3 1 70 Chapter 26 



Wood ash generally has been considered inert (Hall et al. 1976), but this may 

 not be chemically true. In at least one case, wood ash has been shown to be an 

 effective catalyst in the gasification of wood (Feldman 1978). 



Increased use of wood for fuel might make ash disposal a problem (Hall et al. 

 1976). Perhaps ash could be used as a soil conditioner to break up clay, and the 

 alkalinity of ash could help raise the pH of acid soil. If supplemented with 

 nitrogen compounds ash also has the potential for use as a fertilizer. Host and 

 Pfenninger (1978) found that flyash has a natural timed release of nutrients over 

 an extended period of time; field tests showed tree growth response still evident 

 3 years after application. One mill in central Louisiana uses clinkers for road-bed 

 surfaces around the plant. 



Emissions. — Both gaseous and particulate emissions occur when wood is 

 burned (table 26-7). Carbon dioxide and water vapor (equations 26-1 and 26-2) 

 combined with nitrogen and oxygen from the combustion air comprise 98-99 

 percent of the total material emitted from an efficient combustion process. 



In terms of potential air pollution, the United States Environmental Protection 

 Agency (EPA) is concerned with the amounts of particulate matter, sulfur 

 dioxide, carbon monoxide, nitrogen oxides, and unbumed hydrocarbons that are 

 emitted into the atmosphere. In wood combustion, sulfer dioxide emission is 

 very low, and carbon monoxide and hydrocarbon emissions present no problems 

 in most situations. The situation with nitrogen oxides is less certain, and particu- 

 late emissions from wood-fired boilers require attention. 



Table 26-7. — Emissions from combustion of hogged fuel (Junge 1975a) 



There are no published data on the sulfur content of bark from individual 

 species of southern hardwoods. The National Council of the Paper Industry for 

 Air and Stream Improvement, Inc. (1978) sampled sulfur content of bark fuel at 

 four pulpmills in the Southeast (Alabama, Georgia, and Florida) and found 

 contents of 0.010, 0.060, 0.068, and 0. 134 percent; although most of the bark 

 was from southern pines, substantial amounts of hardwood bark were also in the 

 mixtures. It was found that just over 5 percent of the sulfur contained in bark was 

 emitted from the mill boilers as SO2, i.e. , about 0.0001 to 0.0020 pound of SO2 

 per million Btu in the bark fed to the boilers. (Stembark of small pine-site 

 hardwoods has a heat of combustion — higher heating value — of about 7,593 

 Btu/ovendry pound; emissions in these tests therefore suggest about 0.76 to 

 15.19 pound SO2 per million pounds of dry bark.) 



