Water management is a key factor in determining mine profitability, and it is something many mine owners struggle to control. Poorly designed process water management systems negatively impact production, and shutdowns can cost millions of dollars.
While the costs of poor process water management are well known, many times a quick fix is required to keep mines operational, resulting in a series of ad-hoc repairs. Yet to permanently mitigate process water management inefficiencies, changes must be made to the way systems are designed and installed.
In a recent Q&A interview led by Victaulic editorial consultant Judy Murray, global mining manager Marc Carriere and sales representative Wayne Johnstone shared their insights into ways operators of underground mines can use enhanced water management technology to improve mine uptime, productivity, and profitability.
Judy Murray: In your experience, what are the biggest water management challenges mine owners face?
Marc Carriere: The two biggest problems mines face are inconsistent water availability within the mine and broad fluctuations in pressure that can cause broken pipes and flooding.
The reason for the problems is straightforward: the systems in place are not moving water efficiently through the mine. In theory, if a mine has a sufficient supply of water at the surface, there should never be a water shortage in the mine, but this problem comes up all the time. Though the issue has been widespread for years, few new solutions have been put in place to rectify it.
When water flow is unpredictable, it’s difficult to manage mining operations. Equipment doesn’t function properly without the appropriate water supply, and the result often is lost production. These situations are expensive to repair and generally require the mine – or a section of the mine – to halt operations while the problem is being addressed.
Murray: How have underground mines traditionally managed water usage?
Wayne Johnstone: Mines can manage water pressure by installing pressure breaking tanks, but the more common solution is to install pressure reducing valves (PRVs). The valves usually are installed in PRV stations throughout a mine. A traditional installation, what is often referred to as a cascading system, allows the water to flow through several PRV stations on its way down a shaft. Today, most PRVs are also pressure regulating valves. These valves allow the outlet pressure to be adjusted, but they often struggle with system pressure changes, sudden flow changes, and increasing water demand.
When regulating PRVs work in these conditions, they tend to overshoot or undershoot the target pressure. If this happens with even a single valve, it causes issues, but the problem is exacerbated when surrounding valves are attempting to regulate pressure. All valves begin to overshoot or undershoot their set points, creating an issue known as valve hunting, which can negatively impact the water supply in the mine.
What is interesting is that the design of a pressure reducing valve can itself be the root cause of constrained water flow. A lot of the PRVs on the market are designed in a way that creates a dramatic drop in flow. Ideally, only the actuator should be reducing pressure, not the valve body. What often happens is that the valve starts to act like a pressure reducing valve when the flow volume goes up, so it ends up restricting water flow, which drops the pressure far below the set point. Feeding an entire mine through valve bodies that are behaving this way can result in consistent water starvation.
Murray: What are some other repercussions of water starvation, and how have they traditionally been addressed?
Carriere: In gravity-fed installations, water demand at the base of a mine can cause higher levels to experience substantial pressure drops. When that happens, the result can lead to a lack of water around essential equipment. Machinery that isn’t operating efficiently can have a serious impact on production.
In extreme cases, inconsistencies in flow and pressure caused by limitations of traditional process water system designs have resulted in full mine shutdowns.
Historically, mine owners have used quick-fix solutions, but these stopgap fixes only deal with “symptoms” created by poor system design, rather than address the core design issues at the root of the problem.
The only way to solve these types of problems is to take a different, more holistic, approach to process water system design – one that uses technology to mitigate water management issues before they interrupt operations or cause damage to piping or equipment in the mine.
Murray: How can mine owners do that?
Johnstone: Over the past few years, mine owners have started using different types of valves that have special capabilities to solve process water management problems. Valves with the ability to eliminate fluctuations in water pressure and ensure water availability can make a world of difference to the efficiency of mining operations. In fact, they can deliver maximum efficiency at all depths and with all types of orebodies.
These improved systems use ratio valves, which have rarely been used in underground mining operations until recently. Ratio valves manufactured with full flow-through bodies manage water flow efficiently. Unlike regulating valves that have a calculated output flow, ratio valves operate using a fixed ratio pressure, so there is no set pressure on the outlet side of the valve.
Murray: How do ratio valves fit into this new water management system design?
Johnstone: The first step in building an efficient system is to remove regulating PRV stations from the cascade system, creating a standpipe with ratio pressure reducing valves to control the column pressure and regulating valves to feed operating levels. The key is to separate the two systems, which can be done by creating one system for shaft piping and another system to supply the levels. This basically eliminates the risk of valve hunting.
Using ratio valves in shaft systems helps with process water flow issues, but it doesn’t completely fix the problem of water inconsistencies. To mitigate this problem, mines commonly incorporate “priority valves,” which assign “priority” to areas of the mine that require consistent water flow.
Using priority valves ensures that essential equipment runs efficiently and fire protection systems have a consistent water supply. In effect, they improve productivity by delivering consistent water supply to the most important areas of the mine.
Priority valves can also be used in mine expansions to make sure projects receive the appropriate amount of water.
Murray: Can traditional systems integrating PRVs and ratio valves be retrofitted?
Carriere: Yes. There are already a number of success stories that prove that a total water management approach will work when utilized in retrofit applications.
PRV stations with ratio valves are being used around the world for shaft refurbs. Once the issues are identified, components of the system can be arranged optimally for each application to deliver a customized solution that drives efficiency and long-term reliability.
Mines that need more effective water management now have a great option for improving efficiency. With these technologically enhanced systems, there is no need to continue to live with production losses caused by recurring water management issues.