vol 8, issue 6

Carbon cap for shipping - is it workable?

17 June 2013
By Anne Harris
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Cargo ship

The quest to reduce maritime emissions requires innovative solutions

Capping emissions from the maritime sector is the driver behind Rolls-Royce's Enviroship project.

The aviation industry comes in for a lot of criticism for the damage it is calculated to inflict on the environment, yet the global shipping industry emits over 50'per cent more carbon dioxide (CO2). Small wonder then that the regulatory authorities have turned their gaze out to sea.

Those in the maritime field are quick to argue that if you measure the emissions by tonne of cargo carried, shipping is by some way the most environmentally friendly solution, but the top-line figures remain worrying.

Some 90 per cent of the world's cargo travels by sea. Almost 5,000 ships are larger than 100TEU in size (a TEU, or 'twenty-foot equivalent unit', is roughly the volume of a standard shipping container). The latest figures, from 2007, state that the shipping industry emitted 1,046 million tonnes of CO2, or 3.3 per cent of global CO2 emissions, in that year. This was significantly higher than the aviation sector, which only accounted for 1.9 per cent of global CO2 emissions.

Mandatory measures to reduce greenhouse-gas emissions came into force earlier this year under the auspices of the International Maritime Organisation (IMO). Further tightening of the regulations is planned for 2016 and the ship owners are aware that the drive to clean up the shipping industry is unlikely to stop there.

"Due to the continued demand for shipping services as a result of growing world trade our measures can, at best, stabilise the emissions," says Eivind Vagslid of the IMO's marine environmental division. "It cannot lead to an overall total reduction. That is why we are always working to control GHG emissions by expanding measures as well as developing a market-based measure to encourage owners to invest in more efficient ships."

The current measures, on a business-as-usual basis, will reduce emissions by up to 200 million tonnes by 2020 and 400 million tonnes by 2030. But that reduction will be swallowed by the increasing volumes of ships and cargo.

"Merchant ship owners have traditionally been conservative and not always the first to invest in innovative technology, but that is changing fast," Per Egil Vedlog, who leads Rolls-Royce's team responsible for developing innovative designs for merchant ships, says. "The prime driving forces for change are environmental legislation and higher fuel costs."

The Enviroship project

Vedlog's design team is responsible for more than 100 different merchant vessel designs, ranging from general cargo ships, roll-on/roll-off (Ro-Ro), cruise ferries, tankers and even super yachts. "Our core strength is that we can combine our products and propulsion systems within innovative ship designs," he says.

Rolls-Royce's answer is its Enviroship project, focusing on combining a series of technologies into one platform. "We combine four innovative Rolls-Royce technologies to reduce emission and fuel consumption," Vedlog says. "The four components are the Promas integrated rudder propeller system, the hybrid shaft generator system, the gas engine and finally the wave-piercing technology and hull design.

"These are the main areas when it comes to efficiency, but it does depend on what type of vessel you are talking about. If you look at the Ro-Ro market we include more pillars into the concept by including such things as intelligent ventilation."

One vital part of the process is matching the user profile for the vessel against the toolkit of technologies available. "It's vital we build up as detailed a picture as possible about the operating profile of a ship before we even get to the drawing board," Vedlog says. "With a typical design, from our first discussions with the customer, through to the vessel entering service, it can be as little as three or four years, so we try to encourage them to think several years ahead and consider what the legislative landscape and other requirements may be when their vessel takes to the seas."

Rolls-Royce's recent Nor Lines order for NVC 405 cargo vessels is a great example of how attitudes are changing towards innovative technology in the maritime industry. "The owners have taken the decision to invest in a complete integrated system, including gas engines, energy-saving propulsion systems and our new hull shape that will serve them well by reducing costs, emissions and fuel consumption for many years," Vedlog adds.

"The only way to seriously tackle the issue of emissions is to invest in multiple technologies, if you like, selecting the best of what's around and combining it into a system - a whole ship system. While building a ship with a gas engine must be applauded, if we can convince more ship owners to go a step further and combine that with additional technologies, the benefits will be significantly greater."

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Enviroship project: The four key components

Rolls-Royce's Enviroship project focuses on combining a series of technologies into one platform. Team leader Per Egil Vedlog breaks down the major developments.

1 Hybrid Shaft Generator 

The gas engine has a very flat fuel-consumption curve all the way down to 20 per cent load, which makes it very suitable to run combinatory. The traditional method is to run fixed rpm on the motor and propeller to be able to have the shaft generator connected and deliver stable'frequency and voltage to the switchboard.

With the hybrid shaft generator you can take off rpm when you are at lower speed and still have it connected and get stable frequency and voltage. You can then adjust the propeller according to the propeller curve. Instead of using a lot of energy to have a fixed rpm on the propeller you can save a lot of fuel by reducing the rpm and adjusting the propeller pitch.

With a hybrid shaft generator you have great flexibility during optimal operation. This means that we can also use the main engine instead of the auxiliary engine when you are in harbour; you just have to clutch out the propeller and use the shaft generator and gas engine as the auxiliary engine.

2 Promas integrated rudder propeller system 

The Promas system integrates the propeller, a hub cap, a rudder bulb and the rudder itself into one hydrodynamically efficient entity. When you have a hub cap and bulb on the rudder you eliminate the hub vortex that occurs behind it. This means that you can achieve a better load distribution over the propeller blades because you don't need to take the hub vortex into consideration. This allows you to move the load on the propeller from the tips closer to the hub - a problem caused by hub vortices - allowing the propeller to operate efficiently. By taking the load closer to the hub you take away the problem of pressure pulses towards the hull which generate noise and vibration.

The rudder profile is like an aeroplane wing; it gives you a lift. While an aeroplane wing will give you an upward lift, a rudder gives you forward lift. This lift, along with the increased propeller efficiency gives you a total propulsion efficiency improvement between 4 and 8 per cent.

3 Wave-piercing bow 

We focus on increased performance in real sea conditions, not only in the test tank. In the real world you almost never have calm water. So we had to improve performance in rough seas without compromising the calm-water performance.

The wave-piercing technology is a modification of the hull lines below the water. We have taken away the flare of the bow which causes the water to be pushed forward and out, requiring energy. We have a more straight-line cross section allowing the water to flow along the hull line.

We optimised this using computational fluid dynamics and advanced simulation and then finally model tested it. In varying sea conditions we have 10 per cent less resistance.

4 Gas engine 

We believe that gas engines will form the future for marine engines, in fact we have very few projects now with diesel engines. We have a purpose-built gas engine rather than a dual-fuel unit. The engine has a thermal efficiency of more than 48 per cent compared with the best diesel and dual-fuel engines which are between 40'and 44 per cent.

We compared this to a leading dual-fuel engine and at fuel load we had 8 per cent better fuel consumption but when it was at 50'per cent load that increased to a 17 per cent saving. As well as this efficiency it also has a very low methane emission.

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