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Yeroc.us
Searching for Order in this World of Entropy

About the WTE Database

I have an interest in power plants (much as someone else may have an interest in classic cars or Star Wars memorabilia). Waste-to-energy plants are particularly interesting, possibly because of their alchemical allure and the fact that they are an elegantly engineered solution to society's most basic problems.

Just as many other aspiring young people spend their time chasing celebrities around with cameras, building web sites and forums dedicated to hot models, powerful cars, sports teams, and what not, I have decided to build mine dedicated to waste-to-energy plants.

About WTE

Waste-to-Energy (WTE) is a method of waste treatment. Plastics, composite materials, and extreme heterogenity make modern municipal solid waste a treatment nightmare, and separation and recycling of everything is impractical. Landfilling remains the main method of disposition worldwide, though it is nothing more than long-term interim storage. Most wastes which are landfilled can be further treated, providing added benefits to society and the environment.

By far the most common WTE process is combustion, also known by a "dirty" word - incineration. Waste is burned in excess air at temperatures usually exceeding 800°C in a variety of furnace designs. The heat from combustion produces steam or hot water in a boiler which is used for electricity production or heating purposes. Air pollution control equipment is used to clean the flue gases before they are released to the atmosphere.

Management of waste ideally follows the hierarchy below:

  1. Don't produce waste in the first place (cut packaging, make products more durable, reduce consumerism).
  2. Reuse items which would otherwise be considered waste.
  3. Recycle the material value of waste (e.g. melt steel cans down to be used as raw steel).
  4. Recovery of the nutritive value of waste (composting of organic matter such as food scraps, ideally close to the point of production).
  5. Recovery of the energy value of waste (through incineration or other means).
  6. Disposal of treated residues to the environment (land application, landfilling).
  7. Dispose of waste directly to the environment without prior treatment (landfill).

WTE Benefits

Further treatment and reduction of waste with energy production, as opposed to direct landfilling, is the main benefit of waste-to-energy. The extent of this benefit will vary depending upon the nature of waste (how well have recyclable materials been separated?) and the design of the plant (is both the low-grade heat from the process utilized along with the high-grade electricity, or does the plant only utilize one?). Incineration has traditionally been used to render waste inert, to reduce its volume, and in some cases to reduce the toxicity. Energy recovery became much more commonplace beginning in the 1970s. With modern furnace designs and air pollution control equipment, the air emissions of such plants are comparable to any other power station, usually far cleaner than coal-burning plants but worse than natural gas burning plants in terms of “traditional” air pollutants, and lower than all fossil-fuel generation in terms of prehistoric carbon emissions.

WTE Downsides

Ideally, we do not produce waste in the first place. A WTE plant represents a large monetary investment, and subsequently a constant waste stream to run the plant and pay back this investment. This could theoretically lead to waste being diverted to the plant rather than source reduction/recycling efforts. Combustion of high-grade materials for energy will yield less usable energy than recycling those materials would conserve. The crux in this theory is that communities and countries with WTE as their predominant treatment method tend to have higher recycling rates and lower overall waste production. WTE can also aid in the recycling of metals through post-combustion recovery. Disposal cost (WTE is usually more expensive than landfill in U.S., and not many new plants have been built) market conditions (energy prices) and/or government policy (European Union Landfill/Waste Incineration directives) can affect the use and popularity of the plants.

Emissions

By burning (or biologically digesting) organic waste instead of allowing it to decompose and produce methane in a landfill, overall greenhouse gas emissions are lowered. The production of energy and good separation of valuable and hazardous materials from this waste lowers emissions even further.

Mercury, cadmium, and other heavy metal air emissions can be highly controlled at the plant, but they are only transferred from the stack to the air pollution control residue (fly ash). Keeping these metals out of the waste stream is the only sure-fire safe option, for both landfilling and waste-to-energy.

Dioxins and other products from combustion-based WTE facilities are kept to a very low level. Activities such as campfires, wildfires, wood stoves, open burning of waste, and accidental fires results in much higher dioxin emissions per unit of material combusted than waste-to-energy plants. The emissions will never be brought to zero, and we must weigh the benefits of WTE with the emissions that do exist.

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Last Modified: October 05, 2010. 11:17:50 am