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Liquefied Natural Gas (LNG)

- alternative fuel, CNG, LNG

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Liquefied Natural Gas (LNG) is a natural gas fossil fuel mixture primarily of methane (CH4) and ethane (C2H6) that has been converted to a liquid state. The natural gas is a fossil fuel found in natural reserves beneath the earth’s surface. Just like petroleum, it is formed when decomposing animal and plant matter are put under extreme pressure and heat in layers deep underground rock formations over millions of years. The gas is retrieved from the reserves and brought to a liquid state. This is accomplished by cooling the gas to approximately -162 °C or −260 °F, which causes the gas to be compressed to 600 times its original volume and can then be stored in tanks or containers. The liquefying of natural gas is mainly for the ease of transport and logistics.

LNG by itself is not flammable, but only when decompressed and turned back into a gas state. Natural gas is mostly used to produce electricity by burning it in a gas turbines. It also is used to cook and heat buildings, in this case an odor has been added to the gas to identify gas leakages. Since the 21st century, natural gas has been on the rise in road vehicles in contrast to the use of gasoline or diesel in engines.

It is widely known that natural gas is the cleanest of all fossil fuels and is increasingly chosen as the “go-to” electric generation energy source. Natural gas emits lower levels of nitrogen oxide (NOx) and also emits lower levels of particulate matter (PM) than conventional diesel (EN590). The drawback of methane is that the greenhouse gas effect of methane (CH4) emissions is twenty-five times worse compared to CO2. For that reason any spill of natural gas in nature as methane slip should be avoided. LNG is non-toxic, non-corrosive and due to its extreme low temperature also non-flammable. However, it does become flammable after vaporization into a gaseous state.

LNG power offers a number of engine configurations for inland waterway vessels. The following engine suppliers offer LNG(gas)-powered engines: Wärtsilä, Caterpillar, MAK, Rolls Royce, MAN, ABC, MTU, Mitsubishi, Hyundai, DAIHATSU , Deutz, Scania, Agco Power, Dresser-Rand Guascor. These engine manufacturers each have their own engine configurations. More engines may become available in the future. The existing configurations are as follows:

Dual fuel engine: 80% LNG and 20% diesel:
Dual fuel engines are based on diesel engines. The engines have been converted so they can also be powered by LNG fuel. The fuel is a mix of 80% LNG and 20% diesel. This type of engine was applied on the first LNG fueled inland vessel, but will most probable not be applied anymore in newly equipped vessels.

Dual fuel/ pilot diesel engine: 98% LNG and 2% diesel:
In this case the engine is fully optimized for natural gas combustion. This LNG dual fuel system has already been in use for more than ten years in coastal and ocean shipping. The engines are now also supplied for inland shipping. The LNG dual fuel engines are specifically designed as dual fuel systems, so only a limited quantity of pilot fuel is required but needed for combustion. This involves proportions of 2% diesel and 98% LNG. The dual fuel engine can n also run fully on diesel.

Spark ignition natural gas engine:
The gas-electric drive is a system in which an inland waterway vessel uses one or several gas engines (Spark ignition natural gas engine) that drive generators (gensets) that generate electricity. This electricity goes to electric motors that drive the vessel.

Gas-electric engine:
The gas-electric drive is a system in which an inland waterway vessel uses one or several gas engines that drive generators (gensets) that generate electricity. This electricity goes to electric motors that drive the vessel. Besides the engine, special safety provisions (crew training, bunkering requirements) and additional equipment are required to propel an inland waterway vessel on LNG, such as:

– CNG/LNG storage tank;
– Tank connection space;
– Power management system;
– Gas treatment system;
– ESD or gas safe engine rooms.

It is possible to retrofit diesel engines to use LNG as an alternative fuel. The investment is highly dependent on the diesel engine and the size and type of the ship. The investment lies approximately lies around €1,2 mln. It is also possible to apply for a subsidy for a retrofit to LNG. The range depends on the capacity of the fuel storage tank. For example, the ship Eiger-Nordwand has a fuel storage tank on board with a capacity of 60m3. With this capacity on board it is possible for the Eiger-Nordwand to sail from Rotterdam to Basel and back without any refueling. Currently it is only possible to perform truck-to-ship bunkering at locations such as the ports of Amsterdam, Rotterdam, Antwerp and Mannheim. There are no fixed LNG bunker stations operational yet, these will be realized in the future. In contrast to diesel, the quantity of LNG is being expressed in kilograms and not in liters. An indicative price estimate for a ton of LNG is €400. LNG becomes an interesting economic alternative to diesel, when the yearly fuel consumption of the ship is approximately at least 500m3.

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