Energy, fuels, and chemicals 



3179 



INDUCED 

 DRAFT — 

 FAN 



DUST 

 COLLECTOR 



FORCED 



DRAFT 



FAN 



'WATER COOLED 

 INCLINED GRATE 



ASH REMOVAL 

 DOOR 



OVERFIRE 

 AIR SUPPLY 



Figure 26-10. — Inclined grate furnace system. (Drawing after Corder 1973.) 



Spreader stokers can burn hogged fuel containing 45 to 50 percent moisture at 

 1 million Btu per hour per ft^ of grate area while using 35 to 45 percent excess 

 air. However, most boilers in operation use more than 75 percent excess air.^ 

 Spreader stokers are used with boilers that generate from 25,000 to 600,000 lb of 

 steam per hour (Babcock and Wilcox Company 1972; Corder 1973; Bliss and 

 Blake 1977). 



Suspension-fire boilers. — Suspension firing of wood and bark in large boiler 

 furnaces is similar to the firing of pulverized coal (Hall et al. 1976). Most often 

 bark, hogged to small size and pneumatically injected into the furnace, is the 

 fuel. If injection is high enough in the furnace and the fuel particles are small 

 enough, then the fuel will be completely combusted before it falls out of the 

 combustion zone. 



^Personal communication with David C. Junge, Oregon State University, Corvallis. 



