The Marathon (formerly Andeavor Logistics) natural gas and natural gas liquids (NGL) process facilities in the Uinta Basin, centered in Red Wash, Utah, can throughput more than 2,900 MMCF/day with natural gas inlet processing capacity more than 1,500 MMCF/day. It has 16 compressor stations distributed over 4,000 square miles in Utah, and 88 compressor stations in Wyoming and North Dakota.
“We have four I&E technicians doing a lot of drive time—some of the stations are four hours out,” said David Van Leuven, I&E supervisor, Marathon, in a presentation at the 2019 Emerson Global Users Exchange in Nashville, Tennessee.
“The vessels we focused on here are the scrubber bottles, two to four per compressor,” Van Leuvethn said. “The existing float level switches in the scrubber bottles were unreliable--gas coming back in from the first-stage scrubber would have liquid that would shut the compressor down.”
To guard against failed level switches, “We thought we wanted a probe in the gas stream to the compressor that would detect high liquid level,” Van Leuven said. “We tried adding a tuning-fork switch in the compressor inlet, but it always thought it detected liquid, and tuning it didn’t work.” On a suggestion from the vendor, they moved it back in the nozzle, which seemed to work, but they were still concerned.
“Around that time, Karl came in and suggested we try a Rosemount 2140 level switch in the scrubber bottles,” Van Leuven said. Karl White, senior sales representative, Emerson, co-presented with Van Leuven and Derek Hanni, senior I&E technician, Marathon.
The Rosemount 2140 is a vibrating-fork level switch that is virtually unaffected by foam, turbulence, vibration, solids content, coating products or liquid properties. As a HART device, it integrates into existing wired HART loops.
“The design of the switch resists fouling, and you can tune out splashing and false switching,” said White. “They can be partial-proof-tested locally or remotely.”
“The 2140s freed up a lot of time because we didn’t have to pull them out to check them.” Derek Hanni of Marathon (left), co-presented with Karl White of Emerson (center) and David Van Leuven, Marathon.
The scrubber bottle is the last stage of protection before gas enters the compressor. “It removes any residual fluid from the gas stream,” said Hanni, “So, we need a way to shut off the compressor if there’s too much liquid in the scrubber bottle.”
The existing float-style switches had parts that could be sucked into the compressor, which was a safety risk to personnel and the equipment. The float switches also are complicated to disassemble, clean and test. “It’s very time-consuming,” Hanni said.
Technicians were able to put the 2140 in the exact position same as the float switch, which saved a lot of installation time, lockout and tagout. “Before the 2140, the hardest test during maintenance was the float switches,” Hanni said. “Now, the 2140 partial-proof test takes less than a minute. You press a few buttons, the device performs a self-test, and the display shows the status during the test and the test results. The 2140s freed up a lot of time because we didn’t have to pull them out to check them.” That also reduced technician’s PPE requirements, and exposure to the process.
The trial led to the purchase of 220 instruments. That investment is paying off in increased revenue by avoiding maintenance shutdowns and avoided cost of manual testing. Marathon calculates ROI as 34% with payback at 124 days.
The Rosemount 2140 level switch local/remote proof test allows Marathon technicians to confirm their high-level alarm is working properly without having to shut-in and drain the vessel, remove the float switch and place it in a bucket to verify operation. It takes up to two hours to shut-in the vessel and test a float switch.
As a result, using the 2140 freed up approximately 500 hours of maintenance time per year.