Trading Trash For Gas In L.A.

Stuart G. Tays

To convince trash haulers to convert their vehicles to converted natural gas (CNG) and refuel at the landfill after dumping their loads, the Los Angeles County Sanitation Districts (LASCD) sponsors a unique "trash for gas" program.

The LACSD system, in conjunction with the South Coast Air Quality Management District (SCAQMD), uses membrane gas separation technology to produce compressed natural gas (CNG) from landfill gas.

LACSD's Puente Hills landfill has a nominal fill rate of 12,500 tons per day and produces more than 23,000 scfm of landfill gas, which is collected and used to produce approximately 50 MW of power. The landfill now produces excess gas of over 400 scfm, which can be used to produce a clean, alternative vehicle fuel (see chart on page 62).

Limited air filtration is acceptable for flaring and power generation, but must be held to very low limits to produce vehicle fuel, so a new pipe line was added to draw, at a slow rate, a richer "core" gas from deep wells. The gas quality exceeds the specification requirement, with methane concentrations as high as 99 percent and oxygen less than 0.3 percent.

The program primarily depends on engine manufacturers to produce low-emission, dedicated CNG engines, an emerging technology with a limited number of suppliers.

LACSD has a GMC Sierra pickup that runs on CNG and a dedicated CNG GMC water truck with a Hercules 5.6 liter engine.Two private refuse collection companies are participating in a program with LACSD, with funding provided by SCAQMD, to convert a refuse packer and a roll-off to CNG.

Air emission testing is being conducted on all vehicles to ensure their compatibility with CARB regulations.