Pneumatic conveying dilute phase

Pneumatic conveying dilute phase pressure continuous nominal gas velocity 5 to 35 m/s with usual 11 to 25 m/s. Solids loading 3.5 to 15 kg solid/kg air with usual 6 to 15 kg solids/kg air or 1 to 7 m solids/m air. Power 7 to 11 kJ/kg. Problems about 30% air leakage out of the system. Rotary/star valve problem/bridging overcome with bin... 

Pneumatic conveying dilute phase vacuum continuous nominal gas velocity 20 to 35 m/s. Solids loading 2.8 to 11 kg solids/kg, gas with usual 3 to 4 kg solids/kg/air. Power 11 to 18 kJ/kg. Rate and distance sensitive. 

Pneumatic conveying dilute phase for pressure use pressure at the outlet of the blower as prime indicator. "Ap across blower > design or 2 1 ratio restriction in downstream conveying line/check valve jammed closed/dirty intake filter/ plugged discharge silencer/increase in feed to the system/length of pipe... 

To escape aggregative fluidization and move to a circulating bed, the gas velocity is increased further. The fast-fluidization regime is reached where the soHds occupy only 5 to 20% of the bed volume. Gas velocities can easily be 100 times the terminal velocity of the bed particles. Increasing the gas velocity further results in a system so dilute that pneumatic conveying (qv), or dilute-phase transport, occurs. In this regime there is no actual bed in the column. 

Considerably more work has been carried out on horizontal as opposed to vertical pneumatic conveying. A useful review of relevant work and of correlations for the calculation of pressure drops has been given by Klinzing et a/.(68). Some consideration will now be given to horizontal conveying, with particular reference to dilute phase flow, and this is followed by a brief analysis of vertical flow. 

Pneumatic conveying systems and in particular dilute phase conveying systems are known to create a high stress on particulate solids leading to significant attrition. In contrast to fluidized beds, it is not the material loss which is the main problem. Depending on the application, problems may rather occur in a number of different areas. Attrition may, for example,... 

Despite the little experimental data, there are two models available in the literature. Adams etal. (1992) considered dense phase conveying. They tried to predict the amount of attrition as a function of conveying distance by coupling a Monte Carlo simulation of the pneumatic conveying process with data from single-particle abrasion tests. Salman et al. (1992) focused on dilute phase conveying. They coupled a theoretical model that predicts the particle trajectory with single particle impact tests (cf. Mills, 1992). 

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)... 

Knowlton, T., The Effect of the System Pressure/Pipe-Diameter/Mass Flux Interaction on Pressure Drop in Dilute Phase Pneumatic Conveying, Proc. of Pneumatic Conveying Workshop, Powder Technol. Forum, AIChE, Denver (1994)... 

Pneumatic Conveying Pneumatic conveying systems can generally be scaled up on the principles of dilute-phase transport. Mass and heat transfer can be predicted on both the slip velocity during acceleration and the slip velocity at full acceleration. The slip velocity increases as the solids concentration is increased. 

Identification of material specific attrition mechanisms for polymers in dilute phase pneumatic conveying... 

P. Maijanovic, Determination of performance characteristics of dilute phase pneumatic conveying system, Proceedings of the 3rd Symposium of Process Industry Applications, Belgrade, Yugoslavia, 1988, pp. 215-223 (in Serbian). 

A.D. Salman, M.J. Hounslow, A. Verba, Particle fragmentation in dilute phase pneumatic conveying, Powder Technol. 126 (2002) 109— 115. 

Pneumatic conveying systems can be classified on the basis of the angle of inclination of pipelines, operational modes (i.e., negative- or positive-pressure operation), and flow characteristics (i.e., dilute or dense phase transport steady or unsteady transport). A practical pneumatic conveying system is often composed of several vertical, horizontal, and inclined pipelines. Multiple flow regimes may coexist in a given operational system. 

Pneumatic Conveying Dryers A gas-solids contacting operation in which the sohds phase exists in a dilute condition is termed a dispersion system. It is often called a pneumatic system because, in most cases, the quantity and velocity of the gas are sufficient to hft and convey the solids against the forces of gravity and friction. (These systems are sometimes incorrectly called flash dryers when in fact the moisture is not actually flashed off. True flash dryers are sometimes used for soap drying to describe moisture removal when pressure is... 

Rotary, star valve feeder used especially as solids feeders for dilute-phase pneumatic conveying to provide an air lock and to feed solids. Seal/wear depends on Ap and abrasiveness of powder. For pressure systems keep Ap <80 kPa for vacuum systems Ap <40 kPa. Provide an air vent to take the air loss away from the gravity flow of the solids and to control the filling of the star. 

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