Spin filtration systems should be employed to effectively eliminate electrical equipment failures at coal mines, says specialised engineering services provider RTS Africa Engineering MD Ian Fraser.
He explains that coal dust is exceptionally conductive and can cause expensive electrical equipment, such as variable-speed drives (VSDs), switchgears and compressors, to be damaged by electrical short circuits.
While traditional forms of filtration can mitigate these issues, Fraser notes, the high levels of dust at different particulate sizes leads to a significant amount of time, effort and money being spent on cleaning or replacing filters.
“This is becoming more problematic for mining companies because of the current economic climate. Mines simply do not have the resources to constantly maintain traditional filtration systems.”
He points out that RTS’s spin filtration solution can remove 98% of dust at 15 µm, 93% of dust at 10 µm and 80% of dust at 5 µm, stating that, once installed, the system requires little to no maintenance.
“The squirrel-caged electric motors are the only equipment in our spin filters that have moving parts; they are reliable and require little maintenance, making the spin filtration system virtually maintenance free,” Fraser states.
He explains that the ‘heart’ of the system is an imported polypropylene core block consisting of several 35-mm-diameter cylindrical vortexes. Each cylinder contains a moulded vein, causing the air pushed through the cylinder to spin. The rotating air creates a cyclone, resulting in the centrifugal force pushing dust particles out of the air, which is then circulated into a ventilated room.
An auxiliary purge fan keeps the dust in flight and blows all particles out of the polypropylene block and back into the atmosphere. Alternatively, the dust can be blown into a collection system, which can be emptied out when required.
Fraser asserts that 35 mm diameters are the most efficiently sized vortexes for spin filtration technology, as an increased diameter would result in dust particles having to travel further, requiring more energy. Conversely, smaller-diameter cylinders will increase the risk of pressure drops in the system, making it more difficult to maintain airflow velocity.
Meanwhile, he says, RTS can also apply secondary filtration systems to its spin filter to capture dust particles at 3 µm and smaller because spin filtration is unable to remove particulates at 3 µm and smaller, as “the particles are so small that they behave like molecules, reacting to other forces such as Brownian motion and will not react to any inertial force”.
He notes that dust particulates at 3 µm and smaller pose no threat to machinery; however, they can cause lung disease such as silicosis.
Further, traditional filters also last up to 20 times longer when used in conjunction with a spin filter, Fraser says, explaining that, because the larger dust particles are removed by spin filters, traditional filtration systems are required to capture dust at only 3 µm or smaller.
He highlights that a particle distribution analysis was done on RTS’s spin filter that used secondary filtration technology at a well-known steelmaker’s sinter plant.
“The analysis revealed that a significant amount of sub-3-µm dust was present in the system. RTS wanted to determine the mass of sub-3-µm dust that the system was able to extract. According to the particle count, our system extracted less than 71% of the sub-3-µm dust, however, it translated into 96% of the total dust mass.”
Meanwhile, RTS demonstrated its spin filtration system’s ability, when used with secondary filtration systems, to extend the operating life of electrical equipment at an underground coal mine in eMalahleni.
The installation, which was completed at the end of last year, required that a spin filter be used in three different rooms, each containing electrical equipment such as VSDs, switchgear and compressors.
“The objective of the installation was to remove any coal dust that would damage the electrical equipment. “Owing to the size variations of each room, the most effective solution was to install a spin filtration system in each room,” Fraser explains, adding that several ventilation tubes were also installed in the rooms to ensure proper air circulation.
The mine has not reported any equipment failure caused by electrical failures from coal dust in the three rooms.