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Product Code: 00002883

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A motorized rice de-stoning machine was designed, fabricated and evaluated for performance. The traditional method of rice de-stoning machine characterized with a lot of deficiency in terms local rice containing smaller stones during de-stoning operation. A lot of energy is expended in solving the problem of operation. The rice de-stoning consists of the following part: Hopper, Vibrating Sieve, Machine Frame, Pulley, Eccentric Shaft, and Blower. The factors investigated were feed rate (500g/min) and variety off rice (Bokola, Kodoqiche, AlhajiA’aba). The result of the evaluation reveals that in Stone Separation Efficiency the third variety has the highest efficiency of (77.3%) and the first variety has the lowest efficiency of 72.6%, while in Rice separation efficiency the third variety also has the highest efficiency of 81.0% and the second variety has the lowest efficiency of 79.0%, the Impurity levels after separation are 7.8%, 7.5% and 6.5% respectively, the Tray losses remains the same. The rice de-stoning machine was powered by 1hp electric motor and the cost of production was estimated to be 108,700.



Title page                                                                                                                             i

Certification                                                                                                                       ii

Dedication                                                                                                                          iii

Acknowledgement                                                                                                          vi

Abstract                                                                                                                               iv

Table of content                                                                                                                iv


1.     INTRODUCTION                                                                                               1

1.1       Background of the study                                                                      1

1.2       Aim and Objective of the project                                                       3

1.3       Justification of the project                                                                    3        

1.4       Scope of the project                                                                                 3


2.     LITTERATEUR REVIEW                                                                               4

2.1            De-stoning of rice                                                                                    4

2.2            Rice production in Nigeria                                                                   4

2.3            Rice processing                                                                                         7

2.4            Traditional method of processing rice                                            7        

2.5            Modern method of processing rice                                                   7

2.6            Method of de-stoning                                                                             8

2.7            Local method of de-stoning rice                                                         9

2.8            Modern method of de-stoning rice                                                   9

2.9      Review of existing work on rice destining rice                             11      


MATERIALS AND METHOD                                                                13

3.1     Description of the machine                                                               14     

3.2     Design Consideration of the machine                                                         14

3.3     Design Calculation and analysis                                                       14

3.4     Material Selection                                                                             19     

3.5     Fabrication Procedure and Assembly                                                         20

3.6     Principle of Operation                                                                      21

3.7     Bill of Engineering Measurement and Evaluation (BEME)               23

3.8     Performance Evaluation                                                                    24



4.1     Result and Discussion                                                                       26



5.1     Conclusions                                                                                                28

5.2     Recommendation                                                                              28

          Reference                                                                                          29

          Appendix                                                                                          31


1.                                                        INTRODUCTION

1.1              Background of the study

Rice (Oryza sativa) is a cereal belonging to the Gramineae, a large monocotyledonous family of some 600 genera and around 10,000 species (Wibberley, 1989). It is valued as the most important staple food for over half of the world population (International Year of Rice, 2004) and ranks third after wheat and maize in production on world basis. More than half of the world’s population depends on rice as the major source of calories (FAO, 2003).The amount consumed by all these people ranged from100kg to 240kg per annum in the year 2000 alone (FAO,2003). Twospecies have emerged as our most popular cultivated rice,Oryza sativaand Oryzaglaberrima; of these two species the more widely produced is Oryza sativa.

Rice is cultivated in almost all part of the globe including Nigeria. By 2015, it has been estimated that over three-fifth of the world population will depend on rice as their staple food (Echiegu, 2009). Rice is one of the staple foods in Nigeria and it is cherished by almost all the ethnic groups and it is prepare into various delicacies. For instance, in the northern part of Nigeria, rice can be milled and used for flour and also molded and fried into cakes. Large acres of plantation can be found in these areas, Lafia (northern Nigeria), Beneu state (Middle Belt), Osun state (Western Nigeria), Abakaliki (Eastern Nigeria) and several other places.

In Nigeria, rice consumption has risen tremendously at about 10% per annum due to changing consumer preference (Akande, 2003). However, (Ebuehi and Oyewole, 2007) discovered that most Nigerians prefer to consume imported rice brands as compared to local rice varieties. The reason is that most Nigerian rice processors lack adequate technology of rice processing to meet international standard. It is valued as the most important staple food for over half of the worldpopulation (International Year of Rice,2004) and ranks third after wheat and maize inproduction on world basis. More than half of the world’spopulation depends on rice as the major source of calories(FAO, 2003). The amount consumed by all these people ranged from100kg to 240kg per annum in the year 2000 alone (FAO,2003). Twospecies have emerged as our most popular cultivated rice,Oryza sativaand Oryzaglaberrima; of these two species themore widely produced is Oryzasativa.

In Nigeria, rice consumption has risen tremendously atabout 10% per annum due to changing consumer preferences (Akande, 2003). However, Ebuehi and Oyewole (2007) discovered that most Nigerians prefer toconsume imported rice brands as compared to local ricevarieties. The reasonis that most Nigerian rice processors lackadequate technology of rice processing to meet internationalstandard. It is one of the most important staple crops in Nigeria, and local production of the commodity has increased several folds in the last 4 decades. Despite the increasing trend in local production, Nigeria is still a net importer of rice. In the local markets there is a greater consumer preference for imported rice compared to the locally produced commodity because of some quality issues associated with the local rice. Presence of stones in locally processed.

Nigerian rice has been identified as one of the major quality problems. The small Engleberg rice processing mill used by majority of rice processors in Nigeria, which includes a dehusking element and a polisher do not come with de-stoners. De-stoners are found only in a few high-tonnage integrated mills or are sold as separate equipment.

It was in the above context that the DFID-sponsored Promoting Pro-Poor Opportunities in Commodity and Service Markets (PrOpCom, 2012) engaged the services of M & A’s Greenery Ltd to conduct a survey of improved drying and de-stoning techniques and technologies in Nigeria.

1.2                           The aim and objectives of the project

The aim of the projectis to de-stone rice in other to have clean rice for human consumption.

 The specific objectives are to:

i.                    develop a rice de-stoning machine

ii.                  evaluate the rice de-stoning machine in terms of impurity level after separation, tray loss, rice separation efficiency and stone separation efficiency.

1.3       Justification of the project

            This project leads to the followings, to improve the quality of rice, to increase production, to minimize time and reduce human labour, to reduce losses in de-stoning of rice compare to the local method, to reduce import of rice to the country and to produce job opportunity for the youths in the country.

1.4       Scope of the project

 The project work is limited to rice which are abundantly cultivated in Nigeria for human consumption. The project work of the machine is limited to some selected factors such as rice separation efficiency and stone separation efficiency.



2.                  LITERATURE REVIEW

2.1              De-Stoning of Rice

De-stoning is separation of stones mixed with milled rice. Separation of agricultural products can be done by using one of these methods or by the combination of the following methods: screening, shelling, sorting and grading. Many researcher’s effort were made to solve this problem with different levels of success, among them is Oguomaet al., (2002) established that the separation of sand and stones from rice can be achieved by exploiting the difference in the dimensional features of rice and stone.

2.2        Rice production in Nigeria

 Accordingto Hardcastle (Hardcastle, 1959) rice production started in Nigeria in1500 BC with the low-yielding indigenous red grain speciesO.glaberrimaSteud and then widely grown in the NigerDelta area. West Africa Rice Development Association (WARDA 1996) reported about the high-yieldingwhite grain O. SativaL. introduced in 1890, and by 1960 itaccounted for more than 60 percent of the rice grown in thecountry. Also, the chart below shows the trend of rice productionin Nigeria since 1968 through 2008 (four-decade) study.Rice production remained at low level from 1968 to 1978 perhaps due to dietary idiosyncrasy for tubers. WARDA (1996) reported that paddy rice production had risen from 13400 to 344000 tons in 1970 and area was cultivated from 156,000 to255,000ha. Since then, paddy rice production has been on the increase. Tremendous increases in area planted, output, and productivity in paddy rice production were achieved over the last two decades and now stand at 1.09million tons. More so, the     production continued to rise higher from 1978 and since 1980. Nigeria has become the highest rice productions country in West Africa and the third largest in Africa, after Egypt and Madagascar (WARDA 1996).The production reached the peak in 1990 in which the countrywas producing 3.4 million tons of rice from about 1.2 million tons (ImolehinandWada,2000) before it slightly fluctuated down the slope in 1993.

However, the production soared up from 1993 to 2006 where the production remains 3.8 million metric tons. The graph shows that as years increased the production also increased; thismay be due to increase in population growth as well as increase in consumption trend of rice in the country. This healthy production trend would have been sustained but for the unsteady government policy on rice imports. Increased production over the last two decades could be attributed to the ban imposed on rice imports in 1985 and if this restriction had been maintained, Nigerian rice farmers would have risen to the challenge of meeting the domestic demand for the commodity. This has not been the case; however, as the government slackened rice import restrictionin 1997, the resultant effect was that foreign rice flooded back onto Nigeria markets. Restrictions on rice imports were reintroduced later in 1997, and local production has increased in response to the attractive prices offered (Emodi and Madukwe,2008). For rice production to be boosted, Nigerian government introduced institutions to monitor production and distribution of local rice. As the years went by, the indigenous production of rice could not meet the demand for rice. Therefore, Nigeria started importing rice into the country. This shows clearly the rice importation figures as reported by United State Department of Agriculture (2014). This importation of rice did not follow a regular pattern but it is observed from the figure that rice importation was not up to 1 million metric ton per year since 1983–1998. However, from 2006 upwards, the importation figure soared yearly to reach the peak in 2013 with 3.5 million metric tons. The major reason is the preference of foreign to indigenous rice which has a low level of processing technology (Akande, 2003).

          Furthermore, figure2.2 shows the importation yearly rice growth rate from 1983 to 2013. It is observed that growth rate is irregular and in some years there is no growth at all in rice importation business. From this, the growth rate is counted when the curves are upward ones and no growth rate occurs when curves are downward ones. This growth rate implies that the higher the growth rate is, the higher the country depends on importation of rice and the less the production of local rice is. This means that in 1997 Nigeria depended heavily on imported rice to feed its populace. This had negative consequence on the economy.

FIG.2.1 Rice production in Nigeria. Sources United state department of agriculture (2014).

FIG.2.2Rice importation in Nigeria. Source: United State of Department of Agriculture (2014).


2.3       Rice Processing

Rice processing involves several steps: removal of the husks, milling the shelled rice to remove the bran layer, and an additional whitening step to meet market expectations for appearance of the rice kernels. This process generated several streams of material which include the husks, the bran and the milled rice kernel (Schramm 2006). Nigeria has the potential to be self-sufficient in rice production, both for food and industrial raw material needs and for export purpose. However, a number of constraints have been identified as limiting factors to rice production. These include problems with research, pest and disease management. Addressing at least most of these problems is good first step towards attaining the target of rice self-sufficiency (WARDA 2004).

                 There are two methods of processing rice which are: The Traditional method of processing rice and the Modern method of processing rice.


2.4       The Traditional Method of Processing Rice

The traditional methods of processing rice paddy involve soaking of the paddy in water for 2 to 3 days to soften the kernel, followed by steaming of the soaked paddy for 5–10 minutes and dried in the sun as shown in plate 2.2 below, followed by pounding the dried paddy in a mortar and pestle device to remove the husk or use of simple machines for dehulling or milling; then the grain is cleaned using a winnowing basket (B. Srilakshmi, 2003). Though the traditionalmethod of processing rice is simple, but tedious, it has very low outturn and results in breakages of rice kernels and incomplete removal of husks. More so, it has a short storage life as the fat in the bran develops rancidity (B. Srilakshmi, 2003).

2.5       The Modern Methods of Processing Rice

Propoor Opportunities in Commodity and Service Markets Project (Propcom, 2012) carried out survey on modern rice processing and discovered that there has been improvement in rice processing in Nigeria compared to the 1990s. In modern methods, the rough rice or paddy is first cleaned to remove contaminants, and the husks are then removed by the so called shellers; these are most commonly horizontally spaced rotating abrasive stones, but increasing use is being made of rubber roll or rubber belt made shellers. The rice and hulls are separated by aspiration and any paddy remaining with the rice is removed in a paddy separator. It is discovered that the main problem of Nigerian rice is the presence of stone in the rice grains. The reported survey shows that there has been locally produced destoner made in Kano, Nigeria, as shown in plate 2.2. The machine costs N65,000 and was fabricated using angle iron and sheet metals.

             Another improvement in rice processing in Nigeria reported by Propcon is the drying process. The traditional sun drying has been replaced by mechanical dryer or improved sun drying method.This type of dryer is found scattered all over the country. It can process about 3000 kg and remove 50%moisture of rice in 6hrs.

      Apart from this mechanical dryer which uses diesel or electricity, other dryers have been developed such as solar dryer for drying rice paddy. An example of this is as shown in plate 2.3 developed in National Centre Solar Energy Research, Sokoto, Nigeria. The development of this is a result of incessant power outage all over the country. This type of solar dryer is equipped with fan to enhance hot air distribution over the rice paddy.

              Because local rice is of low quality, the rice merchants use this opportunity to expand on rice importation. The solution lies in the provision of incentives, machineries, and government policies to confront these challenges faced by rice processors.

2.6       Methods of De-stoning Rice

             There are two methods of de-stoning which are: Local or Traditional method of de-stoning and the Modern method of de-stoning.


2.7The Local or Traditional Method of De-stoning Rice

The local method of de-stoning involve: handpicking, which is the sorting and separation of rice from stones. Another method of the local method is done by winnowing of the rice manually and manual sieving of rice combine with stones.

2.8       The Modern Method of De-stoning

De-stoning at TADCO

            The TADCO de-stoning machine is QS 40 Model manufactured by Guangui Machinery Plant, Henna, China. It is electrically powered by a motor and is operated by one operator and a mate who helps the operator in feeding and bagging. The machine is provided with a feedrate regulator which allows for variable feed rates for the destoner. At a constant feed rate of 5kg/min, the destoner gave an output of 1 bag (70kg) in 15min. This translates to an output of 280kg/hr. With this output, it means that 4 bags of paddy could be destined in one hour. Hence for an eight hours working day, 32 bags could be destoned.

However, taking downtime (30 mins) into consideration, the machine couldconveniently de-stone 30 bags of paddy per day. The weight of stones separated after destining 70kg of the sample rice was 225g. The destoner has 2 outlets; lighter materials pass through one outlet and the heavier stones through the other. The two were added to give this value. No machine losses were observed in the stone outlet. The electric power rating of the de-stoner is 1.1 kwh. The time taken to destone a bag was15min. Therefore, the electric power consumed per bag is 1.1X15/60 = 0.275 kwh. ThecurrentPower Holding Company of Nigeria (PHCN) tariff is N 8/kwh; this means the energy cost for destoning 1 bag is N 2.20. On maintenance and spare parts, the sieve is the part being replaced usually after a period oftwo (2) years. It has a unit cost of N 2,000.00. The life span of the machine is estimated to be 10 years (M & A Greenery, 20008).



De-stoning at Dandago

The De-stoner at Dandago Agricultural Machinery Co. Ltd is a locally fabricated, manuallyoperated machine. The De-stoner is operated by two people, an operator who operates thereciprocating handle and a mate who helps in the feeding and bagging. The machine also has a manual mechanical linkage that serves as a regulator to the feed rate (similar to that of TADCO De-stoner). At a constant feed rate of 2.5kg/min, the machine was found to destone a bag of 70kg paddy in 35 minutes. This gives an output of about 120kg/hr. However, it was noted that the operator and the mate had to be exchanging positions (i.e. one person could not continuously operate the reciprocating handle for more than 10 minutes) Source: (M & A Greenery, 20008).

De-stoning at Hanigha

The de-stoning machine at Hanigha Nigeria ltd was locally fabricated based on Chinese design and uses an electric motor. It is operated by 2 people; an operator and a mate who assists in bagging. The machine has a feed rate regulator similar to that of TADCO. At a feed rate of 3kg/min the machine was found destinea bag of paddy (70 kg) in 35minutes. This means it has an output of 120 kg/hr. In an 8hrworking day it could, therefore, de-stone about 14 bags. Thus, the estimated capacity taking into account downtime lossesequals13 bags per day. The weight of stones separated after de-stoning 70kg of the paddy was 28.9g. Hence, the stone separation efficiency of the machine is 29%. The company explained that the very low value of this efficiency is due to the fact that they have not fully finished proper adjustments on the machine. However, the scatter (machine) losses observed around the de-stoner were negligible (0.017%).

The replaceable spare parts on the machine were the belts and the bearings. With proper greasing, the bearings could take up to 2 years without replacement. The total annual maintenance cost may not exceed N 1,000.00. The energy, consumption of the 2hp electric motor was estimated at 0.75kwh. Since the time taken to de-stone one bag was 35minutes, the power consumed per bag was therefore 0.75 X 35/60 = 0.4375kwh. With PHCN tariff of N8/kwh, energy cost was (N 8X0.4375kwh) = N 3.50 per bag.

For the machine to be operated on diesel, an engine frame base needed to be constructed. The company could not make the construction within the time frame of this study. The de-stoning analysis at Hanigha was therefore not done with diesel-powered prime mover.

2.9       Review of Existing Work on Rice Destoning Machine

Many researchers and scholars had worked on different types of rice destoning machine, among them are:

Okunola et al,. (2015). worked out on thedevelopment and evaluation of a cereal cleaner. The sieve assembly suspended by hangers experienced horizontal oscillation and small vertical motion thus displacing the grain from its stationary position to effect sorting and cleaning. During the test, the angle of tilt of the sieve was varied between 3 and 8° while the hanger angle and fan speed was maintained at 5° and 240 rpm respectively. The machine optimum performance was 98% product purity at a total separation efficiency of 71 % for Paddy rice at 3° tilt angle. Results indicated that paddy rice could be effectively separated from light materials of much lower terminal velocity and also from heavy materials like stones and leave stalks due to difference in geometrical and aerodynamic characteristics.

Ismail (2013) worked out on a design of a rice destoner. Reported that both sieves of the destoning are vibrated and  powered by a 0.50kW DC and rotational speed of 700rpm electric motor. The de-stonerhas the efficiency of 80% and mass flow rate of 2.10 kg/s which is equivalent to 7.50t/hr capacity.

Adewumi (1996) determine terminal velocities of some rice varieties grown in the South West of Nigeria; he gave the range of their mean values between5.06 to 5.19m/s and there were no significant differences among the different varieties.

Ogunlowo and Adesuyi(1999) determine the size, shape, density and suspension velocity of admixtures of ITA 257 rice variety and other impurities like stones and sticks and found that the sphericity of locally processed ITA 275 rice variety to be 0.41. Oguoma et al., (1992) determine the dimension of Abakaliki and Akeze rice. Their results showed 72% of the rice grains have length between 6.00 and 7.24mm, 23.3% have lengths between 5.25 and 5.99mm and 5% lengths 7.25 and 7.99mm. They also found that 99% of grains have thickness less than 2mm. The average loose bulk density of Abakaliki rice was found to be 0.818gcm-3, Akeze rice 0.785gcm-3at 10% moisture content. However, they did not specified whether it was on wet or dry basis.


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