335 Available online at Association of the Chemical Engineers of Serbia AChE Chemical Industry & Chemical Engineering Quarterly www.ache.org.rs/CICEQ Chem. Ind. Chem. Eng. Q. 30 (4) 335−348 (2024) CI&CEQ CHITRA DEVI VENKATACHALAM 1 PREMKUMAR BHUVANESHWARAN 1 MOTHIL SENGOTTIAN 2 SATHISH RAAM RAVICHANDRAN 2 1 Department of Food Technology, Kongu Engineering College, Perundurai, Tamil Nadu, India. 2 Department of Chemical Engineering, Kongu Engineering College, Perundurai, Tamil Nadu, India SCIENTIFIC PAPER UDC 5/6:620 RELIABILITY-BASED DESIGN OPTIMIZATION OF SCREW SHAFT FOR CONTINUOUS HIGH- PRESSURE HYDROTHERMAL CO- LIQUEFACTION PROCESS Article Highlights • Structural analysis was performed on the screw-shaft to withstand high pressure in HTCL reactor • The uniformly varying pressure was applied to the screw shaft to calculate its structural strength • Helix angle, depth, pitch, and flight length were the dimensional parameters optimized • Stress, deformation, shear, and bending stress were crucial responses used for structural analysis • GFRG, SN ratio, and ANOVA methods were used for optimization and recommended for structural simulations Abstract Hydrothermal co-liquefaction (HTCL) is the prominent process for producing bio-products with a higher conversion rate. It is performed at high temperatures and pressure in the presence of water. Earlier, it was mostly conducted in batch reactors, but it has major limitations including operating volume, back mixing, and tedious process for high productivity. With that, the present investigation is performed on designing the screw shaft for the high-pressure HTCL process. The dimensional factors including flight length, pitch, helix angle, and depth were considered to design the optimal screw shaft. Likewise, principal stresses, shear stress, bending stress, bending moment, and total deformation were regarded as inevitable response variables to analyze the internal strength of the shaft. In this regard, the Taguchi approach provides the L 9 (3 4 ) orthogonal array as an experimental design. Then, the numerical results from the transient structural analysis were analyzed with the assistance of statistical methods such as Grey Relational Grade (GRG), Grey Fuzzy Reasoning Grade, Analysis of Variance (ANOVA), and Taguchi method to find the most influential dimensions for minimizing the response variable. Consequently, the results from both GRG and Taguchi optimization were compared, and selected the most optimum parameters. Keywords: hydrothermal co-liquefaction, screw shaft, finite element method, stress analysis, Goodman failure criteria, multi and single response optimization technique. As stated by the Energy Information Administrati- Correspondence: C.D. Venkatachalam, Department of Food Technology, Kongu Engineering College, Perundurai, Tamil Nadu – 638060, India. E-mail: erchitrasuresh@gmail.com Paper received: 24 November, 2023 Paper revised: 14 February, 2024 Paper accepted: 24 February, 2024 https://doi.org/10.2298/CICEQ231124004V on (EIA), the utilization of liquid fuels was 102.22 million barrels per day at the end of 2022 and also it is expected to increase by 2.4 % in forthcoming years. These gradual increments in the utilization of conventional fuel and its future demand indirectly suggest the need for alternate fuels like biomass energy, which can be produced via thermochemical conversion processes [1]. The commercialization of these biomass conversion technologies would