Effect of Processing Conditions on Yield of Screw Press Expressed Palm Oil

Transcription

1 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 5(4): Scholarlink Research Institute Journals, 2014 (ISSN: ) jeteas.scholarlinkresearch.com Journal of Emerging Trends Engineering and Applied Sciences (JETEAS) 5(4): (ISSN: ) Effect of Processing Conditions on Yield of Screw Press Expressed Palm Oil O. A. Adetola 1, J. O. Olajide 2, and A. P. Olalusi 1 1 Department of Agricultural Engineering, Federal University of Technology, Akure, Nigeria. 2 Department of Food Engineering, Ladoke Akintola University of Technology, Ogbomoso, Nigeria Corresponding Author: O. A. Adetola Abstract Investigations were carried out on the effect of processing conditions (sterilization time, digestion time and screw speed) on the efficiency a typical screw press machine. Palm fruits were collected, cleaned and sterilized for 30, 60 and 90 min; then digested for 4, 7 and 10 min and later pressed at a screw speed of 4, 10 and 16 rpm. The results show that increase in sterilization time and digestion time at optimum screw speed of 10 rpm generally increased the oil yield. The solid impurity content of the oil at 30 and 90 min sterilization was observed to be generally high. The solid impurity at 60 min sterilization time was observed to be low. Increase in digestion time increased the solid impurity at all sterilization times. The highest oil extraction ratio of 17.90% and oil extraction efficiency of 79.56% were obtained at the sterilization time of 60 min, digestion time of 10 min and screw speed of 10 rpm. For palm fruit processing, there is therefore the need to carefully select the processing conditions that will give the least solid impurity content of the oil as a measure of crude palm oil quality, highest oil yield and best oil quality. Therefore, there is need to conduct this research in order to determine the appropriate processing conditions in terms of sterilization time, digestion time and screw speed required for optimum oil yield and screw press operation which will in turn give maximum oil yield and more profit for palm oil processors and farmers. Keywords: palm fruit, processing conditions, oil yield, oil extraction ratio, screw speed. INTRODUCTION The oil palm (Elaeis guineensis Jacq.) originated in Africa where groves of wild palms still exist. Cultivated varieties are now grown, however, on plantations in the equatorial tropics in south East- Asia and South America as well as in Africa (PORIM, 1985). Processing of oil palm fruit into palm oil yields a lot of by-products including palm kernel, palm kernel cake, palm frond, palm bunch and palm trunk which have numerous domestic and industrial applications. Palm oil, the principal product of the crop, has a great number of uses. About 80% of production is destined for human consumption with the balance going to animal feed and to various industries (Babatunde, 1987). Palm oil production output in Nigeria is at low ebb. Nigeria has lost its premier position on the list of world major palm oil producers for the past two decades (Owolarafe et al., 2007). The cause of this poor Nigeria palm oil situation has been traced to lack of improved variety of palm fruit, land tenure system, and lack of appropriate processing technologies (Owolarafe et al., 2002). Palm fruits processing involved five basic operations; fruit sterilization, fruit loosening/stripping, fruit digestion, oil extraction and oil clarification (Taiwo et al., 2000, Owolarafe et al., 2002). Processing factors known to affect yield of oil include sterilization time, digestion time and applied pressure (Baryeh, 2001., Owolarafe et al., 2002). Increase in sterilization time and digestion time has been observed to increase oil yield. MATERIALS AND METHODS Palm fruit bunches were obtained fresh and processed immediately in order to get accurate results. The raw materials made use of were strictly Tenera variety of fresh palm fruit bunches obtained from Teaching and Research Farm, FUTA. Palm fruits were stripped from the fresh fruit bunches and washed to remove dirt and foreign matter present in the fruit mass. The 135 kg of the stripped freshly harvested fruits were sterilized at different times of 30, 60 and 90 min at the temperature range of o C. It was then transferred into a digester and digested for 4, 7 and 10 min. The resulting mash was transferred into an oil palm screw press operating at different speed of 4, 10 and 16 rpm using a 5 hp gear 243

2 motor. For the experiments carried out (see tables 1-2). Where t 1 = sterilization time of 30 min; t 2 = sterilization time of 60 min; t 3 = sterilization time of 90 min; T 1 = digestion time of 4 min; T 2 = digestion time of 7 min; T 3 = digestion time of 10 min; V 1 = screw speed of 4 rpm; V 2 = screw speed of 10 rpm; V 3 = screw speed of 16 rpm; TOS= time of sterilization; TOD= time of digestion and SS= screw speed. For each experimental run, 5.5 kg of digested palm fruit was fed into the hopper of the machine and the machine was operated and allowed to run. After each run, the following parameters were measured using electric balance. M 1 = the mass of the fresh fruit bunches M 2 = the mass of stripped fresh fruit M 3 = the mass of digested fruit (the mash) M 4 = the mass of the digested fruit fed into the machine and the hot water added for pressing. M 5 = the mass of the crude palm oil extracted. M 6 = the mass of the cake i.e. the nut and fibre mixture. M 7 = the mass of the oil extracted (after clarification). SIC= the mass solid impurity content of crude palm oil (in form of digested fibre). T = the time for pressing each experimental run in hour. Experimental Equipment and Instruments The experimental equipment and instruments include heating system, sterilizer, digester, stop watch, weighing scale and clarification tank. Performance Evaluation Parameters The Oil Extraction Ratio (OER) was calculated using equation (1). OER = (%) (PORIM, 1985) (1) The oil extraction efficiency (OEE) was calculated using equation (2). OEE = (%) (PORIM, 1985) (2) The percentage solid impurity content was calculated using equation (3). SIC = (%) (PORIM, 1985) (3) Effect of Time of Sterilization on Mass of Oil Extracted at different Screw Speeds Increase in the mass of oil extracted increases with the increase in time of sterilization since sterilization is a heating rendering and moisture absorption process which achieves the objectives of lowering the viscosity of oil as well as coagulation of protein. This stands to facilitate oil flow (Babatunde et al., 1988, Owolarafe et al., 2002).Figures 1, 2 and 3 show the graphs of the mass of oil extracted at sterilization time of 30, 60 and 90 min at constant time of digestion and shaft speed for all the experiments. The 244 results show that the mass of oil extracted increases as the sterilization time increases with the highest mass of oil extracted recorded at the sterilization time of 60 min, digestion time of 10 min and at the screw speed of 10 rpm for all the experiments. This is in agreement with the findings of other researchers on the effect of time of sterilization, digestion and screw speed on palm fruits: thus the degree of attainment of these objectives increases as sterilization time increases from 30 to 90 min (Owolarafe et al., 2002, 2007; Babatunde et al., 1988). The gradual decreases in the mass of oil extracted from 60 to 90min of sterilization may be due to excessive sterilization which might have caused fine fibrous materials to have been expressed with the oil. Hartley (1988) reported that solid impurity of 1% is desirable in crude palm oil to facilitate clarification. Oil containing high percentage solid impurity content severally resulted in heavy sludge and loss of oil to the sludge (Owolarafe, 1999). Effect of Time of Sterilization on Solid Impurity Content at different Screw Speeds It was also observed in figure 1, 2, and 3 that solid impurity of 1% is desirable in crude oil to facilitate clarification. Oil containing high percentage solid impurity generally results in heavy sludge and loss of oil to the sludge. It was observed that the minimum solid impurity content was attained at 60 min time of sterilization which will facilitate clarification thereby increasing the oil yield but very high at 30 min time of sterilization and high at 90 min time of sterilization. It could therefore, be stated that sterilization time of 60 min satisfy the condition of minimum solid impurity of sterilization. This is in agreement with the findings of Hartley, 1988 and Owolarafe, 1999 on the effect of time on solid impurity content: Hartley (1988) reported that solid impurity of 1% is desirable in crude oil to facilitate clarification. Oil containing high percentage solid impurity generally results in heavy sludge and loss of oil to the sludge (Owolarafe, 1999). Effect of Time of Digestion on Oil Extraction Ratio at different Screw Speeds Digestion is a wet comminuting process of size reduction that induces rupturing of oil cells and, in some cases, complete loss of cellular architecture (Owolarafe et al., 2002, 2007) to release oil. Figures 4, 5 and 6 show the graphs of oil extraction ratio at digestion time of 4, 7 and 10 min for all the experiments. It was observed that oil extraction ratio increases with increase in digestion time. The highest oil extraction ratio was recorded at 60 min sterilization, 10 min digestion and screw speed of 10 rpm. This is in agreement with the findings of other researchers on the effect of time of sterilization, digestion and screw speed on palm fruits. Adequate digestion also ensures homogenous mass devoid of undigested fruits, which enhances the chance of

3 obtaining maximum oil yield (Owolarafe et al., 2007; STORK, 1960). The extent of digestion of the fruit determines the degree of exposure of the oil cells (Owolarafe, 1999). Effect of Screw Speed on Oil Extraction Efficiency at Different Time of Digestion The amount of expected oil (AEO) used in this research is with reference to Robbelen et al., 1989 reported that one oil palm bunch provides up to 20 to 24% palm oil and 2 to 3% of palm kernel oil. Figures 7, 8 and 9 show the graphs of oil extraction efficiency at screw speed of 4, 10 and 16 rpm at constant time of sterilization and digestion within the groups. The results show that the maximum oil extraction efficiency was obtained at the screw speed of 10 rpm, 60 min sterilization time and 10 min of digestion which implies that this is the optimum screw speed for the screw press to operate efficiently within least choking or jamming but the 4 and 16 rpm were characterized by frequent jamming or choking. This is in agreement with findings of other researchers on effect of screw speed on oil extraction efficiency (PORIM, 1985). The input shaft speed is 200 rpm giving a screw speed of 10 rpm (PORIM,1985). Table 1: Time of Sterilization of Fresh Fruit at 30 and 60 min with Time of Digestion of 4, 7 and 10 min at different Screw Speed of 4, 10 and 16 rpm Experiment Time of Time of Screw Speed Sterilization Digestion (rpm) (min) (min) E1 = t 1T 1V E2 = t 1T 1V E3 = t 1T 1V E4 = t 1T 2V E5 = t 1T 2V E6 = t 1T 2V E7 = t 1T 3V E8 = t 1T 3V E9 = t 1T 3V E10 = t 2T 1V E11 = t 2T 1V E12 = t 2T 1V E13 = t 2T 2V E14 = t 2T 2V E15 = t 2T 2V E16 = t 2T 3V E17 = t 2T 3V E18 = t 2T 3V Effect of Screw Speed on Solid Impurity Content at Different Time of Digestion on the effect of time of sterilization and digestion on solid impurity content of palm fruits (PORIM, 1985 and Hartley, 1988). The input shaft speed is 200 rpm giving a screw speed of 10 rpm (PORIM,1985). Hartley (1988) reported that solid impurity of 1% is desirable in crude palm oil to facilitate clarification Table 2: Time of Sterilization of Fresh Fruit at 30 and 60 min with Time of Digestion of 4, 7 and 10 min at different Screw Speed of 4, 10 and 16 rpm Experiment Time of Time of Screw Sterilization (min) Digestion (min) Speed (rpm) E19 = t 3T 1V E20= t 3T 1V E21= t 3T 1V E22 = t 3T 2V E23= t 2T 2V E24 = t 3T 2V E25= t 3T 3V E26= t 3T 3V E27= t 3T 3V Figure 1: Effect of time of sterilization on mass of oil extracted at screw speed of 4 rpm Figures 10, 11 and 12 show the graphs of solid impurity content at screw speed of 4, 10 and 16 rpm at constant time of sterilization and digestion within the groups. The results show that the screw speed has no significant influence on the solid impurity content produced but it is largely dependent on the time of sterilization and digestion respectively. The least solid impurity content was attained at sterilization time of 60 min and digestion time of 4 min which satisfy the condition of minimum solid impurity. This is in agreement with the findings of other researchers 245 Figure 2: Effect of time of sterilization on mass of oil extracted at screw speed of 10 rpm

4 Figure 3: Effect of time of sterilization on mass of oil extracted at screw speed of 16 rpm Figure 7: Effect of screw speed on oil extraction efficiency at 4 min time of digestion Figure 4: Effect of time of digestion on oil extraction ratio at screw speed 4 rpm Figure 8: Effect of screw speed on oil extraction efficiency at 7 min time of digestion Figure 5: Effect of time of digestion on oil extraction ratio at screw speed 10 rpm Figure 9: Effect of screw speed on oil extraction efficiency at 10 min time of digestion Figure 6: Effect of time of digestion on oil extraction ratio at screw speed 16 rpm 246 Figure 10: Effect of screw speed on solid impurity content at 4 min time of digestion

5 Babatunde, O. O., Ajibola, O. O. and Ige, M. T A Modified Process for Low Cost Palm Oil Extraction. J. Food Science Technology, 25(2), Baryeh, E.A Effect of palm oil processing parameters on yield. J. Food Eng., 48, 1-6. Hartley C. W. S The Oil Palm. Longman Press, London, UK, Pp. 78 Figure 11: Effect of screw speed on solid impurity content at 7 min time of digestion Owolarafe O. K Performance evaluation of the digester-screw press for oil palm fruit processing. M.Sc. Thesis, Obafemi Awolowo University, Ile-Ife, Nigeria. Owolarafe O. K., Faborode M. O., and Ajibola O. O Comparative evaluation of the digesterscrew press and hand-operated hydraulic press for oil palm fruit processing. J. Food Eng.,52, Owolarafe O. K., Olabige M. T., and Faborode M. O Macro-structural characterisation of palm fruit at different processing conditions. J. Food Eng.,79, PORIM Palm Oil Factory Process Handbook Part 1. General Description of the Palm Oil Research Institute of Malaysia. Pp Figure 12: Effect of screw speed on solid impurity content at 10 min time of digestion CONCLUSION The study revealed that pressing at optimum shaft speed of 10rpm, increase in sterilization time, and digestion time increased the oil yield, but this was accompanied by increase impurity content which may eventually reduce the quality of the final clarified oil. Thus a balance has to be struck between the yield of crude oil and impurity content of the oil and this calls for adequate selection of combination of processing conditions and monitoring of the whole process. Therefore, 60 min sterilization time, 10 min digestion time and 10 rpm screw speed has been discovered to give the highest oil yield with minimum solid impurity content. Robbelen, G., Downey, R.K. and Ashri, A Oil Crops of the World. McGraw-Hill publishing Company, New York. Pp STORK The development of free fatty acid on palm oil. Stork palm oil review. Gerb-Stork press,wageningen, the Netherland. Taiwo, K. A., Owolarafe, O. K., Sanni, L. A., Jeje, J. O., Adeloye, K., and Ajibola, O. O Technological assessment of palm oil production in Osun and Ondo States of Nigeria Technovation, 20, LIMITATIONS i. The use of precise equipment (sterilizer, digester and boiler) were not easy to come by. ii. The oil palm fruit used is restricted to Tenera specie. REFERENCES Babatunde, O. O Sterilization and mechanical digestion of oil palm fruit, unpublishedph.d. Thesis, Obafemi Awolowo University, Ile-Ife, Nigeria. 247