Multi-dimensional assessment and multi-objective optimization of electricity-cooling cogeneration system driven by marine diesel engine waste heat

Abstract

Although the prosperous shipping industry promotes economic globalization, it causes the environmental issues like air pollution and ecological destruction, due to the emission of harmful substances. Accordingly, many waste heat recovery technologies of ships have been developed and improved, among which the supercritical Brayton cycle has attracted wide attention due to its high energy conversion efficiency. Taking an actual diesel engine as the research object, this study presents four waste heat utilization schemes by combining different supercritical carbon dioxide cycles with a double effect absorption refrigeration system. The indicators of each scheme are calculated from three perspectives of thermodynamics, economy and environment, and the overall evaluation of all schemes is carried out through the analytical hierarchy process. The addition of the refrigeration system to the recuperation supercritical carbon dioxide cycle is considered to be the optimal combination. Parameter study indicates that output power, thermal and exergy efficiency increase with the turbine inlet pressure and temperature. The maximum of these thermodynamic indexes are 5987 kW, 27.35% and 56%, respectively. Furthermore, to lower temperature of high pressure generator is conducive to improving the refrigeration performance and to raise the temperature of low pressure generator also has a similar effect. Before optimization, the capital payback period and product exergoenvironmental impact of the combined system are 6.845 years and 63.023 mPts/s. After operating the optimization program, both of them become 5.81 years and 54.94 mPts/s, which are reduced by 15.12% and 12.83%, respectively.