Numerical Simulation And Experimental Study On SNCR Denitration In Circulating Fluidized Bed Boilers

Coal-fired power plants is the main source of NOxemission. NOxwoulddo damage to the environment and human’s health. At present, in oder to meet ournation’s standard of less than100mg/Nm3, denitration（DeNOx）is required onmost of the coal-fired boilers to reduce the discharge of NOx.Selective non-catalytic reduction (SNCR), with a relatively high efficiency, ischeaper and it is much easier to apply on old boiler units. And it has already hadmany successful applying cases. But the study on the DeNOxof circulating fluid bedboiler is rare except for some basic research. Especially for CFB boilers withmedium temperature separator, SNCR DeNOxis difficult to realize because thereaction must be happened in the boiler where has a complicate two-phase flow.Thispaper, through a combination of experimental study and numerical simulation,studies on the DeNOxtechnology of CFB boilers in order to get a proper denitrationmethod and provide a reference for SNCR application of CFB boilers.Firstly, the SNCR system of a CFB boiler was designed, and a series ofexperiment was expanded, with urea as reductant, exploring the impact on thedenitration efficiency of the boiler load, reductant, spray gun arrangement, atomizedwater pressure. Results showed that the DeNOxrate kept in45%~75%. Lower boilerload and higher reductant flow contributed better denitration efficiency. But theammonia escape became fairly high when NSR is greater than4.5. The bestatomized water pressure was0.1MPa~0.126MPa and two levels’ spraying with16guns was better than one with8.Then, based on the testing boiler, preliminary exploration of numericalsimulation of SNCR was carried on by establishing a model. On the basis of thecalculated boiler temperature, velocity and NOx concentration field, SNCRsimulation was conducted, exploring how the NSR, jet momentum, reductantparticle size and gun quantity affect the denitration rate.Results showed that largerNSR lead to higher denitration rate. The best jet velocity was40m/s and the best particle size was200μm. The calculation results can well consistent withexperimental results.