Municipal waste – household and similar waste, such as office waste – is made up of many different substances, which often contains pollutants. When these materials are burnt in Waste-to-Energy plants they are released from the waste in a controlled way.
The flue-gas cleaning system is one of the most important parts of a Waste-to-Energy plant, as it enables the plant to guarantee the very low emissions that are achieved today. It is a complex set of chemical reactions which aim to neutralize and minimize the emissions.
The residues from the flue gas cleaning system are captured using advanced and proven technology, and different Waste-to-Energy plants have different designs to clean the flue-gases.
During the combustion process hot flue gases are released in the furnace and their heat is transferred to water inside the boiler tubes which produces steam for energy generation.
The gases then enter the flue gas cleaning system, and are cleaned in a number of stages:
- Dust is caught and separated
- Heavy metals are extracted
- Sulphur is removed
- Acid components of the flue gases are removed
- Organic pollutants, such as dioxin are destroyed
Please follow this link to an animation on how a Waste-to-Energy plant works [link]
The flue gas cleaning system represents a significant part of a plant and it accounts for up to 50% of the construction costs of a Waste-to-Energy plant.
The emissions are very closely monitored in every Waste-to-Energy plant and centralized in the control room. A number of plants even have this information live on their web-site so that neighbours living close to the plant can see that the emissions are as low as possible [link to live emissions data from the ISVAG Waste-to-Energy plant in Belgium].
Perhaps a surprising fact about modern Waste-to-Energy plants is that what can be seen coming out of the chimney at the end of the process is mostly water vapour.