Mack Trucks and Acrion are wrapping up a program testing the conversion of Landfill Gas (LFG) to LNG to fuel garbage trucks. John Atkinson, who works for Inform, has details about the project and background about the process on his site.

The joint venture headed by Mack [Trucks] and Acrion is investigating the feasibility that refuse collection trucks serving a landfill operation could be run on fuel made from LFG produced inside the landfill itself. [...]

Converting a 12-year-old diesel refuse truck to run on liquefied natural gas thus yields enormous bang for your eco-buck, with reductions of up to 90% for particulate matter, 70% for NO_x, and 80% for non-methane hydrocarbons (** but no greenhouse gas reductions). [...]

The key to the system is Acrion’s clever CO₂ wash process, developed with DOE assistance...

As noted in Mack’s press release, landfill operators are required to take care of LFG anyway, and this process reuses the gas more fully than electricity generation. Not only that, but the value of the fuel produced is greater than electricity, and Mack is hoping to offer special package deals on equipment and trucks that will make the entire process cost effective for landfill operators without government incentives—an important and rare achievement for alt-fuel projects at this stage in the game.

Landfill gas is a natural product of the biological decomposition of organic waste. The resulting gas has a variety of chemical components, but at most sites the two principal components are methane (CH₄) and CO₂, with much smaller amounts of hydrogen sulfides (H₂S), inerts and volatile organic compounds (VOCs).

With that high methane (natural gas) content, LFG has been seen as a potential energy source for some time. First tapped in the 1980s, it has been burned to power engine- or turbine-driven electrical generators, and used in other natural gas (methane) applications.

A big problem with LFG projects is the gas’ trace components. Typical LFG contains heavy hydrocarbons (both aliphatic and aromatics such as benzene) as well as numerous chlorinated hydrocarbons. These trace compounds are, in some cases toxic or hazardous and also cause rapid failure or engine and turbine components. There are now federal statutes which cover landfill emissions.

In addition to the Acrion process used in the Mack test, there is also the Kryosol Process developed by Kryosol Energy to clean up the LFG.

LNG is not the only possible end product. Because the output of the Acrion (or Kryosol) process is methane, it could also be reformed to produce hydrogen, or chemically changed to produce methanol or dimethyl ether.

Resources:

• DOE report (1999): Liquid Natural Gas: An Alternative Fuel from Landfill Gas (LFG) and Wastewater Digester Gas