Design, Development and Testing of a Screw Press Expeller for Palm Kernel and Soybean Oil Extraction Adesoji M. Olaniyan1*, Kamaldeen A. Yusuf2, Adebayo L. Wahab3 and Kunle O. Afolayan4 1,2,3,4
Department of Agricultural and Biosystems Engineering, Faculty of Engineering and Technology, University of Ilorin, P. M. B. 1515, Ilorin 240003, Kwara State, Nigeria *Corresponding author. E-mail: [email protected]
Abstract Vegetable oils and fats have gained popularity in food, cosmetic, soap, pharmaceutical and medical industries for the production of cooking oil and magarine, pomade, toilet soaps, drugs and medical ointments respectively. Recently, they have found their uses in energy and automotive industries as biodiesel and engineering industry as cooling fluid in machining process and lubricants for machine components. The objectives of this work are: to design a small scale screw press oil expeller for palm kernel (Elaeis guinensis J) and soybean (Glycyrrhza lepidota) oil extraction; to fabricate the components of the expeller based on the design specifications and; to test the expeller after fabrication and assembly of the components. While in designing and in material selection, consideration was given to the techno-economic status of the micro and small scale vegetable oil processors who are the intended users of the machine. The functional parts of the machine included barrel, worm shaft, gear reduction box, prime mover, oil outlet, cake outlet, hopper, pulley, transmission belts and bearings. The worm shaft is at an increasing diameter while the screw system is at a decreasing pitch - a combination that is essential for obtaining maximum pressure for oil extraction and cake extrusion process. In operation, the gradually built-up pressure along the worm shaft travel conveys, crushes, grinds, presses and squeezes oil out of the seeds into the oil outlet via the oil channel. The residual cake from where the oil is extracted is extruded out of the cake outlet in form of flakes. The expeller was tested and results showed a high oil yield and extraction efficiency with low extraction loss. Powered by a 15 hp three-phase electric motor, the expeller has a production cost of $1200. A cottage palm kernel and soybean oil extraction plant based on this technology can provide employment for 3 persons at the same time producing oil for food, soap and cosmetic industries and cake for livestock feed industry at low costs. Key words: Design, Screw press expeller, Worm shaft 1.
Palm kernel (Elaeis guinensis J) and soybean (Glycyrrhza lepidota) oil are rich in protein and are therefore used in food industry as good sources of cooking oil. The residual cakes from which the oil is extracted are also used as ingredients in livestock feed production. These products, in developing countries, have a lot of potential for export and therefore serve as a foreign exchange earner. In addition, palm kernel oil (henceforth referred to as PKO) is used in chemical industries for the production of fatty acids and other products while soybean oil (henceforth referred to as SBO) is used specially for coating fried meat in domestic food
preparation. In Nigeria, locally-extracted PKO, commonly known as Adin Eyan among the Yorubas, is used for the production of local soap (ose dudu), medicine, and local pomade (adi agbon). The traditional method of PKO extraction in Nigeria is known as heat rendering process. In this method, the kernels are fried and roasted in a pot placed over firewood and the oil is expelled by dripping. This method is time consuming, drudgery-prone, involves heat hazards, and grossly inefficient. Apart from this, the oil extracted by this method is very poor in quality and is, in most cases, not used for consumption. Akinoso (2006) studied the effects of storage on quality of palm kernel and sesame oils while the effect of postharvest and pre-extraction treatments on Niger seed processing in a small expeller were investigated by Ayenew (2000). Oil expression from palm kernel was modeled by Akinoso et al. (2006) while Alonge et al. (2003) investigated the effects of some processing factors on groundnut oil extraction. They discovered that heating temperature, moisture content of seeds, and other forms of postharvest pretreatments and extraction conditions had effects on yield, efficiency of extraction and quality attributes of oil. Vegetable oil expellers are of different types and forms based on design, construction and the raw materials they are to process. Alonge et al. (2004) develop a small scale screw press for groundnut oil extraction while a mechanical expression rig was developed by Olaniyan and Oje (2007) for shea butter extraction. Olaniyan (2010) developed a manually-operated expeller for groundnut oil extraction and the performance of a PKO extracting machine was evaluated Olawepo-Olayiwole and Balogun (2004). In most PKO and SBO extraction mills, large and commercial scale industrial expellers are used; such expellers are expensive, involve high level technology which cannot be afforded by small scale and low income oil millers. In order to assist the small scale oil millers in the rural communities, small scale screw press oil expellers need to be designed, built and integrated into the vegetable oil industry. Therefore, the objective of this present study is to design, develop and test a small scale screw press oil expeller for PKO and SBO extraction in the rural communities. This would go a long way in ensuring food security, alleviating poverty, and creating employment for the teaming youth in the communities. 2.
Machine Description and Working Principles
The screw press oil expeller consists of the following components: worm shaft, cylindrical barrel, feeding hopper, gear box, cake outlet, cake tray, oil outlet, and main frame. The cylindrical barrel was made from a mild steel pipe of length 500 mm, inside diameter of 100 mm and thickness 15 mm. The worm shaft was made from a mild steel solid rod of diameter 100 mm and length 730 mm, which was machined on the lathe at a decreasing screw pitch and decreasing screw depth. The worm shaft is housed in the cylindrical barrel at a clearance of 1.5 mm between the screw diameter and inside diameter of the barrel. In operation, the oilseed is introduced into the machine through the feeding hopper; the machine conveys, crushes, grinds and presses the oilseed inside the cylindrical barrel with the aid of the worm shaft until oil is squeezed out of the seed. The oil extracted is drained though the oil channel into the oil tray where it is collected; the residual cake is discharged at the cake outlet and collected at the cake tray. Shown in Fig. 1, the machine is powered by a 15 hp three-phase electric motor and has a
production cost of $1200 with the construction materials being locally available at affordable costs.
FIGURE 1: Isometric view of the Screw Press Oil Expeller: 1-Electric motor; 2-Transmission belt, 3-Pulley; 4-Gear box; 5-Coupling; 6-Central shaft; 7-Feeding hopper; 8-Cylindrical barrel; 11-Cake outlet; 12-Frame; 13-Cake tray; 14-Oil tray 3.
Design Considerations and Calculation Procedures
While designing the machine, consideration included: high oil yield, high extraction efficiency, low extraction loss, quality of oil, quality, availability and cost of construction materials. Other considerations included the desire to design the cylindrical barrel to accommodate the require quantity of raw materials (palm kernel and soybean). Also considered is to design the worm shaft to ensure maximum conveyance, crushing, grinding and pressing of the palm kernel and soybean. Consideration was also given for a strong main frame to ensure structural stability and strong support for the machine. 3.2.
3.2.1. Design of Worm Shaft of the Expeller The worm shaft is the main component of the expeller and is acted upon by weights of material being processed, pulley and screw thread. In operation, the worm shaft conveys, crushes, presses and squeezes the material (palm kernel and soybean in this case) for oil extraction. Therefore, in order to safeguard against bending and torsional stresses, the diameter of the
shaft was determined from the equation given by Shigley and Mischke (2001) and Khurmi and Gupta (2008)as: ds =
16 T 0.27 π δ0
where, ds is diameter of the screw shaft, T is the Torque transmitted by the shaft, and δo is the yield stress for mild steel. Given that T = 928.571 Nm and δo = 200 N/mm2; hence, ds = 44.407 mm. Therefore, a mild steel rod of diameter 50 mm was used for the worm shaft. 3.2.2. Design of the Screw Thread The worm shaft is essentially a tapered screw conveyor with the volumetric displacement being decreased from the feed end of the barrel to the discharge end. In this way, the seeds are subjected to pressure which expels oil from them as they are propelled forward by the screwing process (Sivakumaran et al., 1985). The screw threading system was designed as a step up shaft diameter and decreasing screw depth using the expression in Eqn. 2 below as: Un = a+ n-1 d
where, Un is the screw depth at the discharge end, a is the screw depth at the feed end, n is the number of screw turns, and d is the common difference between next successive screw depths. Given that Un = 5 mm, a = 25 mm, and n = 9; hence, d = -2.5 mm. Therefore, the screw depth would be decreased consistently by 2.5 mm from the feed end to the discharge end of the barrel. 3.2.3. Design of the Load that can be lifted by the Screw The load that can be lifted by the screw was determined from the equations given by Hall et al. (1961) as: We = T
(1- μ tanθ Cosα)
α = tan-1 (tanθn Cosθ )
where, W e is the load that can be lifted by the screw, T is the Torque transmitted by the screw shaft, Dm is the mean thread diameter, μ is the coefficient of friction, n is the thread (lift) angle, and is the tapering angle. Substituting T = 928.571 Nm, Dm = 75 mm, = 30, μ = 0.15, and n = 150; hence, α = 14.980 and W e = 72.88 kN. Therefore, 7.43 kg of seed can be processed at a time. 3.2.4. Design of the Pressure to be Developed by the Screw Thread The pressing area (Hall et al., 1961) and the pressure developed by the screw thread were determined by Eqn. 5 & 6 respectively as:
Ap = πDm nh Pr =
where, Pr is the pressure developed by the screw thread, Ap is the pressing area, and h is the screw depth at the maximum pressure (discharge end). Substituting π = 3.142, Dm = 75 mm, n = 9, h = 5 mm, and We = 72.88 kN; hence, Ap = 10602.88 mm2 and Pr = 6.87 N/mm2. Therefore, a pressure of 6.87 MPa would be available for expelling oil from the seeds during operation. 3.2.5. Design for the Pressure of the Barrel The pressure that can be withstood by the barrel was determined by the equation given by Ryder (1985) and Khurmi and Gupta (2008) as: Pb =
where, Pb is the pressure to be withstood by the barrel, t is thickness of the barrel, δa is allowable stress = 0.27δo, δo is the yield stress of mild steel, and Di is the inside diameter of the barrel. Substituting t = 15 mm, δo = 200 N/mm2, and Di = 100 mm; hence, δa = 54 N/mm2 and Pb = 16.20 N/mm2 or 16.20 MPa. This means that the pressure that the barrel can withstand (16.20 MPa) is greater than the pressure developed by the screw thread for oil extraction (6.87 MPa). Therefore, the barrel will withstand the extraction pressure without bursting. 3.2.6. Design for the Capacity of the Expeller The theoretical capacity of the expeller was determined using a modified form of the equation given by Onwualu et al. (2006) as: Qe = 60
D2s - d2s Ps Ns φρ
where, Qe is the theoretical capacity of the expeller, Ds is the diameter of the screw thread, ds is the base diameter of the screw shaft, Ps is the screw pitch, Ns is the rotational speed of the screw (worm) shaft, φ is filling factor, and ρ is the bulk density of palm kernel. Substituting Ds = 100 mm, ds = 50 mm, Ps = 50 mm, Ns = 90.63 rpm, φ = 0.8, and ρ = 740 kg/m3 into Eq. 8; hence, Qe = 948.249 kg/h. 3.2.7. Design for the Power Requirement of the Expeller The power required to drive the expeller was calculated using a modified from Onwualu et al. (2006) as: Pe = 4.5 Qv ls ρg F
where, Pe is the power required to drive the expeller, Qv is the volumetric capacity of the worm shaft, ls is length of worm shaft, g is the acceleration due to gravity, and F is the material factor.
Substituting Qv = 1.281 m3/h, ls = 500 mm, g = 9.81 m/s2, and F = 0.4 into Eqn. 9; hence, Pe = 8.369 kW. The power of the electric motor to drive the expeller was estimated using the equation given by Onwualu et al. (2006) below as: Pm =
where, Pm is the power of the electric motor and is the drive efficiency. Given that = 75 % or 0.75; hence, Pm = 11.159 kW or 14.959 hp. Therefore, a 15 hp three-phase electric motor was selected to drive the expeller. 4.
Materials Selection and Fabrication of the Machine Components
Fig. 2 shows an orthographic view of the expeller. The hopper was fabricated from a standard length of 1.5 mm thick mild steel sheet. Four pieces of dimension 312 x 290 x 69 mm were cut from the mild and welded together to form hopper. The worm shaft was fabricated from a mild steel rod of diameter 100 mm and length 730 mm which was machined on the lathe to 50 mm base (shaft) diameter. Thereafter, the screw thread was machined at a decreasing screw depth from 25 mm to 5mm thereby forming a tapered screw conveyor of nine screw turns. The barrel was fabricated from a mild steel pipe of 100 mm internal diameter, 15 mm thickness and 700 mm long which was cut and machined to 500 mm length. Using oxyacetylene flame, a slot of 60 x 60 mm was made on the upper side of the barrel for the hopper base. 20 narrow slots were made on the lower portion of the barrel to serve as drainage channels for the expelled oil. The main frame was made from an angle iron of dimension 50 x 50 x 4 mm which was cut to the required dimensions and welded together. Fabrication process included: marking out, machining, cutting, joining, drilling and fitting. The workshop tools and machines used included: scriber, steel rule, compass, centre punch, treadle-operated guillotine for cutting and welding machine for joining. The specification of construction materials is shown in Table 1. 5.
Materials and Methods used for Testing
Palm kernel and soybean were obtained from a produce merchant in Ilorin environment. The seeds were cleaned, weighed and prepared ready for oil extraction. The expeller was set into operation and known weights of each were fed into the machine through the feeding hopper. The worm shaft conveyed, crushed, squeezed and pressed the seeds in order to extract the oil. The oil extracted and the residual cake (palm kernel cake, PKC and soybean cake, SBC were collected and weighed separately. From the values obtained, oil yield, extraction efficiency and extraction loss were calculated according to Olaniyan and Oje (2007) and Olaniyan and Oje (2011) as: OY =
100WOE WOE + WRC
100 WFS - (WOE + WRC ) WFS
where, OY, OE, and EL are oil yield, extraction efficiency and extraction loss respectively in %; WOE, W RC and W FS are weights of oil extracted, residual cake and feed sample respectively in g and x is the oil content of seed in decimal. Each test was carried out in triplicates.
FIGURE 2: Orthographic Front view of the Screw Press Expeller TABLE 1: Materials for Construction of the Screw Press Expeller and their Specifications Materials Mild steel sheet Mild steel rod Mild steel pipe Mild steel coupling bolt Mild steel angle iron Roller bearing Cast iron pulley Cast iron pulley V – belt Bolts and nuts Welding electrode 6.
Specifications 1.5 mm thickness, standard size Φ 100 mm, length 730 mm Φ 100 mm, thickness 15 mm, length 500 mm Φ 22.5 mm, Φ 40 mm 50 x 50mm x 4, standard length Φ 40 mm Φ 260 mm Φ 58 mm B 65 M 22 Gauge 12 mild steel
Quantity 2 1 1 1, 1 1 2 1 2 2 25 1 packet
Results and Discussion of Testing
The average oil yield, extraction efficiency and extraction loss were 13.48, 22.79 and 7.41 % respectively for palm kernel while those of soybean were 9.47, 36.55 and 7.95 % respectively. Olaniyan and Oje (2007), Olaniyan (2010) and Olaniyan and Oje (2011) used these criteria for shea butter and castor oil extraction respectively. The data obtained from the tests shows that the expeller was able to extract some of the oil from the seeds but there is still plenty of scope
for improvement. An improvement in the design of the worm shaft of the expeller is expected to improve the oil yield and extraction efficiency; hence, this is highly recommended. 7.
A screw press expeller was designed, constructed and tested for palm kernel and soybean oil extraction. The expeller was simple enough for local fabrication, operation, repair and maintenance. Powered by a 15 hp three-phase electric motor, the expeller has average oil yield and extraction efficiency of 13.48 and 22.79 % respectively from palm kernel and 9.47 and 36.55 % respectively from soybean with a production cost of USD1200. The expeller can be used for small scale palm kernel and soybean oil extraction in the rural and urban communities. A cottage palm kernel and soybean oil processing plant based on this technology can provide employment for at least two persons at the same time providing palm kernel and soybean oil at affordable costs for rural dwellers palm kernel cake and soybean cake for livestock feed mill. An improvement in the design of the worm shaft of the expeller is expected to improve the oil yield and extraction efficiency; hence, this is highly recommended. References Akinoso, R. (2006). Effects of moisture content, roasting duration and temperature on oil yield and quality of palm kernel (Elaeis guineensis) and sesame (Sesamium indicum) oils. PhD Thesis, Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria. Akinoso, R., Igbeka, J. C., Olayanju, T. M. A., & Bankole, L. (2006). Modelling of oil expression from palm kernel (Elaeis guineensis). Agricultural Engineering International: The CIGR Journal of Scientific Research and Development, 8, 1-8. Alonge, A. F., Olaniyan, A. M., Oje, K., & Agbaje, C. O. (2004). Development of a screw press for village level groundnut oil extraction. Journal of Agricultural Engineering and Technology, 12, 46-53. Ayenew, M. (2000). Processing of Niger seed in small mechanical expeller as affected by postharvest and pre-extraction treatments. Agricultural Mechanization in Asia, Africa and Latin America, 31 (4), 62 – 66. Hall, A. S., Holowenko, A. E., & Laughlin, H. G. (2002). Schaum’s outline series theory and problems of machine design. (1st ed.). New York: McGraw-Hill Companies, Inc., (Chapter 12). Khurmi, R. S., & Gupta, J. K. (2008). A textbook of machine design. (14th ed.). New Delhi: Eurasia Publishing House (PVT) Ltd., (Chapters 7 & 14). Olaniyan, A. M., & Oje, K. (2007). Development of mechanical expression rig for dry extraction of shea butter from shea kernel. Journal of Food Science and Technology, 44 (5), 465-470. Olaniyan, A. M. (2010). Development of a manually operated expeller for groundnut oil extraction in rural Nigerian communities. Asia-Pacific Journal of Rural Development, 20 (1), 185-201.
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