Using Biodegradable Lubricants

The 33-mw Boötanj plant, which began operation in May 2006, is the first hydro facility in Slovenia to use environmentally compatible hydraulic oil. Owner Holding Slovenske Elektrarne (HSE) uses a biodegrable lubricant from Panolin AG in the hydraulic system of five radial gates.

Choosing oils that are environmentally friendly

Hydroelectric resources play an important role in providing power to Slovenia. HSE subsidiary HSE Invest, an engineering company, is constructing the five-powerhouse, 187-mw Lower Sava River Hydro Power Project. The project, with an expected annual production of 720,000 megawatt-hours, will meet about 6 percent of Slovenia’s annual power needs. The Boötanj plant, in southeastern Slovenia about 100 kilometers east from the capital Ljubljana, is the first plant in the Lower Sava group to be developed.

Along the Sava River in Slovenia, Holding Slovenske Elektrarne is developing five run-of-river plants. The company is using biodegradable oil at these facilities.
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At Boötanj, HSE personnel considered the possibility of using biodegradable oil in the turbines in addition to the biodegradable oil for the radial gates’ hydraulic system, but the timing was wrong. Work on the plant was too advanced to use the biodegradable oil in all three turbines. Consequently, HSE decided the use of only one type of oil for all three turbines would mean fewer problems for maintenance.

However, HSE is incorporating the use of biodegradable oil in both the hydraulic systems and the turbines at the next two plants in the Lower Sava River Hydro Power Project: 42.5-mw Blanca, to begin operation in November 2008; and 39.5-mw Kröko, due for completion in 2012.

Because of ecological reasons, HSE prescribes use of biodegradable oil in tender demands. HSE strongly believes that the environmental awareness of the hydropower industry is fundamental to mankind, and we build hydropower plants to operate for 50, and more, years.

Differentiating biodegradable lubricants from one another

Not all biodegradable oils are the same. For example, the biodegradable quality of one lubricant based on vegetable oil worked too well – it decomposed too fast. In other applications, a lubricant based on rapeseed oil separated into oil and residue formations similar to chewing gum in a short time. These oil and residue deposits reduced system output. And over a long time, bearing grease decomposed in place.

Unlike other biodegradable oils that are based on vegetable oil, the oil HSE uses at Boötanj, and plans to use at the other Lower Sava plants, is a saturated synthetic-ester based product supplied by Panolin AG, of Zurich, Switzerland. Synthetic esters are organic compounds made from the reaction of acids and alcohols and can also come from renewable resources. They have a high vaporization point, provide a strong lubricating film, disperse oil deposits, and are highly biodegradable.

There are many experiences with using this kind of oil, and HSE checked on some reference facilities, including Tiwag’s 31.5-mw Langkampfen hydro plant in Austria, which was one of the first hydro plants in Europe to use biodegradable lubricants. HSE also shared experience with operating and maintenance staff at Austria’s 16-mw Bischofshofen and 18-mw Kreuzbergmaut plants before it decided to use biodegradable oils.

Worth the extra cost

The cost of biodegradable oils is rather high, compared to mineral oils, but HSE believes that, in new construction and during the bid period, these costs are much lower than changing the complete system anytime later. In addition, accidental discharge of biodegradable lubricants into a river would result in a far less consequential loss than a discharge of mineral-based lubricants.

– By Sandi Ritlop, manager, Lower Sava project, HSE Invest, E-mail:

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