32
LNG
INDUSTRY
APRIL
2016
The required plot space is less than that needed for traditional
LNG plants and the execution strategy, using standard equipment
and modular construction, can help to reduce construction cost
and schedule risk.
Currently, three LNG projects (each 100%owned by LNG Ltd)
are proposing to utilise the liquefaction process technology:
Magnolia LNG (MLNG) project in Lake Charles, Louisiana, US.
Bear Head LNG project in Richmond County, Nova Scotia,
Canada.
Fisherman’s Landing LNG project in Gladstone, Queensland,
Australia.
The US Federal Energy Regulatory Commission (FERC)
released its Final Environmental Impact Statement (FEIS) for the
MLNG project in November 2015. In the same month, MLNG
executed a legally binding lump sum turnkey (LSTK) engineering,
procurement and construction (EPC) contract for the project with
the KSJV, a contractor joint venture (JV) between KBR Inc. and
SK E&C Group (SKEC).
CAPEX and OPEX benefits
MLNG has achieved a LSTK EPC contract price in the range
of US$495/t – US$544/t (subject to final design capacity at
FID). The design also delivers LNG plant fuel gas consumption
at a guaranteed value of 8%, representing a 92% feed gas
guaranteed production efficiency. Actual fuel gas consumption
is expected to be in the range of only 6%during operation (94%
production efficiency).
The execution of the EPC contract for MLNG represents a
critical milestone for the project. Importantly, this also reaffirms
LNG Ltd’s view that the business model of mid scale,
modular-based LNG trains of nominally 2 million tpy using its
liquefaction process technology is robust, delivering significant
CAPEX and OPEX savings. The benefits of incorporating this
process technology and modular construction approach are
outlined in detail below.
Efficiency
The company’s current projects have a train design capacity of
approximately 2 million tpy each, configured in a two-in-one
parallel design, in which there are two identical cold box
exchanger units per train, each chilled by an independent
closed loop mixed refrigerant (MR) system. Each MR loop has a
dedicated gas turbine driven MR compressor.
Having two parallel MR circuits within each LNG train
provides an efficient turndown capability down to approximately
40%of design capacity per train. This design feature offers tollers
(LNG purchasers) and plant operators flexibility to operate the
LNG trains over a wide range of demand. Plant reliability also
improves, as an LNG train can continue to operate at over 50%
capacity when one MR circuit has tripped or is out for planned
maintenance.
Ambient air temperature directly affects LNG production in
traditional LNG plants. The higher the ambient conditions, the
lower the gas turbine power and, therefore, the lower the LNG
production. Consistent gas turbine power over a range of ambient
conditions can be achieved by pre-chilling the inlet air to the gas
turbines. This inlet air chilling is proven and common in gas
turbine power stations.
The liquefaction process technology aims to maximise the
energy efficiency of the LNG trains. Ammonia refrigerant
precooling of the MR ahead of the cold box increases plant
capacity, as well as efficiency. The impact of ammonia
precooling on plant capacity, and the fact that it consumes
little additional fuel, is fundamental to the overall energy
balance of the process. A combined cycle steam system using
the gas turbine waste heat to generate steam largely powers
the ammonia precooling system. Ammonia precooling
increases the LNG plant capacity without increasing the size
and cost of the major components of the cryogenic
liquefaction plant (cold box, gas turbine and MR compressor).
These two simple enhancements – cooling gas turbine
inlet air and precooling the MR, coupled with the selection of
ammonia as a precooling refrigerant – contribute towards the
reduction in plant cost per unit of LNG produced, and also
enhance the overall plant efficiency.
Using proven technology
A liquefaction train using OSMR process technology
incorporates a low equipment count and a simple
configuration. The equipment used does not require significant
unique specifications and is readily available in the marketplace
frommultiple vendors, reducing long lead times and allowing
for competition throughout the procurement process.
The following components, applied and proven in LNG and
other industries, comprise the core liquefaction process:
Single mixed refrigerant (SMR) liquefaction, using plate-fin
cold box liquefaction units.
Ammonia as a precooling refrigerant, as it has excellent
refrigeration properties, allowing for smaller condensers,
exchangers, piping and general plant size.
Gas turbine waste heat steam generation (combined
cycle process) providing motive power to the ammonia
refrigeration system. This is achieved by utilising a highly
efficient once-through-steam-generator (OTSG) harnessing
the waste heat from the turbine exhaust.
The closed loop ammonia refrigeration circuit itself, driven
by steam recovered fromwaste heat (above), precools
the MR and directly cools inlet air to the gas turbines. The
ammonia also provides additional and efficient process
cooling within the feed gas treatment systems.
Efficient and reliable gas turbines selected for the MR
compressor mechanical drive that serves the MR circuit.
Inlet air chilling to the gas turbines to ensure a consistent
power output and to avoid significant power loss at high
ambient conditions.
Integration of these components in the process technology
enables high overall performance levels.
The liquefaction process technology’s patents include a
boil-off gas (BOG) handling system, in which the BOG is lightly
compressed, reliquefied by passing it through the cold box and
then into the liquid methane separator. Flash gas separation
precedes liquid methane delivery to the LNG storage tank via
the LNG rundown line. The lean vapour phase flash gas from
the liquid methane separator, containing a high proportion of
nitrogen and some methane, provides low pressure fuel gas in
