The famed Hurtigruten line has been a Norwegian institution since 1893. Originally serving as mail boats, today these ships still transport cargo along the Norwegian coastline between Bergen and Kirkenes, though they principally carry tourists now. In doing so, the Hurtigruten AS shipping line attaches great emphasis to environmental sustainability. The company has set itself the goal of replacing the conventional engines on at least six of its ships with a combination of natural gas-powered motors and electric drives with corresponding battery packs by 2021. These hybrid ships will then be able to operate either on liquid natural gas (LNG), with electric power, or with liquified biological gas (LBG), which happens to be particularly sustainable. The effort and expense involved in making the switch is considerable: In order to install the biogas-capable combustible gas supply systems (FGSS) of the Norwegian engine-maker Bergen Engines into existing Hurtigruten ships, the marine outfitter had to develop and engineer a made-tomeasure tank and FGSS system for each ship. These state-of-the-art drive systems feature pistons from Rheinmetall.
A clean alternative to diesel and bunker
Around the world, LNG-powered ship engines are making inroads as an environmentally friendly alternative to diesel motors. While burning LNG produces roughly as much CO2 as bunker and marine diesel, it doesn’t produce soot particles and the ratio regarding NOx and SOx is also significantly better. As opposed to other operators, however, Hurtigruten hasn’t opted for a dual-fuel option in its gas-operated ships, i.e. motors than can use both diesel and LNG. “Dual-fuel drives are always a compromise solution,” notes Ralf Remmler, Head of Rheinmetall’s Large-Bore Pistons unit. If, on the other hand, engines are designed exclusively to operate on gas, they can be specially optimized for this fuel. This enables more efficient, and thus more sustainable, operation.”
By contrast, no compromises regarding efficiency are necessary for engines to run on LBG. LBG is considered to be far and away the most environmentally friendly fuel of its kind. The International Energy Agency has declared it to be virtually climate- neutral. LBG is a liquified gas derived from organic waste. In biogas plants, the solid waste is heated first in order to help the bacteria break it down. A controlled decomposition process takes place in the bioreactors, during which the gas is produced. Finally, the gas is cleaned and cooled until it liquifies, after which it can be used in internal combustion engines. It was very important to Hurtigruten that the entire production and logistics process be taken into account when assessing the sustainability strategy. In Norway itself, the raw material necessary for producing LBG – i.e. organic waste – is available in abundance due to the fish farming and forestry industries. This enables simple, environmentally friendly production to take place on location. Moreover, the transport routes from the production sites of the Norwegian gas producer Biokraft to the Hurtigruten ports are short.
Advantages of biogas
In the road traffic and transport realm, many experts think that biogas could significantly reduce the harmful emissions produced by trucks and ships. Biogas comes from things that already form part of the carbon cycle: manure, for example, or fish offal and other waste products that would normally be destroyed. Liquified biogas, or LBG, is an efficient energy source which, thanks to its high energy density, is easy to transport. LBG is therefore ideal for trucks and ships that until now have relied on diesel, while simultaneously keeping large amounts of CO2 and other pollutants out of the atmosphere. Liquified biogas is now considered to be far and away the most environmentally friendly fuel of its kind. This has led the International Energy Agency to classify it as nearly climate-neutral after taking all factors into account. Moreover, through its Bio-LNG initiative, the German Energy Agency is also promoting the increased use of liquified biogas in the shipping and trucking sectors.
It all depends on the pistons
The piston plays a key role in insuring that the motor can operate efficiently on both LNG and LBG. “We adapted the piston cavity to meet the specific requirements of the Bergen engine,” says Remmler. Extensive computer simulations were conducted in the wake of testbed trials of the engine in order to define the optimum cavity design for this special application. This was the only way to make sure that the combustion process in the combustion chamber would proceed especially evenly and thus especially efficiently. Optimum design of the pistons prevents the development of hot spots, that is to say, those parts of the component walls that become especially hot, in turn leading to uncontrolled ignition of the fuel. Also known as knocking, this kind of ignition causes the temperature and pressure to spike, resulting in further ignitions. The resulting spikes in pressure place a major mechanical strain on the engine.
An important signal for the sector
The pistons from Rheinmetall thus form a small but important element in Hurtigruten AS’s strategic quest for greater sustainability. As a result, the Norwegians have taken on a leading role in the cruise ship industry: Already in service, two Hurtigruten vessels – the MS Fridtjof Nansen and MS Roald Amundsen – are the world’s first hybrid cruise ships. Retrofitting of further ships with LBG-capable drive technology will likely make the Hurtigruten fleet the most environmentally friendly cruise line in the industry. Operating in a sector that’s come under attack for its lack of sustainability in recent years, Hurtigruten is therefore sending an important signal of corporate responsibility.