Experimental Study And Numerical Optimization On A150MW Boiler Retrofitted With Low NO_x Combustion System

The combustion of fuels in utility boiler emits large quantities of pollutants, NOxincluded. With the implementation of the new standard emissions, reducing NOxemissions has become the main objective of utility boiler transformation.A ultra high pressure coal-fired boiler of480t/h in Xinjiang Fukang power plant, theNOx emission concentration mainly distributes in the range of500~600mg/Nm3. Basedon the detailed analysis of coal properties, boiler equipment and NOx emissioncharacteristics, a combustion system retrofit scheme to reduce NOx emissions wasproposed with a technique combining separated over firing air (SOFA) nozzles above thehighest secondary air nozzles and fuel-staged combustion burners in the primarycombustion zone. A combustion modification experiment was carried out, in which theinfluence of SOFA, secondary air, O2distribution and mill combinations was researched.The tests indicate the amount of NOxemission concentration can be decreased to lessthan250mg/m3, reduced by55%when the SOFA ratio is55%or open two layers ofSOFA, effect is obvious. The same time, the boiler efficiency is higher than92%, whichis significantly increased compared with that before the transformation. The flue gastemperature at furnace outlet is lower than850℃, which can avoid coking on heatingsurface effectively, and ensure the boiler operation economically and safely.By using numerical simulation software Fluent, the combustion modificationprocess after reform was simulated for further research, in which the influence oftangential circle and Coal fineness to velocity, temperature, O2concentration, NOx, andburning rate of coal was study. The results of simulation indicate that after reducingtangential circle diameter the phenomenon of pulverized coal skew improve significantly,which can reduce slagging and high temperature corrosion of water wall. While the coalfineness deceased, the burning rate of coal increased, NOx emissions decreased, flue gastemperature at furnace outlet deceased, and reduce the slagging of high temperaturesurface. The simulation results can provide reference information and theoreticalguidance for the further optimization and adjustment.