Solid Wood Products 27 1 5 



22-16 OTHER PARTICULATE WOOD 



Wood in particulate form has numerous uses in addition to energy, paper, and 

 fiberboard production. For many of these uses, particle form is critical; metallur- 

 gical chips, flakes for structural panels, excelsior, and wood flour (see section 

 18-26) are examples of such products. Products for which particle form is less 

 critical include mulches, and poultry and animal litter (see sec. 13-7). 



METALLURGICAL CHIPS^o 



In the electric smelting processes (fig. 22-67) that extract or reduce metals 

 from their ores, woody reductants in the form of metallurgical chips (fig. 22- 

 68) are used, as are other reductants such as coal and coke. Electric smelting is a 

 continuous process in which a mixture of ore and reducing agents — wood chips, 

 coke, and coal — is added into the top of an electric furnace at regular intervals. 

 Carbon electrodes submerged in the mix melt the material, which is periodically 

 tapped from the bottom of the furnace. 



During smelting oxygen in the ore is combined with carbon from the reducing 

 agents, thereby freeing the metal. The carbon and the oxygen form carbon 

 dioxide, which escapes from the furnace as gas. 



Wood constitutes 10 to 75 percent by weight of the furnace mix. This propor- 

 tion varies according to the origin and particle sizes of the ore, the type and 

 quality of the alloy being produced, the furnace design, the moisture content and 

 size of the wood particles, and the artistry of the smelter operator. The metallur- 

 gy of electric smelting depends upon art as well as upon science. Hence the use 

 of wood chips appears to reflect the individual metallurgist's or smelter's con- 

 victions as well as technological and economic considerations. 



Although wood chips provide some of the carbon for chemical reaction, their 

 primary usefulness in the charge is due to their bulk. Some of the reasons 

 metallurgists cite for the use of wood in the charge are: 



• To provide a large surface area for chemical reaction to take place more 

 completely and at improved rates. 



• To maintain a porous charge, thereby promoting gentle and uniform — 

 instead of violent — gas venting. 



• To help regulate smelting temperatures. 



• To keep the furnace burning smoothly on top. 



• To reduce conductivity. 



• To promote deep electrode penetration. 



• To prevent bridging, crusting, and agglomeration of the mix. 



• To make possible the smelting of finely divided raw materials without 

 sintering. 



• To reduce dust, metal vapor, and heat loss; and as a result to improve 

 working conditions near the furnace. 



^^ext under this heading is condensed from Wartluft (1971). 



