3184 



Chapter 26 



Figure 26-16. — Tangential firing concept. (Drawing after Fernandes 1976.) 



Cyclonic furnaces. — Cyclonic furnaces also bum fuel in suspension. In early 

 water-cooled models, cyclone burners were fueled with wood and bark in 

 combination with coal (Fuller 1976). Today, refractory lined models are com- 

 monly used and do not require auxiliary fuel except at startup. 



In the horizontally mounted cyclonic burner, a drumlike combustion chamber 

 is closed at one end (fig. 26-18). Hot combustion gases are discharged from the 

 opening in the other end called the choke. Combustion air is forced by a blower 

 through the air manifold into tuyeres which admit the air tangent to the inner 

 surface of the combustion chamber. The airflow pattern created is a double 

 cyclonic action. Fuel is injected tangentially into the burner with a stream of high 

 velocity air. Mixing of the fuel and air takes place around the periphery of the 

 burner as they transverse toward the choke. Both the high turbulence of the 

 cyclonic airflow and the time in the burner contribute to complete combustion as 

 long as proper temperatures are maintained. Excess air can vary from 60 to 130 

 percent depending on the installation (Levelton and O'Connor 1978). 



Fuel wood for this system must be dry (15 percent moisture content) and sized 

 (Vs-inch or less). The fuel is metered from a bin to a mixing tee and then into the 

 high velocity air stream for injection into the burners. An auxiliary burner is 



