Study Of The Influence Of The Cooling System On The Thermal Performance Of Organic Rankine Cycle

There are a lot of waste heat in all walks of life in China.Fully recycling and utilizing waste heat would significantly improve the energy efficiency,and alleviate the environmental problems and energy problems brought by huge energy consumption.At present,organic Rankine cycle（ORC）technology is a highlight in terms of medium-and-low temperature waste heat recovery and utilization technology.The ORC is more susceptible to cooling source conditions and local climatic conditions than the traditional steam Rankine cycle.Based on many documents,finding that scholars at home and abroad have done a lot of researches on ORC which the main concentration of the selection of working medium,critical components,thermal analysis and optimization of system.But this is seldom the work of the cooling system of ORC,and the formerly research take theoretical analysis as main and lack experimental study.In terms of the output power of system,the power consumption of all auxiliary engines are rarely considered in the former studies.Therefore,in order to obtain the characteristic curves of ORC with the cooling water flow,ambient temperature,single screw expander speed,pressure drop of condenser,which provide reference for control policy of ORC in practical engineering,it is necessary to study the effect of the cooling system on the performance of ORC.The main work is as follows:This theoretical analysis focuses on the effect of cooling system on the performance of ORC was carried out.Research analyzes the influence of the ambient temperature,cooling water flow and pressure drop of condenser on ORC by calculation model,it shows that the result is identical to the previous research conclusion.The performance of the ORC system deteriorates with the increase of ambient temperature which is not stable throughout the year.In terms of the net power and net efficiency of the system,it deteriorates by more than 1.79kW and 1.51%in summer than in winter.Increasing the flow of cooling water makes the heat exchanger load,shaft power increase.But the net power and net efficiency of the system have a parabolic tendency which increase firstly then decrease.When the flow of cooling water is 12 m³·h^-1,the maximum value of the net power and net efficiency of system are obtained when the flow of cooling water is 9 m³·h^-1.The performance of the system deteriorates with the increase of the pressure drop of condenser.Shaft power and the net power of the system increase by 1.03kW and the net efficiency increases by 1.02%than the pressure drop of 60kPa when the pressure drop is 0 kPa.This experimental study focuses on the effect of cooling water on the performance of ORC under different speed and ambient temperature was carried out.Firstly,the ORC system was rebuild that the shell-tube water-cooled condenser instead of the air-cooled condenser.Then the experiment is carried out in summer and in winter respectively.The conclusions are achieved:The maximum value of the net power and net efficiency of the system would be 3.27kW and 3.04%respectively when the power consumption of the circulation pump,lubricating oil pump,water pump and cooling tower fan are all taken into account.In terms of the net efficiency of the system,it deteriorates by more than 16.6%in summer than in winter under the optimal flow of cooling water.Enhancing the speed of single screw expander makes the heat exchangers load,shaft power and shaft efficiency,net power and net efficiency of ORC improve.The optimal flow of cooling water of the system changes with the speed of the single screw expander,and is 12 m³·h^-1,8 m³·h^-1 and 9 m³·h^-1respectively when the rotating speed is 3000±20r·min^-1,2500±20 r·min^-1 and2000±20 r·min^-1.In order to evaluate the relative size of the performance of the subsystem on ORC and provide a clear direction of optimization on ORC system,a method was used.In the method,the power consumption index k is defined as the ratio of the power consumption of the subsystem to the expander power,which was used to indicate the impacts of performance of ORC.On the basis of the research of cooling water flow,the experimental study of the side pressure drop of condenser on the performance of the system was carried out.Firstly,electric control valve was installed in the inlet of the condenser to adjust the pressure drop of the condenser.Then,experiment was carried out in summer and in winter respectively under the optimal flow of cooling water.And conclusions are achieved:In winter,the shaft power and shaft efficiency decreased by 0.03kW and0.01%at every 1kPa increase of the pressure drop of condenser,the net power and net efficiency decreased by 0.03kW and 0.02%.The performance of ORC system operating declines in summer than in winter,and the maximum descend is about58.7%.Through the thermal performance study of ORC system under different conditions,the influence of the flow of cooling water,ambient temperature,single-screw expander speed,pressure drop of condenser on the performance of ORC system is clarified,and provides reference for the future operation of ORC in practical engineering.