Coke formation possibility during production of reducing gas in large scale direct reduction plant

Abstract

For the production of synthesis gas utilised in Midrex direct reduction plants, catalytic steam/CO₂ hydrocarbon reforming in tubular reformer is the major process. Owing to the high heat input through the Midrex reformer tube wall, the endothermic nature of reforming reactions, low mass velocity of feed gas and large tube diameter, the catalyst bed is exposed to considerable axial and radial temperature gradients. These radial concentration and temperature gradients may create local areas with potential for carbon formation. To investigate this phenomenon, a rigorous two-dimensional model is developed for simulating the operation of a Midrex reformer which applies a dual catalyst loading profile. Both process side and furnace side have been included in this integrated model. Simulation results are in good agreement with available data from an actual plant. Using this model, a thermodynamic approach is applied to recognise zones in which the risk of carbon formation is high inside the reformer tubes. The results show that the first half of tubes, both in centre and near the wall, is critical from carbon forming point of view. Furthermore, the model shows that how a certain catalyst loading profile will affect the operation of the reformer.