Distribution Characteristics And Effect Mechanism Of Key Parameters For Natural Draft Dry Cooling Tower

In order to adapt to the continuous development of society and the increasing demand for energy,it is essential to establish a stable,efficient,economic and environmental protection energy supply system for the stable development of national economy and society.The cooling equipment of power plant has an important impact on the safe and efficient operation of the power generation system.So the selection of cooling equipment is very important.The research shows that the natural draft dry cooling system can save 60%?70%water compared with the conventional wet cooling power station because of the reduction of water evaporation.Therefore,the natural draft dry cooling system with natural ventilation has been widely used in coal-fired power plants in some coal rich and water deficient areas in China,and has achieved good economic and environmental benefits.In summary,the technical research on the safe operation and performance optimization of the natural draft dry cooling system is of great practical significance.In the thesis,the natural draft dry cooling units with different power are taken as the research object,and the numerical calculation model of the cooling tower is established by Fluent.Based on the numerical calculation,the distribution characteristics of the aerodynamic field,air temperature field and exit-water temperature of the whole and part of the cooling deltas of the cooling tower are obtained.The results show that for the crosswind area of the cooling tower,the ambient crosswind not only affects the air inlet angle of the cooling deltas,which makes the cooling performance of the two cooling columns in the same cooling delta different,but also reduces the pressure difference between the inside and outside of the tower in the crosswind area.So that the air inlet volume is reduced.The leeward area is blocked by the crosswind area,which is less affected by the ambient wind in the low wind speed.However,the temperature difference between the circulating water and the air will be reduced by the through flow formed in the tower under high wind speed,and the cooling performance will be reduced.The speed of the air flow into the tower in the windward area is strengthened by the ambient wind,and the cooling effect is obviously strengthened.ZigBee technology is used to build a wireless data acquisition system for cooling delta of the natural draft dry cooling tower,which can monitor the relevant parameters in the cooling triangle in real time under complex weather conditions and obtain the data of the whole cooling triangle and special time nodes.By analyzing and summarizing the changes of parameters in the operation process,the cooling performance in the operation process of cooling triangle can be inferred.Due to the influence of ambient wind speed and direction,the air volume and temperature distribution in different cooling deltas and the different positions in the same cooling delta are uneven,which leads to the cooling effect is quite different.The above is of great significance to the cooling performance optimization and antifreeze research of the natural draft dry cooling tower.Taking the exit-water temperature as the key research direction,this thesis analyzes the relevant data of the natural draft dry cooling tower under different working conditions,and demonstrates the anti freezing from the cooling column,cooling delta,cooling section to the whole cooling tower.Based on the comparison of the distribution of the exit-water temperature in the cooling delta under different working conditions,including the averaged exit-water temperature,the lowest exit-water temperature,the unbalanced exit-water temperature difference and the relative exit-water temperature,the anti-freezing parameters based on the distribution of the exit-water temperature for the natural draft dry cooling tower and the relative exit-water temperature are determined.The results show that the environmental crosswind,ambient temperature,heat load,circulating water flow and air-water convection mode have different influence mechanisms on the distribution characteristics of exit-water temperature.Among which the environmental crosswind plays a major role and the impact of ambient temperature can be ignored.Finally,according to the actual working conditions,the critical anti-freezing exit-water temperature of the cooling tower is given,which can guide the safe and economic operation of the cooling tower in severe cold weather.