Combustible waste that cannot be sorted or reused is processed in the waste-to-energy (WTE) incineration plant. As its name suggests, this plant does more than just get rid of waste: it also serves as a power plant and a purification plant.

The waste that arrives at the WTE incineration plant is subject to random inspections on a conveyor belt to make sure the material meets the rigorous acceptance criteria and is suitable for the combustion process.

It is very important that the waste reacts more or less evenly during incineration. If certain waste materials only burn very slowly, for example, the plant will process less waste in the same amount of time. Fluctuations in the composition of the waste can also lead to undesired peaks and drops in the generation of electricity.

To prevent that from happening, crane operators use the enormous mechanical grabs to blend the various streams of household and commercial waste into a homogeneous mass within the waste bunker. The blended material is then funnelled into the two incinerators. With the combustion heat from the ovens, Twence generates enough energy to supply a mid-sized city with electricity both day and night. Technicians run and monitor the entire process from the central control room at Twence.

The hard, incombustible residues that remain after the incineration process of about three quarters of an hour are then treated in Twence’s own facilities to be able to serve as (certified) foundation material in road construction. Metals are also recovered from the combustion residues.

As a result, after processing and treatment, only 3 to 5% of the total volume of waste delivered to Twence needs to be deposited as residue in a landfill.

Flue-gas purification

One of the most important elements of the WTE incineration plant is the flue-gas purification system. This ‘factory within the factory’ takes up two-thirds of the entire building. Here, the flue gasses from the furnace are cleaned by means of a series of filters. As a result, the emission of toxic substances is kept to a minimum and remains well within the rigorous standards that apply: the vapour that ultimately comes out of the chimney is essentially clean and adds almost no pollution to the surrounding area.

The generation of energy in the WTE plant

The walls of the incinerators are lined with water pipes: about 55 kilometres in all. The heat from the oven converts the water into steam, which enables a turbine generator to produce about 24 MW of electricity per hour. The waste that Twence incinerates produces enough electricity to supply energy to every household in a city the size of Hengelo.