/Off-plots (yellow)
LNG Loading
Berths #4 & #5
Common LPG
Storage
Common
Condensate
Storage
Common Lean
LNG Storage
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2.1
Overall Process Flow Scheme
SINGLE TRAIN
09
TO OTHER
TRAIN
OFFSHORE
PRODUCTION
SULFUR
SULFUR
RECOVERY
06
REFRIGERATION
(C3, MR, N2)
31
02
INLET
FACILITY
ACID GAS
REMOVAL
03
DEHYDRATION
MERCAPTAN
REMOVAL
04
05
08
NGL
RECOVERY
LIQUEFACTION
NITROGEN
REJECTION
07
FRACTIONATION
C3, C4 TREATING
LNG
PROPANE
BUTANE
PLANT
CONDENSATE
32
FIELD
CONDENSATE
CONDENSATE
TREATING
The overall process flow diagram for the QG2 onshore facilities is depicted in Figure 2.1
above. Key technologies to be discussed include the Acid Gas Removal, NGL
Recovery, Liquefaction, Refrigeration and Sulfur Recovery.
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3.
ACID GAS REMOVAL SYSTEM
The 8 MTA LNG train size requires a feed gas rate of about 1.5 billion SCFD. In order to
achieve the economy of scale, a single-vessel configuration concept was developed for
major equipment rather than splitting the flow through two or more units in parallel.
Consequently, accomplishing a single-vessel gas treating absorber for this feed gas
rate of 1.5 billion SCFD was a special challenge.
Various leading acid gas removal technologies were studied during the FEED phase of
the project. As a result of the study, the BASF aMDEAR process was selected based on:
having a proven track record, the potential for the possibility of a single absorber design
, and competitive cost. The aMDEAR process is used to remove H2S, CO2 and COS.
Other sulfur compounds, particularly mercaptans are removed from the feed gas using
molecular sieves. The molecular sieve process is licensed by UOP and has a dual role
of dehydration and mercaptans removal.
4. NGL EXTRACTION (ORTLOFF PROCESS)
Early on it was recognized that the Atlantic Basin markets targeted by the Qatargas 2
project, have a preference for lower heating value gas than has been traditionally been
produced from Qatar for sale to the Pacific Basin. Also flexibility to produce spot
cargoes for the Pacific Basin needed to be maintained.
Various methods to meet the Atlantic Basin preference were evaluated such as Pipeline
Gas Blending, Air Injection, Nitrogen Injection, and NGL stripping to various degrees in
both Qatar and at the LNG terminal sites. The results of that evaluation were that NGL
would be extracted and sold from Qatar.
NGL extraction within the Qatargas 2 Project will be achieved prior to liquefaction using
the Single Column Overhead Recycle (SCORE) process technology, licensed by Ortloff
Engineers, Ltd. The SCORE process has been designed to achieve 99% propane
recovery. After NGL extraction, the residual lean feed gas is compressed to high
pressure for efficient operation of the liquefaction process.
A key challenge of the design has been to ensure a high level of reliability and flexibility
in this unit. This has been achieved by using a 3 x 50% NGL turbo-expander
configuration and the application of a steam turbine driver for the lean gas recompressor. The steam turbine will provide a long run time between maintenance
cycles and significant speed flexibility.
Depending on the heating value required by the gas markets, the LNG composition can
be adjusted by modifying the operation of the NGL recovery unit to increase or
decrease the level of heavier components in the feed gas to the refrigeration and
liquefaction sections. The Qatargas 2 design includes the ability to re-inject sub-cooled
8
propane into a slipstream of the lean LNG, thereby allowing production of a rich LNG
product while continuing to produce a lean LNG product.
5.
AIR PRODUCTS’ AP-XTM LIQUEFACTION TECHNOLOGY
5.1
Selection of Air Products AP-XTM Technology
In 2001, ExxonMobil began a study to evaluate the largest feasible LNG train size that
could be achieved with proven LNG technologies (Ref. 1). One of the constraints
imposed on the study was setting a maximum spiral wound heat exchanger (SWHE)
diameter of 5 meters (16.5 feet) based on manufacturing limits at that time. The study
yielded a maximum train size of about 5.5 MTA. This result did not offer a significant
step-out from the LNG trains already in existence (e.g. RasGas Trains 3, 4, and 5 at 4.7
MTA each).
Several other technologies that could produce greater than 5.5 MTA were evaluated.
Air Products’ AP-XTM Hybrid Process, for which Air Products was awarded a US patent
in November 2001 (Ref. 2), was selected for further development. The key feature of
the AP-XTM Hybrid Process is that it adds a third refrigeration cycle using a nitrogen
refrigerant to the conventional Air Products C3MR design. The reasons that Air
Products AP-XTM Hybrid Process was selected over other technologies were:




Offered the potential to increase train sizes beyond current limitations
Combines proven C3MR technology with proven Nitrogen Expansion
refrigeration technology used in air separation plants
Design could be built utilizing existing equipment (e.g. liquefaction exchanger
size within proven 15 foot diameter)
New equipment technology offers opportunity to optimize design and possibly
consider further increases in train sizes or reduce cost
ExxonMobil then embarked on an intensive, multi-discipline, multi-company study to
turn Air Products’ patented process concept into a comprehensive engineering design.
These further studies concluded that the AP-X™ technology was robust and that its
pursuit would produce significant economies of scale. Qatargas 2 would be the first
commercial application of this technology.
Below is a simplified overall process flow diagram utilizing the AP-X™ process:
9
Nitrogen
Rejection
SUBCOOLER
LNG
Expander / Compressor
E
C
PROPANE COMPRESSORS
PROPANE CHILLER &
SMALL EXPANDER
PRE-COOLING:
PROPANE SYSTEM
(Four Pressure Levels)
SWEET
GAS
DEHYDRATION
NGL
RECOVERY
COLD BOX
NITROGEN
COMPRESSOR
NITROGEN REFRIGERATION SYSTEM
MAIN HEAT
EXCHANGER
PROPANE-PLUS
TO FRACTIONATION
MIXED REFRIGERANT COMPRESSORS
5.2
Designed for Operational Flexibility
With three separate refrigerant loops, the AP-X™ technology permits operational
flexibility to maximize production during seasonal temperature changes. This can be
accomplished by shifting the refrigeration load among the three refrigeration loops to
adjust plant capacity and optimize fuel gas balance. The refrigeration power load of the
three refrigeration loops can be changed easily by adjusting some operating variables:


Propane Refrigerant Circuit - The major control variable for the propane
(C3) system is compressor speed. Since the C3 compressor discharge
pressure is set by the C3 condensing temperature, the C3 compressor
speed is used to control the LLP C3 compressor stage pressure, which
produces temperature changes of the feed gas and MR entering the main
cryogenic heat exchanger (MCHE).
Mixed Refrigerant (MR) - Control of the MR system is based on
maintaining the desired LNG temperature exiting the MCHE by controlling
the overall flow rate at an adjusted MR composition with a constant MR
compressor speed. Changing the refrigeration load in the MR system can
10

be accomplished by changing the mass flow rate of the total MR
circulation or adjusting the MR composition. The overall inventory in the
system and the MR compressor speed can also be used to adjust the
overall MR refrigeration system load.
Nitrogen - The major control variables for the nitrogen refrigeration loop
are: N2 recycle compressor speed, N2 inventory in the system, and flow
with the N2 Companders1. The inlet guide vanes of the Companders1 can
be adjusted to vary the refrigeration load of the nitrogen system.
The Qatargas 2 liquefaction unit is designed to maintain the same production capacity
throughout the year up to a design ambient temperature of 43oC (Ref. 3). To maintain
the same design rate, it is expected that the C3 compressor speed will be adjusted
between 95 and 105% of rated speed to supply maximum precooling. The MR and N2
suction and discharge pressures and their respective compressor speeds and
inventories may be adjusted to achieve the production objectives.
To maximize production of the liquefaction unit, the C3 compressor speed will be
increased to provide maximum precooling, the starter-helper motor for the MR
compressor will be in the helper mode, and the MR inventory will be adjusted to provide
additional refrigeration. Similarly, the N2 system inventory and compressor speed may
be increased to supply the necessary refrigeration required to subcool the LNG to its
required temperature for plant fuel balance when the plant is in the maximum production
mode.
In the event of a need to operate the plant at less than the maximum production rate,
the refrigerant compressor-driver sets may be operated at lower speed, or the
compressors can be put on recycle. It is expected that the C3 compressor may be on
recycle at about 80% of design capacity or lower. The MR compressor may be operated
at about 50% of design capacity without going into recycle. For some long term
turndown operations, it may be beneficial to reduce the MR and N2 inventories in the
respective refrigeration loops.
6.
GE FRAME 9E GAS TURBINES FOR MECHANICAL DRIVES
It was clear that these large scale trains would require significant compression power, in
the range of 280 MW per train. Using the current industry standard GE Frame 7EA gas
turbines, four units would be required per train. This scale up also challenged
compressor vendors to produce very large refrigeration compressors with impellers
nearly 2 meters in diameter, which are not well suited for the running speed of 3,600
rpm.
The Frame 9E was the ideal mechanical driver for these compression trains as it can
provide 123 MW of power at ISO rating and 3000 rpm, a speed within compressor
1
Companders is the Air Products name for Compressor-Loaded-Expanders
11
capabilities. Because the Frame 9E had never been applied in LNG mechanical driver
service, a significant qualification effort was undertaken to adapt it from fixed speed
“power generation” service to variable speed “mechanical drive” service (Ref. 4).
In addition, considerable effort was concentrated on reducing plant emissions through
the qualification and use of Dry Low NOx (DLN) burner technology suitable for the low
BTU fuel gas produced as a byproduct of the liquefaction process. Even at fuel gas N2
concentrations up to 38%, the Frame 9E combustion testing has demonstrated that a
reliable operation is possible while achieving less than 25 ppmv NOx emissions.
Further improvements to efficiency required a solution to address the impact of diurnal
and seasonal ambient temperature variations on the gas turbine power output. This
requirement was accomplished through the development of a unique, variable-speed,
starter motor / helper motor / generator. The motor/generator enables pressurized
starting of the compressors, ensures adequate power for refrigeration compression, and
exports surplus power as electricity into the plant grid to fully utilize the capability of the
gas turbine. This enables “Flat” LNG production year round and power sharing between
compressor strings, while minimizing the need for stand-alone gas turbines for power
generation.
7.
WASTE HEAT RECOVERY
In order to maximize plant efficiency while maintaining fuel balance, waste heat
recovery has been incorporated to the C3 and MR Frame 9 drivers in each of the
process trains. Each of these waste heat recovery units is able to generate
approximately 200 t/h of high pressure steam to compliment the steam generated by the
packaged boilers in the utilities plant. The high pressure steam is utilized by various
plant users which include the steam turbine generators; compressor steam turbine
drivers and process heat exchangers. With this configuration the plant is able achieve a
thermal efficiency above 92.5 % (based on HHV). The steam generation facilities for
QG2 onshore facilities are depicted in the schematic below.
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TRAIN 4
HRS
G
HRS
G
TRAIN 5
HRS
G
COMMON FACILITIES
HRS
G
B
B
B
B
B
B
HH
S
COMPRESS
OR
DRIVES
LGC, FGC
COMPRESS
OR
DRIVES
LGC, FGC
COMPRESS
OR
DRIVES
OGC
STG
(3)
BFW
DRIVES
PH
M
S
PH
PH
PH
PH
PH
HRSG
=
B
=STG
=PH
=LGC
=FGC
=OGC
=
HEAT RECOVERY STEAM GENERATOR
GGenerGENERATOR
BOILER
RR
STEAM
TURBINE
GENERATOR
PROCESS
HEATERS,
REBOILERS
LEAN
GAS
RECOMPRESSOR
FUEL
GAS (ENDFLASH)
COMPRESSOR
OFFGAS
COMPRESSOR
L
S
PH
Qatargas 2 Steam System Overview
8.
SULFUR RECOVERY
The State of Qatar has stringent environmental regulations. This requires high sulfur
recovery from the feed gas to satisfy the SOx limits on gas turbine and fired heater flue
gas emissions.
The sulfur (SO2) emissions limits require a high sulfur recovery better than 99%. This
led to production of a commercial-quality liquid sulfur product by the following design
scheme:


Acid gas removal using the BASF activated MDEA (aMDEAR) process.
Mercaptans removal is accomplished using molecular sieves in a process
licensed by UOP. The spent molecular sieve regeneration gas is treated
using a Chilled SELEXOLTM process also licensed by UOP, which reduces
total sulfur in the spent regeneration gas to below 50 ppmv. This spent
regeneration gas feeds the fuel gas system.
13

9.
Sulfur recovery is accomplished using a 2-stage Claus process designed
by Lurgi. The H2S-laden acid gas from the aMDEAR and the mercaptanladen acid gas from the Selexol unit are enriched upstream of the Claus
Unit, and the Claus tail-gas is hydrogenated and then further treated in a
Tail Gas Treating unit. Both the Acid Gas Enrichment and Tail Gas
Treating Units use the ExxonMobil Flexsorb-SE Plus process. The major
challenge has been to ensure that the design is robust to meet the sulfur
recovery requirements for the range of expected sulfur species in the feed
gas to the plant.
CONCLUSION
This paper has provided an overview of the QG2 onshore liquefaction facilities. The
design, construction, commissioning and start-up of the large Qatargas 2 trains has
been an extraordinary undertaking which has presented many challenges over the last
5 1/2 years. Meeting these challenges has been made possible by the teamwork and
cooperation of many outstanding people around the world, representing the leading
companies in their respective fields.
QG2 onshore project has achieved a step function increase in LNG train liquefaction
capacity through the use of new technologies. The application of new technologies has
been made possible through extensive internal qualification processes. The project
personnel worked closely with key vendors in the design, manufacturing and testing of
key equipment. The QG2 LNG plant is the first application of the AP-X™ technology,
powered by GE Frame 9 turbines in mechanical drive and combined cycle cogeneration
service, making it the largest highly thermally efficient LNG plant in the world. The QG2
LNG plant is designed to meet very stringent environmental emissions standards for
NOx and Sulfur recovery set forth by the state of Qatar.
14
10.
REFERENCES
1.
S. Wright, P.W. Sibal, “Technology Challenges for a New Generation of
Ultra-Large LNG Trains”. APCI Owners Seminar, September 2006,
Hershey, Pennsylvania,
2.
Air Products US Patent 6,308,531 for the “Hybrid Cycle” (Trade mark APXTM)
3.
Thompson, G.R., Adams, J. B., Hammadi Ali, Kaabi, S. A., Sibal, P.W,,
“Qatargas 2 Fuel Supply Chain Overview”, LNG 14 Conference, Doha,
Qatar
4.
Roy Salisbury et al, “Design, Manufacture, and Test Campaign of the
World’s Largest LNG Refrigeration Compressor Strings”, LNG 15, April
2007.
5.
Victor Chavez et al, “Technical Challenges during the Engineering Phases
of the Qatargas II Large LNG Trains”, LNG 15, April 2007.
15