Exhaust gas economizer on auxiliary engines - A case study of potential savings that can be made by installing an exhaust gas

Abstract

With more expensive bunker oil prices and much tougher environmental requirements, it is of major importance for shipping companies to reduce their consumption of fuel oil today than it ever has been before. There are many ways to lower the consumption; the most efficient would be to reduce the speed of the vessel. This study has however focused on the potential savings that could be made by installing an exhaust gas economizer for the auxiliary engine on board ships. The reason why many ships have not installed economizers on their auxiliary engines is because the investment has not been considered necessary before. This work is primarily a case study on the vessel M/V Stena Forecaster, but can probably be seen as a general guideline as well. On-board data from the ship and information from manufacturers has been collected, in order to calculate the steam need for the ship during the period of May 2015, as well as how much steam an exhaust gas economizer could produce during the conditions of May 2015. The exhaust gas economizer in this study would be installed on a Wärtsilä 9L20C engine, and the economizer selected is an Aalborg XS TC7A from Alfa Laval. The result shows the possibilities and potential savings of this investment in terms of lower fuel oil consumption for the auxiliary boilers, the environmental benefits with reduced emissions, a possible installation location and a reasonable pay-back time for the current sailing route. This can however differ widely depending on for example sailing routes and weather conditions. An investment of this sort should be discussed having in mind the age of the ship, sailing route, and who pays for the bunker oil. In this particular case the owner does not pay for the bunker, the charter does, and therefore the investment cannot be seen as a direct profit for the owner. However, the ship could be more attractive for future charters if the overall fuel oil consumption is lower. A lower fuel oil consumption is also directly beneficial for the environment.