Just burning gas

Emissions control in Norwegian waters has lead to the introduction of gas engines.

In a joint building venture the German yard of Kroger Werft and the Norwegian yard of Langsten Slip are building a gas-powered ferry with the primary aim of markedly reducing emissions. This, comments Langstens, is an entirely new concept as it is the first occasion that LNG has been used for this purpose. Kroger Werft is building the hull while Langsten Slip is responsible for all internal outfitting. The 94.8m long ferry is being built for More og Romsdal Fylkesbatar of Norway.

Apart from a very limited amount of diesel oil, used for the Mitsubishi 6D22T 165kW (224 bhp) emergency generator rated at 168 kVA, the ship will operate exclusively on LNG. The LNG is stored in two tanks, each with a diameter of 3m and a capacity of 30m3, stowed below the main deck on the ship’s centre line. The liquid gas is stored at —163 degC and each tank is vacuum insulated with a perlite filling.

Prior to injection in the four Mitsubishi GS12R-PTK main engines the gas is passed through a vaporising plant and warmed up by a heating system with fresh water to between 15 and 20 degC. Mitsubishi notes that its gas engines have a thermal efficiency of more than 37 per cent at full load with a lean mixture of gas and air. The engines feature both a pre- and a main chamber which are designed for an ultra lean gas/air ratio. Mitsubishi says this results in very low NOx levels which was a key factor in this contract.

The main engines, which are all located on the main deck each drive a Siemens IFC453-4 generator rated at 720 kVA while the power is distributed through a Siemens 690V/230V switchboard at 50Hz.

Propulsion of the double-ended 640 dwt craft is by a single Siemens thruster at each end. The service speed is 12 knots. The ferry has a capacity of 300 people and 100 cars or eight trailers and 42 cars. Classed by DNV, the ship is expected to enter service in January next year. The ferry can take on bunkers either through a direct pipeline in harbour or gas from a road tanker.