It’s common to find water management strategies at mines that are based on expensive high-pressure pumped systems when more economical gravity flow would be sufficient in many cases, says U.K.-based plastic pipe supplier Polypipe.Mine-duty plastic piping and water management systems present options to reduce costs for mine operators
By Phillip Wood
While many mining applications rely upon the delivery of high-pressure water requiring powerful pumps and heavy-duty pipework, elements of an effective water management system can often operate successfully without the need for pumps. Tailings management and heap-leach processes can sometimes be configured to use “cost-free” gravity flow, along with general rainwater or storm water drainage management as non-pressurized systems. However, it is common to see pumped-pipe systems specified for such applications, leading to unnecessary expenditure on pumps and high-specification pipes themselves, as well as on the ongoing maintenance of the equipment. Similarly, higher-pressure pipes are frequently specified where there is no benefit in doing so. Fully certified, high-quality, high-density polyethylene (HDPE) pipes designed for gravity-application pressure grade would provide all the required corrosion and abrasion resistance required of mining applications without the added expense of a higher rating.
All pressure pipelines carry a Pressure Nominal (PN) rating, which indicates the pressure (in bars) the pipe can support when the water inside is at 20°C. For all too many gravity applications, PN10 or even PN16 is frequently specified, when in actuality the water or slurry within is drip-fed, meaning a less expensive gravity pipeline will be more than sufficient for the purpose.
Pump manufacturers typically estimate that up to 90% of a pump’s lifetime cost is attributed to energy usage, wear and parts, making them one of the most expensive components on a mine site and even more costly if they are specified when not truly required. Poorly maintained pumps or those working in the harsh conditions typical of mining environment fare even worse, with one leading pump manufacturer estimating that, of the 2,700 pumps they have examined since the 1980s, more than a third were running at less than 40% efficiency. These high operating costs can, in some cases, be avoided by designing a gravity flow solution in preference to a pumped system. Plastic pipe supplier Polypipe can assess a mine’s water management system design to determine if a pumped system is required, and identify areas where gravity flow is appropriate.
In designing an efficient and safe tailings management facility, for example, establishing a stable water balance will prevent future problems such as overflow. This can be achieved by taking into account not only the daily inflow and outflow expected of the facility, but also allowing for storm surges. Using a series of gravity pipes to drain into the tailings pond itself can help maintain a manageable, steady flow, while at the other end of the system, gravity pipes can be used to decant water from the dam walls to water treatment facilities.
Heap leaching converts the desired minerals into a chemical compound, which, at the bottom of the leach pile, drains into perforated pipe and is carried by gravity to the final extraction process, usually via a pregnant solution pond. With no pumping required, heap leaching is gaining in popularity—offering a minimal level of capital expenditure compared with other more intensive methods—though it does require a greater time investment over other methods such as tank leaching.
Bypassing pumped systems at the recovery and wastewater stages can provide tangible cost benefits, but must be carefully planned to ensure the chosen pipes perform at their optimum level. At the specification stage, the American Water Works Association (AWWA) offers the following guidance in its Standard for PE Pressure Pipe and Fittings (1990): “The working pressure of the system plus recurrent surge pressure associated with a specific piping arrangement or operation should not exceed 150% of the pipe pressure rating.”
For gravity-flow or low-head pipeline applications, HDPE is an effective solution due to its smooth bore and low resistance to flow. If large volumes of liquid are being transported, there is also very low friction within HDPE pipes, meaning less drag or turbulence at high flow rates and greater resistance to scaling than traditional materials. Used for non-pressurized surface and subsurface drainage as well as sanitary sewers, leachate collection and storm drainage, HDPE solutions are easy to install and maintain while providing the robust durability required of mining environments. Importantly, HDPE has the capability to transfer its load to the surrounding soil and substrate under stress, resulting in long-term structural stability and assisting in the longevity of the pipeline.
Regardless of the PN rating, all HDPE pipes possess the key characteristics that make them suitable for mining applications. Highly resistant to abrasion from both minerals and substrate carried in slurry, they are also resistant to many of the chemicals commonly used in mining and mineral extraction, including acetatic acid, ammonium hydroxide, hydrogen peroxide and calcium hydroxide.
Utilizing a gravity flow system will not only deliver cost savings in terms of avoiding expensive pumps, ongoing maintenance and high-pressure pipes; HDPE pipes are lighter than traditional materials and are therefore cheaper, easier and safer to transport and install. They can be supplied in longer lengths than more expensive concrete or ductile iron solutions, meaning fewer joints are needed, which further reduces the possibility of leakage. Ideally suited to harsh operating environments, HDPE water management solutions can withstand temperatures in the range of -40°C to +60°C.
According to Polypipe, HDPE pipe products for mine applications can be supplied in longer lengths than other traditional pipe fabrication materials, offering reductions in installation labor and leakage problems.Polypipe’s PE100 solution is an effective intermediate pipe solution with all the benefits of PE, capable of handling up to 25 bars (~350 psi) of pressure depending on the temperature. Ridgidrain, meanwhile, is an HDPE twin-wall pipe solution for non-pressurized drainage applications, which is up to 94% lighter than concrete and features a structured wall design for high ring stiffness and strength. For additional storm surge water storage, Polystorm is a crate-based, modular water storage system, which can be integrated with either PE100 or Ridgidrain to provide emergency storage for excessive rainwater or for attenuation and soakaway systems.
Correct specification of pipes for mining applications can help save money in several ways; from the initial purchase cost, to the added expense of running an unnecessary pump system when gravity could be exploited within tailings management and heap-leach applications amongst others. Working closely with a water management specialist such as Polypipe can help optimize a mine’s pipeline design without compromising on quality of materials. When a pipeline points downhill, Polypipe’s recommendation is to use the power of gravity—it is as free as the air we breathe.
Phillip Wood is international business development manager at Polypipe. For further information, visit www.polypipe.com/mining.
Can Renewable Energy Sources Power Mines in Africa?
The power and engineering sector is shifting focus away from diesel and toward lower-carbon options. It is a significant industry sign post when a global engineering and equipment brand like Caterpillar starts to offer renewables to the mining sector. Akram Elhenawy, global mining key accounts manager for the electric power division of Caterpillar, believes the mining industry is increasingly ready for renewable solutions. In this interview, he outlines the new Caterpillar strategy with particular reference to African mines.
With customer concerns about reliability of renewable energy systems abating, the focus now is on overall cost effectiveness..Q: How would you describe the market for hybrid solutions for remote mines in Africa in terms of current opportunities and barriers?
AE: Accessing affordable water and energy has increasingly become a challenge. Government reports estimate that millions of people in Africa are living without any power at all. This is forcing mining companies to look at new energy solutions, especially since Africa has numerous energy resource options from oil and natural gas to solar and wind power.
Today, remote mines in Africa are using diesel generator sets as the core of the system, providing firm, uninterruptable power to run the businesses. However, the price for diesel fluctuates, and there are difficulties with logistics and security as well as operational and maintenance costs. These issues are making renewables look like a very good financial choice for many big mining companies. In addition, there’s a dramatic decline in the cost of renewable energy, especially solar and wind.
We’ve seen significant investment in wind and solar in countries like Chile, where mining companies have been investing in renewables to reduce energy and fuel transportation costs while improving transmission capacity, making these mines generally more competitive.
We believe a similar approach will be adopted in Africa, and this will open more opportunities in the next five years for hybrid power solutions that integrate diesel and PV solar. Wind, biomass and small hydro will also present good opportunities.
The biggest challenge we see right now is that mining companies are very conservative when it comes to using new technologies or alternate forms of energy. Political instability and health concerns are hurting Africa, on top of other barriers facing the development of renewable energy in the market today.
Q: It seems that mining experts are less concerned about the reliability of systems and more focused on the economics. Is that your impression, as well?
AE: Yes. In recent years, renewable energy technology has matured and concerns about reliability have diminished. We’re seeing increased investments, reflecting a better understanding of the benefits of integrated microgrid solutions.
Typically, PV and wind reduce fuel consumption in the range of 30%–70%, but it’s limited due to the high cost of energy storage. In the next few years, we expect storage technology to advance, with the price coming down. When mining companies trust that they can rely on renewable solutions, we’ll start seeing a big shift…. In addition, communities want “green power” around them.
Q: What do you think needs to happen to truly unlock the potential for partnerships between mining operators and renewable energy providers?
AE: Several things. The most important is assuring mining companies that you are there long term for operation, maintenance and support. You have to guarantee the performance and availability of the system throughout the lifetime of the mine.
Providers should help change the mindset within the mining industry by introducing this technology and educating mining operators about the economic, environmental, and social benefits. They have to work with mining companies to understand the real-life costs of integrated microgrid projects and explore all available options to meet the customer’s short- and long-term goals.
Finally, providers need to be flexible and adapt to the financial constraints that mining companies face today. They have to provide long-term project financing or introduce the right international power producer to provide a fully financed, risk-wrapped power purchase agreement.
Q: Would you give us an update on Caterpillar’s approach to hybrid and solar solutions for the global mining sector?
AE: Caterpillar has been partnered with mining companies for more than 40 years, and is now integrating PV solar and energy storage to create a seamlessly controlled microgrid solution with our traditional generator sets and turbines, which are at the core of providing power to run our customers’ businesses. We are bringing the best of all technologies together. Cat dealers are uniquely positioned to act as a central resource for providing customers with fully integrated sustainable solutions that are reliable and cost-effective with lower emissions.
Q: What has been the response from current mining clients when you discuss integrating new energy solutions, including solar?
AE: The response has been amazing. Our mining customers rely heavily on Caterpillar for much of their equipment on the mine site already, so our ability to integrate these new technologies is just another way we can provide value. The key to all of this is our dealer service network. It’s one thing to integrate the technologies and sell a product, it’s the ability to service it and keep it running for the next 20 years that differentiates us from our competition.
This material was provided by Energy and Mines, organizers of the Energy and Mines conference in London, January 28–29, 2016. For information on the conference, visit www.energyandmines.com.
