Sugarcane is a high-yield (up to 155 t/ha), high-moisture content (80+%) crop. It is grown to collect the sugar (sucrose) produced in the stalk. The stalks are crushed and the juice col­lected. This juice is then concentrated into molasses that is subsequently centrifuged to produce crystalline sugar. The raw sugar is washed to produce the pure white product we see in the sugar bowl on our breakfast table.

Harvesting

A sugarcane harvester cuts the stalk at the base, and then cuts it into 30-cm-long billets. Air is blown through the billets as they are cut to blow away as much leaf as possible and leave it in the field. The billets are conveyed into a side-dump wagon that travels with the harvester. There is no onboard storage on the sugarcane harvester, as with the cotton harvester, thus the side-dump wagon must be in place for the harvester to operate.

The side-dump wagons proceed to the edge of the field where an elevated loading ramp is prepared (Figure 7.14). The wagons dump directly into bins on trucks, and these trucks deliver the bins directly to the sugar mill.

Logistics

Cycling of the side-dump wagons and the highway trucks must be well coordinated for the harvest to proceed with maximum efficiency. The cut stalks spoil so quickly that there is no storage between field and mill. This same constraint will apply to any option that proposes to ferment a “sugar biomass " directly to produce ethanol.

Truck trailers hauling the bins are equipped with a pivot point such that the bins can be dumped directly onto the conveyor feeding material into the mill. Time to dump a load (trailer with two bins) is 3 minutes. Some truck tractors pull a double trailer (four bins), and the time to dump this load is 7 minutes. If a given load is not needed to fill the conveyor, the loaded bins are removed and stacked two high on a graveled storage yard. Empty bins are removed from storage and placed on the truck to be returned to the field. This operation takes 3-4 minutes. One sugar mill in South Florida unloads 1000 trucks per day, a total delivery of about 24,500t/day.

Harvesting and hauling is done only during daylight hours, thus the at-plant storage is essential to operate the plant 24/7. Each bin has a pivot point so it can be dumped during the evening when placed in position with the forklift. The sugarcane system is unique in that harvesting and hauling does occur 7 days per week.

One sugar company in South Florida harvests and processes 3.3 million t of sugarcane in a 140-day season. The industry is a unique example of plantation agriculture. The company owns the production fields, the harvest equipment, the service roads through the fields, and the sugar mill. It owns the trailers that haul the bins, but typically contracts with trucking companies for the truck tractors that pull the trailers.

When the truck tractors pull a double trailer, the second trailer is hooked behind the main trailer. Each trailer hauls two bins for a total of four bins, thus the total length of the vehicle is almost 35 m. A vehicle like this would not be legal on most public roads across the United States. The labor productivity (t/hour) for truck drivers in the sugar industry cannot be equaled for any other biomass logistics.

Trucks typically haul 10 loads per day. With no delays, they could theoretically haul 13 loads per day, thus the truck productivity factor is 10/13 = 0.77, or 77%. This exceptional performance is possible because one entity, the sugar company, has control of all segments of the harvest logistics system. The harvest equipment is managed and trucks are scheduled to minimize the load and unload times. This management capability is key to the efficiency of a short-haul operation. It is also significant that the trucks travel on company-owned roads, thus they do not encounter the traffic seen on public roads. It is unlikely that any other biomass system that collects material from fields and delivers it to a central plant can equal the truck productivity, 77%, of the sugar industry in South Florida. Also, it is unlikely that the level of coordination between infield hauling and over-the — road hauling can be duplicated any­where else. It certainly cannot be duplicated if farmers haul in the raw biomass and make deliveries on their own schedule.

Another sugar mill in South Florida uses a “mobile accumulator” concept to supply the mill 24/7. This mill has railroad tracks extending from the mill out through the production fields. There are loading platforms at periodic intervals along these tracks. Side-dump wagons fill the railcars at the loading platforms. When the cars are filled, the train is pulled onto a siding at the mill. As needed for 24/7 operations, the cars are moved into position and dumped.

Again, the plantation model offers an advantage. The sugar company owns the railroad tracks through their production fields, thus they can use railcars as a mobile storage for the sugar mill. Once the investment in tracks and other infrastructure is recovered, the train can be more economical than trucks hauling bins.