Important considerations for pneumatic conveying system design

Many industries require systems for the transportation of bulk powders: grain, fertilisers, cement, metals, ash, sand, flour, sugar. It is important for the end user to understand the parameters that should be specified, for the supplier to optimise the system design. Such parameters cover material characteristics, conditions under which the material is transported and the transportation system itself.

Important considerations for pneumatic conveying system design

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The transportation of bulk powders is often implemented using pressurised air or vacuum systems.

Material characteristics

The system designer will require information about the material to be conveyed. The bulk density of the material aids calculation of the volume flow rate of air required – a higher density material will result in higher power consumption in the system.

Are you wondering what is pneumatic conveying? The Pneumatic Conveying Design Guide, by David Mills provides comprehensive information to answer that question.

According to that guide, various challenging material properties should be considered particularly carefully. Cohesive powders can adhere to the inside of the pipelines and make discharge from hoppers problematic. For combustible materials, an inert gas or closed loop system, to control the oxygen levels, should be used. In systems likely to encounter issues with electrostatic buildup, humidifying the air is a solution. Reducing the system velocity will protect the pipelines and fittings against corrosive materials. Hygroscopic materials can be best handled by drying the motive air.

Transportation conditions

The distance that the conveying system must cover is important. A longer conveying distance requires a greater motive force and therefore larger vacuum pumps. At longer distances it becomes more economical to employ a positive pressure system.

Batch conveying also requires larger pumping equipment to transfer the batch through the system in a specified time frame.

The large equipment sometimes associated with such conveying systems can lead to issues regarding head height and plant orientation.

The environment in which the system will be installed and the materials it will handle are both important factors when selecting materials. Altitude and food and beverage hygiene requirements will dictate the materials that can be used for the system components.

System Characteristics

Designing a system with multiple pick up positions lends itself to a vacuum system. A pressurised system will suffer air leakages across valves. Conversely, a system with multiple delivery positions is likely to suffer air leaks when a vacuum system is employed.

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