A Wet Coal Combustion CFD simulation is an essential tool for engineers designing modern, clean, and efficient power plants. Unlike dry coal, wet coal contains natural moisture. Burning it is a complex process, but it can be more efficient and produce fewer pollutants like NOx. A DPM Combusting particle simulation is the only way to accurately study this process on a computer. It allows us to follow the life of a single particle of coal as it flies through the hot combustor, dries out, releases flammable gases, and burns away.

This report details a Wet Coal Combustion fluent analysis performed in ANSYS Fluent, a leading software for these types of simulations. We use a powerful tool called the Discrete Phase Model (DPM) to create a “digital twin” of a Combusting particle Fluent model. This virtual particle has all the properties of real wet coal, including its 8.2% moisture content. A DPM Combusting particle CFD study is critical because it models all the physics at once: the movement of the particles, the evaporation of water, the release of coal gases, the chemical reactions of burning, and the intense heat transfer. This allows engineers to see exactly where the coal burns, how hot the flame gets, and if the combustor is designed correctly to get the most energy out of the fuel. For more tutorials on DPM simulation techniques and combusting particle modeling, visit our detailed DPM CFD Simulation tutorials covering various applications in Fluent.

Figure 1: Wet coals need combusting particle type in Fluent for realistic modeling

Simulation process: Wet Coal Simulation Using DPM Combusting Particle

The simulation process for this Wet Coal Combustion CFD study was carefully built in ANSYS Fluent to capture the complete journey of a coal particle. A transient, or time-dependent, simulation was used because the burning process changes over time. The Species Transport model was activated to track all the different chemicals involved, such as oxygen, carbon dioxide, and the gases released from the coal, including the prediction of Thermal and Fuel NOx.

The core of the simulation was the Discrete Phase Model (DPM) with two-way coupling. This means the hot gas in the combustor heats the coal particles, and in return, the burning particles release heat and gas that change the behavior of the main gas flow. We specifically used the “combusting particle” type in Fluent. This is a special DPM model designed for solid fuels, and it follows a precise, three-step life cycle for each particle.

First, the particle, which contains 8.2% moisture, enters the hot combustor. The model calculates how long it takes for this water to evaporate into steam. This is the drying phase. Second, once the particle is dry and its temperature rises further, it undergoes devolatilization, where it violently releases flammable gases. This is the main burning phase. Third, after the gases are gone, a solid piece of carbon, called char, is left. The model then calculates the slower burning of this solid char in a process called char oxidation. To accurately model the intense heat in the combustor, the Discrete Ordinates (DO) radiation model was also enabled. This is critical because, in a real combustor, most of the heat is transferred by radiation, like the heat you feel from a bonfire. This complete physics setup ensures a realistic simulation of the entire wet coal combustion process.

Figure 2: cylindrical combustor geometry and the high-quality structured mesh used for the Wet Coal Combustion CFD simulation, with refined cells near the particle injection inlet.

Post-processing: Engineering Analysis of a Wet Coal Particle’s Journey

The simulation results tell the complete life story of a wet coal particle as it travels through the combustor. By analyzing this journey, we can deliver a clear verdict on the combustor’s design and performance. A wet coal particle begins its journey at the inlet (x=0). The temperature here is cool, around 400-500 K, as seen in Figure 5. The particle does not ignite immediately. Fro

m an engineering viewpoint, this delay is a defining feature of wet coal combustion. The particle must first travel through the hot gas, absorbing energy to complete its first critical task: evaporating its 8.2% moisture content. This drying and heating phase takes time. The simulation shows that it takes approximately 1.8 meters of travel for the particle to become hot enough to begin the main combustion stage. This initial, non-burning zone is crucial for designers to understand; it means the first part of the combustor is acting as a “dryer” and not a “burner.”

At exactly x ≈ 1.8 m, the particle’s life changes dramatically. Having dried out and reached a critical temperature, it begins devolatilization, violently releasing its flammable gases. The mass source plot (Figure 3) shows this as a sharp, narrow peak, reaching a maximum value of 0.10 kmol/m³s⁻¹. This peak is the “cause” in our story; it represents the moment of maximum fuel release.

The “effect” is seen instantly in the temperature plot (Figure 5). At the exact same location, x ≈ 1.8 m, the temperature spikes to a massive 2,200 K (over 1900°C). This is the flame front. The temperature contour in Figure 6 visualizes this as the “yellow-bright” inferno. The perfect alignment of the mass source peak and the temperature peak is the single most important achievement of this simulation. It provides definitive proof that the model has correctly captured the physics: the release of fuel gas directly creates the high-temperature flame. The narrowness of the peak shows that this is a very intense and localized reaction, a key characteristic of this type of combustion.

Figure 3: The centerline profile of the volumetric particle mass source from the Fluent DPM simulation, showing a sharp peak of 0.10 kmol/m³s⁻¹ at x = 1.8 m, which pinpoints the primary combustion zone.

Figure 4: 3D volumetric contour of the particle mass source from the CFD analysis, visually confirming that the most intense particle reactions are localized in a specific zone near the inlet.

After the violent gas release, the particle’s journey is not over. It is now a glowing piece of solid carbon, or char. As it travels from x = 2.0 m to the outlet, the mass source drops to near zero, and the temperature gradually cools from 2,200 K down to about 1,100 K. This indicates the final, slower stage of combustion: char oxidation. The temperature remains high enough to ensure that this char burns completely, which is a sign of an efficient combustor design, preventing wasted fuel and harmful carbon monoxide emissions.

Figure 5: The centerline temperature profile, showing a peak temperature of 2,200 K at x ≈ 1.8 m, which directly corresponds to the location of the maximum mass release from the combusting particles.

For a designer or manufacturer, this “life story” provides invaluable intelligence:

1. It Defines the Hottest Zone: The simulation pinpoints the exact location (x ≈ 1.8 m) and intensity (2,200 K) of the main flame. This is critical information for material selection and cooling system design. The combustor walls in this specific area must be made of materials that can withstand extreme temperatures, or they must be actively cooled.
2. It Validates the Combustor’s Length: The analysis shows that the entire combustion process—drying, devolatilization, and char burnout—is successfully completed within the length of the chamber. This tells the designer that the combustor is long enough for efficient fuel consumption but not wastefully oversized, which saves on material costs and weight.
3. It Informs Emission Control Strategies: The peak flame temperature of 2,200 K is a primary driver of Thermal NOx formation, a major pollutant. By accurately predicting this temperature, the simulation provides the essential data needed to design and evaluate strategies to reduce NOx emissions, helping the power plant meet strict environmental regulations.

Figure 6: A side-view temperature contour from the Fluent CFD simulation, visualizing the intense, yellow-bright flame front and the heat distribution throughout the combustor, as calculated by the DO radiation model.