Research on a two-stage humidification-dehumidification desalination system powered by the waste heat of vessel diesel engine

Marine vessels are the vital goods transportation means to facilitate the international trade. In order to improve the energy efficiency and ensure the freshwater supply for crews, a humidification-dehumidification desalination system powered by the waste heat of vessel diesel engine is proposed in this paper. Performance improving methods of two-stage humidification, dual heat source, cascade energy utilization together with simultaneous heating of air and seawater are used to address the space limitation for vessel application. Problems of scaling and corrosion are also considered. With the established and verified thermodynamic and economic models, influence of the water-to-air mass ratio, temperature and mass flow of feed seawater, plant life expectancy as well as the cost of electricity are analyzed and a performance comparison is carried out with the reported data. According to the results, mass flow of the feed seawater should be designed appropriately to use the waste heat effectively. Considering the thermal and economic performance, the water-to-air mass ratio is suggested to be 1.2 and temperature of the feed seawater is better to be lower than 20 °C. The decrease rate in unit freshwater production cost begins to diminish after the plant life expectancy exceeds 15 years. Under the condition that the feed seawater mass flow is 3000 kg/h with a temperature of 12°C and the water-to-air mass ratio is 1.2, recovery ratio of the proposed system is as high as 8.08 and the gained output ratio reaches 1.22. The corresponding unit freshwater production cost is only 2.59 $/m³ at an electricity price of 0.13 $/kWh, much superior to the reported values. Therefore, the proposed system could be a good option for the freshwater supply in marine vessels.