Converting refuse into electricity, WTE plants are a power source of the future Waste-to-energy (WTE) plants are a widespread type of refuse recycling facility. They specialize in processing non-recyclable materials through one of three different methods: direct combustion, pyrolysis or gasification.
Direct combustion facilities are the most common. These WTE plants work by burning waste in a huge furnace to generate high-pressure steam, as well as a number of reusable by-products (bottom ash, for example). The steam is useful as, once created by the combustion unit, it can be redirected to a steam turbine – this in turn can generate electricity. The electric power it produces can then be fed directly back into the power grid.
The second variety of WTE plant employs the process of pyrolysis. This type of facility thermally degrades waste in an oxygen-free conversion unit, breaking down material and producing syngas (synthesis gas), which is a mixture of carbon monoxide and hydrogen that can later be turned into diesel, methane, methanol and dimethyl ether. All of these materials can be reused as forms of energy, most notably in combustion engines.
The final type of WTE facility is the gasification variety. These plants specialize in a process that converts organic and fossil-based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. While slightly more complicated, gasification plants have the advantage of being able to generate electricity in engines rather than steam turbines and also a simplified filtering process compared to direct combustion.
How direct combustion WTE facilities generate electricity?
Dump – Non-recyclable waste products are brought to the plant by dump trucks and placed in a huge hold.
Furnace – The waste is deposited by the feed crane into a large combustion unit, incinerating it and breaking it down into ash and gases.
Clinker – Bottom ash, or ‘clinker’, consists of coke, coal, slag, charcoal and grit residues. It is filtered for reuse.
Flue – In addition to producing bottom ash, the furnace also creates fly ash and flue gases as well as large quantities of steam.
Turbine – The steam from the waste is directed into a turbine generator, which in turn produces electricity that can be directly fed back into the power grid.
Filtration – Flue gases and fly ash are directed via a series of filters and air quality control systems. The ash is captured and ejected for landfill.
Cleaning – Penultimately, the remaining flue gases are cleaned in a series of purifiers, removing large quantities of pollutants, such as sulphur dioxide.
Ejection – Finally, the cleaned flue gases and remaining water vapour (steam) are ejected from the plant via a flue stack into the atmosphere.