Performance Analysis Of Organic Rankine Cycle For Low Temperature Waste Heat Recovery On Ship

As the global environmental deterioration and the increasing of energy crisis,the standards for ship efficiency and marine fuel oil issued by International Maritime Organization become more and more stringent.In order to meet ship energy efficiency standards and reduce operation costs,ships need to further enhance the effectiveness of energy saving and emission reduction.Only less than 50%of the heat generated by the fuel consumed by marine diesel engines is used for ship effectively,and the rest of the heat is lost to the surroundings through various ways.Waste heat recovery technology can effectively improve ship energy efficiency and achieve the goal of energy conservation and emission reduction,which gradually becoming a hot research topic.At present,the research on the ship waste heat recovery technology mainly focus on the waste heat of the high-temperature section of the marine diesel engine exhaust gas.But,the low-temperature waste heat of the low-temperature section of the marine diesel engine exhaust gas and jacket cooling water is ignored.The recovery efficiency of low-temperature waste heat is low,but the total amount of that is large.Low-temperature waste heat recovery can further improve the ship energy efficiency.Organic Rankine Cycle(ORC)can convert low-grade waste heat into high-grade electrical energy,which is especially suitable for low-temperature waste heat recovery on ships.According to characteristics of the ORC,the following research works were carried out in this thesis for the recovery of the low-temperature waste heat of the low-temperature section of the exhaust gas and jacket cooling water of marine diesel engine:Firstly,according to the characteristics of the diesel engine exhaust gas,a thermodynamic model of the ORC with closed heat source was established by converting the open heat source of the marine diesel engine exhaust into a closed hot water heat source which is similar to the diesel engine jacket cooling water.Taking the heat source of hot water at 85? as the heat source,the effects of cooling water control mode and working fluid on the performance of low-temperature ORC were investigated.The results show that the performance of the ORC is more stable by using constant cooling water flow rate control mode.It is found that the non-azeotropic mixing working fluid can effectively coordinate the contradiction between the evaporation pressure and the differential pressure at inlet and outlet of the expander,and can effectively improve the thermodynamic performance of ORC.Compared with the pure working fluid,the non-azeotropic mixing working fluid is more suitable for the ORC with the low temperature closed heat source.R245ca/R1234ze(21.53/78.47)has the best comprehensive performance among the non-azeotropic mixing working fluids investigated in this thesis.Secondly,three schemes of ORC for recovering low-temperature waste heat from MAN B&W 6S50MC diesel engine were designed,such as Basic Organic Rankine Cycle(BORC),Series Organic Rankine Cycle(SORC)and Dual-loop Organic Rankine Cycle(DORC).In addition,the thermodynamic performance and the economy of the three schemes were compared.The results show that the SORC has the maximum net power output under the tropical ambient condition,while,the DORC has the maximum net power output under ISO ambient condition and specified ambient condition.For the economy of the three schemes,the SORC has the maximum annual fuel savings under the tropical ambient condition,while,the DORC has the maximum annual fuel savings under ISO ambient condition and specified ambient condition.On the other hand,the SORC has the shortest payback period under all ambient conditions.Finally,an ORC experimental platform with low-temperature heat source was designed and built.The experimental investigation on power generation performance of the ORC with low-temperature heat source was carried out with R245fa as the working fluid.The experimental results show that the power of the ORC with a scroll expander with constant supply of lubricating oil is proportional to the evaporating pressure,and it is not affected evidently by the change of condensation pressure in a small range,moreover,the power increases afterward steady as the vapor superheat increases.It is found that the power generation efficiency of the ORC is proportional to the condensing pressure,while,inversely proportional to the evaporating pressure.In addition,the power generation efficiency increases first and then decrease as the increases of the vapor superheat.