Hydrocarbon gas liquids explained Transporting and storing hydrocarbon gas liquids

Hydrocarbon gas liquids are transported by various means

Hydrocarbon gas liquids (HGL) extracted from natural gas or produced at petroleum refineries can be transported as liquids in mixtures of HGLs or as separate HGL purity products in pipelines, rail cars, trucks, ships, and barges.

HGLs are transported in five main forms:

• Y-grade (raw, unseparated HGLs)
• E-P mix (most frequently, 80% ethane and 20% propane)
• P/P mix (refinery-grade propane-propylene mixture)
• Liquefied petroleum gas (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 HGLs produced in the United States are transported in pipelines from production sites to either where they are used or to storage.

Most HGLs transported by pipeline are Y-grade quality and destined for fractionation plants. Purity ethane and E-P mix is transported by pipelines from fractionation plants to ethylene crackers, where they are used to produce ethylene and other olefins. P/P mix is mostly transported by dedicated pipelines on the Gulf Coast and by rail in other regions from refineries to propylene splitters. Once transported, the impurities are removed from the P/P mix, resulting in a higher quality, polymer-grade or chemical-grade propylene, which is sold to petrochemical plants. Liquefied petroleum gases (LPG)¹ (propane, normal butane, and isobutane) are transported by dedicated high vapor pressure pipelines or in batches as purity products in pipelines that transport other kinds of petroleum products.

Railroads and trucks transport HGLs to consumers

Many areas of the United States (such as the West, New England, and Florida) are not served by HGL pipelines. In these areas, railroads often transport large volumes of HGLs to wholesale and bulk purchasers in pressurized railroad tankcars. Railroads and trucks also transport HGLs to consumers. The most common HGL product delivered to consumers is consumer-grade propane, which is transported by truck in pressurized tanks. Propane is commonly used in:

• Homes, farms, and businesses as engine fuel
• Crop drying
• Space heating and water heating
• Cooking

Special ships transport HGLs to and from the United States

Special ships are used to transport HGLs (usually LPG) to and from shipping ports in the United States. The ships, called gas tankers, vary in size and by the method used to keep the HGLs in liquid form. The HGLs can be pressurized, refrigerated, or both. Over short distances, propane and normal butane are also moved by barge along intercoastal waterways and navigable rivers.

HGLs are stored in a variety of ways

HGL storage is important because production could exceed the capacity of available transportation modes to carry the HGLs to consumers. HGL production may also not match seasonal demand. For example, propane production 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 withdrawn from storage when demand is high.

Large volumes of HGLs are primarily stored as a pressurized liquid in underground caverns. Most of the caverns are in salt formations, but some propane storage caverns are mined out of shale, granite, or 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 HGLs are transported close to consumers, they are stored in pressurized (or sometimes refrigerated) tanks located above or below ground. LPG 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.