A CO2 Methanation Fluent simulation is a computer model of a chemical reactor. This process, also called the Sabatier Reaction CFD, is a key part of Power-to-Gas CFD technology. It uses hydrogen (H2) to turn carbon dioxide (CO2) into methane (CH4), which is the main part of natural gas. This Methane Synthesis Simulation is important because it can store energy from wind or solar power and reduce greenhouse gases. A Catalytic Reactor Simulation like this helps engineers see where the reaction happens and how hot the reactor gets, which is very important for safety and efficiency. This study uses the Species Transport Fluent model to track all the chemicals involved.

Co2+ H2 ===> 2H2O + 1CH4

Figure 1: The 2D axisymmetric geometry of the Fixed Bed Reactor CFD model used for the methanation simulation.

Simulation Process: Fluent Setup, Modeling the Sabatier Reaction with Species Transport

To perform this CO2 Methanation CFD study, we first created a 2D axisymmetric geometry of the fixed-bed reactor. This smart simplification allows us to get accurate results much faster than a full 3D model. We then built a high-quality structured grid of 25,000 cells using ANSYS Meshing. In the ANSYS Fluent solver, we used the steady-state solver and enabled the Energy Equation because the reaction creates a lot of heat. The most important physics model we activated was Species Transport. This model allowed us to define a fluid mixture made of the four chemicals involved: the reactants (CO2 and H2) and the products (CH4 and H2O).

To control the chemical change, we needed to tell Fluent the exact speed, or rate, of the Sabatier reaction. We did this using a special C code called a User-Defined Function (UDF). This UDF was essential. It contained the precise mathematical formula for the reaction kinetics, telling Fluent exactly how the reaction speed changes based on the local temperature and the amount of each chemical. We compiled this UDF and hooked it directly into the Fluent solver to control the volumetric reactions. Finally, for the boundary conditions, we defined the incoming gas mixture at the reactor inlet and applied a constant, cool temperature of 500 K to the reactor’s outer wall to simulate an active cooling system.

Figure 2: The high-quality structured grid with 25,000 cells used for the Chemical Reaction Engineering analysis in Fluent.

Post-processing: CFD Analysis, Reaction Zone, Conversion Efficiency, and Thermal Management

The CH4 mass fraction contour in Figure 3a provides a clear and direct map of the reactor’s performance. From an engineering perspective, this contour perfectly confirms our simulation setup. The colors show that the highest concentration of methane (the red and yellow zone) is located exclusively within the central core of the reactor. The regions near the walls are blue, indicating zero methane production. This is not an accident; it is the direct result of our modeling decision to only allow the reaction to happen in that specific middle zone. This result proves that the solver correctly followed our instructions and provides a powerful validation of our simulation’s logic.

The velocity contour in Figure 3b tells the other half of the story: how the fluid moves through the reactor. We can see that the fluid velocity is highest along the central axis and decreases towards the walls. This central, high-velocity stream acts as a conveyor belt. It transports the reactants (CO2 and H2) into the defined reaction zone and then efficiently carries the newly formed product (CH4) downstream toward the outlet. By analyzing the two contours together, we can see that the methane is generated and transported within the highest velocity region of the flow. This is a critical insight for reactor design, as it shows how the flow pattern directly supports the reaction process. The most important achievement of this simulation is its ability to visually prove that the targeted reaction zone model works as intended, producing a concentrated stream of methane right where the flow is fastest, which demonstrates a highly controlled and efficient reactor concept.

Figure 3: Contours from the Sabatier Reaction CFD analysis showing a) fluid velocity and b) the resulting mass fraction of methane (CH4) in the reactor.