Solids Processing
Rules of Thumb For Pneumatic Conveying Pipelines
Bend radius vs bend pressure drop
1.2
Amrit Agarwal Pneumatic Conveying Consultants
1.0
Value of k
Proper design, configuration and layout of the conveying pipeline are critical for successful and troublefree operation
0.8
Q
General considerations Materials of construction. For the pipe itself, use carbon steel if contamination is not an issue. Otherwise, use aluminum or stainless steel. Use stainless steel for food and pharmaceutical applications. For special applications such as abrasive solids, high temperatures, and so on, it is necessary to find a suitable material for the conveying line and its components. Pressure rating. Pressure rating of the conveying pipeline should be suitable for the maximum conveying pressure of the conveying system. For most applications with a Roots type blower, a pressure rating of 30 psig is satisfactory. This rating corresponds to the rating of a Schedule 10 pipe. Use thicker pipes, such as Schedule 20, 30 or 40 for higher pressure applications. Temperature rating. The temperature rating of the conveying pipeline should be suitable for the minimum and maximum temperatures experienced by the conveying line. These temperatures depend upon the ambient
d Rough pipes f = 0.0075
0.6
0.4
uite often, during the design of conveying systems, not enough attention is paid to the design of the conveying pipeline and its components. This disregard often leads to some major conveying system problems such as low conveying rates, conveying line plugging, excessive wear and tear in the conveying line, high conveying system pressure drop, product breakage, fines and streamer generation and product cross-contamination. Guidelines presented below help mitigate or avoid such problems.
D/2
Smooth pipes f = 0.0045
temperature, conveying air tem0.2 perature and solids temperature. Pipeline joints. Pipeline segments must not be welded to each 0 0 10 20 30 other because of the need for disRatio of D/d mantling of the pipeline. These Heat loss for 90 deg bends, segments should instead be joined where f = friction coefficient, to allow easy dismantling of the k = number of velocity heads lost pipeline. Flanges can be used, but they are expensive and not easy to FIGURE 1. Studies show that long radius unbolt. They should be used where bends (larger D/d) have a lower pressure drop the joint must be 100% leak proof. (lower k) Use of easy-to-open pipeline couplings is common. Locate the joints for face at the point of contact and leave a easy access to allow dismantling of the thin crayon-like film mark on the pipe wall. This thin film continues to grow pipeline when necessary. The inside diameter of the couplings in length due to subsequent impacts, or the flanges must be equal to the in- cools quickly, and peels off from the side diameter of the pipe. Both ends pipe wall in the shape of a streamer. of the adjacent pipe segments must be The length of this streamer may be a truly aligned with each other so that fraction of an inch or two to three feet there is no internal protrusion and in length, or even longer. Long thin streamers tend to float and swirl on there is no gap between the two ends. Pipeline internal surface. The in- the air current in storage vessels until side surface should be clean and free they ball up to form something that of oil and rust. A smooth interior can resembles a bird-nest. In any case, the net result of streambe used, except when handling plastics that can generate so-called streamers ers is plugged slide gates, feeders, (a product of plastic degradation). In screeners, mechanical conveyers, and that case, inside surface is roughened hoppers. The best solution to solve this problem is to avoid making streamby special tools. For instance, dilute-phase convey- ers, which is done by roughening the ing lines in pelleted plastics service inside of the pipeline. Roughening are generally roughened on the inside (or scoring) is done by a special shotsurface to prevent streamer formation. peening method, either using inhouse (Other common names for stream- specifications or vendors who have ers are angel hair or snake skins). this expertise. Vendors have their own Streamers are formed when a plastic proprietary techniques for applying particle at a high conveying velocity the scoring. A well scored pipe should strikes the smooth pipe wall at a low last at least one year before it needs to angle of incidence. The energy of im- be re-scored. Aluminum elbows should be anpact is enough to melt the particle surCHEMICAL ENGINEERING WWW.CHE.COM MAY 2012
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