Research On Microdroplet Evaporation During Desulfurization And The Integrated Technology Of Desulfurization And Denitration

With the improvement of national environmental protection requirements,the iron and steel industry has widely used a variety of flue gas purification technologies to control SO₂ and NO_x emissions.In order to effectively reduce SO₂ emissions,wet flue gas desulfurization,spray dryer absorption and dry sorbent injection have been popular in the iron and steel industry.Wet flue gas desulfurization inevitably produces a certain amount of wastewater,and the technology of desulfurization wastewater evaporation is a significant way to achieve zero discharge.In the process of spray dryer absorption,Ca（OH）₂ droplets evaporate continuously and undergo the gas-liquid absorption reaction with SO₂ gas.Therefore,it is important to study the evaporation characteristics of micro-droplets in desulfurization technology for the stable operation of the desulfurization system.Up to now,the evaporation process of micro-droplets mainly adopts the fiber suspension method,the surface observation method and the acoustic levitation method.The spatial evaporation process of a single droplet in a thermal environment was not known.In addition,combining multiple separate pollutant removal technologies to achieve comprehensive flue gas purification,the entire system is huge and complex,increasing the floor space and equipment operating costs.Dry sorbent injection coupled with ceramic fiber catalytic filter tube can specifically solve the problem of comprehensive purification of flue gas.Based on the above background,this work carried out the research on microdroplet evaporation during desulfurization and the integrated technology of desulfurization and denitration.Firstly,the self-designed experimental system was used to study the evaporation process of microdroplets during desulfurization.The evaporation processes of deionized water and desulfurization wastewater micro-droplets were studied in the temperature range of 25°C to 150°C.The experimental results showed that the velocity of droplets decreased quickly and then did not change significantly.At 25°C,the maximum evaporation rate was in the area where the falling distance was 200 mm to250 mm.The maximum evaporation rate of deionized water was 0.1699±0.0165μm²/ms,and the maximum evaporation rate of desulfurization wastewater was 0.1031±0.0197μm²/ms.As the temperature increased,the evaporation rate was accelerated,and the temperature had a more significant effect on the evaporation rate of desulfurization wastewater.The evaporation rate of deionized water was approximately twice that of desulfurization wastewater.Secondly,the experiments were conducted to focus on the desulfurization and evaporation characteristics of Ca（OH）₂ droplets in the temperature range of 25°C to110°C.The droplets were sampled under different experimental conditions,and the droplets were observed and analyzed using an offline microscope.The experimental results showed that the Ca（OH）₂ droplets evaporation rate first increased and then decreased during the falling process,and remained constant thereafter.The average evaporation rate of the Ca（OH）₂droplets was less than that without SO₂.When the inlet SO₂ concentration increased from 0 ppm to 200 ppm,the average evaporation rate of droplets decreased by 54.80%.After the introduction of SO₂,the particle crystals inside the Ca（OH）₂ droplets decreased,and the particles on the surface of the Ca（OH）₂droplets increased significantly.With the increase of SO₂ concentration and temperature,the number of particles on the surface of Ca（OH）₂ droplets increased significantly,and the product particle layer became thicker.Thirdly,the self-designed experimental system was used to study the desulfurization characteristics of the dry sorbent injection（DSI）technology.The empirical formula describing the dependence between desulfurization efficiency and experimental parameters was given.The experimental results showed that as the reaction temperature increased,the desulfurization efficiencies initially increased to a maximum at 180°C and decreased thereafter due to the high-temperature decomposition of Na HCO₃.When the SSR was 1.75,the desulfurization cost was economical.With the decrease of the particle size of Na HCO₃,the desulfurization efficiency increases obviously.The desulfurization efficiency increased significantly from 71.93%to 88.89%as the Na HCO₃ particle size decreased from 133.90 to 9.05μm.The desulfurization efficiency was significantly improved after the introduction of steam.When the water content of the flue gas was 1.28vol%,10vol%and 20vol%,the desulfurization efficiency was 71.93%,82.14%and 98.21%,respectively.Finally,the ceramic fiber catalytic filter tubes loaded with V and Mo nanocatalysts were used for denitration experiments.The denitration characteristics of the ceramic fiber catalytic filter tubes in the temperature range of 180°C to 330°C and the contaminant removal characteristics in the temperature range of 230°C to 330°C were studied.The X-ray fluorescence（XRF）results of the ceramic fiber catalytic filter tube showed that the mass fractions of Mo O₃ and V₂O₅ in the filter tube were 1.84%and1.09%,respectively.Ceramic fiber catalytic filter tubes had excellent thermal stability,catalyst stability and dust filtration characteristics.When the temperature was set in the range of 280°C to 330°C,the denitration efficiency was highest.In the simultaneous desulfurization and denitration experiments,the condition with the highest pollutant removal efficiency was that the average temperature in the dust collector was 330°C,and the filtration speed was 0.8 m/min,and the SSR was 2.The highest denitration efficiency was 97.62%,and the highest desulfurization efficiency was 94.23%.