Inverted "N" type of power distribution in a 1000 MW opposed firing boilers
Taking the coal pulverizing system of a 1 000 MW opposed firing boilers with side bunker layout as the research object,the dis-tribution laws of powder quantity,fineness of pulverized coal and comprehensive resistance of powder tubes were analyzed.It is found that the distribution of powder quantity and pulverized coal fineness show an inverted＂N＂ trend generally.The powder pipe with large amount of powder has a large fineness of pulverized coal while the pulverized coal fineness of the powder pipe with less powder quantity is small.The powder quantity and the pulverized coal fineness are positively correlated.The comprehensive resistance of powder tubes shows an"N"trend,which is negatively correlated with the powder amount and the fineness distribution of the pulverized coal.The powder distri-bution trend of powder tubes are caused by the different comprehensive resistance of powder tubes.The change of mill′s parameters does not affect this distribution law.The maximum deviation of powder amount on No.1 unit is 37.7%while the maximum deviation of powder amount on No.2 unit is 84.4%,which are far beyond the±10%deviation required by the regulations.Different manufacturers of dynamic separators has different separation effects which result in different degrees of powder deviation.The characteristics of powder distribution require that the air distribution of burner must be adjusted accordingly.Measures such as increasing the swirl intensity,opening of the sec-ondary air,turning off of the burning wind,and increasing of the operating oxygen are helpful to alleviate the partial combustion.For the burner with large amount of powder quantity,its internal and external secondary air volume and swirl intensity should be enlarged corre-spondingly.When the low load and odd number coal mills was running,the air-coal ratio of the coal mill with the largest deviation of the powder amount should be improved.A single unilaterally operated coal should be blended difficult-to-burn coal or reduces the separator speed to increase its flame center.After the combustion adjustment,the partial combustion problem of unit 1 is solved while the unit 2 still has slight partial combustion due to the large deviation of powder quantity.For the pulverizing system with excessive powder deviation,the problem of partial burning can be completely solved by the transformation of the pulverized coal side and the secondary air side.The char-acteristics of powder distribution and the optimization adjustment strategies provides a reference for the same type of units with partial burn-ing.
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