There are two ways to use waste to create energy.
Incinerators use a large amount of air to burn solid waste and produces polluntants that can only be treated after combustion. Temperatures up to 850C. Lime and carbon are added to remove the acid gases and absorb heavy metals, dioxins, furans and Volitile Organic Compounds (VOCs). Gases are filtered in large stacks to remove dust and reaction particles (also known as fly ash). The residual ash must also be carefully disposed of or can be recycled. The heat generated by the incinerator is used to make steam and generate electricity. Hot water and steam produced in this process can also be used to support district heating systems. Clean gas, steam and CO2 are release via the chimney.
In this process, waste becomes a fuel in much the same way as traditional fuels such as wood, coal and gas.
An example is the Cophenagen’s power plant, designed by Danish architects, Bjarke Ingels Group. The Waste-to-Energy Plant will cost 3,5 Billion DKK will be developed in the industrial area near the city center. When it is complete in 2016, it will be a leading global model in the field of waste management and energy production.
It will also be an architectural landmark in the cityscape of Copenhagen, redefining the relationship between waste and city using a progressive vision. With a 31.000 m2 ski slope, the waste to energy plan will be a destination itself. Accessible via an elevator running along a smokestack exhibiting views to the inside of the plant. The smokestack will expel rings of smoke 30cm in diameter whenever a ton of fossil Co2 is released, acting as a signal to raise awareness of ecological issues and energy consumption amongst the inhabitants of Copenhagen. The smoke rings will be illuminated at night by lasers that will be directed towards them.
Gasification does not actually burn the muncipal solid waste. It breaks down the molecules using heat and a small amount of air or oxygen. It is then recombined to form syngas, similar to natural gas but more sensitive to combustion. Syngas can be used to make chemicals, fertilisers, consumer products and generate electricity.
An example is the Tees Valley Renewable Energy Facility that is building the world’s largest advanced plasma gasification renewable energy facility in the UK. Located on an industrial land near Billingham, the facility will provide renewable electricity, generated from residual waste by 2015. It will produce enough reliable, baseload, and renewable electricity to power up to 50,000 homes and divert up to 350,000 metric tons of non-recyclable waste from landfill per year.