R&D project on 3D-simulation of combustion process in biomass power plants
Driven by climate change the role of sustainable and CO2-neutral energy sources has rapidly grown within the past decades. In this context biomass has registered more importance for thermal power generation. Usage of solid biofuels for the production of heat and electricity is pre¬dominantly based on grate furnace systems. Although grate firing is a flexible technology which requires only a minimum of fuel preparation, utilization of solid biofuels may lead to challenges due to the fuels inhomogeneous nature. In addition to efficiency fluctuation, the formation of pollutants and deposits are common issues of biomass power plants. In order to address these kinds of challenges a better understanding of the entire combustion process is essential.
Numerical simulation offers high potential for detailed investigation of complex processes and has been used for optimization of numerous applications. They are beneficial for analysis of hardly accessible processes and reduce expensive experiments to a necessary level. Moreover, numerical investigation can provide new impulses for improvements of existing plants as well as for design optimization of future systems. Hence, numerical simulation can be profitable for both system operators and manufacturers.
The University of Rostock has developed a highly detailed procedure for numerical simulation of solid biomass combustion which allows for three-dimensional insights into large-scaled furnaces. The multi-purpose concept is based on CFD (Computational Fluid Dynamics) and discrete particle methods (DEM, Discrete Element Method). That is, movement and conversion of individual fuel particles is considered within the combustion system. Thermal interaction between a particle and its neighbours as well as between a particle and its ambient fluid is taken into account. Each particle undergoes thermal conversion processes, such as drying, pyrolysis, char gasification and char oxidization. Depended on fuel type, particle size and local conditions, for a certain particle these steps may either appear sequentially or simul¬taneously. This effect is captured by an extensively validated one-dimensional particle model.
Typical simulation results of the fuel particles include trajectories, mass loss, composition as well as surface and core temperature. Besides, the solution contains three-dimensional scalar fields of fluid velocity, pressure, species and temperature. The concept has been successfully applied for simulation of wood chip combustion in a large-scaled grate firing plant. As tracking of particles is a central feature of the discrete particle approach, simulation has been carried out with a special emphasis on modelling of deposition by adhering fly ash particles. However, the technique is modular and can be extended by further models to address various fuels and tasks, which are for instance:
- Modelling of pollutant and deposit formation,
- Optimization of flue gas cleaning systems,
- Improving system operation or future system design.
Since the concept is flexible, it is not restricted to a specific combustion system. Among technical grate furnaces, the procedure has also been used to simulate the combustion of woody biomass in a fluidized bed reactor. Finally, it is worth stating that a discrete particle method for simulation of municipal solid waste incineration is currently in progress.
Fields of cooperation
- Thermal conversion of biomass
- Biomass and waste combustion
- Flue gas cleaning • Reactor and furnace design
- Power plant operation
For further information please contact: Dorian Holtz Institute of Technical Thermodynamics, Rostock University, Germany
Phone: +49 (0) 381 498 9429