LNG tank construction a sign of progress for Interior gas project

  • The site of a $48-million, 5.25-million gallon LNG tank near the Tanana River in Fairbanks is seen from the air this winter. The project will allow the LNG plant in Southcentral to run at full capacity year-round to store LNG during low-demand summer months. (Photo/Courtesy/ Pentex Natural Gas Co.)
  • Insulation is seen being covered at the site of the LNG storage tank that is the key piece of the Interior Energy Project. Part of the construction involves keeping the soil from dropping in temperature and drawing in water from adjoining areas and creating problems with ice below the tank. (Photo/Courtesy/Pentex Natural Gas Co.)

Backhoes are back digging in south Fairbanks as construction work is again underway on the Interior Energy Project.

Ground-turning work on the effort to expand the natural gas supply to the region had been on hold since the summer of 2015 as IEP leaders looked revise the scope of the project in the face of challenging economics brought on by lower oil prices. The last physical work on the project involved laying gas distribution lines in North Pole and Fairbanks.

Contractors for Pentex Alaska Natural Gas Co., which owns Fairbanks Natural Gas, began foundation work in the final days of December for a $48-million, 5.25 million-gallon LNG storage tank.

As of March 1, excavation for the tank foundation has been completed, which meant removal of up to 15 feet of silt and ice-laden material at the site near the Tanana River.

In place of the topsoil, a series of conduit loops and three feet of insulation have been laid. They’ll be buried under a new bed of gravel that will support the tank, according to Pentex CEO Dan Britton.

The conduit will support a passive cooling system known as a “thermosyphon” to keep the permafrost under the foundation frozen and stable if Fairbanks’ climate warms significantly over the next 75 years, which is the planned life of the tank.

The insulation and a separate heating loop will act as a barrier between the LNG tank, its super-cold contents and the ground below. Natural gas turns to LNG at about 260 degrees Fahrenheit below zero.

Britton noted that while it is counterintuitive to refrigerate the ground beneath a facility that is as cold as the dark side of the moon, the whole system needs to be monitored and controllable.

“The concern from the geotechnical engineers is that if we didn’t have an ability to create a thermal break, the LNG could make the ground too cold. It could take it from our desired temperature of about 28 to 30 degrees (Fahrenheit) down to zero, -10, -15 and then it will become a wick for water,” Britton explained during the March 1 Alaska Industrial Development and Export Authority board meeting.

“They don’t want us to be wicking water from outside the foundation into the foundation and creating ice lenses and jacking the tank.”

He added that if the thick layer of insulation works as intended, the glycol heating loop would be an idle insurance policy.

AIDEA purchased Pentex and Fairbanks Natural Gas in early 2015 and is in the process of transferring it to the borough-owned Interior Gas Utility as part of a $331 million plan to integrate the utilities and expand natural gas availability in Fairbanks and North Pole.

The tank itself will be a double-walled, fully contained facility with plenty of redundancy.

Britton said the request for proposals Pentex issued last summer was for a single-wall tank because the large size of the site and its isolated location meant a single-wall design with an outer containment system would be adequate.

However, when Boston-based Preload Cryogenics submitted a comparably priced bid for a double-wall tank, there was no reason not to go with the more robust protections, according to Britton.

The outer wall of the roughly 100-foot diameter tank will be 10-inch thick reinforced concrete. The primary inner tank will be made of roughly one half-inch thick welded steel plates The steel comprising the tank will also be about 9 percent nickel to keep it from becoming overly brittle when in contact with the super-cold LNG.

“If the inner tank were to breach for some reason the outer tank is designed to contain the full capacity of the LNG. It’s also designed to handle cryogenic temps,” Britton said.

Between the walls will be about 3 feet of insulation — largely perlite similar to the white grains found in potting soil.

Many important facilities have backups for key parts installed. Fairbanks LNG tank will be no different, other than the fact that it will have backups for the backups.

Britton said the tank would have three pump wells, each fully capable of keeping the system operating on its own. Likewise, there will be double redundancy in its vaporizers. They system is also designed to accept LNG from the truck tankers if need be.

“In the event we have a problem with the line from the tank feeding the vaporizers we can take LNG directly out of the trailers straight into the vaporizers and into they (distribution) system,” Britton said. “(We’re) trying to put as much redundancy in the system as we can.”

More than just a visible indicator for area residents that the long-delayed Interior Energy Project is closer to reality, AIDEA board member Gary Wilken of Fairbanks has called the LNG tank the heart “of the Interior Energy Project.”

That’s due in large part to the fact that just the storage tank will allow Fairbanks Natural Gas to nearly double the amount of gas it can provide customers even without additional gas supply.

When the tank is finished in late 2019 — in time to capture a $15 million LNG storage tax credit from the state before it sunsets — it will allow Pentex to run its Titan LNG plant in the Mat-Su Borough full-bore nearly all year because it will now have a place to hold the LNG. That means LNG produced during the low-demand summer months can be stored and drawn down during the winter.

Currently, with just several small portable storage tanks, the Titan plant, capable of processing about 1.5 billion cubic feet of gas, or bcf, per year, must be run to match immediate gas demand from end users.

In recent years that demand has been for between 750 and 900 million cubic feet of gas per year, according to Britton.

The 5.25 million gallon LNG tank will allow Pentex to run the Titan plant to process up to 1.4 bcf of gas, he said, allowing for a few weeks of maintenance downtime each year, he said.

Britton described the tank as providing a “direct line of sight” to when more natural gas will reach Fairbanks customers.

Finally, while the overarching contract for the tank went to an Outside firm, there is no shortage local contribution to the construction.

“We have a lot of work that’s being completed by Alaskan contractors and Alaskans,” Britton emphasized.

He listed 10 Alaska companies that are subcontractors for Preload Cryogenics on the project.

Great Northwest Inc., a Fairbanks-area general contractor handled all of the site preparation and gravel fill.

Anchorage Sand and Gravel is casting the outer tank panels, which will be trucked north to Fairbanks. Three of the 85-foot long concrete test panels will be started later this month and the first will head to the site in early June when spring weight restrictions on the highways are lifted, according to Britton.

Elwood Brehmer can be reached at [email protected].

Updated: 
03/06/2018 - 6:14pm

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