(365b) Experimental Investigation of the Effects of Material Properties On By-Pass Pneumatic Conveying Systems Performance

Bypass pneumatic conveying systems provide a passive capability to reduce conveying velocity and therefore reduce attrition and abrasion in the process of conveying many fragile and erosive particulate solids. Because of these capabilities, bypass pneumatic conveying systems have been widely used in process industry for the last couple of decades. The pneumatic conveying system design and operation are critically dependent on the physical properties of the materials to be conveyed. The objectives of this work were to experimentally investigate the performance of pneumatic conveying of dust-like, powdery and granular materials in bypass systems and conventional pipelines, i.e. flow regimes, minimum conveying velocity and energy consumption. The bypass pneumatic experimental system was built with a main pipe of 79 mm in diameter with an internal bypass pipe with an orifice plate flute arrangement. Alumina, fly ash, sand and plastic pellets, which are located in different zones of the Geldart classification diagram, were tested in the study.

The effect of material properties on the flow regimes and the mechanism of material blockage inhibition of a bypass pneumatic transport system has been investigated. For alumina and fly ash, it was found that particulate material blockages were inhibited in bypass systems due to the air penetration into the particulate volume as a result of orifice plate airflow resistance. For the bypass pneumatic conveying of sand, a long plug being split into two smaller plugs was observed. For bypass pneumatic conveying of plastic pellets, the results showed the full bore plug could not be split into smaller plugs due to the large size and high permeability of the material.

Minimum conveying velocity is one of the key parameters for pneumatic conveying system design. It was found that, compared to the conventional pipeline, the minimum conveying velocity of alumina in the bypass system was much lower as bypass pneumatic conveying systems provide a low velocity dense phase capability to non-dense phase capable bulk materials. However, for plastic pellets, due to the formation of long full bore plugs, the minimum conveying velocity in the bypass system was higher than that in conventional system. Therefore, bypass systems may not be applicable to the transport plastic pellets due to high minimum conveying velocity and the poor performance for blockage inhibition.  

When conveying different materials, the specific energy consumption in conventional and bypass systems is also discussed in this paper. For all the materials tested in this study, it was found that the bypass system consumed more energy than a conventional system when using the same air mass flow rate due to the increase in the surface friction. The results also showed that specific energy consumption increased when decreasing the diameter of orifice plates and the spacing of bypass pipe flutes. Conversely, the specific energy consumption increased with increasing the bypass diameter because of the reduction in cross-sectional area of the main pipe and the increase in wall friction due to larger wall surface area