Glossary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Laid-up tonnage

Ships not in active service; a ship that is out of commission for fitting out, awaiting better markets, needing work for classification. See Layup

Laytime

Time allowed by the shipowner to the voyage charterer or bill of lading holder in which to load and/or discharge the cargo. It is expressed as a number of days or hours.

Layup

To dismantle or unrig a ship for a prolonged period of unemployment.

Line pack

Creation of storage within the pipeline by increasing pressure above that which is required for transmission, but still within a safe limit.

Liquefaction plant

Facility that converts natural gas (gaseous at normal temperatures and pressure) to liquefied natural gas.

Liquefied natural gas (LNG)

Natural gas cooled to around -162°C, the boiling point of its main constituent methane (CH4), so that it becomes liquid. The process, known as liquefaction, reduces its volume by a factor of 600, making it more convenient and less dangerous to store and transport. Natural gas is liquefied in a liquefaction plant, transported and stored chilled and under slight pressure, before being converted back into gas at a regasification plant.

Liquefied petroleum gas (LPG)

Hydrocarbons that are gaseous at normal temperatures and pressures, but that readily turn into liquids under moderate pressure at normal temperatures; for example, propane and butane.

LNG cargo-containment systems

The method of storing LNG during marine transport. One of four methods is normally employed: Self-Supporting Prismatic Type ‘B’ (Conch/IHI), Dual Membrane (Gaz Transport), Single Membrane (Technigaz), and Self-Supporting Spherical Type ‘B’ (Kværner Moss).

LNG feedgas requirements

The amount of gas reserves required to economically support the development of an LNG liquefaction plant, allowing for gas lost in the process of production, liquefaction and transport of the LNG to end-markets (typically 10-15%).

LNG markets

There are two primary LNG markets; 1) Atlantic basin includes Belgium, France, Italy, Spain, Portugal, Greece, Turkey and the east coast of the US; 2) the Pacific basin includes India, Japan, South Korea, Taiwan, China and the west coast of the US.

LNG plant

A facility at which LNG is produced. Usually sited on the coast for easy access to export routes.

LNG project characteristics

Primary LNG project components are: 1) upstream development of long-term, natural gas supply for feedgas to an LNG plant; 2) downstream development of liquefaction, storage and loading facilities; 3) marine transportation; and 4) further downstream, development of receiving terminals for regasification and pipeline transportation to market. Defining economic characteristics of LNG projects include i) commercial activities organised around project components in which the buyer and seller are closely linked for 20-25 years; ii) significant front-end infrastructure investment for each tonne of LNG delivery capacity – the critical mass of infrastructure for an LNG project must be very large in order to achieve production quantities adequate for realisation of economies of scale and to secure project financing; and iii) long-term contracts based on large, proved gas reserves.

LNG storage tanks

Vessels that are specially constructed to contain LNG. The tanks are generally constructed of nickel steel (steel containing 9% nickel) to withstand cryogenic temperatures and are insulated to maintain the LNG at –162°C. Some of the stored LNG boils off and the resulting vapour is used as fuel gas for the plant. There are three main designs of LNG storage tanks: single containment, double containment and full containment. The difference in these systems lies in the functionality of the secondary containment, when the primary containment is breached. For single containment, neither liquid nor vapour will be held by the secondary containment; for double containment, liquid will be contained and for full containment, liquid and vapour will be contained.

LNG terminal

A receiving point for LNG cargoes.

LNG train

See Train.

LNG value chain

In planning, funding and executing an LNG project, each element of the complex chain that links the natural gas in the ground to the ultimate consumer (from the wellhead to the burner tip) is considered. The main links are natural gas production, liquefaction, shipping, receiving terminal (including regasification), distribution of the regasified LNG and, lastly, consumption of the gas.

Load balancing

Process of matching customers’ demand for natural gas with producers’ ability to supply.

Loaded leg

That portion (or subdivision) of a ship’s voyage during which the ship is carrying cargo.

Loading days

The number of days allowed to load a cargo defined in the charter party.

Local-distribution company (LDC)

A utility that takes natural gas from a local delivery point (generally called the city gate) and distributes it to local customers. A business entity that obtains its primary revenues from the operations of a local retail gas distribution.

Long ton (L/T)

2,240 pounds or 1,016.05 kilograms. See Tonne, metric and Ton, long.

Long-term gas contract

A supply contract in the physical market covering natural gas deliveries.

Looping

Laying additional pipeline beside and connected to an existing pipeline in order to increase the capacity of the system.

Lost and unaccounted-for gas

The difference between the quantity of natural gas received into a system and the quantity of natural gas delivered out of a system over a specific period of time.

LPG

See Liquefied Petroleum Gas.

LNG refrigerant (for liquefaction) cycles

Natural gas liquefaction requires removal of sensible and latent heat over a wide temperature range using a refrigerant. The refrigerant may be part of the natural gas feed (an open-cycle process), or a separate fluid continuously re-circulated through the liquefier (a closed-cycle process). Three general types of refrigeration cycle are used:

Cascade refrigerant cycle

Feedstock natural gas is cooled, condensed and sub-cooled in heat exchange with propane, ethylene (or ethane) and finally methane in three discrete stages. The three refrigerant circuits generally have multistage refrigerant expansion and compression, each typically operating at three evaporation-temperature levels. After compression, propane is condensed with cooling water or air, ethylene is condensed with evaporating propane and methane is condensed with evaporating ethylene.

Expander cycle

In its simplest form, process refrigeration in an expander cycle is provided by compression and expansion of a single-component gas stream. High-pressure cycle gas is cooled in counter-current heat exchange with returning cold-cycle gas. The cycle gas is expanded through an expansion turbine, reducing its temperature to a lower temperature than would be given by expansion through a Joule-Thomson valve.

Mixed-refrigerant cycle (MRC)

Uses a mixed refrigerant(s) instead of the multiple pure refrigerants in the cascade cycle. The mixture composition is specified so the liquid refrigerant evaporates over a temperature range similar to that of the natural gas being liquefied. A mixture of nitrogen and hydrocarbons (usually in the C1 to C5 range) is normally used to provide optimal refrigeration characteristics. MRC provides greater thermodynamic efficiency, lower power requirement and use of smaller machinery.