VOC-Burning Dual-Fuel Shuttle Tanker Heading North

A further stage in the evolution of the shuttle tanker fleet deployed in north European waters has been signalled by the delivery of the first of two newbuilds powered by dual-fuel machinery.

The 123,600dwt Frida Knutsen, constructed by Daewoo Shipbuilding & Marine Engineering (DSME) to the account of Knutsen NYK Offshore Tankers (KNOT), also features a volatile organic compounds (VOC) recovery system, VOC-burning auxiliary boiler, a steam turbo genset and a bank of batteries.

Frida Knutsen was handed over and obtained her DNV class assignment on 4 August, and has been constructed for the exacting operational and environmental demands entailed in loading oil year-round direct from offshore installations. Sistership Sindre Knutsen will follow closely, having been readied this month for sea trials from DSME’s Okpo complex on the Korean peninsula.

Both KNOT newbuilds have been assigned long-term timecharters to ENI Trade & Biofuels, an arm of the Italian corporation Ente Nazionale Idrocarburi (ENI). Through Vaar Energi, an ENI-associated exploration and production company, the tankers will be deployed in the North Sea and Barents Sea, loading crude oil direct from offshore fields for transportation to regional refineries and storage terminals.

The phenomenon of VOC emissions from cargo has commanded particular importance in shuttle tankers since operators of oil fields on the Norwegian continental shelf have been obliged to meet stringent regulations relating to such emissions. Oilfield licence holders are responsible for ensuring that dedicated offshore tankers in their employ are fitted with appropriate VOC control equipment. KNOT has taken the treatment and usage of VOCs to a new level with the latest DSME newbuilds, and the VOC recovery plant adopted will ensure compliance with tighter Norwegian government stipulations expected to be implemented in 2030.

An energy storage system (ESS) was included in the technical specification at the client at the client’s request, so as to improve ship performance by optimising engine responsiveness, whatever the load.

The ABB twin battery package on each tanker has a storage capacity of 678kWh. ABB’s scope of supply has also included the shaft generator system, main switchboards, and thruster and cargo pump drives. The ESS will be able to ramp up engine responsiveness by working in conjunction with the ABB medium-voltage AC electrical system to control and optimise shaft generator power flexibility.

Enhanced dynamic support for the batteries will be crucial in the event of sudden load changes and peak loading, including the specific demands of station-keeping and cargo pump operations. As well as enhancing operational flexibility, the capability to call on the batteries means that suxiliaries are needed less frequently, and sometimes not at all, saving fuel and cutting emissions. When the shaft generator produces more power than required at any one time, the excess power will be used to charge the batteries.

Frida Knutsen has a two-stroke propulsion plant comprising a pair of WinGD X52DF engines in six-cylinder configuration, giving direct drive to twin Wartsila controllable pitch propellers. The low-pressure, dual-fuel design fulfils Tier III NOx requirements in gas mode, and has a nominal maximum continuous output of 1,490kW per cylinder in its R1 rating.

The LNG fuel gas supply arrangements and VOC recovery system were sourced from Wartsila, while the VOC-fired auxiliary boiler installation and 3,600kW turbo generator set were supplied by Mitsubishi’s Marine Machinery & Equipment Co (MME). A particular attribute of the specific boiler type is the capability to burn VOCs of whatever make-up.

The requisite level of dynamic positioning power and precision in each ship is achieved through an array of Brunvoll equipment comprising two tunnel thrusters and three retractable, azimuthing thruster units, with a combined effect of around 10,000kW.

Haugesund-based KNOT is a 50:50 joint venture of NYK Line and TS Shipping Invest, parent company of the Knutsen Group. The ships are husbanded from Norway by KNOT Management.

MAIN PARTICULARS -Frida Knutsen