Study On The Growth Characteristics Of Low-Temperature Ash Deposition And Additives For Inhibiting Ash Deposition In Air Preheater

Due to the large amount of energy consumption in China,coal will still be the main fuel in the next few years.Coal-fired power plants will generate a variety of pollutants during operation,causing various environmental problems,and the state and government are also increasing their efforts to control the ecological environment.Selective catalytic reduction?SCR?,as one of the important technical methods for controlling NOx pollutant emissions in coal-fired power plants,has many advantages such as high denitration efficiency,good selectivity,strong stability,and low operating costs,and it is also the most widely used flue gas denitration technology.In coal-fired power plants,the injection of gaseous ammonia reduces NOx emissions while causing ammonia escape from the tail flue.This part of the escape ammonia will form ammonium bisulfate?ABS?with SO₃ at a certain temperature.After ABS adsorbs fly ash particles,it is easy to cause problems such as blockage of air preheaters,which brings great trouble to the operation of coal-fired units.Therefore,studying the growth characteristics of fly ash deposition in air preheaters and how to suppress and remove fly ash deposition has engineering practical significance for optimizing the operation of air preheaters and also has a certain guiding role for the operation of coal-fired power plants.First of all,in this paper,SO₃,which is one of the formation factors of ABS,was prepared and measured.An improved method of atomization and heating of dilute sulfuric acid was proposed,and a SO₃ preparation device was set up.This also provides support for later research on the characteristics of fly ash deposition in a mixed atmosphere.The stability of the preparation device was verified first,and the results show that the atomization amount of the device has little fluctuation and can be used stably for a long time.The controlled condensation method and barium sulfate spectrophotometry were used to measure the prepared SO₃.The results show that although the measured values are smaller than the theoretical values,they are basically linearly distributed.The measured values after linear fitting are about 81.74%of the theoretical values,which shows that the performance of the preparation device is stable and can meet the needs of the experiment.Secondly,using a drop tube furnace system to simulate the air preheater environment and using the probe surface temperature as a variable,the growth characteristics of fly ash deposition in a mixed atmosphere of SO₃ and NH₃ were studied.Digital image technology is used to monitor the growth process of fly ash deposition online,record the temperature change inside and outside the probe in real time,and calculate the thickness change of ash deposition and the change in heat flux density on the probe surface.Finally,X-ray diffraction?XRD?,scanning electron microscope?SEM?,and energy dispersive spectrometer?EDS?were used to further study the mineral composition,microstructure and element composition of ash deposition.The results show that in the mixed atmosphere,it is easy to generate strong adhesive ABS and cause fly ash deposition.The growth of fly ash deposition can be divided into rapid growth,slow growth and stable phases.In the research temperature range of 200²60?,the higher the probe surface temperature,the smaller the ash deposit growth thickness,and the higher the relative heat flux density.Finally,the inhibitory effect of calcium-based additives on the growth of ash deposition was investigated in the drop tube furnace.First,the inhibitory effects of three calcium-based additives,CaCO₃,CaO,and Ca?OH?₂,on ash deposition were compared,and then the growth characteristics of ash deposition under different Ca?OH?₂/ABS molar ratios were compared.After the experiment,XRD,SEM and EDS tests were performed on the ABS ash deposition under all working conditions.The results showed that all three calcium-based additives could inhibit the growth of ABS ash deposition.Among them,Ca?OH?₂ had the strongest inhibitory effect,followed by CaO and CaCO₃.When Ca?OH?₂/ABS=2:1,there is almost no obvious ash deposition formation on the probe surface,indicating that the higher the molar ratio of Ca?OH?₂/ABS,the more favorable it is to suppress the formation of ash deposition.