Bonanza tank farm stabilized with thermosiphons

Bonanza fuel tanks will stay on solid ground for years to come with the help of a $4.5 million U.S. Department of Commerce Economic Development Administration grant that will support the installation of thermosiphons under the tank farm, currently at risk of shifting due to thawing permafrost.
The grant award was announced last week and comes after a successful summer of testing out the prospective technology, according to Scot Henderson, CEO of Bonanza a subsidiary of Sitnasuak Native Corporation.
“We’re not having problems with our tanks yet, we’re trying to get ahead of it,” Henderson said in an interview with the Nugget.
Bonanza’s nine tank farm sits on ground that is very unstable. Located upland of the port, the area was originally built on tundra with layers of gravel and dirt, which over time is susceptible to the thawing permafrost underneath. Every few years Bonanza relevels the fence around the tank farm, combatting the constant settling of the ground.
This wasn’t always a problem, Henderson said. Thirty to 40 years ago, when temperatures didn’t reach the same highs in the summer, “we never worried about it,” he said.
Thermosiphons aren’t a new technology and not new to the company. Three of Bonanza’s newest tanks had them installed underneath before they were placed 10 years ago, working passively to cool the ground. They’re also present at Bonanza Express, and they have protected the building from shifting.
In both locations, a system of underground pipes loop and connect to tall, bristled staffs protruding from the ground. With a coolant fluid in the pipes, the closed system works passively to lower the underground temperature during warm months, releasing the heat from the structure above ground.
“It’s not designed to stop the thawing. It’s to slow it down enough where the ground won’t thaw too much until the winter comes back,” Henderson said.
The active siphons are what Bonanza is now interested in. They’ve switched the three tanks from passive to active by connecting each thermosiphon loop to a compressor, which works like a refrigeration unit that can be switched on in April and turned off in November, maintaining a underground freeze through the summer. Coupled with temperature sensors running deep under the tanks, Bonanza can monitor the ground year-round.
The challenge was replicating this for the other six tanks, which would mean going under the tanks to install the piping. Originally the plan was to move the tanks to install the pipes, which would be costly and risky if the tanks were to get damaged in the displacement.
“They’re designed to stay in one place. You build them. They’re designed to stay there forever,” Henderson said.
Finally, through talks and tests and ideation with engineers, Bonanza decided on directional drilling, which uses a drill rig to dig at a shallow angle. This summer it was tested, placing nine 90-foot thermosiphon pipes under one tank and connecting them above ground to a compressor to make it active. The flat loop network is different from the connected system under the other tanks, but temperature measurements show it to be working.
“When it’s all done, you can literally have a laptop, pull up each tank and see exactly where each thermal probe or temperature sensor is and tell at that point in time, what the temperature is,” Henderson said. “Obviously, the goal is keep it below freezing.”
With the help of the EDA grant, Bonanza will be able to install the siphons under the remaining five tanks, though it won’t cover the full cost of in project. Bonanza will match the grant with $12.7 million.
“We have obviously a lot of capital invested in this, but it’s not only a business investment, it’s basically necessary,” Henderson said.
Bonanza has worked with geotechnical engineers who created models to predict the ambient temperatures in the future. Henderson said they’ve determined that with the installation of the active thermosiphons the tank farm’s life has been extended 30 to 40 years.
“We supply most of the heating fuel, diesel for the community,” said Henderson. “If our tank farm is not safe and stable, Nome’s fuel supply is not it’s not safe or stable.”
The project will pick back up next summer. Getting the tanks stabilized is one of the biggest priorities for Sitnasuak’s board.