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Composting organic waste results in gases such as methane. Capturing these landfill gases and transforming them into biofuel helps the environment and reduces CO2 emissions. Waste material at the Altamont landfill site near Livermore, just east of San Francisco, is put to good use in the on-site biogas plant. The gas released by this material is captured and converted into liquefied natural gas, or LNG.
The largest biogas plant in the world is the result of a partnership: together with America's leading waste management company, Waste Management, Linde built a modern gas liquefaction plant. The Livermore facility has been converting waste to liquefied gas since September 2009. Within one year, it yielded more than 7.5 million litres of the CO2-neutral fuel.
Compared to diesel vehicles, refuse trucks fuelled by biogas produce 97 percent less greenhouse gases. The use of biogas enables savings of circa 9.5 million litres of diesel fuel per year. This reduces greenhouse gas emissions by 30,000 tonnes – which is roughly equivalent to taking 5,000 cars off the road. In addition, combustion of liquid biogas is much cleaner, and motors that run on it emit around 90 percent less particulate matter.
Prerequisite: oxygen starvation and humidity
Methane and other landfill gases are formed when decomposing matter is starved of oxygen in warm, damp conditions. Bacteria then breaks down the organic waste and converts it into methane and carbon dioxide. The adjoining gas liquefaction facility developed by Linde then compresses and purifies the biogas, removing sulphur, carbon dioxide, nitrogen, alcohols and other impurities. Finally, the gas is cooled to minus 162°C in a heat exchanger and thus liquefied.
The electricity required for this process is also obtained from landfill gas. When the gas is burned, it creates steam which drives an electricity generator. Tankers transport the liquefied gas to the landfill site's gas filling stations and beyond to provide the refuse truck fleet with carbon-neutral fuel. Over 300 vehicles per day can be fuelled and operated with the biogas from Waste Management.
Second biogas plant in planning
This project has won a number of environmental awards. The US's EPA (Environmental Protection Agency) selected the facility as its 2009 project of the year. In November 2010, the plant received the Governor's Environmental & Economic Leadership Award from California's then Governor Arnold Schwarzenegger.
Plans are under way to expand this project even further. There are over 1,000 landfill sites in California alone, and Waste Management operates 25,000 refuse collection trucks. Linde and its partner are therefore planning a second biogas liquefaction plant.
At a glance
Biogas is captured, cleaned and either compressed or liquefied into an environmentally friendly fuel
Reduction of methane emissions, which are 25 times as damaging to the atmosphere as CO2
Linde develops and produces plants for capturing, cleaning and liquefying gas from landfill, biomass or animals
Customised solutions so that customers can reuse gas; sale of waste gases to other industries
Altamont, California, USA: Joint venture with the US company Waste Management Inc.: Landfill gas generated via fermentation is used to fuel 300 refuse trucks in California
Participation in joint efforts in Stockholm, Sweden, to deliver up to eleven biogas gas stations