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Complementary power systems and energy storage systems on ships

Waste heat recovery

Waste heat recovery

In most types of ships where space is available and engine operation allows, waste heat recovery systems can allow for further fuel saving by reducing the running time of the ship’s auxiliary engines. Even the most efficient engines waste around 50% of the energy in the fuel through heat. Some may be recovered by the exhaust gas boiler or economiser, which provides the hot water demand of the ship but unless a further means of recovery is employed the rest is wasted.

A waste heat recovery system (WHRS) addresses this issue but is not suitable for all vessels; only those with a high electricity demand such as container vessels with large numbers of reefer boxes. There are various configurations of WHRSs and to obtain the most benefit they should be vessel-specific taking into account the equipment on board and the operating profile of the vessel.

A WHRS can harvest the heat from the exhausts and cooling systems of main and auxiliary engines and the exhaust from oil-fired boilers. Gathering the heat from exhaust systems can be complicated by the need to provide energy for the turbochargers and by exhaust gas cleaning systems or NOx reduction techniques that require lower combustion temperatures to operate. Early WHRSs were designed for working with exhaust systems but the potential for recovery of waste heat in the engine cooling water is now being explored.

Early in 2016 Mitsubishi Heavy Industries Marine Machinery & Engine announced that its link up with US-based Calnetix Technologies had resulted in the first commercial Hydrocurrent Organic Rankine Cycle (ORC) waste heat recovery system being installed on Maersk Line’s 2003-built Arnold Maersk. An ORC system employs very similar principles to a steam turbine but instead of water uses an organic fluid such as n-pentane or toluene. Because these liquids have a lower boiling point than water, the system can operate at lower temperatures and make use of lower grade heat.

Wind assist systems

Wind assist systems

There have been numerous attempts in the last 50 years to revive the use of sails and other means of harvesting wind power for ship propulsion. A small number of sailing cruise ships exist but these are very niche and have limited application. Harnessing wind for cargo ships has been tried using both kites and more traditional variations of sails.

One project to re-introduce sails is run by Hamburg-based Sailing Cargo, which aims to build the world’s biggest sailing cargo ship. The project outlines a plan to build a 170m car carrier, capable of carrying between 1,700 and 2,000 cars, which will be equipped with four DynaRig masts and will operate on hybrid propulsion using sails and diesel-electric engines with an optional battery system for peak loads. The proposed vessel would be capable of sailing at 10-12 knots with the aim of reaching 14-16 knots in the next few years through combined expertise. Lloyd’s Register is involved in the project and believes wind-assisted propulsion offers a realistic option for introducing renewable power into shipping.

The DynaRig is based on traditional square rigged layout and was initially designed almost 60 years ago in Germany. The masts are freestanding and have rigidly-attached curved yards. To adjust the angle of the sails, the entire mast rotates in place. When fully deployed, the sails on each mast have no gaps between them, creating a single panel to capture the wind. It is estimated to have twice the efficiency of a traditional square rig and a few examples have been installed on yachts.

Another project is taking place in Japan where Eco Marine Power (EMP) has been working towards commercial release of the EnergySail. The company announced in 2018 that it has begun collaboration with ClassNK to confirm design requirements and details related to sea trials. The goal is to pave the way to full commercial production of the EnergySail and thus complete the preparation of technologies required for the release of EMP’s Aquarius Marine Renewable Energy (MRE) solution.

The patented Aquarius MRE is an advanced integrated system of rigid sails, marine grade solar panels, energy storage modules, a charging system and marine computers that will enable ships to tap into renewable energy by harnessing the power provided by the wind and sun. The rigid sails developed by Eco Marine Power would be automatically positioned by a computer system to best suit the prevailing weather conditions and could be lowered and stored when not in use or in bad weather.

In 2019, several projects for ships with wind-assisted propulsion were announced. Germany-based rudder and Mewis duct specialist Becker revealed plans for developing a highly efficient wing sail, which will generate significant forward thrust on commercial vessels. The operational profile of the vessel will have to be adapted and weather routeing is an important part of it, but for long-range operation, using wind as a “fuel” source will significantly reduce a vessel’s fuel consumption.

The key shipowner partner for this development is Wallenius Marine. The design is for a modern car carrier that would be fitted with four large wing sails of more than 1,000m2 in area each. In optimal conditions it will be able to propel the vessel up to 10 knots without engine support. Unlike most other approaches, Becker’s wing sail will consist of two vertical sections, forming an aerodynamic foil. It is a great advantage that the wing sails can be operated at a small angle towards the apparent wind, enabling the vessel to use the wing sails on most courses. In order to pass under bridges, provide safe operation in port and “reef” the system in harsh conditions, Becker has developed a special laydown device for the new technology.

Another project is underway in France where a company called Neoline has been established as a prospective ship operator and which is planning a new generation of sailing ships for Transatlantic trading. The company claims to have received assurances from potential customers including car manufacturer Renault for providing regular cargo. Neoline has chosen the offer of the Loire-based company Neopolia to build its first two innovative sailing vessels. This decision follows an international call for tenders launched in 2018 by Neoline to 15 shipyards. In 2020, French shipowner Compagnie Maritime Nantaise took a financial stake in the project boosting chances of its coming to fruition.

The Neoliner – as the company has dubbed its projected design – is a 136m ro-ro vessel with four foldable sails based on yacht technology with a total area of 4,200m2. The ship will also be equipped with a 4,000kW diesel-electric propulsion system and possibly batteries as well.

In Japan, Mitsui OSK Lines and Tohoku Electric Power Company have announced both companies’ intention to move ahead with a joint study related to installation of the world’s first hard sail system on a coal carrier. The Wind Challenger sail is a telescoping hard sail to convert wind energy to propulsive force, developed under the “Wind Challenger Project”. The project began in 2009 with the “Wind Challenger Plan,” an industry-academia joint research project led by The University of Tokyo. In January 2018, MOL and Oshima Shipbuilding took charge of the plan and now play a central role in this project.

Flettner Rotor and variants

Flettner Rotor and variants

Reviving a concept first employed in the 1920s but soon forgotten as improvements in engine and propeller technology appeared to remove the advantage they gave, Flettner rotors are now enjoying renewed interest. The first vessel to be equipped with them in the modern era was the 2008-built E Ship 1 owned by renewable energy firm Enercon. More recently, a Finnish organisation Norsepower has fitted them to a number of ships to the point that there are now more vessels using rotors than when they were first invented.

The concept is often described as making use of wind power, but this is somewhat misleading as the motive power that Flettner rotors can provide is not wind power in the conventional understanding. Instead, it is exploitation of a phenomenon known as the Magnus effect, named after German scientist Gustav Magnus who first described the concept in 1852.

To take advantage of the effect, the rotors must be powered and capable of spinning in forward and reverse directions depending on the wind direction. Thus they will consume power but the propulsive effect can outweigh this. The principle behind the effect is that rotating any round object such as a sphere or a cylinder that is moving through a fluid affects its trajectory and speed in several ways because the friction from the spinning surface affects the fluid’s flow. In the case of a rotor ship, the wind passing over the rotor’s surface creates suction, which is greatest on any part of the surface that does not move with the wind.

If the forward surface of a rotor ship’s cylinder is made to move into the wind – ie clockwise into a starboard wind, counter-clockwise to a port wind – the suction will be strongest on that forward surface and the ship is drawn ahead. Under some wind conditions, the rotors will not confer any advantage and will need to be stopped. The fact that wind speed and direction is constantly changing also means that a much more sophisticated operating system than was possible in 1924 is needed to gain the best results.

Modern sensors and computer technology can adapt the speed of the rotor almost instantly when in use but under some circumstances, the wind will be of a strength and direction that the system will be of little use.

US-based Magnuss Corp is another proponent of the Flettner rotor, although it has not yet entered the market to the same degree as Norsepower. But it has an interesting project aimed at using ‘big data’ to gather information on global wind patterns that could help identify the best candidates for installing Flettner rotors.

Ventifoil is a technology related to Flettner rotors but with the fan inside a wing-shaped sail. It is to receive its first commercial reference in 2019 after Dutch ship management specialist Jan van Dam Shipping contracted for the installation on its 3,600dwt, 2007-built general cargo vessel Ankie.

The device has been developed by Conoship subsidiary eConowind, located in Groningen, Netherlands. It was developed over three years supported by an EU-backed grant and the first installation marks a significant milestone for the company in bringing its technology to market. Together with the Technical University of Delft and MARIN in Wageningen, the ship design office Conoship in Groningen studied several concepts of wind propulsion units for several years. After concluding the suction wings studied by Jacques Cousteau were most promising, eConowind was started in December 2016 to further develop wind propulsion on modern seagoing vessels, supported by a grant from the European Union.

eConowind designed foldable Ventifoils: wing shaped elements with vents and an internal fan that use boundary layer suction for maximum effect and creating very high propelling force relative to its size. Boundary layer suction increases and controls the propulsion force. On demand, the Ventifoils deploy and further operation is done automatically with the optimal angles relative to the apparent wind. The generated force is transferred directly into the deck and thus helps propulsion allowing the main engine to be used at lower load. The Ventifoils can be retrofitted onto existing vessels, integrated in newbuilds or be placed inside a container which can be put onto the deck of a ship. Two Ventifoils housed in a 40ft container could supply the equivalent of 82m2 of sail surface.

Batteries and the modern hybrid ship

Batteries and the modern hybrid ship

For some time now, there has been intense discussion about the ability of shipping to decarbonise. In 2018, IMO adopted an ambitious plan to achieve significant advances in this direction through to 2050 and beyond.

In the short term, the bridge to this target will be achieved through the use of lower carbon fuels such as LNG or methanol but in the longer term, new means of storing and producing power on board will need to be developed.

One that is already being used and which is rapidly achieving acceptance as a useful concept is battery power. Batteries do not produce power in the way that an engine does but merely store energy derived from another source. To avoid being a useless deadweight, batteries need a means of charging. This can be done by connecting to a shore power supply, feeding excess power from engines to the battery or even potentially connecting solar panels or wind turbines.

Battery power provides for emission-free operation but unless the power used to charge the batteries from shore comes from renewable, the pollution is merely moved upstream. Norway, which is self-sufficient in hydroelectricity, is therefore better positioned than many nations to make use of battery technology when it is the sole power source for the vessel. This is one reason why the country is a front runner in wholly battery-powered vessels – mostly ferries.

Battery power as waste energy storage has a much wider sphere of application and offers advantages for many ship types. In these situations, the battery allows auxiliary or main engines to be run at optimum speeds and excess power to be stored in the battery. This stored power can be used either to level out load demand from systems such as dynamic positioning or it can be used to provide emission-free operation in ports and harbours.

Another use for batteries on any type of vessel would be as an alternative to compressed air for starting main engines. All ships are obliged to be able to produce sufficient compressed air for six starting attempts of the main engine, but occasionally more attempts are needed. A battery system can provide for many more attempts and can even provide all necessary power to run a get-you-home propulsion system.

Batteries can only store electricity but even on mechanically-propelled vessels, a power-take-in device can be attached to the gearbox or direct to the shaft – effectively a shaft generator running in reverse. Most of the in-service ships fitted with batteries have had them retrofitted as additions to existing equipment although in a small number of cases, including a quartet of 1997-built Scandlines’ ro-pax ferries, one of the multiple original engines was removed.

Battery installations are increasingly being commissioned for newbuildings with cruise ships, ferries and tankers all having been delivered with energy storage systems.

Shaft generators

Shaft generators

The oil crises of the 1970s were a spur to an earlier generation of efficiency measures well before the IMO had even conceived the need for reducing fuel use and the idea of EEDI. One of the measures that has become commonplace on ships is the shaft generator which uses the rotary motion of the engine in a mechanical drive configuration to also generate electricity. During a voyage when the main engine is burning HFO, operating a shaft generator can give savings compared to an auxiliary operating on MDO.

The mechanical drive systems of both two- and four-stroke engines can run a shaft generator, which can be positioned at either end of the engine. When placed forward, an extension of the crankshaft at the front of the engine is needed. Where gearboxes are incorporated, the shaft generator might be turned by a take-out from the gearbox. Under such circumstances, the generator can be run in reverse and act as a power take-in, boosting the output for more speed or as a get-you-home device.

Shaft generators come in several varieties ranging from simple systems suited to ships operating with a constant shaft speed that are taken offline when the shaft speed falls below a certain level to more complex versions with gearing and speed management to ensure constant supplies of electricity.

On the downside, they are an additional expense and require maintenance. There are also operational issues such as the fact that they increase the fuel consumption of the main engine and cannot be used in port when the main engine is not running. Under conditions where the main engine speed may be constantly changing – such as when entering into a port – the shaft generator may not be providing sufficient power for navigation systems and a generator will need to be running in any case.

Fuel Cells

Fuel Cells

Another new technology that is forecast to revolutionise shipping is the use of fuel cells. It has to be said that the experience to date has been below expectations and for a while most companies that were pursuing the idea seemed to have put it on the back burner. Only a tiny number of fuel cells have been installed and all have been of quite low output considering the typical demands of the ships they were installed on.

Fuel cells are generally seen as being clean with zero emissions other than water and heat. While that may be true of the stack that is the main component of a fuel cell, there are more aspects to the technology that need to be taken into account.

The usual description of a fuel cell is a device for combining hydrogen with oxygen in an electrochemical reaction with electrical energy being produced for power utilisation and water and heat as by-products. What is often omitted is that there are many more components needed to reform the fuel if it is not pure hydrogen: heaters, pumps and more that make up the fuel conditioning and delivery systems along with starting air compressors and exhausts of a conventional diesel engine. These ancillary systems require their own power source which, depending upon the type of fuel cell, may produce undesirable by products and pollutants.

In its simplest form as a proton exchange membrane (PEM) fuel cell, the only requirements are a constant feed of hydrogen to the anode and oxygen via air to the cathode. The hydrogen is fed to the anode of the fuel cell where the electrons in the hydrogen are separated to pass as an electric current to the motor or other system. Splitting of the hydrogen molecule is relatively easy by using a platinum catalyst. The electrons continue on to the cathode to meet the hydrogen ions (protons) which have passed across the membrane and are combined with oxygen from the air to form water.

To function, the membrane must conduct hydrogen ions but not electrons as this would in effect “short circuit” the fuel cell. The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover. Finally, the membrane must be resistant to the reducing environment at the cathode as well as to the harsh oxidative environment at the anode.

Using hydrogen as fuel presents problems for ships that may be unsurmountable for large vessels making long voyages. Hydrogen in gaseous form is by a large measure the least energy-dense fuel possible so must be refrigerated and kept under pressure as a liquid for a PEM fuel cell to be viable for marine use. Although it is the hydrogen that is important for a fuel cell to function, it is not necessary for it to be kept as pure hydrogen. Any fuel that contains hydrogen – including diesel, LNG, methanol and many more – can be used instead.

However, except for a very few fuel types, the fuel has to be reformed to extract the hydrogen before it can be used in the fuel. As an example, methane as LNG (CH4) can be reformed by using steam (H20) to produce hydrogen and carbon monoxide. The hydrogen is then used to power the fuel cell while the carbon monoxide reacts further with some of the oxygen making the waste products of the fuel cell water and carbon dioxide.

In another type of fuel cell, methanol (CH3OH) can be used directly as a liquid or mixed with water with all of the hydrogen atom electrons producing the current. Water and CO2 are again the waste products.

Although it is possible for oil fuels to be used, any sulphur and metals present will contaminate the fuel cell and rapidly degrade it unless great care is taken to remove the contaminants before the hydrogen is fed to the fuel cell. With oils, as with any fuels containing carbon, CO2 will be one of the waste products and this characteristic must be considered as not meeting the decarbonisation targets.

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