Modelling of renewable hydrogen generation from biogas in a plug flow reactor

Abstract

Catalytic dry reforming of biogas produces renewable hydrogen and thereby circumvents two major problems of biogas usage, efficiency and environmental concerns. However, the technology is yet to be fully developed and the search for the best reactor design and optimum process conditions is ongoing. In situ simulation of the reactor helps in this endeavor by alleviating the time and costs involved in building and operating a lab or pilot scale reactor system. However, multiscale simulation of a plug flow/ packed bed reactor too has proved to be quite challenging. The use of in house and commercial codes also make it difficult to utilize the progress. In this study a fully opensource workflow has been used to simulate heat transfer and fluid flow in a packed bed reactor used for catalytic dry reforming of biogas to produce hydrogen. The result from the simulation is compared with experimental temperature data from inside of a catalyst bed. The simulation is performed by dividing the reactor in two segments, the heating zone and the catalyst bed. The simulation for the heating zone is performed using the buoyantFoam solver in OpenFOAM v10. The result shows a temperature gradient from the reactor wall towards the center of the reactor. The temperature range is found to be from 940 to 1073K for 1073K temperature at the outer surface of the geometry. For the catalyst bed, a new strategy of meshing the packed bed reactor has been introduced using the snappyHexMesh utility in OpenFOAM. The resulting mesh dealt with particle-particle contact points in a manner similar to the bridges approach. The bridge to particle diameter ratio is found to be less than 0.45. chtMultiRegionFoam solver is used for this case. Time to steady state is found to be 4 minutes. The temperature field is seen to be decreasing in value with depth from both the reactor wall and the top surface of the bed, going as low as 930K. However, a difference of about 150K between experimental and simulation result is noticed, which may be attributed to heat loss in the experimental case and the choice of rate equation for the simulation. However, the developed workflow can be used for simulation of any exothermic or endothermic reactor system and for different geometries with relative ease.