Cleaning up container shipping

An article by Klaus Rasmussen, MAN Energy Solutions, Denmark, which takes a technical look at the conversion of Hapag-Lloyd’s Sajir containership to dual-fuel LNG. (Published in the May 2020 issue of LNG Industry).

MAN Energy Solutions has signed a contract for the conversion of the Sajir – a 15 000 TEU containership owned by Hapag-Lloyd – to dual-fuel operation. The vessel normally serves a route from Asia to northern Europe via the Suez canal. The pilot project will entail the conversion of an existing, heavy fuel oil (HFO) burning MAN B&W 9S90ME-C low-speed engine to a dual-fuel MAN B&W ME-GI (gas injection) prime mover capable of running on both HFO and LNG. 

MAN Energy Solutions’ fuel-gas specialist, MAN Cryo, will install an entire gas system onboard the 368 m Sajir to supply gas to the main and auxiliary engines, including a MAN Energy Solutions 300-bar, high-pressure, pump vaporiser unit (PVU).

The emission savings for MAN B&W two-stroke engines are significant when converting an existing HFO engine to LNG. Using LNG in the shipping industry can reduce CO2 emissions by 15 – 20% and sulfur dioxide and particulate matter by more than 90%.

The project is scheduled to take place later this year when the five-year old vessel will enter the HuaRun DaDong Dockyard in China for approximately 105 days. 

Figure 1. The 15 000 TEU container vessel, 'Sajir', owned by Hapag-Lloyd, is undergoing a conversion to dual-fuel operation (Image courtesy of Hapag-Lloyd).

Project consortium

The project is being carried out by a consortium of companies, whose scope of supply covers the following:

• Technolog – Main project coordinator and responsible for the ship modification design.
• MAN PrimeServ – MAN Energy Solutions’ after-sales division and responsible for the design and retrofit of the main and auxiliary engines.
• MAN Cryo – MAN Energy Solutions’ fuel-gas specialist and responsible for the design of the fuel gas supply system (FGSS).
• GTT – Designer of the membrane tank.
• Alfa Laval – Boiler provider.
• Shipyard – Ship modification and FGSS prefabrication and installation.

Retrofit first steps

For the retrofit of the propulsion system, MAN Cryo is working closely together with MAN PrimeServ’s two-stroke and four-stroke departments, and has completed a comprehensive onboard survey to determine the various courses of action it can take to optimally execute the retrofit.

Such courses of action include the following:

• Determining the volume of the Sajir’s new fuel tank based on power demands and projected fuel consumption.
• Planning for tank type and location.
• Planned bunkering scenario.
• Possible location of LNG tank(s) and tank connection space (TCS) / fuel preparation room (FPR).
• Routing for bunker, gas and ventilation pipework.

Figure 2. Tank connection space and fuel preparation room above membrane tank with two bunker stations on upper deck.

LNG-ready

When it merged with UASC two years ago, Hapag-Lloyd took over 17 newbuildings described as ‘LNG-ready’, including the Sajir, which was delivered in 2014. ‘LNG-ready’ essentially means that an engine is partially prepared for some of the things you would otherwise need to change to put LNG on the ship, but converting an LNG-ready vessel into one that can use LNG is still a major operation. 

In the Sajir’s case, the original plans for the vessel allocated space for such elements as tanks and piping to allow for any subsequent retrofit. Furthermore, the thickness of the existing steel construction and frames were designed to support any future LNG tank, which saves time and expense. 

The challenges of converting a vessel to run on LNG are immense, even if it is classed as LNG-ready. These challenges include the placement of fuel tanks and the filling equipment on board. To begin with, the liquefied gas is cooled down to -162°C (-260°F), meaning that the tank has to be very well insulated. Since the specific heating value of LNG is approximately 40 – 45% lower than that of HFO, the tank also needs a correspondingly large volume and also has to fit into the existing ship structure during the conversion – a key step that demands precise planning.

Determined FGSS parameters

Stemming from an evaluation of the ship, a 6400 m3 GTT membrane tank was decided upon with a design pressure of 0.7 bar, and a boil-off rate of 390 kg/hr. Accordingly, the gas-flow design rate for the main engine was set at 7100 kg/hr, with the gas-flow design rate for the auxiliary engines set at 2000 kg/hr.

The boiler is supplied with gas combustion unit (GCU) functionality for the handling of excess boil-off gas (BOG), while the TCS will be positioned on top of the tank dome and includes all tank safety valves and instruments.

The FPR will be placed next to the TCS and includes LNG vaporisation equipment, BOG compressors and a gas valve train (GVT).

Bunker stations will be established portside and starboard, with a bunkering capacity of 1400 m3/hr.

Figure 3. Geometry of a bunker station inside a 40 ft container.

Tank placement

Because of its twin-island configuration, the Sajir’s 6400 m3 membrane tank will be located just forward of the engine room, allowing an optimal adaptation to the existing ship shape. This means sacrificing approximately 300 TEU of container capacity, but has the advantage of dispensing with any long pipe-runs throughout the vessel. 

Fuelling strategy

Due to the large quantities of LNG that will be required, Hapag-Lloyd is planning additional refuelling stops for the Sajir’s round-trips between Asia and Northern Europe. Such a bunkering strategy avoids stealing even more container capacity from the vessel and is facilitated by the ample LNG bunker capacity that already exists along the route. 

Unlike gas carriers, which reliquefy any boil-off, LNG-fuelled vessels simply use the BOG emanating from the tank as fuel. Whereas on a traditionally-fuelled ship, the focus is on minimising fuel-oil consumption, the priority aboard the converted Sajir will be to utilise any BOG. This is a primary reason why Hapag-Lloyd has chosen to go with smaller tanks for the conversion as the more gas you carry, the more boil-off you have to contend with, which in turn directly influences the fuelling strategy. 

Engine comparison

The converted ME-GI main engine will have a cylinder head that is equipped with two valves for gas injection and two conventional valves for the pilot fuel-oil. The two engine types – the original ME-C unit and the converted ME-GI – are essentially the same with similar efficiency, power and main dimensions. However, compared to the ME-C, the ME-GI has a modified exhaust system and a modified cylinder head with additional gas-supply lines and gas-control devices.

The ME-GI PVU pressurises and vaporises the LNG fuel to the exact pressure and temperature required by the engine. Pressure is regulated via control of the hydraulic oil-flow to the pump, ensuring prompt and precise control of the engine’s LNG supply. Separate control of each pump head provides full redundancy.

The conversion of the Sajir will see the replacement of most combustion-chamber and gas-injection components. Similarly, the pilot-oil system required for gas operation will also be completely rebuilt, while the control system for the ME-GI engine is more complex and will require new instrumentation.

The maritime energy transition 

By 2050, the shipping industry will have to reduce CO2 emissions by 50% from 2008 levels and by 2100 be emissions-free. In order to achieve zero emissions, the fuel will ultimately have to be decarbonised. Switching to LNG is an important first step, as it immediately reduces greenhouse gas (GHG) emissions, but the conversion of the Sajir in this context can be viewed as an intermediate step on the path to a low-emissions future.

Once a ship is operational on LNG, it is automatically 100% operational on decarbonised fuel as well, e.g. synthetic natural gas (SNG), which can be generated from renewable energy via Power-to-X. Other fuels, such as ammonia, methanol and hydrogen, can be and will have to be generated from renewable energy eventually. Next to retrofitting existing vessels and adding LNG newbuilds, the big challenge will be to add the capabilities and capacities to the market that are needed to provide sufficient amounts of climate-neutral synthetic fuels.

In converting the Sajir, MAN Energy Solutions can reference its successful 2017 conversion of Wessels Reederei’s Wes Amelie – a 1036 TEU containership that was originally fitted with a MAN 8L48/60B diesel engine – for experience. Upon conversion to a dual-fuel MAN 51/60DF unit, the Wes Amelie reported significantly changed emissions. The vessel now meets both the Tier II and Tier III emission requirements set by the International Maritime Organization (IMO). As a next step, MAN Energy Solutions and Wessels Marine GmbH have further announced a technical showcase whereby the Wes Amelie will use liquefied SNG produced from renewable electrical energy as drop-in fuel. To demonstrate that SNG can successfully be used as shipping fuel, 20 t of the 120 t of LNG that the Wes Amelie typically uses per round trip will be replaced by climate-neutral SNG. As a result, CO2 emissions are expected to decline by 56 t for this trip.

The retrofitting of the Wes Amelie, and now the Sajir, to dual-fuel running is part of the ‘Maritime Energy Transition’, an umbrella term that covers all MAN Energy Solutions’ activities in regard to supporting a climate-neutral shipping industry.

Conclusion

MAN Energy Solutions’ retrofit of Hapag-Lloyd’s Sajir will be the first conversion of a containership of this size to LNG propulsion and, as such, will act as an excellent showcase to highlight the potentially massive benefits of such conversions for the market.