| Pulverized coal industrial boiler is a new type of coal-fired industrial boiler,which has the advantages of high boiler thermal efficiency,low pollutant emission,system integration,and complete set of equipment.China’s pulverized coal industrial boiler technology has mainly developed since the beginning of this century.Due to the short development time and immature technology,many problems have arisen in the actual operation of pulverized coal industrial boilers manufactured in China,such as the 46 MW pulverized coal industrial boiler of this paper showed the slagging problem during operation.In order to solve this problem,this paper conducts thermal industrial tests and numerical simulations on the original structure,and proposes an improved scheme.The characteristics of combustion and NOx generation in furnace under the new structure are studied by numerical simulation.This paper provides the basis for determining the optimization scheme and the best mode of operation of the combustion system,and also provides a reference for the commissioning and modification of the same type of b oiler.Industrial tests and numerical simulation were conducted to study the combustion characteristics and NOx generation characteristics in the furnace under the original structure.Industrial tests conclude when the secondary air rate was reduced from 68%to 49%,the circulating flue gas rate increased from 14%to 24%,and the ignition point of pulverized coal was delayed by 150mm;the NOx the NOx concentration at furnace outlet decreased from 402mg/m3（O2=9%）to 396 mg/m3（O2=9%）,slag combustible content increased from 0.11%to 0.38%,the content of combustibles in fly ash increased from 1.93%to 4.46%,the boiler thermal efficiency decreased from 88.44%to 88.13%.Numerical simulation concludes when the boiler is operated under high load conditions,the wind force at the outlet of the burner is large and the rigidity is strong,the pulverized coal particles have the phenomenon of flushing the back wall.Under the condition of changing the secondary and tertiary air ratios,when the secondary air rate is reduced from 65%to45%,the phenomenon of flushing the back wall has not been changed.The temperature in the furnace has decreased,but the temperature near the back wall area is between 1400 and 1600 K,higher than the coal powder ash melting point,will still cause the back wall slagging.NO concentration in furnace decreased,the NOx concentrationatfurnace outletreducedfrom417mg/m3（O2=9%）to381mg/m3（O2=9%）.Due to the limitations of the burner and furnace structure,to solve the slagging problem of the furnace under high load conditions,only the structure of the burner and the furnace be reformed,and after the transformation can continue to strengthen the furnace air classification combustion to further reduce the furnace exit NOx concentration.The numerical simulation was used to study the combustion characteristics and NOx generation characteristics in the new structure.Compared with the original structure,the improved scheme significantly improves the phenomenon of flushing the back wall in the furnace.The temperature near the back wall area has dropped below 1400 K,which is lower than the coal powder ash melting point and can effectively solve the slagging problem of the back wall.Changing the second ary and tertiary air ratio,with the secondary air rate reduced from 40%to 25%,the tertiary air rate increased from 35%to 50%,the furnace air staging combustion was strengthened,the main combustion zone temperature gradually decreased,the NO concentration in the furnace gradually decreased.The NOx concentration at furnace outlet gradually decreased from 302 mg/m3（O2=9%）to 257 mg/m3（O2=9%）,and the content of combustibles in fly ash increased from 2.81%to 4.65%.The pulverized coal gas flow rigidity at the outlet of the burner is gradually strengthened.After the secondary air rate drops to 30%,the phenomenon of particle flushing of the back wall has appeared.Considering that the recommended secondary air rate is 35%,the tertiary air rate is 40%.Under the condition of variable circulation flue gas rate,as the circulating flue gas rate increases from 10%to 25%,the temperature and NO concentration in furnace gradually decreased,and the NOx concentration at the outlet of the furnace decreased from 289 mg/m3（O2=9%）to 253 mg/m3（O2=9%）,the content of combustibles in fly ash increased from 3.54%to 5.11%,the pulverized coal gas flow rigidity at the outlet of the burner gradually increased,the phenomenon of particle flushing of the back wall appeared when the circulating flue gas rate increased to 20%.Considering comprehensively,the recommended circulating flue gas rate is 15%. |
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