Doeksen deploys heat recovery on Wadden catamarans

Compact heat recovery will provide enough power for port manoeuvring on two gas-fuelled passenger catamarans

Later this year, Dutch shipping company Doeksen will put two new catamarans into service on the environmentally sensitive Wadden Sea, which was declared a UNESCO World Heritage site in 2009. The ships, built in Vietnam by Strategic Marine, bundle environmental technologies and materials to make the operation as sustainable as possible.

The 70-m vessels, which will sail between Harlingen and the islands of Terschelling and Vlieland from mid-2019, carry up to 66 vehicles and around 600 passengers. A lightweight aluminium body significantly reduces fuel consumption compared to a traditional steel hull. The vessels are powered exclusively by LNG via pure gas engines from MTU.

Even more innovative than the engines is the process of using waste heat recovery on the ships. Doeksen managing director Paul Melles notes that – however environmentally friendly the fuel you use – more than 50% of the energy contained in fuel is lost as waste heat when using internal combustion engines.

“Using waste heat to generate electricity that can be used on board is a crucial step forward”

“The waste heat simply evaporates in the air or is dumped into the sea,” says Mr Melles. “Using waste heat to generate electricity that can be used on board is a crucial step forward. But installation space on board a ship is strictly limited so we were looking for a solution that not only worked but above all was compact.”

Doeksen selected a system from Munich-based company Orcan Energy, which has been building solutions for converting waste heat into electricity for industry, mobility and power generation for several years. Orcan’s efficiency packs are the size of a shower cabin. In order to use the heat contained in the engine exhaust gases to drive an electric generator, the catamarans were each equipped with two efficiency packs, each generating an electrical net output of up to 100 kW.

The packs are based on the Organic Rankine Cycle, in which a refrigerant is continuously cycled to convert waste heat into mechanical work.

Waste heat is withdrawn from the heat source by a heat exchanger and delivered to an efficiency pack by an intermediate hot water circuit. The heat is transferred through the evaporator into the refrigerant circulation process loop. In the evaporator, the refrigerant is then supplied in vapour form, as superheated steam, to the expansion machine, turning the rotary screws of the expander. This rotational energy is in turn used to drive a generator that generates electricity.

After the expansion machine, the still gaseous refrigerant is liquefied in the condenser and then re-pressurised by the feed pump. The refrigerant has now completed the cycle and re-enters the evaporator to absorb waste heat again.

The power generated is converted into direct current by a frequency converter to charge batteries, which supply electric power to bow thrusters when manoeuvring in harbour. The waste heat recovery system thus covers the entire energy demand for this intensive operation. The result is an annual CO2 reduction of 318 tonnes for each efficiency pack – a saving of 260,000 litres of fuel and 462,600 kWh a year.

The catamarans have yet to enter service, but Orcan is already growing its marine orderbook. According to chief executive Andreas Sichert, the company will soon reach orders for 32 installations. Depending on the size of the heat source on board, Orcan delivers a stack of three to five modules (300-500 kW). For high-powered ships (such as the biggest container vessels), the company could marinise its industrial module, with each module supplying 400 kW, resulting in the supply of 1 MW of electric power to large ships.