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Abstract

Process water is an integral part of mining operations. Underground machinery requires water, with most mine site usage reaching several hundred gallons per minute. Establishing a reliable supply of process water is one of the main challenges affecting underground mining operations globally. Underground water shortages are unfortunately common, often occurring daily and costing millions annually in lost production. Operations must shut down when revenue-generating equipment lacks sufficient water flow and/or pressure. Most mines have struggled to implement a dependable underground process water management strategy. Historically, when water surges or shortages occur, the solution has been to “live with it” and repair the damage caused or to adopt a makeshift approach without addressing the root of the problem – the overall system design. A traditional underground process water system is gravity-fed, allowing water to flow through several pressure-reducing valve (PRV) stations down the mine ramp or shaft, known as a cascade system. Most pressure-reducing valves (PRVs) in use today are pressure-regulating valves that enable the outlet pressure to be set and adjusted. One issue is that traditional process water system layouts require regulating PRVs to perform two functions – supply water at a given level and reduce the pressure sufficiently so that the next PRV station downstream has a reasonable inlet pressure. This approach overlooks four major issues – system layout, valve droop, frictional losses, and valve hunting. These factors are the root of nearly all underground process water delivery problems. Mine owners have begun deploying a new system design approach to avoid costly shutdowns due to poor process water delivery. This strategy, which partly involves valves with specialized capabilities, has proven to eliminate fluctuations in water pressure and availability. It equalizes water accessibility to all areas of a mine simultaneously and thus prevents costly water shortages or surge situations. The first step is to separate the main water supply from the underground levels to create a cascading standpipe. This should incorporate ratio PRVs instead of regulating PRVs throughout the cascade system. Unlike regulating valves with a calculated output pressure, ratio valves operate on a fixed ratio pressure, so there is no set pressure on the outlet side of the valve. This, in turn, mitigates the issues previously associated with valve hunting within the standpipe system. The next step is to separate the water supply to each level by employing specialized regulating valves designed to eliminate droop and address the frictional losses associated with long horizontal pipe runs. By creating one system for the shaft piping and another system to supply each level, mines can effectively manage process water. This paper will review the challenges associated with the current design of most underground process water management systems and explore a new approach to system design aimed at alleviating the long- term challenges related to inconsistent water supply. We will discuss system design modifications, the impact of valve droop in gravity-fed systems, the consequences of frictional losses linked to water delivery, and the benefits of a high-performance underground process water system. Using actual case studies developed from Vale’s Sudbury operations, we will examine the productivity gains achieved in their Canadian mining operations by utilizing this new process water management approach.