A Look at the 3 Main Waste-to-Energy Technologies

A Look at the 3 Main Waste-to-Energy Technologies

In recent decades, waste-to-energy has emerged as a popular waste management method for garbage that can’t be recycled, particularly in densely populated regions where available space for landfills is at a premium. At present, there are hundreds of operational waste-to-energy facilities around the world, all working to convert garbage into electricity, fuel, hot water, and steam via one of three main processing technologies:

  1. Mass-burn incineration

What is it?

incineratorAlso called incineration, mass burn is today’s most commonly used waste-to-energy technology; it’s also the oldest and the most commercially proven—facilities capable of producing steam and electricity from burning waste have been around since the early 20th century.

How does it work?

Modern mass burn facilities are designed to handle raw, post-recycled waste; that is, garbage remaining after recycling that has undergone little or no pre-processing. This waste is fed into a furnace for direct combustion at extremely high temperatures (so high that any toxins present in the garbage are destroyed, which is why no pre-processing is necessary). The heat produced by the combustion generates steam in a dedicated boiler; the steam then can be used directly for things like district heating or industrial processes, or it can power a turbine-generator to produce electricity for homes and businesses. Byproducts of the mass burn system include fly ash, which is sometimes used as a supplementary material in concrete production; bottom ash; and metals recovered from bottom ash that were not broken down by the combustion process.

Today’s mass burn facilities are much safer and better for the environment than their predecessors. They include sophisticated pollution mitigation equipment and techniques such as flue gas cleaning, and they operate in accordance with strict government regulations. Mass burn facilities operate safely in some of the world’s biggest cities, like Paris, London, and Tokyo.

  1. Gasification and pyrolysis

What is it?

Gasification and pyrolysis systems produce synthetic gas (syngas), vapor, or a combination of the two by applying heat to waste. Syngas and vapor can be put to a number of different uses: they can be burned directly to produce heat; they can be used by an engine or gas turbine for electricity generation; and syngas can be further converted into environmentally friendly fuels such as biodiesel, methanol, and ethanol.

How does it work?

Unlike a simple mass burn system, gasification and pyrolysis systems operate by using extreme heat with little or no oxygen. In essence, waste is heated to such high temperatures that it melts and then vaporizes. The device used for this process is a “plasma arc,” an electrical device that passes gas through an electrical spark to create a kind of super-hot torch, similar to the effect produced by a lightning bolt. When applied to waste, this process produces two products: the syngas (and/or vapor stream), and a glass-like, rocky, solid residue that is sometimes used as aggregate in construction or roadbuilding.

Following its production, several things can happen to the syngas: it can be directly combusted for heat; it can be cleaned and used in an engine or gas turbine; or it can be further cleaned and subjected to a catalytic or enzymatic process that converts it into biodiesel and similar products.

In contrast to mass burn incineration, the garbage used for this waste-to-energy method must be pre-processed before it is injected into the gasification or pyrolysis reactors. This ensures that the resulting syngas is free of toxic gases. During pre-processing, inert or chemically non-reactive components like glass, metals, and dirt are removed, and the size of the waste mass is reduced to help it flow more easily through the system.

While there are far fewer gasification and pyrolysis facilities in operation than mass burn incineration facilities, they can still be found all over the world. One of the most recently constructed facilities is located in the Tees Valley in the UK, while one of the longest-running facilities has been operating in Japan since 2006.

  1. Refuse-derived fuels

What is it?

coal like fuelIn this waste-to-energy method, processed garbage is burned directly as fuel; in other words, rather than being burned to produce electricity or another kind of fuel as in the processes above, the garbage itself is the fuel.

How does it work?

To produce refuse-derived fuels, the garbage is first processed to remove any components—like metal, dirt, or glass—that would decrease the heating value of the final solid fuel product. The waste is then shredded, refined, and compressed into pellets, bricks, or bales; it’s in this final form that the waste is burned as fuel, most commonly as a replacement for coal in cement manufacturing or other energy-intensive industries. Refuse-derived fuels can also be fed into gasification and pyrolysis systems as described above. Byproducts of the refuse-derived fuel generation process include wastewater, pre-processing residuals, and fly ash, bottom ash, and metals.

Sorry, comments are closed for this post.