Development And Performance Evaluation Of Rice Destoning Machine

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.