Formation Characteristics Of Ammonium Sulfate Salt In Air Preheater And Its Effect On Particulate Emission

As the most widely used NO_X control technology in coal-fired power plants,selective catalytic reduction?SCR?denitrification technology will make part of SO₂ oxidation to SO₃and produce ammonia slip while removing NO_X.In the air preheater,the SO₃ in the flue gas reacts with escaped ammonia and H₂O to produce ammonium bisulfate which will increase the resistance of the air preheater,exacerbate the corrosion,and may affect the final concentration of fine particulate matter from the coal-fired power plant.Domestic studies have mainly focused on the blockage of air preheaters caused by ammonium bisulfite and their prevention and control measures.The formation characteristics of ammonium sulfate in the air preheater and its impact on particulate emissions have not been fully understood.In this study,firstly,the HSC Chemistry software was used to calculate the thermodynamics.Then experiment based on the self-made simulation air preheater channel was made by using the Electrical Low Pressure Impactor?ELPI⁺?and ion chromatography to study the formation temperature of ammonium sulfate and the effect of ammonium sulfate on the emission characteristics of fine particles The main findings of the full text are as follows:Chemical thermodynamics calculations show that,within the range of typical flue gas temperature and water vapor concentration in the air preheater,SO₃ can easily react with H₂O in the flue gas to form H₂SO₄,making H₂SO₄ instead of SO₃ as the main reactants for the formation of ammonium sulfate and ammonium bisulfate.In general,ammonium bisulfate is the main product in a typical air preheater flue gas environment.It is found that the initial NH₃/SO₃ molar ratio of the reactants is an important factor affecting the product type.When NH₃/SO₃<1,the products of the reaction are all ammonium bisulfate.With the increase of NH₃/SO₃,ammonium sulfate begins to appear in the product.Due to the coagulation mechanism and properties of ammonium bisulfate and ammonium sulfate are different,their influences on the concentration and particle size distribution of particles are also different.Both of them will increase the number of particles,but ammonium bisulfate is prone to coagulation and agglomeration because they are sticky small droplets in the air preheater temperature range,so that the particle size of the particles is slightly larger than the ammonium sulfate solid small particles.In addition,in a typical range of flue gas concentrations,the formation temperature range of ammonium bisulfite in the air preheater is 235-260°C which is positively correlated with the logarithm of the product of NH₃ and SO₃ concentrations.Increasing the concentrations of NH₃ and SO₃ can increase the formation temperature of ammonium bisulfate,but the change of NH₃ concentration has a more significant effect on the formation temperature of ammonium bisulfate.At the same time,the properties of the ammonium sulfate salt particles are also affected by the concentration of the reactants.The ammonium bisulfate particles produced in the air preheater are mainly submicron particles with a particle size of less than 0.2?m.The increase in NH₃ concentration will increase the concentration of particulate matter significantly the particle size of the particle size less than 0.1?m in the flue gas at the exit of the air preheater.In contrast,the increase of the concentration of SO₃ has less effect on the concentration of particles,but it will make the particle size of the particles increase slightly.The formation of ammonium bisulfate will increase the deposition and the particle size of fly ash,and the particulate concentration at the exit of the simulated air preheater.The fly ash particles coexisted in the flue gas will promote the condensation of ammonium bisulfate.While there is no obvious relationship between ammonium sulfate and fly ash.With the increase of ammonium bisulfate concentration,the corrosion rate of carbon steel and Codon steel has accelerated.At low concentrations,ammonium bisulfate erodes carbon steel more faster,but when the concentration reaches a certain level,the corrosion rate of carbon steel and Codon steel are almost the same.