Design and Construction of LNG Storage Tanks

Josef Rötzer, Konrad Bergmeister, Frank Fingerloos, Johann-Dietrich Wörner, Philip Thrift

• Publisher: Ernst & Sohn
• Year: 2019
• ISBN:
  9783433609965
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Worldwide, the use of natural gas as a primary energy source will remain vital for decades to come. This applies to industrialized, emerging countries and developing countries. Owing to the low level of impurities, natural gas is considered to be a climate-friendly fossil fuel because of the low CO2 emissions, but is at the same time an affordable source of energy.
In order to enable transport over long distances and oceans (and hence create an economic and political alternative to pipelines), the gas is liquefied, which is accompanied by a considerable reduction in volume, and then transported by ship. Thus, at international ports, many LNG tanks are required for temporary storage and further use. The trend towards smaller liquefaction and regasification plants with associated storage tanks for marine fuel applications has attracted new players in this market who often do not yet have the necessary experience and technical expertise. It is not sufficient to refer to all existing technical standards when defining consistent state-of-the-art specifications and requirements.
The switch to European standardisation has made it necessary to revise and adapt existing national codes to match European standards. Technical committees at national and international level have begun their work of updating and completing the EN 14620 series.
In the USA, too, the corresponding regulations are also being updated. The revision of American Concrete Institute standard ACI 376 Requirements for Design and Construction of Concrete Structures for the Containment of Refrigerated Liquefied Gases, first published in 2011, will be completed in the spring of 2019, and the final version, published in autumn 2019.
This book provides an overview of the state of the art in the design and construction of liquefied natural gas (LNG) tanks. Since the topic is very extensive and complex, an introduction to all aspects is provided, e.g. requirements and design for operating conditions, thermal design, hydrostatic and pneumatic tests, soil surveys and permissible settlement, modelling of and calculations for the concrete structure, and the actions due to fire, explosion and impact. Dynamic analysis and the theory of sloshing liquid are also presented.

1
Introduction

The use of natural gas as an independent branch of the global energy supply sector began in the early 1960s. Prior to that, natural gas had only been regarded as a by‐product of crude oil production; there was no use for it and so it was either pumped back into the ground or flared. But all that has changed in the meantime – natural gas currently accounts for 22% of global energy supplies. Huge deposits in Australia are now being exploited and deposits in the USA will soon be coming online, which will increase that global share (Fig. 1.1). There are many reasons for this development – economic, political and ecological: Australia is close to the growing Asian economies, the USA is aiming to reduce its dependence on foreign oil and energy supplies by developing its own resources, and global efforts to replace fossil fuels by gas apply throughout the world.

Fig. 1.1 Development of energy demand [1].

The International Maritime Organisation (IMO), a specialised agency of the United Nations, has drawn up new rules that have been valid from 2015 and are particularly strict for the North Sea and Baltic Sea. Complying with emissions requirements is difficult when using diesel and heavy oil as marine fuel. But using liquefied natural gas (LNG) as a marine fuel results in – compared with diesel – about 90% less nitrogen oxide, up to 20% less carbon dioxide and the complete avoidance of sulphur dioxide and fine particles [1]. Det Norske Veritas (DNV), the Norwegian vessel classification body, therefore expects that there will be about 1000 new LNG‐powered ships by 2020, which amounts to almost 15% of predicted new vessel orders. This change is heavily influenced by the huge drop in the price of natural gas, which has been brought about by the global production of shale gas (Fig. 1.2, Fig. 1.3).

Fig. 1.2[[dot]] Gas price developments since 2000 [1].

Fig. 1.3[[dot]] Regional distribution of natural gas potential [1].

The use of natural gas involves transport and storage difficulties. Transport via pipelines is economic up to a distance of 4000–5000 km, depending on the boundary conditions. In the case of difficult geographic circumstances, such as supplies to islands, e.g. Japan and Taiwan, or where it is necessary to cross mountain ranges, supplying gas via a pipeline is much more difficult and costly. Therefore, the method of liquefying natural gas and then transporting it over great distances in ships had already become established by the mid‐20th century.

LNG technology takes advantage of the physical material behaviour of natural gas, the main constituent of which is methane. At the transition from the gaseous to the liquid state, the volume is reduced to 1/600. However, this requires the temperature of the gas to be lowered to ‐162°C. Only this extreme reduction in volume makes transport in ships economically viable. The entirety of the elements required for transporting LNG in ships is known as the “LNG chain”, which consists of the liquefaction plant in the country supplying the gas, LNG tanks for intermediate storage of the liquefied gas, jetties as berths for the special LNG transport vessels, tanks for the intermediate storage at the receiving (i.e. import) terminal and a regasification plant in the country importing the gas.

It is common practice these days to build full containment tanks, which consist of an outer concrete secondary container surrounding an inner steel primary container. The prestressed concrete outer container serves to protect the thin‐wall steel inner container against external actions and also functions as a backup container in the event of the failure of the primary container. The outer container must prevent uncontrolled leakage of vapours into the environment and must also be able to contain the liquefied gas and withstand any overpressure.

The great hazard potential of LNG is the risk of fire. If LNG changes to its gaseous state and mixes with air, the result is a combustible gas that can explode, and certainly burns very fiercely. Safe transport and storage are the technical challenges of LNG. At these low temperatures, the materials normally used in the construction industry exhibit a distinctly brittle behaviour and fail abruptly. During normal operation, the steel inner container takes on the temperature of the liquefied gas and cools to ‐165°C. In order to guarantee sufficient ductility at this temperature, the inner container must be made from 9% nickel steel or stainless steel. Thermal insulation about 1 m thick is placed between the steel inner and concrete outer containers.

Between the underside of the steel inner tank and the base slab of the concrete outer tank, the thermal insulation consists of loadbearing cellular glass (often called foam glass). The annular space between the inner and outer containers is filled with perlite, and a layer of elastic material (resilient blanket) is installed to compensate for the horizontal thermal deformation of the inner container. The insulation on the aluminium roof of the inner container is made from glass fibre or perlite. What at first sight seem to be very generous dimensions are necessary in order to keep the boil‐off rate below 0.05% by vol. per day. Should the inner container fail, the inside face of the concrete outer container cools to ‐165°C, and that calls for the use of special reinforcement that can resist such low temperatures. The dynamic design for the seismic load case must take into account the action of the sloshing of the liquid and the interaction with the concrete outer container. The tank must be designed to withstand a so‐called operating basis earthquake (OBE), i.e. is not damaged and remains operable, and also for a so‐called safe shutdown earthquake (SSE).

Reference

1. 1 Flüchtige Zukunft. Wirtschaftswoche, No. 32, 2012, pp. 58–65.

2
History of Natural Gas Liquefaction

History shows us how the present circumstances have evolved; every new development builds on previous situations. The demand for gas has developed with the demand for energy in general. Technical progress led to the development of the liquefaction of gases, and after this process had been realised for various gases, so it became possible to liquefy natural gas, too. That was followed by the development of storage and transport methods for the liquefied natural gas (LNG), which in turn evolved into a global LNG market. The history of LNG outlined in sections 2.1 to 2.4 below is essentially based on the book by Matthias Heymann: Engineers, markets and visions – The turbulent history of natural‐gas liquefaction [1].

2.1 Industrialisation and Energy Demand

The process of the industrialisation of the production of energy, iron and steel, which began in England and reached the rest of Europe in the...

Table of contents

• Cover
• Table of Contents
• Editorial
• About the Author
• 1 Introduction
• 2 History of Natural Gas Liquefaction
• 3 Regulations and their Scope of Applicability
• 4 Definitions of the Different Tank Types
• 5 Performance Requirements and Design
• 6 Tank Analysis
• 7 Dynamic Analysis
• 8 Construction
• 9 Summary
• Index
• End User License Agreement