| To improve the energy efficiency,the state puts forward the "13th Five Year Plan" including the development of the energy conservation and environmental protection and encourages the development and utilization of the exhaust heat.As an emerging thermoelectric conversion technology in domestic,organic Rankine cycle(ORC)power generation system has many advantages such as the lower temperature of heat source,the lower working pressure,the smaller floor space,the better adaptability,the higher efficient and more environmental friendly.It has become a highlight in the research of the exhaust heat recovery.The research of ORC power generation set for low temperature exhaust heat in domestic starts late,which mainly focuses on the system components and theoretical research.The power rating of prototypes is mostly less than 100 kW.In order to analyze,simulate and predict the operational aspect of unit in off-design condition which is closer to the engineering application of high power generator,this paper makes a steady-state model for 300 kW level ORC power generation set and simulates parts of system performance under off-design conditions.First of all,according to the given heat source conditions,four kinds of working mediums are determined by a preliminary screening from industrial commonly used refrigerants.Through a simple system model,this paper analyzes the relationship between the outlet temperature of the evaporator,the outlet temperature of condenser and the system efficiency.With considering the actual working status of the working mediums,such as the turbine design,the safety in use and the economic efficiency,this paper finally makes sure the R134 a is the most satisfying circulating working medium for the heat source condition and equipment operating condition of the prototype.Secondly,the paper changes the modeling of the ORC power generation set for low temperature exhaust heat from engineering to the theory.This paper makes reasonable assumptions of boundary condition and simplifies the model.Making cold and hot source and pump frequency as the input conditions and considering avoiding the occurrence of abnormal condition,this paper makes the models of system components by adopting the method of moving boundary,polynomial fitting and so on.Finally,the simulation and analysis of the various thermodynamic parameters of the system in off-design condition has been made.The five kinds of off-design working condition include the change of heat source temperature or flow,the change of cold source temperature or flow,and the heat source temperature along with the pump frequency rise up at the same time when the degree of superheat doesn’t change.In these conditions,the research of the heating load,cooling load,the superheat degree of evaporator exit,liquid level,pressure drop of turbine,system efficiency and other performance of the system parameters has been made.The simulation results are as follows.Towards the system efficiency,the influence of heat flow is greater than the cold source.The heat source temperature rising up along with pump frequency is better than only changing the heat source temperature in the aspect of developing the system efficiency.What’s more,the decrease of the cold source temperature has the most significant influence on developing the system efficiency.If the cold source decreases 1℃,the system efficiency would increase 0.2%,which is 10 times higher than the influence of the heat source temperature.This paper enriches the research of system simulation models for ORC high power generation set in domestic,provides the theory basis for commissioning test,and also can provide reference for the design of control strategy in the future. |
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