What is the reason for using more upper layer burners at low loads in industrial boiler systems?
What is the reason for using more upper layer burners at low loads in industrial boiler systems?
The reason why more upper burners should be used in an industrial boiler system during low load is that most medium- and high-pressure boilers have heat exchangers that mainly rely on convection. As we all know, the steam temperature characteristic of a convection heat exchanger is that the steam temperature decreases as the load decreases. When the boiler load is low, it is possible that the feedwater regulating valve is completely closed, and the steam temperature is still below the lower limit. Although it is possible to increase the excess air ratio at the furnace exit or increase the furnace negative pressure to increase the steam temperature, these methods increase the heat loss due to excess air in the flue gas, resulting in a decrease in the boiler efficiency.
If the lower burners are stopped and more upper burners are used, the center of the flame in the furnace moves upward, reducing the heat absorption in the furnace, and the flue gas temperature at the furnace exit increases. The heat exchanger absorbs more heat due to increased radiation and temperature difference, causing the steam temperature to increase. This method of regulating steam temperature is more economical and should be the first method used when the steam temperature is too low due to low load.