Performance Modelling And Optimisation Of Head Rice Yield Of Two Rice Varieties In A Two-Stage Drying Process

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A considerable loss of milled rice (percentage of broken kernels) is traced to inadequate and untimely drying of harvested paddy. Therefore, an effective drying process or technique is required to minimise the reduction of head rice yield during paddy processing for an improved milled rice quality. In view of that, this study sought to integrate multi-criteria analysis and response surface methodology to optimise selection and operation of a two-stage drying process to maximise head rice yield. The study applied the method of Analytical Hierarchy Process (AHP) in the selection of an appropriate two-stage drying technique and factors (influencing the unit operations involved in obtaining a proper milled rice after harvesting and cleaning) based on its level of significance on head rice yield (HRY). A fluidised bed and tunnel dryer were selected as the best two-stage drying technique. Factors selected for the experimental design were fluidised bed drying temperature, tunnel drying temperature, paddy variety and storage time. A central composite design (CCD) in conjunction with a response surface methodology (RSM) based on four factors at three levels, which included six centre points, was used to evaluate the effects of the fluidised bed drying temperature (60 °C, 80 °C and 100 °C), tunnel drying temperature (40 °C, 45 °C and 50 °C), paddy variety (Amankwatia and AGRA) and storage time (1, 2 and 3 months) on the percentage of head rice yield were determined prior to optimising the operating conditions for optimal head rice yield. A regression model(quadratic), with a p-value of 6.5E-0.6 (<0.05), R2 of 0.995, RMSE of 1.14, AdjR2 of 0.986 indicated that the quadratic model was significant. Fluidised bed drying temperature, tunnel drying temperature and paddy variety were found to have significant effects on the head rice yield with p-values of 1.9E-0.5 (<0.05), 5.5E-0.6 (<0.05) and 2.5E-0.5 (<0.05) respectively. However, storage time had no significant effect on head rice yield with a p-value of 0.6 (>0.05). The optimal operating conditions for Amankwatia rice variety yielding 69.25 % head rice yield were as follows: fluidised bed drying temperature of 73 °C, tunnel drying temperature of 41.5 °C and storage time of three months. The optimal operating conditions for AGRA rice variety yielding 62.56 % HRY were as follows: fluidised bed drying temperature of 79 °C, tunnel drying temperature of 42 °C and storage time of three months
A thesis submitted to The Department of Agricultural and Biosystems Engineering, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfilment of the requirement for the degree of MASTER OF PHILOSOPHY IN FOOD AND POSTHARVEST ENGINEERING