In order to burn stably, if the volatile matter of coal is burned and the calorific value is reduced, the excess air coefficient must be increased, then the flue gas temperature of industrial gas steam boiler will inevitably decrease and the evaporation of water wall will decrease, which can be seen from the radiation heat transfer formula of furnace. The influence of the decrease of furnace flue gas temperature on the radiative heat transfer is the relation of fourth power.
In order to maintain the evaporation capacity of industrial gas-steam boiler, Changsha ground heating needs to increase fuel and air according to the same air-fuel ratio, and the flue gas flow rate increases. Due to the constant flow area of the flue, the flue gas velocity of the superheater is also increased. According to the criterion equation of steady forced convection, it is found that the effect of the increase of flue gas velocity on the convective heat transfer coefficient of flue gas side is the n power of flue gas velocity, n �� 0.6 �� 0.65.
To sum up, the volatile and calorific value of coal combustion decreases, and the radiation heat transfer of furnace is reduced, while the convective heat transfer of superheater is increased, that is to say, the endothermic proportion of water wall decreases and the endothermic proportion of superheater increases.
If the calorific value of the coal is lower than that of the designed coal, the burnout time is prolonged, the excess air coefficient is greater than the designed value, the theoretical combustion temperature is reduced, and the flue gas temperature in the furnace is also reduced, so that less ash is melted and evaporated. The pollution degree of water wall decreases and the pollution coefficient increases. On the contrary, the pollution coefficient decreases.
