In business for more than 70 years, Arkansas Western Gas (AWG), a subsidiary of Southwestern Energy Co, provides natural gas to more than 144,000 residents and businesses of northern Arkansas, using turbine-powered compressors to distribute natural gas from fields in the region to its customers. In the small town of Ozark, AR, AWG operates a gas transmission station that supplies natural gas to approximately 110,000 residents, local businesses, and utilities.
"The community really depends on us to provide them with clean, high quality natural gas for things like heating their homes and cooking food," said Junior Bowen, plant supervisor, AWG''s Ozark Station. "We also supply natural gas to utilities and municipalities for things like transportation, infrastructure, and lighting."
During the cold weather months -- October to February -- AWG operates six Solar T-1000 gas turbines on a rotating schedule in order to meet the additional demand for natural gas.
"These turbines are critical to supplying the community with natural gas and any type of disruption in their performance can significantly reduce the amount of gas being supplied," Bowen said.
Diagnosing the Problem
Prior to 1992, AWG used conventional, mineral-based oils to lubricate each of the Solar T-1000 turbines. The mineral oil caused several problems, including deposit buildups, which ultimately led to bearing failures and the need for regular system overhauls. According to Bowen, the costs involved in replacing bearings and overhauling each of the six turbines every few years became overwhelming.
"We were spending approximately $40,000 per overhaul," Bowen said. "With each of the six turbines needing two or more overhauls over a 10 year period, we were looking at close to $500,000 in overhaul costs alone."
AWG consulted ExxonMobil lubricant specialists to help find a better solution.
"When Arkansas Western Gas brought the problems they were having to ExxonMobil it was immediately recommended that AWG switch from using conventional, mineral-based oil to a high-performance synthetic lubricant," said Brent Winter, sales engineer, ExxonMobil Lubricants & Specialties, who currently oversees ExxonMobil''s projects with AWG. "In this case, Mobil SHC 824 synthetic oil was the best choice to solve AWG''s problem with bearing failures."
Switching to Synthetics Saves Time and Money
Today, AWG is successfully operating its six critical Solar T-100 turbines using the original fill of Mobil SHC 824 from back in 1992. The frequent system overhauls resulting from bearing failures are a distant memory, as are the excess time and costs needed for turbine maintenance and parts replacements.
"Switching to a high-performance synthetic lubricant has been one of the best financial decisions that we have made," Bowen said. "Before, when we were using conventional oils, we saved money on our initial oil purchase, but we had only a 6 month drain interval with the conventional oil. And on top of that, all our other maintenance costs were very high and our equipment did not perform nearly as well.
"Think about it; our turbines have now been on the same oil fill for 13 years and our equipment performance has been exceptional since we switched to Mobil SHC® 824 synthetic oil. Also, the costs for maintaining our equipment have been greatly reduced."
Switching to Synthetics = No Need for Heaters
In addition, shortly before meeting with ExxonMobil lubrication specialists in 1992, AWG maintenance personnel suspected that oil whip was occurring during the cold startups, contributing to the frequent bearing failures. They felt that this problem was occurring because the mineral-based oil being used could not perform at such low temperatures.
"When this problem first occurred, we thought the only logical solution was to install oil heaters in each of the turbines to heat the oil before initiating the startup process," Bowen said. "We were in the process of looking to buy the heaters, which would have cost $5,000 each, and we needed one for each of our six turbine units.
"Fortunately, before we made the purchases, the folks at ExxonMobil informed us that because synthetics are designed to protect equipment even under the most demanding operating conditions and over a wide range of temperature extremes, we did not need the heaters," Bowen said. "So that saved us another $30,000."
Today, nearly 13 years after Arkansas Western Gas made the switch to synthetic oil, Bowen says he and AWG''s maintenance crew still cannot believe the difference the changeover has made at the facility.
"We''re all still amazed at the improvements the synthetic has made in our operations and maintenance practices," Bowen said. "We''ve seen significant cost savings for the company by eliminating time-consuming overhauls and extending our oil drain intervals. It is amazing the impact Mobil SHC 824 synthetic oil has had on our business."