Study On Optimizing SCR System For Large Capacity Utility Boilers

It is well known that the nitrogen oxide (NO_x) is a major atmospheric pollutant. It produced the acid rains and town smog, has bad influence on environment and health, the control of the NO_x emission caught our attention. The nation is trying to control the emission of NO_x. SCR is most widely used, has the highest efficiency and its technology is the most nature. But the SCR meet great difficulty for the application of this technology was in the beginning in our nation. The thesis focused on theory and experiment optimization research for the DeNO_x system of large power plants, and explores optimal operation for the DeNO_x system during the projects, which was important for decline the cost of the design and operation on SCR technology.The study about SCR system includes three parts. First of all, according to the self-modeling principle, the physical flow modle had been built to study the properties and the optimization of the flow in SCR reactor, compare the characters and the effect factors of the flow gas in SCR reactor. The structureof the reactor has been changed for realizing the optimization of the flow in SCR reactor. The coefficient of variation of velocity of the flue gas at upsteam of the AIG and the first catalyst were below 20% and 15%, which can fulfill the system operation standard. Second, after the flow of the physical flow modle been analyzed, the standard formulation of the k-εwas used for turbulence and the species transport equations without chemical reaction was used for mixture of the flue gas and the ammonia. The velocity, press and the concentration of the flue has been got to compare with the results of the experimentation, and has been copared in defferent velocity condition. The third, after the results of the experiment, the analyzation of the chemical reation and stress on particle, the laminar finite-rate model was used for selective catalytic NO_x reduction raction and the Discrete Phase Model(DPM)is used to trace the moving track of ash particle and the concentration of the ash particle. With the comparation between numerical results and the previous experiment data, possible structure optimizations were researched and the outlet NH₃ slip was declined below 5ppm.At last a project of of SCR system trial on a 600 MW boiler, the effect of the press drop, bypass and catalyst on boilers for instillation of the SCR system had been investigated. With the analysis on the reaction system, ammonia injection system, ammania storage system, control system of the SCR system, by the trial of the operation of SCR system, some optiming measures had been taken to make variation coefficient of NOx concentration at outlet of the reactor maintain 20%.