| Under the situation of energy saving and pollution reduction, ship that plays a role of transport of international trade consumes huge amount of fuel. At the same time, it is also constrained by international emission regulation. Therefore, energy saving and emission reduction of ship is of great practical significance. Based on the energy balance analysis, the thermal efficiency of a large two-stroke diesel engine is up to 48-51%. However, there is still about half of the energy wasted and delivered to the environment by means of exhaust gas, jacket water and compressed air. Due to steady operation condition, large amount of waste heat and using sea water as coolant directly, waste heat recovery(WHR) of marine engine has become one of the most promising technology to realize both energy saving and emission reduction. Because of large amount waste heat energy and the various energy demands aboard ship, the paper conducted both simulated and experimental researches on the performance of the waste heat recovery system based on Rankine cycle, aiming to improve the efficiency of waste heat recovery system.W?rtsil? 12RTA96 C low speed marine engine is adopted as the research object in the paper. Waste heat streams are analyzed in terms of quantity and quality under different operation conditions. The paper makes an analysis on the content of exhaust gas by means of the combustion reaction equation, and then analyzes the thermal properties of exhaust gas in terms of mixing rule, and theoretically analyzes the characteristics of energy flow and exergy flow of heat source, which lay foundation for the performance research of the waste heat recovery system. The results show that as the engine duty increase, the amount of each energy flow increase. The energy contained in the exhaust gas is the largest, which can reach its maximum value of 42808 kW under 110% CMCR. Both the energy and exergy percentage of the scarving air increase, nevertheless, that of the jacket coolant and exhaust gas decrease.Based on the thermal properties of the waste heat steams, modeling of subcritical Rankine cycle waste heat recovery system that uses high-temperature exhaust gas of engine as the heat source was built by means of EES. 11 subtances were selected as working fluids based on their performance, thermostability, safety, economy and environmental protection, and the influences of system evaporating pressure, condensing pressure and engine operation conditions on system performance were also analyzed. Results showed that as the evaporation pressure increase, the net electricity output of most selected working fluids showed a trend of first increase and then decrease for most selected working fluids. The electricity output increases as the condensing temperature decreases. The WHR system reaches its greatest potential when the engine was operated under heavy duty. The results also showed that the system with cyclohexane as the working fluid has the maximum output power and the engine thermal efficiency is up to 52.08%, which increased by 6.5% compared to the original engine. The waste heat recovery system with water as the working fluid has the highest thermal efficiency and exergy efficiency.YC6L330-30 diesel engine acts as the substitute engine of marine engine. The test bench for the organic Rankine cycle waste heat recovery system with thermal oil cycle was built and experimental research on the performance of three throttling expansion systems, including expansion valve and turbo-expander were also conducted. When the rotation speed and power of engine is 1700 rpm and 225 kW respectively, the exergy of the working fluid in the expansion valve inlet is 19.3kW, which accounts for 8.58% of engine power. When the rotation speed and power of engine is 1900 rpm and 228 kW respectively, the maximum electricity output of the WHR system is 253 W, which only accounts for 0.11% of engine power. Based on these results, the problem is analyzed and the methods of problem solving are proposed.In order to improve the performance of the heat recovery system, we analyze five systems including jacket coolant preheat system, steam reheat system, dual-pressure system, dual-loop Rankine cycle system and Rankine-absorption combined electricity and cooling cogeneration system and the optimal system solution can be obtained. Results show that all the WHR systems investigated improved their performances except jacket coolant preheating system, and the Rankine-absorption combined electricity and cooling cogeneration system(ECCS) has the best performance. The maximum equivalent electricity output of ECCS is 6068 kW, and the electricity and cooling capacity is 2927 kW and 12756 kW. The ECCS is a suitable technology for waste heat recovery, which can meet the multi energy demand aboard ship. The paper makes further optimization of the ECCS according to the energy needs of ships. the output scale of the electricicty and cooling of the ECCS is adjusted, reducing the cold output and increasing the electric output. The electricity ouput increases to 5121 kW while the cooling capacity decreases to 489.3 kW. Thus the supply and demand is met on the quantity and the energy and quality is balanced. |
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