Reaction Kinetics for High-Pressure Hydrogen and Methane Oxy-combustion in the Presence of High Levels of H2O and CO2
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Continued use of fossil fueled heat and power generation calls for a multi-faceted approach to ensure their associated emissions, in particular CO2 emissions, are mitigated in an economically viable manner. A path to sustainable development, not only demands switching from carbon intensive fuels such as coal to the likes of natural gas or biofuels, it also requires equipping fossil-fueled systems with carbon capture, utilization and storage (CCUS) technologies. One promising carbon capture technology, is oxy-fuel combustion with cooling and compression CO2 capture. Oxy-fuel combustion entails reacting the fuel with nearly pure oxygen (95-99 mole %), producing a flue gas composed mostly of CO2 and H2O, with smaller quantities of N2 and Ar. As the flue gas is CO2-rich and is not diluted by large quantities of N2, it can be separated physicaly through compression, cooling, and auto-refrigeration steps. Pressurized variants of oxy-combustion technologies enable integration of CO2 capture and compression with the combustion process, and hold prospects for improved economics and reduced footprint. On the path for these promising technologies to reach their full potential, one of the knowledge gaps lies within the understanding of their combustion chemistry. This is due to the presence of high concentrations of H2O (up to 65%) and/or CO2 (up to 90%) in these systems. The impact of high H2O concentrations on pressurized oxy-combustion kinetics has not been explored. This research aims to fill this knowledge gap by generating new experimental data and developing experimentally-validated reaction mechanisms able to better characterize and model pressurized oxy-combustion kinetics behavior in presence of large quantities of H2O and CO2. To this end, novel shock tube experimental ignition delay time (IDT) test data were generated in collaboration with King Abdullah University of Science and Technology (KAUST) for reactive mixtures involving 4% H2, 0.48-3.44% CH4, at equivalence ratios (φ) of 0.93-1, to delineate the effect of high concentrations of H2O, CO2, and pressure on combustion kinetics. A hierarchical model development and validation approach is presented for high-pressure combustion kinetics in the presence of high levels of H2O and CO2. Two models, one for H2/CO and the other for CH4 high-pressure combustion kinetics were developed with particular attention to pressure- and bath gas-dependent reaction rates. High-pressure H2 IDT experiments were performed at temperatures of 1084-1242 K and pressures of 37-43.8 bar at φ of 1. IDT data for four different bath gases, namely: Ar, 45%H2O/Ar, 30%H2O/15%CO2/Ar, and 45%CO2/Ar are provided. Low-pressure H2 IDT experiments were also conducted across a temperature range of 917-1237 K, pressure range of 1.6-2.4 bar, at φ of 1 in Ar and 45%CO2/Ar bath gases. A minimally-tuned H2/CO reaction mechanism, CanMECH 1.0, targeting high-pressure combustion in the presence of large concentrations of H2O and CO2 is developed. CanMECH 1.0 is validated against both the shock tube IDT data of this work, and other H2 and H2/CO shock tube IDT datasets from literature. CanMECH 1.0 performance is compared to a well-cited incumbent syngas oxidation kinetics mechanism (Keromnes et al., Combust. Flame 160 (2013) 995-1011). It outperformed the incumbent for 16 out of 25 data subsets, and exhibited a similar performance for another two. CanMECH 1.0 improved model predictions of this work’s shock tube IDT data for H2O- and CO2- laden reactive mixtures, as well as all IDT data at pressures of 17-43.8 bar, which are of particular value to pressurized oxy-fuel combustion applications relevant to this work. Overall CanMECH 1.0 brought about a 26% improvement relative to the incumbent in predicting all the IDT validation data considered in this work. High-pressure CH4 IDT experiments were performed at CH4 concentrations of 0.48-0.5%, temperatures of 1536-1896 K, pressures of 37-53 bar, φ of 0.93-1, in the presence of Ar, 45%H2O/Ar, 30%H2O/15%CO2/Ar, and 45%CO2/Ar. Low-pressure IDT experiments were also conducted at temperatures of 1486-1805 K, pressures of 1.8-2.4 bar, CH4 concentrations of 3-3.44%, at φ of 1 in bath gases composed of Ar and 45%CO2/Ar. An improved CH4 reaction mechanism, CanMECH 2.0, is developed, by embedding CanMECH 1.0 (H2/CO mechanism) into a recent and well-validated C1-C4 detailed kinetics mechanism, AramcoMECH 2.0. CanMECH 2.0 performance is evaluated and compared with AramcoMECH 2.0, in addition to AramcoMECH 3.0, in predicting the shock tube IDT validation targets. CanMECH 2.0 is shown to improve the overall performance of the two incumbent mechanisms by 1% and 3%, respectively.
Cite this version of the work
Ashkan Beigzadeh (2021). Reaction Kinetics for High-Pressure Hydrogen and Methane Oxy-combustion in the Presence of High Levels of H2O and CO2. UWSpace. http://hdl.handle.net/10012/17296