Performance Evaluation of a Bambara Ground Nut Sheller

A. A Atiku, N. A Aviara, M. A Haque

Abstract


The shelling of pod to obtain clean seed is one of the most tedious operations in Bambara
groundnut processing. As a result, it has constituted a bottle- neck to the large scale
production and processing of this important proteinous crop. To overcome the problem,
some physical properties of bambara groundnut pod relevant in bulk handling and
processing, were investigated and a sheller using roller mechanism was designed for the
crop, constructed and tested.
Measurements of the physical properties showed that at the moisture content of 5% (wb),
the major, intermediate and minor diameters of Bambara groundnut pod averaged 1.89
cm, 1.57 cm and 1.44cm respectively. The true and bulk densities, porosity and one
thousand-pod weight averaged 754.83 kg/m3 and 432 kg/m3, 42.77% and 1.24 kg,
respectively and the angle of repose and static coefficient of friction of the pod on steel
sheet averaged 30.4o and 0.56.
Results of machine performance tests showed that the moisture content, material feed rate
and the interaction between them had significant effect on the quantity of shelled,
unshelled and partially shelled pods as well as that of damaged seeds and winnowed
chaffs at 1% level of significance. Shelling and winnowing efficiencies decreased while
percentage of partially shelled and unshelled pods increased with increase in moisture
content and feed rate. The maximum shelling and winnowing efficiencies of 80% and
79.5% respectively, were obtained at the moisture content of 5% (wb) and feed rate of
93.6 kg/h. The percentage seed damage increased with increase in moisture content –
between 5 and 10% (wb) - to a maximum value of about 38%, and decreased with further
increase in moisture content. At low moisture levels, it increased with increase in feed
rate but at higher moisture levels, it decreased with increase in feed rate.
Regression models that could be used to express the relationship existing between the
sheller performance indices, pod moisture content and feed rate were established. Further
work would be carried out to modify the sheller and optimize its performance.

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