LPG Terminal Basics

LPG Terminal Basics

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LPG, short for liquefied petroleum gas, is a hydrocarbon compound primarily composed of carbon and hydrogen atoms. It is derived from natural gas processing and crude oil refining.

According to NFPA 58 Section 3.3.36, LPG encompasses materials with vapor pressures not exceeding those allowed for commercial propane. These materials predominantly consist of hydrocarbons such as propane, propylene, butane, and butylenes.

LPG serves myriad purposes, ranging from industrial and commercial uses to power generation, agricultural applications, and cooking. It is also a common fuel for heating and powering vehicles.

To store LPG, it must be conditioned to a liquid state and kept in pressure vessels. When released from these containers at ambient temperature, LPG transitions back to a gaseous state.

This guide focuses on the specific requirements and recommendations found in the NFPA 58 code (Liquefied Petroleum Gas Code).

1.1 LPG Terminal Basics: Manufacturing Process

LPG is sourced from two main processes: natural gas processing and crude oil refining.

Natural gas comprises mainly methane along with smaller percentages of hydrocarbons like propane and butane. These LPG components are extracted during gas processing.

In crude oil refining, LPG is produced as a byproduct through processes like catalytic cracking and crude distillation. The recovered gas is then liquefied to form LPG.

1.2 Categories of LPG Facilities

LPG storage facilities are typically categorized by storage volume rather than other criteria.

Bulk storage terminals house large quantities of LPG for distribution to smaller facilities.

Medium-sized distribution facilities supply LPG to retailers or final consumers and are more common, especially in Africa.

Mini LPG facilities cater directly to consumers and are often strategically located within cities or communities.

Establishing an LPG facility involves rigorous regulatory approval, including various levels of permitting.

2 LPG Terminal Basics: Transportation

The methods for transporting LPG depend on factors like volume, available infrastructure, and safety considerations.

• The volume of LPG to be transported
• Available transportation infrastructure
• Safety considerations

2.1 Road Transportation

Road transportation is mainly used for small to medium volumes of LPG. It is suitable for short and medium distances and can be achieved through several means.

Iso containers or vessels mounted on trailers are common for transporting LPG from bulk storage to medium storage facilities, especially in Africa.

Bobtail trucks are used for delivering LPG to retailers or significant consumers.

Small LPG cylinders are commonly transported on vans, ensuring safe and efficient delivery to consumers.

All safety measures must be meticulously followed during road transportation to prevent accidents.

2.2 Rail Transportation

Rail transport is ideal for large volumes of LPG over long distances, facilitating the transfer from reception facilities or bulk storage terminals to other storage locations.

2.3 Ship/Ocean Vessel Transportation

This method is preferred for transporting large volumes of LPG over long distances, particularly between countries. The liquefied gas is stored in special vessels on ships, which dock at jetties or seaports. Connecting pipelines transfer LPG from ship to storage facilities.

2.4 LPG Terminal Basics: Pipelines

LPG pipelines are predominantly used to transfer gas from jetties to bulk storage, process facilities, or reception stations. Some communities even have built-in networked pipelines supplying LPG directly to homes.

3 LPG Terminal Basics: Components of LPG Facilities

An LPG facility comprises multiple components that together form a functional unit for product reception and transfer.

3.1 LPG Storage Containers

These pressurized vessels are designed according to ASME Boiler and Pressure Vessel Codes, BS Standards, or other approved codes. They come in spherical or cylindrical shapes.

Understanding the advantages and disadvantages of each vessel type is crucial for selecting the appropriate storage solution. Some key points include:

• Spherical vessels can store larger volumes and occupy less space than cylindrical ones.
• Fabricating spherical vessels is more time-consuming and costly, usually requiring on-site assembly.
• Cylindrical vessels can be shop-fabricated and easily transported to the site.
• Spherical vessels have uniform stress distribution, requiring thinner shell plates.
• Spherical vessel piping is generally less expensive than cylindrical ones due to fewer discharge points.
• Cylindrical vessels are easier to maintain, empty, and relocate.

3.1.1 LPG Terminal Basics: Spherical Vessels

Horton Spheres, as they are technically called, are spherical vessels used for storing large volumes of LPG. They offer the advantage of uniform stress distribution, resulting in reduced shell plate thickness.

3.1.2 Cylindrical Vessels

Often referred to as "LPG bullets," cylindrical vessels can be installed horizontally or vertically, either above or below ground. They are typically used when smaller storage volumes are needed.

3.1.2.1 Underground Storage Vessels

These vessels offer additional safety and reduced spacing requirements. They must adhere to standards like NFPA and BS Standards, specifying minimum burial depths based on vehicular activity in the vicinity.

3.1.2.2 Mounded Vessels

Above-ground cylindrical vessels can be mounded with a concrete wall and backfilled with earth. This provides additional safety but necessitates specific design considerations for piping and instrumentation connections.

3.1.2.3 Above Ground Unmounded Vessels

These are suitable for smaller storage volumes and often rest on saddle supports. They are commonly used due to their simplicity and ease of installation. However, they require larger separation distances from buildings.

3.2 LPG Transfer Pumps

Pumps transfer LPG between various containers, including trucks, storage vessels, and dispensing stations. While efficient for liquid transfer, they cannot recover vapors.

Many reputable manufacturers like Corken, Blackmer, and Flowserve (Sterling SIHI) produce high-quality LPG pumps.

3.3 LPG Terminal Basics: LPG Transfer Compressors

Compressors efficiently transfer LPG by utilizing vapor pressure. They are commonly manufactured by companies like Corken and are ideal for large-scale LPG transfers.

3.4 LPG Loading and Unloading Bay

This designated area in an LPG facility is where the transfer takes place. It may include weather shelters or canopies, complying with NFPA requirements.

3.5 LPG Terminal Basics: Loading and Unloading Arm

These specialized arms feature swivel joints for easy movement and quick-connect couplings for safer and more efficient transfers. NFPA guidelines require an isolation valve at the connection point.

3.6 Loading/Unloading Hose

Hoses serve as an alternative to loading arms but are less efficient and harder to handle. They also have an expiration date, necessitating periodic replacements.

3.7 LPG Terminal Basics: Measurement

Proper measurement is essential for accuracy in LPG transfer. Two primary measurement methods are employed: volumetric measurement using flowmeters and weight measurement using weighbridges.

3.7.1 Volumetric Measurement (Flowmeter)

Flowmeters measure the volume of LPG transferred. They are typically installed at loading bays, and manufacturers like Smith produce high-quality meters.

3.7.2 LPG Terminal Basics: Weight Measurement (Weighbridge)

Weighbridges measure the weight of LPG transported by trucks. By comparing the truck's weight before and after unloading, the exact amount of LPG delivered can be determined.

3.8 LPG Transfer Sales Unit

This unit sells LPG in small quantities to retailers or final consumers. It may include automated filling carousels or offline sales scales.

3.9 LPG Terminal Basics: Pump Suction Line

This line connects to the tank's bottom nozzle, equipped with a strainer and isolation valve. Interconnections with compressor liquid transfer lines may be present.

3.10 Compressor Liquid Transfer Line

Used when a compressor is employed for liquid transfer, this line connects to the tank's bottom. Vapors generated by the compressor push the liquid through the line.

3.11 LPG Terminal Basics: Vessel Fill Line

Storage vessels are filled using this line, which connects to a pump discharge or compressor liquid transfer line.

3.12 Liquid Bypass Line

This line operates when excess LPG needs to be diverted back to the storage tank. It is connected to the discharge of the flow control valve.

3.13 LPG Terminal Basics: Vapour Lines

Compressor-connected vapor lines enable LPG transfer. Two such lines are involved: a suction line and a discharge line, controlled by a 4-way valve on the compressor.

3.14 Valves

A variety of valves play crucial roles in an LPG facility, including:

3.14.1 Ball Valves

Used for isolation, these quarter-turn valves provide tight shutoff and are commonly found in suction, discharge lines, and manifolds.

3.14.2 Check Valves

Installed on pump discharge lines, check valves prevent backflow, maintaining unidirectional flow.

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3.14.3 Internal Valves/Excess Flow Valves

These valves, as required by NFPA 58, provide shutoff and regulate excess flow in storage vessels.

3.14.4 Pressure Relief Valves

Essential for safety, these valves release pressure buildup in storage vessels or piping networks when it exceeds set points.

3.14.5 Flow Control Valve

Installed on pump discharge lines, these pre-set valves control flow by diverting excess LPG through a bypass line back to the storage vessel.

3.15 Pressure Indicators

Installed on storage vessels and various pipelines, pressure indicators monitor system pressure. They can trigger automated responses like shutting down pumps or opening relief valves when pressure exceeds safe limits.

3.16 Gas Detectors

Gas detectors are critical in sensing even tiny LPG leaks. Installed strategically, they activate emergency shutdowns and firefighting systems when leaks are detected.

3.17 Temperature Sensors

Temperature sensors monitor areas like storage and transfer points. When they detect high temperatures, they can trigger sprinklers or shut down the facility for safety.

3.18 LPG Terminal Basics:Temperature Indicators

Mostly installed on storage vessels and transfer points, these indicators consistently monitor temperatures and activate sprinklers when temperatures reach unsafe levels.

3.19 Sight Flow Indicator

Primarily installed upstream of pump suctions, sight flow indicators enhance operational efficiency by allowing visual inspection of flow and adjusting pump speeds accordingly.

3.20 LPG Terminal Basics: Breakaway Coupling

Installed on LPG hoses, breakaway couplings ensure safety during transport. They automatically activate in case of excess tensile force, sealing and separating to prevent accidents.

3.21 Instrument Air Compressor

This compressor supplies pressurized air for instrumentation control, crucial for opening and closing actuated valves in the facility.

3.22 Emergency Shutdown Push Buttons

Installed at strategic locations, these buttons can manually initiate a complete facility shutdown during emergencies.

3.23 Instrumentation Control Room

The control room is the facility's brain, monitoring all field instrument readings and allowing remote operation of pumps, compressors, and actuated valves. It also integrates the emergency shutdown system.

3.24 Earthing System

Safety in LPG facilities mandates an effective earthing system. All metallic structures and vehicles unloading or loading LPG must be grounded to prevent static electricity buildup.

3.25 LPG Terminal Basics: Firefighting System

A robust firefighting system, including components like firewater tanks, pumps, and hydrants, is critical for facility safety. Firefighting systems are primarily painted red for easy identification.

3.25.1 Firewater Storage Tank

This tank stores firefighting water. Equipped with level gauges, it ensures sufficient water supply, automatically triggering pumps when levels are low.

3.25.2 Raw Water Pump

These pumps draw raw water from sources like boreholes or rivers, pumping it into storage tanks. They may include water purification systems.

3.25.3 Jockey Pumps

Small centrifugal pumps that maintain pressure in the firewater ring main, jockey pumps initiate the firefighting effort and trigger the main firewater pumps when necessary.

3.25.4 Main Firewater Pumps

Diesel or electrically powered, these pumps provide the primary firefighting pressure. Facilities must have spare pumps available for backup. Main pumps’ discharge pressures must cover the facility's firefighting needs, sourced from storage tanks or rivers.

3.25.5 Firewater Ring Main

This primary pipeline distributes firewater throughout the facility. Process engineers size it to ensure adequate flow to fire monitors and hydrants, routing it appropriately within the site perimeter.

3.26 Fire Monitors

Fire monitors, or water cannons, deliver large volumes of water to fire sources. They can be manually or automatically controlled and are selected for their reach and water delivery capacity.

3.27 Fire Hydrants

Hydrants serve as connection points for firefighting hoses. Strategically located, they include valves and outlets for hose connections and are often paired with hose reels for easy access during emergencies.

3.28 Fire Extinguishers

Widely distributed for quick access, fire extinguishers should only be used by trained personnel.

3.29 Water Sprinklers

Installed in storage areas, loading/unloading bays, and transfer points, sprinklers cool the area and provide initial fire suppression. They activate automatically when temperature sensors detect high heat.

3.30 Utility Water System

This system supplies water for general use, including in toilets and for other non-potable purposes.

3.31 LPG Terminal Basics: Portable Water System

The portable water system ensures a supply of drinkable water, involving purification units, tanks, and transfer piping.

3.32 Power Generating System

An essential facility component, the power system should include primary (e.g., national grid) and backup (e.g., generators) sources to ensure uninterrupted operations.

4 LPG Terminal Basics: LPG Facilities Design Codes and Standards

Facility design, construction, and operation follow specific codes and standards, depending on local and client requirements. Design codes should be selected before project initiation.

4.1 LPG Terminal Basics: Design Requirements

The following are some guidelines from NFPA 58; for comprehensive details, refer to the code itself.

4.1.1 Container Requirements

NFPA 58, Section 4, Table 4.1 requires that LPG containers with a water storage capacity greater than 7.6m3 include excess-flow valves, gauging devices, regulators, and pressure relief devices.

Refer to Table 4.1 for requirements for containers with smaller capacities.

4.1.2 Vessel Separation Spacing Requirement

Spacing requirements are detailed in Section 6.3 and Table 6.3.1 of NFPA 58.

4.1.3 Separation Distance Between Container Pressure Relief Valve and Building Openings

Refer to Section 6.3.9 and Table 6.3.9 of NFPA 58 for spacing guidelines.

4.1.4 Burial Depth Requirements for Underground and Mounded Containers

Section 6.6.6 of NFPA 58 sets burial depths, with a minimum of 15cm for areas with no vehicular traffic and 46cm for areas with vehicular movement.

4.1.5 Minimum Separation Distance Between LPG Transfer Points and Exposures

• Transfers must occur outdoors, not inside buildings.
• Transfers under canopies are permissible, provided no more than 50% of the perimeter is enclosed.
• Minimum separation distances to other infrastructure are specified in Table 6.5.3 of NFPA 58 when transfer points are located outdoors.

5 References

NFPA 58: Liquefied Petroleum Gas Code

Corken LPG Pumps

Blackmer LPG Pumps

Flowserve (Sterling SIHI) Pumps

6 Conclusion

LPG can be transported using various methods like road, rail, and ship transportation.

LPG storage facilities can be categorized by storage volume, and their