With many industrial air compressors being used in dusty conditions, the lack of proper filtration of incoming air can shorten the life span of the compressors by 75% to 80%, says specialised engineering company RTS Africa Engineering MD Ian Fraser.

“Air compressors used in industries are, for the most part, well-proven, reliable pieces of equipment able to operate for years with relatively little maintenance when used with the right air filter system and properly maintained.”

He points out that when small particles of dust from an engineering or mining environment mix with the oil used in compressors, a sludge forms that is extremely abrasive. Once this has been created within the compressor, it is challenging to remove it.

“All compressors have their own air intake filters, which are designed to filter out tiny low-mass particles. However, 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 clog up rapidly.”

To mitigate this challenge, RTS Africa spin filters remove 98% of 15 μm particles and above, 93% of 10 μm particles and 80% of 5 μm particles, notes Fraser. “The spin filter is not designed to remove particles of 3 μm or less. However, using an RTS Africa inertial spin filter, most of the large particulate is removed before it reaches the fine secondary filters – thus preventing blockage of these filters.”

Further, he explains that spin filters can be put in place at the air intake of compressors or compressor rooms to filter particles larger than 5 μm.

Fraser mentions that, on occasions, certain vendors of similar technology claim to be able to remove particles of 3 μm or less with inertial spin filters. He points out, however, that particles of this size no longer ‘behave’ like particles but rather like molecules – at which point they no longer respond to inertial forces.

“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. Dust-laden air is driven to the outer part of the vortex, from where it is evacuated by a second fan and returned to the atmosphere. It can also be recovered if required.

RTS Africa installed a 250 000 m3 spin filter system for a South African glass manufacturer in the 1990s, and the system is still operational, says Fraser. “It is a simple concept, which makes it a very attractive proposition in terms of maintenance, with spin filters running for years, with little or no maintenance, as electric motors – the only moving part in the spin filter – require infrequent attention.”

This means that, even if compressors need to operate 24/7, RTS Africa spin filters will be equal to the task. In an alternative application, spin filters can be very useful in the direct ventilation of variable-speed drives (VSDs), which need to be consistently and continuously cooled, and are used on many compressors and other equipment such as pumps.

“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,” states Fraser.

The company has developed a technique – together with a VSD supplier – which it calls ‘back-channel cooling’ for VSDs. In the past, to cool VSDs installed on compressors, the entire space would be air-conditioned at considerable installation and running cost. However, with VSDs, the cooling cost for an installation is considerably reduced.

“For instance, VSDs will run efficiently at temperatures of 40 ˚C to 50 ˚C and, therefore expensive air conditioning is not needed.All that is required is to channel clean air at ambient temperatures through the VSDs,” he says.

Fraser 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 space and the VSDs then draw on this air.”

As an alternative, 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.

“Compressors – unlike spin filters – do need maintenance at regular intervals, as they have moving metal parts, which do wear over time. Spin filters will greatly extend the time between filter replacements and overhauls and, importantly, will help prevent unscheduled failures,” Fraser concludes.