Feedstock Supply, Logistics,. Processing, and Composition

Jim Hettenhaus1 and David Morris2

1cea Inc, Charlotte, NC; and
2Institute for Local Self Reliance, Minneapolis, MN

For large, economic, and sustainable harvest of biomass feedstock, major changes in cropping practice, collection, storage, and transportation are required. The challenges faced in supplying 0.7-1 million dry short tons (dt) for a single biorefinery are huge—five times larger than previous attempts.

Ultimately, the farmer controls biomass sourcing for biorefineries. The availability of large quantities of residues, stover, and straw is greatly depen­dent on tillage practice. No tillage results in most of the residue available for removal, especially when cover crops are employed for erosion control. By contrast, no excess is available with conventional tillage. Since <20% of crop­land is no till and >60% is conventional till, a major shift in cropping practice is needed for sustainable removal of significant quantities.

Present collection costs are 1.5-2 times the delivered cost target—$35/ dt, including $20/acre or more net income for the farmer. Bulk collection is likely needed, because baling adds cost, $15/dt, and no value. One-pass harvest can lower the delivered feedstock cost to <$20/dt within a 15- to 20-mi radius. Prototypes for one-pass harvest of straw and stover are under development, adapting existing equipment. Many variations are possible, but until a better market definition is available, a new design is probably limited to paper studies.

One-pass harvest also reduces the risk of corn stover harvest if storage of wet harvested material is resolved. For the sugar platform, feedstock can be wet, above 65%, or dry, below 20%. Some are looking at adapting wet, bagasse-type storage, large 250,000-dt piles built via circulating liquor that conveys the feedstock from wagons or trailers directly from the field after it is washed and milled to a particle size that ensures good compaction and preservation in storage. Less area is required; fire is eliminated when stored above 65% moisture. The material processes easier because 80% of the solubles is removed in storage. Water management and other issues remain. Validation of this method is required for other crops such as stover and straw.

Because of the bulky nature, the cost of transportation is 20-40% of the cost within a 50-mi radius. Transportation from the field to a storage site following harvest needs to be kept short if truck requirements are to remain manageable. Collection within a 50-mi radius for one site requires about five times the trucks and wagons compared with a 15-mi radius. While bulk density can be increased, the cost of densification generally offsets any transport savings. Pipelines require huge initial investment. Short-line rail delivery from three or more collection sites to supply the plant appears most advantageous compared to trucking or pipelines.

In conclusion, potential processors want clean liquid, mostly ferment­able sugars, delivered to the processing plant. Thus, in addition to the above, using part of the storage time for value-added treatment offers more potential. Although this processing is probably under different regulatory requirements than storage, it may be segregated and controlled separately. Including preprocessing with harvesting, collection, and storage provides farmers ample opportunity to participate in the value chain, moving away from simply supplying a commodity.

Copyright © 2004 by Humana Press Inc.

All rights of any nature whatsoever reserved. 0273-2289/04/113/0005-0012/$25.00