Marginal Column

The boiler generates 230 tons of steam per hour, at a pressure of 65 bar.
Photo: Aguai SA

Roller conveyors and two drying units, driven with Hägglunds motors.
Photo: Aguai SA

The diffuser, fitted with Rexroth cylinders, processes up to 12,000 tons of sugarcane every day.
Photo: Aguai SA

Freed from its chains

Incorporating the latest in technology, the Ingenio Sucroalcoholero Aguai SA facility in Santa Cruz, Bolivia, is turning sugarcane into ethanol, sugar and electricity. Bosch Rexroth has supplied a fully hydraulic drive system that assures smooth, trouble-free operation.

 

Bioethanol is booming, and above all in Brazil. Bolivia is now looking to profit from this trend, too, by producing ethanol, sugar and electricity. The private sector is also helping to move the development forward by investing in new production plants where sugarcane is transformed into ethanol, sugar and electricity. A Bolivian private corporation made up of sugarcane producers lead by Cristobal Roda from the Roda Industrial Group is now building the Ingenio Sucroalcoholero Aguai.

“This is the first sugar-to-ethanol plant with a fully hydraulic extraction section and thus is one of the most modern in all of South America,” Roda stresses. It is planned to go into operation in August of 2012. Brazilian engineering company Dedini S/A Indústrias de Base worked out the planning for this production facility. It represents a new generation of high-efficiency industrial plants with a new automation concept which, together with the requisite drive system, was supplied by Bosch Rexroth. An international team of specialists – from Germany, Sweden and Brazil – worked out the system layout and the configuration for the hydraulics.

Powerful support

Rexroth products move the sugarcane through the entire system, right from the very first step in the process. A hydraulically powered crane unloads the raw material, arriving by truck, onto the cane table that then takes the product to the so-called cane feeder – a long conveyor that slowly moves the cane into the shredder and on to the heart of the extracting plant, the diffuser. Hägglunds CB motors and Hägglunds PEC hydraulic units power the winch for the crane, ensure uniform, carefully controlled forward motion of the cane table, and drive the conveyor.

Individual drives

The diffuser comprises 16 parallel tracks, each measuring 70 meters. The sugarcane is conducted slowly by the tracks against a stream of warm water. The result is that the sugar is released from the biomass and diffuses into the water. In this newly engineered plant, each of the 16 tracks is driven by two separate hydraulic cylinders from Rexroth, each under individual control. One cylinder for the slow forward motion and one for the fast reverse action. The oil flow for each of the 16 feed cylinders is supplied by an individual, variable-displacement, axial piston pump mounted atop a tank holding 5,000 liters of hydraulic fluid.

It powers the 16 cylinders for the forward movement with a 1,000 millimeter stroke. The 16 Rexroth cylinders connected to the back end pull the tracks backwards with a fast stroke. Here the oil flow is supplied by three bigger pressure controlled axial piston variable pumps each operating a group of multiple tracks. The energy-efficient drive solution uses no throttle valves. The variable-displacement, axial piston pumps control directly the motion of all 32 cylinders. Downline from the diffuser, a combination of three hydraulic power units and five high-torque Hägglunds MB motors powers the dewatering and drying mills where the residue – the bagasse – is then dried. The high degree of automation achieves a significant increase in productivity for the sugarcane industry, which is otherwise very traditional.

Growing to meet new tasks

“This new diffuser drive offers other advantages, too. In factories using the previous design, a centrally powered chain draws all the pushers forward mechanically. Thus the entire system grinds to a halt if the sugarcane jams. This kind of failure is unknown in the Ingenio Aguai plant,” Cristobal Roda explains. There the 16 tracks are divided into three groups. In the event of an interruption in one track in one of the groups, then the drives for the remaining tracks remain in operation. Furthermore, the modular design also lends flexibility to this plant, providing opportunities for future expansion. The system may comprise between twelve and twenty tracks.

Fuel from biomass

The feedstock material: Bioethanol is not entirely uncontroversial. Critics point to increasing competition for arable lands that could be otherwise used for food production. In the case of sugarcane, this issue is less critical, since both sugar and ethanol are produced in the process. Further criticism focuses on the CO2 released during cultivation. In some cases, more CO2 is generated in the field than what is saved in bioethanol combustion – in comparison with conventional fuels. The overall picture is positive for sugarcane, however. The bioethanol derived from it lowers net CO2 emissions.