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Conbustion in ECO cyclone furnace

Dried wastewater sediments in a form of granulate are characterized by a high lower heating value, comparable to lignite. They can be used as an alternative fuel for co-combustion in power engineering or concrete production. They can also be combusted in installations dedicated only for thermal treatment of wastewater sediments. A very good solution for the thermal treatment of wastewater sediments containing 90 % d.s. is their combustion in the Andritz cyclone furnace using the ECO technology.

Process description

Dried sediment in the form of granulate intended for combustion is pneumatically transferred from the  storage chamber, silos to the mixer, which mills the granules to the particles of a size up to 1 mm. Milled granules are fed to a small storage chamber through a screen, where they are pneumatically transferred to the combustion chamber.  

Combustion takes place in a cyclone furnace. The furnace is initially heated by starting burners, so as to achieve the temperature of 750 °C in the primary chamber and 850 °C secondary chamber. Due to the high temperature and vortex air motion (cyclone furnace) the organic part of introduced granules is being burnt. The mineral fraction is discarded from the system in a form of ashes through the lower part of the furnace. The combustion temperature of 850 °C prevents from melting or parching on the surface of the furnace lining. The combustion temperature is measured in three places on the inside of the primary and secondary chamber. The appropriate temperature is maintained through steering of the amount of air distributed by fans.  

In the afterburning chamber all organic compounds, carbon oxides are oxidized. In order to provide those processes the following requirements are fulfilled:  minimum stop time in the afterburning chamber (2 minutes), process temperature (minimum 850 °C) and minimum oxygen concentration (6 %).

Fumes leaving the combustion chamber have a temperature of about  920 °C  and are transferred to the heat exchanger in order to give it away for further use, for example for drying of the sediments. Fumes travel into treatment installation, after which they fulfill all the regulations described by the European Law regarding the thermal treatment of wastewater sediments. 

In contrast to other combustion technologies, Eco Combustion combines the advantages of the cyclone with the dry combustion chamber what results in low contents of fly ash easy separation of the residual ashes in the fumes (about 10 % of ash stream). The latter are directed to the "Big Bag" station for further use. Ashes from the furnace are cooled with technological water and transported to the container. Ashes after the combustion process contain at least 3 % organic parts.

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