Strategic Design Considerations for LNG Terminals
Anand Narayanaswami,
Director, Business Development (Oil & Gas),
Black & Veatch India
Shawn D. Hoffart,
Vice President, LNG Technology,
Black & Veatch India
Dale Williams,
Vice President, Project Director,
Black & Veatch India

The Indian gas market is projected to be one of the fastest growing in the world during the next two decades. To help facilitate this the Indian government aims to significantly increase liquefied natural gas(LNG) import capacity by 2022. This article gives an overview of key considerations during the development and design phases of an LNG import terminal project .

Many subtle factors enter into liquefied natural gas(LNG) import terminal project decisions.Black& Veatch has been involved in the development and design of more than 25 LNG import terminals. The company has performed work ranging from desktop studies, to design and permitting, to full engineering, procurement and construction (EPC) responsibility for terminals in India, the Americas, Europe and Africa.

To design a safe, efficient and cost-effective terminal, a number of factors require careful attention:
  • Terminal siting and environmental factors.
  • Storage tank size and requirements.
  • Marine considerations.
  • Vaporization technology selection.
  • Opportunities for integration with adjacent industrial facilities.
It is important to note that these factors are not entirely independent of one another. For example, both LNG storage capacity and marine design are influenced by ship size, coastal and shipping constraints and terminal throughput.

Additionally, LNG import terminals can be land-based or floating.In some cases, the floating LNG application was selected to reduce the overall project schedule time to startup, while in other situations this application was used to mitigate siting constraints.

In July 2017 Swan LNG Private Limited awarded Black & Veatch the EPC contract to deliver India's first floating storage and regasification unit (FSRU), for the 5 million metric tonnes per annum (MMTPA) plant at Jafrabad in Gujarat. The new FSRU will be moored to a fixed jetty.

Although marine and storage requirements need to be considered in the selection of the terminal site, perhaps more important are the potential safety and environmental aspects of a particular site. Many jurisdictions have quite detailed requirements for siting an LNG facility. These requirements can include regulations covering everything from fish habitat, air emissions and surrounding properties to the potential impact of anincident.

One of the most important criterionto consider for siting is how the plant will get the necessary seawater into and out of the facility. The required frequency and size of LNG carriers can also heavily influence site selection . Environmental impacts arising from shipping and the type of LNG vaporization often determine the viability of a prospective site and the designs of the facility.

Although originally developed for use in the United States, many jurisdictions around the world use National Fire Protection Association (NFPA) 59A, Standard for the Production, Storage, and Handling of Liquefied Natural Gas (LNG), as a reference when establishing LNG terminals. In addition to these widely recognized standards, numerous local codes are typically followed for the design and operation of LNG terminals.

Factors such as the impact on the local community and adjacent industrial areas often dictate the suitability of a potential terminal site. Analyses of potential vapor dispersion and thermal radiation impacts have become much more detailed than just a few years ago. Numerical techniques such as computational fluid dynamics (CFD) modeling and the use of approved calculation protocols (along with risk assessment studies) are part of modern terminal siting considerations.

Because storage requirements are often the largest single part of the terminal capital investment, they are often the focus of potential cost savings. However, storage cost is largely driven by the size of the LNG carriers that will discharge cargos at the terminal. In addition, factors such as weather delays and tide changes must be considered when determining the amount of storage required between ship arrivals. Although larger tanks have been constructed, a typical industry tank size is 150,000 cubic meters (m3) to 180,000 m3. When one considers that carriers of over 260,000 m3 are in the fleet, it is easy to see that multiple tanks are often required for a terminal.

In addition to ship size, another important design parameter is how often ships will arrive and the expected range of LNG send-out rates.Because weather plays an important part in the ability of a ship to dock and load /unload LNG, a clear understanding and study of expected weather and marine conditions is a must. The general practice in the industry is that before an LNG carrier is connected at the berth and begins discharging its cargo, the terminal must have sufficient capacity available to store the entire cargo.

Another factor affecting storage cost is the type of tank design. Generally , large LNG tanks are constructed according to one of three design types: single, double or full containment. The choice of tank design is not only based on tank erection cost but also on safety and location. Generally, single containment tanks have a single metal wall capable of storing cryogenic LNG and a secondary containment provided by an earthen berm. Full containment tanks are constructed with a metal LNG storage container surrounded by a full concrete structure that provides the secondary containment.

Double containment tanks substitute a concrete outer structure for the earthen berm for secondary liquid containment, but do not provide secondary containment for evolved LNG vapor. Few double containment tanks are being constructed because they have no significant advantage over other designs and have higher relative costs. Because of the bermed containment area, single containment tanks require more plot area than full containment tanks. However, full containment tanks have higher costs and longer erection schedules than single containment tanks, which must be considered in the overall designs and economics of the facility.

Terminal designers must consider marine factors such as expected ship size (length, draft, etc.), channel traffic, dredging required (both initial and maintenance) and port restrictions. In addition, parameters such as bathymetry, space for ship maneuvering, tug operation,water depth, tide variations and wave action are key. It is critical, early in the design process, thatthese parameters be researched and the project approach and basis be documented. It is also important that a dialog be established with the local port authority and pilots association.

Once ship size, berthing requirements and mooring requirements are known, the mooring structure, loading arms, piping and equipment must be considered . In addition, the safety protocols that will be observed during LNG transfers must be documented as part of the design basis. Employing a marine contractor with both LNG and local experience is vital.

Many different vaporization technologies are in usein LNG import terminals around the globe. These can be categorized into a few classificationsdepending on the medium used to warm the LNG:
  • Open rack vaporizers--water falling over LNG tubes.
  • Submerged combustion vaporizers--LNG heated in a liquid bath, typically fueled by natural gas.
  • Heat exchange vaporizers--via shell and tube exchange and an external fluid heating loop.
At one time, most LNG facilities around the world used open rack vaporization. This style of vaporizer uses seawater distributed over heated finned tubes to vaporize the LNG. Operating expenses for open rack vaporizers include electricity for pumping water and any needed filtering or treating of the inlet seawater. This type of vaporizer has become less common in new designs because of considerations surrounding the use of large volumes of seawater and potential environmental impacts to sea life from cooling the water used in vaporization. In addition, if the distance to the open sea is considerable, expensive seawater pumping and piping systems can be required. And, if the mineral content of the water in the terminal location is too high, corrosion can be an issue. Seawater to freshwater exchange can be utilized, but this process adds cost. There are still locations where the use of open rack vaporizers is a good choice, but these facilities are less common than they once were.

Submerged combustion vaporizers burn fuel to generate the heat needed to vaporize the LNG. In locations where the use of seawater is restricted, these vaporizers are common. For example, many of the older LNG facilities in Europe and North America use this style of vaporizer. Although these vaporizers are efficient, they still consume fuel and have air emissions. In addition, the combustion air blowers that are part of these systems consume electrical power. The operating cost for a modest-sized LNG import terminal using submerged combustion vaporizers can run into the tens of millions of U.S. dollars per year. Because they are relatively compact and can be put into operation quickly, submerged combustion vaporizers are at least a part of the vaporization system in many new LNG import terminals.

Heat exchange vaporizers are used in an attempt to overcome the limitations of other vaporizer types. Generally, these units are large heat exchangers that conduct energy from either warm water or warm air to the LNG to be vaporized. Because of the potential for freezing, the design of these exchangers is specialized. For example, in the case of a water heated shell and tube exchanger, the water side of the exchanger could freeze and burst if a tube ruptures. Often, the water has added glycol to minimize the impact of the very cold LNG, but even that can freeze. In warmer climates, the water used to vaporize the LNG is heated using the ambient air, but in more extreme climates, some other heat source is often required. Air heated units may have ice buildup from the moisture in the air. Often, multiple parallel units must be installed to allow some exchangers to thaw while others are in service. The main advantage of heat exchange vaporizers is that the source of heat is essentially “free” and that little energy is needed for operation.However, these vaporizers are not without their environmental impacts. The use of toxic glycols and discharge of condensed water can affect a design.

As can be seen from the discussion of LNG vaporizers, some heat sourceis often needed to vaporize the LNG. Therefore, LNG import terminals are often candidates for integration with adjoining facilities. Black & Veatch has developed designs for integration with power plants, chemical plants and other industrial partners. For example, in a power plant, a large portion of the energy used to generate steam is ultimately rejected in a steam condenser. The power produced is a function of the outlet pressure and temperature of the steam turbine condenser. This condenser is limited by the temperature of the cooling system. By exchanging heat with an LNG import terminal, a much cooler condenser outlet can be achieved and more power can be produced for a given amount of fuel. Because many LNG import terminals are co-located with power plants, this type of integration can be a significant boost to project economics, both in reduced energy consumed by the LNG terminal and increased energy produced by the power plant. In fact, LNG vaporization “cold” can be used in a number of ways, including cooling for chemical plants, mineral processing and refrigerated storage.

Black & Veatch References
  • In 2015 IOCL awarded a Black & Veatch led consortium the contract for a new LNG receiving terminal at Ennore. Black & Veatch is leading the EPC and commissioning work on a turnkey basis. The terminal will be the first-of-its-kind on India’s east coast, with a send-out capacity of five million tonnes.
  • The Peñuelas facility for EcoElectrica in Puerto Rico. Black & Veatch was one of many contractors involved in the design and construction of this facility. The power plant has the ability to generate electricity using liquefied petroleum gas (LPG), LNG and other fuels. It is heat integrated with the LNG import facility and very flexible. It is one of the very few facilities with a U.S. permit to use double containment LNG storage.
  • The successful construction of the Energia Costa Azul terminalin Baja California, Mexico. This facility includes two 160,000 m³ full containment LNG storage tanks and seawater open rack vaporizers and is completely self-sufficient in terms of power generation and freshwater production.
  • Complete design packages for U.S. Federal Energy Regulatory Commission (FERC) facilities:detailed design packages for permitting for over 10 North American LNG import terminals for submissions to FERC, including Cheniere Sabine Pass terminal, the Sempra Cameron facility at Hackberry, Louisiana,and theOccidental Chemical Corporation (OxyChem) LNG terminal in Ingleside, Texas. For the OxyChem LNG terminal, Black & Veatch integrated the LNG terminal into the existing facility for the supply of all heat for the plant vaporization.