Effect of Species and Wood to Bark Ratio on Pelleting of Southern Woods

Six common southern hardwoods and loblolly pine were pelleted in a laboratory pellet mill. The pellet furnishes were blended to test the effect of different wood to bark ratios on pellet durability and production rate. Included was a ratio chosen to simulate the wood to bark ratio found in whole-tree chips. This furnish produced good quality pellets for all species tested. Pelleting of the pure wood of hardwoods was not successful, furnish routinely blocked the pellet mill dies. Pure pine wood, however, did produce acceptable pellets. It was noted that, as lignin and extractive content increased above a threshold level, the percentage of fines produced in a pellet durability test increased. Thus, all pine and tupelo wood/bark mixes produced high fines. This reduces the desirability of the pellets in the marketplace. Further research is necessary to confirm this relationship. This study suggests that both tree species and wood/bark ratio affect the durability of pellets and the rate with which they can be produced in a laboratory pellet mill.

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