Rail-supplied midstream propane terminal maximized for safety

The role of rail in propane midstream operations is both substantial and crucial. Rail is key to getting propane to where it is needed, especially when customers are not close to a propane pipeline. Rail keeps costs stable because rail-supplied propane terminals preclude the use of trucks to transport propane great distances to rural areas, where the fuel is used for home heating and agriculture, among other uses.

In a rail-supplied propane terminal, product that is primarily sourced from shale plays like Marcellus, Permian, Eagle Ford and others is offloaded from railcars using compressors, stored and then loaded via pumps into trucks that transport the product to bulk plants, which in turn load local transport vehicles like bobtails. Safety, of course, is the most important consideration in building a rail-supplied propane terminal, which means it’s important to work with a terminal supplier that is an expert in national and local codes and regulations.

Overall design and storage need to be addressed first when building a rail-based midstream propane terminal operation. Distances and aggregate storage capacities (i.e., total storage available) can place limits on storage and rail capabilities. It is also critical to assess necessary storage required to meet regional peak demand. The midstream supplier assesses past purchases, logistics associated with moving fuel from nearby refineries, and geographic needs based on historical data and supply and demand.

The National Fire Protection Association (NFPA) 58 code regulates container spacing. A maximum of six storage containers can be located in a group, regardless of size, and requires 50 feet of separation between groupings.

Rail switches

The most critical part of building an advanced rail-supplied midstream propane terminal lies in efficiency of both rail switches and the unloading of propane tank railcars. Responsibility for the rail switch falls on either the midstream marketer/terminal owner or the railroad operator. When a rail terminal is built, many logistical motions come into play related to the movement or addition of track, the amount of railcar storage and the necessity of separate (on- or off-site) railcar storage locations.

The addition of rail siding is necessary to offload railcars from the main rail line. Average railcars range from approximately 55 to 70 feet in length with a turning radius of approximately 240 feet. Engineering software programs allow terminal builders to determine the amount of land and length of rail siding required to meet the switch demand. (See Figure 1.) The switch demand, therefore, determines the number of gallons the midstream supplier will be able to move out of the terminal in a 24-hour period.

Railcar unloading

The efficient unloading of tank railcars affects the entire terminal operation, determining the speed that gas is unloaded and subsequently, the number of tanker trucks that can be loaded in a given amount of time.

Amount of land space determines the installation of single- or double-sided rail towers. Double-sided rail towers are much more efficient, allowing unloading personnel to unload two cars without walking further down the railcar line. Double railcar siding requires more land space and the two rail lines must be separated by 21 feet, allowing the railcars to move with ease. If less land is available, single rail towers are placed along the siding, requiring personnel to travel to each tower to connect railcars to the liquid transfer system.

Compressor size and unload pressures make a crucial difference in offload speed, as does the process used to remove the propane. Top connections are used to remove liquid propane, due to the nature of the fuel. Vapor removal and recovery is a significant detail that must be considered as well, in order to avoid losing potentially thousands of gallons of fuel over time.

Truck transport loading

Also important in rail terminal efficiency is the truck transport loading process. Land space determines the access road and driveway available to maneuver and stage transport trucks. (See Figure 2.) To meet high-performance requirements, terminal operations load trucks at a rate of 550 to 600 gallons per minute, allowing a transport truck to be filled in less than 15 minutes.

At the truck loading rack, truck metering skids are calibrated to assure accurate custody transfer. Automation is also key. Bill-of-lading management, the programmable logic controller (PLC), tank-level system and terminal management software all come together to benefit both the marketer and the customer.

Permitting, safety and code compliance

Permitting, code compliance and safety are key measures that must be considered in a railcar propane terminal build. Terminals must meet expectations and regulations set by NFPA 58, the local authority having jurisdiction (AHJ), and various local and regional entities, including the fire department, city and zoning departments.

The following aspects help ensure a safe and compliant operation:

OSHA rail guards: Permanent handrails must be installed alongside the rail towers and stairs. Removable safety rails are designed in a hoop-like shape to move up and down with the catwalk, providing the OSHA-required 42-inch fall protection.

Shutdown devices: Operator devices must be installed per NFPA 58 in convenient locations at each rail tower and enable operators to open and close the liquid and vapor connections to each rail car. In addition, one emergency shutdown device is installed 20 to 100 feet from the point of transfer, which can be used to close connections to the entire rail rack.

Hydrocarbon leak detection: Detection mechanisms should be installed around points of transfer and pumping systems (vapor compressors and liquid pumps) to detect propane leaks. When detected, the leak is reported to the PLC, enabling the emergency shutdown device and closing all valves to contain the leak.

Fire hydrant/monitor nozzles: A fixed nozzle or hydrant must be installed at ground level, around the tanks, to provide tank cooling in the event of fire. Nozzle installation reduces tank separation requirements set by NFPA 58, allowing additional tanks to be installed in closer proximity.

Backflow check valves: These are safety valves that allow propane to flow into the piping system, but not back out. The valves are critical in case of hose separation or piping damage.

Positive shutoff valves: Valves are installed throughout the terminal, allowing for convenient isolation of various portions of the system to allow for service, without having to evacuate the entire piping system. They also provide a redundant positive shutoff in conjunction with emergency shutoff valves.

Breakaway devices: These are installed at unloading stanchions to separate at a predictable point in the event of an accidental transport truck pull-away, preventing damage to the loading or unloading equipment and loss of product from the system.

Hydrostatic relief valves: These are installed in the piping system at any point where propane has the potential to be isolated between two positive shutoff valves. This protects the piping system from excessive pressure due to liquid expansion from an ambient temperature increase.

Fire safety analysis

In addition to the measures previously noted, the terminal supplier develops a Fire Safety Analysis (FSA), required by NFPA 58. The main goal of NFPA 58 is to prevent any unintentional release of propane into the atmosphere. The FSA must be completed prior to terminal operation but is often required much earlier, during the permitting process. The FSA determines the safety of the terminal itself based on safety features required by NFPA and additional measures put into place to prevent propane release accidents.

The FSA ensures the terminal will be built to and likely exceed customer requirements, along with meeting appropriate federal, state and local codes and standards, which require:

• All container openings are properly equipped to meet the requirements that incorporate mechanical, thermal and remote means of operation, including activation and emergency shutdown as required by code.
• Containers have the required liquid level devices, such as a float gauge, rotary gauge, slip tube gauge or a combination to prevent overfilling.
• The presence of vapor pressure and temperature gauges.
• Properly sized tank relief valves to protect the tank from overpressure.

Terminal commissioning

The terminal supplier will begin the commissioning process about two weeks before the project is completed, which includes testing the installation of every part of the system, per the design plan.

This rigorous evaluation process includes:

• Performance and functionality testing of the compressors, pumps and motors
• Pressure testing the piping system
• Testing of the PLCs, the core of the terminal’s system
• Testing of additional safety systems, including the hydrocarbon detectors, liquid level systems and emergency safety devices
• Meter calibration.

The terminal contractor then coordinates all inspection approvals to ensure compliance with each issued permit, including walk-throughs by the building, electrical and mechanical inspectors.

Following full testing and inspection approvals, the terminal’s onsite operations personnel is trained. Local AHJ personnel is also trained on the terminal’s features and safety systems. The start-up and first product-transfer is often monitored by the terminal contractor as well as the operations team.

Final words

Railcar-supplied terminals are integral part of the midstream propane landscape, for the simple fact that they ensure propane gets to where it is needed. Terminals allow transport trucks to drive shorter distances for fuel deliveries to local propane providers. This makes the delivery process more cost-effective for those local and regional propane providers.

Developing a rail-supplied midstream propane terminal is a complex process that requires a high level of design and engineering acumen to ensure a terminal is a safe place that meets requirements of national and local authorities as well as the AHJ. In other words, experience counts, and working with a provider that specializes in the nuance of terminal building can significantly increase savings in both capital and time.

Original content can be found at Oil and Gas Engineering.

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