Terntank has always had an eye for technology, and the group’s latest newbuildings will showcase advances that competitors are already looking to copy.

First steel was cut for the 147-metre, 15,000dwt twin-hull chemical tankers at China Merchants Jinling shipyard in June. Designed by Kongsberg and classed by Bureau Veritas, the vessels will feature the same five-cylinder, 500mm bore RT-flex50-D low pressure LNG dual-fuel main engine from WinGD that was pioneered in four earlier vessels built at the same yard and operational since 2016-7. The new vessels benefit from an evolution in design that features a battery system, cold ironing and a hybrid bow thruster.

“We have always liked to work with technical solutions that reduce emissions, that will continue,” says Claes Möller, CEO of Tärntank Ship Management, who is already testing biofuels and envisages further use of battery power in the future. “We are working hard to to become fossil-fuel-free.”

The two vessels will be put into service in the Baltic and the North Sea in 2021.

The journey of their development began when Terntank became the first shipowner to order LNG-powered chemical tankers in 2013. Svein Kleven, Senior Vice President – Energy & Systems, Integrated Solutions, at Kongsberg Maritime, explains that, studying the older vessels in the fleet at that time, it became obvious that the original hullform was not optimised for the routes travelled. Theory predicted that with an optimised hullform and a dual-fuel LNG engine a 40 percent reduction in emissions could be achieved, and when the four vessels were benchmarked against older ships in the fleet, they did perform 30-40 percent better, depending on weather conditions.

“It was very clear in the discussions we had with Terntank that they wanted vessels for the future, taking into account environmental regulations not only today but also in the future,” says Kleven. “We had a very good starting point with the first four vessels which were operating very well and receiving great feedback from the crew. But from that point, it gets harder to achieve even more emissions reductions.”

The next step, adopted for the two newbuildings, was to replace the spade rudders with Kongsberg Promas integrated rudder propellers – offering eight to 12 percent reductions in CO2 emissions. After that, machinery became the focus. The large two-stroke engine was changing RPM in response to the automatic power management system to maintain the service speed of about 14.5 knots, so a next logical step was to introduce an energy storage system (ESS) for peak shaving.

A shaft generator will be used as a power source with the ESS in peak shaving/ load smoothing mode when the vessel is in normal service, with three generators on standby. Typically, harbour manoeuvring would require at least two generators running, but for the newbuildings, Möller anticipates that no auxiliary engines will be required as the shaft generator and the ESS will provide enough power for entering and leaving harbours.

The ESS will also be used for operations such as ballasting and cargo handling and for blackout prevention and “take me home” operation using the shaft generator to run the propeller. Additionally, the ESS allows for emergency rescue operations involving the Man Over Board boat crane which will then be able to continue to operate even if all normal power sources are blacked out.

The ESS includes a 420kWh Corvus battery and is dimensioned for a power takeout of up to 1200kW. Depending on how much time is needed for loading or discharge, it can be recharged by shore power if available. Kleven notes that the ESS can provide all the necessary power from when the first mooring line is set until shore power is connected. This can take up to two hours, and on departure, the ESS will also eliminate the need for auxiliary engine power for about an hour. “This starts to become significant when you consider the number of port visits the vessels will make,” he says.

As well as the three auxiliary engines (Mitsubishi MAS 850-S, 790 kWe @ 1800rpm, 60Hz) that are biofuel compatible, the new vessels will have a liquid biogas (LBG)/LNG-fuelled boiler. The aim is to run the main engine on 30 percent LBG bringing an additional CO2 reduction of 2,500 tonnes/year compared to LNG. The auxiliary engines are anticipated to be run on 30 percent biodiesel bringing an additional CO2 reduction of 625 tonnes/year. Running the LNG fuelled boiler and the inert gas generator on 30 percent LBG reduces CO2 emissions by 155 tonnes/year compared to MGO.

The vessels will have 14 cargo tanks with seven independent submerged pump systems. The electric cargo and ballast pumps will feature variable frequency drives (VFDs) and are a more cost effective solution than hydraulic driven pumps, says Möller. They achieve energy savings of 15 percent. Hydraulically driven pumps suffer power losses in the electrically driven powerpack, filters, oil coolers, control valves and hydraulic pipe system. Electrical driven pumps are connected directly to the VFDs, and the power loss is less than three percent.

Additionally, the exhaust gas from the diesel-powered thermal oil cargo heaters will be processed with a scrubber system to produce gas that can then be used as inert gas.

Terntank worked with the Port of Gothenburg and Cavotec on the shore power connection and anticipates that green quayside electricity will be available around the same time as the vessels’ delivery. The high voltage shore connection eliminates the need for onboard power generation and reduces noise. When the vessels are connected, a VFD will convert the 50Hz shore power to suit the onboard 60Hz power system.

“When we are loading cargo, there will be no fuel consumption at all,” Möller says. “Unloading, our shore power connection will be 800kW, so we can use the shore power up to that level before needing to start an auxiliary engine.” The 800kW system is expected to be able to handle the vessels’ hotel power as well as run the cargo handling and ballast systems.

At the Port of Gothenburg, a shore power station will be located centrally on the quay with approximately 50 meters of cable available. The chosen option for the vessels is to have the shore power connection room located centrally in the EX cargo handling zone to minimise cabling needs and to enable the ships’ cargo cranes to do the cable lifting. When connecting, the cabling must be locked using a locking sock at the connection point and where the cable reaches on to the vessel. The system is equipped with an interlock that ensures the control circuit is broken if the 50-meter cable experiences unacceptable tension. As part of the connection procedures, the plug room, too small for a person to enter, will be over-pressurised with nitrogen. This solution meets ATEX directives and has received approval from DNV GL and Bureau Veritas. The alternative, an EX plug system, was difficult to find and extremely expensive, said Möller.

Digital systems onboard bring further emissions reductions. Using Kongsberg’s K-Chief and Vessel Insight solutions means that voyage data including wind and current predictions will be used to control the main engine and associated electrical control systems. K-Chief will handle many important functions onboard including power management, auxiliary machinery control and cargo, ballasting and bunker monitoring and control. With Vessel Insight’ vessel-to-cloud infrastructure, crew and onshore operational staff will have instant access to vessel specific dashboards and fleet overview data analysis tools.

The vessels will also have Sea Traffic Management (STM) connected to their ECDIS. The STM project is a follow on from the E.U.-funded MONALISA 2.0 project which developed a system that enables vessel route information to be shared between ships and with centres on shore. The project has involved the development of information technology platforms for improving voyage planning and traffic flow.

Over 400 vessels already have the ability to share their routes via ECDIS using STM technology in the Baltic, and in May this year Wärtsilä Voyage won a contract to update the ECDIS onboard 50 tankers. The infrastructure for STM has been contracted out to a newly formed non-profit industry consortium, Navelink, founded by Kongsberg, Saab and Wärtsilä in December 2019. In the future, STM functionality will be expanded on by other service providers which could offer advice to vessels such as recommendations to avoid congestion in areas with high traffic, avoidance of environmentally sensitive areas and other maritime safety information.  

The information exchange between the new Terntank vessels and ports is anticipated to improve planning and performance regarding arrivals, departures and turnaround times. Kongsberg’s K-Chief system will also be connected so that requested time of arrival at the jetty can be use to automatically adjust engine speed, with anticipated fuel savings expected to be up to 100 mt/year.

The electric power system, including the ESS, shore power connection and hybrid bow thruster will reduce emissions from the auxiliary engines by 10 percent, and with all the other design advancements, the new vessels will reduce emissions by over 20 percent more than their four predecessors.

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