We have been studying about types of gas carriers, and LNG ships in our previous articles. In this article we will take a step back and learn about the basics of natural gas that would help us to understand the signifance and importance of non pipeline transport of natural gas via various types of ships. So let us being first by knowing what exactly is meant by natural gas and its composition etc. This information is very useful for a marine engineer as well as a navigating officer to know about one of the types of cargoes that they carry around so frequently.
Natural Gas is a fossil fuel in the gaseous state. It is a gas consisting primarily of Methane (CH4). It is found associated with fossil fuels, in coal beds, it is found in reservoirs underneath the earth. Natural Gas is commonly associated with oil deposits underground as unrefined Methane gas and is created by methanogenic organisms in marshes, bogs, and landfills.
Natural Gas is a vital component of the world's supply of energy. It is one of the cleanest, safest, and most useful of available energy sources. It is colorless, shapeless, and odorless in its pure form.
Natural gas is a combustible mixture of hydrocarbon gases. While Natural Gas is formed primarily of Methane, it can also include small quantities of other gases like ethane, propane, butane and pentane depending on its source. The composition of Natural Gas can vary widely, but the composition before it is refined may be as under;
Methane (CH4) 70-90%
Ethane (C2H6) )
Propane (C3H8) ) 0 – 20%
Butane (C4H10) )
Carbon Dioxide (CO2) ) 0 – 8%
Apart from above, it may contain small quantities of gases like Oxygen, Nitrogen, Hydrogen Sulfide and traces of rare gases, depending on its source.
Once brought from underground, the Natural Gas is refined to remove impurities like water, other gases, sand, and other compounds.
After refining, what is available as commercial fuel is mainly Methane gas. The gas is said to be dry after removal of other hydrocarbons and impurities during refining.
Natural gas often comes out of the ground mixed with water vapor. This "wet gas" can be separated from moisture using two primary methods:
- Glycol dehydration and,
- Solid-desiccant dehydration.
The process of removing sulfur from Natural Gas is therefore called “sweetening." Sulfur in natural gas occurs as hydrogen sulfide, which must be removed because it is toxic when inhaled and is highly corrosive to pipeline walls.
After refining, Natural Gas is transported for distribution via pipe lines in gaseous state, by road transport in compressed gas (CNG) form and by sea in liquefied (LNG) state. Natural Gas is used as fuel in residences, commercial establishments like industry, vehicle transportation (CNG) and electricity generation.
Measuring Natural Gas
Natural Gas can be measured in a number of different ways. As a gas, it is measured by the volume it takes up at normal temperatures and pressures, commonly expressed in cubic feet i.e. a million cubic feet (Mcft) etc.
Like other forms of energy, natural gas is commonly measured and expressed in British thermal units (Btu). One Btu is the amount of natural gas that will produce enough energy to heat one pound of water by one degree at normal pressure. One cft of Natural Gas contains about 1027 Btu. Natural Gas as supplied to residences is measured in “Therms" (Equal to 100000 Btu’s) for cost estimation and billing. Although natural gas and crude oil often can be found in the same location, they take completely different routes from the wellhead to you, the consumer. End Users The Natural Gas we use in our homes is mostly methane, the simplest form of hydrocarbon. But Natural Gas at the well may include other hydrocarbons, such as ethane, propane, butane and pentane which are separated from it during refining process. Therefore, what is left in the final product to the consumer is mainly Methane.