Wärtsilä's Aframax tanker design
An efficient tanker design, developed by marine industry solutions and services provider Wärtsilä, offers solutions for current and forthcoming emissions legislation. With the Aframax tanker, Wärtsilä Ship Design has designed a double hull, single screw crude oil tanker featuring a CFD (Computational Fluid Dynamics) optimised hull to provide less resistance with higher propulsion efficiency. The minimum time at the terminals is ensured by the high loading/discharge rate. The CFD optimisation of the hull form has carefully considered the flow lines and pressure distribution along the hull, while the cylindrical bow accommodates a range of operational draughts even in rough weather conditions.
The propulsion system is based upon the high performance, 2-stroke Wärtsilä X62 main engine. This electronically controlled, common-rail engine has an extra long stroke and low rpm. It also has a minimised physical width to allow a slimmer aft body design, which further benefits the propulsion efficiency.
Compared to currently available main engine options, the Wärtsilä X62 engine can achieve fuel savings of seven per cent on the specific vessel design. Furthermore, the same vessel speed can be reached using one less cylinder, i.e. six instead of seven cylinders. The seven cylinder version provides even greater efficiencies due to the lower rpm and higher de-rating.
For emissions compliance, an integrated Wärtsilä exhaust gas scrubber has been placed on the funnel. Main engine, auxiliary engines and auxiliary boilers are all connected to the integrated scrubber. The scrubber effectively reduces sulphur oxide (SOx) emissions, and meets the 0.1 per cent sulphur limit even with HFO (Heavy Fuel Oil) having a sulphur content of 3.5 per cent. A Wärtsilä SCR (Selective Catalytic Reduction) system has been placed before the turbocharger turbine for the main engine. The SCR is a post combustion nitrogen oxides (NOx) abatement system that permits optimised combustion, in terms of efficiency, while reducing NOx emissions by more than 90 per cent. The abatement equipment is tuned with the main and auxiliary engines for effective operations across the complete load range and IMO Tier III requirements can be fulfilled.
“The new realities of the shipping industry call for higher fuel efficiency, lower operating costs, and better environmental performance. The new Wärtsilä Aframax tanker design meets all these criteria, and we are proud to offer this segment the combination of state-of-the-art design and superb propulsion machinery that can produce meaningful savings,” says Riku-Pekka Hägg, Vice President Wärtsilä Ship Design.
The Wärtsilä X62 is the most compact engine in its class of very low-shaft-speed engines. Thanks to the engine’s agility, it is the optimum choice for several vessel segments. The Wärtsilä X62 has a cylinder bore of 620 mm and its power output is in the 8,000 to 21,280 kW range. It comes in 4 to 8 cylinder configurations.