A steady state and dynamic model for a steam methane reformer with higher hydrocarbons and carbon formation.

A model for a steam methane reformer tube was developed in Python to describe the behaviour of the reformers at Methanex’s Motunui plant. Reformers are widely used in industry to make syngas from natural gas and steam. Syngas is an intermediate in many processes including methanol production. The conditions inside a reformer are difficult to measure so models are a good way to understand their behaviour and predict the effect of changes made to the reformer setup. The final model was 1D, multiscale, included higher hydrocarbons and carbon formation and simulated both steady state and dynamic behaviour. The inclusion of higher hydro- carbons and carbon formation in a dynamic steam methane reformer model has not been seen in literature. A baseline model successfully replicated prior modelling work in the area. It is multi-scale, one-dimensional, including composition, temperature, pressure and incorporates catalyst diffusion. The addition of larger hydrocarbons up to butane showed that these higher hydrocarbons had a noticeable impact on the temperature and composition in the first 2m of the tube. The higher hydrocarbons react faster than methane and as the reaction is endothermic the temperature drops rapidly. Lower down in the reformer, little difference can be seen between simulations with and without higher hydrocarbons as they have all reacted by this point. Modelling higher hydrocarbons is still useful as they affect the tube temperatures near the top of the reformer and carbon formation. Thermodynamic and kinetic models were trialled for carbon formation showing that thermodynamic equilibrium models alone are not enough to predict carbon formation and a kinetic approach is needed. Both approaches showed carbon forming in the first 2 m of the reformer which matches the observations at Methanex where carbon is generally seen in between 1.5-2.5 m