Next-generation turbine oils combat oxidation, thermal degradation and varnish
June 04, 2020
Turbines are a critical technology in power generation, pipeline transmission, marine, chemical and other industries with intensive power requirements. Gas, steam and combined cycle turbine systems represent the most demanding turbine oil service conditions in power plants. Power generation can be for electrical energy production to the grid or site power and steam generation for manufacturing plants, refineries, chemical plants, off-shore oil platforms, primary metal plants, hospitals and other large or remote facilities.
This steam turbine undergoing repair provides a view of the internal components of this complex machinery. Source: alexrow /Adobe Stock
Evolving plant operations and turbine design, with a focus on efficiency, require modern power turbines to operate under severe conditions. A push toward increasing efficiencies and higher levels of energy extraction have caused higher turbine operating temperatures inducing more thermal stress on the lubricant, demanding increased performance against oxidation, sludge and varnish formation.
New high-efficiency turbine designs, such as this General Electric 7HA.02 (formerly frame 7) gas turbine, expose turbine oils to higher temperatures and flows compared to older turbines. Source: Oak Ridge National Laboratory
Turbine oil sumps are also smaller to reduce capital costs of new turbines. Turbine oil is circulated at higher flow rates to compensate for higher turbine temperatures and smaller sump sizes.
The demand for continuous operation with minimized downtime for maintenance or turbine oil replacement further complicates the situation.
The result of new turbine design and extended uptime is higher turbine oil temperatures and thermal stress on the turbine oil, which is well documented. According to Turbomachinery International magazine, “…bearing oil temperatures may approach 100° C in typical steam turbines or industrial heavy-duty gas turbines and exceed 200° C in aero-derivative gas turbines.” The 2013 article, In-service Condition Monitoring of Turbine Oil , from Texas A&M’s Turbomachinery Laboratory, “…lube oil in aero-derivative turbines is in direct contact with metal surfaces ranging from 204° C to 316° C. Sump lube oil temperatures can range from 71° C to 121° C.”
Pipeline transmission facilities use gas turbines to provide power and pressure for the transmission of liquids and gases. Medium-sized remote packages boost oil and gas pressure to facilitate long-distance transmission of products to market. In these applications turbine fluids often serve a dual purpose, lubricating both the turbine and compressor in remote facilities. Large commercial marine vessels and military ships employ turbine engines for both propulsion and power generation. Such remote applications require high reliability lubricants with long service lives because downtime is not an option in harsh environments and conditions, including cyclic loading, saltwater exposure and temperature extremes.
Continue reading this informative e-zine from Phillips 66 (.pdf).