Kamis, 10 Desember 2009

Landfill Gas Capture

Methane is a primary component of landfill gas and a potent greenhouse gas when released to the atmosphere. 20 times more damaging than CO2. Reducing methane emissions by capturing landfill gas and using it as an energy source can yield substantial energy, economic, and environmental benefits. Each day millions of tons of municipal solid waste are disposed of in landfills around the world. landfill gas is created as a natural byproduct of decomposing organic matter, such as food and paper, disposed of in these landfills. landfill gas consists of about 50 percent methane (CH4), the primary component of natural gas, about 50 percent carbon dioxide (CO2), and a trace amount of non-methane organic compounds. Globally, landfills are the third largest anthropogenic (human-induced) emission source, accounting for about 12 percent of global methane emissions or nearly 750 million metric tons of CO2 equivalent (MMTCO2E). Below is a chart of world landfill gas production by country as of 2007.


Figure 1: World Landfill Gas Production By Country As Of 2007


Figure 2 : World Landfill Gas Production By Country As Of 2007

Recycling Waste

The chemical industry continues to find creative ways of recycling and reusing waste streams. Dow recently began operating a novel system for reusing municipal wastewater at the Terneuzen site in the Nether-lands. In collaboration with local authorities and a local water pro-ducer, this site accepts more than 2.6 million gallons of municipal household wastewater every day. The local water producer removes residual contaminants, and Dow then uses more than 70 percent of this water to generate high-pressure steam. After the steam is used in production processes, the water is again used in cooling towers until it finally evaporates into the atmosphere.
This is the first time municipal wastewater is being reused on such a large scale in the industry. Three million tons of water per year was previously discharged into the North Sea after a single use. Now this water is recycled for two more applications and has resulted in 65 percent less energy use at this facility compared to the alternative option of desalinating seawater. The reduction in energy use is the equivalent of lowering carbon dioxide emissions by 5,000 tons per year. This concept can be applied at other locations around the world.
Another unique case of recycling is the use of landfill off-gas (Figure 2). Instead of using natural gas, Dow has piped methane off-gas from a local landfill to its Dalton, Georgia, latex manufacturing plant. The gas is used as fuel to generate steam for the production of latex carpet backing. This site is expected to use approximately 160 billion BTUs per year of landfill gas (the energy equivalent of 1.4 million gallons of gasoline) that would otherwise be emitted into the atmosphere.


FIGURE 3 : Recycling landfill off-gas for energy in Dalton, Georgia.
(1) Landfill waste is structured. (2) Anaerobic bacteria decompose the municipal solid waste. (3) Methane off-gas is generated. (4) A system of pipes and blowers collects gas and delivers it to a central location. (5) Gas is used as fuel to make steam. (6) Steam is used by the Dow emulsion polymers plant to manufacture latex carpet backing.

Municipal landfills are the largest source of human-generated methane emissions in the United States. As a greenhouse gas, methane has more than 20 times as much global warming potential as carbon dioxide. By capturing and burning methane, the Dalton facility will reduce the use of fossil fuels and will reduce methane emissions from the landfill. The reduction of greenhouse gases is equivalent to 24 million pounds of carbon dioxide per year.

Landfill Gas

Produced by the biological decomposition of waste placed in a landfill site, LFG represents both an environmental liability and a unique renewable energy resource. Landfill gas - composed primarily of carbon dioxide and methane - also commonly contains additional trace constituents such as hydrogen sulphide, mercaptans, vinyl chloride, and numerous other volatile organic compounds. Concerns that are often associated with LFG relate to odours, air quality impacts and explosion hazards. If released to the atmosphere untreated, LFG is also a potent greenhouse gas contributing to global climate change. Collection of LFG to control impacts also results in the creation of a source of green energy. The methane component of LFG contains energy that can be used to generate electricity, heat buildings, fuel industrial processes, or run vehicles. Utilization of energy from LFG not only aids in the control of local environmental impacts, but also avoids consumption of fossil fuels that would otherwise be required to generate an equal amount of energy. Collection and utilization of LFG represents a very significant opportunity to reduce greenhouse gas emissions to the atmosphere.


Figure 4: Landfill Gas Collection & Utilization System

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