Do you ever wonder why you hear so much about compressed natural gas (CNG) made from landfill gas but rarely hear of landfill projects involving liquefied natural gas (LNG)? It’s likely because almost all LNG is made from fossil fuel. There’s only one plant in the U.S. making LNG from landfill gas, and these projects are scarce for a few reasons.
The main driver for landfills to clean their gas to be made into transportation fuel is monetary, and CNG can cost as much as 50 percent less to produce than LNG. With both renewable fuel types, owners capitalize on renewable identification number (RINS) credits or, in California, low-carbon fuel standard credits (LCFS).
“While credits are available for both renewable natural gas types, almost no one is using LNG because CNG is typically much more economical,” says Scott Edelbach, COO and general manager at TrueStar, who builds and maintains fueling stations. “It’s less energy intensive to produce. Plus, you can put it in the pipeline and move it to any CNG station in the lower 48 states. Technically, you can put LNG in the pipeline, but it’s much more involved.”
LNG is made through a cryogenic cooling process that liquefies methane so it can be stored as a dense liquid fuel. The temperature must be negative 260 degrees Fahrenheit.
LNG from landfill gas was never very common, but at one time it was somewhat more attractive. Large trucks could hold triple the volume of this dense fuel than CNG. However, as CNG technology improved, tanks got lighter and their capacity increased, significantly raising the hours a truck could stay on the road without having to stop and refuel, explains Sean Mezei, president of Dekany Consulting in Vancouver, Canada, which supports developers and operators of renewable natural gas projects.
Waste Management, with its partner Linde North America, built a LNG facility at the Altamont Landfill in Livermore, Calif., in 2009. In 2017, it generated 6,300 gallons of LNG (about 3,750 diesel gallon equivalents) per day, enough to fuel about 170 of the refuse company’s collection trucks, already configured for LNG.
The project, however, is complex and expensive, necessitating a large-scale operation. For one challenge, making LNG requires far greater reductions in carbon dioxide, to prevent buildup of dry ice in LNG processing equipment, than CNG does.
“You have to get carbon dioxide down to 2 percent to put [CNG] gas in the pipeline, but for LNG, it would need to be .005 percent. And it’s not just purifying carbon dioxide that’s the challenge, but the equipment and processes to cool the methane to make it into liquid are costly,” says Mezei, who hasn’t worked on an LNG project in North America in 12 years.
In late 2006, Prometheus Energy began a small-scale project at Orange County, Calif.’s Bowerman Landfill, with plans to go commercial, providing fuel for the Orange County Transit Authority. The operation shuttered without reaching its goal.
Waste Management still runs the Altamont facility today, which it says is the largest LNG facility in the world and the only plant of its kind in the U.S. The company would not comment on how it makes the project work financially or why it makes LNG at this site.
But landfill gas-to-fuel experts have pointed out that California has made it nearly impossible to put landfill gas in the pipeline. The Altamont plant makes it possible to capture the gas, convert it to LNG and trailer it to already existing LNG stations, which were set up when trucking it was the only option and when trucking LNG was much cheaper than trucking CNG.
The landfill owner also qualifies for credits.
“The way to get a higher value for [LNG or CNG] through the credits is to clean it, convert it and burn it in a vehicle,” says Edelbach.