DEM applied to combustion in boilers
- Alvaro Filho
- Jun 5
- 4 min read
The main function of a boiler is to produce heat to heat water or generate steam, which can be used in different industrial processes and in power generation. This equipment can operate with various types of fuel, including fuel oils, natural gas, electricity and biomass.
In the case of boilers that use biomass, the heat is generated by burning materials of organic origin, such as pieces of wood (chips), sugarcane bagasse and straw, rice husks and other waste from agriculture. This alternative is considered more sustainable because it uses byproducts that, considering their life cycle, have zero or very low carbon emissions.
Figure 1 – Biomass
Figure 2 – Operating principle of a biomass boiler
Using biomass as an energy source brings significant environmental benefits. As it is a renewable resource, it allows the use of organic waste, such as agricultural and forestry remains, and helps to reduce the emission of greenhouse gases — especially when compared to the use of fossil fuels such as diesel oil.
This is because biomass participates in a more balanced carbon cycle: plants absorb carbon dioxide (CO₂) from the atmosphere as they grow, and this same CO₂ is released again during combustion. In addition, because it contains shorter carbon chains, its combustion is more efficient, generating fewer pollutants such as carbon monoxide (CO), nitrogen oxides (NOₓ) and unburned hydrocarbons. Fossil fuels, especially those with longer carbon chains (such as C₈ or C₁₂), are more difficult to break down during combustion, which favors the formation of intermediate species and increases the emission of these pollutants. Thus, the net impact of biomass tends to be much smaller than that of fossil sources.
Figure 3 - Carbon cycle
The efficiency of biomass combustion inside boilers depends directly on how the fuel is distributed over the grate. In fixed grate systems, it is common for the material to accumulate unevenly, resulting in partially burned layers over other unburned layers. This creates areas with incomplete combustion, compromising the boiler's thermal performance.
In addition, this accumulation of unburned fuel can cause accidents due to spontaneous combustion that can occur when it is removed from the boiler hot and comes into contact with oxygen in the air again. Some companies report accidents, for example, when blowing compressed air to unclog the ash collection hopper and with unburned biomass at high temperatures.
Combustion modeling using STAR-CCM+
As already shown in the post DEM simulation applied to boilers, initially only the flow of biomass over the grate was evaluated, comparing the cases with fixed and vibrating grates. At this stage, the combustion process was incorporated into the model.
Using Simcenter STAR-CCM+, it is possible to simulate biomass combustion, observing the reduction in particle mass due to carbon volatilization during combustion. The primary air flow, which acts as an oxidizing agent, is also considered, allowing its influence on combustion efficiency and gas flow to be evaluated.
Figure 4 – Discrete Element Method (DEM)
By associating the DEM model with the combustion model, it is possible to map biomass combustion.
Figure 5 - Computational model of the grate and reaction environment
The Simcenter STAR-CCM+ Eddy Break-up combustion model enables detailed simulation of the biomass burning process. It combines a fluid domain, which represents the air where the reactions will occur, and the DEM itself, in addition to other auxiliary models such as turbulence and mass transfer.
With this, it is possible to observe the evolution of the combustion process, evaluate the time required for complete combustion, the temperatures reached during the reaction, the products generated (such as CO₂, CO, H₂O, among others) and the mass flow required to maintain combustion in a steady state.
Figure 6 - Molar fraction of air, fuel, carbon monoxide and carbon dioxide during the combustion reaction
This makes it possible to map the entire thermal system, identifying zones of high and low reactivity, regions with incomplete combustion, areas of material accumulation or oxygen deficiency, in addition to optimizing the air supply and the internal geometry of the boiler.
Video 1 – Air and particle temperature during biomass burning
This integration between the DEM flow model and the combustion model allows a complete understanding of the behavior of biomass within the system, promoting improvements in thermal performance, greater efficiency in energy conversion and reduction in pollutant emissions.
Video 2 – CO₂ concentration and particle mass during biomass combustion
Using Simcenter STAR-CCM+ to simulate biomass flow and combustion allows the entire thermal process to be accurately represented, from fuel movement to complete combustion. This approach makes it possible to identify operational failures, optimize boiler design, and adjust variables such as geometry, vibration, and air supply. This makes it possible to increase energy efficiency, reduce fuel consumption, minimize emissions and waste, and make the plant safer, more reliable, and more sustainable. Simulation thus becomes an essential tool for the modernization and improvement of industrial thermal systems.
References:
CARVALHO, Leonardo Lima de. Estudo da dinâmica de escoamento da unidade Microwave Paddle Dryer. 2021. Dissertação (Mestrado em Engenharia Química) – Faculdade de Engenharia Química, Universidade Federal de Uberlândia, Uberlândia, 2021. Available at:
OLIVEIRA, Luiz. Avaliação numérica do fenômeno de mistura em tambores rotatórios. ENEMP – Congresso Brasileiro de Sistemas Particulados, 2022.
Do you want to understand how to optimize the performance of your biomass boiler and reduce emissions using advanced simulations? Schedule a meeting with CAEXPERTS now and find out how applying the combustion model coupled with DEM can transform your operation in efficiency, safety and sustainability.
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