Simulation studies on direct ash recycling and reburning technology in a tangentially fired 500 MW pulverized coal boiler

For thermal power generation companies, the use of refined ash (defined as having a loss on ignition (LOI) of less than 6%) has not only made it suitable to produce lightweight aggregate, but has also introduced significant cost benefits through recycling. However, the ash having a high unburned carbon content (greater than 6%) cannot be recycled and still must be disposed of underground and by landfill. In this paper, an ash recycling and reburning technology was examined to improve ash usage in 500 MW pulverized coal (PC) boiler and simulation was performed to find the optimal conditions of ash supplying position and its amount that would not affect the boiler condition. Kinetic parameters for the reaction rate of ash were derived from a drop tube furnace (DTF) and adopted to accurately describe the characteristics of high LOI ash. In addition, the simulation results were then validated through real scale tests. Based on the simulation results, this paper suggest that the optimal supply condition for ash reburning is D burner sight window and 4 ton/h (with 0.01% of total air) in terms of combustion stability and burnout because the upper burner location has more sufficient oxidizer in the particle pathway as well as maximized mixing effect between coal and oxidizer. The real scale tests evidently represent that ash reburning can be method to make low LOI ash.