The journey of the electric submersible dewatering pump in mining applications

What used to be considered okay as a lifetime for an electric submersible drainage pump is now held to higher standards. On top of that, sustainability considerations require submersible pumps to be economically viable to repair to a larger extent than ever before. This fundamentally changes the way submersible pump manufacturers must think. Repairability needs to be factored into the design from the first sketches of a new pump design however, this sometimes conflicts with manufacturability. One of the absolute best ways to avoid repairs is to extend the service intervals. 

Unique to mining, compared to many other applications, is the incredibly abrasive and harsh working environments these pumps are put in. Apart from hydraulic challenges in pump design such as avoiding wear hot spots for example, the pumps need to be robust in order to to survive the unavoidable rough handling that is part of everyday life in an active and ever-changing mining environment. These requirements may be at odds with other important design aspects for submersible dewatering pumps in mining applications, such as transportability.

It's one thing to carry a 30kg (67lbs) pump when standing upright, with your arm straight, not having to provide more muscle strength than needed to grasp the handle. But, if the pump is too high so that one is forced to bend the arm, this 30 kg (67lbs) pump can suddenly become very heavy to carry around. Add to that the very cramped spaces typical for underground tunneling jobs, it becomes even more obvious that the degrees of freedom for designing a lightweight, small-form-factor, robust, wear-resistant submersible drainage pump are heavily reduced.

And that’s only the pump. Electric submersible pumps need power cables and, in some cases, start and motor protection panels that add to the complexity of moving a pump with its long cable plus bulky starter panel around in cramped spaces with limited lifting devices.

Only very few global submersible pump manufacturers can combine all of the above design requirements. Especially since the product design lifecycle for submersible pumps easily stretches over decades, it’s important to look at what upgrades can be made by using submersible pumps that were designed, say, in the past 5 years.

Today’s submersible pump design engineers have at their disposal tools that were inconceivable only 5 or 10 years ago. Advances in cloud computing have made Computational Fluid Dynamics (CFD) simulations more scalable than ever. 3D-printing techniques allow for rapid prototyping and development iterations can be many more before the product design deadline imposes itself. Geometries that were hard or even impossible to cast 10 years ago, can today be reliably cast due to advances in the techniques making use of casting cores and moulds that are (partly) 3D-printed.

All of the above are only as good as the after-market support that will inevitably be required to keep the pumps running for the extended periods of time that mining operations demand. Choosing a global brand of submersible pumps with the ability to develop new products but also provide spares and support to products for their entire service life is more important than ever. Global electric pump suppliers will be better equipped to keep track of changes and advances in pump technology and implement those improvements in the product range.

Global players are often better positioned to find top-of-the-line fully-fledged local partners, such as resellers and distributors, that are not merely selling a product, but selling solutions, pre-sales product selection, technical training, warranty support and, last but not least, maintaining a local stock of products and spares. Smaller players will usually not be able to attract many of the companies on regional markets that are actually able to provide all that is needed to make optimal use of the entire potential of the pump. 

Pump repairability can be inhibited by the simplest things. The use of glues or epoxy may be technically tempting to achieve a water-tight cable entry. However, from a service and repairability point of view, this makes subsequent repairs more prone to water ingress, especially when repairs are performed without necessarily having the clean environment that is required to get a suitably water-tight entry. Other submersible pump best practices, such as “never reuse O-rings” are easily followed with the availability of repair kits, including all the necessary O-rings. Repair kits ensure that all necessary parts that need changing are actually changed. Otherwise, the technicians servicing the pump might find themselves forced to reuse an old O-ring, which in a submersible electric pump can lead to premature failure.

But repairability is more than that. Pumps that are designed with a readjustment possibility for wear, recovering performance to as-good-as-new, are desirable from a sustainability point of view. This is required as they postpone the exchange of wear parts to the absolute last moment. Repairs can be more reliably executed if essential service moments are made more secure from a service standpoint. For example, a crucial part of a submersible dewatering pump is the mechanical seal. The mechanical seal solves the technical challenge of making the combination of a rotating shaft, with a hole in the wall of a part, water-tight. Conventional mechanical seals consist of many parts that need to be fitted in the right order, in a relatively clean environment which is next to impossible to find in a mining job site. Recently designed submersible pumps typically use cartridge-type mechanical seals, where the entire seal system is changed as one unit. This avoids the pitfalls of wrong assembly and contamination of critical sealing systems. 

In hydraulic engineering, new CFD tools make predictions on potential wear-exposed hot spots more accurate. This means that in the simulation stage, already these areas can be redesigned or reinforced. Other difficult-to-predict hydraulic phenomena such as cavitation can today be more reliably identified and mitigated in the simulation stage as opposed to having to rely on expensive testing and end-user trials. Using these tools, pump manufacturers that have developed new ranges of pumps after, say, 2018 have had a completely unique chance to increase efficiency, wear-resistance and mitigate problems related to cavitation.

When it comes to choosing submersible pumps, it is important to pay attention to what workers in mining operations consider important aspects. Mostly, it will be durability (less time and effort spent on pumps that need service) and portability (inevitable mobility of pumps to clear blast areas).

Often, operators will prefer the easiest plug-and-pump type of submersibles that provide incorporated start and motor protection. These are increasingly available on most higher-power pumps. Technological advances in electronics are also making built-in soft starters increasingly common, thus providing lower start currents and related start jerks when repeatedly starting electric submersible pumps. Lower stress on mechanical structures around the pump translates into longer service life. 

An important trend in all industries, including mining, is the constant search for technology that improves the environmental footprint of the operation. In that sense, electric-powered pumps have obvious advantages over diesel-powered pumps. Even more so in confined underground mining environments where exhaust fumes of internal combustion engines are a huge concern for safety. Electric submersible pumps will contribute to a better work environment not only as they are lighter, but also because of their electric and often submerged character, the sound pressure levels will be much lower compared to dry-installed pumps. When it comes to physical footprint, and the amount of space needed, electric submersible pumps outperform dry-installed pumping solutions when compared like-for-like. For example, a 7.5kW submersible pump will measure as little as 33x76cm (13x30 inches) and come in at about 60kg (135lbs.). An equally powerful dry-installed pump will have both a larger footprint and weight.