Pipes dilute-phase pneumatic

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)... 

There is a greater tendency for particles to salt out in a horizontal pipe which is preceded by a downflowing vertical to horizontal bend than in any other configuration. If this type of bend is present in a system, it is possible for solids to remain on the bottom of the pipe for very long distances following the bend before they redisperse. Therefore, it is recommended that downflowing vertical to horizontal bends be avoided if at all possible in dilute phase pneumatic transport systems. 

Design a positive pressure dilute-phase pneumatic transport system to carry 500 kg/h of a powder of particle density 1800 kg/m and mean particle size 150 pm across a horizontal distance of 100 m and a vertical distance of 20 m using ambient air. Assume that the pipe is smooth, that four 90° bends are required and that the allowable pressure loss is 0.7 bar. See below for Blasius correlation for the gas-wall friction factor for smooth pipes. 

The accurate determination of minimum transit conditions for a particular product and application is an equally essential requirement for many areas of dilute-phase pneumatic conveying (e.g. system ign optimisation of operating conditions minimisation of product damage, pipe nd wear and power consumption). Consequently, a considerable amount of research work also has been undertaken for many years resulting in a wide selection of correlations. Also, based on various comparadve- pe studies, e.g. [7-9], several models have been labelled as best bi s . 

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... 

In the region E and F some solids may move in dense phase flow along the bottom of the pipe whilst others travel in dilute phase flow in the gas in the upper part of the pipe. The saltation velocity marks the boundary between dilute phase flow and dense phase flow in horizontal pneumatic transport. 

The material of construction has a minimal effect on the overall dilute-phase conveying characteristics of pneumatic conveying. Some manufacturers have had success in treating the inside of a pipe so as to create a roughened surface for plastic pellet conveying. 

The layout of the piping systems has many important factors in pneumatic conveying. One should keep the flow path as the most direct between two points. Bends should be eliminated as much as possible. Care should be taken in the design that the distance after a feed point before the first bend is inserted in a minimum of 3 meters (10 feet) when two-phase conditions are present. If the flow is dilute or dense, this distance is not crucial. The two-phase condition tends to cause a sloshing of the solids in the bend in an unsteady condition. This sloshing behavior causes plugging and other upsets in the operation of the pneumatic conveying systems. As noted before, one should at all costs avoid more than two bends in quick succession. 

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