There are two principles common to the logistic system for the herbaceous biomass examples (cotton, sugarcane), and the woody biomass example (fuel chips).

1. Hauling efficiency (t-per-day-per-truck) is maximized by procedures that minimize the truck load time and unload time. This principle is the key to any short-haul logistics system.

2. Some at-plant storage is unavoidable, thus a system must be in place to facilitate the flow of material into and out of at-plant storage. The sugarcane harvest operates closer to just-in-time delivery than the other two harvests, because it is an integrated system under one management. Even the sugarcane system, however, requires some minimum at-plant storage to provide for uninterrupted operation during the night hours.

An advantage is gained when the infield hauling and over-the-road hauling operations are uncoupled, as is done with the cotton system (Figure 7.15). An additional advantage is gained when the harvesting operation is uncoupled from the infield hauling. Two new cotton harvesters have recently been introduced. One bales the seed cotton in a block about half the size of a conventional module, a concept that emulates the big square bale in hay har­vesting. The other concept bales the seed cotton into a 2.4-m diameter round bale and wraps it with a solid plastic sheet. Both these concepts were developed to uncouple the harvesting operation from the infield hauling. With this uncoupling, the harvester can proceed without having to wait for the infield hauling. In fact, the hauling can be done several days, or perhaps several weeks, later.

Gin

(Some at-gin storage on gravel yard)

Fuel chips are a flowable material. Size reduction is done in the forest, and the flowability advantage is then realized throughout the remainder of the logistics system. The truck can be unloaded by flowing the material out of the back. When there is no queue, unloading (total time at the plant) is 10 minutes. The use of the bulldozers to flow the fuel chips into and out of at-plant storage is expensive, but study has shown that it is a least cost option; the estimated cost to operate the at-plant storage is less than $2/t. This cost is increasing as diesel fuel costs increase, thus other options may become competitive in the future.

One option for a herbaceous biomass system is to emulate the fuel chip system and do the size reduction in the field. Another option is to remove biomass from storage (woody biomass can be harvested year-round but herbaceous has a limited harvest season, thus some storage is unavoidable) and chop the material and blow it into a van trailer, as is done with the fuel chips. Can chopped grass be dumped out of the back of a van trailer after it has been vibrated during transport? Also, a plan must be put in place to flow the chopped material into and out of at-plant storage, and the question remains—can this be done in a cost-effective manner?

The need for some minimum at-plant storage is acknowledged by most bioenergy plant design teams. The alternative is just-in-time delivery from field/forest for 24/7 operation, and this is not judged to be a practical option.

It is appropriate to review the two at-plant storage options currently in place. In the cotton system the modules are stored on the ground in a graveled area at the gin. When a module is needed, the “yard” module hauler picks up a module and places it in the conveyor that feeds the module into the module feeder, which meters a continuous flow of seed cotton into the gin. The sugarcane system is similar to the cotton system—the raw biomass remains in the hauling “package” until it is processed. In this case, the hauling bins are stacked two high in a graveled lot at the mill and dumped as needed throughout the night shift to maintain a continuous supply of material into the mill.