Using split roller bearings in coal-fired power stations can save time and money

Paul Boughton

In the UK, 31 per cent of electricity currently comes from coal-burning power stations. However, a third of these power stations are expected to close by 2016 due to EU air quality legislation due to be implemented. The result will be increased pressure on the existing infrastructure to perform more efficiently and reliably.  

Efficient maintenance is key to running a profitable power station and reliability requires un-planned down time to be minimised. Both of these objectives can be met by ensuring that the vast number of bearings across the site will provide optimum performance with minimal service costs.

Coal-fired power plants face a multitude of challenges that can adversely affect their profitability, including efficiency, reliability, safety, and environmental standards. The power plant has many critical operations that are exposed to harsh conditions with the potential to reduce bearing performance and overall bearing life which drives up operating costs.

Solid housed roller bearings are employed widely in coal fired stations, for example on coal conveyors, coal crushers  pulverisors, fans and mill motors. They operate in an environment contaminated with coal dust and problems usually start when this dust finds a route past protective seals and enters the bearing causing it to fail prematurely. When such a bearing failure occurs, the cost of the replacement bearing itself is extremely small in relation to the cost of the plant downtime.

More than 50 per cent of the operational bearing reliability issues in a coal-fired power station are due to inadequacies in bearing protection. As coal dust enters a bearing, it contaminates the lubricant reducing its effectiveness, the bearing operating temperature increases, the lubricant degrades and the bearing rapidly seizes. On the surface, a single bearing in a pillow block may appear inexpensive, but if the pillow block supports a boiler primary air fan impellor, bearing failure will directly affect boiler efficiency and therefore the capacity to generate electricity.

However, coal dust does not just cause increased wear in bearings, it is also a potential fire hazard, and as a result an array of safety measures must be in place to mitigate such circumstances. Prevention of bearing failure and the resulting increase in bearing temperature is a key maintenance objective which can be achieved with regular bearing inspections and replacement if required.

One way to improve bearing performance and reliability is to use SRB split roller bearings of the type manufactured by Revolvo UK, and now used extensively in power generation and process industries worldwide.  SRB split roller bearings perform exceptionally well in harsh operating conditions (even fully submerged using appropriate sealing), even under conditions of serious shaft misalignment, whereas solid mounted spherical roller bearings can suffer from non-concentric ineffective seals that will rapidly lead to expensive premature bearing failure.

Experience shows that SRB split roller bearing fitting time is typically reduced by 90 per cent compared to the time taken to fit an equivalent sized trapped solid roller bearing. As well as solid bearings being time consuming to fit, they are impossible to inspect while in situ, therefore routine inspection is often overlooked. Over their operational lifetime, SRB split roller bearings usually offer the operator lower total operational costs, but because split roller bearings are initially more expensive compared to solid roller bearings, many operators ignore these long term lower cost advantages.

From the technical, economic and pure design perspectives, SRB split roller bearings offer a host of advantages compared to solid types. The simplicity of fitting a split roller bearing, compared to a solid bearing, is a major factor in its longevity. They can be removed and replaced by simply supporting the shaft; there is no need to lift the shaft, or obtain access to the shaft ends, therefore expensive and awkward to handle lifting equipment is not required. This feature is extremely valuable for all applications, especially regarding large machines, where sheer size and weight is a barrier to fast and cost effective servicing.
Another reason for replacing solid housed bearings with split roller bearings is their effective seals, where they have inherent advantages compared to conventional solid housed bearing seals. With the split roller bearing design, the spherical location between the cartridge housing and the support pedestal ensures that under conditions of shaft misalignment, irrespective of whatever type of seal is used, it will always remain concentric to the shaft.

Revolvo has developed special labyrinth seals to exclude fine abrasive dust encountered in coal handling equipment, and these specialist sealing solutions are proving to be far more effective in stopping coal dust contamination, providing much improved bearing reliability, longer service life, and greatly reduced levels of maintenance.  

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