Water | Sludge dryer

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Sludge dewatering: sludge dryer

Purpose

  • Dewatering physicochemical sludge
  • Substantial dewatering paint sludge

Principle

Different drying systems allow for energy-efficient drying of industrial products or waste sludge. A lot of types of sludge dryers operate in a closed circuit with hot air energy recovery. The water fraction is released in this process as a condensation stream, and the recovered waste heat is used to heat the cooled, dried air again. The airflow can continue to feed the closed circuit in this way while drying the sludge, with the added advantage of avoiding odor and unwanted emissions. There are numerous implementation possibilities depending on the amount of sludge. In its simplest form, the drying is done in batch. Depending on the increase of the amount of sludge to be dried, this can also be done in dryer drums or via conveyor belts.

A thin layer dryer gets the sludge dispersed in a thin layer on the walls by means of a screw or rotor. These walls in turn get heated by steam or thermal oil. The sludge is cooled by an airflow which also removes the moisture.

Applications

The sludge disposal costs are a significant expense in both physicochemical and biological wastewater treatment and varies greatly on the amount of pollution components in the sludge. The lower the dry matter content of this sludge, the more there will be paid for the drainage of water. Therefore it can be beneficial in certain cases to further dewater the sludge by means of a sludge drier subsequent to a mechanical dewatering.

Energy costs related to sludge drying are rather high. Therefore, the degree of drying service has to be found where the ratio between the operation cost of the dryer and the discharge costs for the sludge is optimal. In practice sludge drying is only interesting for sludge types with high disposal costs (incineration or landfill) and/or availability of usable waste heat.