In reality, it is estimated that the majority of new combined-cycle power plants being installed will not routinely be over 60% net efficiency until after 2020.
In the meantime, operations will need to continue to look within their ongoing maintenance practices to realize the benefits of better energy efficiency.
Operators can use several methods to improve the efficiency of their operations; however, one simple but often overlooked solution is to tackle the issue of varnish formation and deposits sometimes initiated by the turbine lubricant.
Choose a Turbine Lubricant that Protects from Varnish
A great first step, especially with turbine units that stop and start many times a year, is to make sure the turbine oil does not contribute to varnish formation, which is common for turbines going through repeated heating and cooling cycles.
Varnish formation is a continuous cycle and occurs when the solubility limit of the turbine oil is exceeded.
This figure shows a typical cycle of varnish formation caused by the degradation of the turbine oil.
Specifically, insoluble varnish deposits tend to occur when the temperature of the fluid is cooler as their solubility in the turbine oil decreases with temperature.
Varnish in the lubricant, just like most solids in solution (e.g., sugar in water) has greater solubility in warm solutions than cold solutions. Therefore, every shut-down represents an opportunity for more harmful varnish deposits to occur as the oil temperatures decrease. This is especially concerning when it occurs in system components with tight internal clearances, such as in servo valves. It can lead to valve sticking, erosion, malfunction and possibly costly replacement.