HUBER Disc Dryer RotaDry® Partial contact drying of sewage sludge for recycling in fluidized bed incineration plants

The HUBER Disc Dryer RotaDry® 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 selfsustaining combustion in the fluidized bed incinerator.

The HUBER RotaDry® is available in different sizes, so that a water evaporation of about two to six tons per hour and dryer can be achieved. By using different disc diameters and numbers of discs, the heating surface can be optimally adapted to the amount of generated sludge and the dryer can be operated in the ideal capacity range.

The heat requires for drying is provided and, depending on the size of the plant, electricity is also generated by means of steam turbine.

A reliable condensate removal system, an innovative concept for moisture control, an optimized feed and a steam control line with minimized pressure loss characterize the HUBER Disc Dryer RotaDry® as the perfect sewage sludge dryer in combination with a monoincineration plant.

All dryers are optionally available with jacket heating.

Vapour condensation

The overall dryer system always includes the condensation of the vapours produced by the disc dryer. Depending on the project-specific conditions, there are various possibilities here.

• Tube bundle condenser (indirect condenser)
  Compact design to maximise the extraction steam for district heating, as heating water is raised to the required temperature level directly in the condenser.
• Injection condenser (direct condenser)
  Circulating and cooled vapour condensate is sprayed in the head of the condenser to knock down the condensable vapours. Robust and universal design.
• Multi-stage condensation system
  Consisting, for example, of a sludge preheater (for energy optimization and polymer consumption reduction in the dewatering process) and an injection condenser as residual condenser.

Steam and condensate system

In order to operate the dryer as efficiently as possible, the use of saturated steam is essential. Depending on the concept in the water-steam cycle, steam cooling is therefore necessary in addition to  steam pressure control. Due to the ideal configuration of the controlled system. Both pressure-loss-minimized operation at nominal load and reliable regulation to the required  steam pressure can be achieved. Even after it has passed the dryer, the liquid  steam condensate does not remain energetically unused and is returned to the water-steam system. It is advisable to utilise the flash steam.

Vapour condensate treatment

Due to the high contact temperatures of the disc surface and sewage sludge, a high load of ammonium as well as particulate and dissolved COD (Chemical Oxygen Demand) is produced in the vapour condensate, which does not allow for immediate indirect discharge into the municipal sewage network and requires separate treatment on request, HUBER SE can develop a project-speficic solution for the treatment of the vapour condensate.

Vapour condensation

The overall dryer system always includes the condensation of the vapours produced by the disc dryer. Depending on the project-specific conditions, there are various possibilities here:

• Tube bundle condenser (indirect condenser)
  Compact design to maximise the extraction steam for district heating, as heating water is raised to the required temperature level directly in the condenser.
• Injection condenser (direct condenser)
  Circulating and cooled vapour condensate is sprayed in the head of the condenser to knock down the condensable vapours. Robust and universal condenser variant.
• Multi-stage condensation
  Consisting, for example, of a sludge preheater (for energy optimisation and polymer consumption reduction in the dewatering process) and an injection condenser as residual condenser.
   

Ease of maintenance disc dryer

Maximum reduction of the activities during walkarounds

• The main rotor bearings and the discharge screw bearings are supplied with automatic grease lubrication.
• Highly efficient direct drive with peripheral speed adjustment capability. Wear-optimised driving style and startup under load possible.
• Discharge screw is easily accessible and removable for replacing wear plates and screw spiral.