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WendeWolf® Solar Sludge Drying System

MAK Water is the exclusive representative in Australia and New Zealand for the WendeWolf® Solar Sludge Drying technology which is designed and supplied by German engineering company IST-Anlagenbau GmbH.
The WendeWolf® sludge drying system was developed in collaboration with the University of Munich, and IST-Anlagenbau has more than 30 years of experience in delivering this technology.
Worldwide there are over 170 WendeWolf® systems installed at over 100 locations across 11 countries. In Australia there are currently 9 WendeWolf® Solar Sludge Dryers in operation at 4 locations.

MAK Water provides full design, costing and technical support of the WendeWolf® sludge drying technology, from concept stage through to final project delivery. We provide the complete package that includes design, supply and installation of the WendeWolf® system and associated mechanical and electrical works, as well as design, supply and installation of the greenhouse drying hall(s). All WendeWolf® systems are commissioned by IST-Anlagenbau and supported by MAK Water in Australia and New Zealand. MAK Water also offers refresher training to operators and provides spare parts and servicing to existing sludge drying equipment.


WendeWolf® Sludge Drying System Overview

The WendeWolf® sludge dryer system includes a tiller & turner machine that processes dewatered sewage sludge cake into a dry granulated product. The WendeWolf® machine is installed inside an enclosed greenhouse building or drying hall. The greenhouse serves to prevent rain from re-wetting the sludge and capture solar radiation to evaporate the moisture from the sludge. The WendeWolf® machine spreads, turns over and breaks up the sludge in the bed, as it transports it along the length of the drying hall. The final granulated product at the end of the drying hall is on average approximately 10 mm in size and can have up to 85% dry solids content. This granulate is suitable for agricultural reuse, as fertilizer, as well as secondary fuel in coal fired power plants or in cement plants.

How does soldar sludge drying work?

  • Dewatered sludge cake from as low as 13% dry solids content is brought into the front end of the drying hall in batches or continuously as it is produced. This cake in-loading process can be manual (e.g. tip truck or skip) or automated (e.g. belt or screw conveyor).
  • The WendeWolf® machine moves along the length of the drying hall on dwarf walls. It spreads the dewatered cake across the width of the drying hall, turns it over, and transports it along the length of the drying hall. During this process the dewatered cake is transformed into a granular product that can range in dry solids content from around 40% to 85%.
  • Captured solar radiation inside the greenhouse causes evaporation of moisture from the sludge bed. The warmer the air is the more water vapour can be transported. The difference between the partial vapour pressure inside the sludge and the ambient air, drives the drying process.
  • This process is enhanced by the WendeWolf® machine as it breaks up the sludge, and turns the sludge over to expose moisture-rich sludge to the surface. As the sludge dries and the WendeWolf® machine moves it along the length of the hall, the sludge is transformed from dewatered cake into small granules.
  • In order to avoid an equilibrium between the vapour pressure inside and outside the sludge, the humid air has to be evacuated. This is naturally helped by the fact that water vapour is lighter than dry air. Active and passive ventilation systems are used to control the humidity inside the greenhouse. Ventilation fans installed above the sludge bed force warm air onto the sludge bed to drive evaporation. Water vapour is vented through automated roof vent(s) in the greenhouse. Dry and cooler (than inside) air is pulled in from outside the greenhouse along the length on both sides of the hall.
  • The WendeWolf® control strategy to maximise evaporation and sludge drying (for operating with only solar radiation) involves the following. Temperature and relative humidity are monitored inside and outside and inside each hall. The Programmable Logic Controller (PLC) calculates the temperature difference and the absolute water content inside and outside for each hall separately. The respective thresholds can be altered.
  • Due to seasonal variation in solar radiation, the rate of evaporation varies accordingly. As a result, in order to maintain a granular product with a desired minimum dry solids content, the sludge bed depth in the drying hall varies throughout the year. The throughput of a Solar Sludge Dryer system is therefore expressed on a yearly basis.
  • The granular product that is produced at the end of the drying hall, can be removed from the hall in batches or continuously. This out-loading process can be manual (e.g. Mechanical loader) or automated (e.g. conveyor).
  • By reducing the moisture in the dewatered cake from 15% dry solids content to 85% dry solids content in the granulate, there is a 78% reduction in wet mass. This mass reduction is directly proportional to savings in transport costs.

What components make up a Solar Sludge Drying system?

A Solar Sludge Drying facility can comprise one or more drying halls. The drying halls can be configured as standalone greenhouses or, two or more drying halls within a single greenhouse.

The WendeWolf® machine is installed inside a drying hall and runs on two dwarf walls that are 11.3m apart and 850 mm high, up to 120m in length. The WendeWolf® solar sludge drying system contains the following mechanical & electrical equipment as standard:

  • WendeWolf® machine i.e. tiller and turner assembly
  • Control Hardware and Software, including Operation Switchboard and Machine Switchboard
  • Festoon system that includes power cable
  • Ventilation fans; quantity depends on hall length
  • Four (4) safety lanyards with emergency stop pull switches; two (2) on the WendeWolf® machine and one (1) at each entry to the drying hall
  • One (1) set of Meteorology Instruments installed inside each drying hall
  • Position Labels installed along the length of the drying hall

Common equipment for the complete WendeWolf® Solar Sludge Drying facility include:

  • One (1) set of Meteorology Instruments installed outside the drying hall(s)
  • Main Switchboard (for power distribution to each WendeWolf® Operation Switchboard, ventilation fans, greenhouse vents and other miscellaneous equipment)

What Process Design considerations are relevant?

The process design and sizing of a Solar Sludge Drying facility is determined by IST – Anlagenbau using modelling or process simulations. Each simulation requires the following inputs:

  • Location-specific climate data including Daily Radiation in J/cm², Average Daily Temperature in °C, and Average Daily Relative Humidity in % (data is sourced directly by IST-Anlagenbau)
  • Sludge quantities to be treated in tonnes Dry Solids (tDS) per month throughout a year. Specify whether INPUT per month is fixed or variable
  • Dewatered sludge cake INPUT in percent Dry Solids (%DS) content
  • Dried granulate product OUTPUT in percent Dry Solids (%DS) content. Specify whether OUTPUT target %DS is based on Minimum Monthly %DS or Annual Average %DS
  • It is required to store dried granulate product must be stored temporarily inside the drying hall(s), and the required duration for storage
  • Is auxiliary heat is available for a heating system to be installed in the hall(s). Heat systems can include, Floor Heating, Hot Air Blowers and Infrared Radiators.
  • Selected systems for dewatered cake in-loading and dried granulate product out-loading.
  • Requirements for staging of works
  • Site constraints

Key features of the WendeWolf® solar drying system

The WendeWolf® machine:

  • Control system has pre-set programmes to operate the process. These pre-set programmes are operator adjustable, and by combining these into a sequence, all plant operation is automated.
    • LOADING – used to import and flatten input piles of sludge into the hall, and to spread it across the width of the hall, over a selected length in the hall.
    • TURNING – used to turn over the drying sludge for a selected sludge bed depth, over a selected length in the hall. Turning can occur in both directions; there is no preferred direction.
    • DISPLACING – used to move the sludge for a selected sludge bed depth, over a selected length in the hall. Displacing can occur in both directions.
    • ACCUMULATING – used to accumulate or stockpile dried granulate product
    • CLEARING (optional) – used to remove dried granulate product from the end of hall, where an automated out-loading system is available
  • Can operate in Batch mode or Continuous mode without changing the programming.
  • Turns over and conveys the sludge homogeneously in one single process along the full width and length of the hall.
  • Can handle dewatered cake input piles up to 110 cm high.
  • Operates (Turning and Displacing) a sludge bed depth up to 40 cm.
  • Can stockpile the dried granulate product up to 80 cm high.
  • Does not touch the floor, and therefore does not damage the floor. At start-up the WendeWolf® machine’s on-board sensors are used to “map” the floor surface. This process determines the minimum operating height from the floor across the width and length of the hall.
  • Can be used to “back-mix” dried granulate with wet sludge (as an option if required).
  • Uses robust, low wear, easy to maintain, and exchangeable tilling tools.