Mechanical Technology May 2016

⎪ Materials handling and minerals processing ⎪

Centrifuges for achieving zero liquid discharge In this article, Multotec Process Equipment’s Gerrit du Plessis describes the role of Conturbex centrifuge installations in zero liquid discharge (ZLD) applications at the back end of existing process plants.

centrifuge installations in ZLD applica- tions, with some 7 000 machines in more than 1 000 applications across a spectrum of industries. Multotec markets this range of centrifuges in southern Africa, and du Plessis says it has the requisite depth of minerals processing knowledge and ability to assess any given application and to provide a customised solution capable of meeting process expectations. He says the Siebtechnik Conturbex centrifuge offers a number of major advantages in the ZLD process. “Chief amongst these is significantly increased reliability as the machine is designed for a short product residence time, which means that its performance is not im- pacted by the fluctuating flow rate or fluctuating concentration of solids.” The Siebtechnik Conturbex centrifuge has been engineered with a scrolled product transporting mechanism that distributes the solids product evenly across the basket. This allows vibration free operation ensuring better mechanical integrity of the equipment. “This is an important feature as uneven distribution during this process results in increased stresses on the components, with eventual mechanical failure. Unplanned downtime as a conse- quence of this sort of stress would have serious knock on effects for the plant, as well as a significant environmental impact,” he explains. A third major benefit is that the machine is self-cleaning. This feature is particularly relevant during a power outage or stoppage on the plant. When this occurs, the rotating components slow down while simultaneously cleaning the basket. This then allows the machine to be restarted without the need to do any form of manual cleaning. Significantly, this feature is unique to the Conturbex machine. Materials of construction are always important when equipment operates in extreme conditions, as this ensures durability and optimum component life. Where extremely high temperatures and highly corrosive elements are found in the effluent being processed, specialised ma- terials of construction are recommended. And in applications subjected to harsh abrasion, abrasion resistant materials are applied to the flight of the scroll to ensure long life of both the rotating components and the centrifuge itself. The double drive functionality of the

W ith the increased focus on environmental legis- lation and the need for companies to comply with ISO 14001 it has become critical for process plants to deal effectively with effluent streams. This typically involves the introduction of zero liquid discharge (ZLD) processes at the back end of exist- ing process plants. ZLD is used across a number of indus- tries including mining, pulp and paper, chemical processing and the petrochemi- cal sector. Its application is typically to evaporate and concentrate an effluent or waste stream. It is also sometimes used, however, to produce a saleable product. The process involves a suite of equipment from Multotec including dewatering cen- trifuges and CleanTeq solvent extraction. Gerrit du Plessis, product specialist for solid/liquid separation at Multotec Process Equipment, explains that be- cause ZLD is always at the end of a process flow, the equipment used is generally subjected to extremes such as the chemical composition concentra-

tion in the slurry and how its flow rate fluctuates. “Due to both these issues, it is es- sential that the equipment selected for the ZLD process is capable of dealing with these varying factors, while still effectively producing the desired end result,” he says. “Often, where engineers have only previously known and used pusher cen- trifuges they may not be aware that there is an option that is far more suited to the ZLD process. And more importantly, one that will provide significant benefits, including more reliable performance with associated cost savings,” Du Plessis adds. He recommends that those imple- menting the ZLD process ensure that they have access to an OEM that under- stands the entire process and is able to take all factors including flow rate, solids concentration, temperature, particle size distribution, chemical composition and corrosive properties into account. There is an extensive global reference base of successful Siebtechnik Conturbex

A Conturbex centrifuge dewatering glaubersalt product in a ZLD plant.

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Mechanical Technology — May 2016