International Journal of Iron & Steel Society of Iran

International Journal of Iron & Steel Society of Iran

CFD Analysis of Thermal Stress and Shear Stress in the First-Stage Feed-Gas Tube Bundle of a Midrex Recuperator: Critical Zone Identification

Document Type : Research Paper

Authors
M. Salehi
H. Soltani
M. Ehsani
H. Farhadi
Mechanical Engineering Group, Department of Engineering, South Kaveh Steel Co, Bandar Abbas, Iran
10.22034/ijissi.2026.2070833.1329
Abstract
In the Midrex direct reduction process, the process gas is preheated by a recuperator made of a group of steel tubes, known as tube bundles, which work as a shell-andtube heat exchanger. One of the key parts of this system is the first-stage feed-gas tube bundle, which is the main focus of this study. In this study, the thermal behavior and shear stresses in the feed-gas tube bundle were investigated to identify critical zones and inform design optimization. To this end, numerical simulations were conducted using Computational Fluid Dynamics (CFD), and the distributions of temperature, pressure, and local gradients along the flow path were analyzed. The results revealed that significant variations in temperature and pressure gradients cause a sharp increase in both shear and thermal stresses at the tube inlet region. These conditions are accompanied by intensified convective heat flux, and repeated thermal cycles lead to thermal and thermo-mechanical fatigue at high tube-bundle operating temperatures. Over the long term, this fatigue mechanism promotes crack initiation in the inlet region, followed by local wall thinning, leakage, and progressive structural degradation. Validation of the numerical results through field inspection of damaged samples confirmed the existence of these critical regions. Based on these findings, the appropriate selection of geometry and structural materials is crucial to enhancing the reliability, efficiency, and safety of heat exchangers in direct reduction processes.
Keywords
Direct Reduction of Iron
Recuperator
Reformer
Tube Bundle
Feed Gas
Subjects
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