Difference Between LPG & Natural Gas

In New Zealand, we mainly rely on two types of gas for our energy needs.  LPG and Natural Gas are widely available and used for thousands of applications in homes and business.  However, there are variations of these gases based on composition and method of delivery.
There are also two main differences in the way that LPG (Propane-Butane mix) and natural gas (Methane) are burnt.  The first difference is in the energy content. LPG has a higher calorific value, or energy content, so less gas is required to produce the same amount of heat.
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The second difference is in the oxygen to gas ratio required for proper combustion. LPG requires an oxygen to gas ratio of approximately 25 to 1.  Natural gas requires a ratio of around 10 to 1.  To achieve this difference, LPG is typically provided in a smaller quantity but at a higher pressure, drawing more oxygen with it into the combustion process.

LPG (Liquefied Petroleum Gas)

The term LPG actually encompasses more than one type of gas.  There are a number of hydrocarbon gases that fall into the category of LPG.  Their common characteristic is that they can be compressed into liquid at relatively low pressures.  The two most common are Propane and Butane.
propane molecule C3H8LPG (Propane):  A Propane-Butane mix is the gas that is supplied to virtually all homes and most businesses that purchase LPG in NZ.  LPG is supplied in gas bottles that are either exchanged or refilled on site by LPG tankers.  LPG goes by a number of names in NZ including LPG, LPG gas, bottled gas, BBQ gas, camping gas and LP gas.  It’s all the same gas.  The chemical formula for Propane is C3H8.  
Butane molecule C4H10LPG (Butane):  Butane is supplied to certain businesses that specify Butane, as opposed to Propane.  Butane has some specific applications where it has advantages over Propane.  These include greenhouse applications and use as a propellant in aerosols.   The chemical formula for Butane is C4H10.
Autogas (Propane/Butane mix):  Autogas that is sold at NZ petrol stations is typically a Propane/Butane mix.  Not only is running an LPG car economical, but Autogas is also cleaner burning fuel than petrol, so engine life is actually extended and greenhouse gas emissions reduced.

Natural Gas (Methane)

Methane molecule CH4Natural gas is primarily Methane.  When it is extracted from the ground it may also contain Ethane, Propane, Butane, and Pentane, although most of these are usually stripped out for other specific applications before it is passed along through the pipelines.  Impurities are also removed, including water and sulphur.  The chemical formula for Methane is CH4.
Piped Gas:  Natural gas or “mains gas” is the gas supplied to homes and businesses by gas pipelines or “gas mains” (reticulation systems).  This is how most NZ consumers receive their gas.
CNG (Compressed Natural Gas):  Methane gas can be stored at high pressure, typically over 200 bars, but it is not very economical for long distance transport.  CNG does have some specific applications where the product is used in close proximity to where it is compressed.  City buses are a good example of a successful CNG application.
LNG reduces volume by 600 timesLNG (Liquefied Natural Gas):  Methane gas is processed into LNG by cooling it to −161°C, at which point it becomes a liquid.  This reduces the volume of the natural gas by a factor of more than 600 times as it goes from its gaseous state to liquid.  That's like going from a beach ball to a ping pong ball.  This reduced volume facilitates economical transport by sea or road.
Common LNG uses include industrial applications and long haul trucking.  The technology involved with LNG is generally not cost effective for small volume users, such as homes and small businesses.  

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