Compressed Natural Gas (CNG) is an alternative fuel source that consists primarily of methane, stored at extremely high pressures. This compression reduces the gas volume to less than one percent of its standard atmospheric volume, making it feasible for storage and transportation in durable containers. CNG is typically stored at pressures ranging from 2,900 to 3,600 pounds per square inch (200 to 250 bar). The fuel is increasingly adopted globally for its benefits over traditional gasoline and diesel, including lower emissions and a more stable price point. Understanding the applications of CNG requires examining how this fuel is used across various sectors.
Primary Application in Vehicle Fleets
The primary application of compressed natural gas is within the transportation sector, particularly among vehicle fleets. CNG is a popular choice because these vehicles operate on fixed, predictable routes that simplify centralized refueling logistics. Fleet operators frequently install their own fueling stations, providing a consistent and often lower-cost supply compared to fluctuating liquid fuel prices.
Common users include municipal vehicles like city transit buses, which benefit from the fuel’s cleaner-burning nature in densely populated urban areas. Waste collection trucks and school buses use CNG, as their stop-and-go operation is well-suited to the engine characteristics of natural gas. Medium-duty delivery vans and utility trucks are also transitioning to CNG for regional distribution and service routes.
Adopting CNG requires specialized equipment, including high-pressure storage cylinders mounted on the vehicle’s chassis or roof. Although the initial cost of a Natural Gas Vehicle (NGV) can be higher than a conventional vehicle, the clean-burning nature of methane leads to reduced engine wear and lower maintenance costs over the lifespan. CNG allows for a significant reduction in smog-producing pollutants and greenhouse gas emissions compared to diesel, making it a favorable option for environmental compliance.
Use in Industrial Processes and Stationary Power
Beyond transportation, compressed natural gas serves various needs in industrial and commercial settings. CNG is used as a fuel source for process heating or steam generation, replacing dirtier fuels like coal or heating oil in boilers and furnaces. Its clean combustion provides reliable thermal output for industrial operations.
CNG is also employed for stationary power generation, ranging from prime power to backup electricity supply in commercial facilities. In areas lacking a connection to a natural gas pipeline, CNG can be transported via specialized tube trailers, creating a “virtual pipeline” to deliver fuel to remote industrial sites. This delivery method is valuable where the capital expenditure for a permanent pipeline is not justified.
CNG is delivered in high-pressure cylinders and then decompressed before being fed into gas turbine generators or reciprocating engines. The use of CNG offers cost savings compared to diesel-fueled generators and provides a cleaner environmental profile for localized power production. It can also act as a bridging fuel, offering a stable energy source until permanent pipeline infrastructure is developed.
Distinguishing CNG from Liquefied Natural Gas
Compressed Natural Gas (CNG) and Liquefied Natural Gas (LNG) have distinct applications based on their physical state. CNG remains gaseous, stored under high pressure at ambient temperatures. In contrast, LNG is natural gas cooled to approximately -260°F (-162°C), transforming it into a liquid.
CNG is ideal for short-haul transportation and local applications due to its simpler storage and refueling infrastructure. However, the energy density of CNG is lower than LNG, meaning it requires a larger volume to store the same amount of energy. This limitation makes CNG less suitable for vehicles requiring very long ranges or carrying high-volume payloads.
LNG, with its high energy density, is preferred for long-haul transportation, such as heavy-duty trucking and marine vessels. Storing LNG requires specialized, insulated cryogenic tanks to maintain its liquid state, which is a more complex and expensive infrastructure than the high-pressure cylinders used for CNG. Therefore, CNG is the practical choice for city fleets and local industrial needs, while LNG is reserved for high-volume, long-distance energy requirements.