The clean-burning properties of natural gas have made it an attractive fuel alternative for transit, refuse, and other heavy-duty vehicles, and with new retrieval methods like ‘fracking’ lowering prices, the time could be right for natural gas to become a viable alternative fuel. There are two primary types of natural gas fuel: compressed natural gas (CNG) and liquefied natural gas (LNG); while CNG is already in use in many fleet vehicles and public transport systems in the US, LNG so far has only smaller real-world examples of its utility, but perhaps greater promise in the long-term.
In order to use CNG, natural gas is extracted directly from an existing pipeline, without the need for intermediary transportation or processing. To create LNG, however, natural gas must be cryogenically liquified to -260°F in order to reach a liquid state, and then usually shipped via refrigerated tanker trucks to fuelling stations. Both fuels are lightweight to transport, and cost up to 50% less than diesel. In most cases so far, CNG has been used for vehicles that only need to travel shorter distances and return to the fuelling station often, while LNG has been the choice for long-distance shipping.
Both CNG and LNG are considered alternative fuels under the Energy Policy Act of 1992. Yet while natural gas as a clean-burning alternative to gasoline has long been in use for commercial and industrial purposes, only a fraction of the 1% of all the natural gas in the US is used for transportation fuel. But that is poised to change. As oil prices continue to rise and political tensions in many oil-producing countries remain highly volatile, there are strong incentives for drivers to move towards natural gas as a fuel alternative. As a secure, domestic fuel supply, natural gas helps reduce US dependence on foreign oil, while providing additional environmental benefits.
Natural gas powered vehicles (NGVs) of all sizes are, theoretically speaking, a viable alternative to gasoline and diesel vehicles. Depending on the driver’s requirements, either form may be suited to meet their needs.
Comparing LNG and CNG
A clear, non-toxic liquid, LNG is produced at a relatively low cost. When natural gas is converted to liquid by a cooling process, it can then be safely shipped to a regasification facility or held in an insulated storage tank specifically designed to handle the low temperature of LNG. Typically warmed to make natural gas again once it has reached its destination, LNG can also be kept as a liquid to be used as a transportation fuel. In this case it is principally used for Class 8 tractor trailers or semis travelling over long distances.
LNG is more economical to transport and can be stored in larger quantities than CNG because it occupies 1/600th the volume of natural gas. When compared to CNG, LNG contains 2.4 times more energy per diesel gallon equivalent. Additionally, because LNG is a liquid, it has a refuelling speed similar to that of gasoline or diesel. Although according to the US Federal Energy Regulatory Commission (FERC), there are only eight LNG processing facilities located in the US, and there are plans in the works for 40 more.
CNG, however, has penetrated the US market with somewhat greater success thus far. Primarily sourced from domestically drilled natural gas wells, CNG is like LNG in that it is odorless, colorless, and non-toxic, but it is already available as a viable renewable option in many areas; to take one prominent example, Honda is currently building a CNG gas station in Columbia, Ohio, in concert with Columbia gas of Ohio, building on the car company’s success by helping to build CNG infrastructure in California and other states. California, the state most open to the idea of NGVs in general, utilises CNG exclusively for its transit agency buses. CNG vehicles are also increasingly seen on the street as UPS delivery vans and USPS vehicles, commercial trucks, taxi cabs, and light-duty trucks, and heavy-duty vehicles like street sweepers and school buses.
When comparing both options to diesel or gasoline, it is important to remember the relative energy density and the cost, weight and size of the necessary on-board storage equipment. CNG only has an energy density equal to about a quarter that of diesel, whereas LNG is approximately twice that. LNG is the best option for a truck that will be going over 200 miles, because CNG trucks would have to add additional tanks to achieve longer ranges.
While most consumers are enthusiastic about the idea of NGVs finding a place on the road, David Friedman, deputy director of the Clean Vehicles Program of the Union of Concerned Scientists, believes that there are "serious challenges in spreading NGVs to the general public", because of the exorbitant cost of creating a domestic fuel infrastructure. Many state transit officials are also interested in natural gas fuel, but some have been swayed by the lower costs associated with propane, a by-product of oil and natural gas drilling. CNG and propane are increasingly at odds, as different transportation fleets seek out cheaper alternatives to gasoline and diesel.
The enormous costs associated with building the stations necessary to dispense natural gas are its weakest attribute. But energy producers and the owners of refuelling stations should remember that while they would foot a larger bill now to develop the infrastructure, it would offer a more sustainable business model for them in the long-term. Additionally, they would ultimately be bringing the US that much closer to having autonomy over its energy – never mind the pollutants and emissions this would help to reduce.
Written by Spencer Blohm. Edited by Ted Monroe
Read the article online at: https://www.lngindustry.com/small-scale-lng/11092014/spencer-blohm-looks-at-the-benefits-of-lng-and-cng-for-small-scale-usage/