Experimental Research On Optimal Control Of Back Pressure Of Direct Air-cooled Units Under The Influence Of Ambient Wind

Direct air-cooling technology uses air as the cooling medium,and strengthens the air flow through the axial fan group to cool the exhaust steam and reduce the back pressure of the unit.The water consumption of the direct air-cooled unit is only 20%of the traditional wet-cooled unit,because of its significant Its water-saving effect has been applied on a large scale in the coal-rich and water-deficient northern regions of my country.However,the back pressure of the direct air-cooled unit is often high,which will reduce the output of the unit.In addition,because the condenser is arranged outdoors,the outdoor ambient wind will significantly affect the flow of the air-cooled fan.The horizontal ambient wind will reduce the working efficiency of the fan and the ambient wind is the main cause of the unevenness of the fan volume flow and the condenser outlet temperature.the reason.At present,the experimental research mainly focuses on the flow characteristics of the fan group operation of the air-cooled array and the heat transfer effect of the finned tube,and the analysis of the air flow characteristics of the fan inlet under the influence of ambient wind is still based on numerical simulation and lacks experimental data support.Based on the existing research results,relying on the direct air-cooled array experimental platform built,the measurement methods of the ambient wind direction and wind speed and the air volume flow rate at the fan inlet are found;Kalman filtering is used to process the ambient wind speed data,and the unit vector averaging method is applied to the ambient wind direction.After the data is processed,a smoother wind speed and wind direction change curve with the same trend is obtained.Experiments on the flow characteristics of the fan group under the influence of ambient wind have been carried out.The results show that the volume flow of the fans in the first row(column)on the windward side of the air-cooled array is significantly reduced under the continuous influence of ambient wind,while the volume flow of the fans on the leeward side is larger;The fan flow trough area changes rapidly with the wind direction without delay;the total volume flow of the fan group under different winds is not much different,and the wind direction only affects the location of the flow trough area;the volume flow of the first column on the windward side is greatly affected by the wind speed,both It shows a negative proportional coefficient relationship.The higher the wind speed,the smaller the flow of the first row of fans on the windward side,and the change of wind speed is the main reason for the fluctuation of the volume flow of the first row of fans on the windward side.Calculate the volume flow of the fan based on the experimental data,and then the back pressure of the computer group.The results show that the accuracy of the built back pressure model is 2%to 5%higher than that of the traditional model;compared with no wind conditions,the back pressure of the unit is more affected by the ambient wind during actual operation,and the ambient temperature and operating load are higher.The impact of high-temperature environmental wind is more significant.The traditional model of back pressure was revised,and suggestions were made for the design of air-cooled array speed controller.Based on the calculation of the static variable operating conditions of the air condenser,the mathematical model of the air condenser is established.Subsequently,the back pressure linearization control model was obtained by the method of small deviation linearization,and the back pressure feedforward predictive control(MPC-ff)device was designed.Finally,an example simulation was carried out with a 600MW direct air-cooled unit.The results showed that the back pressure predictive control model It can reduce overshoot and effectively overcome disturbance.