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

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Fly Ash Conveying Trials

Conveying trials were undertaken with two samples of fly ash. One had a mean particle size of about 110 micron and the other had a mean particle size of about 30 micron. Each Fill in your article's text here batch of material was conveyed many times through the 133 m long pipeline of 68 mm bore shown in Figure 1.

FIG 1: Sketch of Pipeline Used for the Conveying of Fly Ash
(Picture: Dr David Mills)

The trials were undertaken with air at pressures up to about 2 bar gauge. Tests were carried out with air flow rates as low as possible, which means that the pipeline blocked on many occasions, but this was necessary to identify the minimum conveying conditions for the materials being tested.

Conveying Data for Fly Ash

The fly ash was fed into the pipeline by means of a blow tank and the flow rate was determined by means of load cells. Some thirty or so individual tests were carried out with coarse ash over a wide range of conveying conditions as possible. For fine ash, having a greater degree of conveyability, twice as many tests were required. The test data for coarse ash is presented in Figure 2 and for fine ash is given in Figure 3.

FIG 2: Conveying data for coarse grade of fly ash.
(Picture: Dr David Mills)

The figure displays different plots of fly ash flow rate achieved drawn against the air flow used for conveying. The lines of constant solids loading ratio have been added for reference.

FIG 3: Conveying data for fine grade of fly ash.
(Picture: Dr David Mills)

The solids loading ratio, is the ratio of the mass flow rate of the solids conveyed to the mass flow rate of the air used. It is generally expressed in a dimensionless form:

The lines of constant conveying line inlet air velocity have also been drawn and from these it will be seen why the conveying capabilities of these two grades of fly ash differ. The difference in the values for the various conveying parameters plotted on these two graphs gives an immediate indication of the difference in capability between these two very different materials, despite the fact that they are both called ‘fly ash’.

The situation with regard to the fine grade of fly ash in Figure 3 is dramatically different. With no significant difference in air supply pressure employed, with exactly the same pipeline, values of solids loading ratio are increased by a factor of about ten.

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