Continued increases in generation of industrial and municipal solid waste (MSW) has resulted in increased use of landfill sites worldwide. The U.S. Environmental Protection Agency estimates that the MSW generation in the U.S. is approximately 240 million tons (U.S. E.P.A. 2009). A significant portion of the waste is disposed of in landfills. As MSW landfills undergo normal operation, the primary byproducts of the landfill processes are heat, gas, and leachate (i.e., contaminated liquid generated due to passage of liquid through the waste mass). Significant amounts of other types of wastes such as industrial waste, agricultural waste, mining waste, and other types of wastes also are generated in the U.S. on an annual basis.
Turning to FIG. 1, an example of a typical waste landfill 100 is illustrated. Generally, a low permeability barrier 103 is placed over ground surface 105. The waste mass 101 is deposited and landfilled upon the barrier 103. Waste mass 101 may consist of, for example, alternating layers of soil and trash. The landfilled waste mass 101 is covered with a low permeability cover 102. The total depth 104 of waste landfill 100 varies, for example, between tens to hundreds of feet.
In the waste that is buried or landfilled, the organic components decompose resulting in generation of heat and gas that can be converted to usable energy. A considerable amount of energy is produced in this manner. In fact, a mid-sized landfill—such as the Riverview Landfill in Riverview, Michigan—can provide energy equivalent to 10,000 residential homes. A number of recognized techniques for effectively using landfill sites are based on, for example, collecting the gas produced from decomposed waste and converting to energy or maintaining conditions for recycling leachate. Furthermore, these techniques attempt to minimize both nearby contamination and atmospheric pollution.
For example, waste decomposition in a landfill produces an effluent gas, which contains about fifty percent (50%) methane (CH4). This landfill gas in the interior of the landfill is often at a higher pressure than that of the surrounding atmosphere. Consequently, this pressure differential creates a migration pattern of the landfill gas towards both the surface (vertically) and near the edges/perimeter (horizontally) of the landfill. However, methane is an inflammable gas that not only can damage plants in a nearby area but also lead to a danger of explosion. Additionally, emission into the atmosphere of the landfill gas contributes to the “greenhouse effect” as a direct factor to abnormal climate phenomena. With respect to environmental pollution, where the level of methane contained in the landfill gas is in the amount of 50 to 60%, the influence on the “greenhouse effect” is approximately 21 times or greater compared to that of carbon dioxide (CO2). However, as methane also has a beneficial combustion property, it is possible to collect the gas from a landfill to provide an efficient energy resource.
A conventional technique of controlling the withdrawal of gas from a landfill site is to drill deep vertical wells, such as well 106 in FIG. 1, into the landfill. These vertical wells are attached to a network of pipes and gas pumps (not shown) to vacuum/extract gas from the wells. An example of such a system implementing this technique is disclosed in U.S. Pat. No. 7,448,828, to Augenstein et al., filed Feb. 23, 2007 for a “Landfill design and method for improved landfill gas capture,” which is hereby incorporated by reference in its entirety. This system contemplates an improved method for collecting landfill gas by minimizing the collection of atmospheric air with the gas.
Another example of effective landfill use controls gas generation rates of the landfill through leachate regulation. This technique involves regulating both temperature and pH levels of leachate to be recycled and continuously injected into a deposit of wastes. For example, see U.S. Pat. No. 6,334,737, to Lee, filed Dec. 17, 1999 for a “Method and apparatus of controlling landfill gas generation within a landfill,” which is hereby incorporated by reference in its entirety. Monitoring and controlling a variety of conditions for recycling leachate provides the advantage of maintaining, as consistently as possible, the level of gas production during the landfill process.
Significant amount of research and development has been reported for gas and leachate. However, less information is available on heat generation in landfills. Elevated temperatures can affect the ongoing biochemical processes (e.g., decomposition) and mechanical and hydraulic properties/behavior of the wastes. Operational and climatic conditions have significant effects on heat generation and transfer in landfills. For example, see Yesiller et al., for “Heat Generation in Municipal Solid Waste Landfills” (Yesiller, N., Hanson, J. L., and Liu, W.-L., Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 131, No. 11, p. 1330-44 (2005)) and Yesiller and Hanson, for “Analysis of Temperatures at a Municipal Solid Waste Landfill” (Yesiller, N. and Hanson, J. L. “Analysis of Temperatures at a Municipal Waste Landfill,” Sardinia 2003, Ninth International Waste Management and Landfill Symposium, Christensen et al. Eds., CISA, Italy, p. 1-10 (2003)), which are hereby incorporated by reference in their entirety. These effects may be short-term (e.g., reaction rates) and/or long-term (e.g., microbial population balance within the waste). In general, waste decomposition rates generally increase with increased temperatures up to a point of killing microbial populations (e.g., approximately 70° C.).
Temperatures within landfills undergo seasonal fluctuations near the surface and edges/perimeter of the landfill due, in part, to conductive and convective heat transfer. Elevated temperatures are correspondingly observed within the landfilled mass at central locations. Accordingly, optimal decomposition and gas production conditions are not uniform within a landfill mass.
Current systems for energy extraction from MSW landfills focus on the generation and distribution of gas and leachate in landfills. However, such systems do not take advantage of a detailed analysis of spatial heat distribution or a long-term thermal trend of landfills. In addition, systems are not available for controlling and manipulating temperatures in landfills. Furthermore, current systems do not provide a method for creating a symbiotic energy source between the landfill and nearby facilities to create optimal operating conditions.
Accordingly, a system and method for controlling and manipulating temperatures and extracting heat from a landfill that considers heat generation and temperature distribution within a landfill is desired.
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