Bulk Solids Conveying

The above categories include all the possibilities of materials handling within a processing plant, that is, either in bulk or packed. For bulk particulate or powdered materials, which fall within the scope of this book, a simpler and more convenient classification would comprise the following fypes of conveyors belt, chain and screw, as well as pneumatic equipment. In the 

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Eocus Conveying Belt Technology," Bulk Solids Handling (Nov. 1991). 

H. Cohjn, Mechanical Conveying for Bulk Solids Elsevier, Amsterdam, 1985, pp. 236—328. 

Kliniworth, J., and Marcus, R. D., A review of low-veiocity pneumarit conveying systems. Bulk Solids Hand ., 5 (198S), No. 4, pp. 747-753. 

Salman, A. S., Verba, A., and Mills, D., Particle Degradation in Dilute Phase Pneumatic Conveying Systems, Proc. of the 1992 Powder Bulk Solids Conf. and Exhibition, Rosemont, USA (1992)... 

Destoop, T., Mathematical of Dense Phase Conveying Systems - A Revolutionary Move Towards Smart System Control, Woe. of1994 Bulk Solids Handling Conf, Rosemont, IL (1994)... 

Legel, D., and Swedes, J., Investigation of Pneumatic Conveying of Plugs of Cohesionless Bulk Solids in Horizontal Pipes, Bulk Solids Handling, 4(2) 53-59 (1984)... 

Firstly, as described previously, characterize the bulk solid to be conveyed by undertaking particle size, particle density, loose-poured bulk density, fluidization and deaeration tests. 

Cabrejos, F. J., and Klinzing, G. E., Minimum Conveying Velocity in Horizontal Pneumatic Transport and the Pickup and Saltation Mechanisms of Solid Particles, Bulk Solids Handling, 14(3) 541-550 (1994)... 

Mainwaring, N. J., and Reed, A. R., Permeability and Air Retention Characteristics of Bulk Solid Materials in relation to Modes of Dense-Phase Pneumatic Conveying, Bulk Solids Handling, 7(3) 415-425 (1987)... 

Pan, R., and Wypych, P. W., Bend Pressure Drop in Pneumatic Conveying of Fly Ash, Powder Bulk Solids Conf., Reed Exhibition Companies, USA, Proc, pp. 349-360, Rosemont, Illinois, USA (1992b)... 

Wypych, P. W., Pneumatic Conveying of Bulk Solids, PhD Thesis, Department of Mechanical Engineering, Univ. of Wollongong (1989b)... 

Wypych, P. W., and Arnold, P. C., A Standardised-Test Procedure for Pneumatic Conveying Design, Bulk Solids Handling, 5(4) 755-763 (1986b)... 

As shown in Fig. 4.1, resin feedstocks have a considerable level of interparticle space that is occupied by air. This level of space and thus the bulk density of the feedstock depend on the temperature, pressure, pellet (or powder) shape, resin type, and the level and shape of the recycle material. For a specific resin feedstock, the bulk density Increases with both temperature and the applied pressure. Understanding the compaction behavior of a resin feedstock is essential for both screw design and numerical simulation of the solids-conveying and melting processes. Screw channels must be able to accommodate the change in the bulk density to mitigate the entrainment of air and the decomposition of resin at the root of the screw. Typically, screw channels are set by using an acceptable compression ratio and compression rate for the resin. These parameters will be discussed in Section 6.1. 

Figure 4.4 Bulk density as a function of temperature and pressure for an LORE resin in the pellet form. This is the same LORE resin used in the solids-conveying studies of Section 5.3.2...

A number of issues relative to the prediction of solids conveying in smooth bore single-screw extruders are exposed from the theoretical fits to the data in Fig. 5.32. First, the data needed to carry out an effective simulation is difficult to take and is very time consuming, and only a few labs have the proper equipment that is, bulk density measurement, dynamic friction data, lateral stress, and solids conveying data. Moreover, care must be taken to develop an accurate representation of the surface temperature for the barrel and screw as a function of the axial position. This would be quite difficult in a traditional extruder with only a control thermocouple to measure the temperature at the midpoint of the barrel thickness. Second... 

The experiments were repeated with a mixture of 60% small-diameter pellets and 40% low-density GPPS recycle material. The bulk density for this feedstock was measured at 0.10 g/cm a bulk density that was about 40% less than that for the commercial pellet-low-density recycle blend. This relatively large difference in density was attributed to the variability of the recycle material density. As indicated by the data in Table 12.11, the rate with no ledge was 20 kg/h, a rate that was about 30% less than that for the commercial pellet blend. Like before, the rate difference is primarily due to the differences between the feedstock bulk densities. When the ledge plates were positioned in the equipment, the solids-conveying rate was about 75% of the original rate. This rate decrease is very similar to the rate decrease that was experienced with the 114 mm diameter commercial extruder. Recall that the commercial extruder was operating at the maximum screw speed and at a rate that was only about 60% of the expected rate. 

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