TAPS reaching a milestone
Final steps of electrification near as pump station 1 upgrades go into action
Having started up the new electrically powered pumping system at pump station 1 of the trans-Alaska oil pipeline in October, Alyeska Pipeline Service Co. is in the process of completing the electrification upgrade of the pump station, Alyeska engineering manager Rob Annett told Petroleum News Feb. 1.
Alyeska operates the pipeline system on behalf of the oil companies that own the line. Pump station 1 is the facility that accepts oil delivered from the North Slope oil fields and pumps that oil into the northern end of the pipeline.
Completion of the work at pump station 1 will mark the end of a major multi-year project in which Alyeska has replaced the aging turbine-powered pumps that were originally installed on the pipeline with a system of modern electrically powered pumps that can flexibly handle varying flow rates - the pumps drive oil through the line. While the old pumps were grossly oversized for the declining oil throughput, “the new pumps and the new drives that can control those really give us great control and they give us much higher efficiency,” Annett said.
Remote monitoringThe electrification project has also involved the installation of a state-of-the-art system that enables the remote monitoring from Alyeska’s Anchorage control center of equipment along the pipeline, thus enabling operators in Anchorage to anticipate equipment problems and initiate maintenance and repairs before a significant problem arises.
“You can, for example, monitor any anomaly in a pump’s performance and send someone out there to check it before it becomes a problem,” Annett said. “You can monitor how equipment is behaving over time, to predict any potential failures and use predictive maintenance.”
In conjunction with shutting down some of the pipeline’s original pump stations in response to declining oil flow, work on the electrification of the four pump stations that remain in operation began in 2004. Alyeska completed the electrification of three of those pump stations, pump stations three, four and nine, in 2009, but deferred the conversion of pump station 1, given the higher complexity of that facility.
Testing firstHowever, work on pump station 1 has since moved ahead, leading to the October startup of the electrical pumping system. In fact, the electric pumps had started up in test mode, in parallel with the operation of the legacy turbine pumps, prior to the live use of the new pumps, Annett explained. While under test, the new pumps continuously recycled some oil to simulate full-scale operation.
Then, on Oct. 14, Alyeska opened the two discharge valves that allowed oil from the electric pumps to enter the pipeline, thus putting the new pumps into full operation and allowing the old pumps to be turned off. For the time being, the old pumps can be turned back on, should a problem arise with the new pumps.
Booster pumpsBecause of the complexity of the operations at pump station 1, there are smaller booster pumps at the pump station that are also being replaced by electrically powered pumps. Essentially, with oil arriving at the pump station at different pressures from different oil fields, the arriving oil often has to be channeled into a holding tank for pressure balancing. The booster pumps then deliver the oil from the tank at the appropriate pressure to the mainline pumps, Annett explained.
Alyeska is in the process of going through the same commissioning process for the booster pumps as was used for the mainline pumps, Annett said. In addition, some of the remote diagnostics upgrades for some non-critical equipment at the pump station remains to be completed, he said.
Power for the electrical pumps and other electrical equipment, and for accommodation facilities, at pump station 1 comes from a new 13.8 megawatt gas turbine electricity generator that went into operation at the time that testing of the electrical pumps started. Alyeska has yet to complete the work of installing an additional 5-megawatt generator, to act as a backup power source, should the larger generator fail. However, the pump station can also, as a backup arrangement, use commercial power from the North Slope power grid, Annett said. In fact, depending on the level of electrical power demand in the pump station, Alyeska could sell any excess power from the 13.8 megawatt generator back into the grid, he said.
A gas compression module at pump station 1 routes natural gas from the North Slope oil fields to the power generators at the pump station, and to the other two operational pump stations north of the Brooks Range, all of which have gas turbine generators.
Wrapping up the workAnnett said that Alyeska anticipates the remaining upgrade work at pump station 1, including the switch over to the new booster pumps, the implementation of the backup generator and the completion of the remote diagnostic systems, to be wrapped up in the next few months. And the air permits for pump station 1 require dual operation of the new and old pumping systems to end within 270 days of the new system firing up.
“So there’s a date looming large in June when we will be decoupling the legacy system,” Annett said.
Annett commented that the most complicated aspect of the pump station 1 conversion has been executing the transition from the old system to the new system, while at the same time keeping the pipeline fully operational. During the peak of the work involved, some 170 contractors were on site, in the confined space of the pump station, setting up the new system, he said.
However, Alyeska was able to use lessons learned from the conversion of the other pump stations when carrying out the conversion at pump station 1, Annett said.