CFD Letters 17, Issue 11 (2025) 145-159 145 CFD Letters Journal homepage: https://semarakilmu.com.my/journals/index.php/CFD_Letters/index ISSN: 2180-1363 Design Analysis of Cyclone Separator for Air Classifier in the Processing of Oil Palm Trunks of Cutting Age using CFD Bayu Novariawan 1,* , Sigit Purwanto 1 , Bambang Triwiyono 2 , Banon Rustiaty 2 , Novi Kuswardani 2 1 2 Research Center for Process and Manufacturing Industry Technology, National Research and Innovation Agency (BRIN), Jakarta 10340, Indonesia Research Center for Agroindustry, National Research and Innovation Agency (BRIN), Jakarta 10340, Indonesia ARTICLE INFO ABSTRACT Article history: Received 9 February 2025 Received in revised form 11 March 2025 Accepted 12 April 2025 Available online 31 May 2025 Oil palm trees will become waste after passing their productive age. Oil palm trunks can be processed into starch-rich flour. The process of separating starch and fibre uses a cyclone by flowing flour that has been blown with air from a blower. The desired result is that the palm trunk starch will fall down and the fibre will rise up following the air flow. The molecular weight of palm stem starch is heavier than the fibre, causing the starch to fall to the bottom. In this study, the author tried 6 different variations of inlet speeds ranging from 10 m/s to 20 m/s to observe the phenomena that occur inside the cyclone. Changes in inlet speed can affect axial speed, tangential speed and drop pressure. In addition, the author has changed the mass flow rate of palm trunk flour to enter the cyclone. The flow rate of mass and particles entering the cyclone will influence efficiency. The result is that this cyclone separator can be used for physical separation of starch and oil palm frond fibre with the recommended parameters using an inlet velocity of 20 m/s with a mass flow rate of incoming raw materials of 1 ton/hour. Keywords: Cyclone; waste oil palm trunks; CFD; starch oil palm flour 1. Introduction Oil palm plants have a productive period of 24 to 30 years, after which new plants need to be replaced to produce good fresh fruit bunches (FFB) [1]. Every hectare of oil palm plantation has an average of 128 old oil palm trees or the equivalent of 220 m³/hectare and every year there are 81.5 million m³ of oil palm trunks that will become waste [2]. Efforts to use palm trunk waste vary, including as raw material for fibre-based industries such as the pulp and paper industry [3] and the starch industry [4], as well as the woodworking industry, by lamination or palm trunks can be combined with high-quality wood [5]. In the starch industry, palm trunk waste can be processed to produce starch-rich flour and biomass. With an efficient dry separation process, about 17.76% of palm starch flour can be obtained [6] and the remaining biomass flour as a high-calorific fuel [7]. In the anatomical structure of oil palm trunks, the middle and edges of the trunk are composed of thick-walled vascular tissue (vascular * Corresponding author. E-mail address: bayu008@brin.go.id (Bayu Novariawan) https://doi.org/10.37934/cfdl.17.11.145159