CRYOGENIC ABOVE GROUND STORAGE TANKS: …

1 1 CRYOGENIC ABOVE GROUND STORAGE tanks : FULL CONTAINMENT AND MEMBRANE COMPARISON OF TECHNOLOGIES J r me Thier ault Caroline Egels Technical Division BOUYGUES Travaux Publics 1 Avenue Eug ne Freyssinet 78061 Saint-Quentin-en-Yvelines - France ABSTRACT Over the last couple of years the LNG industry has shown a continuous trend for: Being more cost effective Improving land area utilization Being able to provide larger and larger tanks to accommodate the progressive increase in the gross capacity of ocean going methane carriers Reducing construction schedules Reducing carbon footprint. The aim and purpose of the proposed paper is to compare the different technologies of ABOVE GROUND STORAGE tanks with regards to: Safety and integrity of the tank (including seismic event) Construction cost and schedule Carbon footprint.

2 Note: This comparison will reflect latest development in STORAGE tank technologies. Special attention will be paid to the comparison of carbon footprints from a life cycle perspective, knowing that it appears that membrane tanks provide a significant reduction compared with conventional self standing technologies. BACKGROUND Bouygues is in perfect position to compare available technologies of CRYOGENIC STORAGE tanks , thanks to: Its leading position among civil EPC Contractors, Its large experience of both membrane and full containment technologies, Its involvement in normative working groups dealing with CRYOGENIC STORAGE tanks , Its constant commitment to reduce the impact of construction on the environment. INTRODUCTION This paper dealing with CRYOGENIC ABOVE GROUND STORAGE tank is aimed at providing technologies comparison, with special focus on carbon footprint.

3 In the first part of this note: The most commonly specified tank technologies will be introduced, Their basic design concept will be presented. 2 A second part will provide high level comparison of their performances and discuss their design limitations. Finally, carbon footprints and how it compares between both technologies will be discussed. MOST COMMONLY SPECIFIED TANK TECHNOLOGIES FOR LNG CONTAINMENT Full Containment Tank For this containment technology: The primary container is a thick 9% Nickel welded steel tank. The secondary container is a pre-stressed concrete tank equipped with a thermal corner protection. The space between primary and secondary container is filled with thermal insulation. The primary and secondary containers each possess separate hydrostatic stability and are thus referred to as self-standing.

4 Keys: 1. Primary container (9% Ni steel) 5. Insulated suspended deck (aluminum & fibreglass) 2. Bottom insulation (load bearing rigid cellular glass) 6. Hemispherical dome roof (reinforced concrete) 3. Slab (reinforced concrete) 7. Sidewalls (pre-stressed concrete) 4. Slab heating system 8. Wall insulation (loose fill perlite / 1m thick) Notes: - The inner face of items 3, 6 & 7 (red bolded line) is covered by a carbon steel liner aimed at ensuring gas tightness. - The thermal corner protection extending 5m ABOVE the bottom slab protects the wall-to-base joint. - The annular space 8 is connected to the vapour space on the tank and is thus filled with methane gas. Figure 1: Full Containment Design Concept Membrane Tank For this containment technology: The primary container is a thin stainless steel corrugated membrane.

5 The secondary container is a pre-stressed concrete tank equipped with a thermal corner protection. The space between primary and secondary container is filled with thermal insulation. This concept is based on the separation of structural and tightness functions. The primary container ensures liquid and gas tightness, The secondary container provides the hydrostatic stability, The load bearing insulation system transfers hydrostatic loads to the secondary container and limits the heat entrances to meet the specified boil-off rate criteria. 3 Keys: 1. SS corrugated membrane ( thick) 5. Slab heating system 2. Sidewalls (pre-stressed concrete) 6. Insulated suspended deck (aluminum & fibreglass) 3. Bottom insulation (load bearing PU / 40cm thick) 7. Hemispherical dome roof (reinforced concrete) 4.

6 Slab (reinforced concrete) 8. Wall insulation (load bearing PU / 40cm thick) Notes: - The inner face of item 7 (red bolded line) is covered by a carbon steel liner aimed together with the primary container (item 1) at ensuring gas tightness. - The thermal corner protection extending 5m ABOVE the bottom slab protects the wall-to-base joint. - The insulation space between the membrane and the concrete vessel is isolated from the vapour space of the tank. A nitrogen breathing system operates on the space to monitor the methane concentration and keep the pressure within normal operating bounds. The nitrogen system can be used to purge the insulation space in the unlikely event of a leak. Figure 2: Membrane Tank Design Concept Others Other tank technologies exist, but none of them compares to the ABOVE .

7 Most well-know technologies are: Single and double containment tanks (because of their reduced safety in operation such tanks are limited to remote located areas, where very limited population or facilities are present and/or where modest STORAGE capacity is to be provided), Double concrete tanks (felt difficult to implement because of the lack of references and codes recognizing this technology). PERFORMANCE COMPARISON Intrinsic Key Performances Figure 3 below provides a multi-parameters summary of how both technologies compare in term of intrinsic performances: 4 012345 Robustness / ReliabilitySafety in operationThermal efficiency (BOR)Compliance with legislative contextEfficiency in severe seismic contextFull ContainmentGST Membrane Figure 3: Comparison of tank intrinsic key performances Both technologies are considered proven, safe and reliable, with few differentiating strengths and weaknesses.

8 Implementation Performances Figure 4 below provides a multi-parameters summary of how both technologies compare from an implementation constraints standpoint: Figure 4: Comparison of tank implementation performances Membrane tank exhibits a number of implementation advantages as against full containment. As a matter of fact, where large tanks are required, membrane can be considered 15% less expensive and 3 months shorter to implement, for the same STORAGE capacity. However, particular attention needs to be paid to the specifics of the project under consideration that may dictate the STORAGE tank technology. Key parameters of influence are: Local circumstances, local codes and/or corporate practices, Lack and/or cost of skilled mechanical workforce, Tank size, Earthquake magnitude.

9 Design limitations In both cases, the most stringent limiting factor is the size of the hemispherical dome roof. Numerous studies have led to the conclusion that both tanks exhibit similar boundary limit in that regards, namely: In benign and mild earthquake areas, an internal diameter of 110m has been found as the limiting factor. This large tank span could be accommodated by the current concrete section thickness, but more limiting is the extent of peripheral demand to constrain the dome outward thrust. In this case 5 has been found to require substantial/impractical post-tensioning patterns ( 11 no. 37-strand tendons provided at 500mm distance). In severe earthquake area it has been found practical to set the radius of curvature to (in lieu of the typically adopted d) and that inner tank behaviour need be looked at with due care.

10 CARBON FOOTPRINTS COMPARISON Case Study The carbon footprints displayed in this paper have been established on the following case study: One (1) tank of 190,000 m3 STORAGE capacity to be built in Gladstone (Australia). Battery limit lies in nozzle flange on dome top. Externals are thus excluded (can be neglected because there is no difference in these components, between full containment and membrane tank). Tank is assumed to rest on shallow foundation (in case of deep foundation, the corresponding carbon footprint is expected to be slightly larger for full containment as against membrane tank). System Boundaries The system boundaries include the complete life time cycle from raw material extraction to LNG tank dismantling (cradle-to -grave): Figure 5: Tank Life Cycle However, for the sake of simplification, the contribution of operation, maintenance and dismantling have been neglected.