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    Question ID:   3742         Current Version: 1
Question: Can we burn waste to generate energy?
Category: Science > Environment & Ecology
Keywords: waste-to-energy, generate, energy, plant, turn, burn, waste, trash, combustion
Type: other
Rating:(0 ratings)    Views: 491    Discussions: 0   In Watch Lists: 1  

 
    Answer:

Americans are producing more and more waste with each passing year. In 1960, the average American threw away 2.7 pounds of trash a day. Today, the average American throws away 4.5 pounds of trash every day! What are we going to do with all that trash?

One solution is to burn it. (Burning is sometimes called combustion.) All organic waste contains energy. Organic waste is waste that is made from plant or animal products. People have burned one type of organic material for millions of years. Can you guess what that material is? It's wood. Ancient people burned wood to keep them warm and to cook their food. In many parts of the world, wood is still the number one source of energy.

Today, we can burn garbage in special plants and use its heat energy to make steam to heat buildings or to generate electricity. This may sound amazing, but it is really nothing new. More than half of electric power companies already burn another type of solid material to make electricity.

That material is coal. Coal is a mineral that was formed from the remains of plants that died millions of years ago. Power companies use the heat energy in coal to make electricity.

Garbage does not contain as much heat energy as coal, though. It takes one ton (2,000 pounds) of garbage to equal the heat energy in 500 pounds of coal. Today, there are 90 waste-to-energy plants in the United States. Plus, there are another old-style solid waste incinerators that simply burn trash to get rid of it. They do not use the heat energy to make steam or electricity.

Today, the U.S. burns 14 percent of its solid waste.

Why Burn Garbage?

Waste-to-energy plants generate enough electricity to supply almost three million households. But, providing electricity is not the major advantage of waste-to-energy plants. In fact, it costs more to generate electricity at a waste-to-energy plant than it does at a coal, nuclear, or hydropower plant.

The major advantage of burning waste is that it reduces the amount of garbage we bury in landfills. Burning waste substantially reduces the amount of trash going to landfills. Waste-to-energy plants dispose of the waste of 40 million people.

The average American produces more than 1,600 pounds of waste a year. If all this waste were landfilled, it would take more than two cubic yards of landfill space. That's the volume of a box three feet long, three feet wide, and six feet high. If that waste were burned, the ash residue would fit into a box three feet long, three feet wide, but only nine inches high!

Why is reducing the amount of waste buried in landfills so important? Some communities in the congested Northeast may be running out of land for new landfills. And, since most people don't want landfills in their backyards, it has become more difficult to obtain permits to build new landfills. Taking the country as a whole, the United States has plenty of open space, of course, but it is expensive to transport garbage a long distance to put it into a landfill.

Some people are concerned that burning garbage may harm the environment. Like coal plants, waste-to-energy plants produce air pollution when the fuel is burned to produce steam or electricity. Burning garbage releases the chemicals and substances found in the waste. Some chemicals can be dangerous to people, the environment, or both, if they are not properly controlled.

Environmental Issues

AIR EMISSIONS

The Environmental Protection Agency (EPA)-an agency of the federal government-applies strict environmental rules to waste-to-energy plants. The EPA requires waste-to-energy plants to use anti-pollution devices, including scrubbers, fabric filters, and electrostatic precipitators. The EPA wants to make sure that harmful gases and particles are not going out the smokestack into the air. Scrubbers clean chemical gas emissions by spraying a liquid into the gas stream to neutralize the acids. Fabric filters and electrostatic precipitators remove particles from the emissions. The particles are then mixed with the ash that is removed from the bottom of the waste-to-energy plant's furnace when it is cleaned. Waste-to-energy plants also have a kind of built-in anti-pollution device. A waste-to-energy furnace burns at such high temperatures (1,800 to 2,000 degrees Fahrenheit) that many complex chemicals naturally break down into simpler, less harmful compounds.

ASH DISPOSAL

Another challenge is the disposal of the ash after combustion. Ash can contain high concentrations of various metals that were present in the original waste. Textile dyes, printing inks, and ceramics, for example, contain the metals lead and cadmium. Separating waste before combustion can solve part of the problem. For instance, because batteries are the largest source of lead and cadmium in the solid waste stream, they should be taken out of the mix and not burned.

The ash from waste-to-energy plants is tested by the EPA to make sure it is not hazardous. The test looks for chemicals and metals that would contaminate ground water through leachate, or water trickling through a landfill. Ash that is safe can be reused for many applications. About one-third of all the ash produced is used in landfills as a daily or final cover layer, to build roads, to make cement blocks, and even to make artificial reefs for marine animals.

Waste to Energy Plants 

Waste-to-energy plants work very much like coal-fired power plants. The difference is the fuel. Waste-to-energy plants use garbage-not coal-to fire an industrial boiler. The same steps are used to make electricity in a waste-to-energy plant as in a coal-fired power plant:

  1. The fuel is burned, releasing heat.
  2. The heat turns water into steam.
  3. The high-pressure steam turns the blades of a turbine generator to produce electricity.
  4. A utility company sends the electricity along power lines to homes, schools, and businesses.

You can think of garbage as a mixture of energy-rich fuels. In 100 pounds of typical garbage, more than 80 pounds can be burned as fuel to generate electricity at a power plant. Those fuels include paper, plastics, and yard waste. A ton of garbage generates about 525 kilowatt-hours (kWh) of electricity, enough energy to heat a typical office building for one day.

The high-temperature incinerator in a waste-to-energy plant burns most of the waste. All that is left is a substance called ash. Ash is the solid residue left over when something is burned. It's like the ash left over from a wood fire in the bottom of a fireplace. In a waste-to-energy plant, 2,000 pounds (one ton) of garbage is reduced to 300-600 pounds of ash.

Many countries have built waste-to-energy plants to capture the energy in their trash. There are more than 600 waste-to-energy plants in 35 different countries. The graph shows the top five countries that burn their trash to recover the energy in it.

For example, the use of waste-to-energy plants in some European and Asian countries has grown, in part because they have little open space and few energy resources.

The U.S. burns 14 percent of its trash in waste-to-energy plants. Denmark, on the other hand, burns 54 percent.

Source: Energy Information Administration

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