Study On Thermal Performance And Comprehensive Utilization Of Ocean Thermal Energy Conversion

Energy consumption is growing with the development of economy and the depletion of traditional fossil energy causes serious environmental pollution.So the use of renewable energy is one way to solve the energy shortage and reduce pollution.As a maritime country,the development and utilization of ocean energy has become an important option for the future energy strategy.Because the ocean thermal energy conversion(OTEC)is huge reserves,clean,renewable and multiple purpose utilization,it has attracted much attention in recent years all over the word.But because the ocean temperature difference is small,the generating efficiency of OTEC system is low and the cost is high.In this paper the key technical problems of OTEC is cycle mode,which is theoretical analyzed,programed calculation and experiment test,and also explore theoretical and technological ways to improve the performance of transformation.This result can provide the reference for the design and operation of the OTEC system.The Rankine cycle of OTEC is studied.Theoretical analysis of Rankine cycle based on the first law and second law of thermodynamics is carried out,and mathematical model of individual equipment of the cycle is established to program.Through programming calculation of cycle thermal efficiency and net power output,the change rule of thermal efficiency and net power output with turbine inlet pressure,temperature and condensation temperature has been obtained.Also a 15kW ocean thermal energy conversion system with Rankine cycle has been constructed and variation law of the thermal efficiency with various parameters under the simulated working condition of ocean temperature difference has been obtained through analysing the experiment results,and also the thermal performance of heat transfer is obtained.The consistency between the results of theoretical calculation and experiment has verified.In the mean time,practical operating experience about OTEC has been achieved.Then aimed at the low efficiency of Rankine cycle,analyze and calculate the Uehara cycle with non-azeotropic refrigerant as work fluid based on mass and energy conservation equation.Thermodynamic analysis model was constructed by dividing the essential component of the overall system,parameter of each node has been determined,thermal efficiency and net power output has been provided.The influence rule of parameters,such as the pressure of turbine inlet,temperature of warm and cold seawater,concentration of ammonia-water mixture,rate of intermediate extraction gas,on thermal efficiency of system is also analyzed.On the basis of the above study,develop the approach which can increase thermal efficiency,remodel a new thermodynamic cycle(GUO HAI cycle)by analyzing the thermal efficiency of Rankine cycle and Uehara cycle.In addition to use heat recovery of poor ammonia solution,intermediate extraction,and other existing measures of improving thermal efficiency,the new cycle adds the secondary heat recovery,in which the work fluid is heated by poor ammonia fluid before entering the evaporator,in order to reduce the heat loss of cycle and further increase thermal efficiency.Meanwhile,the internal mechanism between the residual heat of poor ammonia solution and the thermal efficiency of the new cycle is exposed based on basic principle of thermodynamic.Combined with numerical simulation,the quantitative analysis of two regenerators influence on the node parameters and thermal efficiency of the new system is completed.The change rule of thermal efficiency and net power output with concentration of ammonia-water mixture and turbine inlet pressure is proposed under different temperature condition.Research shows that:the new cycle proposed in this paper can further improve the thermal efficiency of OTEC efficiency,and also provides the theoretical basis.For the the optimal operating condition and the parameter design of OTEC system,the thermal efficiency and net power output of Rankine cycle,Uehara cycle and new cycle under the same working condition is researched based on the results of numerical simulation,and also the optaimal opterationg condition is obtained.This study also can provide theoretical basis for the selecting thermodynamic cycle form and the optimal operating parameters of the OTEC system.The results also can provide the corresponding reference for optimization analysis of industrial waste heat,geothermal and other low temperature waste heat utilization cycle system.Finally,seawater desalination based on OTEC system is also studied for the theory of comprehensive utilization and the characteristics of the OTEC system.Design the whole system of seawater desalination based on OTEC and built desalination experiment system with two kinds of heat exchanger of the light tube and fin tube based on the OTEC,and the properties of the two kinds of heat exchanger respectively and freshwater production of system is studied under the same work conditions.Change regularity of the fresh water output and system efficiency with the flow rate and temperature of warm and cold seawater are obtained,and also the characteristic of the two kinds of heat exchanger system is given.The results verify the feasibility of seawater desalination based on OTEC and it is important value for design and development of comprehensive utilization based on OTEC.