Shipping Sees New Use for Ammonia Tanker Barge

In 2015, Vigor, the Pacific Northwest’s biggest shipbuilder, launched the Harvest, the first liquefied ammonia barge built in the U.S. since 1982. It was built for the Mosaic Co. of Minnesota, a leading producer of concentrated phosphate and potash fertilizers, and will be operated as an ATB in the Gulf by a subsidiary of the Savage Company. The 508‘ hull was constructed at Vigor’s HQ and base facility, the Swan Island shipyard in Portland, with the assistance of other Vigor divisions in the region. (The Harvest is the biggest, most complex vessel built in Portland since Henry Kaiser established the Swan Island shipyard in 1942 to build T-2 oil tankers for the US Navy in World War II.)

Ammonia, a molecule comprising one nitrogen and three hydrogen atoms, has been nurturing mankind as a fertilizer for many decades–as a source of nitrogen–but the Harvest was the first vessel built to meet all the requirements of the latest safety and environmental rules for transporting liquid ammonia from the ABS (American Bureau of Shipping) and U.S. Coast Guard. This cargo is a key ingredient in fertilizer and must be transported in a dedicated tank barge with specialized handling and safety systems. It was completed two days ahead of schedule and was moored in the Willamette River and open for inspection on June 21, when the dedication ceremony took place at the shipyard in shirtsleeve weather.

“This is a significant project for both the maritime industry and our community,” Vigor CEO Frank Foti told the crowd. “The Harvest project combines Vigor’s capabilities in large vessel construction with decades of experience building complex structures like nuclear containment devices, dam lift-gates and bridges.  Remarkably, only three years later, the shipping industry was looking at ammonia in an entirely new light–as a promising carbon-free energy carrier for maritime transportation.

Anhydrous ammonia is a gas under ambient conditions. It must be liquified to achieve higher volumetric density by compression, refrigeration or both. The phase change of ammonia from liquid to gas, and vice versa, happens when heat or pressure is added or withdrawn. The ammonia bunkering process is based on handling ammonia as a saturated liquid.  The project team has studied all possible bunkering configurations and categorized them into truck-to-ship, ship-to-ship, shore pipeline-to-ship, as well as cassette bunkering. The study also highlighted the lack of ammonia bunkering standards–in contrast to the US fertilizer industry, which has vast experience to share with maritime stakeholders.

Vigor relied on the J.H. Kelly Company, based in Longview, Washington, as a key partner in the project, providing the onboard electrical work as well as pre-fabrication and installation of the cargo piping systems. The plant, cargo pumps, dual hose-handling cranes from Techcrane International, the 2,000 HP Schottel rotating bow thruster, and all other gear and systems are powered by the four CAT Tier 3, 960 Kw gen-sets. They are housed in the generator room aft where up to three engines are required to operate all equipment simultaneously, with the fourth engine as a back-up. Fuel tanks in the engine space contain over 24,000 gallons. Fuel transfer and electric power transfer from tug to barge is possible in an emergency.

The SmartChief power management system is fully automatic to maintain electrical supply to all essential services. It uses a dual computer set-up for redundancy and active back-up. When the main generators are off line, power for control and safety systems comes from a 163kW Caterpillar harbor generator. This free-standing unit is air-cooled and is housed in the central control room (CCR) amidships on the port side, along with the work stations for the Cargo Master and CargoMax cargo-transfer programs. Vimex gas detection for the cargo tanks, re-liquefaction status, and CO2 fire prevention monitors are routed to the CCR, where all personal safety equipment, first aid, fire safety plans, breathing masks, and survival suits are stowed. (Liquid ammonia is considered non-flammable by USCG rules.) The CCR and deck manifolds are protected with water sprays in case of an ammonia release.

The hull was fabricated from 9,000 tons of American steel and fitted with 4,400 tons of equipment. The project involved close to a million labor hours, and employed approximately 1,500 people for nearly two years, at Vigor facilities in Oregon and Washington and subcontractors throughout the region. The barge will be partnered with a dedicated 4,000 HP tug to form an articulated tug and barge (ATB) via an Articouple Connection System. It is not manned during transit, when an umbilical cord to the tug allows the crew to have remote control of all the barge’s systems including alarms and tank levels.

The Harvest has four cargo tanks, each capable of holding 5,500 tons of liquid anhydrous ammonia at very low pressure. Because of the tight schedule, the tanks were fabricated in Korea and delivered by heavy-lift ship. The installation of the 1,100-ton tanks into the corresponding hull modules was sub-contracted to Oxbo Mega Transport Solutions of Scappoose, Oregon. The tanks had to be lifted over 50 feet off the ground and then precisely lowered into place. Oxbo designed a self-climbing gantry, utilizing four 600 metric ton, diesel-powered strand jacks, mounted 160 feet in the air on the four 135-foot-tall, 55,000-pound legs. The gantry was also used to turn and position the 680-ton bow and the 470-ton stern module.

Each tank has an instrument dome and a pumping dome with a pair of Wartsila deep-well cargo pumps that can complete full discharge in less than 24 hours. Loading and unloading locations on both sides of the vessel allow flexibility in docking. The manifold design allows for loading arm type connections as well as hose type connections of various diameters. The manifolds use fail-safe valves to ensure fast shut down in an emergency—and can be closed from shore side in an emergency.

The re-liquifaction deck module aft houses three ammonia compressors, two for duty and one as a spare. They are run by an independent control system to monitor tank pressures and cycle compressors on and off as needed to keep the cargo within the temperature range of -25 F. to -27 F. during transit, and loading. The rectangular tanks are approximately 100′ x 40′ x 40′ and fully insulated to a thickness of 6”. The Air Products nitrogen generator is supplied by two redundant air compressors and supplies gas to maintain an inert gas space around the tanks. A vacuum system allows for all voids to be evacuated of water should the need arise.

Deck equipment consists of pairs of double-drum Rapp 76-ton anchor winches anchor winches with 10 shots of chain (900 ft.), two 12,000 lbs., and an emergency tow wire, with a pair of Coastal wire mooring winches aft. The barge is equipped with a water-ballast system with a capacity of 343,000 cubic feet in 16 ballast tanks that can be filled or emptied in under 20 hours. It allows the crew to perform cargo and ballasting operations at the same time. Pilot boarding ladders are installed fore and aft to allow pilot boarding during light or heavy-draft connections, as well as provide access to life rafts if needed. Accommodation ladders on both sides allow access at any operating draft.  Savage President and CEO Kirk Aubry said “We look forward to operating the ATB and providing safe transportation services for liquid ammonia.” 

• Length: 508’

• Beam: 96’

• Depth: 51’

• Draft (Full Load): 26.6’

• Articouple Connection System

• Cargo: Refrigerated Liquid NH3 carried at –27 degrees F

• Cargo Capacity: 22,000 ST @ 96%

• Cargo Tank: Type A Prismatic Tank, (4)

• Onboard re-liquefaction system for cargo maintenance

• GENSETS: 4 x 940kW, 1 x 163kW

• Fuel Storage Capacity: 27,250 Gal

• Displacement 13,400 short tons

• USCG and ABS approved U.V. Ballast Water Treatment System

In its 2022 report, the Singapore team noted that besides public perception, the main barriers to adopting ammonia in the maritime industry include concerns about its toxicity, lack of crew’s familiarity and expertise in handling. However, extensive knowledge can be drawn from the fertilizer, refrigerant and chemical industries, where ammonia has been managed and transported worldwide for decades with well-established processes and regulations in place.

The ammonia bunkering process is somewhat similar to ammonia handling as a commodity cargo, but the key differences include the quantity of ammonia transferred, tank types and capacity, operating mode and frequency. This leads to a unique set of safety issues that need to be addressed. At various acute exposure guideline levels, ammonia can cause harmful effects to humans ranging from transient (30 ppmv), irreversible (160 ppmv), to life-threatening or death (1100 ppmv).

By early 2024, the first ammonia-ready ships engines will be ready for installation on newbuilds. The first models will be dual-fuel, able to run on traditional marine gas oil as well. Engineers have proposed utilizing waste heat from the combustion process to partially decompose/crack the ammonia, which results in a fuel mix of ammonia, nitrogen and hydrogen. Such technology is relatively easy to scale-up to even the largest cargo vessels.