The development of the dry discharge of bottom ash added an additional process variable to the incineration process, the tertiary air. Like the primary and secondary air, tertiary air supports an optimal incineration process and is therefore integrated in the firing power control. The amount of tertiary air is less than 10% of the total combustion air.
To keep the total amount of combustion air equal, the secondary air was reduced by the same amount, without increasing the CO figures of the raw gas. Besides supporting the incineration process the tertiary air fulfills another important task, it cools down the bottom ash; it supports the afterburning of organic parts and the air sifting of the bottom ash.
The bottom ash is discharged continuously via ash drum. By falling down on special baffle plates, the bottom ash is crushed again. Any glowing embers in agglomerates are also torn apart. The vibration conveyor then transports the ash parts to the screening machine. It supports the cooling of the bottom ash, the afterburning, the air sifting and the screening.