The Energy Collective has an interesting look at the relative merits of CNG and LNG for fueling heavy road transport vehicles (which seems to be part of the general effort on the part of Shell and others to try to boost the use of natural gas for transport) - A New Debate Emerges: LNG or CNG for the Long Haul
Amidst the constant discussion of plentiful domestic natural gas and its use as a transportation fuel, an unusual technological and philosophical debate has emerged. Those familiar with the industry know that until recently, fleet managers considering the conversion from gasoline or diesel to natural gas had basically two options: compressed natural gas (CNG) was the choice for any return-to-base, short mileage vehicles, and liquefied natural gas (LNG) was the option for long-haul on-highway Class 8 trucks, also known as tractor trailers or semis. The reasoning behind this was relatively straightforward, and more or less a product of a few issues inherent to gaseous rather than liquid fuel (energy density, tank storage capacity, re-fueling time). However, due to a variety of innovations, a paradigm shift may be under way.
In comparing alternative fuels to gasoline or diesel, a major consideration is the relative energy density and associated cost, weight and size of on-board fuel storage. For natural gas, when compressed, its energy density is only about a quarter that of diesel, and when liquefied just 60% of the energy density of diesel. Therefore, either option requires greater fuel storage capacity to achieve a comparable range, which means more and/or larger tanks.
Compared to CNG, LNG contains 2.4 times more energy per diesel gallon equivalent (DGE). Moreover, since LNG, like diesel and gasoline, is a liquid, one could achieve comparable refueling speed, whereas the level of compression required to “fast-fill” with CNG is very high (~3,600 psi). As a result, for the long-haul trucking sector, the energy density and associated cost(s), weight and on-board storage capacity of LNG have long been viewed as the more attractive, viable option.
Relatively recent advances in tank storage capacity and “fast fill” refueling technology have allowed room for debate as to whether LNG really is the only natural gas option for the long-haul trucking industry. To best highlight the philosophical nature of this emerging debate, it may be best to look at two of the leading natural gas refueling infrastructure providers, Clean Energy Fuels (CLNE) and Trillium CNG (TEG subsidiary), each of which has taken an opposing view on this topic.
Clean Energy was the first mover in the industry and is now by far the largest provider of natural gas refueling infrastructure in the US. They are betting big on the fact that CNG is the choice for local urban fleets (refuse vehicles, delivery trucks, etc.) but that LNG is the option for long-haul tractor-trailers. Alternatively, Trillium CNG, along with their partners at AMP Americas, a Chicago-based investment firm, strongly believe that CNG should be the choice for all heavy-duty fleets, regardless of distance traveled or route. Without commenting on which approach is better, the following will help to explain each company’s thought process.
CNG and LNG are both proven forms of natural gas storage, with distinct advantages over diesel and gasoline when used as a transportation fuel. To produce CNG, natural gas is taken directly out of the United States' expansive network of natural gas pipelines, whereas LNG must be cryogenically liquefied to -260 degrees F (to become a liquid) and often must travel via ground transportation (tanker truck) to stations across the US. With pipeline access, LNG can alternately be produced from the gas grid through MMLS (movable modular liquefaction system) units. On-site, CNG is compressed immediately and enters a truck in a process that is almost identical to traditional fueling practices, from the driver’s perspective. On the other hand, LNG requires drivers to wear a mask and gloves to protect themselves against cryogenic burns.
For the Class 8 truck sector, Trillium/AMP have made the decision to build CNG stations because, in their words, “it is a cheap, simple and safe way to transport and store natural gas.” They have also found that the additional simplicity of CNG over LNG makes it an easier product to maintain, as well as a less expensive product to produce. For example, according to their general pricing model and marketing materials, on average, “end users of CNG gain a $.48 advantage over LNG, for a product that works equally well, has less associated hazards and a greater built-in infrastructure across the US.”
Alternatively, Clean Energy has invested heavily in LNG infrastructure, including two liquefaction facilities, to supply their network of 150 existing refueling stations and more in the works that they refer to as America’s Natural Gas Highway. While the production and transport of LNG require greater technical expertise and significantly more capital than for CNG, LNG cost savings are realized on refueling infrastructure/operation. This is primarily a result of the high electricity demand/cost required to achieve the compression necessary for a “fast-fill” CNG station. There is also greater flexibility in where a station can be located (no need for natural gas pipeline access) and in future expansion of existing stations.