Open Journal of Optimization, 2013, 2, 26-32 http://dx.doi.org/10.4236/ojop.2013.21004 Published Online March 2013 (http://www.scirp.org/journal/ojop) Optimizing the Performance of a Manually Operated Groundnut (Arachis hypogaea) Decorticator A. N. Gitau 1* , P. Mboya 1 , B. N. K. Njoroge 2 , M. Mburu 3 1 Department of Environmental and Biosystems Engineering, University of Nairobi, Nairobi, Kenya 2 Department of Civil and Construction Engineering, University of Nairobi, Nairobi, Kenya 3 Department of Plant Science and Crop Protection, University of Nairobi, Nairobi, Kenya Email: * gitauan@yahoo.co.uk, ayub.gitau@uonbi.ac.ke Received January 14, 2013; revised February 15, 2013; accepted March 7, 2013 ABSTRACT Shelling of groundnut pods using manual decorticators in Kenya is characterized by high kernel breakages and low shelling efficiencies. As a result, farmers get low income due to low cost of broken kernels and a lot of time is lost in the tedious shelling operation. To overcome this problem, pertinent parameters that influence shelling efficiency of manually operated groundnut decorticators were identified. Two manually operated decorticators were tested and modi- fications done on one of the decorticators to optimize its technical performance. Results of machine performance tests showed that for WBS (Wooden beater sheller) at a feed rate of 30 kg/hr and 22.6 mm clearance, shelling efficiency in- creased with decrease in moisture content for all the groundnut varieties. The highest shelling efficiency was 55.3% for ICGV 99568, 39.2% for ICRISAT Groundnut Variety (ICGV) 90704 and 29% for ICGV 12991 at moisture content of 5.92% wb. For RBS (Rod beater sheller) at a feed rate of 30 kg/hr and 22.6 mm clearance, the highest shelling effi- ciency was 58.3% for ICGV 99568, 42.7% for ICGV 90704 and 35% for ICGV 12991 at moisture content of 7% wb. Identification of the pertinent parameters showed that pod moisture content, clearance and sieve size influence per- formance of manually operated groundnut. Theoretical predictive models developed were optimized which showed that a maximum shelling efficiency of 88.73% can be achieved with percent damage of 4% when the sieve size is 11 mm and clearance is 16 mm with a regression coefficient of over 85%. With the modifications done on the WBS decortica- tor, the highest shelling efficiency of 87% was obtained at a clearance of 10 mm for ICGV 99568 which is the largest in size from the three varieties. The shelling efficiency of the modified decorticator is far above those of the RBS and WBS because the sieve sizes and clearances of the later were not optimized. The results of the theoretical optimization of the manually operated groundnut decorticator implies that farmers who shell for seeds can now obtain more seeds shelled with low breakage and therefore will get more income. Keywords: Decorticator; Shelling; Efficiency; Optimization; Clearance; Groundnut; Varieties 1. Introduction Groundnut (Arachis hypogaea) is a species in the family Fabaceae native to South America [1]. Its seed contains about 63% carbohydrate, 19% protein and 6.5% oil [2]. As the groundnut seed is contained in pod, which is usu- ally developed underground, the pod is harvested by pulling or lifting the plant manually or by using a hoe as the mechanization system [3]. The pods are stripped from the haulms, dried, stored and processed. Shelling is a fundamental step in groundnut processing as it allows the kernels and hull to be used as well as other post harvest- ing technologies to take place such as oil extraction or in hull briquetting [4]. Shelling can generally be done by hand or machines. Hand shelling is the process in which the pod is pressed between the thumb and first finger so that the kernel is released. It is the most predominantly used method in Kenya’s smallholder agriculture. While hand shelling keeps the rate of Kernel breakage low, it is labour intensive, energy requirement is high [5] and leads to “sore thumb syndrome” when large quantities are han- dled. A decorticator is a machine for stripping the husk off kernels in preparation for further processing, storage or use as food. The machine can dramatically reduce the labour costs associated with decortications, cleaning and preparing groundnuts for further processing. Decortica- tors are basically classified as manual or motorized. Manual decorticators are powered by human hand while motorized decorticators are powered by a motor or an engine. Optimizing the performance of a manually oper- ated groundnut decorticator is important so that the shelling efficiency is set at maximum possible and kernel breakage set at minimum possible. Manual shelling of * Corresponding author. Copyright © 2013 SciRes. OJOp