In December it was announced that Teekay Tankers had placed a contract with the Samsung Heavy Industries (SHI) yard for four shuttle tankers designed to be the most environmentally friendly shuttle tankers ever built.
Shuttle tankers load crude oil from offshore platforms working under dynamic positioning conditions, transport oil relatively short distances to land-based terminals, discharge the cargo and return to the platform.
Power systems will operate on a combination of liquefied natural gas (LNG), as a primary fuel, and volatile organic compounds (VOC) which is the environmentally harmful gas evaporating from the oil cargo tanks – as a secondary fuel. A recovery plant uses compression and cooling phases to liquefy the heavier hydrocarbons to liquid VOC (LVOC) that is stored in a tank on the deck of the vessel. The LNG and LVOC will be used in combination as the main power source for the Wärtsilä 34DF engines. Methane gas emerging from the crude oil cargo during loading or transit, referred to as surplus VOC, is burnt in a gas turbine for electricity generation.
34DF engines together with 5.5MW Alconza´s generators are the main power source for the full electrical system that energizes the vessel, a hybrid solution which includes 4x 3.8MW propulsion motors designed and manufactured by Alconza and Wärsilä batteries for peak load saving, and added overall system redundancy.
Compared with the current standard of shuttle tankers, the new design will improve fuel economy by 22%, reduce annual emissions of CO2 equivalents by up to 42%*, the reduction equals the emissions from 22.000 cars per vessel per year.
The elimination of VOC emissions to the atmosphere will eliminate 84% of NOx from the engine exhaust, practically eliminate SOx emissions, and reduce particles to less than 4%. (Storage and loading of crude oil onto ships are responsible for more than 50% of Norway’s VOC emissions)
One of the most critical systems on board of a Shuttle Tanker is the Dynamic Positioning System (DP2) that allows the vessel to maintain a fixed position despite external forces, such as wind, waves and current. To achieve that the computer automation system contains a mathematical model that includes information captured from a satellite-based GPS, wind sensors and gyrocompasses to detect positioning deviations, once the information is collected the control system ask for an instant response to the azimuth thrusters and tunnel thruster fabricated by Alconza in complete synchronization with the electric propulsion motors.
Wärtsilä´s Eniram performance management system concept is also included into the technical features of the ship, a data collection platform with the capability to optimize vessel´s operations providing analytics and reporting for a real-time decision making.
* From a typical North Sea platform installation, each crude oil loading of a cargo size of 850.000 bbls, will recover 100 tons of LVOC and 10 tons of SVOC. By avoiding these amounts of VOC escaping into the atmosphere, the yearly reduction of emission goes from 43.000 to 25.000 tons of CO2, i.e., a reduction of 42%, assuming around 32 loadings per year.
With an average of 100 tons of recovered LVOC per loading, the recovered amount could represent up to 30% the total fuel consumption of the Shuttle.