Is your mill discharge pump maximizing profit?

The reality is that pumps in mill discharge applications are used in highly abrasive and challenging operating conditions. This can lead to high maintenance costs, particularly if there is no standby pump to assist with production.

Unfortunately, many mining facilities focus solely on grinding or extracting ore, neglecting the crucial role of selecting and sizing slurry pumps to match their application. Slurry pumps may represent a small percentage of all centrifugal pumps in the industry, but they can account for up to 80% of operating costs. As a result, the costs of owning and maintaining a pump can quickly add up, which can significantly decrease your profitability.

In this article, we explore the factors that contribute to total cost of ownership (TCO) and offer tips for selecting and maintaining mill discharge pumps to ensure maximum profitability. There is a total cost for every piece of equipment you have in your plant, and that needs to be the critical element for deciding on which pump to choose.

This is broken down in the following areas:

Capital: The very first cost is the capital cost. That is the initial cost involved in buying the equipment.

Energy: Once the pump is installed and running, power required comes at a cost. Depending on where you are in the world, this could be higher than other regions. On top of that, in a duty stand by set up, the energy cost alone could be substantial depending on pump size and application details.

Maintenance costs: This comes in two ways: Spares and labor. You want to make sure the pump is running at its optimum condition, so you will need a reliable kit of spares. Especially if you have an unreliable pump, as you will need an inventory on the ground to support the constant changeouts. In relation to this extra cost, if the frequency of changing out components is considerably high, then in turn, the maintenance cost would become higher as well.

Inventory costs: Dwindling mineral basins are leading mining companies to remote locations with limited infrastructure. If you are constantly having parts not available, or the site is remote and the frequency of change out parts is high, and these costs can add up. Sites cannot risk having unpredictable failures with no available components, so it is critical in this case to always have high stock.

Availability: The pump is the heart of the mill circuit – if the pump is down, nothing moves, so it needs to be consistently pumping. When downtime occurs, there is inevitably a loss of production. If it’s a duty only pump, the cost involved with the downtime could be very large and that alone could be a profit killer. During downtime, the cost per hour can add up to a significant financial loss.

Service water cost: Water has become more of a luxury these days for mine sites as there are costs associated with fresh seal water, such as the clean water required for gland sealing. Access to clean water as well as water quality are extra costs to consider. Thankfully, Metso has responded to this challenge and incorporated the EnviroSet™ gland as a standard feature. The water is utilized three times before it is pumped out, saving almost 65% water consumption against a full flush setup.

“The key characteristics of a good mill discharge pump is a reputable OEM, who can make sure the pump is sized for duty, can lend itself to fine-tuning (up-size/down-size), has long component wear life, ease of maintenance and the availability of spares and condition monitoring and automation ready,” says Diwakar Aduri, Global Product Manager, Mill Discharge Pumps. “Ultimately, the sum of each of these elements and their related costs give us a true picture of the total cost of ownership per year.”

Of course, the factors that lead up to the total cost of ownership are a case-by-case basis. The below infographic (fig 2) highlights the significant secret costs involved, and the importance of finding the right pump when it comes to cost savings. There is the capital cost of the equipment ($400,000). When including the costs of energy, maintenance, availability, inventory and service water, the total cost of ownership can result in closer to 3 million.

“When selecting the right mill discharge pump, it is crucial to consider all the factors,” says Alan Varghese, Product Manager, Digital Products, Pumps. “The criticality of the pump within the circuit itself is so high, that once the pump goes down, there are substantial production losses. Having no standby pump is becoming more and more the trend recently, and this risk can be seen financially in a big way.”

How to find the right pump for the job

When selecting the best mill discharge pump to suit your needs, you want to ask the right questions. We know what you’re thinking – this is a lot to take in. Thankfully, our experts have broken down these considerations and tips for you, so you can be sure you’re choosing the right pump for your production needs.

Is your manufacturer reliable and reputable?

Firstly, it's essential to ensure that the manufacturer has application experience within the industry. They should not only have experience in supplying mill discharge pumps into large mines, but also have the industry know-how when it comes to handling class 3 and 4 applications with slurries. It's also important to consider the manufacturer's past performance outcomes – have they been successful?

Other key factors to keep in mind when evaluating an OEM is their global service footprint, and whether they can respond in case of emergencies on site. This includes whether they have enough parts supply available or if they meet local and global safety certifications. Additionally, you should assess whether the OEM is focused on a one-time sale or is looking for a mutual partnership for success. A partner delivers long term success instead of short-term payoffs.

A reliable manufacturer will continuously improve and set benchmarks, demonstrating improvement over time – so working with a manufacturer that has your best interests in mind is crucial. They should be legitimate experts in the field and able to recommend operational tips to get the most out of your equipment. For example, following are a few pump maintenance recommendations to help in equipment performance, such as:

• Adjusting the front gap of the pump
  • Most of the high performing mill pumps have a regular interval for adjusting the internal clearance between the impeller and the inlet liner or throat bush, so that clearance setting is something to keep in mind, such as how complicated it is or if anybody is doing anything to minimize that effort.
• Rotating standup pump shafts
  • For applications where there is a something idle next to the pump, make sure you regularly rotate those shafts. Bearings which are usually at the top of the bearing assembly are not getting enough lubrication, so they tend to get dry. Periodically rotating them will get you that redundancy you have invested in available when you need it.
• Torquing down the bearing assembly bolts prior to commissioning
  • When you get a brand-new pump or installation done prior to commissioning, always follow the recommended manufacturer’s checklist to make sure everything is recommended, including torque on mechanical elements.

With over 250 global installations since the launch in 2015, both gold and copper, Metso is a reliable and reputable manufacturer that can ensure a safe and smooth operation from start to finish.

What is the wear life of the components, and will they last given a large slurry configuration?

Given the importance of the mill discharge process, it is crucial that pumps are designed to withstand the harsh conditions of the slurry and have a long service life.

Recent advancements in technology have allowed for greater understanding of how particles behave within slurry mixtures, leading to the development of more efficient hydraulic passages. Here at Metso, we have leveraged Computational Fluid Dynamics CFDs and Finite Element Analysis FEA tools to design our latest mill duty pump. This modern design incorporates the most recent technological advances in the industry.

When selecting, you should consider the material used in its construction. A manufacturer with a range of options allows operations to adapt to changes in the application.

“Not all materials are perfect for every application, slurry composition along with the particle sizes and shapes, within the slurry dictate what material will be the most optimal,” says Diwakar. “With that in mind, does your manufacturer have options if your duty changes? Do you have rubber, metal, polyurethane or any other options that can be deployed for optimal performance? You always have to think ahead and ensure you’ve covered your bases.”

Inlet velocities are also crucial in mill discharge pump design, particularly for slurry class 4 applications. The reason for that is simple: Particles with lower velocities do less damage. Low inlet velocities reduce damage to the pump and ensure longer wear life. Thus, it is beneficial to select a pump that spins at a lower RPM (Revolutions per minute). With reduced inlet velocity at Best Efficiency Point (BEP), this ensures minimized impact damage from sharp, coarse and heavy solids.

Overall, the importance of design cannot be overstated when it comes to mill discharge pumps. The latest technological advances, materials, modularity, and inlet velocities are all critical factors to consider when selecting a pump that can withstand the demands of the mining industry and ensure a long service life.

Is it easy and cost effective to maintain?

Maintenance should always be part of selections when you’re comparing manufacturers, as mill pumps should be able to be serviced quickly and efficiently to minimize downtime.

One key factor in this regard is design. If the design is modular, you can maintain individual elements of the pump. Since a pump is a combination of a mechanical elements and a fluid containing elements, it’s beneficial if the two can be separated and maintained independently in different intervals.

There are a variety of advantages from having a pump which has a modular design and various wet-end material options, such as the opportunity for quick rebuilds and the advantage of combining various wet-end materials based on need. In terms of maintenance, you can change the whole pump out or just change the wet end out, depending on how the cycles are. An added benefit of this is the ability to synchronize your outages and maintenance schedules, as well.

After considering a variety of designs during development, Metso recognized the importance of a modular design in terms of adaptability, availability, safety and ease of maintenance.

“It’s always beneficial if you have a modular design, because then you can upsize the wet end with a little amount of piping changes, spool pipes, and more,” says Diwakar. “An operational tip from me is to always keep that re-size capability and flexibility when selecting a mill discharge pump – you won’t regret it.”

Can the pump be digitalized once technological advancements become available?

As technology advances, pumps are becoming more sophisticated. There is an increasing interest in implementing digitalization as this offers the advantage of predictive maintenance. It’s important to consider if your existing mill discharge pump can be integrated into a digital system, and what advantages this can provide.

One of the key advantages of digitalization is the ability to monitor the performance of the pump in real-time. Modern high-tech pumps often have assisted adjustments that can be made while the pump is still running, allowing for optimization of performance and minimized wear. Vibration accelerometers and temperature measurement devices are also commonly integrated into the bearings, providing valuable insights into the mechanical side of the pump.

"It's important to be able to use any advantages from the features available on the pump," says Diwakar. "Whether it's bearing assemblies with temperature and vibration sensors, alerts that can be set for undesirable operating conditions, assisted or automated nose-gap adjustment, or our slide-base option that allows for quick inspections and maintenance, there are unique features from each manufacturer – it's all about finding the right one."

Metso’s MD Series includes an innovation called the slide base, which allows for the suction and discharge piping to remain on the pump while the mechanical end can be moved backwards. This enables quick inspections and maintenance on the impeller or back liner while the pump is open.

As the mining industry continues to embrace digitalization, the ability to integrate mill discharge pumps into a digital system will become increasingly important. While it may not be possible with all existing pumps, those with advanced features and modular designs offer the greatest potential for integration. The benefits of predictive maintenance and real-time monitoring help to optimize performance and reduce downtime, providing significant cost savings long term.

Your partner for positive change

As the most recent development within the mill discharge pump market, the MD Series pumps boast the latest designs with all of the points discussed in this article taken into considerations as part of the design.

“Mill discharge pumps can affect your overall profitability, and every improvement is valid,” says Alan. “We look for improving in every step of the way so we can all maximize customer success and minimize total cost of ownership.”

With smart innovations at the forefront of development, the pumps are modular, thus being fast and safe to maintain. They have reduced inlet velocities of under 5.5 m/s, up to 4000+ hours of long service life, have the highest impeller aspect ratio in the industry, and they spin much slower, which directly correlates to speed of wear. In summary, the Metso MD Series Pumps will provide you with the lowest cost of ownership – which is, ultimately, what all operations are after.

“With the MD series, we aim to be the partner for positive change,” says Diwakar. “With that in mind, we have gone back to the drawing board. We have implemented the latest technologies to find the most premium solution for our customers. Together, we can optimize your success and keep your profit at a maximum.”