Sustainable tribology

An ancient and constantly evolving science to support technological innovation in respect of environmental and economic sustainability: the example of wind farms

"Ecological transition is not a choice, it is a necessity": this was Mario Draghi's heartfelt appeal at PreCop26, held from 28 September to 2 October in Milan. A stance that adds to the many messages that are increasingly pressing the international community.

Working professionally in renewable energies is a real opportunity to turn this appeal into an active mission in everyday operations. The wind energy sector is also of interest to non-specialists, as it is perceived as environmentally sustainable by definition and innovative for historical reasons. For those operating in this sector, many aspects linked to environmental sustainability are intrinsic: ensuring that sustainability is also economic is a logical consequence of this, as well as an imperative in a company's vision. However, it is not easy to do business in the wind energy industry in Italy today, as there are countless political, legislative and technical obstacles. There are many concrete problems to be solved: from permits to install new plants or to expand or renovate existing ones, to management issues linked to logistically inconvenient site locations; from the presence of infrastructures that are not up to standard, to the difficulty of finding competent and qualified personnel to manage a plant on site.

All these cases entail heavy costs, which risk becoming uncontrollable and therefore unsustainable if they are not carried out according to a well-defined plan that must therefore be drawn up and managed by technically competent professionals. Competent figures in this field can in fact identify activities - in parallel with those that we can define as the core activities of a wind energy company, such as turbine, park and energy management - which may appear secondary but are equally important as they constitute a fundamental key to success: among these is lubrication. Tribology - the discipline that deals with friction, lubrication and wear - is not an exact science, as no two lubrication points in the world are identical; it is also a highly technical field, where it is necessary to act on the basis of specific in-depth knowledge and experience gained in the field. This is all the more true in the field of wind energy.

The standard configuration of a turbine includes many mechanical parts that must be lubricated. On average, there are 10 lubrication points: from the blade bearings to the generator bearing, through the main bearing to the gearboxes and the hydraulic system. Because of this, we can generally speak of at least 3 types of special lubricating grease and 2 types of synthetic oil. The ideal approach to lubrication is in principle guided by the reduction of complexity and costs - both of the lubricant itself and of maintenance and servicing. In addition to ensuring optimal lubrication, therefore, there are other aspects to focus on:

reduce the number of lubricants as much as possible, always using the most suitable product for each application

move towards a predictive maintenance approach, reducing as much as possible both the number of planned interventions and the risk of having to make emergency interventions

monitor the status of applications through lubricant analysis

Choosing the right lubricant, using it appropriately and monitoring its condition throughout the life of the wind turbine are all fundamental elements which, as we said at the beginning, also have a strong impact on environmental sustainability; in fact, they are actions that tend towards the ideal optimisation of operations and consumables. Unfortunately, this aspect is often underestimated in standard industrial maintenance, and not at all taken for granted in the case of wind farms. Obviously, these actions must be integrated with all other existing activities, including routine and extraordinary maintenance and the life-time extension programme for turbines. Optimum results can be achieved by choosing lubricants with the right chemical and physical characteristics and monitoring their condition through regular chemical analysis.

Many experiences from the field have verified the functionality of this approach. Here are three practical cases.

  • Extension of maintenance times: for a wind farm made up of turbines subjected to a life time extension campaign, by periodically monitoring the condition of the applications through diagnosis by chemical analysis of the lubricants, it was possible to extend the mechanical maintenance work from 6 months to 1 year.
  • Predictive maintenance: using a predictive approach through lubricant analysis, it was possible to identify the serious condition of a main bearing that contained a high amount of wear elements. Investigation using sophisticated measuring instruments (including PQ index and X-ray fluorescence), precise measurement of the type of particulate matter and, finally, interpretation of the results, made it possible to identify that the greatest wear was in the bearing cage. This made it possible to take all the necessary steps to keep the machine operational until the scheduled bearing replacement.
  • Detection of anomalies: chemical analysis of the grease in use in a blade bearing revealed that an unsuitable lubricant had been used by mistake, as it was specific for another application; prompt replacement by flushing with the appropriate grease made it possible to avoid serious repercussions and the consequent costly intervention and replacement of the bearing.

There are, therefore, important experiences where lubrication management integrated with other methods of investigation - such as chemical or vibrational analysis - makes a significant contribution to environmental sustainability, which cannot be separated from economic sustainability. The first example cited above, in all its simplicity, is clear: extending the useful life of an oil in operation means not only reducing operating costs, but also significantly reducing both the impact of complex maintenance work and the quantity of used lubricant to be disposed of.

Environmentally aware plant management must necessarily also be economically sound and well organised. Lubrication science can make a small but fundamental contribution to achieving the goal of functional and, as we have just seen, fully sustainable management.

Luciano Peyron, Manlio Astolfi

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