Incineration has been, and still is, the most common way to recover energy from waste. It also reduces the volume of disposal waste by about 90%.
More than 800 WTE incinerators now operate in 40 countries, with the vast majority in Europe and Asia. The story is far different in the U.S., where public concern over emissions from incinerators remains entrenched, even with ever-tightening air quality regulations imposed by federal and state authorities. But that’s starting to change. In Florida, the Solid Waste Authority of Palm Beach County is completing the first WTE plant built in the U.S. since 1995. It will burn 99% of the municipal waste it receives and generate enough electricity for 85,000 homes.
Today’s WTE advocates argue that modern incineration facilities work differently from old-fashioned municipal incinerators. Modern
WTE facilities combust post-recycled waste in highly controlled and efficient combustion systems that are equipped with proven air emissions control components (such as fabric filters, electrostatic precipitators and scrubbers) that minimize potential emissions. Moreover, the process in modern facilities is closely monitored via control equipment, remote sensors and computers to ensure optimal combustion of the waste.
Other WTE technologies
While incineration dominates the WTE arena, other technologies are emerging that may appeal to cities where residents object to burning garbage.
Anaerobic digestion for biogas. Anaero-bic digestion (AD) technology is gaining traction in Europe, spurred on by European and national legislation aimed at reducing municipal waste going to landfills. The technology relies on anaerobic digesters that, with the help of bacteria, break down organic waste in an oxygen-free environment. Once confined to use on farms to break down manure waste, that’s no longer the case today for AD. One natural product of AD is biogas, which typically contains between 60% to 70% methane.
Gasification and pyrolysis. Some cities are using a process called gasification to extract biogas, a fuel that contains hydrogen and methane and can be used in various applications. Gasifica-tion involves heating of mixed waste or derived fuels at high temperatures. Oxygen is introduced to allow partial oxidation, but not enough for full combustion. In Australia, the city of Sydney is pushing forward with gasification, with the goal of producing syngas that can be fed back into a natural gas grid.
Another advanced thermal WTE pro-cess is pyrolysis. It involves energy-assisted heating of waste at controlled temperatures but with no oxygen introduced. Byproducts include volatile liquids and syngas – with relative proportions determined by process temperature.
Because gasification and pyrolysis technologies have limited operating history processing solid waste, it is difficult at this time for cities to draw conclusions about their viability.