Multi-scale Modeling of Steam Methane Reformer Heated by Electrical Current
Creators: Lu, Yi Ran
Publisher: name: University of Alberta Library
Year: 2022

<p>The study is dedicated to investigating the possibility of a new type of fixed-bed steam methane reformer heated by an electrical current flowing through the particles.<br>
The objective of the thesis is to develop multi-scale modeling for the electrically heated reformer made of bi-disperse particles.<br>
The electrically conductive metal particles act as heating elements,<br>
providing the heat of reaction for the endothermic reactions, and the catalyst particles provide the active sites for reaction.<br>
To verify this concept, a new multi-scale 1D-3D Euler-Lagrange model has been developed and validated.</p>

<p>A single catalyst particle is simulated using 3D CFD software.<br>
The catalyst is exposed to a stream of reacting gas using LHHW kinetics.<br>
The full thickness of the boundary layer is resolved. A 0D submodel was developed based on the results of the 3D CFD simulation.<br>
Excellent agreement was demonstrated. The 0D submodel is contrasted against 1D solutions in a parametric study to verify its usage for various temperatures (650K-1000K), particle size (2mm-25.4mm) and boundary conditions.<br>
Good agreement was found using the 0D model comparing the 1D results.<br>
The submodel is assembled in a 1D-3D Euler-Lagrange model to simulate reactions in a steam methane reformer.<br>
The results from the new model were validated against results from particle-resolved 3D-CFD simulation published in the literature.<br>
The comparison between our DEM-based model and 3D CFD case demonstrated good agreement.</p>

<p>The volt-ampere characteristics of a fixed bed heated by the Joule heating were calculated using the node-voltage method by treating the particle centers as nodes and the contact points as resistors.<br>
An experiment was conducted to validate the method using a cylinder filled with metal spheres.<br>
Electricity was flown through the bed and the voltage and current were measured.<br>
Open-source DEM software is used to model the packing of the fixed bed.<br>
Based on the packing, the electric field distribution is calculated using a new DEM-based model, coupled with heat transfer simulation to account for the temperature dependency of the steel particles&#39; electrical conductivity.<br>
The results were found to be in good agreement with experimental data.</p>

<p>The multi-scale model is then used to simulate a steam-methane reformer with electrically heated particles.<br>
The Joule heating term for each electrically conductive particle was calculated.<br>
The interparticle heat conduction is calculated based on contact area, particle size and thermal conductivity.<br>
The most important feature of the multi-stage model is that it retains 3D characteristics of the system in the solid phase,<br>
such as a strong radial temperature gradient in the wall-heated case, yet demands computational power significantly less than that of a 3D simulation.<br>
A cylindrical electrically insulated tube filled with 23000 particles was simulated to test the performance of the model and the feasibility of the concept.<br>
The limit for maximum power and temperature and a correlation between conversion and flowrate was found.</p>

<p>A larger SMR comprising 1 million particles was simulated in the scale-up study.<br>
The reformer has a diameter of 0.5 m and a height of 0.88 m and is filled with metal particles and catalyst particles with diameters of 10 mm and 4 mm, respectively.<br>
The modeled results show that electric current and Joule heating are widespread and well scattered in the fixed bed.<br>
The main distinguishing feature of the reformer is the relatively uniform temperature distribution in the radial direction regardless of the diameter of the fixed bed.<br>
Parametric runs have been carried out for different flow rates from 0.04 kg/s to 0.1 kg/s and electrical power from 185 kW to 462 kW.</p>

<p>The multi-stage model proved to be a useful way to resolve the intricacies of the complex phenomenon inside a reactor, not only for the new electrically heated SMR but also in other<br>
cases with a strong internal heat source and sink for energy conversion and storage.<br>
It fills the gap between the continuum model and the particle-resolved model.<br>
Future steps towards realizing and implementing the new reformer have been laid out in this study.</p>