Avaliação de tensões através do método de elementos finitos nos tubos de fornos de pirólise sujeitos a carburização e camadas de coque

Abstract

Pyrolysis furnaces are critical equipment in an ethylene plant for the hydrocarbon cracking process. Typically, the cracking reaction occurs in the radiant coil tubes, which can be heated to 1000°C or higher temperatures. Furnaces under these severe temperature conditions create an environment conducive to coke and carburization, both of which pose high risks of equipment failure, especially during an emergency shutdown. To understand how carburization and coke influence stress generation in the furnace coil tubes, the finite element method was adopted for this study. The objective is to evaluate the stresses experienced by the tubes when subjected to variations in carburization levels and coke layer thickness at different temperatures in order to identify the most critical combinations that could lead to failure during furnace cooling. Finite element models were used, incorporating both linear and nonlinear analyses, with different coke layer thicknesses (5 and 10 mm) and various levels of carburization (0%, 25%, 50%, 75%, and 100%). The results indicated that without a coke layer, stresses exceeding the material's yield strength would not appear. However, with the formation of this layer, stresses increased around 10 times. This suggests that with 75% carburization and a temperature reduction from 1000°C to 200°C, crack propagation could occur, leading to tube failure.