Although landfill gas (LFG) typically is used to generate electric power, researchers have developed a new compression process that allows LFG to be used in vehicles as fuel.
The Puente Hills Landfill in Los Angeles County contains more than 70 million tons of refuse, producing 27,000 standard cubic feet per minute (scfm) of LFG.
Approximately 250 scfm of this gas is used in the landfill's Clean Fuels Facility, an outdoor prototype which consists of compressors, activated carbon for pre-treatment, semi-permeable membranes to remove carbon dioxide and water vapor, compressed landfill gas (CLG) storage tanks and a CLG dispenser.
The resulting CLG contains 96 percent methane and is dispensed at 3,000 psi using commercial compressed natural gas (CNG) nozzles. After two and one-half years of operation, the facility has produced more than 25,000 gasoline gallons equivalent (GGE) of CLG.
The gas was tested in a 13-vehicle fleet including Dodge, GMC, Freightliner and International trucks which had been converted to use dedicated or dual-fuel compressed natural gas. When the compressed LFG was analyzed, researchers found that NMHC, CO and NOx emissions were essentially the same as those of compressed natural gas, which emits less pollution than gasoline or diesel.
Likewise, dynamometer tests showed CLG-powered vehicles are not significantly different than CNG-powered vehicles. However, CLG generates approximately 5 percent less energy and its octane rating approaches that of pure methane.
Despite these results, compressed LFG is not yet economically competitive with compressed natural gas. Still, landfills can produce CLG economically with rates reaching 2,000 to 3,000 GGE per day (see chart).
Ideally, CLG will reduce a refuse vehicle's refueling time - re-using LFG efficiently and saving money for collection fleets.