HYDRAULIC TRANSPORT OF COAL IN PIPES WITH DRAG REDUCING ADDITIVES†

The aim of the investigations was to determine the drag reduction produced by polymer additives in the hydraulic transport of coal. As no systematic results were available in the literature, experiments were undertaken using a wide range of flow velocities and polymer concentrations (up to 440 ppm) to obtain a clear picture about the processes involved. Special attention was paid to the effects of polymer degradation. The experiments were carried out on two different facilities for hydraulic transport with pipe diameters of 40 and 250 mm

Two criteria were used for selecting the polymer with the most favourable properties. It was to produce the largest possible amount of drag reduction and have the greatest stability against degradation. Six different types of polymers were investigated. Experiments were undertaken to establish the dependence of drag reduction on the polymer concentration for the polymer showing the best results according to the above-mentioned criteria. It was found that the drag reduction on coal-watei mixtures containing polymer was less than in “pure” polymer solutions (not containing any solid particles). Furthermore, for both coal-water mixtures and “pure” polymer solutions there was always found to be a polymer concentration at which drag reduction reached a maximum and this concentration was higher for the coal-water mixtures. The value of drag reduction increased as the flow velocity was increased. In the polymer degradation experiments the decrease in drag reduction as a consequence of polymer degradation was stronger when the polymer concentration was lower for both the coal-water mixtures and the “pure” polymer solutions. Experiments of longer duration showed that even after several hours of transport in the facility, there was still considerable drag reduction. Finally, it was found that for coal-water mixtures polymer degradation was greater at higher flow velocities.