| Along with the increase of energy consumption,development and application of energy-saving technology has been a significant demand for social and economic advancement.Technologies of organic Rankine cycle(ORC)system are applied to transform low-grade heat energy into high-grade electric energy,and it is an effective technology of rationally utilizing medium and low temperature heat source.The expander is the key equipment for work-heat conversion in ORC system,and its property exert great influence on ORC system.However,present expanders have many disadvantages,such as low efficiency,serious leakage,poor reliability,etc.These disadvantages are key issues for limiting the development of ORC system.Therefore,there is an urgent need to develop efficient and stable turbo expanders.Besides,owing to fluctuation and instability of heat and cold source,there is important engineering application value to study on dynamic property of ORC system and formulate corresponding control strategies.Aimed at above-mentioned issues,the turbogenerator with aerostatic bearings is designed in this paper,and relevant experimental study is conducted.Meanwhile,dynamic property of ORC system and the control strategies are studied.PLC control system based on PID control strategy is equipped in the test device,and influence from working condition parameters on ORC system performance is analyzed to provide reference for industrial application of ORC system.Main research contents and results are as follows.(1)Based on a 3 kW ORC low-temperature waste heat power generation system,the experimental study on the influence from operating load variation on the system performance is conducted,and the system maturity evaluation is carried out.Researches show that there is the optimum matching between load power and other elements,such as isentropic efficiency,output power,electric power,thermal efficiency and exergy efficiency.Electric power has the closest tie with load power,and its grey relational degree is 0.632.The maturity of 3 kW radial inflow turbine-generator set lies in Ⅲ grade,which indicates the overall performance of the set reaches the standard,but there is large space for reinforcement and improvement of different components in the set.(2)By response surface analysis,optimization study of the radial inflow turbine in ORC low-temperature waste heat power generation system is conducted.Researches show that the influence degree on peripheral efficiency of the turbine is in the following order from the biggest to the smallest,ratio of wheel diameter,relative airflow angle at the rotor outlet,degree of reaction,velocity ratio,rotor velocity coefficient,absolute airflow angle at the rotor inlet,nozzle velocity coefficient.After the optimization,the total-to-static efficiency of the turbine increases by 1.39%,reaching 74.55%.(3)A 50 kW radial inflow turbogenerator with aerostatic bearings is designed,and the experimental study on its performance is conducted by using CO2 as the working fluid.Variation rules of turbogenerator performance along with rotational speed,inlet temperature,load of the generator are studied.When the rotational speed of the turbogenerator is set as 26000 r·min-1,the isentropic efficiency,the expansion work and the electromechanical efficiency are the maximum values,80.6%,20.47 kW and 91.1%,respectively.Compared with the separate design,the isentropic efficiency and electromechanical efficiency of the turbogenerator increase by 28.5%and 10%,respectively.(4)Dynamic property of the ORC low-temperature waste heat power generation system is studied and the control strategies are designed.Combined with project cases,dynamic operational models for ORC system are established.Simulated results show that relative to the initial running value,the larger the input disturbed values are,the more rapid the system response process is.The control strategies based on PID control algorithm are designed.Closed-loop feedback regulation of the disturbance is conducted,which is about heat source flow,cooling water flow and pump rotational speed.The overshoots of thermal efficiency and exergy efficiency are both no more than 5%,and the response time is no more than 14 seconds.It indicates that the control system with external disturbance maintains preferable control effect and favorable robustness.(5)The test rig of a 50 kW radial inflow turbogenerator with aerostatic bearings is set up,PLC control system is established,PID control strategy is formulated,and dynamic property of ORC system is studied.Various state parameters of the system are controlled and regulated by heat source flow,cooling water flow,working fluid flow,rotational speed of working fluid pump.Superheat degree and pressure of evaporator outlet,pressure of condenser outlet are successively sensitive to rotational speed of working fluid pump,working fluid flow and cooling water flow.Making the system maintain the setting working condition will guarantee the safe and stable operation of ORC low-temperature waste heat power generation system. |
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