Numerical investigation of interacting turbulent free jets and biomass particles

• Applicant: Professor Dr.-Ing. Wolfgang Schröder
• Subject Area: Fluid Mechanics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 437787677

In the 2°C-scenario to mitigate the worldwide consequences of climate change of the International Energy Agency (IEA), the direct combustion of biomass in thermal power plants plays a significant role. As carbon dioxide (CO2) is absorbed in plants and wood, these regenerative energy sources provide an opportunity of a CO2-neutral energetic utilization. According to the IEA the so-called bioenergy should account for 17% of the world’s total energy demand until 2060 [1]. To achieve the 2°C-scenario, the greenhouse gas emissions need to be reduced by 50% every decade between 2020 and 2050, while at the same time greenhouse gases have to be actively removed from the atmosphere from 2030 on [2].Unlike coal dust particles, which can approximately be modeled as spheres of a certain diameter, biomass particles for industrial firing possess a wide range of different geometries and sizes. This fact massively influences the residence times and heating times of the particles in the combustion chamber, their mixing with the combustion air, the flame stability, and consequently the efficiency and emissions of the whole power plant. To design and optimize the industrial combustion of fine-scale fuels numerical simulations of single burners or whole power plants are already widely performed. However, no accurate models have been established yet, to describe the acceleration and heating of biomass particles. Instead, these simulations typically rely on simplified models, the accuracy of which is unknown. Moreover, the high mass loading of the particles significantly impacts the structure of the turbulent free jet which forms at the burner outlet. This results in a complex interaction between both phases which significantly depends on the size and shape of the particles. However, the mechanisms of this interaction are still hardly understood.In this project the particle-jet interaction will be analyzed and classified based on novel highly resolved numerical simulations. Using direct particle-fluid simulations all length and time scales of the turbulent flow and the flow about individual particles will be resolved. This enables innovative analyses of the interaction between biomass particles and all scales of the turbulent free jet. Via the detailed understanding of these processes inferences on the global behavior of the system and a classification of the interaction with respect to the particle shape will be obtained.In conclusion, the overall objective is, based on the numerical investigation of the fundamental mechanisms, to quantify and classify the influence of the shape of biomass particles on the turbulent mixing between the carrier gas and the particles in turbulent free jets.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Matthias Meinke