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 3 to 44% to meet the estimated increase in demand. Clearly (30,000m ) 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 SomeSome companies companies are now are consideringnow considering vertical integration vertical in of LNG [3]. whichintegration they provide in which both supply they provideof LNG as both well supplyas demand Global trade was 245 MMTPA in 2015. The average yearly inof terms LNG of LNGas well to Power. as demand According in terms to Anatol of LNGFeygin to of growth of LNG demand since 2000 has been 6.6% pa. If Cheniere “that will be the major growth for LNG demand goingPower. forward” According and is a to model Anatol it is lookingFeygin to of replicated Cheniere this continues, demand would reach 358 MMTPA by 2021, “that will be the major growth for LNG which would represent a utilization of 80% on the planned globally [3]. Lower LNG prices are also making the fuel liquefaction capacity by 2021, without allowing for capacity moredemand attractive. going However, forward” for thoseand iscountries a model that it do is not taken offline. Some recent reports [2] have suggested the so havelooking an established to replicated gas distribution globally network [3]. Lower the capital LNG costs called glut in LNG has not materialized, and the numbers ofprices receiving, are storingalso making and regasification the fuel more at each attractive. power station can inhibit the development of LNG to power projects. above could lend support to that view. 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 3 of 490 MMSCFD or almost 23,000m 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 3 to power projects. The storage capacities at the end of have exceeded 160,000m . Indeed as the capacity of LNG 3 each spoke are relatively small. If the capacity for the carriers has increased up to 266,000m (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 TheThe key key modular modular LNG LNG tank drivers tank driversare: are: The small to midscale LNG market, supplying power – –Standardize Standardize tank tank design design by volume by volume based on basedsite specific 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 andfabrication higher quality yard leading to production volume. – Offsiteimproved pre-commissioning productivities of tank and higher quality The modular LNG tank seeks to reduce the unit cost – –Reduced Offsite manhours pre-commissioning executed on site of tank for smaller LNG storage volumes by targeting offsite manufacturing productivity levels. The economies of scale These– Reduced drivers targetmanhours a “plug executed and play” capabilityon 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. traditionalThese drivers solution. target a “plug and play” 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 m3 Material Steel ASTM A36 Gross Capacity 42,696 m3 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/m3 SSE (pga) 0.074 g Density (max) 470 kg/m3 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 bearings Gas 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 AdditionalThe key design modular benefits LNG of atank membrane drivers LNG are: tank are: reduce significantly. –– –Thermal Standardize cycling tank of 9% design Ni tanks by is volume not recommended based on because of the inner tank radial movements. However, –– Stainless steel and A537 Class 2 have much shorter site specific seismic isolation procurement lead times and will continue to exhibit the membrane tank is not subject to the same constraints much lower price volatility. –as Offsite the liner tank accommodates pre-fabrication the thermal in parallel strains within with the –– The total volume of wall insulation, based on PUF stainlessfoundation steel corrugations.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 purge fabrication which is continuously yard leading monitored. to This corresponding tank height is reduced, further reducing isimproved considered productivities a more effective andmethod higher of leak quality detection the shell quantities. than temperature sensors which rely on a spill of LNG – Offsite pre-commissioning of tank –– The tank transportation weight is lighter than the 9% Ni rather than vapor. steel option, despite having all insulation installed prior –– –The Reduced membrane manhours liner permits executed the use onof sumpssite in the tank to load out. bottom thereby increasing the net useable tank volume. –– Membrane tanks do not require hydrotesting. Leak –– TheseIn summary, drivers the target membrane a “plug modular and LNG play” tank takes tightness is demonstrated through the ammonia leak test. capabilityimportant steps while towards reducing the “plug costs and and play” 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 Tanks Gas 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 Tanks Gas 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

References

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