Analytical models for heat transfer in the tube bundle of convection section in a steam cracking furnace

Abstract

In steam cracking furnaces, about 45% of the heat released from fuel combustion is recovered by preheating cracking feedstock and high pressure steam. This is achieved mainly by indirect convective heat transfer from flue gas to feedstock and steam in a series of tube bundles located in the so-called convection section. Radiation also plays in an important role in lower bundles where flue gas temperature is high. Thus, accurate heat transfer simulation of the convection section is crucial for operation optimization and control of steam cracking furnace. This paper aims to develop a heat transfer analysis (HTA) model for combined convective and radiative heat transfer calculation in tube bundles with both inline and staggered layouts. Computational fluid dynamics (CFD) was employed to validate the HTA model in the first stage. Based on the HTA model, coupled steady-state simulations of the convection section were performed for an industrial steam cracking furnace with naphtha feed capacity of 30 t/h. The predictions of the HTA model are in good agreement with the design data. The study shows that convective heat transfer is significantly enhance by fins in the tube bundles where the flue gas temperatures are too low to effectively heat up the feedstock. Radiative heat transfer at the bottom of the convection chamber is much larger than the convective heat transfer and thus cannot be ignored in heat transfer calculation.