Thermal Sludge Drying

Maximum energy efficiency, optimum drive utilization


Leading Manufacturer of Thermal Sludge Drying Equipment


  • Fan wheels for modular sludge drying plants
  • Maximum energy efficiency
  • Optimal drive utilization


  • Development of a detailed requirements profile
  • Design of the optimum unhoused fan wheel
  • Flexible wheel widths to cover the operating points


  • One fan wheel type for all plants
  • 75% max. static efficiency
  • Reduction of component variety

Project overview

Our client is part of a group of companies from the environmental sector. In 2008, the client approached punker with the challenge of supplying suitable fan impellers for new types of modular thermal sludge drying plants that make a significant contribution to maximizing the energy efficiency of the entire plant. punker supplies highly efficient fan wheels with a diameter of 1,000 mm. Flexible wheel widths do justice to the modular character of the plant and ensure optimum utilization of the motors used.


Our Client

Our client is part of a stock listed group in the environmental sector. Their mission revolves around developing access to drinking water, protecting resources and ecosystems, optimizing the use of resources and producing new resources. The group’s self-declared goal is to become the worldwide leader in environmental services.

The group’s main activities include management solutions for the water cycle, recycling & waste recovery, and solutions for water treatment. Since 2008, the company has been purchasing air handling solutions from punker for its thermal sludge drying plants, which are used worldwide.


The goal of our customer was to develop thermal sludge drying plants with maximum energy efficiency. The customer approached punker with the challenge of supplying suitable blower wheels for the modularly designed plants, which make a significant contribution to the energy efficiency of the entire plant. In addition to a high static efficiency of the fan impellers, this also required exact matching of the fan wheels to the different operating points resulting from the modularity of the systems and the motors used, which were to be optimally utilized in terms of overall system efficiency.

Solution & Results

The punker application engineers drew up a detailed requirement profile for the thermal sludge drying plant and determined backward-curved fan impellers as the optimal aerodynamical solution. With a maximum static efficiency of 75%, these make a significant contribution to the energy efficiency of the entire plant, which is being used in a project for drying bio-solids in the watershed area of a large metropolitan are in the USA. With 34 wheels with a diameter of 1,000 mm and different widths, all operating ranges of the modular plant are covered and at the same time the motors used are optimally utilized. Due to the special suitability of the fan wheels for unhoused operation (without spiral housing), they can be flexibly used in existing box-shaped system designs. punker supplies all fan wheels with inlet cones specially adapted to them, which are a prerequisite for optimum air performance.


The client’s system is a thermal sludge dryer that operates at low temperatures. While other manufacturers’ sludge dryers usually operate with hot air up to 180°C, this belt dryer requires only 90° C hot air. This low temperature requirement, the used heat recovery and the use of punker fan wheels make our client’s sludge dryers extremely energy efficient. Energy consumption is reduced, greenhouse gas emissions are lowered and odour formation is controlled by closed air circulation.

Thermal Sludge Drying

Sewage sludge is dried to minimize its quantity and thus transport and disposal costs. Dried sludge is easy to store and handle so that it can be disposed of or recycled in a variety of ways. In addition to being used as fertilizer, dried sludge can also be used as fuel for energy production, with a calorific value comparable to that of lignite.

The limitations of mechanical sludge drying sometimes make thermal drying by water evaporation necessary. The company has developed a range of sludge drying processes that allow the sludge to be used for a variety of applications as fertilizers, by-products for composting or as fuel for incinerators.

Benefits of sludge drying:
  • By removing the water from the sludge through evaporation, the volume and weight of the sludge is reduced, which facilitates storage and transport.
  • Drying stabilizes the sludge, reducing odor and improving hygiene.
  • By evaporating the water, the final product can be used use in a composting plant. This means that the sludge can be recycled for use in agriculture.

Fan wheels for thermal sludge drying

Many materials, goods and substances must be dried before further processing. In thermal drying, moisture is removed from the dry material in a controlled process by means of evaporation or vaporization. When drying sewage sludge, wood, chicken manure, wood chips and other dry goods, the exact temperature, the drying speed and the degree of residual moisture play a major role. Fan wheels from punker for industrial drying meet precisely these requirements and at the same time enable energy-efficient use of the blowers and fans used.

Select fan wheel for your thermal drying system

With puncat WEB you can perform the pre-selection of fan wheels directly on our website. Display suitable products for your application by specifying operating point, speed, and diameter and specify your search by energy efficiency requirements.  

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