What’s inside a waste incinerator?

These hulking machines burn hot enough to melt metal and send rubbish up in smoke

Image source: Pexels

The UK alone produces approximately 220 million tons of waste annually, a figure that contributes to a global yearly total that hit 1.3 billion tons in 2017. Experts have predicted that this number could reach 2.2 billion by the year 2025 as urbanisation continues to increase. All of this waste has to be collected and handled safely, and one method that is commonly used is incineration.

Running at around 750 degrees Celsius, incinerators come in a variety of designs (including those fitted with a rotary kiln), but they all share the same purpose – to safely destroy waste and treat the by-products of this process in order to mitigate the chances of potentially hazardous materials being released into the atmosphere.

This is achieved by first burning the municipal materials collected and then inspecting the ash produced as a result. This ash comes in two forms: fly (or flue) and bottom ash. The latter is the least dangerous as it clings to the searing sides of the incinerator. This type of ash is inspected with a magnet to retrieve any valuable metals for recycling. However, the finer variety of fly ash can be unsafe to expel from chimneys, as it often contains gaseous traces of heavy metals such as lead and mercury. Fly ash is therefore passed through a scrubbing device to treat and remove any harmful substances from the exhaust before it is released.

There are currently 44 waste incinerators in operation in the UK, and many environmentalists are concerned about the emissions released from incinerators. Another disadvantage is the high cost required to keep an incinerator working, but with plans in place to double the number of these rubbish burners in the UK, it seems that waste incineration  will continue to be used in the near future.

Your burning question

What happens to our rubbish when it’s incinerated?

Image credit: Future PLC

This article was originally published in How It Works issue 124, written by Charlie Ginger 

For more science and technology articles, pick up the latest copy of How It Works from all good retailers or from our website now. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, subscribe today!