modelling and optimisation of head rice yield of two rice varieties in a two-stage drying process Performance
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Date
2019-11
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KNUST
Abstract
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), R
2
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.
Keywords: AHP, two-stage drying, performance modelling, CCD, RSM, HRY, Paddy
Description
A thesis submitted to The Department of Agricultural and Biosystems Engineering, in partial fulfilment of the requirement for the degree of MASTER OF PHILOSOPHY in food and postharvest engineering