Multotec offers unique design of its classification cyclones, incorporating engineering that makes it possible to alter several components during the design stage, or even after installation, to ensure that the cyclone meets the customers’ exact performance requirements. “At Multotec our metallurgical engineers have the necessary levels of expertise and skill to ensure the most appropriate cyclone solution,” Ernst Bekker, Product Specialist, Multotec, says.
“When designing and engineering a cyclone or cyclone cluster, we take into account not only the cyclone itself, but also our understanding of up-front and downstream processes. For example, if a very fine cut point is required, standard simulations will dictate the use of small diameter cyclones. However, if the feed stream contains fairly large particle sizes, this could cause blockages at the inlet of a small diameter cyclone. Therefore the selected cyclone configuration has to take into consideration operational constraints, while still satisfying the process requirements.”
An example which clearly underpins this capability is a classification cyclone cluster Multotec recently installed in a milling circuit. The grind of the mill circuit was much coarser than what was originally anticipated, and this resulted in extreme circulating loads that limited the throughput capacity of this process.
“The customer asked us to present an alternative solution,” Bekker relates. “Essentially, a change in cut point was required on the cyclones and one of two options could have been selected to achieve this. The first option was to install larger diameter cyclones and the second, which was considered a far more cost effective solution, was to alter the existing cyclone configuration. In this first instance, installing the larger diameter cyclones would have necessitated a total re-engineering of the cyclone cluster with associated infrastructure changes, downtime and cost implications.
“Multotec proposed the second option as we believed it was more appropriate, being faster and cheaper and requiring limited modifications to the cluster. The seriousness of this situation cannot be understated, as the significantly reduced throughput from this milling circuit could have had severe long term financial implications for the operation. The conventional cyclone was converted to a flat bottomed cyclone by modifying certain components and the cone angle. This design modification achieved the required throughput and the bottleneck in the milling process was successfully relieved.”
The vortex finder is used to control the cut point inside a classification cyclone, which means that the vortex finder can be selected to allow for more or less material reporting to the overflow, as well as for finer or coarser particles. This ability to make an appropriate selection makes it is easier to control the performance of the cyclone, and to fine tune the product requirements. Bekker cautions however, that if the vortex finder is changed, it not only changes the cut point, but also the operating pressure and this must be taken into account.
Without changing the entire cyclone design, Multotec is able to accommodate varying spigot diameters and achieve optimum underflow densities. The Multotec spigot has a parallel throat design, which enables it to maintain the correct spigot opening over a longer period of time.
“This design is important, the reason being that in most operations where conventional cyclones are used as the spigot starts to wear, the amount of by-pass water to the underflow starts to increase, as the spigot diameter increases, which then leads to an increase in the misplacement of fine material to the underflow, and reduced hydrocyclone efficiencies ,” he explains.
The cone angle is selected based on the customers’ requirements. By changing the cone angle for the same cyclone diameter as opposed to altering the cyclone diameter, the cut point of the cyclone can also be altered to make the separation cut point coarser or finer. This also allows for a high degree of flexibility and the ability to customise for specific applications.
An advantage of the rubber lined hydrocyclone is the inclusion of weep holes, which have been a feature of this range from the mid 90’s. This allows for the early detection of internal damage which reduces the frequency of unplanned stoppages. Early detection allows for higher overall cyclone efficiencies as the damaged liner, which could result in particle misplacement, can be easily and quickly replaced due to the loose rubber lining technology used inside these units.
The scrolled evolute inlet design, when compared to the conventional cyclone inlet design, assists in obtaining high separation efficiencies at lower operating pressures. With the increase in the cost of energy, using hydrocyclones which offer higher capacities can assist in reducing the overall energy consumption in a process.
The Multotec hydrocyclone range comprises cyclone diameters from 25 mm to 1 400 mm. Most of these diameters can accommodate a range of cone angles, while different vortex finders and spigot diameters are standard for all diameters. The small diameter cyclones, up to 100 mm, are predominately polyurethane, while the larger diameter units can be supplied in polyurethane, steel cyclones with bonded or loose rubber lining, and steel with ceramic lining.
Multotec can, and has, provided alternative options for specialised applications to the market which include special materials of construction and wear linings.