Study On Failure Causes And Countermeasures Of Panel Superheater Of Coal Fired Boiler For A 300MW Unit

With the vigorous implementation of national energy conservation and emission reduction policy,new units with large capacity,high parameters and high efficiency are gradually appearing on the stage of power industry.With the continuous development of thermal power generating units to supercritical units and ultra-supercritical units,the pressure bearing parts of boilers are in the harshest environment,and the higher requirements are put forward for the temperature resistance and creep resistance of boiler materials.Due to the combustion system and steam water system,superheater tubes have long-term risks of corrosion,deformation,wear,scaling,over burning and leakage,which leads to the failure of furnace tube metal materials and the occurrence of tube burst accidents,which not only increases the workload of rush repair,but also causes a great waste of fuel resources,causing great economic losses to power production.As the main cause of non-stop of generator set,it is of great significance to study the occurrence principle and preventive measures of tube burst on boiler heating surface.In this thesis,a pulverized coal fired boiler for 300 MW unit is taken as the research object.In view of the frequent tube explosion of the platen superheater,the technical scheme to prevent the tube burst of the platen superheater is put forward through the analysis of the boiler combustion system and the operation parameters of the platen superheater,and the technical transformation is carried out.The results show that the crater is horn shaped after deformation,with a length of 50 mm and a width of 20 mm.The metallographic structure shows that the tube burst is caused by the combined action of long-term and short-term overtemperature.By replacing partial platen superheater tubes with TP347 HFG material,testing and replacing pipes with low residual life,and adopting technical measures such as adjusting reverse cutting of the third air outlet and installing outer ring tube throttle ring at the inlet header of platen superheater,the maximum value of non-uniformity coefficient of flue gas is reduced from 2.44 to 1.40,and the average value from 1.72 to 1.26.The ratio decreased from 1.67 times before adjustment to 1.22 times,and the difference of wall temperature between screens decreased from 30 ℃ to 14 ℃.The operation results after comprehensive treatment show that the working conditions of platen superheater have been effectively improved,the heat load of outer tube in the same platen is reduced,and the tube burst rate of the unit is significantly reduced when the wall temperature under various tube conditions is within the design value range.The proportion of unplanned shutdown times caused by tube burst per year is reduced from 50% to 20%,which improves the safety of platen superheater operation.