3218 



Chapter 26 



EXHAUST 

 STACK 



AIR POLLUTION 

 CONTROL 

 EQUIPMENT 



WOOD FEED 



EXTERNAL 



COMBUSTION 



CHAMBER 



PYROLYSIS 

 GAS 



DRYING 

 ZONE 



PYROLYSIS OF 

 VOLATILES 



■COMBUSTION AIR 



COMBUSTION AIR* 



BOILERj 



«— COMBUSTION AIR 



^ CONTROLLED AIR BYPASS 

 FOR TEMPERATURE 

 REGULATION 



Figure 26-33. — Feed and gas flow diagram for the Nichols-Herreshoff multiple hearth 

 furnace. 



10,000 to 13,000 Btu/lb, is obtained by passing the pyrolysis vapors through a 

 condenser. Remaining non-condensable gases which contain about 200 Btu/ 

 sdcf, are used to pre-dry incoming wood fuel (fig. 26-34) to about 4 percent 

 moisture content. The non-condensable gases are sufficient to pre-dry fuel of up 

 to 50 percent moisture content (wet basis). About 35 percent of the energy 

 content of the wood fuel is in the charcoal and about 35 percent in the pyrolytic 

 oil. On a weight basis, charcoal yield is 23 percent while pyrolytic oil yield is 25 

 percent. Charcoal heating values range from 11,000 to 13,500 Btu/lb. The 

 process has been operated on a scale of 50 dry tons of fuel per day, and 

 processing up to 200 tons per day appears feasible (Bliss and Blake 1977). 

 See section 28-10 for an economic analysis of a portable pyrolyzer. 



OCCIDENTAL FLASH PYROLYSIS 



Preston (1975) described a pyrolysis system that internally recycles the char- 

 coal produced in order to supply heat energy for the pyrolysis process. The 

 primary products are pyrolytic oil, off gases, and water. The process was 

 developed primarily for pyrolyzing municipal refuse while recovering valuable 



