Municipal landfills are becoming an increasingly attractive host for CHP, providing unique opportunities to address community energy and environmental needs.
Modern landfills are not simply holes in the ground where we toss our garbage. Rather, modern solid waste management facilities must meet stringent performance requirements to prevent contamination of air, water and land. Typically, clay or plastic barriers and leachate collection systems are required to prevent the migration of contaminants to surrounding soil and water sources. Additionally, refuse is regularly covered with clay or dirt to limit its exposure to air. In this oxygen-starved environment, bacteria that lives in organic materials such as food wastes, paper or yard clipping cause these materials to decompose, producing methane and carbon dioxide. Though not a renewable resource, landfill gas will be in great supply absent major innovations in solid waste management systems and could supply up to 1 percent of the nation's energy demand.
The US Environmental Protection Agency (EPA) requires all large landfills to install collection systems at landfill sites to prevent landfill gas from building up and causing an explosion, and to minimize the release of methane, a major contributor to global climate change. Methane is a highly potent agent of global climate change, having about 23 times the negative impact on a pound-by-pound basis as CO2.
Landfill gas is collected from landfills by drilling "wells" into the landfills, and collecting the gases through pipes. Once the landfill gas is processed, it can be combined with natural gas to fuel conventional combustion turbines or used to fuel reciprocating engines, turbines, microturbines and other energy technologies. Landfill gas may also be used in fuel cell technologies, which use chemical reactions to create electricity, and are much more efficient than combustion turbines. According to the U.S. Department of Energy, more than 350 landfills tap into this source of energy.
Because landfills do not require much energy on-site, a key component to a successful landfill gas CHP proect is close proximity to industrial or other facilities with significant power needs. Other factors to consider include:
Landfill Gas Case Study [PDF file]