Despite the production and pricing challenges seen in 2020, liquefied petroleum gas (LPG) exports continue to remain strong in 2021. Propane exports are still topping 1 billion barrels (BBL) per day. Additionally, a rise in ethane crackers in China is leading to an increase in demand for exported ethane.
For grassroots and revamped export terminals, thoughtful optimization is key to minimizing installed capital. Optimization maximizes terminal and dock utilization, while still reducing operation costs and overcoming plot constraints. Once forecasts are made, pipeline capacity from a fractionation facility to the terminal will need to be built or expanded. Many other logistical factors need to be considered to provide plants with the ability to continue operations, while producing enough product to match demand.
Considerations to Efficiently Meet Demand
Managing both total installed cost (TIC) and operational efficiency is a difficult balance to maintain. A major consideration in planning for these drivers is the decision to install a tank or use a direct load system. While a significant investment upfront, tanks can help plants manage inventory and uncertainties in ship scheduling. Product supply into the tank is steady, with the tank level effectively managing load swings. This allows use of a smaller supply pipeline diameter and smaller refrigeration equipment installed at the plant. Having a tank at the terminal at least the size of the ship load provides the ultimate flexibility; however, there are other factors for operators to consider.
Operators will also have to make the decision between using a double-wall or single-wall tank. With external containment, single-wall tanks are appropriate for LPG products such as propane or butane. A disadvantage to using single-wall tanks is that the containment will take considerable plot space. Although an increase in capital investment, double-wall tanks can be designed for full containment, greatly reducing the plot space required. Ethane tanks are typically double-walled for insulation purposes. Considered a more hazardous material, ammonia typically requires double-walled tanks for containment to meet appropriate permitting regulations.
Double-walled tanks do not allow side connections, so loading pumps must be submersible, which in turn carries particular design and maintenance considerations. Any export terminal tank can require significant maintenance, which can be both time-intensive and costly. For a tank that is in the range of 300,000 to 900,000 BBL or more, the requirement to drain, hydrocarbon-free, and then perform inspection at five- to 10-year intervals is daunting. The tank may require particular attention with potentially costly features that must be incorporated during the tank design phase to avoid even more expensive inspections and downtime long after the capital project is completed.
Additionally, plant operators have the option to use a direct load concept to batch material from a fractionator or storage cavern to load a ship upon arrival at the dock. This eliminates the need for a tank and greatly simplifies the plant design. However, for the same average production rate this requires significantly greater pipeline capacity to account for idle time between loading ships. Larger diameter pipelines and larger, higher horsepower (HP) refrigeration equipment will then be used. The ultimate decision on whether to employ a tank is therefore dependent on several considerations and can vary from project to project.
Plant operators will need to consider potential water sources near the plant, as well as the availability of space for other equipment needed for the refrigeration systems. The presence of nearby water sources affects the refrigeration condensing options. Nearby water will allow use of cooling water or wet surface air coolers, which are the most efficient condensing media. Plot considerations, or even owner preference, may then dictate selection of one over the other. Without enough water, fin-fans will need to be used, which can ultimately result in higher HP compression and increased energy costs.
A determination must be made about which type of refrigeration system to use: open loop or closed loop. An open-loop refrigeration system utilizes the export product itself as the cooling medium and is especially useful for products such as ammonia, propane and ethane. Closed-loop refrigeration systems might be preferred for cascaded systems, if there are additional light ends, or contaminants that might potentially end up at the terminal. For high energy use refrigeration systems, such as for ethane, mixed refrigerant systems have also been successfully employed.
Implementing Solutions Safely
A combination of any of these solutions can be built and installed as open-art designs or a combination of packaged systems and open art. Refrigeration HP size, logistical issues and site accessibility may dictate solutions. A phased approach with pre-investment can also be used to balance schedule and cost considerations. Owners will need to consider overall electricity costs of new equipment installed, as well as the life cycle of parts used to determine the longevity of the solution implemented.
Regardless of the type of product transported — ethane, propane, butane or ammonia — safety must be addressed during design, construction and operation. For ammonia, this is often the key consideration. Valued practices that limit safety hazards and reduce risk include designing to proper specifications and standards; minimizing heat and ignition sources; adhering to industry spacing guidelines; conducting formal risk reviews and process hazards analysis; and developing constructability and field safety plans.
Plot Plan
For any refrigerated product export terminal, plot plan development is critical during design. As the refrigeration equipment and piping is all very large, a non-optimized plot plan can add significant cost to a project. Generally, equipment should be as compact as possible to minimize piping, cabling, cable tray, and conduit linear footages, and associated steel and foundations. Yet, equipment still needs to be spread out enough to facilitate operability, constructability and maintenance needs. The relative location of process equipment, tanks, docks, and associated flares or thermal oxidizers must be considered.
In addition to general industry and company-specific spacing guidelines and project-specific analysis for operability and maintenance, refrigeration terminals should be evaluated using consequence-based modeling for toxic releases, fire, radiation and potential blast contours that could affect in-plant and off-site personnel and structures. These studies form an integral part of plot plan development.
Taking the Next Step
Optimization is important, especially when loading 30,000 BBL per hour. At such high load rates, the line size can easily be 24 to 30 inches and be nearly a mile long. Refrigeration HP can typically fall in the range of 20,000 to 40,000 or more. The phrase “time is money” rings true in terminal logistics and it is often worth the extra engineering upfront to optimize processes to reduce a plant’s schedule and long-term costs. Solutions can be proposed and implemented in a variety of stages, but for the most efficient process, an integrated engineering, procurement and construction team can take a project from start to finish — managing scope, vendors and budgets for seamless, successful results.
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