Potential causes and mechanisms of pipeline blockage in pneumatic conveying systems

Pneumatic conveying has many noteworthy capabilities, and hence its popularity, but it generally has a perceived mystery in terms of reliable operation. The mode of flow of a material in a pipeline, for example, is often misunderstood, and likewise the influence and role of the properties of the material to be conveyed are not fully appreciated. With so many materials being either abrasive or friable there is a demand for systems that will convey materials at low velocity, apart from the constant need to minimise power requirements. A low velocity system is generally considered to be more economical to operate than a high velocity dilute phase conveying system. The requirement, therefore, is often for a low velocity dense phase conveying system, regardless of the material to be conveyed and the distance over which it is required to be conveyed. The value of the conveying air velocity required to convey a material is critical to the successful operation of pneumatic conveying systems and this is considered in detail. The lowest value possible will minimise problems of erosive wear and particle degradation in all cases. The power requirements for the conveying system will also be minimised, but the influence on the flow rate of the material is not so predictable. There is, in virtually all cases, a minimum value of conveying air velocity that must be maintained if the system is to operate successfully. A safety margin clearly needs to be added to take account of fluctuations in performance and problems relating to the fact that the conveying medium is compressible, but this should not be excessive.