| Zhundong coalfield is currently the largest integrated in China.The combustion of Zhundong coal has more prominent characteristics of coking and contamination,the power plants in Urumqi can only burn Zhundong coal in mixed burning mode with part of low alkali metal coal in Eastern Urumqi,which reduces the economy of power generation.It is of great significance to study the high temperature corrosion,coking and NOx generation characteristics of Zhundong coal combustion and their correlation for alleviating its coking and contamination and realizing combustion of Zhundong coal only.Taking a 660MW ultra supercritical tangentially fired boiler as the research object,Zhundong coal and Beitashan coal as the fuel,the effects of mixed-burning ratio and air distribution on the combustion characteristics of the boiler under 600MW load were studied by numerical simulation method.The high temperature corrosion,coking and NOx generation characteristics and their correlations in the water wall area of the boiler are analyzed.The influence of the position of the Separated Over-fire Air nozzle on the combustion characteristics is studied.The influence of NOx concentration at furnace outlet and pulverized coal burnout ratio on the combustion process is analyzed.First of all,by adjusting the operating parameters,the phenomenon of wall brushing on the cross-section of D burner in the actual operation process is improved.the central air nozzle of D is recommended to be arranged with reverse by 5 degrees,and the DE nozzle is turned off to reduce the disorganized air leakage.The coking risk is the lowest and the burnout ratio is the highest under the operation mode with the momentum ratio of secondary and primary air of 1.695 and 1.624 respectively.Then,by changing the air-coal ratio and air rate,the high-temperature corrosion,coking and NOx generation characteristics and the correlation in the water wall area of the boiler under different working conditions are analyzed,and the optimal working conditions are obtained,Meanwhile,the optimal operation mode is explored to improve the Zhundong coal purely-burning.The lower Separated Over-fire Air ratio(17.6%)under different mixed burning conditions can minimize the coking risk and maximize the degree of burnout of the boiler.At the same time,when the mixed burning ratios are 9:1 and 10:0,the variation of NOx emission at the furnace outlet with the ratio of Separated Over-fire Air is obtained.Finally,the influence of the nozzle position of the Separated Over-fire Air on the NOx concentration and pulverized coal burnout ratio at the furnace outlet when the mass ratio of Zhundong coal and Beitashan coal is 8:2,9:1 and 10:0 is predicted,so as to determine the optimal position of the Separated Over-fire Air.The height of reduction zone is 4m,the NOx concentration at furnace outlet and the burnout ratio of pulverized coal reach the best value.Keep the height of reduction zone at 4m,change the distance between high and low separated Over-fire Air,When the distance between the high and low Separated Over-fire Air is 2.5m,the NOx emission and the coal burnout ratio at the furnace outlet reach the best value.The research results can provide a reference for the similar furnace to improve the mixed burning ratio of Zhundong coal until purely-burning. |
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