Fuel gas is any one of a number of fuels that under ordinary conditions are gaseous. Many fuel gases are composed of hydrocarbons ,hydrogen, carbon monoxide, or mixtures thereof. Such gases are sources of potential heat energy or light energy that can be readily transmitted and distributed through pipes from the point of origin directly to the place of consumption.
Properties of gaseous fuels
The fuel should be compared based on their net calorific value and especially true for natural gas because increased hydrogen content results in high water formation during combustion.
There is a video link of refining the gaseous fuel
Chemistry 