Project
Unsteady modelling and simulation of oxy-fuel combustion chambers
Figure 1. Instantaneous gas-phase and particle temperatures (left) and time averaged gas-phase temperatures (right) of
pulverized Rhenish Lignite combustion with air. Averaged gas-phase streamlines and blue Uz=0 m/s isolines indicating
recirculation zones are also shown. The escalating climate crisis calls for urgent CO2 emission reductions, especially in the energy sector, which continues to be dominated by fossil fuels. Air fired coal combustion plants are still widely used in Europe and across the globe. For decreasing the environmentalimpact of coal combustion, oxyfuel combustion coupled with carbon capture and storage(CCS) is a promising alternative. In oxyfuel combustion, high purity O2 is mixed with recycled
flue gases. Unlike air combustion where N2 is abundant, oxyfuel combustion leads to a combustion medium and exhaust gases that are rich in CO2, which allows for an easier application of CCS. Oxyfuel combustion of pulverized coal or biomass can be potentially achieved by retrofitting of traditional power plants as a near term solution for clean energy. The aim of this project is the identification of the effects of oxyfuel atmospheres on pulverized solid fuel combustion through computational fluid dynamics (CFD). This project is part of the Collaborative Research Center (CRC) 129 Oxyflame.
Project Details
Project term
February 10, 2023–March 1, 2024
Affiliations
TU Darmstadt
Institute
Institute for Simulation of reactive Thermo-Fluid Systems
Project Manager
Principal Investigator
Methods
Simulating pulverized solid fuel combustion poses significant modeling challenges due to the complex interplay between turbulent transport, turbulence-chemistry interaction (TCI), and the intricate kinetics of solid fuel particles like coal and biomass. On the larger combustors, radiative heat transport also becomes significant. Capturing these phenomena requires advanced and detailed models. In this study, a heavily customized version of the open-source solver OpenFOAM is used. The particle conversion model is enhanced for precision, turbulence is resolved using Large Eddy Simulation (LES), and the chemical kinetics are handled through a flamelet tabulation approach specifically adapted for solid fuels. Radiation models are included, considering both the particle and gas-phase radiation. As part of CRC 129, various burner configurations of different complexity levels are studied. The two burners simulated with this computing project are both swirled combustion chambers, one lab-scale and the other semi-industrial. The lab-scale burner has similar design characteristics to the semi-industrial one and due to its high optical accessibility, advanced measurement data is available to validate the simulation framework. The lab-scale burner is simulated and analyzed in detail for six different operating conditions (three singlephase methane and three methane assisted coal), where atmosphere (air or oxyfuel), flowrates and thermal powers are systematically varied. Lastly, the simulation of the semiindustrial
burner operated with pulverized walnut shells is demonstrated.
Results
The LES of the lab-scale swirled burner is shown to capture different characteristics of operating conditions. The simulations are validated with the gas-phase velocity and temperature measurements. The comparison of single-phase methane and methane assisted coal combustion revealed a flame locations shifted downstream due to particle heat up. Among multiphase simulations, the oxyfuel atmosphere resulted in a few changes due to the higher heat capacity and density of the CO2 compared to air. The particles in oxyfuel conditions are found to heat up more quickly and react earlier due to the higher gas-phase heat capacity. Additionally, the higher density of oxyfuel atmosphere resulted in increased drag forces on particles, changing their trajectories and increasing their residence times near the reactive regions. For the semi-industrial burner, the preliminary simulations demonstrated reasonable and comparable results to the smaller burner. Some particle behavior differences are identified between the larger and smaller burners, such as varying residence times in the flame and varying heating rates for the particles.
Additional Project Information
DFG classification: 404-03 Fluid Mechanics
Software: OpenFOAM, Python3, Cantera
Cluster: CLAIX
Publications
Pascal Steffens, Leon Berkel, Sandro Gierth, Paulo Debiagi, Burak Özer, Anna Maßmeyer, Hendrik Nicolai, Christian Hasse, LES of a swirl-stabilized 40 kWth biomass flame and comparison to a coal flame, Fuel, Volume 372, 2024, 132098, ISSN 0016-2361, https://doi.org/10.1016/j.fuel.2024.132098.
Leon Loni Berkel, Pascal Steffens, Hendrik Nicolai, Sandro Gierth, Paulo Debiagi, Henrik Schneider, Andreas Dreizler, Christian Hasse, Comprehensive Analysis of the Effect of Oxyfuel Atmospheres on Solid Fuel Combustion Using Large Eddy Simulations, Fuel 2024, (In revision, preprint available: http://dx.doi.org/10.2139/ssrn.4874714)
Felix Bernards, Numerical Investigation of the Transition of Single Particle to Group
Particle Combustion, Darmstadt, 2023