Waste-to-Energy

What is waste-to-energy? (WtE)

Waste-to-energy (WtE) also known as energy-from-waste (EfW) is the production of energy in the form of electricity, heat or fuel from urban and/or industrial waste. This is achieved by using waste-to-energy technologies that break down waste through a series of biochemical or thermal processes.

This technology is used in waste-to-energy plants where waste is first received, sorted, classified and then transformed.

In this way, landfills are reduced by up to 90%, while the waste generated is used to obtain valuable resources or to produce energy.

Energy from municipal solid waste (MSW)

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
• Nonbiomass combustible materials such as plastics and other synthetic materials made from petroleum
• Noncombustible materials such as glass and metals

In 2018, about 12% of the 292 million tons of MSW produced in the United States was burned in waste-to-energy plants.

 

How waste-to-energy plants work

Waste-to-energy plants burn municipal solid waste (MSW) to produce steam in a boiler, and the steam is used to power an electric generator turbine.

MSW 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, about 85 pounds can be burned as fuel to generate electricity. Waste-to-energy plants reduce 2,000 pounds of garbage to ash that weighs between 300 pounds and 600 pounds, and they reduce the volume of waste by about 87%.

The most common waste-to-energy system in the United States is the mass-burn system. In this system, unprocessed MSW is burned in a large incinerator with a boiler and a generator to produce electricity (see illustration below). A less common type of system processes MSW to remove uncombustible materials to produce refused-derived-fuel (RDF).

 

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Reference : https://www.eia.gov/energyexplained/biomass/waste-to-energy-in-depth.php
https://www.energy.gov/eere/bioenergy/waste-energy

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 2021, 64 U.S. power plants generated about 13.6 billion kilowatthours of electricity from burning about 28 million tons of combustible MSW for electricity generation. Biomass materials accounted for about 61% of the weight of the combustible MSW and for about 45% of the electricity generated. The remainder of the combustible MSW was nonbiomass combustible material, mainly plastics. Many large landfills also generate electricity by using the methane gas that is produced from decomposing biomass in landfills.

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.