Innovation in shipping can come by way of a single new idea or concept that can be applied to all ships or it can be a single ship that combines many new technologies and challenges established thinking.
Aside perhaps for the first ever, oil tankers are not renowned for being the type of ship most linked to innovation. However, shuttle tankers have been a very specialised type of ship from their first use in 1977 and have been platforms for numerous innovations over the years although often out of the spotlight.
The shuttle tanker concept allowing the North Sea offshore fields to work without the need for pipeline connections to shore was innovative in itself, but this was not the only use of new thinking. As an example of another, dynamic positioning is mostly thought of as being limited to offshore ships, but it has been used on shuttle tankers since the 1980s. Shuttle tankers were not the first platform for the double acting principle but there have been several shuttle tankers that have employed it since Vasily Dinkov was delivered to Sovcomflot in 2007.
The Teekay Group through its Teekay Offshore subsidiary has been a major player in the shuttle tanker sector for many years and has been an enthusiastic supporter of forward thinking ideas. Ever since the Norwegian authorities imposed restrictions on environmentally damaging volatile organic compounds (VOC) emissions in 2003, Teekay has explored many options for reducing emissions from its shuttle tankers.
Last year, Wärtsilä and Teekay began discussing a new shuttle tanker concept which would incorporate several of the new technologies Wärtsilä has been working on. An initial order for two Suezmax-size, DP2 shuttle tanker newbuildings was announced in August with two further options following in November.
At the time of the first order the owner said the new vessels will be constructed based on its new Shuttle Spirit design. Although stating that the new design would incorporate proven technologies to increase fuel efficiency and reduce emissions and would include LNG propulsion, full details of the innovative features of the design were not released at the time. At the beginning of January this year Wärtsilä released further details of its scope of equipment supply for the four vessels to be built by Samsung Heavy Industries.
The concept is expected to reduce annual emissions of CO2 equivalents by more than 40%, compared to conventional shuttle tankers. In addition to operating on LNG as the primary fuel, the dual-fuel engines will also be able to run on a mixture of LNG and recovered VOC.
Finding a use for waste VOC
Offshore loading of crude oil by shuttle tankers is responsible for more than 50% of Norway’s VOC emissions which is why the restrictions on VOCs were first introduced. The inert gas introduced to the tanks during unloading of crude to prevent an explosive atmosphere affects the hydrocarbon equilibrium and actually promotes the release of VOC from the crude when shuttle tankers take on cargo at sea.
Capturing the VOC and recycling it to cargo tanks reduces release of VOC from the crude. VOC emitted from the crude oil during loading is condensed in a process plant and stored in separate tanks on the deck of the vessel. Components such as methane and ethane are burned in a boiler to produce steam to be used for operation of the plant.
Wärtsilä has long experience in developing VOC recovery plants that can satisfy the requirements from the Norwegian authorities. In fact, one of the earliest VOC recovery systems aimed at the 2003 regulations was developed by Hamworthy KSE and installed in a tanker belonging to Navion; the first was acquired by Wartsila and Navion by Teekay in the intervening years. Wärtsilä has now designed a new generation of VOC recovery plant that will satisfy also the more stringent authority requirements expected from 2030 and will be installed on the new tankers.
The Wärtsilä VOC 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 lighter hydrocarbons that are not liquefied, referred to as Surplus VOC (SVOC), which mainly consists of methane gas, will be burnt in a gas turbine for electricity generation, chosen because of the two times better efficiency than the traditional use of boiler with steam generator.
The quantity of recovered VOCs from each loading operation will be in the region of 100 tonnes of LVOC and 10 tonnes of SVOC. By avoiding these amounts of VOC escaping into the atmosphere, the yearly reduction of emission drops from 43,000 to 25,000 tonnes of CO2 equivalent.
The new tankers will depart from convention for the type by being powered by Wärtsilä 34DF four-stroke dual-fuel engines instead of the usual single two-stroke diesel prime mover. With both LNG and LVOC onboard, Wärtsilä explored the possibility of mixing LNG with LVOC in gas form for potential fuel for the engine.
Because LVOC comprises heavier gas hydrocarbons such as propane and butane that have a relatively low methane number (MN) of 25, their use as fuel alone would cause knocking in the engine. By mixing the LVOC with LNG with an MN between 70 and 90, the gas engine can run at any required power. Depending on the MN of LNG the engines will run at less than 100% MCR due to the de-rating mode. This de-rating mode is fully acceptable due to the operational flexibility built into the new shuttle tanker concept.
Using LNG as the primary fuel and LVOC as secondary fuel, the new tankers will make use of 100% of the recovered LVOC as fuel for electric power generation. With an average of 100 tonnes of recovered LVOC per loading, the recovered amount could represent up to 30% the total fuel consumption of the ships.
By using the recovered VOC as fuel rather than venting it to the atmosphere, the ships will be effectively running on their own waste gases. The concept also means that NOx emissions from the engines’ exhaust will be reduced by more than 80% and since LNG contains almost no sulphur, SOx emissions will be almost entirely eliminated and particulate emissions will be reduced by more than 95%.
Batteries add further flexibility
The fuel saving element is further enhanced by a power distribution system based on the Wärtsilä Low Loss Hybrid (LLH) system using batteries for further fuel savings, peak load shaving and added overall system redundancy. With electric main propulsion motors and 4-stroke DF generating sets as the only power plant onboard the vessel, flexibility and overlapping functionality is achieved. This has resulted in the potential for reducing the total installed power on board from 26 to 23MW with further reductions in fuel consumption.
The battery storage system will handle dynamic load variations when the gensets are operating at their optimum loading without the need to start further gensets due to transient load variations. The new tankers are the first ships of their size to be equipped with a battery storage system.
While a hybrid system could be useful under many circumstances, shuttle tankers will be able to make more use of one than most other cargo ship types because of their DP requirements. The DP system of a conventional shuttle tanker will use 60% of thruster power, whereas in the new ships with the LLC concept only 40% will be used. Thus improving fuel efficiency or giving more manoeuvring capability.
Wartsila claims that the LLH electric equipment room is more compact compared to a conventional electric room. For crude oil offloading operations at the onshore terminals, Wärtsilä says it can supply either electric-driven pumps for pump room installation, or electric-driven deep well cargo and ballast pumps that enable a distributed pump solution, eliminating the need for a separate pump room and interconnecting pipelines in the cargo holds.
The space gained from eliminating the pump room can be used either to increase the cargo capacity or to shorten the engine room with a shorter hull, giving lower building cost and better DP capability.
Also included in Wärtsilä’s integrated solution for this vessel concept is Eniram’s Vessel Performance Management system. Eniram, a Wärtsilä company, will provide a data collection platform having the capabilities to optimise the vessel’s operations, while also providing the owners with analytics and reporting. The Performance Management system ensures that the full potential of the vessel as well as the fleet, will be utilised.