Chapter One

1. Introduction

1.1 Background

In Ethiopia one of the economical cereal crops is teff. It is grown inside Ethiopia and some other African countries, and it is a fundamental part of the culture, tradition, and food security of the people. This crop is not only gaining international recognition and acceptance but also it has become means of foreign currency earning in addition to its value as food and industrial crop inside our home country. Currently, teff is grown on approximately 2.80 million hectares of land which is 27% of the land area under cereal production. Teff accounts for about a quarter of the total cereal production and is highly economical food grain in Ethiopia. Approximately, 6 million households grow teff and it is the dominant cereal crop in 30 of the 83 high-potential agricultural woredas (Bekabilet al., 2011). The grain, after grinding and fermentation of the dough, is used to make a thin flat pan cake called ‘injera” (Eleni, 2001). The potential of teff as raw material for new food products development is high due to its protein composition; it is gluten free and has a very high quality amino acid composition. Teff protein is comparable with that of egg, an ideal protein for children between two and five years of age. It has been demonstrated that teff starch has a low glycemic acid, and has a mineral composition better than other cereals (Gamboa and Ekris, 2008).

Characteristics of teff

Teff (Eragrostis tef), a cereal grain that is included grass family of Poaceae, Teff is endemic to Ethiopia and it has been widely produced for many centuries (Teklu and Teffera 2005). Teff grain is found widely in most part of the country mainly in the in the altitude ranging from 1800 to 2100 meters above sea level due to this reason Teff can be grown under diverse agro-ecological conditions. The major Teff producing areas are Amhara, Oromia, Tigray and SNNP regions. Teff is concedered as a low risk grain because its vulnerability to pest and diseases is very low (Fufa et al. 2011; Minten et al. 2013).

Consumption of teff in Ethiopia

Teff is used in Ethiopia to produce the nation’s staple dish enjera. Grinding Teff grain into flour and mixing with water results in a spongy type of pancake. Teff is also used to brew local beer known as tela. It has high protein, fiber and complex carbohydrates content, relatively low calorie content, and is gluten free (Berhane et al. 2011; ATA 2013c). It accounts for between 11 and 15 percent of all calories consumed in Ethiopia (Berhane et al. 2011, ATA 2013c) and Teff provides about 66 percent of day to day protein intake (Fufa et al. 2011). More than 60 % of the Ethiopian population uses Teff as their daily staple food.

The traditional methods of harvesting, threshing and postharvest handling of teff usually lead into contamination of the product with stones, sticks, chaffs or brans, dirt and dust. Materials obtained after threshing include long straws, chaff, small fragments of spikes, leaves and grains. Therefore, teff grain, after threshing cannot be stored or used for consumption or as planting material due to the very fact that the presence of straws, chaff, small fragments of spikes, leaves, dust, dirt and other foreign materials in the grain will accelerate deterioration, thus lead to poor physical condition and quality of grain becomes eminent or famous. Grain primary processing usually improves grain condition and quality and the process is a vital and necessary link between production, storage and distribution. As a result, the teff owners or the labors that doses the separation tasks inside the teff milling houses are compelled to do additional work of separating and cleaning grains from undesirable materials that will otherwise reduce the quality and the value of the product.

Teff inspecting, separation and cleaning i.e. removal of undesirable materials, is accomplished manually by putting the grain into on a wide flat plate called “sefed”.And continuously shaking it and releasing it form a convenient height to the ground and letting the wind do the separation and cleaning, removal of lightest impurities such as chaffs and brans and large amount of fragments with certain amount of grains, shown on the figure below.

 

Figure  SEQ Figure * ARABIC 1. Separation of the chaff using “sefed” and the velocity of the wind.

For further cleaning is usually done using sieves to remove small stones & soils and any dirt larger than that of teff grain. That is shown on figure 2.

 

Figure  SEQ Figure
* ARABIC 2. Removal of small stones & soils or any dirt larger than that of teff grain using sieve.

Andonce again it will be blown by the “sefed” after the teff reached the floor. The traditional methods of separating and cleaning are not only labor-intensive and exhausting but also time consuming. In certain circumstances, the velocity of the wind may be too low so that heavier impurities (gravel, ear, chaff, etc.) remain mixed with the grains. Minus all the odds, Agricultural production, productivity and its sustained development depend on the advancement of science and technology that will enhance production, processing, handling, transportation, distribution and marketing processes of strategically important crops. In this regard, concerted efforts are underway to modernize the production and processing of teff.

However, the development and demonstration of separating and cleaning machinery, destined to improve the pressing problem of the workers that doses the separation tasks inside the milling house, were done on trial and error basis or were simple reproductions of basic machines developed elsewhere without appropriate performance evaluation and realities on ground. Yet it hasn’t been successful so far. As a result, the workers that doses the separation tasks were forced to do separation and cleaning of grain from straw, chaff, dirt and dust using sieves manually in order to maintain high quality and minimize weakening. To alleviate problems associated with chaff, straw, dirt and dust separation and cleaning teff grain it was felt appropriate to develop a machine that can separate undesired materials and clean teff grain after the commencement process of teff, after it has been presented inside the teff milling house or the preparation process for grinding.This project involves the use of induction motor, simple reciprocating mechanisms and centrifugalblower along with other components.Although this research attempt is mainly concerned with teff grains, the techniques and the equipment will be applicable to almost all types of grains only by replacing the sieve based on the size of the sieve hole diameter that is required for the selected grain.

1.2 Problem statement

Grains after they have been delivered to the grain milling housesthey require cleaning before directly starting the grinding processes. Such as: – teff, soybean, wheat, sorghum etc.The cleaning processes tends to be not onlyvery exhausting and time consumingbut also hazardous to the labors health causing “asthma” and “catarrh”. The cleaning process of teff consumes a lot of time compared to other grain types. And requires large amount of labors working on the cleaning tasks in order to finish the operations with in short time. For example, if 1 quintal teff must be cleaned within 45 minutes or less than 4 to 5 numbers of labors are requiredTherefore, a machine must be developed that will help us overcome this problem.

 

 

 

 

 

 

 

 

 

1.3Objectives

1.3.1General objective

The general objective of the study was:

Ø  To design and simulate a machine for the separation of teff chaffs from the desired grain (for filtration purpose).

1.3.2 Specific objective

Ø  To minimize the time taken for the separation of the chaff from the neat teff grain.

Ø  To minimize the amount of labor that works on the cleaning processes and make it easy as possible&managed by a single person.

Ø  To select appropriate inductions motors with a low price.

Ø  Determine the size of the components for reciprocating mechanisms based on design parameters for teff sieving machine.

Ø  Determine size of shaft that is required for this project.

Ø  To determine the efficiency of the teff sieving machine.

Ø  To select a centrifugal blower.

1.4 Limitations

The seeds are so small that this alone makes the crop hard to deal with. The fields are tedious to prepare, and it is difficult to get an even stand. Also, wind can bury the minute seedling. Threshing, winnowing, and grinding such tiny seeds by hand is very laborious. Handling and transporting them is also a problem because they tend to fall through any crack.