Abstract:
There are many methods for grain drying including open sun drying, solar drying and mechanical drying. The problems with open sun drying include contamination, and poor drying performance during rainy and cloudy seasons leading to high post-harvest losses. The use of alternative and renewable energy sources including agricultural waste is becoming common with emergence of new combustion technologies and increasing costs of conventional fuels. This study undertook a field survey in Mwea Rice Irrigation scheme to gather technical data to assist in developing a rice husk fueled paddy drying system. The survey was conducted via questionnaires in which 300 farmers and 20 millers were interviewed. From the field survey findings, it was observed that about 98% of farmers desired to have low cost dryers that uses low cost energy source for paddy drying. This is because harvested paddy rice at a moisture content of 25% to 26% (wb) required further drying. On the other hand, 100% of the millers experienced challenges in drying newly harvested paddy because of high moisture content. The millers had challenges disposing the rice husk generated as 100% of millers had to damp and burn the husks in the open yard. Therefore, a model rice husk fueled paddy dryer capable of drying 250 kg per batch of harvested paddy was designed and fabricated at KIRDI. Paddy at a moisture content of 26% was dried to 14% (wb) in 4 hours. The combustor efficiency was computed to be 64% with consumption of 2.6 kg rice husks per hour. The emissions from the combusted husks were evaluated using flue gas analyzer and found to be 7% to 11% for CO2, 42.6 to 77.6 ppm for CO, 32 to 39 ppm for SO2 and 99.8 ppm to 104.3 ppm for NO2. It was observed that incorporating an exhaust fan on the flat bed dryer resulted in achieving in uniform moisture content across the bed height. From the economic analysis, the dryer shows a short payback period of 1.5 years and a cost benefit ratio of 1.4. On the basis of these findings, it was concluded that the developed dryer is economically viable and should be promoted in Kenya and other countries for paddy drying.
