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Biomass Explained

Energy from municipal solid waste

Municipal solid waste (MSW), often called garbage, is used to produce energy at waste-to-energy plants and at landfills in the United States. MSW contains

  • Biomass, or biogenic (plant or animal products), materials such as paper, cardboard, food waste, grass clippings, leaves, wood, and leather products
  • Non Biomass combustible materials such as plastics and other synthetic materials made from petroleum
  • Noncombustible materials such as glass and metals

Waste-to-energy plants make steam and electricity

MSW is usually burned at special waste-to-energy plants that use the heat from the fire to make steam for generating electricity or to heat buildings. In 2016, 71 U.S. power plants generated about 14 billion kilowatt hours of electricity from burning about 30 million tons of combustible MSW. Biomass materials accounted for about 64% of the weight of the combustible MSW and for about 51% of the electricity generated. The remainder of the combustible MSW was non biomass combustible material, mainly plastics. Many large landfills also generate electricity by using the methane gas that is produced from decomposing biomass in landfills.

Waste-to-energy is a waste management option

Producing electricity is only one reason to burn MSW. Burning waste also reduces the amount of material that would probably be buried in landfills. Burning MSW reduces the volume of waste by about 87%

How waste-to-energy plants work

Waste-to-energy plants burn municipal solid waste (MSW), often called garbage or trash, to produce steam in a boiler that is used to generate electricity.

There are different types of waste-to-energy systems or technologies. The most common type used in the United States is the mass-burn system, where unprocessed MSW is burned in a large incinerator with a boiler and a generator for producing electricity (see illustration below). Another less common type of system processes MSW into fuel pellets that can be used in smaller power plants.

image showing how a mass burn waste-to-energy plant work

A mass-burn waste-to-energy plant

 

The process of generating electricity in a mass-burn waste-to-energy plant has seven stages:

  1. Waste is dumped from garbage trucks into a large pit.
  2. A giant claw on a crane grabs waste and dumps it in a combustion chamber.
  3. The waste (fuel) is burned, releasing heat.
  4. The heat turns water into steam in a boiler.
  5. The high-pressure steam turns the blades of a turbine generator to produce electricity.
  6. An air pollution control system removes pollutants from the combustion gas before it is released through a smoke stack.
  7. Ash is collected from the boiler and the air pollution control system.

Municipal solid waste is a mixture of energy-rich materials such as paper, plastics, yard waste, and products made from wood. For every 100 pounds of MSW in the United States, more than 85 pounds can be burned as fuel to generate electricity. In 2016, one ton (2,000 pounds) of MSW burned in waste-to-energy plants in the United States generated about 474 kilowatthours (kWh) of electricity, or about the amount of electricity used by 16 U.S. households in one day.

In a waste-to-energy plant, 2,000 pounds of garbage is reduced to 300 pounds–600 pounds of ash.

Waste-to-energy around the world

Many countries use waste-to-energy plants to capture the energy in MSW. The use of waste-to-energy plants in some European countries and in Japan is relatively high, in part because those countries have little open space for landfills, and they have few energy resources.

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