Learn how advanced CFD-DEM coupling techniques can be used to simulate coal combustion, capturing particle dynamics, gas–solid interactions, and both surface and gas-phase reactions for more accurate predictions of performance and emissions.
Modeling coal combustion processes that involve multiple chemical reactions is highly challenging due to the complex interplay between particle dynamics, interactions with the surrounding gas flow, heterogeneous surface reactions occurring on the coal particles, and homogeneous reactions in the gas phase. Accurate simulation requires capturing the motion, collisions, and fragmentation of particles, as well as the effects of these behaviors on combustion rates, heat release, and pollutant formation, making it essential to use advanced coupled modeling approaches.
Here, we modeled a simplified fluidized bed consisting of a rectangular-shaped geometry. The model is set up in both Fluent and Rocky using 2-way coupling. This is achieved using Rocky's CFD-Coupled Particle Combustion beta module.
The model consists of a simple rectangular block (400 mm x 200 mm x 75 mm), where air mixed with steam is injected at the bottom of the domain with a velocity of 0.7 m/s and a temperature of 300 K, thus allowing for fluidization of the DEM particles to occur. A single phase (gas mixture) is created using species transport with reactions enabled. Turbulence is modeled with SST k-omega model. The model is initialized to 1000 K to facilitate ignition, and particles in Rocky are also set at 1000 K. Two particle sizes were considered: 3 mm and 4 mm, with a volumetric inlet initialized at t=0 s. and The high temperature in the reactor can be maintained by the combustion of the particles and the exothermic gas phase reactions.
Ansys Rocky handles the particle reaction using the added CFD Coal combustion module, which includes the oxidation of carbon into CO2 and the conversion of CO2 to CO at the surface of the particle.
Ansys Fluent handles the gas-phase reactions, which includes the oxidation of carbon monoxide and the water shift reaction between CO and H2O.
Rocky and Fluent can then be set to run at the same time, allowing us to track the particle behaviour and the flow, temperature, and compositions in the gas phase. Here is the particle profile colored by velocity and temperature. We can observe that the higher velocity on the top layers tend to undergo an increase in temperature.
We can also view the two-way coupling between the gas and the particles in action, as the gas fluidizes the particles, thereby increasing combustion.
The contours for heat of reaction in the gas phase, temperature in the gas phase, mass fraction of CO2 and CO at the end of 8 seconds are shown below:
Using Rocky's time plots, we can also see how the reaction rate for the oxidation of carbon is affected by the particle's average velocity, and how the average temperature of particles change with respect to time. Notice that only a small fraction of the particle mass is burned during the 8-second run.
Detailed explanation of the model setup in both Rocky and Fluent is shown in the video below:
Rocky simulation software uses DEM to model coal combustion, capturing particle motion, collisions, breakage, and fluid interactions. Coupled with Ansys Fluent, it enables two-way CFD-DEM simulations to analyze combustion, heat transfer, and emissions. Its high-performance solvers handle millions of particles, while post-processing and multiphysics integration support detailed evaluation and optimization of industrial-scale systems.
Accurate Particle Modeling: Realistic shapes and sizes improve predictions of combustion behavior.
CFD-DEM Coupling: Simulates interactions between particles and fluid, including heat and reactive flows.
Scalable Simulation: Multi-GPU solvers handle large particle counts and complex geometries.
Advanced Analysis: Post-processing and multiphysics integration support performance and emissions evaluation.
Ozen Engineering Inc. leverages its extensive consulting expertise in CFD, FEA, optics, photonics, and electromagnetic simulations to achieve exceptional results across various engineering projects, addressing complex challenges.
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