| In order to solve the problems occurring in a600MW supercritical W-shape flame boilerof certain power Plant, such as pipe expansion in heating surface, high NOXemissions,numerical simulation on the combustion process of the boiler is conducted with the softwareof FLUENT in researching the effect of different loads, different coals, different particle sizeof pulverized coal, different air distribution, and analysing the possible causes of pipeexpansion in relation to the temperature fields, which can provide guidances for reducing pipeexpansion in heating surface and decease NOxemissioms in the bolier operation.First of all, mathematical model was built on the combustion process of furnace,including equations of mass conservation, momentum conservation and energy conservation,turbulent flow model, gas and soild two phase flow model, volatile pyrolysis and combustionmodel, coke combustion model, radiation model and NOxmodel.Secondly, the boiler structure was introduced and physical model was built, at the sametime, boundary condition of inlet, outlet and wall also were set.Finally, numerical simulation was made under real running parameters, comparisonbetween the calculation result and measurement data proved that the calculation result was ina good accuracy, then, numerical calculation of other conditions were made based on modelof real condition, it was analyzed effect of different loads, different coals, different particlesize of pulverized coal, different air distribution on velocity field, temperature field, O2concentration field and NO concentration field. The results showed, the velocity field and thetemperature field were symmetrical in600MW, the velocity field and temperature fieldappeared skew, hige temperature flame badly sweep over water-wall, the temperature gradientwas greatly and NO emission was most highest in450MW, the velocity field and temperaturefield were symmetrical and the central position of flame was low, hige temperature flamebadly sweeped over cold ash hopper in350MW. The central position of flame was differentfrom different coals, which can made temperature fields pulsation, in addition, NO emissionis decided by the [N] of fuel. The furnace overall temperature rised, temperature fieldbecomed more even and NO emission was lower when particle size of pulverized coal wasdecreased. The velocity fields and temperature fields appeared skew and NO emssions risedwhen air ratio of the front and the rear arch or the front and the rear walls is different.In short, the change of load, coal and air distribution would cause to pulsatingcombustion in the furnace, high-temperature flame swept the heating surface, which can leadto pipe expansion severely. |
