Contact drying of sewage sludge
Partial drying of sewage sludge for recycling in fluidized bed incineration plants
The HUBER RotaDry® Disc Dryer is designed for homogeneous partial drying of dewatered sewage sludge. Due to its compact design and high specific water evaporation, it is not only ideally suited for use in new sewage sludge mono-incineration plants, but also for capacity expansions of existing plants. The dryer can dry exactly to the required DR content and thus enable a self-sustaining combustion in the fluidized bed incinerator.
A reliable condensate removal system, an innovative concept for moisture control, an optimised feed and a steam control line with minimised pressure loss characterise the HUBER Disc Dryer RotaDry® as the perfect sewage sludge dryer in combination with a mono-incineration plant.
Mono-incineration of the sewage sludge achieves an enormous reduction in volume and mass and provides for the recovery of phosphorus. At the same time, the heat required for drying is provided and, depending on the size of the plant, electricity is also generated by means of a steam turbine.
The HUBER RotaDry® is available in different sizes so that water evaporation of two to six tons per hour and dryer can be achieved. By using different disc diameters and numbers of discs, the dryer surface can be optimally adapted to the amount of generated sludge and the disc dryer can be operated in the ideal capacity range.
Function principle and vapor condensation
- Feeding from the sludge bunker optionally via an impurity separator
- Sludge drying by steam-heated rotor and optionally steam-heated jacket
- Vapour condensation for heat recovery
- Optional condensate treatment
- Delivery of dried sludge and non-condensable residual vapours to the incineration plant
From a sludge bunker, the sludge is delivered to the dryer by a pump in the standard case. Dewatered sludge is normally supplied with a DR of 20 – 30%. Inside the dryer the sludge is heated, turned, dried and conveyed towards the dryer discharge. Between 40 and 64 hollow discs are welded onto the dryer rotor. Saturated steam streams through the discs and heats them. Before entering the dryer, the steam must be conditioned so that it flows into the interior of the rotor as saturated steam or only slightly superheated.
The rotor is driven by a gear motor, the speed of which can be changed by a frequency converter. The (partially) dried sewage sludge leaves the dryer with 40 – 45% DR via the discharge screw. The vapor dome is used to remove the water vapor produced. In a condenser, the condensation heat of the vapor can be partially recovered and fed into a district heating network, for example.