Gas and LNG Storage The Future of Modular LNG Tanks - Arup
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Gas and LNG Storage The Future of Modular LNG Tanks
Gas and LNG Storage | The Future of Modular LNG Tanks
1. Introduction
1.1 LNG and LNG to Power But the LNG market is changing, oil prices are lower, LNG
prices are being driven down, even renegotiated, and buyers
Market Overview are seeking shorter term, more flexible contracts. Despite
these challenges there was 890 MMTPA of proposed new
The LNG supply market has doubled in the last decade to liquefaction capacity in January 2016, key regions being
301.5 MMPTA [1], and it is anticipated that the next decade US, Canada, East Africa and FLNG. Clearly many of
will see further growth, particularly in the USA, Canada, these projects will not proceed as they compete for supply
East Africa and FLNG, increasing by 46% to 443 MMTPA contracts, but this should encourage demand side expansion.
by 2021 based on projects currently under construction. This
expansion is associated with very high and increasing LNG A number of factors will drive demand side expansion
liquefaction costs. For those terminals coming on line by including conversion to cleaner cheaper fuels for power
2021 the estimated CAPEX is over $1,500/tonne. Efforts generation, to either reduce particulate pollution from coal
to lower the unit costs of liquefaction has seen a move fired power stations or convert from fuel oil. In addition,
away from very large scale, bespoke trains to a modular, those countries that seek to honor their COP21 commitments
multi-train approach, based on smaller, midscale 0.5 to 1.0 are likely to see natural gas and liquefied natural gas (LNG)
MMTPA trains, such as Energy World’s proposed plant in as an essential transition fuel to a lower carbon future.
Sengkang, Indonesia. For those countries with an established gas distribution
At the beginning of 2016 regasification capacity, or potential network, large scale regasification terminals, in excess of
demand, was 757 MMTPA, including just over 10% FSRU 1.0 bcfd are appropriate, whereas archipelagoes such as the
capacity, but from 2000 to 2015 utilization has remained Caribbean [4], Indonesia and the Philippines need to consider
between 30% to 40%. With capacity only expected to expand a hub and spoke solution in which large scale LNG imports
to 810 MMTPA by 2021, utilization would need to increase (7.0 MMTPA) can be distributed by smaller LNG carriers
to 44% to meet the estimated increase in demand. Clearly (30,000m3) directly to the power station.
there has not been a lack of regasification capacity for the
LNG supply, but some analysts have predicted an oversupply Some
Some companies
companies areconsidering
are now now considering vertical in
vertical integration
of LNG [3]. which they provide
integration both supply
in which of LNG asboth
they provide well supply
as demand
Global trade was 245 MMTPA in 2015. The average yearly inof
terms
LNG as well as demand in terms of LNG toof
of LNG to Power. According to Anatol Feygin
growth of LNG demand since 2000 has been 6.6% pa. If Cheniere “that will be the major growth for LNG demand
Power. According to Anatol Feygin of Cheniere
going forward” and is a model it is looking to replicated
this continues, demand would reach 358 MMTPA by 2021,
“that will
globally be theLNG
[3]. Lower major growth
prices formaking
are also LNG the fuel
which would represent a utilization of 80% on the planned
liquefaction capacity by 2021, without allowing for capacity demand
more going
attractive. forward”
However, and is
for those a model
countries thatitdo
isnot
taken offline. Some recent reports [2] have suggested the so have
looking to replicated globally [3]. Lower LNGcosts
an established gas distribution network the capital
called glut in LNG has not materialized, and the numbers ofprices
receiving,
are storing and regasification
also making at eachattractive.
the fuel more power station
above could lend support to that view. can inhibit the development of LNG to power projects.
However, for those countries that do not
have an established gas distribution network
the capital costs of receiving, storing and
regasification at each power station can inhibit
the development of LNG to power projects.
Gas and LNG Storage | The Future of Modular LNG Tanks
Offtaker Power Station Capacity(MW) Storage Tank Capacity (m3)
2018 (Conv) 2032 (New) Total By 2018 By 2023 Total
The Bahamas, BEC (NP) 393 320 713 70,000 90,000 160,000
The Bahamas, GBPC 240 0 240 20,000 20,000 40,000
Barbados, BL&P 60 245 305 35,000 45,000 80,000
Belize, BEL 62 40 102 5,000 15,000 20,000
Dominican Republic, All 1,025 1,800 2,825 370,000 460,000 830,000
Guyana, GPL 140 240 380 35,000 45,000 80,000
Haiti, EDH 238 560 798 55,000 225,000 280,000
Jamaica, JPS 621 1,320 1,941 140,000 155,000 295,000
Suriname, EBS 299 640 939 50,000 105,000 155,000
Total 3,078 5,165 8,243 780,000 1,160,000 1,940,000
Table 1 LNG Storage Tank Capacities for Caribbean hub and spoke scenario [4]
1.2 LNG to Power The Caribbean is only one example. Other countries, such
as the Philippines and Indonesia have much greater demand
Storage Requirements for power station conversion and new build. Also, projects in
Central America are being considered, but based on receiving
For the Caribbean the IADB report [4] forecasts gas demand 150,000m3 LNG carriers unloading to FSRUs or onshore
of 490 MMSCFD or almost 23,000m3 of LNG per day. LNG regasification terminals that are effectively oversized
Assuming a hub and spoke scenario for distribution from for the power station capacity.
the Dominican Republic, Table 1 summarizes the storage
capacity by country required in 2018 and then expansion 1.3 Background to Modular
through to 2032 to meet the forecast demand.
LNG Tanks
For perspective a modern combined cycle gas turbine has
a thermal efficiency of between 45% to 55%. Therefore The authors have been involved with LNG tank design and
a 100MW power station consumes approximately 800m3 development for almost 20 years. In that time the traditional
of LNG per day or over 24,000m3 per month. The report solution for LNG storage in excess of 10,000m3 has been
outlines conversion and new build forecasts for CCGT, a stick built 9% Ni steel single or full containment LNG
single cycle gas turbines and reciprocating gas fueled storage tanks. Most LNG projects have targeted throughputs
power stations. greater than 1000 MMSCFD or 7MMTPA. The storage
The results highlight a key issue for development of LNG volumes for this size of regasification or liquefaction plant
to power projects. The storage capacities at the end of have exceeded 160,000m3. Indeed as the capacity of LNG
each spoke are relatively small. If the capacity for the carriers has increased up to 266,000m3 (Q-Max) the onshore
Dominican Republic is ignored the average storage capacity storage tank size has also increased to ensure filling or
is approximately 50,000m3. If Belize is also ignored and a discharge can be achieved within 24 hours.
nominal tank size of 20,000m3 is assumed, each phase of
development could be based on multiples of a standard tank
size. By 2018 the Caribbean market could require 20 x 20k
m3 LNG storage tanks with perhaps another 40 x 20k m3 or
20 x 40k m3 LNG tanks by 2023.
Gas and LNG Storage | The Future of Modular LNG Tanks
Figure 1 27,500 m3 ethane/ethylene/LNG carrier operated by Evergas ©
Relatively little work has been done to develop cost effective Presentations at the Trinidad Oil and Gas Conference in
storage tank sizes for the LNG to Power market. Tank sizes 2014 [5] and Gastech 2015 [6] have highlighted the market
greater than 160,000m3, required to receive a standard export opportunity for LNG to power and emphasized that the
LNG carrier, would provide 10 months of storage for a design and delivery of smaller LNG tanks is essential to
100MW CCGT. Even for a larger power station it is clear reduce overall cost and schedule to ensure that the cost base
that there is a mismatch between the storage tank and the is reasonable and the market sustainable.
exporting LNG carrier. Smaller carriers exist, using Type C
Another market that is expected to see significant expansion
or membrane technology, but there is a definite requirement
is the LNG marine fuels business. Eagle LNG has recently
for smaller ships to support cost effective LNG to power
completed its project in Maxville, FL, USA and Conrad
delivery. Ships in the range of 10,000m3 to 30,000m3 would
Shipyard is building an LNG bunkering barge. The LNG
allow smaller marine facilities and be compatible with the
volumes for each ship are suitable for Type C storage
required onshore storage.
containers, but aggregated onshore LNG storage tank
volumes in excess of 10,000m3 are necessary.
Figure 2 Economies of scale- tank volume [8] or number of tanks [9]
Gas and LNG Storage | The Future of Modular LNG Tanks
1.4 The opportunities
The
The key
key modular
modular LNGLNG tank drivers
tank drivers are: are:
The small to midscale LNG market, supplying power – –Standardize tanktank
design by volume based on based
site specific
Standardize design by volume on
stations or the marine fuels business, requires a smaller seismic isolation
capacity LNG storage tank, in the range of 10,000m3 to site specific seismic isolation
– Offsite tank pre-fabrication in parallel with foundation
100,000m3. The traditional solution based on 9% Ni steel –construction
Offsite tank pre-fabrication in parallel with
technology is stick built on site. It is well known that the unit
foundation construction
price of LNG stored reduces as the single tank size increases – Dedicated fabrication yard leading to improved
[8]. However economies of scale can also be achieved by –productivities
Dedicated and
fabrication yard leading to
higher quality
production volume. improved productivities and higher quality
– Offsite pre-commissioning of tank
The modular LNG tank seeks to reduce the unit cost
– –Reduced
Offsitemanhours
pre-commissioning of
executed on site tank
for smaller LNG storage volumes by targeting offsite
manufacturing productivity levels. The economies of scale These drivers target
– Reduced a “plugexecuted
manhours and play” capability
on site while
are based not on the volume of a single tank but the number reducing costs and schedule compared to the stick built
of units produced to achieve the required volume. traditional solution.target a “plug and play”
These drivers
A good reference case was the production of 25,000 m3 capability while reducing costs and schedule
tanks in South Carolina [9]. The estimated productivity compared to the stick built traditional solution.
improvements, interpolated from the stated productivity for
the initial 10 tanks, are shown in Figure 2. It is noted that the
first sphere in that project experienced severe component fit
up and some welding issues.
Since the basic tank unit can be in the range of 10k m3 to 40k
m3, larger total volumes can be achieved with multiple tanks,
which can also align with project phasing goals.
The following sections in this paper will provide an update
on development of the modular LNG tank concept.
Gas and LNG Storage | The Future of Modular LNG Tanks
2. Technical Development
Figure 3 Initial Modular Tank Concept [6]
2.1 Initial Concept 2.2 Current Concept
The initial concept [6] was based on either 9% Ni or 2.2.1 Design
membrane technology. To reduce the overall weight the
After the presentations in 2014 [5] and 2015 [6], specific
modular tank provides single containment capability,
project opportunities focused further development.
thereby eliminating the concrete wall and roof. The tank was
erected on a cellular concrete base which provided a robust The initial concept considered a maximum volume of
susbstructure for subsequent transportation by water from the 36,000m3, and this was considered to be close to the upper
fabrication yard to the project site. bound of what could, or should, be pre-fabricated and
transported, before costs were negatively impacted. However,
At the project site the tank was supported on bearings,
an opportunity to consider a 40,000m3 single containment
founded on shallow footings or piles. Trenches between the
design on the US GoM coast provided the basis for the next
foundations allowed access for the self-propelled modular
phase of development. Technical assumptions are presented
transporters (SPMTs).
in Table 2. The updated design in shown in and Figure 5
Gas and LNG Storage | The Future of Modular LNG Tanks Figure 4 40k m3 9%Ni Steel Single Containment Modular LNG Tank General Arrangement Figure 5 40k m3 9%Ni Steel Single Containment Modular LNG Tank Details
Gas and LNG Storage | The Future of Modular LNG Tanks
Remark Value Remark Value
Design Standards NFPA59A, API625/620 Outer Tank
LNG Storage Tank Type Single Containment Material Steel ASTM A36
Foundation Type Piled supported, elevated Outer tank diameter 40.000 m
Inner Tank Min width annular space 1.250 m
Material 9Ni ASTM A533 Type 1 Dome Roof
Net Capacity 40,000 m 3
Material Steel ASTM A36
Gross Capacity 42,696 m 3
Spherical Radius 40.000 m
Inner Tank Diameter 37.500 m Insulation Material
Height (ambient) 39.380 m Bottom Cellular Glass
Annular Expanded Perlite
Suspended deck Glass fiber blanket
LNG Product Seismic Design
Temperature -170 oC OBE (pga) 0.037 g
Density (BOG) 440 kg/m 3
SSE (pga) 0.074 g
Density (max) 470 kg/m 3
Wind
Latent heat of vaporization 511,000 J/kg ASCE 7-05 63 m/s
Design boil off rate (vol) 0.05 %/day Soils US GoM typical
Maximum filling rate 850 m3/hr very soft to firm cohesive 0-30 ft
Max out pumping rate 2,250 m3/hr firm to stiff cohesive 30-100 ft
Pressures slightly over consolidated >100 ft
Maximum design pressure 190 mbar
Minimum design pressure -5 mbar
Table 2 40k m3 Single Containment Tank Design Data
The key technical developments are summarized below. –– Side wall discharge is proposed. This is consistent with
NFPA 59 and if in-tank shut off valves are provided the
–– The tank is elevated above ground to provide both
design spill is significantly reduced. The tank elevation
space for the SPMTs and also air flow to eliminate
also ensures that the pump does not need to be recessed
base slab heating.
below ground to achieve the minimum NPSH. Typical
–– The cellular concrete base slab is replaced with a steel details were presented at LNG 12 [10] refer to Figure 6.
grillage and concrete deck. This reduced weight which is The results of the techno-economic evaluation concluded
a significant issue for the larger tank volume. that side wall pump discharge could reduce costs by up
–– 9%Ni was chosen over membrane based on owner to $6MM for a 2 x 140k m3 storage tanks (1998 prices).
preference and concerns over permitting delays that But the prize is even greater for the modular LNG tank.
might arise since membrane tanks have not yet been Not only is the pump platform significantly reduced in
approved by FERC. This issue is discussed further in the size, refer to Figure 7, but the tanks can be manifolded
next section 2.3.2. reducing the total number of pumps. The pumps can also
be located outside of the bunded areas with easy access
for maintenance.
–– For larger total volumes, based on multiple units, the
modular LNG tank will require individual bunded areas.
This area can be optimized based on the work carried out
by Coers (2005) [11].
Gas and LNG Storage | The Future of Modular LNG Tanks
Figure 6 Proposed side entry pump suction nozzle for a single integrity LNG tank [10]
Figure 7 Comparison of roof platforms with and without side wall discharge (courtesy Cheniere and Coers [11])
2.2.2 Execution –– The hydrotest is not carried out at the fabrication yard.
It was concluded that owners and or regulators may
Based on the design described above an execution plan
require proof that the 9%Ni inner tank was not damaged
was developed working with Great Basin Industries and
during transportation. Transferring the test to the project
Mammoet. The overall scope of work was divided into a
site significantly reduces the foundation loads at the
number of work packages as summarized in Table 3.
fabrication yard.
The following notes highlight some important issues –– The inner and outer tanks are erected as complete
regarding the execution plan. prefabricated rings in a stepped sequence starting with
–– Fabrication yards do exist along the US GoM coast. The the outer tank then the inner tank. A linear layout for
work to date has not undertaken a detailed evaluation multiple tank erection is shown in Figure 8. A heavy lift
of potential sites, but greenfield development is also crane is used for ring installation.
an option. This approach will increase the initial start- –– The roof is prefabricated as one piece and lifted into
up costs and therefore it has been assumed an existing position. No air lift is envisaged.
facility will be utilized. –– After roof erection the bottom insulation and inner
–– Fabrication facilities are not limited to the project tank bottom plate can be installed, providing weather
country, indeed the modular LNG concept envisages protection to the insulation.
regional fabrication yards that will support LNG storage –– It is assumed that the fabrication yard has a bulkhead
tank in that area, thereby reducing the shipping times suitable for load out of 5,000 te, however temporary
and costs. loading ramps can be used, founded on a piled ground
beam where soil conditions are not strong enough.
Gas and LNG Storage | The Future of Modular LNG Tanks Figure 8 Modular LNG Tank erection (courtesy of GBI and Mammoet) Figure 9 Modular LNG Tank Transportation (courtesy of Mammoet)
Gas and LNG Storage | The Future of Modular LNG Tanks
Tank prefabrication Tank Transportation Project Site
Fabrication yard enabling works Supply of all heavy lift equipment Enabling works for receiving tank
Tank fabrication line foundations Supply of all marine equipment Construction of tank foundation
Material procurement Load out at fabrication yard Hydrotesting
Steel grillage fabrication Tow to project site Perlite insulation
Tank ring prefabrication Offload at project site Tank hook up
Tank erection Set down at project site on plinths Bund construction
Tank roof prefabrication Demobilization Final pre-commissioning of tank
Roof Erection Ready for cooldown
Pre-commissioning
Preparation for transportation
Table 3 Execution Work Packages for 9% Ni steel single containment modular LNG tank
–– The tank will be moved on to the transportation vessel 2. Tank fabrication and erection can start once material is
using SPMTs. Whether the SPMTs remain for the procured and delivered to the fabrication yard.
duration of the tow depends on distance. For short –– Many large LNG tanks have seen lead times for 9%
tows the SPMTs will travel with the tank, although Ni steel plate of 12 to 18 months. This is very market
the tank will be lowered on to temporary supports on dependent but it has mitigated the schedule delay waiting
the transportation vessel. For long tows (more than for foundation construction and outer wall construction.
several days) two sets or SPMTs are require, one at the
–– Material pre-ordering can reduce the lead times, and
fabrication yard and one at the project site.
financial commitments prior to final regulatory approval
–– Sea fastenings will depend on the specific tow route. For can further reduce the schedule.
inland water way tows or sheltered water tows initial
–– Tank erection commences with fabrication and erection
calculations indicate vessel motions will not require
of the steel grillage and outer tank carbon steel outer
any seafastening for the inner tank. The outer tank will
tank rings. This material is on much shorter lead times.
be fastened to the vessel deck. For longer tows or open
water tows, temporary sea fastening of the inner tank –– Based on an established fabrication yard, tank erection
will be required. Calculations have shown that the inner can commence well ahead of a stick built tank at the
tank top ring stiffening and or shell thickness could be project site.
increased to cater for the inertial loading. Alternatively 3. Significant, labor intensive activities are transferred from
temporary restraints to the outer tank shell will provide the project site to a dedicated fabrication yard.
resistance to the inertial loads. These restraints can be –– Project site, stick built tanks are often remote from large
removed once the tank is installed at the project site and resource centers, reducing productivity and or increasing
prior to hydrotesting. labor costs.
–– Enabling works at the project site are relatively modest –– Specialist welders are required for the inner 9% Ni tank
and cost effective. For load below 5,000 te temporary which incurs a premium for remote sites. Further, in tight
unloading ramps can be used. This will be founded on a labor markets, the transient labor force may be difficult
piled ground beam. Temporary onshore mooring onshore to secure, whereas an established fabrication yard can
points will be required for a traditional Mediterranean provide a more reliable resource.
spread mooring pattern. 4. Improved productivities and quality
The key benefits of the proposed execution plan are –– An established fabrication yard focused on tank
1. Tank erection is not waiting on construction of the fabrication can invest in training and equipment to
project site tank foundation. increase productivities and reduce costs.
–– Regulatory processes normally prevent any construction –– Prefabrication of tank parts can be done in covered
on site before project permits have been secured. areas, further increasing productivities and
–– Many LNG sites require significant enabling works workmanship quality.
including, but not limited to, bulk earthworks before
foundation construction can commence.Gas and LNG Storage | The Future of Modular LNG Tanks
Figure 10 23m diameter tank under tow (courtesy of Smith Group)
Figure 11 Peru LNG Tank 130,000m3 with 256 Triple PendulumTM bearing (courtesy of EPS)
Figure 12 Incheon LNG Terminal founded in elastomeric bearingsGas and LNG Storage | The Future of Modular LNG Tanks
2.3 Further Development The key driver on tank shell design and quantities is seismic
loading. This is the most significant lateral load on the tank
2.3.1 Standard Tank Design by Volume and in areas of moderate to high seismicity, will govern the
tank geometry and shell weight. Some tank designs have
The work carried out on the 40k m3 modular LNG tank adopted seismic isolation to reduce the inertial loading and
confirmed technical feasibility and schedule advantages shell quantities, refer to Figure 11 and Figure 12. According
over a stick built solution. It also highlighted the to Earthquake Protection Systems Inc. (EPS) [12] an 85%
importance of fabrication yard set up costs. When these reduction in seismic loading was achieved, which reduced
are spread over many tanks they are not significant, as the overall cost of the tank construction.
for any pre-engineered, manufactured product. To ensure
that competitive pricing is achieved from the start it was Despite the cost savings on the Peru LNG tanks, seismic
recognized that offsite pre-fabrication should not be isolation is not the default approach for dealing with
delivered on a bespoke design basis for each project. The moderate to high seismic loads. Lowering the tank aspect
modular LNG tank concept would be enhanced if standard ratio (H:R), using inner tank straps to prevent uplift and
designs could be offered for any site, anywhere in the world. advanced nonlinear dynamic soil structure interaction
(DSSI) can be used to lower the inertial load effects on the
A standard tank design would permit the fabricator to further tanks. Seismic isolation automatically elevates the tank and
improve its fabrication and erection methods. Key site introduces a second foundation or base slab. This increases
specific drivers for modular LNG tank design are: schedule and cost, to which the isolator cost is also added.
1. Soil conditions and foundation design For the modular LNG tank these costs are already included
2. Seismic conditions and inertial loads on tank and and the elevated tank is part of the overall concept to allow
foundation for installation using SPMTs. In fact the modular LNG tank
3. Other environmental loading conditions (such as wind is very well suited to adopting seismic isolation because
and snow loading) all components are included in the existing design for
other reasons.
4. Temperatures and effect on insulation design
5. Tow route, duration and storm conditions Initial calculations confirm that tuning the elastomeric
bearing will lower the seismic loads to those of the base
The soil conditions will always be site specific and provided design. The base design could be chosen utilizing the 33%
settlement criteria are satisfied then there is no direct impact over stress permitted under the Operating Basis Earthquake
on the modular tank design, except for seismic response. (OBE). For areas of high seismicity, friction pendulum
bearings of the type provided by EPS may be required. The
Other environmental loading conditions are not significant
solution for any specific site requires a detailed analysis
drivers of tank shell and roof quantities and conservative
of the tank foundation system incorporating isolators. It is
assumptions could be made to eliminate this variation.
important that the foundation system (shallow or deep) is
Preserving a standardize design is always a compromise. incorporated into the model, because significant reduction in
Perlite insulation could be maintain a constant thickness and loads can arise due to non-linear response in the soil resulting
heat leak variations addressed by changes in the roof and in longer period response and higher levels of damping.
base insulation thicknesses. This would impact the overall
height of the tank and is not necessarily the most efficient
solution. Further work will be required to understand the
sensitivity to this issue, but if insulation properties cannot
be easily adjusted for a given thickness then conservative
insulation thicknesses could be appropriate.
Tank response during the tow has been investigated. It is
clear that any extreme motions that would impact the basic
tank design can be addressed with temporary sea fastenings
and strengthening to the outside of the tank which can be
ultimately removed and reused.Gas and LNG Storage | The Future of Modular LNG Tanks
Figure 13 Effect of seismic isolation on acceleration and displacements [13]
Seismic isolation results in longer period response which is 2.3.2 Membrane Modular LNG Tank
accompanied by an increase in tank transient displacements.
Membrane tanks are not new, indeed more than 100 onshore
This will impact the design of incoming pipework but
membrane tanks have been built since 1972, and over 85% of
experience has shown that differential movements can be
all LNG carriers utilize the membrane technology solution.
accommodated in the piping design. If displacements are
Two membrane tanks are currently under construction
considered too high then viscous dampers can be added to
for Energy World Corporation at Sengkang, Sulawesi,
the isolation system to reduce peak displacements.
Indonesia and Pagbilao, Philippines. In addition there
Isolation of vertical ground motions is not as common, have been recent developments in international codes to
and has not been proposed for LNG tanks to date. Vertical recognize and incorporate design provisions for membrane
accelerations will increase the effective weight of the LNG tanks. Nevertheless, the dominant tank technology for LNG
and therefore the hoop stresses. In areas of high seismicity, storage remains 9% Ni steel. A description of the membrane
such as the west coast of the US, peak spectral accelerations technology and comparison with above ground 9% Ni
approaching 1g can occur, but careful DSSI can mitigate storage tanks is presented by Ezzarhouni etal (2016) [7].
these effects.
Whilst this comparison was for a full integrity or full
Long period ground motions cannot be isolated and these containment design there are many attributes of the system
give rise to sloshing effects on the liquid surface. The codes that are compatible with the objectives of the modular LNG
are clear on the requirements for freeboard under both OBE tank and would enhance the overall concept, further lowering
and SSE conditions. As seismic intensity increases, the the costs and reducing the schedule.
freeboard height for a given tank aspect ratio increases. To
preserve a standard tank design, baffles could be installed
on the underside of the roof to disrupt the sloshing wave,
but this is a novel approach which might not be acceptable
to owners or regulators. Alternatively, it is accepted that the
tank height must be increased to address this issue. However
it would require only a minor height adjustment to the
standard tank design.
Further work is required to understand the variations and
impact that vertical and horizontal seismic accelerations
have on the modular tank design, but initial results are
encouraging and a standardized tank design is possible,
which should translate into further reductions in cost Figure 14 Top view of the bottom floor showing membrane system
and schedule. (courtesy GTT)Gas and LNG Storage | The Future of Modular LNG Tanks
These benefits are summarized below and quantified in –– The design is fundamentally more robust with respect to
Section 3: transportation loadings. Recalling that 85% of all LNG
carriers use the technology it is a well proven technology
–– GTT has developed a highly modular membrane system
able to accommodate the strains associated with vessel
based on pre-engineered, manufactured components.
motion. Further, all transportation loads can be designed
This is well aligned with the objectives of a standardized
into the outer tank which can easily accommodate
tank design.
seafastening and temporary strengthening. There is no
–– There is only one structural tank and it is located on thin walled inner shell to seafasten.
the outside. The inner 9% Ni and outer A36 shells are
replaced with a 1.2mm stainless steel liner and A537
Class 2 outer shell. Total steel weight and costs Additional
The keydesign benefits
modular LNG of a tank
membrane LNG
drivers tank are:
are:
reduce significantly. –– –Thermal cyclingtank
of 9% Ni tanks
Standardize design byisvolume
not recommended
based on
–– Stainless steel and A537 Class 2 have much shorter because of the inner tank radial movements. However,
site specific seismic isolation
the membrane tank is not subject to the same constraints
procurement lead times and will continue to exhibit
much lower price volatility. –asOthe linertank
ffsite accommodates the thermal
pre-fabrication strains within
in parallel with the
stainless steel corrugations.
–– The total volume of wall insulation, based on PUF foundation construction
filled plywood boxes, is less. Hence, for the same –– The membrane insulation space is maintained under a
overall external tank diameter and volume the –nitrogen
Dedicated
purgefabrication yard leading
which is continuously to This
monitored.
corresponding tank height is reduced, further reducing isimproved
consideredproductivities
a more effective and higher
method quality
of leak detection
the shell quantities. than temperature sensors which rely on a spill of LNG
–rather
Offsite
thanpre-commissioning
vapor. of tank
–– The tank transportation weight is lighter than the 9% Ni
steel option, despite having all insulation installed prior –– –The
Reduced manhours
membrane executed
liner permits the useon site in the tank
of sumps
to load out. bottom thereby increasing the net useable tank volume.
–– Membrane tanks do not require hydrotesting. Leak –– These drivers
In summary, thetarget a “plug
membrane andLNG
modular play”tank takes
tightness is demonstrated through the ammonia leak test. important steps towards the “plug and play”
capability while reducing costs and schedule objective.
Foundation proof loading is of questionable value even compared to the stick built traditional solution.
for 9% Ni LNG tanks and is not required for membrane
LNG tanks which use polyurethane foam (PUF)
bottom insulation.
–– No hydrotest means that the tank can leave the
fabrication complete with all insulation installed and
fully pre-commissioned. After installation at the project
site the ammonia leak test could be rerun to satisfy
the owner and regulator that no damage was sustained
during the sea tow.Gas and LNG Storage | The Future of Modular LNG Tanks
3. Comparison of 9% Ni Steel
and Membrane Tanks
Dimension 9% Ni Modular LNG Tank Membrane Modular LNG Tank
Net LNG storage volume (m3) 40,000
Outer tank diameter (m) 40.000
Inner tank diameter (m) 37.500 38.800
Design Maximum Liquid Level (m) 38.802 36.280
Outer tank height to roof joint (m) 42.280 39.460
Roof rise (m) 5.365 5.365
Overall tank height from ground (m) 50.447 47.627
Table 4 Comparison of principal dimensions for 9% Ni and membrane modular LNG tank
3.1 Quantities 3.2 Schedule and Cost
Table 4 and Figure 15 summarize the principal dimensions of A comparison of construction schedules is shown in Table
the 9% Ni and membrane modular LNG tanks. 7. The schedule is based on an EPC contract, with all design
data, including soils information available at notice to
Table 5 compares the weights, and thereby the quantities,
proceed. The membrane tank is estimated to be ready for
for 40k m3 9% Ni and membrane modular LNG tanks. The
transportation at the same time as the 9% Ni but the overall
following notes explain the key differences.
schedule is 2 months quicker because there is no hydrotest
–– The outer tank shell weights are similar weight. The and annular insulation to complete at the project site.
membrane tank is the same diameter, but is shorter
Costs are sensitive to local labor conditions and material
because of lower wall and base insulation thicknesses.
costs. The costs have, therefore, been normalized and
The membrane tank uses ASTM A537 Class 2 steel
compared to a traditional stick built single containment LNG
compared to A36 for the 9%Ni tank. This is a stronger
tank at 100%.
steel and whilst more expensive per tonne, is more
efficient in terms of weight and subsequent welding
costs. Bottom shell thickness is 23mm compared to
16mm for the 9% Ni tank.
–– The inner tank compares the weight of ASTM A533
Type I 9% Ni steel with 1.2mm A304L stainless steel
membrane. Since the membrane is not structural the
weight is substantially less, saving 476te on the inner
tank weight.
–– Roof insulation weights are similar, however the PUF
insulation system shows a saving in weight of 336te over
the perlite, resilient blanket and foam glass blocks used
on the 9% Ni tank.
–– The elimination of the inner structural tank and use of
PUF insulation has resulted in overall weight savings of
20%. Further the membrane transportation weight is less
than the 9% Ni which excludes the perlite.
These results demonstrate that the membrane tank is a lighter
design than the 9% Ni steel tank.Gas and LNG Storage | The Future of Modular LNG Tanks
Figure 15 General arrangement for 9% Ni and membrane modular LNG tanks
Item 9% Ni Modular LNG Tank Membrane Modular LNG Tank
Total (te) Transport (te) Total (te) Transport (te)
Outer Tank
Shell 504 504 544 544
Base 74 74 74 74
Roof 107 107 107 107
Inner Tank
Shell 467 467 45 45
Base 66 66 12 12
Insulation
Bottom 502 502 234 234
Wall 368 300 300
Roof 50 50 54 54
Pump Platform 350 350 350 350
Grillage
Concrete 990 990 990 990
Steel 212 212 212 212
Sub-total 3,690 3,323 2,922 2,922
Contingency 554 498 438 438
Total 4,244 3,821 3,360 3,360
Table 5 Comparison of tank weights for 9%Ni and Membrane Modular LNG TanksGas and LNG Storage | The Future of Modular LNG Tanks
9% Ni Single Containment 9% Ni Modular LNG Tank Membrane Modular LNG Tank
100% 90% 80%
Table 6 Cost comparison of 9% Ni and Membrane Modular LNG Tank 40k m3
Activity Months from notice to proceed
9% Ni Modular LNG Tank Membrane Modular LNG Tank
Notice to Proceed 0 0
Purchase and fabricate material +5 +4
Grillage construction complete +6 +5
Outer tank erection complete +14 +10
Inner tank erection complete +14 +16
Roof installation complete +15 +11
Insulation complete at fab yard +17 +17
Transport and set tank +18 +18
Hydrotest +19 n/a
Insulation complete at project site +20 n/a
Final pre-commissioning +22 +20
Ready for Cooldown +22 +20
Table 7 Comparison of schedules for 9% Ni and Membrane Modular LNG TanksGas and LNG Storage | The Future of Modular LNG Tanks
4. Conclusions
The ongoing development work on the modular LNG tank
concept has confirmed technical feasibility of both 9% Ni The small to mid-scale LNG and LNG to
and membrane solutions. The membrane option will offer a Power markets require smaller tanks. Cheaper
more robust design for transportation and also lower costs
and faster, smaller tanks will greatly assist this
and shorter schedules.
developing market.
More importantly, the concept of a cheaper and quicker
prefabricated small to medium sized tank with “plug and
play” capability, based on a standard design that can be
installed for any site, anywhere in the world is achievable.
Single containment is not appropriate for all projects and
jurisdictions. Full containment options are too heavy to
transport cost effectively, but initial work looking at precast
wall panels and wire wound prestressing as used in the water
tank industry, combined with the membrane technology
should offer cost and schedule savings.Gas and LNG Storage | The Future of Modular LNG Tanks
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