Cooling and Heating Screw Conveyors

Use of Screw Conveyors as Heat Exchangers

Screw conveyors are traditionally used to transport bulk materials from one point to another, but they also represent a significant and largely untapped potential as heat exchangers. By utilizing the screw principle in combination with heat transfer, energy can be recovered from or supplied to a process in an efficient and space-saving manner.

Principle

A screw conveyor consists of a rotating screw that moves material through a tube or trough. The material is in constant contact with the central pipe, screw flights, and trough, providing favorable conditions for heat transfer. By supplying a heating or cooling medium to the screw shaft or the surrounding casing, continuous heat exchange can be established.

This can be achieved in several ways:

• Jacketing of the screw housing with a hot or cold medium
• Hollow central shaft and screw flights through which a heating/cooling medium circulates
• A combined solution using jacketing, central shaft, and screw flights

Typical Applications

Screw conveyors used as heat exchangers are particularly suitable where material already needs to be transported and where temperature control is part of the process:

• Wastewater and sludge treatment: Recovery of heat from warm sludge prior to further processing
• Food industry: Heating or cooling of powders and granulates
• Biomass and waste: Energy recovery from hot material streams
• Chemical industry: Temperature control during reactions or drying processes

Energy Recovery

In many processes, materials are transported at elevated or reduced temperatures—representing either excess heat or cold. By installing a heat-exchanging screw conveyor, this energy can be:

• Transferred to water or glycol for further distribution within the facility
• Used for preheating raw materials
• Used to reduce the need for external energy input

This results in:

• Lower energy costs
• Improved energy efficiency
• Reduced environmental and climate impact

Advantages of Screw-Based Heat Exchange

• Compact solution: Material transport and heat exchange combined in one unit
• Continuous process: Stable and uniform heat transfer
• Good controllability: Regulated via screw speed and medium temperature
• Robust design: Suitable for demanding industrial environments

Challenges and Considerations

To ensure a successful solution, the following factors must be carefully evaluated:

• Heat transfer coefficient: Dependent on material properties and contact area
• Coating and fouling: May reduce efficiency over time
• Material selection: Must withstand temperature, corrosion, and wear
• Seals and rotary joints: Critical for operational reliability

Typical Design Considerations

An efficient screw conveyor used as a heat exchanger requires:

• Optimal fill level (neither too low nor too high)
• Appropriate rotational speed
• Good turbulence within the material

Summary

Screw conveyors used as heat exchangers provide an energy-efficient and cost-effective solution by combining two functions in a single unit: material transport and heat transfer. For the process industry, wastewater treatment, and energy recovery applications, this represents significant potential for optimizing both operations and energy consumption.