Project Abstract

<p>&nbsp;                     <b>ABSTRACT&nbsp;</b></p><p>A low-cost, 250kg to 1-tonne capacity continuous-flow mixing grain dryer (LSU type) was designed and developed. The dryer consists of three main parts 1) the drying chamber made of inverted V-shaped ducts, to which the plenum inlet is connected; 2) the blower, with a 750 W (1 hp) electric motor and centrifugal fan which provides the drying air; 3) 1 kW electric heater, 4) discharge rollers powered by a 3kW electric gearmotor with a 37.51 reduction gearbox. Trials conducted between April and June, 2011 showed that paddy rice, at initial moisture content (MC) of 19.7%- 26.6% dried to 11.8%- 13.5% respectively. Sun drying was also carried out as control. The drying period for the mechanical drying ranged from 4.8-5.7h and that for sun drying was 5h. The moisture reduction rate ranged form 1.16-2.41%/h for the mechanical drying and 2.18% for sun drying. Milling recovery and head rice yield from mechanical drying were better than for sun drying. The heat efficiencies of drying the four consignments ranged from 36.40%-62.70%. Although power consumption was not measured, the operating cost would reduce if a biomass (rice husk) burner is used instead of electrical energy. <br></p>

Project Overview

<p><b>1.0 INTRODUCTION&nbsp;</b></p><p><b>1.1 BACKGROUND</b></p><p>Information Agricultural processing may be defined as an activity which is performed to maintain or improve the quality or to change the form or characteristics of an agricultural product. The main purpose of agricultural processing is to minimise the qualitative and quantitative deterioration of the material after harvest (Sahay and Singh, 2001). Drying, as part of agricultural processing, is the removal of moisture to a safe moisture content by the application of heat. Drying is practised to maintain the quality of grain during storage to prevent the growth of bacteria and fungi and the development of insects and mites. The safe moisture content for cereal grains is usually 12 to 14% on wet basis (Bala, 1997). Thus drying is the universal method of conditioning the material by removing moisture to such a level that it is in equilibrium with the normal atmospheric air in order to preserve the quality and nutritive value of the food product and seed quality. Also, grain drying refers to the removal of some of the moisture from grain by mechanically moving air through the grain after it has been harvested (Wehrspann,1998). Grain in the field dries naturally as the crop matures, giving up moisture to the air until the grain moisture is in equilibrium with the moisture in the air 2 (equilibrium moisture content). Conditions become less favorable for grain to dry to moisture contents considered safe for storage as the harvest is delayed. 1.2 Drying of Paddy rice Paddy is a hygroscopic, living and respiring biological material. It absorbs and gives off moisture depending upon the grain or paddy moisture content (m.c.), air relative humidity (RH) and temperature of the surrounding atmosphere (Lantin, 2006 ). As a living biological material paddy respires at an increasing rate with m.c. Paddy respiration is manifested by a decrease in dry matter weight, utilization of oxygen, evolution of carbon dioxide and the release of energy in the form of heat. Respiration is negligible at moisture content of about l2-l4 percent (Lantin, 2006 ) Paddy is usually harvested at moisture content of about 24-26 percent (wet basis), higher during the rainy season and lower during the dry season (Lantin, 2006). At this moisture content at harvest, paddy has a high respiration rate and is very susceptible to attack by micro-organisms, insects and pests. The heat evolved during the respiration process is retained in the grain and in the bulk because of the insulating effect of the rice husk.&nbsp;</p><p>This heat increases the temperature of the grain resulting in increased mould growth, fungi, insect and pest infection, which increases the quantitative loss and qualitative deterioration (Bala, 1997). Grains become rancid, mouldy, yellowish, and insect and pest infested. Newly harvested grain with high moisture content must therefore be dried within 24 hours to about l4 percent for safe storage and milling or to at most 18 percent (Lantin, 2006 ) for temporary storage of up to two weeks in case the drying capacity will&nbsp; jeopardize the drying of the rest of the wet paddy and thus get them spoiled. At moisture content of 14 percent or less, wet basis, paddy will be less susceptible to fungal infestations and likely to retain its germination potential. Its shelf life will likely be prolonged and its quality preserved. In wet grain, vapour pressure is high because of the high moisture content. When this grain is subjected to an atmosphere where vapour pressure is low, vapour transfer or movement will occur from high to low until such time that the vapour pressure is the same or the grain is in equilibrium with the atmosphere. Drying therefore is subjecting the grain to an atmosphere of low vapour pressure and providing the necessary heat to vaporise and means to remove the evaporated moisture from the grain (Lantin, 2006). The same is true of moisture movement within the grain. Moisture from the outer surface of the grain is evaporated during drying. Moisture transfer from the core to the grain surface occur s during and after drying until such time that moisture is evenly distributed within the grain. Thus, in sun or solar drying, energy from the sun heat the grain evaporating the moisture and the natural air movement on top of the grain removes the evaporated moisture.&nbsp;</p><p>Also, in heated air drying, the heat from the drying air vaporise the moisture from the grain and the same drying air removes the evaporated moisture away from the grain. The higher the temperature of the drying air the faster is the drying rate. Rice is one of the major staple crops in Ghana. The demand for rice in the West African sub-region is growing faster than any other major source of calorie for especially urban dwellers. Local production and processing usually yield rice of poor quality for storage and consumption.&nbsp;</p><p>&nbsp;1.3 Why the need of dryers by farmers? Grains deteriorate due to heavy rains at the time of harvesting. If there is a facility like dryers in every village during this season, this heavy loss may be eliminated. Normally the problem faced by farmers is that during rainy season grains which are harvested spoil and result in bad quality as they decolorize. Due to this reason, the price is reduced. This loss can be recovered if the dryers are used at this stage. After drying farmers can store the grains for a long period which will give them good prices. Drying and storing rice on the farm can be an excellent marketing strategy. The way that rice is handled during the drying and storage processes will determine its quality at the point of sale, thereby influencing its value. Rice should be quickly dried down to a moisture level of about 12 percent for storage, especially if it is going to be stored for several months. The reduction of grain moisture is done by passing relatively large quantities of dry air over the rice after it is place in the bin. The quality and quantity of this air determine the final moisture content of the rice kernel.&nbsp;</p><p><b>1.4 Rice Production and processing in Ghana&nbsp;</b></p><p>Rice is increasingly becoming an important staple food consumed throughout Ghana. Per capita consumption rose from 13.9 kg/y in 1995 to 14.5 kg/y in 2000 (MOFA, 2001), and to 38kg in 2009, as compared to per capita production of 20kg paddy/year or 13kg milled/year (NRDS,2009). Consumption of rice in Ghana has increased tremendously over the last few years and based on population and demand growth rates, had increased to 41.1kg/year milled in 2010 and will increase to 63.0kg/year by 2015, giving a demand of 1 680 000t/year (NRDS,2009). This is mainly as a result of 5 increased urbanization and the relative ease with which it can be cooked. However, the increasing demand for rice (both in quantity and quality) far outweighs local production. Over the past few years, rice production in Ghana has stagnated around 170,000 metric tonnes of milled rice with a self sufficiency ratio of 22% (MOFA, 2005). In addition to this, the quality of the rice produced is variable. To make up for the shortfall, a greater part of rice consumed in Ghana is imported. In the year 2005, figures from the Ministry of Trade and Industry showed that about 600,000 metric tonnes of rice was imported,and increased to about 800,000t/y in 2010 (NRDS,2009). These represented a value of roughly $200 and $266 million respectively, contributing 6% and 8% of Ghana‟s trade balance deficit in each case. Imported rice is also perceived to be of better quality than local rice and thereby reported to command higher prices. But locally produced rice from industrial mills associated with irrigation schemes is clean, white with a low percentage of broken grain (&lt;10%) and is at par with some varieties of imported rice. Some of this rice is branded, graded and marketed competitively alongside imported rice in Accra markets (NRI, 1997). Traditional sun drying, which is practiced in Ghana, is weather dependent and harvest seasons sometimes coincide with the rainy season in the southern sector of the country. In order to prevent deterioration after harvest, paddy should be dried down to a level of water activity that will enable safe storage by reducing respiration, inhibiting mould growth and preventing production of mycotoxins. This corresponds to a moisture content of about 13-14%wb, which is considered adequate for safe storage, milling and further storage as milled rice (Hall, 1970). The quality of milled rice, the predominant edible form of rice, is largely determined by the yield of well−milled, whole kernels,&nbsp; referred to in the rice industry as head rice. Broken rice kernels are sold at a much lower price than head rice. Head rice yield (HRY), defined as the percentage weight of rough or unprocessed rice that remains as head rice after milling, is a critical quality parameter used to quantify rice quality, and thus the economic value of rice. HRY is sensitive to production and environmental conditions and can also be dramatically affected by post−harvest processing (Siebenmorgen and Qin, 2005). The moisture content (m.c.) at which rice is harvested directly affects milling quality, field yield and drying costs. Milled rice, including both whole and broken kernels, is that which remains after the bran has been removed during milling. Head rice denotes milled rice that is comprised of kernels that are three-fourths or more of the original kernel length. The weight of milled rice expressed as a percentage of the rough rice is defined percent milled rice (PMR) while the weight of head rice as a percentage of the rough rice is defined as percent head rice (PHR) (Lu et al., 1992). The reduction in PHR is directly related the fissuring of rice caused by rapid adsorption of water. Early studies by Satel (1935) and Craufurd (1962 and 1963) showed that adsorption of water had no or little effect on rice fissuring when rice m.c. was above 15%. This was further confirmed by other researchers (Srinivas et al., 1978; Kamau and Kunze, 1986; Siebenmorgen and Jindal, 1986; Siebenmorgen et al., 1992). Craufurd (1962 and 1963) also reported that the adsorption of water vapour by rice with an initial m.c. above 12% did not cause any fissuring, but the presence of liquid water from dew caused rice to fissure. Chen and Kunze (1983) reported PHRs for the long-grain variety „Labelle‟ and the medium-grain variety „Brazos‟ were not reduced when the 10.7% m.c. rice was remoistened until an environmental relative humidity of 92% was used. Siebenmorgen and Jindal (1986) found that PHR for the long-grain variety „Tebonnet‟ was reduced by three percentage points when rice with an initial m.c. of 12% was exposed to a 90% relative humidity environment, the reduction in PHR was less than two percentage points.&nbsp;</p><p>These studies indicate that a high relative humidity environment does little damage to head rice if the rice m.c. is above 13%. The reduction in PHR in the field is mainly caused by the adsorption of liquid water by rice with an initial m.c. below 15% (Lu et al., 2005). From a technical point of view, drying and milling are the major constraints in the rice processing industry in the southern sector of the country. Widespread introduction of grain dryers will be important in the near future in the country. Although numerous experimental results have been reported on sun-drying of rice in Ghana, no studies on heated-air drying are available in the literature, especially of the new varieties developed. For this purpose, a study of milling properties of heated-air dried rice varieties was undertaken.&nbsp;</p><p>&nbsp;1.5 General Objective The main aim of this project was to design, develop and evaluate the performance of a locally constructed continuous flow-mixing (Louisiana State University, LSU type) grain dryer, to dry 250kg of paddy using locally avai&nbsp;</p>