New turbine oil improves efficiency

Materials World magazine
6 Jan 2020

A new oil is claimed to improve bearing and turbine efficiency. Idha Valeur finds out more.

In November 2019, oil and gas giant ExxonMobil and multi-industry company General Electric (GE), USA, announced their collaboration to create a new oil. Called Mobil SHC 918 EE, it is specifically for GE 7HA, 9HA, 6FA.01 and 7FA gas turbines. ExxonMobil Field Engineer, Tara Nickels, told Materials World that the turbine oil is made of a base stock and additives.

‘That general formulation does not change across the board. The energy efficiency benefits were actually just realised through the viscosity changes, and we tweaked the additives and base stock to achieve that, ultimately reducing fuel consumption,’ she said.

With cost reduction at the forefront of the industry’s agenda, the companies claimed the new lubricant will lower energy consumption and subsequently save expenses associated with power generation.

‘It has the potential to dramatically improve turbine bearing efficiency by up to 15% compared to conventional ISO VG 32 turbine oils, reducing overall energy consumption. Improving turbine energy efficiency is a significant focus for the power generation industry, as fuel costs can account for up to 80% of total running costs,’ Nickels said.

According to Nickels, the oil’s low viscosity enables equipment to operate at lower temperatures than other oils, for reducing energy and fuel consumption, plus extending component life. ‘These benefits can help operators potentially save tens of thousands of dollars in operations and maintenance costs,’ she said.

The new lubricant necessitated a new specifications document, GEK 121603, to ensure a minimum performance characteristic as, due to its lower viscosity, it did not fit other current parameters.

Oil testing

Nickels explained that while ExxonMobil carried out the research and formulation of the oil, GE performed the testing, which was completed in three stages.

First, a test rig was created that simulated turbine bearing surface speeds under different load conditions to assess which offered maximum energy efficiency benefits. Then, it was tested in GE’s test stand on both the 7HA and the 9HA gas turbines, while 4,000 sensors monitored the performance under several conditions. ‘We had an oil we were running through the GE test stand. We knew the change in temperature from a conventional oil to our energy efficient oil needed to have a drop in temperature that would correlate to energy efficiency, so we had a temperature probe that went into the bearing,’ Nickels said.

‘As we provided load to the bearing or changed the feed, we monitored the change of temperature. We could use that temperature change to calculate the overall energy efficiency.’