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  Optimising industrial fan performance

12  January  2012

  Jeremy Salisbury, Brammer UK

Industrial fans are a critical plant asset employed in a wide variety of applications ranging from burners and furnaces, heating, ventilation and cooling systems, to provide ‘blow-off’ air for clearing or drying. It is an area where compromise on maintenance or spare part quality should not be an option as asset failure can impact significantly on productivity.

Whether centrifugal or axial in action, industrial fans are generally driven by a motor, meaning they have the potential to consume high levels of energy if not correctly controlled or maintained – particularly given that, as with many other industrial applications, motors larger than necessary for the applications are frequently specified as contingencies are built into the design process. This is amply demonstrated by a recent Defra study which revealed that some 22 per cent of industrial motor energy consumption relates to fans. It is clearly an area where appropriate product specification, maintenance and asset management can impact very positively on profitability.

The issue is further complicated by the highly demanding environments in which fans often have to operate – frequently contending with extremes of heat, gases, dust and particulates, all of which have the potential to affect performance.

The problems of misalignment

One of the most common causes of failure in fans, misalignment, typically results from damaged or incorrectly installed shafts and worn bearings, as well as incorrect alignment of the drive train. Related to this is the issue are poorly balanced components such as rotor blades. The presence of poorly aligned and balanced components can result in issues such as excessive vibration, noise and heat, all of which increase energy consumption while subjecting both the fan and other components to unnecessary stress, potentially shortening product life. Meanwhile, the load on motors is also increased by misaligned shafts, meaning the motor consumes more power to deliver the extra turning effort to rotate the shaft.

Even more concerning than the additional energy use is the possibility of catastrophic failure resulting from misalignment – with the likelihood of extended plant downtime, lost productivity and production schedules thrown into disarray.

To prevent the problems of misalignment, a properly implemented predictive maintenance regime is key. Once products have been properly installed and configured in line with both manufacturer and customer requirements, a condition monitoring programme should be established. Products such as thermal imaging cameras, in-service vibration sensors and monitoring equipment can deliver both snapshot information and real time, continuous analysis of performance, identifying any areas of concern and allowing for planned shutdown if required to realign, repair or replace key components. The costs of the condition monitoring products pale into insignificance compared with the cost of an unplanned shutdown.

The importance of correct lubrication

As with so many other engineering components, timely and appropriate lubrication is integral to delivering optimum performance and service life. Incorrect or insufficient lubricant application is one of the most significant contributors to industrial bearing failures, being responsible for more than one third of total bearing failures. Once again, the costs resulting from unplanned downtime can be significant, but they are even further exacerbated if the location of the bearing in the industrial fan is hard to access.

Correct lubricant specification and lubricating at the correct intervals go a long way towards removing these concerns by protecting the surfaces of bearings, eliminating metal-on-metal contact which can cause wear and misalignment, and also guarding against corrosion.

Lubricant specification will be governed by a number of factors, including, but not limited to, plant environment, fan operating speed and temperature, contamination risk and ease of relubrication. For fans operating at high speeds in high temperature environments, an oil-based lubricant will both protect and cool. However, in dusty or dirty operating conditions, a grease lubricant may be preferred as it will ensure bearings are protected against contamination and offer enhanced sealing. An independent maintenance, repair and overhaul (MRO) specialist will be able to provide advice on both lubricant selection and the establishment of an appropriate lubrication programme.

A new approach to asset management

In instances where a fans in-service life is deemed insufficient or the mean time between failure of bearings and other components is becoming a serious issue, a complete review of assets and their use and performance may be required. This is increasingly the case in applications where fans, and the components within them, are operating at high speeds and in extremes of heat – conditions which create greater potential for downtime and urgent maintenance and repair.

Rather than simply continuing to order and install replacement components, key to this strategic approach is examining the reasons for the issue, assessing the cause or risk of fan damage and using root cause failure analysis to identify areas of improvement to the system. These could range from the specification of a different type of bearing, low friction seals and even automated lubrication systems. As well as self-aligning bearings which negate the need for manual realignment, products such as spherical roller bearings and toroidal bearings which allow for axial expansion and misalignment are proven in a variety of demanding applications.

These enhancements offer significant potential for both process improvement and cost savings as fans running at lower temperatures can often operate at higher speeds, while maintenance and lubrication intervals can be increased.

Once again, an authorised MRO distributor such as Brammer, working in partnership with one or more specialist component manufacturers, can provide best practice advice on specifying the right combination of products for the application, as well as offering advice on appropriate condition monitoring and maintenance planning. It is this combination of independent advice and technical expertise, supported by guaranteed and rapid availability of genuine components, which is increasingly adding value in MRO spares management for companies across all manufacturing sectors.

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