On 10 April 2013, the product tanker Greenstream was handed over to her customers. This is the first inland waterway vessel to be fully powered by liquid natural gas (LNG), but the list of innovations in this vessel does not stop at its cutting-edge propulsion system. There are also a new impact-resistant double hull skin type, a modular power generation system, a distinctive styling, a lounge with a panoramic view aft and a fuel-saving hull design with raised anchor pockets. The use of LNG instead of diesel alone should lead to a reduction of 80% in NOx, 100% in SO2, 100% in particles and 20% to 25% in CO2.
The market of inland waterway tankers is one of the spearheads of Dutch maritime innovation. The last two years saw diesel-electric propulsion showcased in Amulet, hybrid propulsion in Semper Fi and Duandra, dual fuel propulsion (direct diesel and LNG) in Argonon and now LNG-electric propulsion in Greenstream. The choice for 100% LNG propulsion is partly an environmental consideration (there is no other oil on board than lubricating oil), but it is also closely linked to the unique mo dular propulsion concept, developed by Peters Shipyards. This is expected to result in fuel saving during low-load periods – sailing down the Rhine in ballast on one generator only – and the reduction of downtime for maintenance.
Greenstream is propelled by two electrically powered Z-drives from Veth. These azimuthing thrusters with a single propeller (in a nozzle) ensure that the aft ship sections can be optimised for shallow water, resulting in V-shaped frames. The nozzles reduce propeller ventilation and therefore reduce the amount of ballast needed. Also, the thrusters ensure excellent manoeuvrability and eliminate the need for separate rudders. Their electric motors are placed inboard, which keeps the hub of the pod compact. Electric power is generated in four 300 kW LNG-powered gensets which are mounted in pairs in containers on the aft deck. An LNG generator set consists of a marinised Scania engine, supplied by Sandfirden Technics, with spark plugs to enable the combustion of natural gas, and an alternator.
Each container, housing two LNG gensets and the necessary ventilation and fire extinghuising equipment, is called an LNG Pack* and can be easily uncoupled and shipped to a workshop by truck. When the fleet of LNG ships grows, it is expected that a spare LNG Pack* will be available to be swapped with an onboard unit in a matter of hours. This will reduce downtime of the vessel from a week to half a day. Furthermore, it is much easier to carry out the maintenance in a dedicated workshop than onboard in an engine room.
A remarkable fact of the LNG generators is that they can run at either 1,500 or 1,800 rpm, depending on the load, or to ensure quieter operation in port. This is due to the fact that the AC power (at 3×480 V) generated by the gensets goes to a direct current (DC) busbar. The deepwell cargo pumps are powered directly from this DC network, and other consumers are powered through a DC/AC inverter. Using the DC bus eliminates the need to synchronise the generators. Only a small battery bank is provided to make sure the ventilation fans of the LNG Packs* can run for a while before starting up the gensets. There are no other power sources on board than the four LNG generators of 300 kW each. The entire electrical installation was done by Alewijnse Noord.
The advantage of a tanker barge – and probably the reason why these vessels are pioneering in LNG technology – is that there is ample space on deck for the LNG tanks. These pressure vessels keep the natural gas in liquid form at a pressure of three bar and a temperature of 165 degrees Celcius below zero. Each tank is the size of a 40-foot container and is double-walled with vacuum in between to minimise heat transfer. Before it can be used in the engines, the liquid fuel has to be heated to turn into gas again. This is done in a heat exchanger, using the heat of
The modular propulsion system with LNG Packs® ensures redundancy and reduces downtime for maintenance
the cooling water of the gensets. To protect the freestanding tanks from impact, the bulwarks are strengthened in this area. Should a tank ever be dislodged from its position, automatic closing valves will contain the LNG within the tank. For short periods of time, the tanks can withstand a pressure increase from the boil-off of the LNG, but the generators should never be switched off for more than a couple of days. The capacity in the tanks is enough to sail upriver to Basel and back to Rotterdam without refuelling.
To achieve full redundancy, Greenstream has two completely independent propulsion installations on either side of the vessel, consisting of a fuel tank, an LNG Pack* and an engine room below deck housing the electrical equipment and the azimuthing thruster. A cross-over connection can be made between the tanks.
Another interesting aspect on Greenstream is its side plating construction. Although it looks like normal longitudinally stiffened steel side plating, Peter Shipyards has obtained approval for increased impact strength of this type of shell, allowing for larger cargo tanks. Named ‘IJsselhuid®’, it allows for fuel tanks of up to 600 m3 instead of the standard 380 m3. The double-hull tanker has U-shaped ballast tanks, shielding the cargo tanks from impact on the sides or the bottom.
It is a recent trend, but it is probably here to stay: commercial ships with a distinctive styling. Greenstream is not only intended to ship diesel and gasoline up the river Rhine, but it is also a showcase for charterer Shell to show the possibilities of LNG as a fuel for the future. Royal Dutch Shell is the world’s prime supplier of LNG and is betting heavily on its future as a transportation fuel. With stricter NOx emission norms entering into force in 2016 in Emission Control Areas such as the Baltic and the North Sea, the demand for diesel – and subsequently its cost – are expected to go up significantly. For inland waterway vessels, the rules are stricter. It seems the two most likely options to comply are either to burn diesel with exhaust after treatment to eliminate particles and noxious emissions, or to switch to LNG as a fuel, which burns cleaner than diesel.
To match the looks of Greenstream with her progressive innards, the styling department of Vripack Naval Architects was called in. A sleek look was obtained with a colour scheme in various shades of green, fashion plates along the bow – which also provide impact protection to the wheelhouse and accommodation – and glued windows instead of framed windows, resulting in a modern trimless appearance of the superstructure.
A lot of effort was put into optimising the hull form, also designed by Vripack. This was not based on the fully-loaded condition in deep water, but on a realistic draft of 2.90 metres, which corresponds with full tanks with the specific gravity of the commonly shipped cargo. Greenstream s maximum draft is 3.45 metres. Model tests were conducted in the towing tank at three loading conditions and two water depths. The research resulted in a longer fore ship with a fairly sharp and straight bow and a shorter aft ship with V-shaped sections.
To obtain the right weight distribution, but also to create a safe distance between the LNG zone and the living quarters, the accommodation was placed on the bow. Although this is fairly
For charterer Shell, Greenstream paves the way for LNG as a cleaner fuel of the future
common on river cruise vessels and fast ferries, and allows for a better view of oncoming traffic around a river bend, tanker captains will have to adjust their habits. The view from the bridge is excellent and unobstructed in all directions. When the wheelhouse is temporarily lowered to pass under a bridge, only a small section in the bow allows a view straight forward, and Greenstream s four CCTV cameras on deck will come in handy.
The attention to detail in the design is visible throughout. To avoid the hydrodynamic drag of the anchor pockets in the loaded condition, they are placed higher up, and the hawse pipes extend above the main deck, with the anchor winches mounted on pedestals at about 1.5 metres above the deck.
The accommodation consists of two captain’s cabins on the main deck and three crew cabins on the lower deck, one of which has an ensuite bathroom. Also on the lower deck are a laundry and a dry store. The living room with an open kitchen, a dining table and a settee is located on the main deck and provides a great view of the aft deck through the frameless windows spanning the entire width. A typical Peters Shipyards characteristic is the use of colourful materials and ample LED spot lighting, creating a pleasant atmosphere. Feedback received from other ships from Peters Shipyards shows that this is very much appreciated by the crew.
Harry Kikkert, manager design & engineering at Peters Shipyards: ”The LNG-electrical propulsion installation represents an extra cost estimated at about € 2 million, when comparing with a standard diesel-direct driven ship. Depending on the evolution of the price difference between diesel and LNG, this investment represents a payback period of five to eight years, and thus already makes business sense today.” With diesel consumption set to increase because of upcoming emission standards, and with shale gas from the U.S. keeping the natural gas price low, LNG has a lot going for it. The fact that it is the cleanest burning among the fossil fuels available for shipping is a big plus for the environment. So far, with only two ships plying the rivers on LNG, bunkering is still done by truck, but a wider LNG infrastructure is expected to evolve over time.