Particulate and granulate materials play a major role in many industries. How they are handled and processed has a decisive impact on the quality of the final product and on business performance. In the international market, German and European companies are among the mechanical process market and technology leaders. Increasing demand for continuous processing and transport of raw materials in the food processing, chemical and pharmaceutical industry create lucrative market opportunities for these companies. Chemical, pharmaceutical and food-processing plants handle powder and granulate on a daily basis. An impressive selection of material-handling systems with a proven track record are available including conveyors, separators, crushers, filters, mixers, screens and centrifuges. However, requirement profiles and expectations continue to evolve.

Learning From Nature

The skink (Scincus scincus) moves through sand as fast as a fish in water. Also known as the sand fish, the lizard is about 15-20 cm long and lives in the deserts of North Africa and the Middle East. Material handling and process engineers could learn a thing or two from this inconspicuous desert creature. The skink, which normally stays below the surface of the sand, shows us how to move with maximum energy efficiency in this environment. Researchers from the Department of Cellular Neurobionics at the RWTH Aachen, Germany, are convinced that what we learn from nature has relevance for industrial granulated material handling technology. The scientists were able to demonstrate, that the movements of the skink always have the same frequency. The animal creates vibration as it wriggles through the sand. The researchers discovered that the motion frequency is always 3 Hz (three movements per second). It seems reasonable to assume that the animals do this to save energy when they are moving from one place to another. The team constructed a model to confirm their theory. They moved an artificial motorized sand fish made of aluminum back and forth in the sand at different frequencies. The results showed that the minimum amount of energy was expended at exactly 3 Hz, because the surrounding sand was least compact at that frequency.

Taking these observations into account, it is possible to determine the ideal transport frequencies for a wide range of granular materials with the aid of computer and mathematical models.

Pilot Studies Are Indispensable

How relevant are bionics to practical industrial applications? Manufacturers and users would undoubtedly like to have access to models which would allow them to predict the behavior of powder, granular material and bulk goods. Problems such as blockages, de-mixing, vibration and erratic flow (flushing) can occur, particularly when power and bulk goods are discharged from silos, funnel feeders, transport containers, etc. However, in many cases the only way of avoiding the problem is to conduct trials.

The German company Coperion Waeschle has set up an industrial-scale bulk goods test center. The specialists have experience with more than 10,000 different powdery and granulate materials. Characterization of the flow properties of powder and granulate material is necessary to optimize the design of material handling equipment. Granulate material can pose a number of different engineering challenges depending on the density, elasticity and grain shape. Powder can behave as a solid or a fluid in material handling systems. A good understanding of bulk material properties and mechanical parameters such as particle friction, adhesion and flow pressure is essential during the design of conveyors and storage silos in material handling applications. Coperion Waeschle points out that engineers can choose one of eight conveyor types ranging from lean-phase to stabilized slug conveying when they are designing a reliable, cost-effective bulk material handling system.

Dust

The following scenario is typical in the practical world of bulk material handling. A company in the plastic industry grinds up PMMA panels (acrylic glass). A fan is used to convey the granulated material to the bagging facility which is 80 m away. 6 kg of dust is produced per 1,000 kg of material that is conveyed, and it has to be separated out. In order to do this, a side channel compressor sucks in the granulated material and an Esta counterflow separator removes the dust. The material is put into the counterflow separator from above and falls downwards following the gravitation. At the same time air streams upwards from the bottom. The air takes the lighter particles and transports them to the top. Only 55 g of residual dust is left per metric ton of material being transported (55 ppm). Once the granulated material has been cleaned, it moves on to the filling station. A filter cyclone removes the dust from the air, and the unpressurised material falls from a bucket wheel feeder into a collection bag. This of course is only an example. There are many ways to ensure compliance with air pollution regulations. When the goods are delivered or shipped by truck, keeping the material under cover (silo trailers, containers canvas covers) can be very helpful. On continuous systems, enclosed or largely enclosed solutions (covered belt conveyors, bucket conveyors, screw conveyors, feed screws and pneumatic conveyors) help contain dust.