Abstract
The design methodology for pipeline systems conveying thickened and paste tailings systems has been well developed over the last decade. This series of papers outlines the process for designing and implementing a typical surface tailings or underground backfill pipeline system. The papers comprise the following parts: Part 1 (this paper) discusses: o development of the design criteria document, o issues to be considered for the test work, and o pipeline flow behaviour modelling, friction loss calculation and pipe diameter selection. Part 2, to be presented at Paste and Thickened Tailings 2007, will include: o centrifugal pump performance derating, o hydraulic and mechanical design, o operational and control considerations, and o specific considerations for thickener underflow and gravity flow systems. 1.1 Terminology Our company classifies tailings and backfills according to the following criteria: The upper limit for conventional tailings is considered to correspond to the freely settled packing concentration. This typically corresponds to yield stresses of between 5 and 20 Pa. High concentration tailings or thickened tailings is considered to cover the range from the freely settled concentration to the concentration at which the mixture has a fully sheared yield stress corresponding to 100 Pa. Figure 1 illustrates the slump of a mixture with a 100 Pa yield stress. Paste tailings and fill are considered to be mixtures with yield stresses greater than 100 Pa. The practical upper limit for pipeline transport is about 800 Pa. These mixtures may be transported in turbulent or laminar flow: Paste\u00192006\u0019–\u0019R.J.\u0019Jewell,\u0019S.\u0019Lawson,\u0019P.\u0019Newman\u0019(eds)\u0019 ©\u00192006\u0019Australian\u0019Centre\u0019for\u0019Geomechanics,\u0019Perth,\u0019ISBN\u00190-9756756-5-6 Paste\u00192006,\u0019Limerick,\u0019Ireland\u0019 371 Turbulent flow – inertial forces dominate and the friction losses are relatively insensitive to the tailings rheology. Laminar flow – viscous forces dominate and the friction losses are directly related to the tailings rheology, which in turn is strongly effected by the tailings material properties, water chemistry and solids concentration. The transition zone from laminar flow occurs over a range of pipeline flow rates and is characterised by fluctuating pressure gradients. Thickened tailings are typically transported in laminar flow, but turbulent flow operation is possible for low yield stress mixtures, large diameter pipes and high operating velocities. Paste tailings are always transported in laminar flow. Iron ore tailings 64%m, 100 Pa yield stress Figure 1 Slump at transition from high concentration tailings to paste 1.2 Design process The procedure outlined in this paper is a guideline defining the typical steps to be followed when designing a pipeline system transporting thickened tailings or paste. It is not a definitive procedure that can be followed without a suitable background in the field and a proper understanding of thickened and paste tailings flow behaviour. It is also important to note that the design process is iterative in nature. So while the steps have been laid out in an ideal linear path, the reality is that the process will be more chaotic with frequent jumps between the various steps of the process.
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Published on 01/01/2020
Volume 2020, 2020
DOI: 10.36487/acg_repo/663_32
Licence: CC BY-NC-SA license
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