Determination of Sieve Aperture Size(s) Required for Effective Kernel Separation

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 7, Issue 10, October 2017)

115

Determination of Sieve Aperture Size(s) Required for

Effective Kernel Separation

Orua O. Antia

1

, Kessington Obahiagbon

2 1

Department of Agricultural and Food Engineering, University of Uyo, Nigeria

2_{Department of Chemical Engineering, University of Benin, Benin city, Nigeria}

Abstract-The development of sieve aperture size(s) required for effective separation of kernels from cracked nut mixture to obtain high purity kernels was studied. In this study, the Dura and the Tenera nut varieties were classified into eight mass ranges. Each nut minor axis dimension in each classified mass range was measured and then cracked to release whole kernel. The cracked nut shell thickness and minor axis dimension of the kernel released were measured since they are the smallest dimensions; and so would engage in elongated sieve aperture by their minimum dimensions during kernel separation. The size distributions for the shell thickness, nut and kernel minor axis were examined by classifying their measured values into fourteen size ranges; and the percentage frequency of the measured values were computed for each size range.

Result showed that kernel minor diameter

d

1 irrespective of the nut mass, size and varieties (Dura and Tenera) fall within 4 and 16 mm. The shell thicknesses of both nut varieties were mostly less than 6 mm. The nut minor

diameter

d

₁ was less than 30 and 24 mm for the Dura and the Tenera varieties, respectively. The mode of kernels minor diameters and shell thicknesses were evaluated as 9.8 mm and 3.0 mm respectively for the Dura variety; while the Tenera variety has 8.8 and 2.5 mm respectively. The percentage frequency distribution of the measured values analyzed revealed that elongated sieve aperture sizes 4, 6, 10 and 16 mm are effective combination for separating kernels from cracked nut mixtures to obtain kernels of high purity.

Keyword: Kernel, Nut, Separation, Shell, Sieve, Thickness.

I. INTRODUCTION

The major varieties of oil palm grown in Nigeria are the Dura, Tenera and Pisifera. The Tenera variety is the Hybrid of the Dura variety and shell less variety called the Pisifera [1], [2].The oil palm fruits shape and size vary considerably and each fruit consist of three major layers: an outer epicarp; a middle fibrous mesocarp from which oil is extracted and a hard breakable endocarp called nut which encloses the kernel [3]. The kernel is obtained following nut cracking. The oil extracted from kernel is used for the production of soap, edible

vegetable oil, cosmetic, candle, confectionaries,

explosives margarine, etc. The kernel cake obtained after oil extraction is useful for formulation of animal feeds.

The shell fragments are used as cooking fuel, for decoration of premises, as packing material in distillation; as coarse aggregate in road binder courses with emphasis on strength of the asphalt concrete [4], [5], [6], [7].

Palm nuts obtained for further processing by local farmers in Nigeria are mostly of mixed varieties (Dura and Tenera). It is difficult for each variety to be identified for separation from a mixed bulk of nut varieties before processing to obtain kernel(s). The kernels following nut cracking irrespective of the nut variety has to be separated from the cracked nut mixture in order for each of the products (kernels and shell particles) to be effectively utilized commercially. If there is reasonable percentage of shell fragments in the recovered kernel, the shell fragments would cause problems such as: formation of more sludge in the extracted oil due to fine crushed shell particles, wear and tear of milling basket, and fracturing of crushing shaft. These problems are associated with overall high production cost and low performance of the oil extractor [8], [9]. To enhance effective kernel separation, the production of whole kernel accompanying low percentage of split kernels and high percentage of small shell fragments relative to kernel sizes is necessary. The technique of achieving high percent of whole kernels, minimal production of split kernels and high yield of small particle size of shell fragments comparable with size of kernels have been studied [10], [11]. Reference [12] showed from sieve analysis that conventional sieves could be used in palm kernel separation only as a means of pre-cleaning. Sieves designed based on the shape and size differences between the nuts, kernels and shell fragments could enhance the recovery of high percentage of whole kernels of high purity (kernels free of shell fragments and dirt) from cracked nut mixtures [11].

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The smallest dimensions of the nut, kernel and cracked shell particles are expected to be the least equivalent dimension of sieve aperture that could allow such nut(s), kernel(s) and cracked shell(s) to pass through it. The smallest dimension for the nut and kernel is the minor diameter while that of the cracked shell is the shell thickness.

This study therefore, seek to determine the size distribution of shell thickness, nut and kernel minor diameter for the Dura and the Tenera varieties in order to provide basis of determining sieve aperture sizes that would be required to achieve high rate of recovery of kernels of high purity from cracked palm nut mixtures.

II. MATERIALS AND METHOD

Fresh Dura and Tenera nuts were obtained from a processing mill. Each nut variety was dried separately at

ˆ

 12 g. For each mass

range, twenty (20) nuts were randomly selected and their

smallest dimension (minor diameter d1) measured using

venier caliper and then recorded. Each of the nuts was cracked using a static nut cracker to release whole

kernel(s). The minor diameter d1 of each kernel released

following cracking was measured and recorded. The shell thickness was also measured and recorded. Three replicates were carried out. A total of 160 Dura nuts were used per replicate. The same procedure used for Dura nuts was followed for the Tenera nut variety. The values of the dimensions measured for the Dura and Tenera nuts, kernels and shell thicknesses were classified into fourteen size ranges that fall between 4 and 30 mm; with each size range at 2 mm intervals. The data obtained were evaluated. Statistical analysis was employed to determine (a) percentage frequency and size distribution of (i) shell thickness, and (ii) minor diameter of nuts and kernels for Dura and Tenera varieties of oil (b) sieve aperture size(s) required for effective separation of

kernels from cracked nut mixt

ures.

III. RESULTS AND DISCUSSION

The mean values of the nuts minor diameter d1, kernel

minor diameter d1*and shell thickness ts were computed

[image:2.595.42.540.479.746.2]

for each classified mass range of the Dura and the Tenera nuts. The values are presented in Table1.

TABLE 1

Mean Dimensions of Palm Shell Thickness, Palm Nut and Kernel Minor Diameter for the Dura and Tenera Nut Varieties Based on Classified Mass Ranges.

Classified mass range (g)

Nut variety Nut minor diameter d1

(mm)

Kernel minor

diameter d1

*



m

Dura 24.6 (1.8) 12.2 (1.7) 4.4 (0.6)

Tenera 21.3 (0.9) 11.0 (0.6) 3.8 (0.6)

Overall Average Mean

Dura 17.4 9.9 2.6

Tenera 14.5 8.7 2.1

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For each nut variety, there is a wide difference between the values of the minor diameters of the nuts and kernels in each classified mass range. This suggested that nut dimension less kernel dimension is the contributory aspect of shell thickness and clearance between shell and kernel in the nut. The clearance existing between kernel and nut is due to loosening of kernel from shell when nut is subjected to drying.

The loss of moisture from nut enhances efficient release of whole kernel following cracking if suitable cracking energy is applied on the nut. The size distributions of nut, kernel and shell thickness were evaluated by utilizing the values of their dimensions measured. These values were computed into fourteen size ranges and the frequency of the values recorded per classified size range. The values are presented in Table 2.

TABLE 2.0:

Average Size Distribution of Palm Nuts, Kernels and Shell Thickness for three replicates of the Dura and the Tenera Nuts

Size Range (mm)

Dura Variety Tenera Variety

Frequency of Nut Minor Diameter

1

d

% of Nut Sample Distribu-tion

Frequency of Kernel Minor Diameter

*

1

d

% of Kernel Sample Distribu-tion

Frequency of Shell Thickness ts

% of Shell Sample Distrib-ution

Frequency of Nut Minor Diameter

1

d

% of Nut Sample Distribu-tion

Frequency of Kernel Minor Diameter

*

1

d

% of Kernel Sample Distribu-tion

Frequen cy of Shell Thickne ss ts

% of Shell Sample Distribu-tion

d < 4 - - - - 127 79.4 - - - - 149 93.1

4 ≤ d < 6 - - - - 32 20.0 - - 31 19.4 11 6.9

6 ≤ d <8 - - 34 21.2 1 0.6 27 16.9 27 16.9 - -

8 ≤ d <10 2 1.2 60 37.5 - - 19 11.8 38 23.7 - -

10 ≤ d <12 21 13.1 38 23.8 - - 5 3.1 51 31.9 - -

12 ≤ d <14 30 18.8 21 13.1 - - 20 12.5 13 8.1 - -

14 ≤ d <16 17 10.6 7 4.4 - - 18 11.3 - - - -

16 ≤ d <18 14 8.8 - - - - 15 9.4 - - - -

18 ≤ d <20 20 12.5 - - - - 18 11.3 - - - -

20 ≤ d <22 27 16.9 - - - - 33 20.6 - - - -

22 ≤ d <24 14 8.8 - - - - 5 3.1 - - - -

24 ≤ d <26 12 7.5 - - - -

26 ≤ d <28 2 1.2 - - - -

28 ≤ d <30 1 0.6 - - - -

[image:3.595.9.596.271.626.2]

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Table 2.0 indicates that there is a wide overlap of size range distribution between kernels of any variety (Dura or Tenera) group. The minor diameter of kernels ranges mostly from 6 to 14 mm for Dura nuts and 4 to 14 mm for Tenera nuts. The percentage distribution of each of d1, d1*, ts for the Dura and the Tenera in each classified

size range is presented in Table 2.0. Table 2.0 showed that 79.4 % and 93.1 % of shell thickness for the Dura nut and the Tenera nut varieties, respectively and 86.25 % average for mixed nut variety are less than 4 mm. 20 % and 6.9 % are within the range of 4 and 6 mm; and the average dimension of this range is 13.45 %. The minor diameters of kernels for the Dura and the Tenera fall between 4 and 16 mm. This implies that the maximum sieve aperture for kernel separation from cracked nut mixtures is 16 mm and the minimum sieve aperture size of 4 mm. The nuts minor diameter values for the Dura nuts vary from 8-30 mm; Tenera from 6-24 mm.

[image:4.595.48.551.417.519.2]

This suggests that high recovery of kernels of purity is possible if most nuts are broken to release whole kernel; and the cracked shells are further fragmented in a manner that would achieve low percent of split kernels and high percent of small fragments that can pass through sieve aperture size of 4 mm. These fragments would be dislodged through sieve by utilizing their shell thickness dimension for passage. Table 1.0 showed that the mean average of kernel minor diameter for the Dura and Tenera are 9.9 and 8.7 mm, respectively. Table 2.0 showed percentage frequency distribution of minor diameters of nuts, kernels and shell thicknesses. The mode for kernel minor diameter and shell thicknesses computed were 9.8 mm and 3.0 mm, respectively for the Dura variety; and Tenera variety as 8.8 mm and 2.5 mm respectively. In separating the shell fragments from the kernels, four (4) different aperture sizes of separator namely: 4, 6, 10 and 16 mm were chosen based on Table 1.0 and 2.0 data analysis. The percentage distribution of nuts and kernels minor diameters; and shell thicknesses based on the chosen aperture sizes are shown in Table 3.0.

TABLE 3:

Percentage Distribution of Nut and Kernel Minor Axis Dimensions and Shell Thicknesses based on Aperture Sizes (4, 6, 10 and 16 mm)

Size Range(Mm) Percentage Frequency Distribution (%)

Kernel Minor Axis Shell Thicknesses Nut Minor Axis

d4 _ 86.25 _

4d 6 9.70 13.45 _

6d10 49.65 0.30 14.95

10d16 40.65 _ 34.70

d16 _ _ 50.35

Total 100 I00 100

Table 3.0 confirms that the chosen sieve aperture sizes are sufficient to separate kernels from cracked nut mixture to obtain high purity. The 4 mm sieve is expected to allow high percentage of shell fragments to pass through and retain small percentage of kernel with some shells. In a study by Reference [6] it is possible to separated shell fragments reasonably from the kernel by utilizing rotating rug table position at a favorable angle of repose that would allow kernels to roll out while shells are trapped and removed in the opposite direction. The 16 mm sieve aperture removes any uncracked nut larger than this aperture. The uncracked nuts from a study by Reference [10] are generally recycled for impact to yield kernels. The 6 mm sieve aperture retains a small percentage of kernels with more shell fragments. The 6 and 10 mm sieve apertures are likely to have high percentage of kernels with little percentages of medium and large sizes of shell fragments, respectively.

Reference [3] noted that shell fragments could be reduced to small particles for easy removal from the sieves when suitable impact energy is applied repeatedly in a manner that would have little or no damage to kernel wholeness. The impact energy model was developed. In general, a combination of sieve aperture sizes 4, 6, 10 and 16 mm and rotating rug table inclined at kernel angle of repose would enhance kernel separation from fragmented cracked nut mixtures.

IV. PRACTICAL APPLICATION

The combination of sieve aperture sizes 4,6,10 and 16 mm was tested using cracked nut mixtures subjected to repeated impact. The yield of purity kernels achieved was 94 %.

V. CONCLUSION

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Most palm nuts have shell thickness less than 6 mm and kernel minor diameter falling between 4 and 16 mm irrespective of the nut varieties. High percentage recovery of kernels of high purity is guaranteed if nuts are cracked to obtain shell particle sizes less than 6 mm accompanying high percentage of whole kernel and low percentage of split kernels. Effective combination of sieve aperture sizes is 4, 6, 10 and 16 mm for separation of kernels from cracked nut mixtures to yield high purity kernels.

REFERENCES

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[2] FAO 2009. Small Scale Palm Oil Processing in Africa, FAO Agricultural Services Bulletin, 148, 1-56

[3] Aladewolu, C. 1989. A Small Scale 3 ton FFB/hour Mill. International Conference on Palm and Palm Products, NIFOR, Nigeria, 772-773

[4] Bek – Nielson, B. 1974. Technical and Economic aspects of Oil Palm Fruit Processing Industry, United Nations Publication, ID/128, 40

[5] IFESH. 1998. Palm Oil/Palm Kernel Oil Processing. International Foundation for Education and self Help Training Course Manual, 32

[6] Illechie, C. O., Omoti, U., Bafor, M. E., Ogblechi, S. B., Aibangbee, G. F. ,and Amiolemhen, P. E. 2004. Palm Waste Briquette Substituted for Fuel Wood. Journal of Engineering Science and Technology, 2(3) 64-67

[7] Emeka, V. E. and Olomu, J. M. 2007. Nutritional Evaluation of Palm Kernel Meal Types I, Proximate Composition and Metabolizable Energy Values. African Journal of Biotechnology, 6(21), 2484 – 2486

[8] Poku, K. 2002. Agricultural Services Bulletin, Publishing Management Services, Information Division, FAO, Rome, 148, 1- 56

[9] Adebayo, A. A. 2004. Development and Performance Evaluation of a Motorized Palm-Nut Cracking Machine, Proceedings of the Annual Conference of the Nigerian Institution of Agricultural Engineers, .26, 326-330

[10] Koya, O. A. 2006. Palm Nut Cracking under repeated Impact Load. Journal of Applied Sciences, 6(11)2471 – 2475

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[12] Koya, O. A., Idowu, A., and Faborode, M. O. 2004. Some Properties of Palm Kernel and Shell Relevant in Nut Cracking and Product Separation, J. Agric. Eng. Technol, 12: pp 27-39. [13] Henderson, S. M. and Perry, R. L. 1981. Agricultural Process

Engineering, 3rdEdition, The AVI Publishing Company, Incorporated, West Port, Connecticut pp.108-122, 170-189 [14] ASAE 1983: ASAE Standard: ASAE 352.1 Moisture

Measurements – Grains and Seeds. American Society of Agricultural Engineers, St. Joseph, Michigan, USA