With the tender awarded to the Singaporean Sembawang shipyard in late 2010, to ensure compliance with a very tight programme, Envirogroupwas engaged to design and manufacture a new containerised unitary HVAC plant room to be shipped with the Aratere for installation by the shipyard.
The Christchurch earthquakes delayed the project so Envirgroup was engaged in August 2011 to assist with project management and design support in Singapore in preparation for the vessel return to New Zealand, with the completion of commissioning to be carried out upon Aratere’s return to New Zealand.
The Interislander’s competitor marketed the arrival of a replacement ship that was publically advised as being more environmentally friendly; to overcome this marketing threat we reviewed other opportunities to incorporate energy efficiency into different areas of the vessel to enable Aratere to proudly exhibit a new eco-friendly feature.
Our recommendation was to complement the auxiliary generators that were being installed to provide electricity to the vessel’s new mid section, with a waste heat recovery system that would meet the heating demand of the ship’s new hull section.
Waste heat recovery is a proven energy efficient technology, however there were several challenges to its implementation. For instance, the possibility to utilise energy from high temperature exhaust gases required a careful analysis on material compatibility to mitigate gas corrosiveness and ensure a long economic life of the components involved. In this instance, because the heating demand did not require high temperatures, a more cost-effective solution was based on utilising the heat rejection from the engines’ cooling water.
In our pre-feasibility study we estimated the duration and level of the heating requirement and consideredthe logistics of reticulating cooling water to the end user heat exchanger.
Our analysis indicated that about 8% of the electricity generated by the Wartsila generator sets was to be used for ambient heating during the winter season by means of electrically heated elements. This was equivalent to an annual fuel consumption of nearly 80,000 kg or just over $ 70,000 per year. Our study also highlighted that 17% of the generators’ waste heat was recoverable at a useful temperature and was sufficient to satisfy the whole additional winter demand without the need for an electric resistive heating boost.
Considering the small increase in cost due to the heat recovery pumps and with a payback of less than one year, the economic benefit of this solution was apparent and our heat recovery concept was incorporated in the Aratere’s upgrade.