Study On Condition Monitoring And Operation Optimization Of Direct Air-cooled Condenser

Northwest China is rich in coal and poor in water,so direct air-cooled units have developed rapidly.In non-summer working conditions,the heat exchange area of direct air-cooled condenser is rarely fully utilized,but its large heat exchange area leads to the lack of intuitive and reliable feedback of operation state,resulting in high power consumption of fan and easy freezing of tube bundle in winter,which seriously affects the safe and economic operation of unit.Aiming at a 600 MW direct air-cooled condenser system,this paper constructs the calculation model of the complete condensation position of the steam in the tube considering the influence of the flow pressure drop through the cyclic iterative method.Considering the influence of flow pressure drop,the segmented method is used to modify the thermophysical properties of steam in the tube.Under the design condition,the accuracy of this calculation method is verified by comparing the condensation heat release with the condenser heat load calculated by the mathematical model.Under the typical working conditions with ambient temperature of 10℃ and 20℃,the complete condensation position of steam in the condenser mostly appears in the lower part of the parallel-flow area.The calculation model matches well with the monitoring results of temperature measuring cable,and the heat exchange area of the condenser under each load is not fully utilized.Considering the influence of flow pressure drop,there is little difference between the calculati on results when the steam complete condensation position is in the parallel-flow area and that without the influence of flow pressure drop.However,when the steam complete condensation position is in the couter-flow area,there is a great difference between the calculation results of the two.In this case,the influence of flow pressure drop on the length of steam condensation section cannot be ignored.Considering the change of effective heat exchange area of condenser,the off design characteristics of cold end system of direct air-cooled unit and the influence of fan frequency adjustment on net output of unit are analyzed to determine the optimal fan frequency.The optimization effect of the air cooling fan is analyzed when the load rate of the unit is 50%,75% and 100% respectively,and the ambient temperature is 0℃,10℃ and 20℃.It is found that when the heat exchange area of condenser is not fully utilized,the utilization rate of air cooling heat exchange area gradually increases with the decrease of fan frequency,and the optimal fan frequency under current back pressure gradually increases with the increase of unit load and ambient temperature.When the air cooling heat exchange area increases by the same proportion,the fan frequency reduction under high load is greater than that under low load,and the reduction at high air temperature under the same load is greater than that at low air temperature.With the increase of unit load,both the fan power consumption reduction and the unit output reduction increase.Except the low temperature and low load conditions,the unit output reduction is far less than the fan power consumption reduction.Based on the calculation model of the complete condensation position of steam in the finned tube,the working state of the condenser is monitored online.By adjusting the fan frequency,the energy consumption of the fan group is optimally matched with the current back pressure of the unit,so as to save the power consumption of the fan and improve the energy-saving and economic operation level of the air cooling fan.