Onboard auxiliary power and desalination unit with a free piston Stirling engine

The work examines an onboard auxiliary unit powered by a Stirling engine that can produce fresh water through a thermal desalination plant and recharge the service batteries with surplus electricity. In small boats fresh water requirements are met either by filling the water tanks at ports or by producing it onboard. However, both currently available technologies, i.e. reverse osmosis and thermal desalination plants, consume electricity and involve a certain amount of noise from the power unit. Nearly noiseless operation makes Stirling engines well suited for mounting on sailing boats. This work studies a 1 kWe Stirling engine coupled to a reverse osmosis or to a thermal desalination plant. Since both designs use thermal energy recovered from the Stirling engine, to reduce water dynamic viscosity (reverse omosis plant) or for water evaporation (thermal plant), the main design differences lie in how heat is transferred to the salt water. A technical and economic analysis is also provided, comparing the performances and cost of the two plant solutions.