Source: Stock photography (copyrighted)
Source: Dorian LPG Ltd. (copyrighted)
Source: Stock photography (copyrighted)
Hydrocarbon gas liquids are transported by various means
Hydrocarbon gas liquids (HGL) that are extracted from natural gas or that are produced at petroleum refineries may be transported as liquids in mixtures of HGL or as separate HGL purity products in pipelines, rail cars, trucks, ships, and barges.
There are five main forms in which HGL are transported:
- Y-grade (raw, unseparated HGL)
- E-P mix (most frequently 80% ethane and 20% propane)
- P/P mix (refinery-grade propane-propylene mixture)
- LPG (mixture of liquefied propane, normal butane, and isobutane)
- Purity products (separate, distinct products; mostly ethane, propane, and normal butane)
Pipelines carry hydrocarbon gas liquids from where they are produced to where they are stored
Most of the HGL produced in the United States are transported in pipelines from where they are produced to places where they are used or to places where they are stored for distribution.
Most of HGL transported by pipeline is Y-grade quality and is transported to fractionation plants. E-P mix is mostly transported in pipelines from fractionation plants to ethylene crackers, where it is used to produce ethylene and other olefins. On the Gulf Coast, P/P mix is often transported by dedicated pipelines to propylene splitters that separate refinery-grade (lower grade or quality) propylene into higher quality, polymer-grade or chemical-grade propylene, which is then sold to petrochemical plants. Propane and normal butane are transported in liquefied petroleum gas (LPG)1 pipelines or in batches as purity products in pipelines that transport other kinds of petroleum products.
Railroads and trucks transport HGL to consumers
There are many regions in the United States (like the West, New England, and Florida) that are not served by HGL pipelines. In these areas, railroads often transport large volumes of HGL to wholesale and bulk purchasers in pressurized railroad tankcars. Railroads and trucks are also used to transport HGL to consumers. The primary HGL product delivered to consumers is consumer-grade propane, which is transported by truck in pressurized tanks to homes, farms, and businesses where it can be used as engine fuel, for crop drying, for space heating and water heating, and for cooking, among other applications.
Special ships are used to transport HGL to and from the United States
Special ships are used to transport HGL (usually LPG1) to and from shipping ports in the United States. The ships, called gas tankers, vary in size and vary by the method used to keep the HGL in liquid form. The HGL may be pressurized, refrigerated, or both. Over short distances, propane and normal butane are also moved by barge along intercoastal waterways and navigable rivers.
HGL are stored in a variety of ways
Storage of HGL is required because HGL may be produced in volumes that exceed the capacity of different modes of transportation used to carry the HGL to consumers. Production may also not match HGL seasonal requirements. For example, production of propane is relatively consistent throughout the year, but demand for propane is usually lower in the summer and higher in the fall and winter. Propane is stored when demand is low, and propane is withdrawn from storage when demand is high.
Large volumes of HGL are primarily stored as a pressurized liquid in underground caverns. Most of the caverns are in salt formations, but there are also some propane storage caverns mined out of shale, granite, and limestone rock. In regions where geology is not well suited for underground caverns, large aboveground tanks may be used. Aboveground tanks are the primary storage method for propane and butanes in New England.
Once HGL are transported close to consumers, they are stored in pressurized (and sometimes cooled) tanks located above or below ground. LPG, which can refer to propane, butanes, or a mixture of the two, is stored and distributed in many different sizes of tanks, from the small canisters used for torches and camping stoves, to 90,000-gallon bullet-shaped tanks used at industrial facilities.
1Liquefied petroleum gas (LPG) is a generic industry term that is used to refer to propane, butanes, or a mixture of these. These products are generally not distributed as mixtures. Virtually all HGL product distributed in the U.S. consumer market with the LPG label is HD-5 propane. Propane constitutes most of U.S. marine HGL/LPG imports and exports.