Reconstruction Of Air-cooled Heat Transfer Surfaces Adapted To Complex Ambient Winds And Air Leading Strategies

Dry cooling system is widely used in north China thanks to its superiority in water saving,which is basically composed of forced draft direct dry cooling system and natural draft indirect dry cooling system.The forced draft direct dry cooling system has a lower initial capital cost and the air-cooled condenser comprises dozens of condenser cells in a rectangular array,which are in the shape of A-frame with an axial flow fan below.The natural draft indirect dry cooling system can reduce the operation and maintenance cost,which consists of the hyperbolic dry-cooling tower and air-cooled heat exchanger bundles vertically arranged around the circumference of cooling tower,or horizontally configured inside cooling tower.Lots of researches over the world have been published with respect to the dry cooling system,especially the ambient wind effects.For the forced draft direct dry cooling system,the flow distortions are generated at the windward axial flow fan inlets under crosswind conditions.What's worse,the reverse flows may occur,and the inlet air temperature of air-cooled condenser increases.In addition,the outlet hot plume of air-cooled condenser is suppressed by the crosswinds.As a result,the thermo-flow performances of air-cooled condenser are greatly deteriorated under crosswind conditions.For the natural draft indirect dry cooling system with vertically arranged air-cooled heat exchanger,which is widely used,the flow pattern under crosswind condition is similar to the flow around a cylinder,which causes uneven cooling air flow distribution for the air-cooled heat exchanger sectors.Therefore,the thermo-flow performances of the windward sectors are enhanced,while the lateral sectors are deteriorated due to the lateral low pressure area formed at high wind speeds.In conclusion,the thermo-flow performances of the forced draft and natural draft dry cooling systems are suffered from the ambient winds.Focused on the ambient wind effects on the dry-cooling system,many measures have been proposed by domestic and overseas researchers.In this work,the CFD method is adopted to deeply investigate the ambient wind effects with the commercial software FLUENT.Based on the regulation of ambient winds and application of wind power,the guideline of the reconstruction of forced draft air-cooled heat transfer surfaces is proposed,and the utilization of wind dynamic energy by means of air flow field optimization is suggested,which can weaken the wind effects and utilize the wind power simultaneously.For the forced draft direct dry cooling system,a novel layout of air-cooled condensers with vertically arranged condenser cells is recommended to greatly restrain the adverse wind effects and effectively utilize the wind power.Based on the flow distortion improvement at the fan inlet,the V-frame condenser cell configuration with the induced axial flow fan is proposed,which can improve the thermo-flow performances of air-cooled condenser under wind conditions.As for the natural draft indirect dry cooling system,the exterior windbreakers at the lateral side of air-cooled heat exchanger,as well as the interior air leading measures are suggested,which can weaken the adverse wind effects and improve the thermo-flow performances of dry cooling system.As a result,the turbine back pressure is significantly reduced by the reconstruction of air-cooled heat transfer surfaces and air leading strategies.The ambient wind effects on the anti-freezing of natural draft indirect dry cooling system in cold winter and on the flue gas diffusion of the integrated dry cooling and stack system are also numerically simulated in this work.Under cold and windy ambient conditions in winter,the air flow equal distribution strategy is applied to the opening degree adjustment of the louvers in each sector,by which the air flow rates of the windward sectors with strong cooling capacities are restricted.Finally,both the anti-freezing and lower turbine back pressure are achieved,which can contribute to the safe and energy efficient operation of natural draft dry cooling system in winter.For the integrated natural draft dry cooling system with flue gas injection,the flue gas diffusion inner and outside the dry-cooling tower under crosswind conditions is numerically studied including the flue gas concentration on the inner tower shell,the rising height of flue gas and the flue gas concentration on the ground level.In addition,the thermo-flow performances of the integrated dry cooling system under crosswind conditions are obtained.The results show that the integrated natural draft dry cooling system with flue gas injection is superior to flue gas diffusion.For the integrated dry cooling and stack system,the wind effects can be restrained to a great extent,which is beneficial to the flow and heat transfer performances of natural draft indirect dry cooling system.