Methane steam reforming with axial variable diameter particle structures in grille-sphere composite packed bed: A numerical study of hydrogen production performance

Highlights: • The axial variable diameter particle structures have better performance. • With inlet velocity rising, the outlet hydrogen production is increased by 24.8%. • Both solid particle method and equivalent medium method are used. • The values of equivalent medium method are 5.5–8.5 times higher than another. • Reasons of differences between two simulation methods are found and analyzed. Methane steam reforming with packed bed is an important approach to get hydrogen in industrial production. Compared with the conventional packed bed, the grille-sphere composite packed bed has the advantages of lowering the pressure drop, increasing the uniformity of the radial temperature distribution and improving overall efficiency. In the present paper, the axial variable diameter particle structure of grille-sphere composite packed bed has been proposed, and four different structures are studied to compare their performances. Moreover, two simulation methods are used in study: (a) the solid particle method which can show details of the simulation, (b) the equivalent medium method which can show the macro situation of simulation. Through these two methods, performances of four structures in different parameters are compared and analyzed. It is found that the axial variable diameter particle structures have better performance than the typical structures in different parameters cases. Inlet temperature, inlet velocity and inlet steam-carbon ratio are set to parameters respectively in simulation. According to the simulations, higher inlet temperature and inlet steam-carbon ratio will facilitate the reactions, however, higher inlet velocity will hinder the reactions. Through the solid particle method, the reasons of better performance have been found, and two methods difference are also studied. Compared with typical structures, the specific axial variable diameter structure brings 4.5% higher outlet hydrogen mass flow and 5.2% higher outlet hydrogen selectivity. Analysis of this study can guide the design of packed beds in industrial production and the results of this study have significance in industrial hydrogen production.