Study On Design Optimization Of Direct Air-Cooling Condenser

At present,several direct air-cooling units which can save mass water have been run in the rich coal and water depletion midwest of our country,the article studies on design optimization of the unit aiming at the disadvantage of more investment and high coal-loss.The study is carried out in three aspects, the design optimization of single object is first,whereas two factors which are fix investment and running expense of the unit ,the object function which is set minimum of annual fee as the goal is established according to the principle of thermdynamics and thermoeconomics,considering not only annual running expense and investment cost,but also residual value,bank rate , economy seniority of the project and depreciation rate of the installation,the formulae are concluded at each items respectively. Because the amount of Initial Temperature Difference(ITD) and the velocity of air side have relation with cost of air-cooling system and system's running expense, these two are acted as design variable,the optimized results are reasonable.Subsequently the sensitivity analysis are put on two design variables ,electrovalency , coal price and design temperatrue these five parameters,discussing how they affect annual convert fee of heat exchange area, annual convert fee of fans,annual energy change cost of fan group,annual coal change cost and annual fee,the charts show that the selection of two design variables is reasonable, the change of electrovalency infuence optimization results a lot of two economy parameters,and total annual costs are very sensitive to the design temperatrue changing, so the estimation of electrovalency and the design temperatrue must be accurate.The change of ambient temperature influence on unit's economy is also be analyzed,showing that the change of ambient temperature influence on unit's backpressure a lot, temperature rising and backpressure rising,causing heat consume value augments,so coal consume of power supply increase,it is required the economy vaccum must be fixed and maintained by adjusting fans'operation.Secondly multi-objective design optimization is acted on direct air-cooling condenser,weight is the direct function of structure and geometry dimension,and specific structrue and dimension have relation with else factors of the equipment,available work loss of the condenser is caused by heat transfer difference and differential pressure,this can be refered as whole available work loss fee of unit amount of heat transfer,therefore, two goals minimum weight and minimum loss fee have been chosen.Gap between finned tube, the number of pipes in every line,fin pitch, the number of fin per meter, the head-on wind speed and the exhaust steem pressure are set as design variable, making the demand of manufacture and operation as the restrict condition,using modified Non-Dominated Genetic Algorithm to optimize, optimization results gained are reasonable, which provide a foundation for setting more complex multi-objective optimum model in futrue。Vacuum is one important index of unit's economy. Study on vacuum change when the unit is running can provide foundation for optimum operation and optimum design. Because vacuum body of direct air-cooling condenser is huge, easy to leak air in inevitability, the article studies on how thermal load, dirtiness resistance outside the pipe, ambient temperature and the speed of the air flow etc. operation parameters influence on change rate of vacuum in condition of leaking air, the results show that in case of a certain amount of air leaking in, the former three have more influence. Finally, the designed unit is studied on varying duty, studying the influence of thermal load, dirtiness resistance outside the pipe, ambient temperature and the speed of the air flow changing on vacuum.