Abstract: Owing to its computational efficiency, the two-fluid model is widely used in computational fluid dynamics (CFD) to describe gas–solid flows in large-scale industrial processes. The motion of the solid phase is commonly modeled by the kinetic theory of granular flow (KTGF). The main conceptual difference between the two commonly used KTGF closure relations, namely the closure models by Lun e al. (1984) and Agrawal et al. (2001), is the treatment of the interstitial fluid. We theoretically compare both models and investigate their effects on simulation results. The interstitial fluid effects are essential during the raceway shape prediction but can be neglected in the fluidized bed regime. The correct prediction of the raceway size and shape is essential for predicting the processes in the raceway zone of ironmaking blast furnaces. Our results show that considering the interstitial fluid effects in the KTGF enables more accurate predictions in the raceway regime.