LNG STORAGE SYSTEMS
Natural gas provides clean, reliable, and cost-effective energy to people all around the world. Natural gas is a cryogen, which implies that at extremely low temperatures it is a liquid. Natural gas may be transported as a liquid from locations with abundant supply to areas with high demand in an efficient and safe manner.
LNG storage tank systems keep the gas in a liquid state for storage or transmission. These tank systems are meticulously designed and well-built. In LNG storage systems, auto-refrigeration is employed to maintain constant pressure and temperature in the tank. This method is, in reality, quite old. West Virginia built the first natural gas liquefaction plant in 1917. Many advancements have been made since then to increase natural gas storage, but the systems continue to function in the same way. Here’s what we need to know before designing and constructing an LNG storage system.
API Standards and Codes
In the 1960s, the American Petroleum Institute (API) established rules for the design, construction, and material selection of storage tank systems. These standards contribute to the overall safety and quality of the industry. API codes are also continually updated to reflect industry innovations and best practices.
Types of LNG Storage Tanks
Liquefied gas storage tanks are classed based on their kind and size using a range of standards and guidelines that differ in terms of when they were published and the quantity of information they give. The wording used by the two German standards, DIN EN 1473 and DIN EN 14620, is even diametrically opposite. This section will utilize either the vocabulary from the British equivalent, BS EN 1473, or the nomenclature from API 625. API 625’s British counterpart is BS EN 1473. From a practical sense, the phrase “containment tank system,” as used in API 625, seems to be the most appropriate, since the multiple, yet coordinated, components interact to create a cohesive system. Containment tank systems are categorized as single, double, or complete according to the standards EEMUA, BS 7777, EN 1473, EN 14620-1, NFPA 59A, and API 625. The membrane tank is an extra tank type that is detailed in further detail in the European standards EN 1473 and EN 14620.
Until the 1970s, the only kind of tank built was the single-wall tank. The hazard scenarios that resulted from abnormal actions such as inner tank failure, fire, blast pressure wave, and impact inspired the subsequent further development of the various types of tanks or tank systems, as well as the associated requirements placed on the materials and construction details. Because of the threats that a tank failure brings to the surrounding areas, it is essential to choose the proper kind of tank system.
The repercussions of a failure of the inner container on the tank as a whole and its surroundings for three commonly used tank systems will be shown utilizing the failure of the inner container. The evolution of these three tank systems will also be studied.
System with a single containment tank
A container that is both liquid and vapor tight is referred to as a single containment tank system. It may be built as a single-wall, liquid- and vapor-tight structure, or as a combination of inner and outside containers. In the latter case, the inner container is open at the top and liquid tight. When an outside container is used, it is largely to enclose the insulation and protect it from moisture, as well as to accommodate the gas vapor overpressure. It is not designed or intended to store LNG that has spilled from the tank. If there is just one containment tank, it must be surrounded by some form of safety barrier, usually an earth embankment, to prevent the liquid from escaping uncontrolled and causing damage.
The inside container of an EN 14620 container must be made of steel, but API 625 permits for the use of prestressed concrete in some situations. If you use an outside container, it is normally made of carbon steel to keep the elements out.
System with two separate containment tanks
Double containment tank systems are made up of a liquid- and vapor-tight primary container that satisfies the criteria for a single containment tank system but is contained within a secondary container that fits the criteria for a double containment tank system (Fig. 4.2). In the event of a leak, it is intended to be open at the top and capable of capturing any liquefied gas that escapes. On the other hand, it is not meant to obstruct gas escape. In order for the primary and secondary containers to operate effectively, no more than 6 m must be left between them. According to API 625, both steel and prestressed concrete are permissible materials for both containers.
System with a Complete Containment Tank
A complete containment tank system is made up of primary and secondary storage containers that work together to provide a comprehensive and integrated storage system. The primary container is a cylindrical steel tank with a single self-supporting and self-contained shell. Alternatively, it might be open at the top, rendering it incapable of holding any vapors, or it could be built with a dome roof, preventing vapor from escaping in such a case.
The secondary container must be a self-supporting tank made of steel or concrete with a dome roof in order to qualify. If the main container is open at the top, the secondary container must function as the primary vapor containment for the tank during normal operation. In the case of a leak from the primary container, the secondary container must be capable of storing the liquefied gas and remaining liquid-tight while also functioning as the primary vapor containment structure. It is permissible to vent in a regulated way using the pressure release mechanism. API 625 states that “product losses due to permeability of the concrete are permitted” when the outer container is made of concrete. According to API 625, both steel and prestressed concrete are permissible materials for both containers. The existence of vapor-tightness is required for normal operation. Figure 4.3 displays a number of various design options, one of which incorporates a prestressed concrete inner tank.
The standards EN 14620-3 (Annex B) and ACI 376 (Appendix A) specify and illustrate sliding, pinned, and fixed connections between a wall and a foundation slab. Sliding or pinned joints are employed in certain circumstances, however this is only possible in small tanks operating at less severe low temperatures and consequently with less overpressure. Due to the nature of the material, the monolithic wall/base slab connection is the only practical method for LNG tanks.
In order for the system to continue to work properly in the event of inner container failure, the conventional complete containment tank with a concrete outer container and solid monolithic connection between wall and base slab must have two constructional qualities. In such a circumstance, the wall experiences a temperature difference of roughly 100 K and temperature gradients of up to 200 degrees Celsius. With the tank sizes that are commonly employed, this temperature disparity results in a radial shortening of the tank wall of 4–5 cm, depending on the diameter. If no further safeguards are taken at the wall/base slab junction, a failure of the concrete cross-section will occur. One alternative is to build a transition zone at the base of the wall that is at least 5 meters high in order to reduce the contraction of the concrete wall to a level that is commensurate with the surrounding environment. In practice, this is done by including an insulating layer between the base slab and the wall, which comprises a secondary bottom made of nickel steel (9 percent nickel content). The secondary bottom is higher up the wall than the main bottom. Thermal corner protection refers to this section, which is protected with insulation and steel plates (TCP).
This feature protects the insulation while also aiding it in retaining its thermal function, reducing the influence of temperature on the cross-section of the concrete and smoothing the development of deformation. Despite the fact that experience has shown that the risk of a single containment tank failing (assuming it was built in accordance with regulations) is extremely low, such risks can be reduced even further by introducing even stricter requirements regarding material selection, design, construction, inspection, and testing. However, the implications of a tank collapse are so severe for particular hydrocarbon chemicals that an even more complex tank design is necessary to avoid them. The tank system should be chosen with the location, operating conditions, and environmental standards in mind, among other things.
https://www.gmsthailand.com/blog/what-is-lng-storage-systems/
What is LNG STORAGE SYSTEMS
Natural gas provides clean, reliable, and cost-effective energy to people all around the world. Natural gas is a cryogen, which implies that at extremely low temperatures it is a liquid. Natural gas may be transported as a liquid from locations with abundant supply to areas with high demand in an efficient and safe manner.
LNG storage tank systems keep the gas in a liquid state for storage or transmission. These tank systems are meticulously designed and well-built. In LNG storage systems, auto-refrigeration is employed to maintain constant pressure and temperature in the tank. This method is, in reality, quite old. West Virginia built the first natural gas liquefaction plant in 1917. Many advancements have been made since then to increase natural gas storage, but the systems continue to function in the same way. Here’s what we need to know before designing and constructing an LNG storage system.
API Standards and Codes
In the 1960s, the American Petroleum Institute (API) established rules for the design, construction, and material selection of storage tank systems. These standards contribute to the overall safety and quality of the industry. API codes are also continually updated to reflect industry innovations and best practices.
Types of LNG Storage Tanks
Liquefied gas storage tanks are classed based on their kind and size using a range of standards and guidelines that differ in terms of when they were published and the quantity of information they give. The wording used by the two German standards, DIN EN 1473 and DIN EN 14620, is even diametrically opposite. This section will utilize either the vocabulary from the British equivalent, BS EN 1473, or the nomenclature from API 625. API 625’s British counterpart is BS EN 1473. From a practical sense, the phrase “containment tank system,” as used in API 625, seems to be the most appropriate, since the multiple, yet coordinated, components interact to create a cohesive system. Containment tank systems are categorized as single, double, or complete according to the standards EEMUA, BS 7777, EN 1473, EN 14620-1, NFPA 59A, and API 625. The membrane tank is an extra tank type that is detailed in further detail in the European standards EN 1473 and EN 14620.
Until the 1970s, the only kind of tank built was the single-wall tank. The hazard scenarios that resulted from abnormal actions such as inner tank failure, fire, blast pressure wave, and impact inspired the subsequent further development of the various types of tanks or tank systems, as well as the associated requirements placed on the materials and construction details. Because of the threats that a tank failure brings to the surrounding areas, it is essential to choose the proper kind of tank system.
The repercussions of a failure of the inner container on the tank as a whole and its surroundings for three commonly used tank systems will be shown utilizing the failure of the inner container. The evolution of these three tank systems will also be studied.
System with a single containment tank
A container that is both liquid and vapor tight is referred to as a single containment tank system. It may be built as a single-wall, liquid- and vapor-tight structure, or as a combination of inner and outside containers. In the latter case, the inner container is open at the top and liquid tight. When an outside container is used, it is largely to enclose the insulation and protect it from moisture, as well as to accommodate the gas vapor overpressure. It is not designed or intended to store LNG that has spilled from the tank. If there is just one containment tank, it must be surrounded by some form of safety barrier, usually an earth embankment, to prevent the liquid from escaping uncontrolled and causing damage.
The inside container of an EN 14620 container must be made of steel, but API 625 permits for the use of prestressed concrete in some situations. If you use an outside container, it is normally made of carbon steel to keep the elements out.
System with two separate containment tanks
Double containment tank systems are made up of a liquid- and vapor-tight primary container that satisfies the criteria for a single containment tank system but is contained within a secondary container that fits the criteria for a double containment tank system (Fig. 4.2). In the event of a leak, it is intended to be open at the top and capable of capturing any liquefied gas that escapes. On the other hand, it is not meant to obstruct gas escape. In order for the primary and secondary containers to operate effectively, no more than 6 m must be left between them. According to API 625, both steel and prestressed concrete are permissible materials for both containers.
System with a Complete Containment Tank
A complete containment tank system is made up of primary and secondary storage containers that work together to provide a comprehensive and integrated storage system. The primary container is a cylindrical steel tank with a single self-supporting and self-contained shell. Alternatively, it might be open at the top, rendering it incapable of holding any vapors, or it could be built with a dome roof, preventing vapor from escaping in such a case.
The secondary container must be a self-supporting tank made of steel or concrete with a dome roof in order to qualify. If the main container is open at the top, the secondary container must function as the primary vapor containment for the tank during normal operation. In the case of a leak from the primary container, the secondary container must be capable of storing the liquefied gas and remaining liquid-tight while also functioning as the primary vapor containment structure. It is permissible to vent in a regulated way using the pressure release mechanism. API 625 states that “product losses due to permeability of the concrete are permitted” when the outer container is made of concrete. According to API 625, both steel and prestressed concrete are permissible materials for both containers. The existence of vapor-tightness is required for normal operation. Figure 4.3 displays a number of various design options, one of which incorporates a prestressed concrete inner tank.
The standards EN 14620-3 (Annex B) and ACI 376 (Appendix A) specify and illustrate sliding, pinned, and fixed connections between a wall and a foundation slab. Sliding or pinned joints are employed in certain circumstances, however this is only possible in small tanks operating at less severe low temperatures and consequently with less overpressure. Due to the nature of the material, the monolithic wall/base slab connection is the only practical method for LNG tanks.
In order for the system to continue to work properly in the event of inner container failure, the conventional complete containment tank with a concrete outer container and solid monolithic connection between wall and base slab must have two constructional qualities. In such a circumstance, the wall experiences a temperature difference of roughly 100 K and temperature gradients of up to 200 degrees Celsius. With the tank sizes that are commonly employed, this temperature disparity results in a radial shortening of the tank wall of 4–5 cm, depending on the diameter. If no further safeguards are taken at the wall/base slab junction, a failure of the concrete cross-section will occur. One alternative is to build a transition zone at the base of the wall that is at least 5 meters high in order to reduce the contraction of the concrete wall to a level that is commensurate with the surrounding environment. In practice, this is done by including an insulating layer between the base slab and the wall, which comprises a secondary bottom made of nickel steel (9 percent nickel content). The secondary bottom is higher up the wall than the main bottom. Thermal corner protection refers to this section, which is protected with insulation and steel plates (TCP).
This feature protects the insulation while also aiding it in retaining its thermal function, reducing the influence of temperature on the cross-section of the concrete and smoothing the development of deformation. Despite the fact that experience has shown that the risk of a single containment tank failing (assuming it was built in accordance with regulations) is extremely low, such risks can be reduced even further by introducing even stricter requirements regarding material selection, design, construction, inspection, and testing. However, the implications of a tank collapse are so severe for particular hydrocarbon chemicals that an even more complex tank design is necessary to avoid them. The tank system should be chosen with the location, operating conditions, and environmental standards in mind, among other things.
https://www.gmsthailand.com/blog/what-is-lng-storage-systems/