Experiments And Simulation Studies On Urea Pvrolvsis Coupled With SCR Denitrification Technology

Nitrogen oxides plays important roles in destruction of environment, causing acid rain, photochemical smog, ground level ozone pollution and so on, as well as damage to human health. NOx in the coal-fired flue gas emitted from combustion processes consists of95%NO and5%NO2, which is a major source of nitrogen oxides. As increasingly strict emission limitations are being imposed, it is imperative to find ways to control NO emission which could achieve both high denitrification efficiency and moderate capital expense in power plants.First, a plug flow model is created to study the common SNCR process, the factors including temperature, normalized stoichiometric ratio, residence time, oxygen concentration are researched. Furthermore, the urea pyrolysis products of NH3and HNCO are analyzed in the SNCR reaction process, HNCO is stable at low temperature, but HNCO occurs reaction and produces some N2O at high temperature, the current results show that it can effectively control ammonia slip and N2O generation by selecting proper reaction temperature and residence time.Second, an in-furnace urea pyrolysis coupled with SCR system is investigated on a125MW tangentially coal-fired utility boiler, the coupling system is well designed to make NO and NH3distributed more uniformly in the flue gas at the inlet of the SCR reactor, and the experimental results show that can result in better performance of the SCR reaction.15wt%urea solutions is directly injected into the furnace at the same flow rate of1.2t/h with different boiler loads, the coupling system show a high denitrafication efficiency up to85%with ammonia slip less than5ppm. The effects of the urea solution flow rates are studied at100MW and125MW boiler loads, it is found that1.2t/h is the optimal flow rate of the urea solution, and the NO emission could be controlled lower than40ppm. The coupling system is stable, efficient and cost-efficient in practical operation.Finally, numerical simulation was taken to optimize the SCR system for a300MW utility boiler, the type and arrangement position of the guide plates is found as a optimal solution, the velocity deviation is3.84%and NH3concentration deviation is3.79%at the inlet of first catalysts, the SCR reduction efficiency is83%with ammonia slip1.6ppm. A1:15scale physical model is built to conduct experiments, and the flow model test results are in accord with the numerical simulation very well, thus it can provide a guide of optimization for actual SCR project.