Authors: Coulton, D

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Coulton, D 2023, 'Pressure instrument slack flow detection – three methods to determine flow status of a paste reticulation system', in GW Wilson, NA Beier, DC Sego, AB Fourie & D Reid (eds), Paste 2023: Proceedings of the 25th International Conference on Paste, Thickened and Filtered Tailings, University of Alberta, Edmonton, and Australian Centre for Geomechanics, Perth, pp. 170-186,

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One of the most significant operational problems that paste backfill systems face is detection and mitigation against slack flow. Slack flow occurs when there is an excess of gravity head energy within the reticulation system, resulting in high-velocity conditions that increase wear. It is a primary cause of borehole failure. Hydraulic modelling can predict where slack flow might occur and is a principal component in designing a reticulation system to mitigate against slack flow. However, hydraulic modelling relies on accurate rheological measurements to estimate friction losses and requires a distinct predetermined pipeline route. Both these factors become increasingly hard to evaluate during operation; variation in tailings mineralogy or PSD can cause significant shifts in the rheological characteristics of the paste, and as-built reticulation networks frequently differ from the designed routing and/or pipe class. Furthermore, providing real-time feedback to plant operators via hydraulic grade lines is difficult. In a study conducted by Paterson & Cooke for Boliden’s Garpenberg mine located in central Sweden operating a paste backfill system, three distinct methods were developed to detect slack flow in real-time from underground Pressure Instruments (PI). These methods provided immediate feedback to plant operators on whether the system was in slack flow, regardless of filling location and tailings variability. This paper provides details of each of the three methods, including derivation, implementation, and comparison to operational data.

Keywords: cemented paste backfill, underground mine, backfill plant, underground reticulation system, slack flow, pipe wear, paste operation, SCADA

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