Dewatering DecChoosing the correct type of pump for dewatering applications

Managing water is one of the most important aspects of any quarrying application, whether

controlling/dewatering site ingress or ensuringa steady supply for process plant applications.Quarries, like many other major industrial

applications, use a wide variety of pumpsincluding centrifugal and positive-displacementtypes, both of which can be further broken downinto sub-products such as submersible, self-priming, progressive cavity, AOD, end suctionetc.It is perhaps not surprising, therefore, that

many quarries around the world end up usingpumps that are not best suited to the applicationin hand, resulting in low-efficiency pumping and,more importantly, increased costs.As this subject area is vast, this article

focuses solely on dewatering pumps and theiruse in keeping a quarry dry in very wetconditions.In simple terms, three main types of pumps

are used to keep quarries dry, two of thembeing centrifugal and the third being positivedisplacement. Accepting that a positive-displacement pump is generally used as a low-flow, low-energy solution, the focus of thisarticle is on centrifugal pumps, which are often

misused and can cost operators a significantamount in terms of increased energy use andreduction in profits.In broad terms, centrifugal pumps for

quarry applications come in two forms,solids or slurry handling and those for cleanor dirty water. The design of the pumps forthese two applications differs quiteconsiderably and, therefore, their operatingperformances also are different, causinglarge disparities in the energy required for thepumps to operate successfully.In broad terms, slurry pumps are hard iron

pumps with open clearances, heavy-dutydesign and minimal machining involved intheir production. As such, these pumps arewell suited to pumping large solids or large amounts of solids contained in slurry.Dredging/slurry pumps such as Warman

or Metso (end suction) and Dragflow/Toyo(submersible) are prime examples of thesetypes of pumps where hydraulic efficiency isnot as important as their ability to handlerocks, sand, ore and solids-laden fluids,without experiencing excessive wear ordowntime, while operating in highly arduousconditions for extended periods.

Clear or dirty water pumps, such as thosemanufactured by Pioneer Pump, are verydifferent from slurry pumps in terms oftheir hydraulic performance. These pumpsare designed to be rugged enough to operatein mining and quarrying applications (thanksto the use of materials such as ductile ironand CA6NM stainless steel as standard inmost versions) where their primary use is indewatering a site as fast as possible using theleast amount of energy.Dewatering a quarry often does not require

a slurry pump, yet many sites, whether forhistoric reasons or through resistance tochange, suffer from increased costs throughthe use of such pumps when a dewateringpump may be far more suitable.For example, consider a dewatering

application that requires four pumps, eachcapable of 450m3/h of flow at 120m head, todewater a site on a continuous basis. Becauseof the lack of electricity on site these pumpshave to be engine driven. Table 1 shows theoperating parameters of a slurry pumpversus a high-efficiency dewatering pump and the savings that could be made by using the correct pump in this application.

38 www.Agg-Net.com September 2012

Dewatering DecisionChoosing the correct type of pump for dewatering applications

As can be seen from the figures, use of thecorrect pump for the application can saveenormously on running costs and directlyimpact the bottom line of a quarry’s profit andloss account.Equally important is the environmental

impact. Based on the above comparison, thedewatering pump would be able to operateusing a 9-litre engine with a maximumoutput of 225kW, whereas the slurry pump,because of its reduced efficiency, would need a larger engine, eg an 11- or 13-litre unit, thereby resulting in increasedemissions.When comparing the overall cost, including

capital and running costs, choosing thecorrect dewatering pump is business criticalbut is often overlooked. Quarries tend to lookfor an overall package that includes sparesand support, but most international pumpcompanies offer these capabilities andtherefore the decision comes down tochoosing the right type of pump for theapplication. And in dewatering applications,where the pumps are often large, making thecorrect choice is paramount.For further information visit:

www.pioneerpump.co.uk

Dewatering pump Slurry pump

Flow (m3/h) 450 450

Head (m) 120 120

Speed (rev/min) 1,800 1,900

Solids handling size (mm) 30 80

Materials of construction Ductile iron Hard iron

Impeller design Enclosed Semi-open

Efficiency (%) 79 65

Power required (kW) 186 225

Fuel burn in litres/h based on 250g/kW/h 59 70

Daily fuel consumption in litres running 12h a day 708 840

Annual fuel burn (litres) running 300 days a year 212,400 252,000

Cost of fuel ($0.50/litre) $106,200.00 $126,000.00

Saving per pump $19,800.00

Overall annual savings based on four pumps $79,200.00

Based on lifetime of the pumps (seven years) $554,400.00

Table 1

September 2012 www.Agg-Net.com 39