Research On Multi-Objective Optimization And Overall Operational Characteristics Of Ocean Thermal Energy Conversion Systems

The South China Sea has abundant marine thermal energy resources.Ocean thermal energy conversion system can not only provide electricity,but also provide deep seawater for refrigeration,seawater desalination and other related production activities to meet production and daily needs,which is of great significance for the development of remote islands.Although it has low efficiency and high cost,ocean thermal energy conversion system can not only achieve power generation benefits,but also obtain additional benefits from the comprehensive utilization of deep seawater(such as refrigeration,seawater desalination,etc.).The sum of the power generation benefits and the additional benefits of comprehensive utilization of deep seawater is the comprehensive benefits of the power generation system.The comprehensive utilization of deep seawater can bring more than a hundred times the benefits of power generation.Sacrificing a portion of net output power to obtain more deep seawater can improve the comprehensive benefits of the power generation system,shorten the investment payback period,attract investment,and accelerate the commercialization and promotion progress of ocean thermal energy conversion technology.This article qualitatively represents the improvement of the comprehensive benefits of the power generation system with the increase of deep seawater flow rate.Based on the data of thermal energy resources in the waters near a certain island in the South China Sea,with the goal of reducing equipment costs and improving comprehensive benefits,a multi-objective optimization and overall operation characteristics study of the ocean thermal energy power conversion system is carried out.In terms of optimization,this article conducts interactive optimization design of power generation systems and centripetal turbines.The optimization of the power generation system includes optimizing the structural parameters of the evaporator and condenser,while providing the optimal isentropic efficiency and corresponding inlet and outlet parameters for the turbine as design objectives and design conditions.In terms of system optimization,this article establishes a comprehensive system parameterization model that is modified based on the experimental data,analyzing the impact of thermodynamic and structural parameters on the performance of the power generation system.This article proposes the second optimization objective of maximizing the ratio of deep seawater flow rate to heat exchange area,and conducts multi-objective optimization design in conjunction with the first optimization objective of maximizing the net output power per unit heat exchange area.Compared with the minimum cost scheme,the multi-objective global optimal scheme has a cost increase of 0.79%,but an increase of 29.06%in deep seawater flow rate.While maximizing equipment cost optimization,the comprehensive benefits of the power generation system have significantly improved.In terms of centripetal turbine optimization,this article establishes a parameterized model,and analyzing the impact of key structural parameters and energy loss coefficient on turbine performance.An interactive optimization design method for power generation systems and centripetal turbines was proposed.Turbine isentropic efficiency is one of the design parameters for optimizing the performance of power generation systems.Based on multi-objective optimization of the power generation system,the optimal isentropic efficiency and its corresponding inlet and outlet parameters are used as the design objectives and conditions for turbine optimization design.This method achieves good parameter adaptation between the turbine and the system,and both the power generation system and the turbine achieve optimal performance.Further analysis was conducted on the impact of changes in inlet operating conditions on the operating characteristics of fixed structure centripetal turbines.This article analyzes the overall operating characteristics of a fixed structural parameter power generation system from both theoretical and experimental perspectives.In theoretical research,this article analyzes the impact of changes in internal operating parameters and external environmental parameters on the overall operating characteristics of fixed structure power generation systems.Based on the non-dominated sorting genetic algorithm,with the goal of maximizing net output power and maximizing deep seawater flow rate,this article optimizes the optimal operation plan of the power generation system under different surface seawater temperatures,and summarizes the control strategies for the operating parameters of the power generation system,and obtains the main control strategies that can improve the maximum net output power of the power generation system by reducing the turbine output power.In the experimental research,this article established an indoor experimental platform of a 50kW ocean thermal energy conversion system.Taking the annual surface seawater temperature conditions near an island in the South China Sea as the experimental input conditions,this article conducted continuous variable operating conditions experiments and achieved the design goal of 50kW power generation.The article obtained the key operating characteristics of the turbine and heat exchanger through experiments,as well as the variation of internal operating parameters and overall operating characteristics of the power generation system with seawater temperature conditions,making up for the lack of understanding of the coupling law between internal and external parameters of the system caused by the control variable method in theoretical research.Promoting the promotion and application of ocean thermal energy conversion technology in low latitude seawaters is an important way to achieve the "dual carbon" goal,and is of great significance for promoting the construction of islands and reefs,promoting the development of marine economy,and strengthening national defense construction.This study provides a new optimization design method for reducing investment costs,improving comprehensive benefits,quickly recovering funds,attracting investment,and promoting the commercialization of the marine thermal energy conversion industry.It also provides theoretical guidance for the operation and control of the entire power generation system under non-design conditions,and provides experimental data support for the practical application of marine thermal energy conversion technology in low latitude waters.This study has important theoretical significance and engineering application value in promoting the development of ocean thermal energy conversion technology.