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Fly Ash Conveying Flexing Conveyor Muscles: Influences of Fly Ash Grades on Power Consumption

| Author / Editor: Dr David Mills, Dr VK Agarwal / Dominik Stephan

The conveying performance of both a coarse grade and fine grade of fly ash are examined in detail to illustrate the range of conveying capabilities that can be reliably achieved with the assistance of these materials.

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It is important to understand the effects of fly ash as a modern power station is likely to be generating between one and two million ton per year of fly ash.
It is important to understand the effects of fly ash as a modern power station is likely to be generating between one and two million ton per year of fly ash.
(Picture: depositphotos.com / Serz72)

The capability of a pneumatic conveying system for conveying bulk particulate materials depends mainly upon five parameters. These include pipe bore, conveying distance, pressure available, conveying air velocity and material properties. The influence of many of these variables is reasonably predictable but that of the conveyed material is not. The name of a material alone provides little guidance here, particularly if the material is available in a range of grades, and this is certainly the case with fly ash.

Typically fine grades of a material that have good air retention properties are naturally capable of being conveyed at a low velocity and in a dense phase. Coarse grades of a material that have poor air retention properties are generally limited to dilute phase suspension flow, requiring much higher values of conveying air velocity and cannot be conveyed at a low velocity in a conventional conveying system, regardless of the air pressure available.

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In this article, the conveying performance of both a coarse grade and a fine grade of fly ash are examined in detail in order to illustrate the range of conveying capabilities that can be reliably achieved with the assistance of these different materials.

Conveying Characteristics of Fly Ash

If a pneumatic conveying system is to be designed to ensure satisfactory operation, and to achieve maximum efficiency, it is necessary to know the conveying characteristics of the material to be handled. The conveying characteristics will inform the designer about the minimum conveying velocity for the material and whether there is an optimum velocity at which the material can be conveyed. If previous experience with the material is not available, it will be necessary to carry out pneumatic conveying trials with the material.

Scale up in terms of air supply pressure, pipe bore, conveying distance and pipeline geometry from the existing data is reasonably predictable, provided that the extrapolation is not extended too far. Scale up in terms of mode of conveying, into regions of much higher solids loading ratios and lower conveying air velocities, however, should not be attempted unless evidence of the potential of the material for such conveying is available.

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