Design, construction and performance evaluation of a castor seed sheller for three varrieties

ABSTRACT

A bulk quantity of castor seed pods (WBS, GMS, and GSS) was purchased from the local market in Baga, Borno State Nigeria. The pods were prepared by removing the tree stock and varying their moisture content to have three different moisture levels (6.1, 7.25 and 8.4% db) respectively.

Three groups of sieves were used with three different bore diameters (15.59±0.6, 14.27±0.3 and 9.25±0.94) were used for the shelling of the pods. Lump sum of each sizes were selected and introduced into the Sheller at different feed rate. This was replicated five more times for the three sizes at different moisture levels. Results shows that the moisture content, sieve geometry, rasp bar diameter, clearance and tolerance and the interaction between these variables affected the performance of breakage, percentage of partially shelled, percentage unshelled, shelling efficiency and winnowing efficiency at a significance of 5%.

The result shows WBS sieve (15.59±0.6) gave the best at 70.8% shelling efficiency, 10.86% unshelled efficiency and 10.26% breakage at a feed rate of 26.7kg/hr, GMS sieve (14.27±0.3) 65.9% shelling efficiency, 15.9% unshelled efficiency and 10.5% breakage at a feed rate of 36.30kg/hr while GSS sieve (9.25±0.94) had 14.67% shelled, 73.5% unshelled and 2.13 % breakage at a feed rate of 32.84kh/hr.

Keywords:  Sheller, pods, castor seed, WBS (White big size), GMS (grey medium size) GSS (grey small size), sieve, rasp bars, shelling and winnowing efficiency.

INTRODUCTION

Castor beans (Riscinus Communis) is an important draught–resistant shrub belonging to the family  Euphorbiaceous, native to the Ethiopian region of tropical Africa and has naturalized in tropical and temperate region throughout the world [1]. They are common along stream banks, river beds, bottom land and areas with well drained and sufficient nutrient to sustain its growth although a perennial crop in tropical, subtropical and temperate climate, and an annual crop in harsher climates [1].

The oil extracted has already being internationally accepted by more than 700 users, ranging from medicines and cosmetics to substituting petroleum in the manufacturing of bio-diesel, plastics and lubricants [2]. The seed contains 46.0-51.8% oil, 17.1-24.4% protein, 18.26-26.5% crude fiber and 2.1-3.4% ash [1], depending on the varieties in question. It also contains mineral salt, water, oleic acid, toxalbumine, enzymes, vitamin E and some macro elements [2].

In Nigeria castor plant grow 1-3metres in height with a pivot ramified root, erect green or reddish stems. The leaves are large, the flowers have yellowish color. The fruits come in the shape of capsule which holds 3 brownish or ash colored molted seeds, located between latitude 7.20 and 8.00N and longitude 6.00 and 6.50N, the plants blooms from July to September as a commercial product [3].

The yield per hectare per year could reach up to 1000kg of oil, the de-oiled residue or castor bean cake contains toxins and allergens which remain in the cake after oil extraction, the Ricin component an unusual hydroxyl fatty acid (18.1∆9C -12OH)[1] with conjugate un-saturation a serious Impediment to the uses of castor bean meal in animal diet. The castor seed contains over 85% Ricinoleic acid contains which gives the oil the unique technological properties [4] such properties are of great applications in paint, varnishes, synthetic polymers, hydraulic fluids lubrication, cosmetics and food[5].

Resent research efforts have been directed to identify and evaluate certain novel legume seed as alternative / additional protein sources for the future world. The exploitation and development of castor bean as protein source for animals may offer a scope to meet the increasing protein requirement at large, particularly in developing countries. However, chemical evaluation of the seeds and cake of castor grown in Nigeria could reveal chemical composition that may be useful for feed materials and those that could be improved upon or eliminated before use.

Castor shelling is time consuming and a tedious process which has over the years evolved considering various shelling methods and several other crops to be shelled. Many are still being modified for their ease of application based on the increase in demand for castor bean.

In the shelling of Bambara groundnut seed, [6] recommended that Bambara groundnut should be dried in the sun to about 8-12% db moisture content after harvesting. [6] Carried out a performance evaluation of a Bambara groundnut Sheller working with the principle of rollers and pneumatically separated seeds from the shell. They obtained a maximum shelling and winnowing efficiency of 60% and 79.5% respectively at a pod moisture content of 5%db and a feed rate of 93.6kg/hr. the percentage seed damaged was about 12 %, while the percentage of partially shelled are 10% and 17% with a machine loss of 3% respectively. While [7] evaluated the effect of moisture content on shelling ability of bambara groundnut using a centrifugal cracker at three moisture levels (5.3,9.6 and 12.2% db) and found that the effective performance was 5.3%db moisture content with a shelling efficiency of 95%, 3.4% breakage and 0.6% partially shelled. [8] Developed and tested a shear-nut cracker working on the principle of impact and pneumatically separating the shells from the kernel. They evaluated three types of impeller similar to that of [9] but with slight difference in the vanes angulations, radial vane impellers (35⁰ and 45⁰) which gave 100% efficiency on cracking and 97% winnowing efficiency.

This paper presents the results and evaluations obtained on the effect of moisture content, three different sieve geometries, three varieties of castor seed by applying the principle of a centrifugal “drum and beater” Sheller on the castor pods.

1.       MATERIALS AND METHODS

The three samples of matured dried castor seeds were purchased in jute bags at a local market, the moisture contents of the pods were varied to have three levels using the methods described by [6], [8] and [11]. This involves soaking a bulk quantity of pods in ordinary water at room temperature for a period of 60minutes for the first sample and 90minutes for the second sample. The soaked pods were spread out to dry in natural air for about eight hours and them sealed in marked polythene bags for another twenty four hours to enable a stable uniform moisture content of the pods to be achieved.

The moisture contents of each sample was determined using the methods described by [11], this method involves oven drying the pods at 130⁰ with the weight loss monitored on hourly basis to give an idea when there is a constant weight, after oven drying for 6hours, the pods were weighed using an electronic balance weighing to 0.001g to determine the final weight. The moisture content was determined by [8].

Where    Mc = moisture content, %

                W_i = initial mass of pods, g

                W_f = final mass of pods,   g

                db = dry basis      

This was replicated three times for each sample and the average values were determined.

2.       DESCRIPTION OF THE SHELLER

The Device is similar to [7] Fig.1 (prototype) and Fig.1b (AutoCAD drawing), it consist of a hopper, shelling drum, discharge unit and a winnowing unit. The hopper rectangular in shape 3500mm length, 295mm width and 50mm height cut and shape from a gauge 16” steel plate. This is welded to the top of the housing leading to the shelling chamber 300 mm diameters with a circumference of 956mm, an inner diameter of 270mm with a circumference of 722mm; rasps bar with diameter 1.5m and 18mm long was cut and welded 15mm apart in an helical pattern on the shelling  drum. Fig2. The concave sieves 270mm length with an angle of 135⁰ Fig.3a, 3b and cc respectively was drilled with the geometry of each  seed pods variety in question at 500mm apart. The sieve slides in between the shelling drum and the trunk leading to the winnowing unit via a measured groove created for it the slide of the Sheller. The winnowing chamber with circumference 1256mm, diameter 400mm and 300mm width houses four blades made from gauge 20” welded at 90⁰ to the winnowing shaft. This winnowing unit is driven manually by a horizontal shaft connected via a V-belt and pulley at a ratio 1:6, from the shelling unit to the winnowing side.

3.1. PRINCIPLE OF OPERATION

The hopper is filled with a know mass of castor seed pods with the flow rate device closed, the hand lever is gradually rotated at a constant speed which actuates the shelling drum and in-turn the winnowing unit. The flow valve is opened and the pods slides into the shelling unit; the reaction, abrasion and impact forces between the sieve, pods and rasp bars forces the pods through the geometry on the sieves causing shelling or removal of the pods from the seeds. The seeds and the chaff falls under gravity through the trunk to the winnowing unit which supplies the need amount of air for separation of the seed and the chaff.

  3.2. PERFORMANCE TEST

Three different varieties (WBS, GMS and GSS) were varied with three different types of sieves, each of these sieves were used at different moisture content ranging from 6.1-8.4% db. Some quantities of the castor seed pods were randomly selected and weighed (N_T), the average feed rates were obtained using stop watches for five different runs as 32.84 kg/hr,36.30kg/hr and 26.70kg/hr*. The pods were carefully collected after going falling via gravity through the exit and the number of pods fully shelled (N₁), number of broken shells (N₂), number of unshelled (N_3­), total number of pods fed into the machine (N₀) as grouped below:

         I.            Pods shelled, N₁

        II.            Pods broken, N₂

      III.            Pods unshelled, N₃

      IV.            Total pod fed into the machine, N₀

each experiments were replicated five more times at each moisture levels were determined and recorded as follows to evaluate machine performance shelling efficiency (ɳ _s) and winnowing efficiency (ɳ _w) as follows

Where:   W₁= weight of winnowed shell

W₂= weight of un-winnowed shell

W₃= weight of pod

a.        Shelling efficiency, ɳ =

b.       Percentage shelled, ɳ_s =

c.        Percentage broken,  ɳ_b =

d.       Percentage unshelled,  ɳ_us =

e.       Winnowing efficiency, ɳ_w =

3.3. RESULT AND DISCURSION

The Table 1a,b and c shows the result of the performance tests, by applying Duncan Multiple Range Test (DMRT) [11] to the mean effect of the moisture content on the performance indicators Table 2 shows that the moisture content, number of slots on the sieve, sieve curvature, settings and position of the sieve affected the gross shelling efficiency(ɳ_s), percentage  breakage (ɳ_b), percentage Unshelled (ɳ_us) at a significant of about 5%, while the winnowing efficiency was very low at 90%. Also the interaction between the moisture contents at varied levels with each varieties, the rasps bar length and geometry also contributed to the high percentage loss in the unshelled pods while the breakage was very low in GSS due to the sieve geometry that allowed large amount of the pods to pass through pore spaces unshelled and undamaged. But the GMS pods brought about and edge with the shelling efficiency of 65%, 10.05% breakage efficiency and 15.9% unshelled pods due to the sieve geometry, sieve clearance and alignment when compared to GSS. However WBS with a moisture content of 8.4%db gave the best result of 70.8% fully shelled pod, 10.26% percentages of broken and 10.86% percentage of unshelled pods with a significant of 5% losses.

It was observed that the percentage fully shelled increased as the moisture content increases from (6.1%, 7.25% and 8.4%db) which also affected reduction in broken pods respectively (Graph1). This may be attributed to earlier report by [6] and [7] in their study of brittle and susceptible nature of Bambara groundnut pods and its mechanical damage.

Table 1a: Result of the performance test for GSS

RUNS	Mass of Seed (Kg) N0	Pods shelled N1	Pods broken N2	Pods unshelled N3	Feed rate (kg/hr)	Total Number of seed (pieces)
1	1.5	0.25	1.2	0	30	1000
2	1.5	0.25	0.7	0.06	36	1000
3	1.5	0.20	1.25	0.05	33.75	1000
4	1.5	0.22	1.15	0.05	34.8	1000
5	1.5	0.20	1.10	0.032	29.67	1000
Average	1.5	0.22	1.10	0.032	32.84	1000
S.D*	1.5	0.0249	0.0226	0.029	2.862	1000
ɳ (s, b, us)		14.67	73.50	2.13
ɳw					11.67

Table 1b: Result of the performance test for GMS

RUNS	Mass of Seed (Kg) N0	Pods shelled N1	Pods broken N2	Pods unshelled N3	Feed rate (kg/hr)	Total Number of seed (pieces)
1	0.4	413	56	95	46	600
2	0.4	405	63	67	43.63	600
3	0.39	391	77	110	30.52	600
4	0.395	360	74	106	21.54	600
5	0.35	410	73	100	39.37	600
Average	0.387	395.8	68.6	95.5	36.21	600
S.D*	0.021	21.71	8.79	16.97	10.12	600
ɳ (s, b, us)		65.9	10.05	15.91
ɳw					12.6

Table 1c: Result of the performance test for WBS

RUNS	Mass of Seed (Kg) N0	Pods shelled N1	Pods broken N2	Pods unshelled N3	Feed rate (kg/hr)	Total Number of seed (pieces)
1	0.85	623	90	107	25.5	900
2	0.87	647	100	82	29	900
3	0.90	680	87	80	28.4	900
4	0.92	640	95	100	25.09	900
5	0.90	598	90	120	25.92	900
Average	0.89	637.6	92.4	97.8	26.78	900
S.D*	0.027	30.30	5.12	16.94	1.78	900
ɳ (s, b, us)		70.8	10.26	10.86		900
ɳw					9.67

*standard deviation

Table 2: Effect of moisture content and sieve geometry on the three varieties

PODS	ɳs	ɳb	ɳus	ɳw	Sieve geometry (mm)	Moisture content (db %)	Feed rate Mean (Kg/hr)
GSS	14.67	2.13	73.5	11.67	9.5	6.1	32.84
GMS	65.9	10.05	15.9	12.6	10.5	7.25	36.21
WBS	70.8	10.26	10.86	9.67	16	8.4	26.78

*5% significant losses.

3.       CONCLUSION

The results show that a centrifugal Sheller operating with the drum and beater principle can be used to shell castor seed pods effectively at a stable moisture content range of 7.25% - 8.4%db.

The moisture content, sieve geometry, curvature and the alignment significantly affected the performance indicators. The WBS sieve gave the best performance at 70.8% shelling efficiency at a moisture content of 8.4%db, the shelling efficiency increased with increase in moisture content, while percentage of broken and unshelled pods decreased with increase in the moisture content.

 However there is need to increase the performance of the winnowing unit as against the initial average of 11.3% winnowing efficiency obtained during the test, this will reduce the drudgery of manually separating the shelled pods from the seeds after shelling.

4.       REFERENCES

1.  Seyed, M. G. and Seyed M. M. (2011).  A Survey on moisture-dependent physical properties of castor seed (Ricinus communis L.). AJCS 5 (1):1-7 (2011).

2.  Annogu, A. Azor and Joseph, J.K². (2008). Proximate Analysis of castor seed cake. J.Appl.sci Environ. Manage. March, 2008 Vol.12 (1)39-41

3.  Olaoye, J.O.(2000).  Some physical properties of castor nut relevant o the design of processing equipments

 Engineering Research 77(1),113-118, 2000.

4.  Alam, I., Sharmin, S.A., Mondal, S.C., Alam, M.J., Khalekuzzaman, M., Anisuzzman M., and Alam, M.F. (2010).

                    In-vitro micro-propagation through cotyledonary node culture of castor bean (Ricinus communis L).

                    Aust. Journal of crops science 4(2): 81-84.

5.  Labalette, F.A., Estragnat, A. and Messean A. (1996).  Development of castor bean production in France.

                    In: Janick J.   (ed) Progress in new crops, Alexandria, ASHS Press.

6. Atiku, A.A., N.A. Aviara and M.A Haque. (2004). Performance evaluation of a bambara groundnut Sheller. Agricultural Engineering International: the CIGR Journal of Scientific Research and Development. Manuscript P 04002 Vol. VI. July, 2004.

7. Oluwole, F.A., Adulrahim, A.T., and Olalere R².K. (2007). Evaluation of some centrifugal impact devices for  Shelling Bambara groundnut. Agricultural Engineering International: the CIGR Ejournal. Manuscript PM 07 007. Vol. IX. October, 2007.

8. Oluwole, F.A., Abdulrahim, A.T., and Haque M.A. (2004). Development and performance test of a shea-nut     cracker. Journal of Food Engineering 65. 117-123.

9. Odigboh, E.U. (1979). Impact Egusi Shelling machine.

                    Transaction of the ASAE; 22 (6), 1264-1269

10. Ajibola, O.O., Eniyemo, S.E., and Adeeko, K.A. (1990). Mechanical Extraction of oil from melon seeds.  Journals     of Engineering Research. 45, 1. (1990).

11. ASAE 1994.  ASAE Standards: ASAE 352.1 Moisture measurement. Grains and seeds.  American Society of   Agricultural Engineers. St. Joseph, Michigan.