MechChem Africa talks to KSB Pumps and Valves’ Frikkie Botma (left), Market Area Manager for Water, Petro/Chemicals and Energy; and Hugo du Plessis (right), senior project engineer for wastewater in Southern and sub-Saharan Africa, about the need for the wastewater sector to go back to specifying the right pump for the right application.
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“Globally, KSB’s strength lies in its ability to supply customised solutions, products and/or systems that best meet the needs and wants of customers. From a pump perspective, we don’t only sell boxed products, which may satisfy the basic requirements but are seldom the best solution available. Instead, we also offer engineered and customised solutions that are tailored to the needs of the application,” begins KSB’s Frikkie Botma.
In Southern and sub-Saharan Africa, KSB Pumps and Valves strives to use its engineering expertise, its local manufacturing capability and the extensive range of product solutions developed across its 150-year history to develop pumping solutions that go beyond market norms. “We have an extensive range of standard pumps for most market sectors – Water, (incl. Wastewater), Energy, Petro/Chemicals, Mining, Building Services and General Industry – and these are purpose designed for the extraction or distribution of water, chemicals, hydrocarbons, slurries, sludges and a host of other media.
“But, within that range, we have access to alternative design options and materials that can be applied to enable us to customise specific pumps to make them more energy efficient, more reliable and longer lasting when pumping the specific media in the local environment. Ultimately, our goals are to increase reliability and reduce the lifecycle cost of solutions and, to do this, there has to be a very good match between pumps and the pumping systems into which the pumps are installed,” Botma argues.
In addition, through KSB’s SupremeServe after sales pump and valve service offering, spare parts for current and discontinued models; onsite installations, service support, assistance and problem solving; and workshop-based pump repairs and refurbishments are available to pump and valve users across the region.
Best-fit solutions for the wastewater sector
With a view to restoring a market leading position in the Wastewater sector, KSB in Southern and sub-Saharan Africa has identified experienced people such as Hugo du Plessis to focus specifically on the sector. “The Wastewater sector is a very active market and there are many competing solutions out there, not all of which, we believe, are sensible,” says Du Plessis.
Du Plessis is finding that the pump installations being preferred by local wastewater consultants, contractors and end-users are every so often inefficient and non-practical. “We at KSB can offer state-of-the art equipment for the wastewater segment, and we believe our solutions are more enhanced than those of the opposition, because they incorporate new developments that have become benchmark standards in almost all markets of the world outside of Southern Africa,” he informs MechChem Africa.
“End users are favouring unsuitable installation methods because they are convenient with respect to maintenance, but the downside is that they are less efficient with respect to energy and may also be damaging in some instances, such as RAS and WAS pump stations where delicate handling impellers are required, and they are not more reliable or durable, either. We believe the local market needs to better understand which pumps are most suitable per application and are, therefore, more appropriate for that installation,” he adds.
Giving an overview of wastewater pumping in Southern Africa, Du Plessis says that along the coastline from Cape Town to Richards Bay and beyond, the wastewater sector is mostly serviced using submersible wastewater pumps. These pumps are fully submersible with the motor and impeller close-coupled into a single unit. They are used to transfer wastewater from underground sumps into main sewer lines and on to wastewater treatment plants.
“Submersible pumps are simply dropped into a flooded sump and, because they are submerged, they do not require self-priming. Also, the modular design means they can be purpose designed, built and tested in a factory so they arrive on site ready to drop and pump. State-of-the-art submersible technologies such as these offer low capital and installation costs with high energy efficiencies and reliability, which make for low lifecycle costs if sized and customised appropriately,” he says.
Du Plessis highlights KSB’s Amarex submersible pumps as an ideal submersible wastewater solution: “For wet wastewater installations, the F-max free-flow vortex impeller or the open single-vane impeller (D-max), are ideal for passing the solids typically found in wastewater,” he says, adding that in and surrounding Cape Town, there are over 600 pumps stations using submersible pump technology and over 400 in the Durban area of KZN.
However, inland in the Free State, Limpopo, North West and, to an extent, Gauteng, Du Plessis reveals that many wastewater system operators have moved to using surface mounted dry-installed self-priming pumps. “This is where we feel change is necessary. We do not believe this technology is the best choice for flooded suction applications. Self-priming pumps are designed for above-ground installation and, while they are useful where it is difficult to incorporate an underground pump chamber or sump, it makes no sense to use them underground or when an underground chamber can be built,” he notes.
The key advantage of dry-installed self-priming pumps over submersibles is that the pump itself is easily accessible for maintenance. “Our argument is, if any of the two pump models – submersible or self-priming – has to be unblocked or serviced, the operator still has to handle the pump physically. Maintenance, screening of solids into the sump and correct pump selection is key when operating any sewage pump station.”
From an energy efficiency, reliability and lifecycle costing perspective, however, Du Plessis argues there is a far better option which offers all of the convenience with few disadvantages. “We believe that using end-suction pumps in flooded suction installations, which also offer dry access to the pumps themselves, is far better,” he notes.
With flooded suction installations, a horizontal end-suction pump is used with the pump inlet, impeller volute and motor installed below ground in a dry underground chamber alongside the wastewater sump, with an inlet suction pipe passing through the wall separating the flooded sump and the dry chamber.
In these applications, self-priming is unnecessary, because the head of the flooded wastewater in the sump provides the suction pressure (Net Positive Suction Head or NPSH). “But we are seeing more and more self-priming pumps installed underground in flooded suction applications. While these are still centrifugal pumps, there is no advantageous reason to install these pumps in flooded-suction applications,” stresses Du Plessis, adding: “In a dewatering applications from the surface, where clogging and fouling are less problematic, self-priming pumps may sometimes be a better choice, but they does not make sense for flooded suction wastewater applications.”
Botma continues: “Self-priming pumps are being seen as a universal solution for all problems. This is not the case. They may be convenient to work with, because a surface pump can be accessed and cleaned more easily. These advantages are not nearly reason enough to use them routinely while disregarding specific application requirements. Compared to flooded-suction or submersible wastewater pumps, self-priming pumps are considerably less energy efficient and more expensive with respect to Capex. We argue that people should think about efficiency and operating cost first and convenience later,” he suggests.
With respect to convenience, KSB’s end-suction pumps have a back pull-out design, which makes access to the wet-end of the pump in a dry underground chamber as easy as, if not easier than, surface mounted self-priming alternatives. “By simply removing four bolts, the whole volute can be slid back on its rails to give access to the wet end of the pump. On the suction side, we also have a cleaning and inspection hatch to give easy access to the suction of the pump. So why use an inefficient and expensive self-priming pumps underground?” asks Du Plessis.
In addition, KSB end-suction pumps are purpose designed for sludge. On the KSB range end suction pumps use the same hydraulics as submersibles, so the same vortex or single vane delicate handling and clog-free impellers can be used. This transfers all the efficiency and reliability advantages of submersibles to flooded suction installations, but with the additional cleaning convenience of dry access and easy maintenance.
“Globally, energy efficiency and sustainability are what KSB stands for. We believe in being responsible to the environment and society. Core to achieving this, though, is persuading the pumping market to go back to specifying the right pump for the right application, which will be better for all of us in the long term,” Botma concludes.
