Performance of steam turbines operating under wet steam is known to worsen proportionally to the increase in wetness at turbine exhaust. Numerous strategies have been attempted in the past to minimize the efficiency loss and mechanical damage associated with liquid phase formation, mostly with limited success and poor commercial viability due to increased complexity.
The application of hydrophobic coatings is a simple economically favorable strategy and is expected to partially inhibit the formation of water films on blade surfaces and associated consequences.
This paper addresses a need of turbine manufacturers: the development of a methodology to test, rapidly and economically, performance impact and endurance of coatings to allow a systematic selection. The resulting methodology employs specialized equipment to measure the fog rejection effectiveness of coatings and to generate droplet impingement and thermal loads comparable to real applications, all under laboratory conditions. Measurement results indicated that different materials cause different wetness losses and turbine efficiency can be improved with the coating of blades. Transfer functions used to generate the correspondence between laboratory and representative turbine conditions enabled the coating selection for turbine application. Finally, tests in a model turbine allowed validating the prediction of efficiency improvement, confirming the suitability of the developed methodology.
This work demonstrates that this technology delivers an important improvement in turbine efficiency.