THE STEP-WISE ENLARGEMENT OF PNEUMATIC CONVEYING LINES WITH PARTICULAR REGARD TO DENSE-PHASE CONVEYING

The diameters of pneumatic conveyor lines are increased in steps to counteract excessive increases in velocity resulting from the expansion of the conveying gas. At each step there is a drop in velocity as a result of the widening of the diameter. A design method developed originally for unstepped lines is extended to cover stepped conveying sections; the consequences are analyzed and checked experimentally. In this case the conveying line is treated as independent individual pipes connected in series. The investigations show that the proposed calculation model gives a very accurate description of the behaviour of the stepped conveying sections, both qualitatively and quantitatively. It is demonstrated that, among other things: - each step-wise enlargement system for a conveying line must be designed for the specific solid material; the criterion for the step-wise enlargement used in this work includes other familiar graduation criteria as special cases; conveying states which are operationally reliable and are favourable from the energy point of view generally occur when the same distance from the conveying limit is maintained at each stepped enlargement along the conveying line; for a given series of diameters in the conveying pipe there are minimum stepped pipe lengths, so there cannot be any arbitrary number of step-wise increases, in a line; the optimum arrangement of the steps (= length of individual stepped pipes) is dependent on the conveying gas speed selected; energy savings of up to about 30% are possible with suitable step-wise enlargements in the conveying line; from the energy point of view step-wise increases should also be used in slow conveying systems.