Energy, fuels, and chemicals 



Figure 26-17. — Photograph of fire circle produced by tangential firing inside a large 

 boiler. (Photo courtesy of Combustion Engineering, Inc.) 



required for startup and additional controls and components can be added for 

 automation. A recirculation system can be incorporated to bum the volatile 

 hydrocarbons associated with the blue haze produced by some veneer dryers 

 (Cherewick 1975; Neild and Weyer 1975). A trap can be added to the basic 

 burners for automatic removal of slag and grit. 



Capacities range from 5 to 60 million Btu per hour. Applications for this type 

 of burner include direct firing of lumber kilns, rotary and veneer dryers, and 

 boilers. 



Fluidized bed burners. — Particles such as sand contained in a vessel can be 

 fluidized by passing a stream of gas upward through them with a certain velocity 

 (Bryers and Kramer 1977; Wiley 1978). When the particles are fluidized, the 

 bed has a hydrostatic head, and light objects float on its surface, while heavy 

 ones sink. Individual particles undergo a high degree of mixing by moving about 

 in the bed. 



Particle size determines the rate of gas flow needed to effect fluidization. With 

 a low rate of gas flow the bed of particles behaves as a porous medium, allowing 

 the gas to pass through. As the rate of flow is increased, the point of incipient 

 fluidization is reached where the pressure drop across the bed equals the weight 

 per unit area of the bed. At this point, the particles start to float on the gas flow. 

 Increasing the gas flows gives no further rise in the pressure drop across the bed. 

 The extra flow passes through the bed as bubbles, and when 3-5 times the 



