No matter how modern and how efficient the plant technology may be, there will always be some residual materials left over at the end of the incineration process. At GMVA, we make the very most of these substances. Using a number of – in some cases highly complex – processes, we focus on making them safe and ensuring they can be re-used wherever possible. Thanks to these efforts, we are able to supply industrial businesses with important secondary materials and aggregates.
The chimney that releases the cleaned flue gases into the atmosphere is 140 metres high
Each of GMVA’s boilers produces approx. 131,000m3 of flue gases an hour and these gases may not be released into the atmosphere before they have been treated. They are, therefore, fed through a multi-stage cleaning system – not only so that they comply with legal regulations but also so that they meet our own expectations as to how an environmentally friendly incineration plant should be operated.
The solid residue is extracted as filter cake
The flue gas scrubbers extract a number of substances, including heavy metals, which are removed as solids after they have passed through our wastewater treatment system. This residual material is known as hydroxide sludge. So-called flocculating agents are then added to the hydroxide sludge to make it easier to separate the solid matter from the filtrate. The two are actually separated from each other and the solids removed in our plate and frame filter press.
Fly ash – the very fine incineration residue extracted from the gases when they are cleaned
What is a nuisance at home is actually very useful for cleaning flue gases. Particulates are removed from the gases in the electrostatic precipitator using ionisation – the same process that causes dust to settle on TV screens. The final product here is called fly ash which is sent for separate disposal.
FGD gypsum has the same properties as natural gypsum and can be processed into building materials such as gypsum-based plaster and floor screed
A further product of this flue gas cleaning process is the so-called FGD gypsum. The sulphur dioxide contained in the flue gases reacts with the milk of lime added to the system to form gypsum. Once this gypsum has been cleaned and dewatered in a centrifuge, it is stored in a silo before being sent on for recycling so that it can be re-used.
Bottom ash, i.e. the material left over after the incineration process, on the conveyor belt
The pieces of waste which are not incinerated or are unable to be incinerated fall onto a conveyor belt after they leave the boiler and are stored in a separate bunker. This bottom ash is just 8% of the original volume of waste. The amount of combustible material is less than 1%. The bottom ash can be processed and recycled and then used as a secondary aggregate to build, for example, roads.
Potassium chloride concentrate is recovered from the brine
The wastewater from the flue gas cleaning process is concentrated in our evaporation plant to approx. 25% of its original volume. This produces a potassium chloride concentrate which can be recycled for re-use.