The “Rack System Concept” envisions that round bales will be loaded into a rack in the field or at a Satellite Storage Location (SSL). This rack is off-loaded at the plant, emptied when the bales are needed to supply the plant, and then returned to be refilled. It is cycled multiple times each week within the closed logistics system operated for a specific plant.

When reading this specific example, the reader should understand that others are imple­menting the feedstock logistics principles in a different way because they are dealing with a different crop in a different region with a different harvest season. Also, the farming culture is different in different regions, and this can have an influence on logistics system design.

All the different options cannot be discussed here; however, a specific example is needed to help the reader “think through” an entire logistics system. The selection of the Rack System Concept for this example implies no criticism for the other ways of implementing the multibale handling unit concept currently being developed.

In this example, cost to grow, harvest, and store in an SSL is covered in the farmgate contact. The analysis begins with round bales in single-layer ambient storage in the SSL and ends with a stream of size-reduced material entering the bioenergy plant for 24/7 operation. To understand this example, it is appropriate to summarize the “baseline”constraints:

1. The rack and trailer design must conform to the standards for highway transport.

(The rackused for this example holds 16 5-ft diameter x 4-ft long (5 x 4) round bales. With two racks on a truck, a truckload is 32 round bales. Other rack designs are being investigated.)

2. The bales will be pre-loaded into the racks while the trailer is parked at the SSL. When a truck arrives, a trailer with two empty racks is dropped, and the trailer with two full racks is towed away. The goal is to exchange trailers in 10 minutes, or less.

3. At the bioenergy plant, the racks are unloaded from the truck and placed on a conveyor to be conveyed into the plant for immediate use, or stacked two high in at-plant storage. The goal to unload the trailer should be 10 minutes, or less.

4. The plant will operate with a minimum of 2.5 days of storage. All at-plant storage is bales in racks.

5. Hauling will be done 24 h/d. Truck drivers will work five 8-h shifts per week and operations will be continuous for a 6-day work week. The rack loading crew at an SSL will be organized such that each worker will work a 40-h week. SSL operations will proceed such that racks are loaded six 10-h workdays per week.

6. The example assumes that the plant processes one bale per minute. A bale at 15% moisture content weighs 900 lb = 0.45 ton. The dry ton per bale is:

0. 45 ton/bale x (1 — 0.15) = 0.3825 dry ton/bale

Assuming one bale is processed per minute, the processing rate is:

0.3825 dry ton/bale x 1 bale/min x 60 min/h = 23 dry ton/h

(For comparison, 23 dry ton/h = 552 dry ton/d. This size is in the 100-1000 dry ton/d range recommended for Regional Biomass Processing Depots by Eranki et al. [1].)

The processing of racks is:

3.75 rack/h x 24 h/d x 7 d/wk = 630 rack/wk = 315 truck loads/wk