Removal of grease from wind turbine bearings by supercritical carbon dioxide

This work aims to test the ability of liquid carbon dioxide to remove grease from bearings in wind turbines. Currently, the removal of grease from wind turbines offshore in the North Sea is done by dismantling the bearing covers and scraping off the grease. This procedure is long, labour intensive and raises maintenance cost. Another issue is the environmental policy, the approval for newly introduced chemicals for flushing purposes are procedurally long. If the problems with grease removal could be solved in a different way other than manual removal or using chemicals, it will open many new market opportunities and would carved out a niche for the wind turbine maintenance industry. The solution of flushing grease could lower cost, time and reduce environmental impact by applying Supercritical Carbon Dioxide. The oil based grease SKF LGWM 1 was designed to handle extreme pressure and low temperature conditions. The grease covered the main bearing for 4 - 5 y in a wind turbine at Horns Rev 1 Offshore Wind Farm in the North Sea, 14 km from the west coast of Denmark. The series of experiments focused on higher pressures and temperatures as well as the use of some co-solvents. The highest recovery by pure carbon dioxide is 26 % and was achieved at 60 MPa and 80 °C while the addition of Kirasol-318SC improved the recovery by 8 % at the same conditions. Outgassing losses increase with the addition of kirasol. The low recoveries and high pressures obtained by the experiment do not provide an applicable method for grease removal; however it can be implemented for the removal of the contaminants from grease wastes.