Fri. Sep 24th, 2021

City gas distribution

Transporting future fuel

#2 Natural Gas

5 min read

Natural gas is a vital component of the world’s supply of energy. It is one of the cleanest, safest, and most useful of all energy sources.

Natural gas is a mixture of gases which are rich in hydrocarbons. All these gases (methane, nitrogen, carbon dioxide, etc) are naturally found in the atmosphere. Natural gas reserves are deep inside the earth near other solid & liquid hydrocarbons beds like coal and crude oil.

Natural gas is a fossil fuel, It consists mainly of methane which is a combination of hydrogen & carbon. It may also contain other hydrocarbons namely, ethane, propane, butane etc. Sometimes nitrogen, helium, carbon dioxide, traces of hydrogen sulphide and water are also associated with natural gas. Mercury may also be present in natural gas in small amount in some fields. Normally, these are filtered out before it is distributed to the consumer.

The exact composition of natural gas varies between gas fields.

Natural gas properties vary to some extent with the composition of gas. Processed natural gas is harmless to human body, but it may lead to asphyxiation in confined space.

The first characteristic of Natural gas is its weight. Natural gas is lighter than air & will rise, on the other hand butane/propane is heavier than air & will accumulate near the floor on ground.

Second important characteristic of natural gas is the heat content or flammability. If we heat/ignite natural gas & butane/propane, butane/propane flame seams much brighter, that’s because butane/propane has higher heat content.

Natural gas in its natural state has no odour or colour. So, to help us locate a gas, a chemical called mercaptan is added that give the gas a distinct smell (like a rotten egg). This odour help us to find leaks in pipe & appliances.

Natural gas is safe, non-toxic & non-poisonous.

We get energy from these gases from a process called combustion. 3 things are necessary for combustion to take place.

The combustion triangle has 3 sides. (Fuel- Natural gas, Oxygen & an ignition source). If any of these 3 are absence combustion won’t occur.

With proper combustion natural gas produces a harmless mixture of Carbon dioxide & water vapour.

2 sides of triangle, fuel & air must be in certain proportion for combustion to take place. In other word for gas to burn & release energy, it must be mixed with a certain amount of air.

Natural gas will burn only if the mixture of gas & air is between 5% & 15%. Below 5% the mix is too lean to burn and above 15% the mix is too rich to burn.

The composition of natural gas can vary widely, but below is a chart outlining the typical makeup of natural gas before it is refined.

MethaneCH470-90%
Ethane, Propane, ButaneC2H6, C3H8, C4H100-20%
Carbon DioxideCO20-8%
OxygenO20-0.2%
NitrogenN20-5%
Hydrogen sulphideH2S0-5%
Rare gasesA, He, Ne, Xetrace

In its purest form, such as the natural gas that is delivered to your home, it is almost pure methane. Methane is a molecule made up of one carbon atom and four hydrogen atoms, and is referred to as CH4. The distinctive “rotten egg” smell that we often associate with natural gas is actually an odorant called mercaptan that is added to the gas before it is delivered to the end-user. Mercaptan aids in detecting any leaks.

Natural gas has many uses in residential, commercial, and industrial applications.

Properties of Natural gases is as listed below;

Specific Gravity (Air 1.0)0.56 to 0.67
Boiling Point-161 °C
Melting Point-182 °C
Flash Point-161 °C
Auto Ignition Temperature560 °C
Flammable Limit5% to 15% by volume in air
Critical Pressure45.99 Bar
Critical Temperature-82.59 °C

Note: These properties in detail are explained in the technical category post.

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