Choosing The Best Containment
Choosing The Best Containment
In this reprint from the March LNG Industry issue, Bob Watson reviews flat-bottom tank containment types and highlights two single containment tanks for companies in the final stages of construction and commissioning. Read more below or download the PDF here.
You will get efficient and thoughtful service from CIMC ENRIC.
Bob Watson, Matrix PDM Engineering, USA, reviews flat-bottom tank containment types and highlights two single containment tanks for companies in the final stages of construction and commissioning.
Overview of Containment Solutions
North America is rich in natural gas due to advancements in extraction technology utilized in gas-producing shale formations across the United States. Predictions suggest that reserves could last for centuries. Given its cost-effectiveness and stability, natural gas is seen as a more affordable alternative to other fuels for the foreseeable future.
The affordability and dependability of LNG, along with its ability to drastically cut emissions, have led to its popularity across a variety of sectors, including marine bunkering, energy production, and transportation fuel. The demand for localized LNG solutions is on the rise, prompting the establishment of smaller LNG facilities rapidly.
In the realm of small to medium LNG facilities, different methodologies exist for storing natural gas post-liquefaction and prior to its intended delivery. Depending on the storage capacity required, solutions may range from several high-pressure tanks interconnected through piping to large-scale applications which often utilize a single low-pressure flat-bottom tank. This tank design is generally the most budget-friendly option, featuring an integrated insulation system that can be configured as single, double, or full containment to meet site-specific spill containment regulations.
Types of Storage Tanks
A single containment system encompasses an inner primary liquid container safeguarded by an outer insulation and vapor container. This structure ensures that only the inner container is responsible for holding liquid securely. The outer container, designed to withstand the vapor pressure from the inner tank, covers the insulation but does not contain any liquid in case of an inner tank failure. Such systems require spill impoundment dikes to be situated far from neighboring landowners, existing infrastructures, and other tanks.
The double containment tank comprises a primary inner tank that is both vapor and liquid-tight, encased within a secondary liquid-tight tank. Meanwhile, full containment tanks offer both liquid and vapor tightness in their primary and secondary tanks, thus ensuring independent containment of the stored product, while also managing vapor release should a leak occur from the primary container.
Capacity Ranges of Storage Tanks
In the United States, field-erected flat-bottom LNG tanks can vary significantly in size, with some accommodating up to 52.8 million gallons. Economically, single containment configurations typically function well for capacities down to roughly 1 million gallons.
Foundation Considerations
The type of foundation selected depends on several factors, including soil properties, seismic activity, and the chosen containment type. Favorable soil conditions may allow for options like ring walls or slabs on grade, often complemented by heating systems designed to prevent issues from freeze-thaw cycles. In locations with less stable soil, elevated tank foundations utilizing piles are recommended. Ultimately, the choice of foundation is influenced by both installation expenses and long-term operation and maintenance costs.
Criteria for Selection
For sites that have sufficient space for spill impoundments and can ensure adequate distances from adjacent properties, the single containment tank is typically the most cost-effective choice. However, constrained sites with limited buffer zones may necessitate double or full containment systems. Therefore, thorough calculations concerning vapor and thermal dispersion effects must be conducted early in the design phase to determine the most economically viable solution.
Maxville LNG Case Study
Location
The LNG tank for Eagle LNG is situated in Maxville, Florida, near the Jacksonville harbor.
Function
This facility will be instrumental in the liquefaction and storage of LNG for marine bunkering. The LNG will be loaded on-site and transported via trucks to ships.
Capacity
The tank will operate at a working capacity of 1 million gallons.
Configuration
The tank setup involves an outer cylinder at ambient temperature, while the inner cylinder holds LNG at -270°F. An insulation system of expanded perlite aids in minimizing boil-off. The outer cylinder features a domed roof designed for an internal vapor pressure of 2.5 psig.
JAX LNG LLC Overview
Location
The LNG tank for JAX LNG LLC is located at Dames Point on the Saint Johns River, also in the Jacksonville area.
Function
This facility will cater to ship bunkering, trucking, and small-scale power production through ISO containers.
Capacity
The tank boasts a larger capacity of 2 million gallons.
Configuration
This tank has a similar design to the Maxville facility, although it features larger diameters and heights.
Conclusion
Although full containment LNG tanks are prevalent internationally and in U.S. locations with restricted space, single containment solutions like the ones discussed provide a cost-effective and timely option. These storage systems fit well within the small to medium LNG market, especially for marine and remote energy applications. Facilities like Maxville LNG and JAX LNG exemplify reliable performance based on well-understood construction materials that have stood the test of time.