During low load operation of a boiler, the reason for using more upper combustion burners is as follows
During low load operation of a boiler, the reason for using more upper combustion burners is as follows
In most medium and high-pressure boilers, the superheater relies primarily on convective heat transfer. It is well-known that the steam temperature characteristic of a convective superheater decreases with reducing load, leading to a drop in steam temperature. When the boiler operates at a relatively low load, there may be situations where the desuperheating water regulating valve is completely closed yet the steam temperature still remains below its lower limit.
Although methods such as increasing the excess air coefficient at the furnace exit or increasing the furnace negative pressure can be employed to raise the steam temperature, these approaches lead to increased flue gas temperatures and an elevated excess air coefficient in the flue gas, which results in increased flue gas heat losses and consequently a decrease in boiler thermal efficiency.
By preferentially shutting down lower combustion burners and instead utilizing more upper combustion burners, the flame center within the furnace shifts upward. This reduces the furnace’s heat absorption and increases the flue gas temperature at the furnace outlet. The superheater experiences an increase in radiant heat absorption and the temperature difference for heat transfer becomes larger, thus enhancing the overall heat absorption by the superheater. As a result, the steam temperature rises. This method of adjusting steam temperature is more economical, and it should be the首选 approach when the boiler is operating at a low load causing suboptimal steam temperatures.