Modelling of steam reforming reactors

Reactor modelling is an essential step in a scale-up of new steam reforming reactors. Fixed-bed modelling has always been a challenge to chemical engineers and it is one of the first applications where computers have been used extensively for the tedious property calculation in the numerical solution. An early example by Kjaer is shown in [274], and later in [275]. Modelling of steam reformers is widely used and among the early ones are Hyman [250] from 1968 and an early Topsoe publication [493]. 

Applied and fundamental research can give adequate descriptions of these phenomena, but usually scale-up requires experimental work due to the shortcomings of the correlations. Steam reforming reactor experiments at pilot scale are costly, so parameter identification is usually combined with other key points such as durability of a specific catalyst system or consfruction material. 

Conventional modelling of the catalyst side distinguishes the significance of the catalyst particle itself for the reactor performance and how heat transfer is taken into consideration. The following modelling concepts are generally accepted [199]  

Homogeneous gas and catalyst in the bed is a continuum so that temperature, pressure, and concentrations do not distinguish whether they are inside the catalyst or in the gas phase. The kinetic rate expressions are so-called effective or pellet kinetic rates, where the catalyst effectiveness factors have been included in the reaction rate expressions. 

Heterogeneous intra and external gradients are included and catalyst effectiveness factors are calculated continuously during the integration. The kinetic rate expressions are intrinsic rates. This is definitely the preferred model, but rigorous modelling of transport processes is tedious for all catalyst sizes and shapes in syngas processes. 

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