Characteristics and features of natural gas

For some people it is enough to know that natural gas is a comfortable and stable source of energy that provides enough heat to your living room, hot water to fill your bathtub, or lets you cook a meal for the entire family. Others--who want to know what is behind the blue flame, how it originates and what it consists of--will enjoy reading the following text.

What is natural gas?

Natural gas is a naturally flammable gas that is an important gaseous fossil fuel. It is a mixture of hydrocarbons of which 93% to 99%, by volume, is methane. In addition to methane it also contains propane, butane and other substances. It is lighter than air, has no colour, taste nor smell and for that reason it is odorized (an odorant – an odorous substance is added) during its processing to make it identifiable in the air. Natural gas is used as fuel for heating and in the form of compressed natural gas (CNG) as a fuel for motor vehicles. It is also the basic material for production of a wide variety of synthetic polymers and other chemical products such as fertilizers.

Natural gas is the common name for several kinds of fossil fuels which are categorized by their origin:

Coal gas: originates from deposits of coal
Oil gas: originates from crude oil under the effects of temperature and pressure

What are the features of natural gas?

The composition and calorific value of gas is highly dependent upon its origin (type of deposit). The features of natural gas are determined mainly by concepts such as calorific value and combustion heat.

Calorific value of natural gas

Calorific value Qi is heat released from complete combustion of a unit amount of gas with a stoichiometric amount of oxygen or air under a constant pressure and temperature where all combustion products are cooled to their original temperature and are in a gaseous state. For heating gases, heat and calorific value are usually expressed in kWh.m^-3 or in MJ.m^-3 where the volume unit is expressed under standard conditions, meaning at a temperature of 15°C and at a pressure of 101,325 kPa.

Combustion heat

The definition of Qs combustion heat is the amount of heat released from complete combustion of a unit amount of gas with a stoichiometric amount of oxygen or air under a constant pressure and temperature where all combustion products are cooled to their original temperature and are in a gaseous state, except for water which condensates. The values of combustion heat are used mainly in the gas industry where they are expressed as limit values of energy that can be generated from a unit amount of gas provided that the combustion products are cooled to temperatures below their dew point. That condition is met in modern condensation gas appliances.

The Qs/Qi ratio for common gases is a value approximating 1.11, meaning that the combustion heat is higher than the calorific value by about 11%