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Numerical Simulation Of The Combined Denitration By SNCR And Air Staging And The Effects Of Additives On SNCR

Posted on:2013-05-22Degree:MasterType:Thesis
Country:ChinaCandidate:Y ShiFull Text:PDF
GTID:2251330392967923Subject:Thermal Engineering
Abstract/Summary:PDF Full Text Request
In China, NOx pollution is mostly caused by the combustion of coal in coal-firedpower plants. The large amount emission of NOx is seriously harmful to the health ofpeople、animals and plants. Air staging combustion and selective non-catalytic reduction(SNCR) are the denitration technologies with considerably lower investment costs andoperating costs, and medium denitration efficiency. Air staging combustion is a kind oflow NOx combustion technology. However, SNCR belongs to flue gas denitrification.The combined application of air staging and SNCR has broad application prospect.Based on Fluent software, numerical simulation research of air staging combustionin a200MW boiler was conducted. The temperature field in furnace, the concentrationof O2, CO and NO were analyzed respectively under the original condition and thereformed condition by air staging. After adopting the technology of air staging, thetemperature in furnace decreases because the O2concentration in primary combustionzone was low; the CO concentration at furnace outlet slightly increases due to theincomplete CO oxidation; the concentration of NO at furnace outlet decreases sharply.When the boiler operated at100%load and70%load,37.9%and33.8%NO removalefficiency could be obtained respectively by using air staging combustion technology.According to the numerical simulation result of coal combustion in furnace, theSNCR process in the upper furnac was simulated using Fluent code. When the molarratio of NH3/NO increases, both the NOx removal efficiency and the NH3-slip rise. Thedenitration efficiency and NH3-slip reduce with the increasing of the concentration ofurea solution. When the reductant droplets size rises, the NOx removel efficiencyslightly rises, but the NH3-slip represents decreaseing tend followed by a slight rise. Bychoosing the appropriate molar ratio of NH3/NO, the concentration of urea solution anddroplets size, the denitration efficiency of SNCR can be as high as30%. After thereform of SNCR and air staging, the NOx emission can be less than200mg/m3.Additive had a great influence on SNCR. In order to get better NOx removalefficiency in utility boilers by SNCR, some additive can be injected into furnacetogether with the reductant. By experimental study and reaction kinetic analysis, theinfluence of biomass-gasified gas additive on SNCR process was investigated. Theresult showed that: injection of biomass-gasified gas additive could shift the tempraturewindow to the lower temperature, but the temprature window becomes narrow and theNOx removal efficiency decreases slightly. Compared with the experiment result ofbiomass-gasified gas additive and single additive, H2component in biomass-gasifiedgas has the greatest influence on SNCR, whereas the influence of CH4component andCO component were minor. The result of the simulation study by Chemkin4.1softwarealso confirms the experiment conclusion. It provides theory support for the application of biomass-gasified gas additive in SNCR reform on large furnace.
Keywords/Search Tags:SNCR, air staging, numerical simulation, biomass-gasified gas, additive
PDF Full Text Request
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