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Landfill Gas Overview
All across the country, landfills release gas containing methane and carbon dioxide, two well-known greenhouse gases, along with other compounds identified as pollutants by the US Environmental Protection Agency (EPA). While landfill gas poses many hazards to safety, health, and the environment, it also presents a unique opportunity to create value from a waste stream through the generation of electricity, heat, or steam. Procurement of energy from landfill gas projects can improve a corporation's environmental profile, a significant issue for corporations that have made public commitments to reduce their greenhouse gas (GHG) emissions or procure green power. Landfill gas (LFG) procurement is both an opportunity for corporations to reduce their GHG emissions footprint and to create a more diversified energy portfolio.
Landfill gas is an attractive renewable energy alternative for many applications because of its 24x7 availability and high capacity factor (between 95 and 98%). The primary means for industrial and commercial consumers to use LFG is through direct use or electricity generation. Medium BTU direct use applications typically present a more competitive option for many industrial consumers. However, a potential reinstatement of production tax credits, deregulation in electricity markets, and expansion of net metering provisions provide increasing opportunities for electric generation from landfill gas to be competitive with market alternatives.
Landfill Gas Resources
As can be seen from the figure below, landfill gas-to-energy projects have steadily increased since the 1980s. According to the US EPA Landfill Methane Outreach Program as of April 2002, 325 landfill gas-to-energy (LFGTE) projects in operation or under construction with an additional 500 landfills are large enough support future projects[1]. The average capacity of LFGTE projects currently in operation is 4.1MW. Using this average capacity results in potential capacity (in addition to the 814 MW that are currently in place) of between 820 and 2050 MW throughout the US.
Many medium to large landfills (5,000-15,000 metric tons) required to flare LFG may find it economically attractive to convert the LFG to energy rather than collecting the gas as a waste product. Under the Public Utility Regulatory Policies Act (PURPA), a local utility is required to buy power generated at a landfill (which is a "Qualified Facility") if the power can be sold at a price typically offered by the utility. With deregulated markets, however, prices for power generated from LFG would need to be competitive with conventional electricity generators.
Depending on the size of the landfill and the technology used, LFGTE projects can produce gas at economically feasible volumes between 10-20 years. LFG is continuously produced by landfills, although the rate at which it is produced depends on the temperature, moisture, and type of wastes contained in the landfill. Older landfills and small landfills (less 500,000 metric tons) are usually neither economically feasible to develop or capable of supporting LFGTE gas systems. LFGTE developers usually prefer a landfill with at least 2 million tons of waste in place.
Technology
LFG can be used to generate electricity or can be used directly into some industrial processes to generate heat and steam. LFG is captured from a closed portion (cell) of a landfill. A typical landfill gas collection system is composed of the extraction well in the cell, a condensate collection and treatment system, and a compressor or blower to pull the gas from the collection well. Each landfill will have numerous cells from which the gas is collected and piped to the user, generation equipment, or flared.
Currently, internal combustion engines and gas combustion turbines are the most economically feasible technologies for landfill gas-to-electricity projects. IC engines are by far the most commonly used technology due to their low costs and high efficiency. However, IC engines can emit a high level of NOx and may not be appropriate for non-attainment areas. Gas turbines emit lower levels of NOx, but require a higher, consistent volume of gas. Micro turbines can also be used in non-attainment areas where NOx emissions must be minimized. There is also current experimentation with landfill gas powered fuel cells.
Environmental Impacts
Landfill gas is produced in landfills by the decomposition of organic materials. The primary components of LFG are methane (50%) and carbon dioxide (48%). In addition to these gases, LFG contains trace amounts of hydrogen, oxygen, nitrogen, and non-methane organic compounds (NMOCs), which include volatile organic compounds (VOCs), hazardous air pollutants (HAPs), and odorous compounds.
The United States is the largest contributor to global man-made green house gas (GHG) emissions. Methane is one of the most damaging GHGs, with 21 times the global warming potential of CO2, and landfills account for 35% of all man-made methane emissions in the U.S.[2] Landfill gas-to-energy projects provide environmental value by capturing methane emissions from landfills and displacing fossil fuel.
Since the 1980s, landfill operators have been installing systems to collect and reuse landfill gas. In 1996, EPA created the New Source Performance Standards (NSPS) and Emission Guidelines for Municipal Solid Waste (MSW) landfills. The regulation requires LFG to be collected at landfills that: (1) have a potential capacity greater than 2.5 million metric tons (MMT), and (2) have the potential to emit more than 50 MT (metric tons)/year of non-methane organic compounds (NMOCs). The process of reducing NMOCs (which contribute to smog production) also simultaneously reduces methane emissions. This regulation affects between 600-700 landfills, which is approximately 18% of landfills in the country.
Estimated Annual Carbon Equivalent Emission Benefits From Operating LFGTE
Projects at NSPS & non-NSPS Landfills (LMOP, 2000)
Projects operating as of the beginning of 2000 resulted in the annual methane reduction of 12.8 million metric tons of carbon equivalent (MMTCE). The EPA LMOP estimates that for every MW of electricity generated from LFG, the greenhouse gas benefit is equivalent to taking 8,800 cars off of the road, or planting 12,000 acres of forest, or preventing the use of 93,000 barrels of oil. The benefits of LFGTE systems for greenhouse gas reduction are apparent.
However, when LFG is converted to energy in an internal combustion engine or through another form of combustion, dangerous compounds are emitted, including NOx, carbon moNOxide, and sometimes dioxin. Dioxins are formed in combustion processes and the EPA reported that dioxin emissions from LFG combustion are comparable to oil or coal combustion (Inventory of Sources of Dioxin in the United States, EPA/600/P98/002Aa). The highest dioxin emissions from LFGTE systems are also reported to be 75-430 times less than municipal waste combustion.
Challenges for Landfill Gas
The primary risk associated with electric generation projects fueled by landfill gas is whether the supply of landfill gas will be sufficient to support the generating capacity installed for fifteen to twenty years, making long-term purchase power agreements difficult to negotiate. In addition, the cost of electricity from lfg projects is higher relative to conventional fossil fuel based electricity. With the sunset of the Section 29 and Section 45 tax credit developers are finding it difficult to compete in the electricity market. However, provisions for tax credits for landfill gas (in the range of $10 per MWh to $18 per MWh) is included in many of the energy bills circulating in the Senate and Congress.
The viability of medium btu direct use projects are require that the landfills be situated well within a ten mile radius of the procuring facility. In the case of direct use applications, the industrial user must invest in equipment or processes that are capable of switching between landfill gas and traditional fuels is required. The industrial user must also manage the long-term uncertainty and variability of flow, Btu value, and impurities in the gas stream. In spite of these challenges, the EPA Landfill Methane Program estimates that 390 direct use lfg projects projects are operating or under construction.
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