A large amount of heat is required to dry the sewage sludge, which can be obtained from the incineration of the sludge and a steam boiler. However, this thermal energy is not lost in the drying process, because vapour condensation offers the possibility of heat extraction and (partial) recovery of the heat used. When using a tube bundle heat exchanger for vapour condensation, a temperature level of up to 90 °C can even be achieved, so that direct integration into a district heating network is possible. If the injection condenser, which is less sensitive to contamination, is used, the cooling water can be heated up to 80 °C.
Disc Drying
Disc Drying of Sludge
The entire disc dryer process consists of the following main components and process steps:
Intermediate storage and feeding
To ensure continuous drying operation, the dewatered sludge is temporarily stored in a sludge bunker and conveyed to the disc dryer by a pump (alternatively screw conveyor).
Disc dryer
The sludge falls into the HUBER Disc Dryer RotaDry® on the feed side and is slowly conveyed towards the discharge by the rotary motion of the discs and shovels mounted on the disc periphery. A discharge screw completes the disc dryer system and determines the fill level inside the dryer by its frequency converter controlled speed. The disc dryer is mostly used for partial drying to a DR of 40 - 45% and the sludge is then thermally utilised in a fluidized bed incinerator.
Provision of heat
The HUBER Disc Dryer RotaDry® is heated with saturated steam (1.5 bar(a) and 10 bar(a)).
Vapour condensation
Two product streams leave the disc dryer after drying: the partially dried sludge and the water vapour with leakage air content (vapours) expelled from the sludge. The water vapour is precipitated in the vapour condenser, the vapour condensate is stored temporarily and then passed on for treatment.
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