Fri. Sep 24th, 2021

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Transporting future fuel

#12 LPG vs PNG vs CNG vs LNG

6 min read

LPG & Natural Gas are chemically different gases, as natural gas is methane gas whilst LPG – liquefied petroleum gas – is propane or butane (bottled gas). Gas bottles are used to supply LPG vs natural gas conveyed by pipeline.

LPG has a higher calorific value, or energy content, so less gas is required to produce the same amount of heat. The second key 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.

LPG is heavier than air vs natural gas which is lighter than air. LPG has a higher energy content at 93.2MJ/m3 vs natural gas at 38.7MJ/m3. LPG is liquefied through pressurisation vs natural gas which is cryogenically turned to liquefied natural gas – LNG. LPG is not natural gas but it is derived from natural gas processing.

LPG is better than natural gas because it has a higher energy content, it is portable and available everywhere.

Natural gas is better than LPG when it comes to delivery through pipes and the fact that it produces slightly less CO2 when burned.

Comparing LPG vs natural gas, propane is heavier than air and will settle whilst natural gas is lighter than air and will dissipate more quickly if there is a leak, which may be a safety benefit over LPG.

In summary, the differences between LPG vs natural gas are different energy content, density, storage, delivery methods and the amount of air required for proper combustion.

Propane is not natural gas but natural gas processing is one source of propane.

So, LPG gas is not the same as natural gas, even though both are flammable hydrocarbon gases. However, they are used for many of the same applications.

LPG vs LNG vs CNG

LNG – Liquefied Natural Gas is natural gas (methane) cryogenically liquefied. LPG – Liquefied Petroleum Gas is mainly propane and butane alone or in mixtures liquified under pressure. LPG is produced from crude oil refining and natural gas processing. CNG – Compressed Natural Gas is natural gas stored at high pressure.

Natural gas (methane) is lighter than air and will typically disperse in the event of a leak. This is advantageous, over LPG, from a safety point of view. With LPG vs LNG, modest pressure is used to liquefy LPG vs LNG liquefied cryogenically. Both are gases at normal temperature and pressure (NTP).

LPG is stored, shipped and distributed in cylinders or tanks. LNG is stored and shipped in special cryogenic tanks and then typically distributed via pipeline, after regasification.

When considering LNG vs LPG vs CNG, LNG – Liquefied Natural Gas is natural gas (methane) cryogenically liquefied at −161°C and stored in tanks. LPG is propane liquefied under modest pressure in cylinders. CNG – Compressed Natural Gas is highly compressed natural gas (methane) in cylinders. All are gas at NTP.

LNG is stored and shipped in cryogenic tanks then distributed through pipelines, after regasification. LPG and CNG are both stored and distributed in cylinders.

CNG is highly compressed natural gas in cylinders. LPG, propane and butane, are gas at 20°C and 1 atm (NTP) and liquefied under low pressure. Methane remains gas under pressure. LNG only liquefies cryogenically.

Also, Methane has an autoignition temperature of 537°C (999°F). Propane has an autoignition temperature of 470°C (878°F)

The autoignition temperature is the lowest temperature at which a substance spontaneously ignites in air, with no other ignition source. 

So, based on their respective autoignition temperatures, propane is more flammable than methane because it spontaneously ignites at a lower temperature.

The difference between PNG and LPG is the same as the difference between natural gas and LPG. PNG or natural gas is methane whilst LPG is propane, butane, isobutane, or a mixture of the three. All of the other differences are the same as stated above.

PropaneMethane
Chemical FormulaC3H8CH4
Energy Content: MJ/m393.238.7
Energy Content: Btu/ft325721011
Energy Content: MJ/kg49.5852.5
Boiling Temp: Cº-42-161.5
Flame Temp: Cº19671950
Flame Temp: Fº3573
3542
Gas Volume: m3/kg0.5401.499
Specific Gravity1.52190.5537
Density @15ºC: kg/m31.8990.668

Note: Specific gravity refers to the ratio of the density of an object and the reference material. Furthermore, the specific gravity can tell us if the object will sink or float in reference material. Besides, the reference material is water that always has a density of 1 gram per cubic centimeter or 1 gram per millimeter.

In simple words, specific gravity defines whether an object will sink or float in water.

The density of the object refers to how heavy or compact the object is in the given volume. Also, we measure it in mass per unit volume. Furthermore, it is written as grams per cubic centimeter (g/cm3), grams per millimeter (g/mL), or kilograms per liter (kg/L).

In simple words, density refers to the heaviness or lightness of an object in the given volume. Moreover, the density of the object directly relates to the mass of the object means that the object that has more molecule will have high density and the object that is less molecule will have lower density.

Formula

Density = mass/volume

Specific Gravity = density of an object / density of water (taking water as a reference)

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