What is Propane Gas?

Propane gas, also called LPG, is available almost everywhere.

We use it to heat our homes & hot water, cooking our food, power our BBQs and fuel our cars.

Propane is also used by business and agricultural for all sorts of applications.

It is an amazing transportable gas that comes in a bottle, but what exactly is propane, where does it come from and how does it work?

"What is Propane Gas?"

Propane is a flammable hydrocarbon gas liquefied through pressurisation.

It is classified as LPG, along with butane and mixtures of these gases.

Propane comes from natural gas processing and oil refining. It is used as heating, cooking and auto fuel.

Propane Physical Properties

Propane Properties Chart
Propane Properties
Properties Propane
Chemical Formula C3H8
Energy Content: MJ/m3 95.8
Energy Content: MJ/kg 49.58
Energy Content: MJ/L 25.3
Boiling Temp: Cº -42
Pressure @ 21ºC: kPa 858.7
Flame Temp: Cº 1967
Expansion: m3/L 0.270
Gas Volume: m3/kg 0.540
Relative Density: H2O 0.51
Relative Density: air 1.53
kg per L 0.51
L per kg 1.96
Specific Gravity @ 25ºC 1.55
Density @ 15ºC: kg/m3 1.899
  Note: Some numbers have been rounded.

Where Does Propane Come From?

Propane is a fossil fuel that does not occur in isolation.

Propane is found naturally in combination with other hydrocarbons.

It is produced during natural gas processing and oil refining. It is isolated, liquefied through pressurisation and stored in pressure vessels.

How is Propane Made?

Propane is made during natural gas processing and oil refining. It is separated from the unprocessed natural gas using refrigeration.

Propane is extracted from heated crude oil using a distillation tower.

It is then pressurisation and stored as a liquid in cylinders and tanks.

What is Propane Used For?  The condensed version:

Propane is utilised in numerous applications.

Propane is used as a fuel for many residential, commercial and agricultural heat applications, including cooking.

It is also employed as a propellant, refrigerant, vehicle fuel and petrochemical feedstock.

7 Important Propane Facts

Propane Gas

1. Propane is LPG but not all LPG is propane. LPG is the acronym for Liquefied Petroleum Gas.

2. Propane is a flammable hydrocarbon gas that is liquefied through pressurisation and commonly used as fuel.

3. Propane comes from natural gas processing and petroleum refining.

4. Propane is LPG but not all LPG is propane.  Propane, along with a number of gases, falls under the “LPG” label.  The other gases include butane (n-butane) and isobutane (i-butane), as well as mixtures of the three LPG gases.

5. Propane gas can be compressed into liquid at relatively low pressure.

6. Propane is frequently used for fuel in heating, cooking, hot water and vehicles.

7. Propane is generally stored, as a liquid, in steel vessels ranging from small BBQ gas bottles to larger gas cylinders and storage tanks. (45kg gas bottles shown)

Propane Goes by Many Names

In Australia, propane has many names.

It is also called LPG, LPG Gas, LP Gas, BBQ Gas or Autogas.

In the USA it is just called Propane.

In the UK, it is referred to as either propane or LPG.

How Does Propane Work?

Propane is stored under pressure, as a liquid, in a gas bottle.  

It turns back into gas vapour when you release some of the pressure in the gas bottle by turning on your appliance.

Almost all of the uses for propane involve the use of the gas vapour, not the liquefied gas. 

What is Propane Made of?  Propane Composition

LPG - propane molecule

Propane is a hydrocarbon gas with 3 carbon and 8 hydrogen atoms in a propane molecule.

The chemical formula for propane is C3H8(Propane molecule model shown)

Propane is not made or manufactured, it is found naturally in combination with other hydrocarbons.

Propane is produced during natural gas processing and petroleum refining. 

Both processes begin by drilling oil wells.

Propane does not occur naturally in isolation. 

Propane processing involves the separation and collection of the gas from its petroleum base and other Natural Gas Liquids (NGLs).

Following its refinement, LPG is stored and distributed as a liquid under pressure until used, at which point it is utilised as either a liquid or a gas (vapour).

What is Propane Used For?

Propane has hundreds, if not thousands, of uses.

The propane uses most people can name are around the home, in their cars or for their business.Propane for leisure

It is used in leisure time activities including caravans, boats, recreational vehicles, hot air balloons and camping.

Business and industry use propane for a multitude of processes including steam boilers, kilns, ovens and forklifts.

Crop and produce drying, heating greenhouses, hot water for dairies, irrigation pumps and heating animal enclosures are just some of the agricultural applications for propane.

Transport is also a big user of propane, either alone or mixed with butane, to power various vehicle types.

There are also many, many more propane applications, including power generation and the hospitality industry.

What are the Properties of Propane?

Propane Boiling Point

Water boils at 100°C, becoming a gas (steam).  

In contrast, propane boils at -42°C becoming gas vapour.  

Propane stays liquid because it is under pressure in a gas cylinder. 

As a liquid, it looks a lot like water.

It is colourless and odourless in its natural state. 

Odourant is Added for Safety

Odourant is added to propaneIn its natural state, propane is an odourless gas.
The distinctive smell that people associate with propane is actually added to it as a safety measure.
Without the addition of an odourant, leaking gas could collect without being detected.

Avoid Direct Contact - Cold Burns

Caution should always be used to avoid direct exposure, as liquid propane is cold enough to cause severe cold burns on exposed skin.

Specific Gravity of Propane - Density

Density of propaneUnlike water, 1 kilogram of propane does NOT equal 1 litre of propane. 
Propane density or specific gravity is about half that of water, at 0.51.  
1kg of propane has a volume of 1.96L. 
Conversely, 1L of propane weighs 0.51kg. 
1lb of propane @ 60ºF has a volume of 0.24 US gallons.
Conversely, 1 US gallon of propane @ 60ºF only weighs 4.23lbs, instead of the 8.34lbs it would weigh if it was water.

Propane Gaseous Expansion

Gaseous expansionPropane expands to 270 times the volume when it goes from liquid to gas. 
So, 1L of liquid LPG equals 270L of gaseous propane.   
As there are 1000L in a cubic meter (M3), 1L of liquid propane expands to 0.27M3.
1 US gallon of liquid propane equals 36.38ft3 of gaseous propane

Energy Content of Propane

Propane contains approximately 25MJ per litre. 
This also converts to 6.9kWh.
More propane energy content facts:
1 US gallon of propane = 91,502 BTU @ 60ºF
1ft3 propane gas = 2,488 BTU of Gas @ 60ºF
1 US gallon propane = 1.1 therm
1 therm = 100,000 BTU
1 watt = 3.41214 BTU/h

Combustion Formula

In the presence of sufficient oxygen, propane burns to form water vapour and carbon dioxide, as well as heat.
Propane + Oxygen → Carbon Dioxide + Water + Heat
(C3H8 + 5 O2 → 3 CO2 + 4 H2O + Heat)
If not enough oxygen is present for complete combustion, incomplete combustion occurs with water, carbon monoxide, and carbon dioxide being produced.

Propane Flame Temperature

Blue flame with complete combustionAn propane flame burns at 1980ºC (3596ºF). 
When it is burning properly, the flame is blue
A yellow or red flame is usually indicative of incomplete combustion.

Limits of Flammability

The lower and upper limits of flammability are the percentages of propane that must be present in an propane/air mixture. 
This means that between 2.15% and 9.6% of the total propane/air mixture must be propane in order for it to be combustible.

Propane Flash Point

The flash point of propane is  -104ºC (-155.2ºF).  
This is the minimum temperature at which propane will burn on its own after having been ignited.   
Below this temperature, it will stop burning on its own.  
However, if a source of continuous ignition is present, it will burn below  -104°C.

Dissipation

Propane gas is heavier than air and will sink to and collect at the lowest point.  
If propane is vented to the outside air, it will quickly dissipate with the slightest movement of air.
Conversely, if propane is vented into a sealed structure, with no air movement, the propane gas will collect on the floor and rise vertically as more propane is vented into the structure.

Propane Vapour (Gas) Use vs. Liquid Use

Propane can be supplied in either liquid or vapour. 
The difference is in the extraction from cylinder or vessel in which it is supplied.
Most propane applications use vapour.  
Appliances such as water heaters, room heaters and cookers all use vapour.  
If these appliances were to have liquid propane flow to their burners, the result could possibly be a fire or similar safety hazard.  
This is why propane cylinders should always be kept upright, so that only vapour is released.
 
 
 

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The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.

 

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