Effects of drying on the physical and chemical properties of palm kernels

In Malaysia, silo drying is the most common drying practice to reduce the moisture content of palm kernels from 30% to about 7% (dry basis). Long drying hour, high energy consumption, lack of a systematic drying procedure, and lack of proper study are some of the palm industry challenges. Plus, Non-homogenous drying, lack of a systematic drying procedure, variation in air velocity and temperature reduce the palm kernel drying efficiency. Computer simulation has been used in the drying process to develop information which could be utilized to improve, modify, design or evaluate the drying system. For simulation purpose, data on physical properties, equilibrium moisture content and thin layer drying characteristics of palm kernel are required. Thus, the first objective of this study was to investigate the properties of palm kernel. Selected physical properties of palm kernel were studied as a function of moisture content in the range of 2-31%. The equilibrium moisture content of palm kernels was determined by static gravimetric method and modified Oswin model was selected as the best-fitted equation. Moreover, thin layer drying characteristics of palm kernel was studied and Henderson & Pabis model was chosen for simulation purpose. In order to study fixed bed drying of palm kernel, a semi-pilot scale fixed bed dryer was fabricated. Drying was carried out with different air temperatures and air velocities. Drying capacity and electricity cost increased 44.23% and 57% when air velocity changed. Drying significantly (P<0.05) reduced free fatty acid, colors, and moisture & impurities. However, no peroxide was detected. Fresh palm kernel had 0.72% free fatty acid which was reduced to 0.32% at 80°C, 3 m/s drying experiment. Saturated fatty acids increased when the moisture content decreased while unsaturated fatty acids decreased slightly. FTIR result showed a reduction in O–H stretching, while long chain alkyl and C=O stretching started to appear. Cellulose/ hemicellulose and lignin compounds were decomposed from palm kernel while saturated fatty acids were decomposed from palm kernel oil. Drying promotes membrane rupture and cell wall degradation and therefore oil started to be detached from the cells. The approach of simulation program was initiated by modifying an existing computer procedure to meet the purpose of this study. Computer simulation was validated using the fixed bed drying data. There was a relatively good prediction of the moisture content but, simulation somewhat reduced the drying time by about less than 1 h. The differences between the experimental and simulated values were under 13% which in drying simulation studies is regarded as a satisfactory agreement. Hence, this computer simulation may be used to modify the current industrial palm kernel dryer.

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