Industrial solutions provider RTS Africa Engineering (RTS) states that air compressors used in the mining industry – including in Zambia – are, for the most part, well-proven, reliable pieces of equipment that can operate for years with relatively little maintenance.
However, RTS Africa MD Ian Fraser notes that the reliability of air compressors can lead to problems when the quality of their intake air is neglected.
“Many industrial air compressors work in very dusty conditions, particularly in the mining industry, where dust from newly broken rock is particularly abrasive,” he explains to Mining Weekly.
Fraser adds that, when dust gets into a compressor’s cylinders, it combines with the oil present to form a highly corrosive grinding paste, which will dramatically accelerate wear.
All compressors have their own air intake filters, which are mainly designed to filter out tiny low-mass particles. However, Fraser further explains that, if a compressor is exposed to excessive dust from manufacturing or mining where the particles are larger than 3 μm, the compressor’s air filters will rapidly become blocked.
In this instance, one of two things will happen – either a lot of money will be spent more frequently to change the proprietary air filters or the compressor will be neglected.
“With a blocked air filter, the compressor is increasingly starved of air and its efficiency levels drop. Ultimately, this leads to compressor failure. With large industrial compressors costing anything (upwards) of R500 000, unscheduled replacement and the cost of lost production can have serious consequences for a company’s bottom line,” Fraser says.
He explains that, primarily, inertial spin filters are used to remove dust from air streams or dust that is exhausted from a process on the mine into the atmosphere.
RTS inertial spin filters, which the company is currently aiming to supply to the Zambian mining industry, remove 98% of 15 μm particles and bigger, 93% of 10 μm particles and 80% of 5 μm particles.
By installing an RTS inertial spin filter at mines to remove most of the coarser particles from the air entering a compressor room, the compressor’s filters will need less frequent replacement.
The cost of spin filters, depending on the application and amount of air to be cleaned, can start at about R30 000 and range to more than R1-million, depending on the size of the installation.
Companies buying spin filters need to be aware that there are certain manufacturers claiming to be able to remove particles in the 3 μm or lower range. However, dust of this size no longer behaves like particles but rather like molecules and no longer responds to inertial forces, explains Fraser. For smaller particles, a conventional secondary filter is used.
“A spin filter consists of a cyclone-shaped tube, through which air is propelled or drawn. On entering the tube, the air is induced to spin using vanes. Particles in the tube move to the outside of the vortex and the clean air in the vortex centre exits through a central orifice at the end of the tube. A secondary stream of air is used to evacuate the dust-laden air to where it came from.”
It is a simple concept, Fraser notes, which makes it an attractive proposition in terms of maintenance, as there are no media or other filters that will need to be replaced and overhauls are unlikely to be required for up to 20 years.
“Only the spin filter’s electric motors – the only moving part – require infrequent attention,” he continues. This means that, even if compressors need to operate 24/7, RTS Africa spin filters will be “easily equal to the task”.
An alternative application of spin filters is the direct ventilation of variable-speed drives (VSDs), which are used on many compressors and need to be consistently and continuously cooled.
“The use of a spin filter is a truly effective means of feeding clean air at ambient temperatures to VSDs within a compressor room environment,” says Fraser, highlighting that RTS has developed a technique to cool VSDs called ‘back-channel cooling’.
In the past, the entire compressor room would be air-conditioned at a considerable running cost to cool a VSD, he points out.
“However, as VSDs will run efficiently at 40 ºC to 50 ºC, expensive air conditioning is not needed.” All that is required, is to channel clean air at ambient temperatures through the VSDs, he says.
The air from a spin filter can be used to fill the entire compressor room with clean, dust-free air.
“We have supplied many systems where we have pressurised the entire room and the VSDs will then draw on this air,” says Fraser.
As an alternative, he notes that, if air needs to be channelled to specific VSDs, air from spin filters is directed along a plenum at the back of the compressors, from where it is drawn by fans into the various VSDs.
The air is supplied at about 100 Pa, which is sufficient to maintain a slightly positive pressure. The air then passes through the VSDs and is vented out to the exterior of the VSD room.
Often compressors, once installed, are forgotten about until they give trouble, Fraser avers. Unlike spin filters, they do need regular maintenance, as they have moving metal parts, which do wear over time.
“Although, spin filters will greatly extend the time between filter replacements and overhauls, and, importantly, help prevent unscheduled failures,” Fraser adds.
He concludes that the reduction in airborne dust improves the working conditions at mines and facilitates the removal of airborne flammable dust, which, in turn, reduces the risk of fire or explosions, providing obvious occupational health benefits.