Numerical Simulation And Experimental Study On Low-NO_x Technique By Micronized Coal Reburning

Pollutant NO_x emission by coal combustion in power plant is an increasing threatto environment and human health. Low-NO_x strategies have emerged as the timesrequire, and one of them is fuel reburning technique. For second fuel maybe beneeded and combustible efficiency maybe be minished, micronized coal is broughtforward as reburning fuel. In this paper, experiments and numerical simulations ofmicronized coal reburning technique have being studied supported by 863 project ofStudy on Low-NO_x Technique by Micronized Coal Reburning.In the paper three combustion zones of micronized coal reburning as a whole isresearch object. Based on laboratory-scale experimentation, numerical simulations ofmicronized coal reburning have been studied on bench-scale combustion researchfacility,full-scale 600MWe coal fired tangential utility boiler and full-scale330MWe swirling burner wall utility boiler.First NO_x of experiment and numerical simulation about general combustion andmicronized coal reburning in combustion research facility has been processed. NO_xdecreasing ratios are 52.3~65.4% in experiments and 58.20~75.06% in numericalsimulations. NO_x decreasing ratio of micronized coal reburning comparing withgeneral combustion is not proportionable to NO_x reduction ratio in reduction zone,which depends on both NO_x reduction ratio and NO_x increment in burnout zone.Numerical simulation of full-scale 600MWe coal fired tangential utilityboiler showed NO_x decreasing ratios are 42.36~62.8%. A structured grid partitionfor full scale coal fired tangential utility boiler has been given in this paper. It hasa small amount of grids and can decrease false diffusion effectively as it is inagreement with fluid flow direction. Accurate simulating results can be gainedwith the grid partition. Inverse flows are captured near the wall at four corners incombustion simulating through the above grid and temperatures simulating agreewell with them measured.NO_x numerical Simulation by coupled with combustion and post processinggeneral model provided by FLUENT can be satisfied by qualitative analysis, butcan't meet quantitative requirement. So an improved NO_x model was connectedto software by user defined function. The model has the different NO_x formationand reduction rates in oxidizing and reducing atmosphere, and the effect ofreburning fuel on intermedia HCN of NO has been considered. Simulating resultsgiven by improved NO_x model reflect NO_x formation and reduction moredistinctly than by the former NO_x model. It is more applicable to micronized coalreburning technique.At last numerical simulation of full-scale 330MWe swirling burner wallutility boiler showed NO_x decreasing ratio is 50.57%. The combustible loss isbiggish in this boiler. Modifying cases have been suggested after analysis ofpyrolysis experiments. Experimental and numerical simulating data of gas-solidflow all predict the modifying cases can solve the existing problem effectivelyand NO_x emission can't be increased.Above experiments and numerical studies argued that temperature rising at outcaused by micronized coal reburning technique has a little effect on heating surfacesafter furnace, and micronized coal ruburning has nearly same combustion efficiencyas general combustion. NO_x decreasing ratio and effects on boiler safety andcombustible efficiency all showed micronized coal reburning technique is practicable.