MadSci Network: Earth Sciences

Re: How does trash become electricity?

Date: Sun Jun 28 00:28:09 1998
Posted By: Madhu Siddalingaiah, Physicist, author, consultant
Area of science: Earth Sciences
ID: 896656053.Es

Some types of trash is disposed by burning in large incinerators. The heat from the fires can be used to generate electricity in the same way is coal fired power plants. The heat is used to boil water and produce high pressure steam. The steam is allowed to expand and cool inside turbines. The turbines turn electric generators which produce electricity.

Recycling aluminum doesn't directly produce electricity but it helps to reduce the demand for electricity. Extracting pure aluminum from the ore consumes a large amount of electricity. The ore is called Bauxite, named after a city in France where it was first found. Recovering pure aluminum through recycling takes much less electricity, so we save energy and money.

Bob Peeples adds:
Because of big changes in the public utility regulations, this has beco me one of the fastest growing industries in the United States. I spoke wit h Ms. Ann Murphy, Recycling Edu cation Specialist for the Spokane, Washington Regional Solid Waste System.

There are two common ways to recover energy from refuse:
  1. If the waste material has already been sent to a landfill, it will be decomposing and will be producing methane gas. This is a "greenhouse ga s" and is normally burned up in a flare so that it is not released to the environment. The methane gas can be used to power large engines that dr ive electric generators. The City of Spokane has two G398 Caterpillar engin es that convert methane to 900,000 watts (enough energy to run 15,000 60W light bulbs, 24 hours a day). Spokane started producing commercial powe r with these new engines about two weeks ago.
  2. Waste can also be delivered directly to a steam turbine electric po wer plant. The City of Spokane also has one of these. The picture above is a schematic diagram of the Spokane waste to energy plant, and is linked t o their web site if you would like more detailed information. They have u sed this plant to produce electric power since 1991, and have processed abo ut 2 million tons of solid waste into electric power since it opened. They f eed the trash into a burner that operates at about 2000°F to heat a boiler. The boiler produces steam to drive a turbine generator. Twenty truckloads of waste is reduced to one or two truckloads of ash in the process, so the landfill will last much longer. Special filters and gas "scrubbers" clean the exhaust for release into the air.
The Spokane Regional Solid Waste System also prints a really nice newsletter called Recycling RAP. I got some of the information a bove from their February, 1998 issue. I'll bet that Ms. Murphy would send yo u one if you e-mailed her with your Postal address!

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