Waste to Energy
JUST BURN IT!
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 4.4 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 103 waste-to-energy plants in the United States. Plus, there are another 26 old-style solid waste incinerators. These old-style incinerators 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 17 percent of its solid waste—16 percent in waste-to-energy plants and one percent in old-style incinerators.
WHY BURN GARBAGE?
Waste-to-energy plants generate enough electricity to supply 2.4 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 39 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.
TO BURN OR NOT TO BURN?
Some critics of waste-to-energy plants are afraid that burning waste will hamper recycling programs. If everyone sends their trash to a waste-to-energy plant, they say, there will be little incentive to recycle. Several states have considered or are considering banning waste-to-energy plants unless recycling programs are in place. Massachusetts, New Jersey, and New York City have delayed new waste-to-energy plants, hoping to increase the level of recycling first.
So, what’s the real story? Can recycling and burning waste coexist? At first glance, recycling and waste-to-energy seem to be at odds, but they can actually complement each other. That’s because it makes good sense to recycle some materials, and better sense to burn others.
Let’s look at aluminum, for example. Aluminum ore is so expensive to mine that recycling aluminum more than pays for itself. Burning it produces no energy. Also, because aluminum melts at a low temperature, it can clog up the works in a waste-to-energy plant. So clearly, aluminum is valuable to recycle and not useful to burn.
Paper, on the other hand, can either be burned or recycled—it all depends on the price the used paper will bring. A few years ago, the East Coast experienced a glut of old newspapers. Some East Coast communities were paid almost nothing for the paper they collected. And some communities couldn’t find anyone who wanted to buy their old newspapers, so they ended up paying a trucking company to haul the newspapers to a landfill!
In these cases, burning the newspapers for their energy value would have been a good alternative. Other types of paper, such as those using colored inks and glossy finishes, are not easily recycled and usually should be burned for their energy content.
Plastics are another matter. Because plastics are made from petroleum and natural gas, they are excellent sources of energy for waste-to-energy plants. This is especially true since plastics are not as easy to recycle as steel, aluminum, or paper. Plastics almost always have to be hand sorted and making a product from recycled plastics may cost more than making it from new materials.
To burn or not to burn is not really the question. We should use both recycling and waste-to-energy as alternatives to land filling.
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 those 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.
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 must be disposed of carefully. Like regular garbage, it is not a good idea to place ash in an unprotected landfill because water trickling through the landfill, called leachate, will pick up the chemicals and metals in the ash and could contaminate the ground and surface waters nearby. Ash is now used in some places for building roads, making concrete stronger and as artificial reefs for marine animals.
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.
Many countries have built waste-to-energy plants to capture the energy in their trash. The graph shows the top five countries that burn their trash to recover the energy in it.
Japan burns 62 percent of its trash, in part because it has little open space and very few energy resources.
The U.S. ranks fourth in the world, burning 16 percent of its trash in waste-to-energy plants.
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.
"This article was copied from a website of the US Energy Information Administration".