Furnace waterwall slagging is a common low NOx combustion problem. Slagging is commonly a result of staged combustion and excessive coal imbalances, leading to high carbon fly ash that can deposit on furnace waterwalls.  Both bulk and locally reducing atmospheres can yield low-melting ash phases, increasing furnace slagging potential.   There are several means to minimize reducing conditions and furnace slagging:　pulverized coal nozzle balancing devices, CFD simulations to design flow corrections devices for balancing burner secondary air flow, and sufficient air to blanket furnace side walls.  

Furnace waterwall corrosion can also occur due extreme reducing conditions near tube surfaces.  Tube failures often result from localized reducing conditions and flame impingement on the furnace rear wall.  Analysis of these tube failures has shown tube cracking due to thermal fatigue and breakdown of the protective oxide layer.   In order to eliminate rear wall corrosion we have designed a special air flow system to blanket the rear wall, especially for boilers with limited space.

Sidewall corrosion can also occur with low NOx combustion due to reducing conditions in the burner zone as a result of staging with OFA.  This type of failure is generally due to sulfidation of the tube oxide layer from iron sulfides in the ash in a reducing atmosphere.  CFD modeling is used to design air ports and identify their location between the outer burners and the sidewalls.  Special design features such as tilt and yaw can be incorporated into these ports to ensure air coverage of potential corrosion regions. 

Furnace waterwall slagging and corrosion are unique to the fuel fired, furnace operating conditions and design of each individual boiler.  As a result, we evaluate the existing conditions responsible for corrosion and apply a cost effective, engineering solution.  A brief summary of slagging and corrosion phenomena and solutions is shown below.