Understanding Alternative Fuels: CNG vs. LNG vs. Propane
Fossil fuels like gasoline and diesel have been the cornerstone of our energy needs for decades. Yet, as we seek safer, cleaner, and more efficient energy solutions, natural and renewable energy sources have emerged as pivotal players in the next generation of fuel supply.
Among these, compressed natural gas (CNG), liquefied natural gas (LNG), renewable natural gas (RNG), and propane stand out. But how well do we understand each of these fuels?
Each has distinct advantages and considerations, carving out unique niches within the alternative fuel landscape. Today, we’ll examine their roles, benefits, and most suitable applications.
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Natural Gas vs. Renewable Natural Gas
Understanding Alternative Fuels
Natural Gas vs. Renewable Natural Gas (RNG)
When discussing energy, "natural" and "renewable" gas often come into the conversation. But what's the real difference between them?
Natural gases come from deep within the earth, having been formed underground for millions of years. However, there's a modern twist to how we can produce these gases today. By using biogas (created from decomposing organic material), we can make what's known as RCNG (renewable CNG) and RLNG (renewable LNG). This method turns something as simple as leftover food waste into valuable, clean energy.
Just like RCNG and RLNG, RNG starts its life as biogas. But it transforms into high-quality RNG through a cleanup process to remove impurities. This gas is just as versatile and useful as its fossil-fueled counterparts but comes from renewable (and often local) resources.
Understanding Alternative Fuels
Let's take a closer look at CNG, RNG, and LNG. These fuels bring unique advantages, contributing to a more sustainable and diverse energy mix. In this section, we'll break down what sets them apart and why they matter for the future of fuel.
Compressed Natural Gas (CNG)
Compressed natural gas is a gaseous petroleum product that produces a much lower percentage of greenhouse gases (GHGs) than other fuels. CNG compresses natural gas to less than one percent of its volume at standard atmospheric pressure.
CNG is odorless, tasteless, and nontoxic, and it consists mainly of methane with small amounts of nitrogen, carbon dioxide, propane, and traces of ethane. Because CNG emits a lower percentage of greenhouse gases during its combustion process, it is one of the most popular types of renewable fuel. In addition, it costs about 50 percent less than conventional fuels and creates up to 97 percent fewer carbon monoxide emissions.
Commercial vehicles and mass transit buses using CNG typically display a blue diamond CNG sticker. While CNG won’t provide the same amount of power as diesel fuel, it is exceptionally adaptable to modern engines, thanks to its high octane rating.
CNG Pros
- Odorless and tasteless
- Nontoxic
- Produces fewer carbon emissions than gasoline
CNG Cons
- About the same fuel economy as conventional gasoline
- Production creates methane, which is 21 times worse for global warming than carbon dioxide (CO₂)
- Requires high-pressure storage tanks and filling stations
Liquified Natural Gas (LNG)
LNG, or liquefied natural gas, is produced by purifying natural gas and super-cooling it to -260°F (-162°C) to transform it into a liquid. During this process, the gas cools below its boiling point, removing most extraneous compounds. As a result, LNG is primarily methane with small amounts of other hydrocarbons like its compressed counterpart.
Because LNG must be kept at extremely low temperatures, its use in commercial applications is relatively limited. However, LNG is an ideal alternative fuel option for long-range trucks because it takes up less vehicle space than CNG. In addition, the volume of liquefied natural gas is about 600 times smaller than compressed natural gas.
In the United States, some power plants produce and store LNG onsite as an alternative fuel option when electricity demand is high (like during cold and hot weather) or when pipeline delivery capacity cannot meet the increased demand for natural gas. If handled correctly, LNG can be converted into CNG.
LNG Pros
- Easier to store and transport than regular natural gas
- Great transitional alternative fuel for developing areas with less energy infrastructure
- Produces fewer carbon emissions than gasoline
LNG Cons
- Relatively high production cost
- Must be stored in expensive cryogenic tanks
- Limited filling stations and infrastructure
LNG vs. CNG
While LNG and CNG serve as cleaner energy solutions, distinct differences in production, storage, and application make each uniquely suited for specific uses. Understanding these differences is key to making informed decisions about which fuel type best meets the needs of various energy projects.
Let's compare LNG and CNG to shed light on their characteristics.
LNG
- State: Liquefied
- Storage temperature: -260°F (-162°C)
- Storage pressure: Low (just above atmospheric)
- Usage: Long-haul trucks, ships, industrial applications
- Transport & infrastructure: Requires cryogenic storage facilities
- Cost: Higher initial infrastructure and storage costs
CNG
- State: Compressed gas
- Storage temperature: Ambient Temperature
- Storage pressure: High (up to 3,600 psi)
- Usage: City buses, light-duty vehicles, municipal fleets
- Transport & infrastructure: Requires high-pressure storage and filling stations
- Cost: Lower storage and refueling infrastructure costs
LNG vs. Propane
Also known as liquefied petroleum gas (LPG), propane is one of the most widely used types of renewable fuel. Propane is separated from unprocessed natural gas using refrigeration or extraction from heated crude oil using a distillation tower. It is then pressurized and turned into a liquid stored in cylinders and tanks.
In addition to its use in cooking and heating, propane is often used in industrial, refrigeration, agricultural, and catering applications because it is easy to find and transport. In addition, propane is becoming a popular alternative fuel for vehicles because it burns cleaner than gasoline, cutting smog-producing hydrocarbons by 70 percent.
Understanding the distinctions between LNG and propane can help stakeholders make informed choices in their energy usage and infrastructure development. Here’s how LNG and propane stack up against each other in key areas:
LNG
- State: Liquefied
- Storage temperature: -260°F (-162°C)
- Storage pressure: Low (just above atmospheric)
- Usage: Industrial applications, heavy-duty trucks, marine shipping
- Transport & infrastructure: Specialized cryogenic storage and refueling stations
- Cost: Higher due to cryogenic storage and transport requirements
Propane
- State: Liquefied
- Storage temperature: -44°F (-42°C) to room temperature
- Storage pressure: Moderate to high
- Usage: Residential heating, cooking, automotive fuel, industrial applications
- Transport & infrastructure: Standard pressurized storage and widely available refueling stations
- Cost: Generally lower infrastructure and operational costs
Renewable Natural Gas (RNG)
Renewable natural gas (RNG), an energy source that produces zero carbon emissions, can replace natural gas derived from fossil fuels. RNG is made from methane through the decomposition of organic matter.
After the methane is captured, it is processed to ensure that it meets purity standards, resulting in a high-quality gas that behaves similarly to traditional natural gas. Due to its affordability, cleanliness, and reliability, RNG is an attractive option as a fossil fuel replacement.
RNG fuel can power homes, businesses, and vehicles and has the added benefit of being a carbon-negative energy source, removing more emissions than it generates. Although RNG is currently used primarily as a transportation fuel, it has significant potential for use in other applications, such as heating, electricity, and bio-product feedstock.
RNG Pros
- Utilizes existing refueling infrastructure
- Benefits local economies by creating jobs
- Improves local air quality
- Reduces greenhouse gas emissions
RNG Cons
- Limited supply
- Higher production costs
- Limited refueling infrastructure
- Risk of methane leaks during production and transportation
Call FASTECH For Your Alternative Fuel Needs
Whether you’re already committed to using alternative fuel or planning to transition in the future, choosing the right type for your business application is an important decision. FASTECH can help.
At FASTECH, we have over two decades of experience in the energy industry. We specialize in end-to-end solutions, from planning and construction to ongoing maintenance and testing for many renewable and alternative fuels, including hydrogen, CNG, LNG, RNG, and propane. To date, we’ve built more hydrogen stations in California than anyone else.pane. To date, we’ve built more hydrogen stations in California than anyone else.
To start designing your renewable energy infrastructure project, contact us today.
