Cold End Optimization Of Direct Air Cooled Generator Sets

After entering the 21st century,China’s economy has been developing rapidly,the dependence of economic development on electric power is becoming stronger and stronger.In order to save energy and protect environment,China has begun to vigorously build more large capacity units.Conventional coal-fired generators consume a lot of water,but there is a real contradiction between uneven distribution of coal and water resources in China.The appearance of direct air-cooling technology effectively solves this problem.The greatest advantage of direct air-cooled units is excellent water-saving performance,which makes it possible to vigorously build air-cooled coal-fired power plants in the vast northern coal-rich and water-scarce areas,effectively alleviating the problem of electricity shortage.However,there are also many problems with the direct air-cooling technology when put into operation.For example,the direct air-cooling unit has problems such as relatively high coal consumption,high back pressure and wide range of variation,easy ash accumulation of air-condensator tube bundles and so on,which seriously affects the safe and economic operation of the unit.Therefore,it is imperative to optimize the cold end of direct air-cooled units.In this paper,firstly,the variable condition characteristics and influencing factors of direct air-cooled condenser are studied,and a 600MW unit is taken as an example for calculation and analysis.Based on the heat transfer unit number method and the heat exchange model of the wet cooling unit,the variable condition calculation model of the condenser of the direct air cooled unit is established,and the calculation model of the exhaust pressure is improved.The heat transfer coefficient of the design condition and the variable condition is calculated by MATLAB programming,and the relevant variable condition characteristic curve of the direct air cooling unit is drawn.The influence of cold end parameters,such as ambient temperature,head-on wind speed,exhaust flow and exhaust pressure loss,on the exhaust pressure of the last stage of steam turbine is quantitatively analyzed by using the variable condition model.In the past,the influence of fan speed on the exhaust pressure of the last stage of the steam turbine is often ignored in the study of the variable condition of the air-cooled condenser.In this paper,the influence of fan speed on the exhaust pressure of the last stage of steam turbine is considered,and the influence of different fan speed on the exhaust pressure of the last stage of steam turbine is studied.After that,the fouling calculation model of the condenser is established,and the influence of the fouling inside and outside the condenser tube on the exhaust pressure of the last stage of the turbine is studied.Then the optimal exhaust pressure of the last stage is studied.Starting from the definition of the best exhaust pressure of the last stage,the method of increasing the power of the steam turbine unit is studied firstly.The relationship between the increasing power of different load units and the exhaust pressure of the last stage is calculated by the equivalent enthalpy drop method.At the same time,the power consumption characteristics of the fan are studied.The relationship between the power consumption of the fan and the exhaust pressure of the last stage of the steam turbine is deduced by the theory of wind mechanism.When the difference between the incremental power of the turbine and the incremental power of the fan is the largest,the exhaust pressure of the last stage corresponding to this point is the best exhaust pressure of the turbine unit.The research results of this paper play a guiding role in the variable condition operation of the direct air-cooled condenser,guide the operation regulation of the unit,make the unit operate under the best final stage exhaust pressure,and play the role of energy saving and consumption reduction to reduce the exhaust pressure.