Experimental Research On The Effects To Flue Ash Particles Characteristics Of NH₄HSO₄Generating During The Denitrification Process

SCR is the major promoting denitrification technology of coal-fired power plant which having high NOx emissions. Having high NOx removal efficiency, SCR brings a lot of adverse effects as well. In order to improve the efficiency of the unit after the installation of SCR device, increasing study of these effects is necessary.Air preheater ash clogging, heat transfer efficiency decreasing, low temperature corrosion being heavier are most serious problems arising from NH4HSO4generating during denitrification process. However, these problems have close relationships with the flue ash. Based on these problems, the NH4HSO4generating during denitrification process effects to flue ash’s particle size, hygroscopicity, adhesion and heat conductivity are experimented in this paper. The ash samples are made of obtained fly ash by adding NH4HSO4manually. NH4HSO4and ash mass ratio of treated ash samples are1/150,1/90,1/60,1/30.Ash particle size change experiments by using sieving method show that, due to the existence of NH4HSO4, the ash particle size show a tendency to increase. And when the ratio is above1/90, this effect is more obvious. It also shows that, ash particles above75μm range are less affected. Ash hygroscopicity experiments by using hygroscopic rate method show that, it’s hygroscopicity increases with the increasing amount of NH4HSO4.What’s more, the high RH can strengthen the effect.With the homemade law to pull off adhesion test device, ash adhesion testing shows that, ash adhesion increases with the increasing amount of NH4HSO4. And when the amount become bigger, the tendency is more obvious. The experiments also considered pressure, particle size and RH these three factors, and the results show that the ash particle sizes are larger, the adhesion are smaller. Besides, when ash particles are above75μm, its’ adhesion can be hardly test out with this method; When the surface pressure is between1.57kPa-5.99kPa, the adhesion grows faster and slows down when the pressure is larger than5.99kPa; If the RH is less than50%, the ash adhesion has slower growth and if it’s greater than50%, the ash adhesion’s growth becomes very significant.With the homemade parallel wire method heat conductivity test bench and designed data processing procedure, ash heat conductivity is studied and the results show that the heat conductivity of flue ash increases with the increasing amount of NH4HSO4. The increasing trend slows down when the amount of NH4HSO4becomes larger. The experiments also considered packed density, temperature, particle size and moisture content these four factors, and the results show that ash heat conductivity increases with the increase of packed density, and the greater the packed density is the slower the heat conductivity grows; Between60℃-170℃, ash heat conductivity increases with increasing temperature slightly and the change is very little. Especially when the temperature is near the melting point of NH4HSO4, it doesn’t change significantly; The lager ash particle size is the greater the heat conductivity is; Heat conductivity of flue ash increases with the increase of moisture content. When the moisture content is less than1.5%, ash heat conductivity grows fast and when the moisture content is larger than1.5%, the increase begins to slow down.