| In the process of particle fluidized combustion in fluidized bed boiler,a large number of solid particles impact the tube wall,which causes serious erosion wear problem to the tube wall.Meanwhile,SNCR-SCR combined method will be used by the existing fluidized bed boilers to reduce NOx emission in order to meet the NOx emission limits required by the environmental protection administration.Reductive ammonia gas and urea are sprayed in the process of denitration,but ammonia gas has a certain corrosivity,which will cause corrosion of the pipe wall.The phenomenon of erosion wear and high temperature corrosion will lead to thinning of tube wall,and serious tube burst will occur after long operation in fluidized bed boiler.A high-temperature gas-solid phase erosion wear experimental facility was built in this paper.20G steel commonly used on the heating surface of the boiler and quartz sand were selected as the research object and abrasive to explore the erosion wear characteristics of pipe wall,ammonia gas corrosion characteristics and ammonia gas corrosion coupling erosion wear characteristics under high temperature conditions.The experiment mainly studied the influence of erosion angle,heating temperature and erosion velocity on the erosion wear characteristics of 20G.Four different erosion angles(15°,30°,60° and 90°)were selected.Referring to the temperature in the near area of boiler water wall,the heating temperature(350℃,400℃,450℃)were chosen as test temperatures,and the erosion speed(29 m/s,36 m/s,43 m/s)were set.It is shown that the wear loss of 20G specimen is the largest and the pits caused by the wear are the deepest in erosion angle 30° in the experiment.However,when the erosion angle is 90°,the airflow stagnation prevents a mass of particles from impacting on the surface of the specimen,thus leading to the minimum wear loss of the specimen.At low erosion angles,the main wear of the specimen is cutting wear,but at high erosion Angle,the main wear is deformation wear,supplemented by crack.At different heating temperatures,the surface of the specimens showed obvious erosion pits.With the increase of heating temperatures,the wear loss increases slightly.The wear loss of the specimen increases significantly with the increase of erosion velocities.At larger erosion velocities,obvious and consistent furrows are found on the surface of the material.Ammonia gas can promote the corrosion of 20G to a certain extent,but the change of weight gains and surface morphology of the specimen are not obvious.In ammonia gas atmosphere,the wear loss of the specimen decreases initially,followed by an increase,with the increase of heating temperatures and reaches the lowest point at 400℃.It is basically consistent with the critical temperature for the minimum wear of 398℃ in ammonia gas atmosphere calculated by polynomial nonlinear fitting method,and which increased by 50℃ compared with air atmosphere.The reduction of ammonia gas accelerates the wear of the specimens to some extent,but the erosion wear phenomenon is still the main factor causing the tube burst in the fluidized bed boiler.the general calculation model of erosion wear of fly ash under ammonia atmosphere is as follows by fitting the test data:△I=1.5204×10-7 d1.876V3.3413T0.1356... |
