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.
Efficient drying process for partial drying of sludge
The HUBER Disc Dryer RotaDry® is used for the disc drying process. A disc dryer is a contact dryer that transfers heat to the medium to be dried via direct contact of the hot disc.
HUBER is an expert in drying processes and designs the optimal drying plant based on the individual requirements to ensure an economically and ecologically optimal utilisation of the sewage sludge.
HUBER solutions for disc drying of sludge
Installed Disc Dryers for a mono-incineration plant
Lifting a Disc Dryer with a caterpillar crane
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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FAQ
Frequently Asked Questions
The sludge-specific design of a disc dryer with regard to water evaporation is best done in a test plant. HUBER has a test disc dryer that can be used for such sludge tests. Condensation of the resulting vapours is also provided for, so that sludge-specific analyses of the vapour condensate can also be carried out here.
In combination with sewage sludge mono-incineration, disc dryers exploit the full potential. On the one hand, the steam generated during incineration can be used to heat the dryer, and on the other hand, partial drying of the sludge is sufficient for self-sustaining incineration.
The sludge to be dried must comply with the HUBER sewage sludge specification for the disc dryer. Ideally, it should be well-stabilised municipal sewage sludge.
The water vapour produced during drying is precipitated by the vapour condenser. There are various ways to process the vapour condensate so that it can be disposed of safely afterwards. Part of the heat used for drying can be recovered and fed into a district heating network, for example.
