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Design of a crop residue burner for cereal drying

P.Chemweno, W.O.Ogola, P.M.Wambua, J.Githaiga, S.A.Odhiambo, N.Kiplagat, P.Nziu

Annually, farmers in Kenya, farmers incur heavy losses on their harvested cereal crops as a result of employing unorthodox cereal drying methods that include drying on tarmac roads and other unused open spaces in urban areas. This in most cases compromise on grain quality due to in-house grainmoulding. Fewdrying facilities are available but apply stringent quality standards on purchases of grain, and on the other hand cannot effectively handle all the cereals harvested due to their limited capacity. This research seeks to design and develop a crop residue burner to produce heated air for utilization in a direct-fired batch-in-bin dryer. The burner utilizes crop residue left underutilized in the field after each harvest season as fuel. The design concept entails developing a two-section chamber burner with primary and secondary sections. Mild steel plates of 3mm and 5 mm sections are used in the fabrication. Thermal stress computations are used to determine choice of fastening method, with the eventual choice being a combination of arcwelding, riveting and fastening. To achieve optimal combustion efficiency, computation of both stoichiometric and actual combustion of exhaust gases is conducted. To achieve complete combustion of the fuel, computational fluid dynamics technique (CFD) is applied and a cyclonic secondary combustion chamber is incorporated to the burner. Fouriers heat transfer equations are applied in the determination of suitable refractory materials in which clay and alumina-silica cement are selected as the optimal choice. It was found that the burner design achieves thermal efficiencies of 57.7%, produces smokeless heated air for use in a batch-in-bin dryer capable of drying approximately 17.82 tonnes of cereals per day.