Tacoma: new LNG hub comes to North America’s west coast

Extensive design work and engineering was carried out on other project features to meet rigorous safety standards. US federal government regulations prescribe seismic requirements for the tank and facility that are more stringent than those for bridges and overpasses. “Our plant is designed to withstand a once-every-2,450-year earthquake with no loss of LNG,” says Mr Hogan. “As a comparison, US interstate bridges are engineered to a 1,000-year earthquake standard.”

Additionally, the entire facility sits atop approximately 2,000 concrete columns that are 91 cm in diameter and extend to a depth of 24 to 30 m. These columns create an island of improved soil that will remain in place during an earthquake. They were formed in a unique process where an auger drill removes the soil while simultaneously injecting concrete. In all, 34,400 m³ of soil was replaced with the same amount of concrete. This aspect of the project received a Bronze Best in State Award in the Future Value to the Engineering Profession category from the American Council of Engineering Companies (ACEC) in 2018.

Of course, protecting the port’s unique environment remains an ongoing priority. On-site remediation efforts include steps to significantly restore habitat in the surrounding waterways for fish and other marine life. Additionally, once construction is complete, up to seven rain gardens – ‘enhanced treatment beds’ – will be installed to filter the site’s storm water run-off before it discharges into the Hylebos Waterway. This will greatly improve storm water management on the site, which previously had uncontrolled run-off and numerous buildings coated in lead-based paint and asbestos siding.

Considerable thought was also put into handling the site’s pre-existing structures. While the property has a rich history – including operating as a shipyard and subsequent US Navy facility – only two original buildings could feasibly be preserved. One was repurposed as a control room and office facility; the other became a warehouse. All other buildings needed to be removed, with a priority on minimising the impact of the demolition and ensuing construction. In all, more than 32,516 m² of building space was demolished, generating roughly 18,131 tonnes of debris. However, 83% of those materials were recycled or repurposed. “We were also able to save a huge amount of concrete from the demolished buildings to use as fill for on-site grading later,” adds Mr Hogan.

That fill was put to good use when the team advanced to the facility’s largest and most distinguishing feature – a 30.3M litre LNG storage tank and the only one if its kind in North America. Designed and constructed by CB&I Storage Solutions, the Tacoma LNG tank is unique for two reasons: its full-containment tank design and the seismic isolators that support it.

The tank’s 88 foundation isolators above ground are designed to minimise any shaking motion from a seismic event – allowing 66 cm of movement in any direction.

Likewise, the facility’s non-pressurised, full-containment tank is as robust as they come. In the LNG industry there are single-containment tanks, double-containment tanks, and full-containment tanks. Tacoma LNG’s is a nickel steel inner tank (which holds the LNG) which is fully encapsulated by 0.9 m of perlite insulation, and then again by another 61 to 91 cm of post-tensioned concrete outer tank and roof. This full-containment construction is designed to withstand a total failure of the inner tank with no loss of LNG. With 1,300 tonnes of steel forming the inner and outer tank and encased in 8,400 m³ of concrete, the tank is as much a visual marvel as a technical one.

As the construction phase of the Tacoma LNG project draws to a close, work is underway to commission the plant, which is poised to serve Puget LNG and PSE customers in early 2021. Doing so will propel the Port of Tacoma, and the Puget Sound, into the spotlight as the first LNG bunkering facility on the west coast – joining a growing number of global supply points fueling the next generation of low-carbon vessels.

“The Puget LNG facility is leading the way for the maritime industry with the first marine LNG bunkering pier on the west coast, capable of providing our customers with a safe, reliable and economic LNG source that’s cleaner than the alternatives,” says Mr Littauer. “Vessels that switch from diesel to LNG will reduce greenhouse gases [by] more than 30% and dramatically reduce dangerous particulate emissions, advancing the shipping sector’s transition towards decarbonisation,” he concludes.