Hybrid propulsion, coupled with the improved integration of fuel and cargo systems, will save gas carrier operators time and money
Dual-fuelled LNG carriers have long dipped into their cargoes to power their engines. But even with easy access to cheap fuel, efficiency remains important. Any gas that can be re-liquified, instead of used in engines, means more cargo at the end of the journey and more profit for owners. New technologies, including hybrid propulsion and advanced system integration, offer the opportunity for operators to increase these savings.
In April a partnership was formed that aims to drive the uptake of hybrid propulsion among gas carriers for the first time. Wärtsilä and Samsung Heavy Industries (SHI) are seeking to optimise the capital and operational costs associated with gas carriers.
The project is based on a successful co-operation in the shuttle tanker segment. Batteries form part of the hybrid arrangement for a series of six shuttle tankers being built by SHI for Teekay Offshore. The package includes LNG-burning engines that are also capable of using volatile organic compounds as well as a battery system.
According to Wärtsilä sales director, merchant segment Stein Thorsager, the Teekay project encouraged SHI’s interest in the hybrid propulsion. “They see the advantage of using batteries as part of the energy demand on board and strongly believe this will be of value for other tankers and gas carriers,” he says.
SHI is also interested in entering the marine market with its own batteries. It will be able to use Wärtsilä’s hybrid centre in Trieste – a facility that enables the full-scale testing of hybrid propulsion arrangements – to explore the best battery properties and specifications for marine use.
“These concepts will revolutionise gas carrier propulsion and offer a step change in fuel efficiency”
The agreement provides a “greater level of equality” than under a conventional shipyard-supplier relationship, allowing the companies to spread risks associated with research and development. It will also provide SHI with a knowledge of hybrid propulsion and power arrangements that it can apply when adapting ship designs and construction practices to accommodate these systems.
The partners cited the strong LNG carrier newbuilding market as another driver for the deal, noting “potentially dozens of new vessels to be ordered for transporting increasing volumes of LNG from new and extended export terminals in Africa, Australia, Middle East and the US.”
Gas carrier propulsion is usually provided by two-stroke engines, with medium-speed engines catering for on-board power demand including re-liquefaction and cargo loading. Batteries could replace an auxiliary engine and be used to tackle peaks in energy demand, allowing the remaining auxiliaries to be operated at a more optimal load. This would reduce fuel consumption as well as cutting maintenance on the remaining engines.
Mr Thorsager notes that many LNG carriers – recently those being used for the Yamal LNG project in the Russian Arctic – already deployed electric propulsion. These arrangements make it easy to consider adding batteries to the set-up he said.
“We believe in electric propulsion for smaller LNG carriers,” he says. “In the future you could see a row of generators on one deck with an electric propulsion motor down in the hull connected to the propeller shaft. We already see interest in such concepts from shipowners and charterers who are looking at all options to reduce their emissions to meet IMO targets.”
The partnership could also extend to retrofit hybrid solutions. Wärtsilä has already developed containerised retrofit solutions comprising batteries, switchboards and controls, mainly deployed on offshore vessels. Solutions could be developed for larger vessels, says Mr Thorsager.
Wärtsilä and SHI are not the only companies to note the potential for hybrid propulsion in the gas carrier segment. Two small-scale LNG carrier design concepts from Keppel Offshore & Marine have just won approvals in principle from DNV GL, one of which features a hybrid power system with batteries. Bringing these concepts from the drawing board and into operation will revolutionise gas carrier propulsion and offer a step change in fuel efficiency.
Hybrid propulsion is not the only way to improve efficiency on gas carriers; integration of onboard systems is an often-overlooked area for driving economies. A new 30,000 m3 LNG carrier being built at Hyundai Mipo Dockyard for Norway-based Knutsen OAS Shipping is a good example of what can be achieved.
“[There are] potentially dozens of new LNG carriers [needed] to transport increasing volumes of LNG from new and extended export terminals in Africa, Australia, Middle East and the US”
An integrated propulsion and cargo handling solution will ensure effective interfacing between the vessel’s propulsion, onboard auxiliary power generation, and cargo control processes. The package from Wärtsilä includes fuel gas supply, cargo control system, boil-off gas re-liquefaction and safety management.
The vessel’s five-cylinder WinGD X52DF dual-fuel main engine and the Wärtsilä auxiliary dual-fuel engines are essential consumers for the boil-off management system, which monitors and controls the cryogenic cargo. Used in combination with a mixed-refrigerant re-liquefaction unit, this will offer the operator control over cargo tank pressure and temperature at all times. The vessel will also be one of the first LNG carriers in its size to deploy space-saving Type-C bilobe cargo tanks.
The scope of supply includes three Wärtsilä 20DF dual-fuel auxiliary engines that power the board net, thrusters, cargo control system, and re-liquefaction module. The main engine and controllable pitch propeller system allow the vessel to operate at its highest fuel efficiency design point through a single control for shaft power, pitch and speed.
The vessel will be operated by Knutsen and chartered to Italian energy services provider Edison. It will be used to supply coastal LNG depots in Italy. The Wärtsilä equipment is scheduled for delivery in 2020 and the vessel is expected to be delivered during the first half of 2021. The contract includes an option for an additional sister vessel.
Benefits of bio-gas
Another emerging route to improving the environmental efficiency of LNG-fuelled ships is bio-gas. Gas fuels made from biomass avoid the significant greenhouse gas emissions associated with the production of natural gas. Because biogas (like LNG) consists mainly of methane gas, existing LNG supply infrastructure can be used without modifications. The same trucks, ships, tanks and marine filling stations can be used for both products.
In June last year, Skangas performed what is understood to be the first liquefied biogas (LBG) bunkering of a ship, Furetank’s chemical/product tanker Fure Vinga. The fuelling took place at the Port of Gothenburg, transferring the fuel directly from a tanker truck to the ship. The Swedish LBG was delivered to Furetank’s ship from Skangas’ parent company Gasum’s biogas facility in Lidköping.
Six ferries to be retrofitted by Norwegian shipowner Hurtigruten will become the first of their kind to operate on biogas.
The vessels, which are due to be converted from diesel-electric to LNG-battery power and propulsion, will be fitted with fuel gas supply systems and tanks designed by system integration specialist Høglund Marine Solutions and naval architect HB Hunte Engineering. Høglund Gas Solutions will provide the fuel-gas supply system (FGSS), including process design and related automation, while HB Hunte will provide mechanical gas engineering and gas tank design.
The conversions will help Hurtigruten to meet the strict emissions reduction requirements imposed by the Norwegian government when it awarded coastal route concessions (starting in 2021) to Hurtigruten and Havila Kystruten last year.
Stena abandons debut LNG retrofit plan
The technical and financial challenges of retrofitting ropax ferry Mecklenburg-Vorpommern proved too daunting for Stena Line
Swedish shipowner Stena Line has highlighted the cost challenges associated with LNG retrofits after reporting that it has decided not to proceed with its first dual-fuel retrofit.
The project to convert the 38,000 gt ropax ferry Mecklenburg-Vorpommern for LNG received a grant from the German Ministry of Transport and Digital Infrastructure in March. But Stena Line trade director Germany Ron Gerlach said that it was not going ahead, citing discussions around “budget, technical challenges and both operational and financial risk”.
According to Mr Gerlach, the company is not ruling out gas as an alternative fuel for its vessels. Stena has ordered a series of ropax vessels from Avic International shipyard in China that will be LNG-ready, with the final ship expected to operate on gas from its delivery in 2021.
“We will stay open with regard to technologies at hand in order to allow us full flexibility in our European route network,” says Mr Gerlach. “We will also continue to focus our efforts on other projects such as looking at expanding our battery project on Stena Jutlandica to further vessels and to extend our onshore power supply solutions to include more of our ports.”
At 22 years’ old, the Mecklenburg-Vorpommern would have been one of the oldest vessels to be retrofitted for LNG. The age of a vessel can affect the viability of a conversion by limiting payback time and because of the constraints of installed engine technology.
Stena Line is familiar with challenging retrofits, having converted four Wärtsilä four-stroke engines for methanol fuel on board the then 14-year-old cruise ferry Stena Germanica from 2015.
Heat exchanger advances deliver cool fuel savings
New research on glycol freezing has driven developments in heat exchanger technology that are set to benefit users of LNG fuel. A fluid mix including glycol is often used as a medium for heat exchange, but the extreme temperatures at which gas is liquefied means that freezing of the mix is a risk. This has challenges for the use of plate-and-shell heat exchangers used in the vaporisation of gas fuel.
“With more and more ships relying on LNG as fuel, we are seeing greater demand for durable vaporiser technology that can dependably resist freezing and the fatigue caused by pressure and temperature,” says Alfa Laval head of marine heat transfer equipment Jonny Hult. “A glycol mix with a freezing point of around -50°C has the potential to freeze when it meets plate surfaces as cold as -90°C. Solving this problem with a higher glycol flow is a very expensive solution for our customers.”
Jonny Hult (Alfa Laval): Seeing greater demand for durable vaporiser technology
Alfa Laval has worked with SINTEF Energy Research to find the optimal correlation of flows on both sides and thereby avoid freezing of fluid on the hot side. This will allow shipbuilders use a more compact design with smaller pumps and pipes, reducing cost.