| Organic Rankine Cycle(hereinafter referred to as ORC)power generation technology is an effective means to convert low quality thermal energy into high quality electricity energy.It has broad application prospects in the field of power generation in industrial heat,geothermal,solar energy and ocean thermal energy.It has important theoretical significance and social value to carry out ORC system thermal characteristics and control research,master the operating characteristics of the system,propose key component optimization methods,develop advanced control strategies,and promote its technological development and engineering application.In the existing researches on ORC,the research on system heating characteristics that meet the needs of engineering applications is insufficient.The coupling relationship between operation characteristics of key equipment and thermodynamic parameters of the system is not completely clear.It is urgent to establish the control methods of the system in the face of complex and variable external disturbances and load variation requirements.Aiming at the above requirements,this paper designed and constructed the 350 k W ORC experimental system with the characteristics of miniaturization and skid mounted and carried out the thermodynamic performance experimental study of the system,clarified the operating characteristics of the system,proposed the optimization method of key components,introduced the active disturbance rejection control(ADRC)strategy and proposed the multi-objective ADRC method suitable for the ORC characteristics.In summary,the main research contents and conclusions of this paper are as follows:Firstly,the installed capacity of 350 k W was determined based on the calculation of heat source conditions,and the economic analysis model of the system construction scheme was established.The system scheme using radial flow turbine + plate heat exchanger was determined through comparative analysis,and R134 a was selected as the working medium.The optimal design method of radial flow turbine with multivariable constraint genetic algorithm and the iterative optimization design method of the system thermodynamic design were proposed.Under the design conditions,the optimal system efficiency is 7.7% and turbine efficiency is 79.94%,which provides support for the subsequent experimental system construction.Secondly,the 350 k W ORC experimental system was constructed,and the design and research of organic working fluids cycle system,cold source system,heat source system,measurement and control system and experimental scheme were completed.The automatic control method of the whole process of load up and down is proposed.Experiments on the influence of heat source and cold source temperature on system performance were carried out.The results show that the turbine power has a dynamic delay response of about 50 s with the change of heat source temperature.When the heat source temperature is 95.7℃,the output power of the turbine is 354.4k W,and the thermoelectric conversion efficiency of the system is 7.73%,which reaches the design value of the system.Exergy loss of system exergy and system efficiency before and after optimization of quick-closing valve were analyzed.It is pointed out that reducing pipeline pressure loss and improving heat exchanger insulation are optimization directions to improve system efficiency.Thirdly,carried out experimental analysis and optimization research on key equipment of ORC,and established the coupling relationship between operation characteristics of key equipment and thermodynamic parameters of the system.The results show that compared with the experimental results,the calculation error of liquid level distribution model of plate heat exchanger based on moving boundary method is within ±5%.The increase of working medium flow and the decrease of superheat will make the gas-liquid balance of working medium move to the heat source,while the increase of cooling water flow will make the working medium gather in the working medium tank.The average error of cavitation prediction model of working medium pump based on data analysis is 3.9%.Considering system efficiency and cavitation suppression,a cavitation suppression method based on parameter optimization control is proposed.The safety adjustment rate of working medium pump under load reduction condition is less than 0.1Hz/s and the lowest starting frequency under different working conditions are obtained.Combined with finite volume method simulation analysis and experimental verification,a flash cooling design method for turbo-generator unit is proposed.The cooling fluid consumption in rated working conditions only accounts for0.75% of the system.The scheme takes into account the tightness and reliability,and has higher thermal and power conversion efficiency and power generation efficiency than other technical schemes,which provides methods and supports for the development of turbine-generator sets.Finally,a dynamic thermodynamic model is constructed for ORC system which is sensitive to heat source and load changes.A multi-objective ADRC control strategy is proposed.The control performance such as tracking efficiency and overshoot when the system load changes is analyzed.The results show that the load tracking performance of multi-objective ADRC control is better than that of PI control,and compared with single-objective ADRC,overshoot and integral absolute error(IAE)are reduced by 50%and 16%.When the output power reached the design value,exergic efficiency increased by 8.64%.The multi-objective control strategy based on ADRC could effectively control system stability.This paper systematically reveals the operating characteristics of ORC system.Relevant research results can provide powerful theoretical and data support for the optimal design of key equipment and system control scheme in practical engineering applications.And it is an important supplement and improvement to the research on the thermal characteristics and control of ORC system. |
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