Optimization of Process Parameters of a Conductive Rotary Dryer for Gari Production

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1 Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 6(7): Scholarlink Research Institute Journals, 2015 (ISSN: ) jeteas.scholarlinkresearch.com Journal of Emerging Trends Engineering and Applied Sciences (JETEAS) 6(7): (ISSN: ) Optimization of Process Parameters of a Conductive Rotary Dryer for Gari Production L. A. Sanni, O. O. Odukogbe, M. O. Faborode, R. O. Ibrahim Department of Agricultural and Environmental Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria. CorrespondingAuthor: L. A. Sanni Abstract In this study, the Taguchi method was used to optimize the parameters of a conductive rotary dryer which was developed for the roasting of wet cassava meal (Manihot esculenta Crantz) for gari production. The optimum levels of batch quantity, vapour extraction rate and drum, at which good quality gari was produced were 5 kg, m 3 /s and 190 o C respectively. Both signal-to-noise ratio (S/N) and analysis of variance (ANOVA) showed that the three parameters respectively contributed %, % and % to the quality characteristic of the gari with at least 99 % confidence. By increasing the drum from 190 o C to 200 o C at batch quantities of 5 kg and 6 kg, the swelling index of the gari increased from 2.63 to 3.11 and 3.20 respectively. The use of the conductive rotary dryer for roasting gari removed most of the limitations associated with the traditional method. By scaling up the capacity of the dryer, it can fit into an industrial process line for commercial production of gari, and contribute to regional food security. Keywords: Taguchi method, optimization, process parameters, conductive rotary dryer, gari INTRODUCTION Cassava (Manihot esculenta Crantz.) is a major food crop and it supplies about 70% of the daily calorie requirement for millions of people in Nigeria (Oluwole et al., 2004). It is widely reported that over 500 million people around the world derive their daily carbohydrate intake from cassava (Cock, 1985; FAO, 2000; Udofia et al., 2010), and the industrial application of the crop is also growing, due to the increasing demand for cassava-based products such as glucose syrup used by pharmaceutical companies, and cassava flour used as substitute for wheat flour in confectionaries. Nigeria is the largest producer of cassava in the world with an estimated annual production of between 34 and 37 million metric tons in 2002 (FAO, 2004; FAO, 2006). Estimate of cassava use in Nigeria shows that about 84% of annual production in 2001, equivalent to 28.9 million metric tons was processed into various food forms for local consumption (Phillips et al., 2004). Among many of the staple foodstuffs produced from cassava, gari is by far the most popular (Oluwole et al., 2004). Gari is a toasted granular product that is readily consumed as a snack by soaking in water in combination with pea-nuts, sugar and milk. It is also consumed as dough called eba in Yoruba language, with rich soup which provides additional nutrients (Irtwange and Achimba, 2009). According to Nweke et al. (2002), gari is produced traditionally by peeling and washing fresh cassava tubers which are grated into a watery pulp and packed in clean perforated polyethylene bags. The grated mash is left to ferment in the bags for a few days after which they are placed under a press to be dewatered. The pressed cakes of cassava are manually pulverized and sifted using a hand-woven sieve to produce a wet meal of between % moisture content (CIGR, 1999). The wet meal is toasted on a hot frying pan, to produce a gelatinized, dried and ready-to-eat meal a process known as garification (Achinewhu et al., 1998). High quality gari should have maximum moisture content of 11 % wet basis, and when soaked in water its swelling capacity should be at least three times its initial volume (SON, 2004). Challenges with Traditional Method of Gari Production Despite many research efforts to mechanize the roasting of gari (Igbeka, 1995), the process is still carried out by local processors who use the traditional method in many parts of Nigeria (Ajibola et al., 1998). Survey of cassava processing centers in Southwestern Nigeria Sanni (2014), shows that an open metallic tray (round or square in shape) made from mild steel sheet is placed on a firewood stove and heated to a of 180 o C 220 o C depending on the calorific value of the wood and the local weather. A batch of the wet cassava meal, weighing between kg is poured on the hot tray and by conduction the activation energy required for gelatinizing and drying the cassava meal is absorbed. The processor uses a wooden paddle or short broom to stir the cassava meal in order to allow for uniform 255

2 heat distribution and breaking of unwanted cassava lumps. Because the vapor extraction takes place by natural convection, the drying of the cassava meal is affected by the local atmospheric air condition (especially air relative humidity and velocity). After about 25 to 40 minutes, the cassava is dried to 11 % (wet basis) or below and the gari is evacuated and cooled before bagging. The quantity of gari recovered is generally about half the initial mass of the wet meal introduced (Sanni, 2014). During roasting, the pan is regulated by removal or addition of firewood. Other limitations of the traditional method are: continuous stirring and prolonged exposure of the handler to heat and smoke from the fire place, exposure of the cassava meal to contamination from the environment and corrosive effect of the frying pan, environmental pollution due to use of firewood, limited quantity of cassava meal handled per batch and spillage of the cassava meal in the process of stirring. To mitigate the problems associated with the traditional method of roasting and increase the capacity for commercial production of gari, a conductive rotary dryer (CRD) was designed and constructed in the Department of Agricultural and Environmental Engineering of Obafemi Awolowo University, Ile-Ife, Nigeria. Plate 1 shows a typical traditional method of roasting gari and Plate 2 shows the CRD used for the study. Experiments carried out were aimed at optimizing the performance of the dryer with a view to industrializing gari production (Sanni, 2014) Plate 1: Popular traditional method of roasting gari MATERIALS AND METHODS The Taguchi method was used to study the effects of four process parameters namely, shape of flights in the drum, quantity of wet cassava meal fed into the drying chamber, rate of vapor extraction from the drying chamber and drum. Each parameter was varied at two levels as presented in Table 1 (Akhyar et al., 2008). Table 1: Four process parameters at two levels each Symbol Process Unit Level 1 Level 2 Parameters A Flight shape - Straight Curved B Batch quantity kg 5 8 C Vapour m 3 /s extraction rate D o C Using the Taguchi array selector, an L8 orthogonal array was chosen for the experimental investigations. This implied that eight drying experiments were sufficient to study the effects of the four parameters on the quality of gari produced in the CRD. The use of the L8 experimental design was justified by the fact that the degree of freedom of the L8 orthogonal array (DF orthogonal array = 7) was greater than that of the four process parameters that were varied at two levels each (DF process parameters = 4). The experimental design used for the study is presented in Table Table 2: Experimental layout of the L8 garification experiments Number of Experiment Flight shape Batch quantity Vapor extraction rate 1 Straight Straight Straight Straight Curved Curved Curved Curved Quality Characteristic and the Taguchi Loss Function Studies have shown that swelling index (SI) of gari is a good quality characteristic which measures how gelatinized and dried the gari is (Ajibola et al., 1987). When soaked in water, high quality gari is expected to swell well beyond its initial volume and previous works have shown that the swelling index of gari can vary between 2.0 and 4.0 depending on the cassava cultivar and processing method used (Irtwange and Achimba, 2009; Owuamanam et al., 2010; Apea-Bah et al., 2009). Each of the eight drying experiments outlined in Table 2 above was run for 35 minutes at the end of which the swelling index of the gari was determined. The swelling index (SI) of the samples was determined by the method of Apea-Bah et al. (2009) with slight modification. At the end of each experiment a volume of 18 ml of the gari was introduced into a 100 ml measuring cylinder. The cylinder was filled with distilled water to the 100 ml

3 mark and shaken for proper mixture. The solution was allowed to settle for 5 minutes before shaking again. The intermittent shaking and settling lasted for 20 minutes and after the last settlement, the final volume of the cassava meal was recorded. The swelling index for each sample was calculated as: The Taguchi loss function was determined according to the method used by Kamaruddin et al. (2004) and Esme (2009). The relationship between the swelling index and quality of gari is that, the higher the swelling index the better the quality. Therefore the Taguchi loss function which is equivalent to the mean squared deviation (MSD) was based on the-largerthe-better and the following mathematical expression was used to calculate the corresponding signal-tonoise ratio (SN) for each experiment: (i) (ii) where, n = number of experiments in the orthogonal array y i = swelling index of the dried cassava from the i th experiment An estimate of the swelling index of the gari at the optimum parameter levels was predicted using the following regression equation (Kamaruddin et al., 2004). (iii) y opt = predicted value of swelling index when the optimal levels of parameters are used = grand mean of quality characteristic parameter A at its optimum level parameter B at its optimum level parameter C at its optimum level parameter D at its optimum level RESULTS AND DISCUSSION The swelling index and corresponding S/N ratio for each experiment are summarized in Table 3 and the S/N ratio analysis and the corresponding values of swelling index for each parameter at the two levels are presented in Table 4. Table 3: S/N responses to swelling index of gari from L8 experiments Exp. No. Code Flight shape Batch quantity Vapour extraction rate Moisture content Swelling index 1 A1B1C1D1 Straight A1B1C1D2 Straight A1B2C2D1 Straight A1B2C2D2 Straight A2B1C2D1 Curved A2B1C2D2 Curved A2B2C1D1 Curved A2B2C1D2 Curved The parameter level with the highest S/N ratio is the optimum and the difference between the highest and lowest S/N ratios indicates the extent of its effect on the swelling index of the gari. As shown in Table 4, the drum has the greatest effect with S/N difference of 3.16, followed by the batch quantity and vapor extraction rate with S/N differences of 2.52 and S/N ratio 1.58 respectively. The shape of flight used has a much lower S/N difference of 0.02 which is an indication that its effect on the swelling index of gari is not significant. However the S/N ratio analysis shows that the optimum levels at which the four CRD parameters should be combined for best performance is A 1 B 1 C 1 D 2 as shown in Figure 1. Table 4: S/N responses to swelling index of gari produced in the CRD CRD Parameter Symbol Average S/N Ratio Parameter Shape of flight A 4.92 a Level 1 Level 2 b 1.89 Batch quantity B 6.17 a Vapor extraction C b a b Average Grand Mean S/N: SI: Difference of S/N Ranking th nd rd D a b st a Highest value of S/N ratio indicate the optimum level of each parameter: A 1 B 1 C 1 D 2 b Corresponding values of swelling index of gari at optimum levels of parameters 257

4 S/N Ratio for swelling index A1A2 B1 B2 C1 C2 D1D2 CRD Process Parameter Levels Average Figure 1: Graph of effects of CRD parameters on the swelling index of gari The figure shows that batch quantity of 5 kg, vapor extraction rate of m 3 /s and drum of 190 o C are optimal for proper roasting of gari. The S/N ratio line for shape of flight did not deviate from the mean significantly, meaning that shape of flight did not significantly affect the swelling index of gari in the CRD. Only batch quantity, vapor extraction rate and drum have main effects on the S/N ratio roasting process. Production cost can therefore be reduced by removing the flights from the CRD without affecting the quality of the gari. The analysis of variance (ANOVA) in Table 5 below corroborates the S/N analysis. It shows that drum and batch quantity have significant effects with F-values of 7.22 and 4.22 respectively at 99% confidence. The contributions of each parameter to the performance of the dryer in order of strength are % from drum, % from batch quantity, % from vapor extraction rate and only 1.47 % from flight shape Table 5: Result of ANOVA on the swelling index of gari Parameter Process Degree of Sum of Mean F Contribution Code Parameter Freedom Square Square A Type of flight B Batch quantity * C Vapour extraction Rate D * Error Total *At least 99% confidence process. The process was therefore improved upon by By substituting the corresponding values of swelling index from Table 4 into Equation (iii), an optimum swelling index of 2.63 was estimated. Although the swelling index falls within the range of established in previous works, there is still room to increase the value by improving the cassava roasting removing the flights from the drum and slightly increasing the drum from 190 o C to 200 o C. To confirm the effects of the changes, two new experiments were conducted in line with the optimum parameter levels and the results are recorded in Table 6 Table 6: Result of experiments to confirm process improvement Exper Flight Batch Vapor extraction Swelling Moisture iment shape quantity rate index content At batch quantity of 5 kg and 6 kg with other parameters held at the optimal levels, the swelling index of the gari increased from 2.63 to 3.11 and 3.20 respectively. The removal of flights and slight increase of the drum therefore caused an improvement in the performance of the conductive rotary dryer. CONCLUSION The outcome of the study shows that the conductive rotary dryer improved the process of gari production when compared with the popular traditional method. While removing the disadvantages associated with the traditional roasting method, the use of the conductive rotary dryer increased the quality of gari produced. The development of the conductive rotary dryer therefore promises to increase the production capacity of local cassava processing plants and thus boost food security and contribute to poverty alleviation in Africa. However the application of the dryer for gari production requires electricity. REFERENCES Achinewhu, S.C., Barber, L.I. and Ijoma, I.O Physicochemical properties and garification of selected cassava cultivars in Rivers State, Nigeria. Plant Foods for Human Nutrition. 52:

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