The Research Of Optimization On Blended Coal Combustion Of 660MW Supercritical Opposed Firing Boiler

Nowadays,Coal accounts for 59%of Primary energy consumption,Coal consumption of heat-engine plant accounts for 45-50%of total coal consumption.Coal dominated energy pattern will not change in a short time.inferior coal is commonly used in power plant boilers,which often deviates from the designed coal in operation,resulting in the reduction of boiler efficiency,It leads to the reduction of boiler efficiency,which seriously affects the economy,safety and load capacity of the boiler.Coal blending and combustion adjustment can improve coal adaptability of boiler,Improve the stability and efficiency of boiler operation and realize the combustion of all coal in the boiler,It is of great practical significance for utility boilers.The supercritical opposed flame boiler of 2×660WM Unit in Hunan Province are taken as the research object,According to the actual situation that the power plant mainly burns local coal and purchases some coal from other provinces at the same time,Combined with the combustion characteristics of supercritical opposed flame boiler,three typical coals are selected which are medium sulfur lean coal,low sulfur long flame coal and high sulfur lean coal.The coal quality characteristic analysis with combustion characteristic experiment of single coal sample and mixed coal sample with different blending ratio are carried out,the influence rule of blending ratio on the coal quality characteristic and combustion characteristic were studied.On the basis of the experiment,combined with the theory and method of coal blending,the best blending proportion based on three kinds of coal blending were determined.Combustion adjustment and optimization test on boiler according to optimized coal blending scheme.Under the condition of 100%,80%and 50%load,the influence of different air distribution mode,oxygen content and coal pulverizer shutdown mode on the combustion efficiency of the boiler were studied to find the best operation scheme of the boiler based on the operation coal.The results shows:(1)When sulfur lean coal,low sulfur long flame coal and high sulfur lean coal were blended and burned,the best blending ratio is 3:5:2,which has the best ignition,stable combustion and burnout characteristics.(2)Through the combustion adjustment test,the combustion stability of the boiler can be improved,the heat loss of mechanical incomplete combustion,the heat loss of chemical incomplete combustion and the NOX,SO2 emission of pollutants can be reduced.(3)The way of air distribution has a great influence on the combustion and burnout of coal in the boiler.The influence degree of fly ash combustibles varies with the load,Under rated load,the difference of fly ash combustibles is about 6%,and under low load,the difference is about 1%.Ensure that the exhaust air in the lower layer is fully open and the exhaust air in the upper layer is 10%-40%,the air distribution is optimal.(4)The change of the shutdown mode of the pulverizer has a great influence on the stable combustion of the boiler and ensure the thermal load of the boiler.The difference of the fly ash combustibles for the rated load is about 5%,and the difference for the low load is about 4%.Stop coal mill at the top layer under rated load,keep the pulverizer fully open at 80%load,and stop coal mill A,D at the top layer and coal mill E at the bottom layer at 50%load are the best.(5)The oxygen content in the furnace has a great influence on the excess air coefficient.The difference of the fly ash combustibles for rated load is about 4%,and the difference of the fly ash combustibles for low load is about 5%.The oxygen content of furnace is 2.8%?3.0%for rated load and 4.0%?5.8%for low load are optimal.