Evaluation of Process Systems for Floating LNG Production Units

Evaluation of Process
Systems for Floating LNG
Production Units
Presented by Inga Bettina Waldmann
Kanfa Aragon AS
Tekna Conference 18-19th June 2008 – Floating Production in Challenging Environment
Presentation overview
Who we are
Why Floating LNG (FLNG)
FLNG Concepts
FLNG Process selection
Aragon
Kanfa Aragon AS is a limited
company in the Sevan Marine
Group.
Located in Bergen, Norway.
Kanfa Group topside references:
Process packages
5 FPSO topsides
2 FPSO topsides this year
Developed FLNG technology and
involved in a number of FLNG
studies for FPSO ship owners and
LNG shipping companies
What is LNG
Liquefied Natural Gas, LNG = natural gas in its liquid form
Cooled to typically -155 to -165 deg Celsius
The specific power consumption (kWh/kg LNG) is a common way to
specify the efficiency of the liquefaction system
NATURAL GAS
1,000,000 Sm3
100 x 100 x 100 m
LNG
1,000,000
Sm3
12 x 12 x 12
m
Why FLNG?
Exploration of stranded gas fields can meet the worlds
energy demand
Recovery of oil-associated gas
The energy demand and gas prices are increasing
Source: Poten and Partners
Source: Ingvar Tjostheim
Stranded gas fields - a large potential for FLNG
Note: 0.25 TCF = 250 BFC = 5.2 million ton LNG
Corresponds to 8 years production with LNG given production capacity
of 1 million ton LNG p.a and a normal production profile
Oil-associated gas
Annually a tremendous amount of oil-associated gas is
flared or vented due to the distance from the fields to the
markets
Annual gas flaring exceeding 150 Billion m3 pr year
More than 350 million tonnes CO2 emissions per year
West Africa, South America and Asia topping oil-associated gas
flaring statistics
Political trends and increased energy demand will
change the existing flaring philosophy
Oil-associated gas liquefied to LNG clearly can
represent a new energy supply source
Solutions for FLNG production
With well stream reception and separation system, or
Gas from new or existing oil FPSO (separate hull)
Converted ship, new hull or barge
Mid-size, 0.3 – 3.6 mtpa LNG
For small and medium stranded gas fields
For associated gas fields
LNG storage & offloading
Up to 14 Mill Sm3/day
1 – 4 LNG trains
Gas processing sequence and requirements
CO2, H2S
FEED
GAS
SEPARATION/
FEED TREATM.
WATER
SOLVENT
REGENEN.
DRYER
REGENEN.
ACID GAS
REMOVAL
WATER
REMOVAL
50 ppm
CO2
>1 ppm
H2O
Hg
REMOVAL
>0.01 µg/Nm3
Hg
LNG
LIQUEFACTION
HHC
Offshore liquefaction technology selection criteria
Compact and low weight
Simple operation and start-up
High inherent process safety
Robust to vessel motions/ marine enviroment
Robust to changes in process conditions
High availability
High efficiency
Cascade Cycle
Chosen technology for the first LNG base load plant
1 mtpa of LNG production
Cascade Cycle
Separate refrigerant cycles with
propane, ethylene and methane
High efficiency (~0.3 kWh/kg LNG)
Optimised technologies are evolved
and proposed
Large equipment count
Requires large plot area for
refrigerant storage and management
Increased risk due to flammable liquid
inventory
Not recommended for offshore
environments
Source: Natural Gas Processing Principles and Technology part II
Mixed Refrigerant (MR) Cycle
Dominant baseload plant technology
Source: Foster Wheeler Energy Limited
Mixed Refrigerant (MR) Cycle
Uses a single multi-component refrigerant
comprising typically nitrogen, methane,
ethylene, propane and butane
The MR evaporates over a wide range of
temperatures and thereby follows the natural
gas condensing curve closely
High efficiency (~0.3 kWh/kg LNG)
Up to 50% less equipment items than the
cascade process
Several modifications are developed and
proposed
Sensitive to change in feed composition
Requires extensive plot space for
refrigeration generation, storage and
management
Flammable refrigerants
Source: Cryoplants Ltd.
Expander Cycle
Based on the classic Reverse Brayton / Claude Cycle
Several options:
Single expander cycle
Double expander cycle
Open expander loop (methane as refrigerant)
Closed expander loop (nitrogen as refrigerant)
Efficiencies down to 0.4 kWh/kg LNG
A pure refrigerant (typically nitrogen) is deep-cooled by expansion to
condense the natural gas to LNG in the cold box
LNG
PRETREATED
FEED GAS
HEAT
EXCHANGER
CYCLE
COMPRESSOR
BOOSTER
COMPRESSOR
TURBO
EXPANDER
Proposed FLNG Processes
Multifluid Cascade Process (MFCP) by Linde
Standard single and dual nitrogen expander cycle
NicheLNGSM by CB&I Lummus
LNG SmartR Liquefaction Technologies (open and
closed loops) by Mustang Engineering
Optimised Expander Cycle by Kanfa Aragon
Start-up
Expander cycles are superior to MR cycles related to
start up
Typically a nitrogen expander cycle need 24 to 36 hours from
warm to maximum production.
MR Cycles requires 1 to 2 weeks to reach the same level
Operation
The Expander cycle is easier to operate than the MR Cycle
No sophisticated level control, phase or composition exchange in the
refrigerant loops are giving operation upsets
No complex control system coupled to the process gas composition
High turndown
The N2 Expander Cycle has additional advantages
The expander refrigerant loop contains nitrogen which gives the highest
availability for rotating equipment
Seal leakages are non hazardous and easily compensated by nitrogen
from the refrigerant loop.
Turndown down to approx. 25% for one single train is obtained by
reducing the nitrogen containment in the loop. Rotating equipment is
maintained at fixed speed during turndown.
Safety
The N2 Expander cycle has a significantly higher inherent safety
level than MR cycles, Cascade cycle and Open Expander cycle
Nitrogen is a non-flammable refrigerant
Half of the plant does not contain hydrocarbons and can be
regarded as safer than most FPSO topsides.
There are minor volumes of LNG in the plant, since the produced
LNG are led directly to cargo thanks
Proven equipment offshore (compressor,
gas turbines, heat exchangers)
Safe area
Change in feed gas composition
The Nitrogen Expander Cycle is by it’s nature much less
sensitive to feed gas changes than MR Cycles
MR Cycles have higher efficiency since the refrigerant
evaporation curve are ideally following the LNG condensation,
minimizing the exergy loss
Change in the feed gas composition requires changes in the
refrigerant or acceptance of lower efficiency
At off-spec operation, the nitrogen expander cycles can
have higher efficiency than a MR Cycle
The Aragon Optimised Expander cycle optimises the
split between NGL and LNG products
This increases the efficiency and increases the acceptable
window for the feed composition
Offshore enviroment
Floating production units are subject to motion
The Expander cycle is robust for the offshore
environment as no liquid phase refrigerant is present
Avoids high focus on equal distribution of two phase/
liquid flow
MFLEX LNG producer
Incl. Kanfa Aragon’s Optimised expander cycle
Refrigeration generation
For the N2 Expander Cycle the nitrogen can easily be
generated on board
For Open Cycle Expander Processes, feed gas or LNG
can be used
By Kanfa Aragon’s patent pending system the N2-refrigerant can
be easily stored during maintenance or turndown operations.
For MR Cycles the sophisticated refrigerant must either
be produced onboard by advanced distillation systems or
specially purchased. Feeding of the refrigerant is a
thorough operation
Warm up during longer shutdown periods often require
blowdown of the MR to flare
Complexity and cost
Expander Cycles are superior to Cascade and MR Cycles when it
comes to simplicity
Can be built compact and light
Example for 2.7 mtpa:
Aragon expander cycle
MR Cycle
Topside weight estimate
Cost estimate pr production capacity
[ton]
[MMUSD/mtpa LNG]*
10,000
450 - 700
up to 35,000**
>1000**
*Including vessel, gas pre-treatment, liquefaction and offloading (excluding field spesific items and cost of financing etc. )
** Source: SBM Offshore and CB&I Lummus
N2 Expander Cycle
2.7 mtpa
Optimised Dual N2 Expander Cycle
Kanfa Aragon has developed new liquefaction
technology (patent filed)
Based on the well-proven Dual Nitrogen Expander Cycle
and optimised for offshore liquefaction application
Maximised LNG production for given driver
Minimal or no condensate bi-production if preferred
Integrated LPG / NGL recovery if preferred
Very high efficiency
Integrated and optimised power generation
LNG specifications adjusted acc. to Client requirements
Aragon liquefaction technology
SUITABLE FOR MEDIUM/ LARGE SCALE FLNG
SPECIFIC POWER @ TROPICAL CONDITIONS
(kWh/kg LNG)
SUITABLE FOR MEDIUM/ LARGE SCALE FLNG
SINGLE EXPANDER
N2 CYCLE
HIGHLY COMPLEX AND LOW INHERENT SAFETY
HIGHLY COMPLEX – SUITABLE FOR SOME
LARGE SCALE FLNG PLANTS ONLY
~ 0.8 kWh / kg
DOUBLE EXPANDER
N2 CYCLE
0.55 – 0.65 kWh / kg
KANFA ARAGON OPTIMISED EXPANDER
CYCLE*
0.40 – 0.55 kWh / kg
PRECOOLED
DOUBLE EXPANDER
N2 CYCLE
~ 0.45 kWh / kg
SINGLE MIXED
REFRIGERANT
~0.40 kWh / kg
CASCADE,
PRECOOLED MRC,
DUAL / CASCADE MRC
<0.3 – 0.4 kWh / kg
PLANT COMPLEXITY
(QUALITATIVE)
* PATENT PENDING TECHNOLOGY
Lat out design example
Includes all required topsides utilities ans auxilliary systems
PRE-TREATMENT MODULE
LIQUIFACTION MODULE
COMPRESSOR MODULE
Liquefaction capacities
PARALLEL LNG TRAINS
LNG PRODUCT
FEED GAS
1 LNG TRAIN
UP TO 0.9 MTPA
UP TO 125 MMSCFD
UP TO 3.5 MSm3/d
2 LNG TRAINS
UP TO 1.8 MTPA
UP TO 250 MMSCFD
UP TO 7 MSm3/d
3 LNG TRAINS
UP TO 2.7 MTPA
UP TO 375 MMSCFD
UP TO 10.5 MSm3/d
4 LNG TRAINS
UP TO 3.6 MTPA
UP TO 500 MMSCFD
UP TO 14 MSm3/d
SINGLE PRE-TREATMENT TRAIN FOR ALL SIZES
Expander Cycles for LNG liquefaction
Nitrogen Gas Expander Cycles are better suited
for offshore liquefaction than more traditional
systems because of their compactness, weight,
ease of operation, safety and cost.
THANK YOU!
Tekna Conference 18-19th June 2008 – Floating Production in Challenging Environment