Compressed Natural Gas (CNG) is natural gas stored under high pressure. This process reduces its volume for efficient storage and transportation.
Understanding Compressed Natural Gas
Compressed Natural Gas is predominantly composed of methane (CH4), making it chemically identical to natural gas.
The “compressed” aspect refers to the process where natural gas is pressurized significantly, typically to over 3,000 pounds per square inch (psi) or approximately 200-250 bar. This high-pressure compression substantially reduces the gas’s volume, allowing for more compact storage and transportation in specialized tanks. Despite this high pressure, CNG remains in a gaseous state, which differentiates it from Liquefied Natural Gas (LNG), which is cooled to a cryogenic liquid.
Distinguishing Characteristics
Its density is lower than that of air, meaning that if a leak occurs, CNG tends to rise and disperse into the atmosphere. This characteristic influences its safety protocols and storage considerations.
CNG has a specific flammability range, indicating the concentration in air at which it can ignite. While naturally odorless, a distinctive scent, typically from an additive like mercaptan, is introduced for safety purposes, enabling detection of leaks. Although CNG possesses a high energy content by mass, its volumetric energy density is lower compared to liquid fuels due to its gaseous state.
Everyday Applications
Compressed Natural Gas is widely used as a transportation fuel for various types of vehicles. It powers light-duty vehicles, such as passenger cars, and is commonly found in heavy-duty applications like refuse trucks and transit buses. Fleet vehicles, which operate on fixed routes or within specific areas, frequently utilize CNG due to established fueling infrastructure.
Beyond transportation, CNG finds application in certain industrial processes where natural gas is a primary fuel or chemical feedstock. In some instances, it is also used for residential or commercial heating in areas without direct access to natural gas pipelines. These uses demonstrate its versatility across different sectors.
Emissions and Atmosphere
When Compressed Natural Gas undergoes combustion, the primary byproducts released are carbon dioxide (CO2) and water vapor. These are the main products of complete hydrocarbon combustion. The combustion process also generates other emissions, though typically in lower quantities compared to traditional liquid fossil fuels.
Trace emissions can include nitrogen oxides (NOx) and particulate matter. However, the amounts of these pollutants are generally reduced compared to the combustion of gasoline or diesel. The specific emission profile of CNG is a direct result of its chemical composition, predominantly methane.