Disc Drying

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.

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.