Choosing the right dewatering pump

Managing water is one of the most important aspects of any quarrying application, whether controlling the dewatering ingress or ensuring a steady supply for the processing of the minerals.

Quarries, like many other major applications, use a wide variety of pumps, including centrifugal and positive displacement, both of which may be broken down into sub-product categories such as submersible, self-priming, progressive cavity, AOD, end suction, etc. It is perhaps not surprising then that many quarries around the world end up using pumps that are not designed for the application and therefore result in low efficiency pumping and, more importantly, increased costs.

As this subject is so vast, this article focuses solely on dewatering pumps and their use in keeping a quarry dry in very wet conditions.

In simplistic terms, there are three main types of pumps used to keep quarries dry. Two of them are centrifugal and the third is positive displacement. If we accept that the positive displacement solution is a low flow, low energy solution and is often used as such, then we can focus on the centrifugal pumps which are often misused and therefore can cost quarries enormous amounts of energy and profits through their misuse.

In broad terms, centrifugal pumps in quarry applications come in two forms – solids or slurry handling and those for clean or dirty water. The design of the pumps for these two applications differ quite considerably and therefore the operating performance is also different, causing large disparities in the energy required for the pumps to operate successfully.

In general, a slurry pump is a hard iron pump, with open clearances, heavy duty design and minimum machining involved in its production. As such, these pumps are well suited for pumping large solids, or large amounts of solids contained in slurries. Dredging/slurry pumps such as Warman or Metso (end suction) and Dragflow/Toyo (submersible) are prime examples of these types of pumps where hydraulic efficiency is not as important as their ability to handle rocks, sand, ore and other solids-laden fluids without experiencing excessive wear or downtime, while operating in incredibly arduous conditions for extended periods.

Clear or dirty water pumps such as those manufactured by Pioneer are very different from slurry pumps in terms of their hydraulic performance. These pumps are designed to be rugged enough to operate in mining and quarrying applications (thanks to the use of materials such as ductile iron and CA6NM stainless steel as standard in most versions) where their primary use is in dewatering a site in the fastest possible manner using the least amount of energy.

Dewatering a quarry often does not require a slurry pump yet many sites, whether for historic reasons or through resistance to change, suffer increased costs through the use of such pumps when a dewatering pump may be more suitable.

For example, consider a dewatering application that requires four pumps, each capable of 450m3 per hour flow at a 120 metre head, to dewater a site on a continuous basis. Due to the lack of electricity, these pumps have to be engine driven. Table 1 shows the operating parameters of a slurry pump versus a high efficiency dewatering pump in action and as such the savings that could be made by using the correct pump in this application.

As can be seen from the figures, use of the correct pump for the application can save enormously on running costs and directly impact the bottom line of a quarry?s profit and loss account.

Equally important is the environmental impact. Based on the above comparison, the dewatering pump would be able to operate using a nine litre engine with a maximum output of 225kW, whereas the slurry pump, because of its reduced efficiency, would need a larger engine, eg an 11 or 13 litre engine, thereby resulting in increased carbon emissions.

When comparing the overall cost, including capital and running costs, choosing the correct dewatering pump is business critical but is often overlooked. Quarries tend to look for an overall package that includes spares and support but most international pump companies offer these capabilities and therefore the decision comes down to choosing the right type of pump for the application. In dewatering applications, where the pumps are often large, making the correct choice is vital.

Source: Pioneer Pumps

This article first appeared in the September 2012 issue of Quarry Management (UK) and is reprinted with kind permission.


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