Performance Optimization And Economic Analysis Of Pre-cooled Natural Draft Dry Cooling Towers

As a key component of the cool-end system in thermal power plants,cooling tower is used to extract waste heat to the atmosphere.A natural draft dry cooling tower(NDDCT)is an alternative cooling method when large quantities of water are not available.NDDCTs rely mainly on convective heat transfer to reject heat from the working fluid,and the heat transfer process is easily affected by ambient temperature and humidity.The performance of a NDDCT is severely reduced when the ambient air is hot.It is difficult for the NDDCT to meet the requirements of the cool-end load of the power plant,which leads to the low cycle thermal efficiency and seriously affects the economic benefits of the power plant.Through literature review,evaporative cooling technology can effectively enhance the heat transfer performance of NDDCTs under high ambient temperature.Only a small amount of water can significantly improve the power generation efficiency of power plants in summer.However,there are still the following problems in the current research:(1)The layout of wetted medium needs further optimization.(2)Scholars have not analyzed the thermal performance of pre-cooled NDDCTs with spray nozzles.(3)Whether evaporative cooling technology can bring economic benefits to power plants still needs to be studied.This paper focuses on the above problems.Firstly,the MATLAB iteration calculation program of wetted media evaporative pre-cooled cooling tower is established based on theoretical analysis.The effect of different wetted media layout on the cooling performance of the air cooling tower is obtained by comparing the performance of evaporative pre-cooled cooling towers with different wetted media layout.Secondly,the MATLAB iteration calculation program of evaporative pre-cooled cooling tower with spray nozzles is established.The influence of the spray cooling system on the cooling performance of cooling tower is explored,and the mechanism of the spray cooling system on the heat transfer enhancement of the air cooling tower is revealed.Finally,the economic model of evaporative pre-cooled cooling tower is established.The influence of wetted media/spray nozzle evaporative pre-cooling technology on economic benefits of air cooling unit is analyzed based on Ebsilon software.In addition,the performance optimization scheme of air cooling tower is put forward to guide the energy saving and efficiency increasing design of air cooling tower.This research found that:(1)The evaporative cooling technology can improve the heat transfer performance of NDDCTs when the ambient air is hot.In the hottest month,July,the improvement of NDDCT performance is most obvious.The outlet temperature of the circulating water decreased from 40.6 ? to 37.4 ?,which is 3.2 ?after the installation of the evaporative pre-cooling system with annular wetted medium;the outlet temperature of the circulating water decreased by 3.5 ? after the installation of the evaporative pre-cooling system with A-frame wetted medium;the outlet temperature of the circulating water decreased by 3.3 ? after the installation of the evaporative pre-cooling system with spray nozzles.(2)For the 167 m air cooling tower studied,when the environment temperature is less than 32 ?,the improvement effect of evaporative pre-cooling system with spray nozzles is the best,followed by the evaporative pre-cooling system with A-frame wetted medium,finally the evaporative pre-cooling system with annular wetted medium.(3)The loss of power generation capacity can be solved by adding the evaporative pre-cooling system in the NDDCTs.For 350 MW air cooling units,the loss of power generation capacity in summer can be solved technically by adding the evaporative pre-cooling system with wetted media or spray nozzles.The evaporative pre-cooling system with annular wetted media is the most economical,and the static investment recovery period of the retrofit is 4.2 years.It is found that both wetted media and spray nozzle evaporative pre-cooling technology can improve the cooling performance of air cooling tower at high temperature in summer based on the analysis of the performance and economy of wetted media/spray nozzle evaporative pre-cooled cooling towers.Considering the economic factors,it is suggested that the annular wetted media evaporative pre-cooling technology should be adopted in the air cooling tower to maximize the cooling performance of the air cooling tower under the control of certain evaporation amount in the high temperature period in summer.It is recommended to install temperature and humidity sensors to monitor the ambient conditions so as to instruct the operation/shutdown of the pre-cooling system.It is also suggested to mount the wetted media on hinged doors so that the wetted media can be removed when not in use.