In order to stabilize the combustion, if the volatile content and heating value of coal are reduced, the excess air coefficient must be increased, the temperature of the flue gas in the boiler furnace will inevitably decrease, and the evaporation of the water-cooled wall will decline. The effect of temperature reduction on radiant heat transfer is a 4th power relationship.
In order to maintain the evaporation capacity of industrial steam boilers, Changsha floor heating needs to increase fuel and air at the same air-fuel ratio, and the flue gas flow increases. Because the flue flow area is unchanged, the flue gas flow rate of the flue where the superheater is also increased. According to the criterion equation of forced convection, the influence of the increase of the flue gas velocity on the convective heat transfer coefficient of the flue gas side is the nth power of the flue gas velocity, n = 0.6-0.65.
In summary, the volatile content and heat generation of coal combustion are reduced, the radiant heat transfer of the furnace is reduced, and the convective heat transfer of the superheater is increased, that is, the heat absorption ratio of the water-cooled wall is reduced. The proportion of heat absorbed by the superheater rises.
If the calorific value of the coal type is lower than the design type, the burn-out time will be prolonged, the excess air coefficient will be greater than the design value, the theoretical combustion temperature will be reduced, and the flue gas temperature in the furnace will also be reduced, so that less ash will melt and evaporate, and the water wall The degree of pollution decreases and the pollution coefficient increases. Conversely, the pollution factor decreases.
