Factors that influence the quality of the sugarcane harvest

The quality of sugarcane raw material is directly influenced by several factors, and harvesting speed is one of the main ones. Defining the ideal speed determines the levels of impurities, the quality and value of the product and also reduces costs and problems with machines and equipment.

Sugarcane cultivation is one of the most important in Brazilian agribusiness, consolidating the country as the largest producer in the world, occupying an area of ​​8,6 million hectares destined for sugar and alcohol production and, more recently, its residual products have been used to generate renewable electrical energy from burning bagasse and straw.

Given the demand for biofuels to replace petroleum derivatives, changing the harvesting method has helped to promote, at a global level, the idea of ​​the sustainability of ethanol fuel as an alternative source of energy, with a strong social and environmental appeal.

The operational quality in mechanized sugarcane harvesting is evaluated taking into account its effectiveness both in operational capacity and in the various process operations, namely: cleaning of the raw material (at the end of processing), quality technology of the harvested material and the loss rate of industrializable raw material during harvesting, not restricted only to the effective capacity in kilos per hectare, as is generally considered in studies of the operational performance of sugarcane harvesters.

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Travel speed and engine rotation are significant factors in the fuel consumption of sugarcane harvesters, and the higher the speed and rotation, the greater the hourly fuel consumption. However, the choice of speed and rotation configuration is influenced by the condition of the crop at the time of harvest, being a fundamental factor in reducing fuel consumption per ton harvested.

Sugarcane losses during harvest can be classified as visible and invisible. Visible losses are those that occur in the form of whole sugarcane, stumps, billets and pieces of sugarcane and are easily identified and collected in the field. In addition to visible losses, another portion of sugarcane is lost during mechanized harvesting, called invisible losses, which occur in the form of juice, sawdust and small fragments, during the internal processing of the raw material in the harvester, due to the mechanical impacts of the processing systems. cutting, processing, transportation and cleaning.

The result of mechanized harvesting should consist only of chopped sugarcane. However, they may contain unwanted materials, called impurities, which can be of two origins: mineral and vegetable. The presence of this material in the load causes interference in the sugar and alcohol manufacturing process, causing unnecessary wear and tear on equipment and interfering with the quality of the final product. As the cleaning of the harvested material is carried out by extractors (primary and secondary), there is a direct relationship between losses and impurities. To reduce losses, we must use an extractor rotation appropriate to the sugarcane variety and the conditions of the sugarcane field.

The mineral impurity is made up of earth and pebbles and the vegetable impurity is made up of straw and pointers coming from the raw material. In Table 1 it is possible to observe the classification of levels of vegetable and mineral impurities, as low, medium and high.  

The harvester's cleaning system's function is to separate these materials from the load. However, part of it still remains with the sugarcane, being taken to the mill where it can change the quality of the sugar, and also generates a reduction in the amount to be paid for the raw material. Mineral impurities are extremely harmful to equipment (harvesting and industry), as they cause excessive wear on numerous pieces of equipment due to abrasion, increase the loss of sucrose, increase plant downtime due to wear and tear, equipment breakdowns and require changes in the process.

Researchers from the Mechanized Harvest Study Group (Gecom) linked to Fatec “Shunji Nishimura” Pompeia (SP), conducted an experiment in the Santa Tereza Farm area, located in the municipality of Cabrália Paulista, in the state of São Paulo. The aim was to evaluate the amount of vegetable and mineral impurities found in the raw material that would be sent to the sugar and alcohol industry, depending on different feeding rates in the mechanized harvesting of sugar cane.

The variety of culture planted in the area was RB6515, with an age of four cuts and a spacing between streets of 1,5 meters. A Case class XII harvester, year of manufacture 2008, was used, equipped with a Cummins engine (power of 335 hp), hydrostatic transmission, Heavy Duty chopper conveyor with pressure of 1.000 psi and hydraulics with 2.200 psi. During harvest, the primary exhaust fan was calibrated to maintain a speed of 800 rpm.

To support the harvest, two Valtra model BM125i tractors, manufactured in 2008, were used, coupled to two transshipments with a capacity of ten tons of sugar cane.

To compare the actual production of the area without losses, with that harvested in the trial, biometric analyzes were carried out at representative points of the sugarcane field, manually harvesting ten linear meters of sugarcane for each sampling.

The harvester's travel speeds were determined, being 5,6km/h and 7km/h, and a 30-meter path was demarcated to be harvested with the help of the harvester. After the machine performed the harvest at the desired speed, the operation was stopped to remove a portion of this harvest from the transshipment and each sample was properly separated and identified.

According to the test sketch represented in Figure 1, the procedure for collecting samples in the transshipment was repeated three times for each travel speed 5,6km/h and 7km/h, that is, in the end nine samples were collected, separating the materials found in vegetable and mineral impurities.

The already separated samples were weighed and identified according to each collection speed and feeding rate. After the tests carried out, the information collected in the field was tabulated. We can see in Table 2 that the biometric analysis showed an average of 65.177t/ha.

To calculate the feeding rate, biometric data was used, multiplying the average production value by the machine's travel speed. Thus, having the feeding rate in kilos per second, calculations were also carried out to obtain the average weight of the samples collected during transshipment, as can be seen in Table 3.

To quantify mineral and vegetable impurities, the percentages of impurities found in the tests were calculated.

Analyzing Table 4, greater root uprooting can be seen when harvesting occurs at the highest speed, and with this, an increase in the amount of sand was obtained, increasing the level of impurities.

In the study, it was possible to observe that the processing capacity of the raw material during harvest did not change and when the harvesting speed increased, the feeding rate consequently increased. When harvesting at a speed of 7km/h, there was an increase in mineral impurities of 42% compared to harvesting at 5km/h.

Therefore, it can be concluded that the quality of the raw material is directly influenced by the increase in the harvester's travel speed, presenting an increase in the levels of mineral impurities. With an increase in these impurities in the raw material that will be delivered to the sugar and alcohol industry, damage may occur that will interfere with the quality of the sugar and consequently generate a reduction in the amount paid for it. It is worth mentioning that this impurity is also harmful to the harvester and equipment in the sugar and alcohol industry. Therefore, it is preferable that processing is carried out at the lowest speed of 5km/h, thus preserving the quality of the raw material.

Danilo Tedesco de Oliveira, Aline Spaggiari Alcântara, FCAV/Unesp; Edson Massao Tanaka, Eduardo Eugênio Smaniotto, Gilberto Saturninho Francisco, Vagner Varandas, Fatec “Shunji Nishimura”

Article published in issue 171 of Cultivar Máquinas