Single-fuel LNG ferries with waste heat recovery systems
A Dutch ferry operator has recently commissioned two new ships with single-fuel LNG engines. The ships are also equipped with a waste heat recovery system to generate electricity.
In July 2020 and January 2021 respectively, Dutch ferry operator “Rederij Doeksen” put into service two LNG-fuelled ferries which are reportedly the first ships in the world in which single-fuel LNG engines directly drive fixed propellers. Each ship can carry over 60 vehicles and about 600-700 passengers, operating on the connection between the Dutch islands of the Wadden Sea.
According to the ferry operator, emissions from the LNG engines are in compliance with the current International Maritime Organization standards. In order to further improve energy efficiency, the LNG-fuelled ferries are also equipped with waste heat recovery systems to generate electricity.
Based on Organic Rankine Cycle technology, the waste heat recovery systems on board use the waste heat from the propulsion and auxiliary engines to generate electricity. The system operates with a heat exchanger that transfers waste heat from the exhaust gases to the waste heat recovery system. The jacket cooling water is routed directly through the waste heat recovery system. There, the hydrocarbon refrigerant is evaporated and fed to the expansion device as superheated vapour. The highly- pressurised refrigerant is expanded, thereby driving the expansion device. The rotational energy is used to drive a generator that produces electricity.
When the engines operate at full power, the system is expected to provide 154 kW of additional net electrical power. Usually, more than half of the energy from the fuel in a ship’s propulsion system is lost as waste heat and dissipates into the atmosphere. According to the Dutch ferry operator, using these waste heat recovery systems could save 318 tonnes of CO2 emissions, 260,000 litres of fuel and 462,600 kWh of electricity per vessel per year.