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Fundamental Studies on the Field Stripping System of Oil Palm Fruitlets
Dissertation Abstract:
In the present oil palm harvesting system, a fresh fruit bunch (FFB) is transported and sterilized in the mill as a whole material instead of the fruitlets only. This procedure has caused some problems such as extra costs due to transport and sterilization of the stalk, difficulty in heating the heavy bunch, and oil loss from absorption by the empty bunch.
To overcome these problems, the study attempted to separate the fresh oiI palm fruit lets from the cut spikelets in the field, so that only the fruitlets will be transported to the mill while their stalks will be left in the field as mulch. The steps in the proposed in-field stripping system were the red uction of the removal force of the fruitlet, preparation of the cut spike lets as threshed material, and detachment of loose fruitlets from the cut spike lets us ing a drum thresher.
To accomplish the in-field stripping process, attempts were made to: 1) identify effective treatments which may accelerate the loosening process offruitlets so that it can be stripped easily without deteriorating the oil quality; 2) establish design parameters for cutting the spikelets from the treated bunch by using a knife blade or a circular saw; and 3) develop an experimental drum thresher and study the effects of various design constraints on the th reshing performance. Bruise index, an indicator of the quality of stripped frui tlets, was developed. Some physical properties of the oil palm fruitlets pertaining to the design of the thresher were also identified.
The fruitlets abscission could be hastened by spraying ethephon on cut spike lets or brushing it on the cut stalk of FFB. This application had a significant effect on the percentage of detached fruitlets and the removal force of the fruitlet, but did not affect the development of free fatty acid (FFA). Low-speed cutting tests using a knife blade showed that the specific cutting force and energy for the stalk and spikelet were significantly influenced by the knife edges' angle (i.e., oblique, shear), but not by the cutting speed. Experiments using a circular saw showed that the total cutting power requirement for the bunch was directly proportional to the materials' thickness, feeding rate, and the rotational speed of the saw.
Tests on the performance of the experimental drum thresher showed that threshability increased by increasing the inner drum speed and the number of rubber teeth of the outer drum. The threshing power requirement was influenced by the rotational speed and the diameter of the inner drum and the feeding rate. The threshing operation slightly increased FFA content of the threshed fruitlets, however, it was still less than the five percent (maximum allowable content in traded oil). This showed that the FF A content was closely related to the bruise index of the fruitlets.
Based on the results of the study, it was suggested that the threshing machine should use an inner drum with a diameter of 16 cm at the speed of about 300 rpm and drum angle of about 2.5°. The rubber teeth arranged at 5 cm x I 0 cm would be suitable for various lengths of spikelets. Moreover, stripping of spikelets under these conditions produced more than 95 percent threshability, provided that the spikelets were taken from FFB treated with four grams of ethephon at 30 percent concentration and stored for 24 hours.