LPG and LNG are by-products of petroleum and they are increasingly used for fuel as countries are increasingly concerned about their environment.
So what are LPG and LNG, and how are they different?
LPG – Liquefied Petroleum Gas
LPG is liquefied petroleum gas which consists mainly of propane and butane.
LPG is commonly used as fuel in heating appliances, cooking equipment, and vehicles. It is also increasingly used as an aerosol propellant and refrigerant, replacing chlorofluorocarbons to reduce damage to the ozone layer.
As a clean fuel, LPG is also increasingly used to power cars and buses. For this application, LPG is referred to as autogas or CNG (compressed natural gas).
At the normal condition, 15 degrees C and 14.7 PSI, the mixture of propane and butane is in the gaseous state. However, when its pressure is increased to above 120 PSI, the gaseous mixture turns into liquid. The liquefaction of the LPG makes it easier to store and transport.
In the liquid state, the volume of the mixture is only 1/270th of its volume in gaseous form. So, when LPG is released to the atmosphere, it will expand 270 times as it turns into vapor.
LPG is produced by extracting the propane and butane from the gas and condensate produced from oil reservoirs and gas reservoirs. This extraction process usually takes place in a gas processing plant located at an oil or gas field.
LPG is also produced from crude oil as one of the distillates from the refining process in a refinery.
LNG – Liquefied Natural Gas
LNG is liquefied natural gas. In remote places where a large quantity of natural gas is discovered and no gas pipeline is available, the produced natural gas is often turned into a liquid allowing it to be transported in bulk by LNG carriers. At its destination, the LNG is offloaded from the tanker and stored in insulated tanks. The LNG will be processed back into a gas, and the gas will be put into the pipeline for further distribution.
To produce LNG, natural gas consisting mainly of methane is super-cooled to -162 degrees C to turn it into a liquid. This decreases the gas volume 600 times making it easier to store and transport. It also plays a very important and useful role in meeting peak demands for gas, which the normal pipeline infrastructure cannot do. LNG is finding many new applications, and its demand is increasing. According to a Shell report, the global demand for LNG is expected to increase 4 to 5 % per year until 2030 while the demand for natural gas will increase at 2% per year.
In places where demand for natural gas cannot be met locally, the use of FSRU is gaining popularity. FSRU is a floating, storage and regasification unit. An FSRU can be constructed and installed quite quickly and economically to receive LNG from an LNG carrier and deliver the gas to the end-users as needed.
In summary, LPG and LNG have similarities and differences.
Similarities of LPG and LNG
- Both LPG and LNG are by-products of crude oil and natural gas.
- They are both in liquefied form making them easier for storage and transportation.
- They are commonly used as fuel.
- They are considered as clean fuel as they leave no smoke or soot.
Differences between LPG and LNG
- LPG consists mainly of propane and butane whereas LNG consists mainly of methane.
- LPG has a much higher heating value than LNG, and therefore it is also used to power cars and even buses.
- LPG is liquefied by increasing its pressure whereas LNG is liquefied by lowering its temperature.
- LPG is usually distributed to consumers in pressurized cylinders whereas LNG is gasified before it is transmitted to end-users by pipelines.
- Finally, as their names imply, petroleum – the crude oil, condensate, and natural gas – is the source of the propane and the butane contained in the LPG, whereas natural gas is the main source of the methane contained in the LNG.
The article is written by Jamin Djuang, the author of The Story Of Oil and Gas: How Oil and Gas are Explored, Drilled and Produced.