Waste heat recovery by using the exhaust gas boiler - A comparative analysis of wet-steam turbine and steam screw expander

Since 2015, ships operating in waters around Sweden are not allowed to use fuel for propulsion and power supply on board with a sulphur content of 0.1 percent or more. The stricter rules resulted in ships exchanging their fuels. The change of fuel could be to a more fluid fuel. A more fluid fuel does not require the same amount of heating as the previously used fuels. The reduced heating requirement can result in a ship's steam production plant, which is dimensioned to a greater need, now having to cool down steam to condensate. This thesis explains how a ship can recover this energy source by allowing steam to expand through a power plant instead of cooling it. A qualitative case study has been carried out on the vessel Stena Saga. Data has been collected primarily through own observations. During the observations, field notes have been taken. Some information has also been obtained by reading manuals for the vessel's machine components. In order to confirm the perception of observations, machine personnel have answered questions. The study gives a result that shows how much energy that is available to use in the steam that otherwise has to be cooled down. A comparison of two different power plants is made. The work also shows how a ship's various load conditions can affect a possible decision to install a steam turbine. The result shows a significant difference in power outtakes between the different systems, but with a similar pay-back time because of the systems different prices. Both systems pay-back time is around 9 years