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The different conveying performances for the two materials with respect to both conveying
distance and pipeline bore illustrate the problems to be encountered when a
pipeline or conveying system has to be used for the conveying of more than one material.
Totally different flow rates must be expected when different materials are conveyed
through the same pipeline, even if the conveying line pressure drop is the same.
The parameter that this last group of curves does not show is that of the conveying air
requirements, although it was shown clearly in Figures 8.2–8.4.
If more than one material has to be conveyed through a given pipeline, the air supply
has to be sufficient, in terms of volumetric capability, to convey the material with
the requirement for the highest value of minimum conveying air velocity. When conveying
other materials, however, the volumetric flow rate may need to be reduced,
otherwise the conveying potential may also be reduced.
This effect can be illustrated by reference to Figure 8.2. If 0.38 kg/s of air is used to
convey material type B, a flow rate of about 7 tonne/h could be expected in a 200 m long
pipeline of 75 mm bore with a conveying line pressure drop of 3 bar. If this same air flow
rate was to be used with material type A, a material flow rate of about 15 tonne/h would
be obtained. If the air flow rate was to be reduced to 0.10 kg/s for material type A, however,
a material flow rate of about 28 tonne/h could be expected in this same pipeline.
This aspect of system design is considered in detail in Chapter 19, together with
similar influences of system design with respect to systems having multiple delivery
points. Air requirements and consequent power requirements are also considered. This
present chapter is concerned essentially with the performance of the pipeline. There
will, of course, be problems with material feeding into these pipelines