Evaluation of Kinetic Mechanisms for Direct Fired Supercritical Oxy-Combustion of Natural Gas

Abstract

Existing kinetic mechanisms for natural gas combustion are not validated under supercritical oxy-fuel conditions because of the lack of experimental validation data. Our studies show that different mechanisms have different predictions under supercritical oxy-fuel conditions. Therefore, preliminary designers may experience difficulties when selecting a mechanism for a numerical model. This paper evaluates the performance of existing chemical kinetic mechanisms and produces a reduced mechanism for preliminary designers based on the results of the evaluation. Specifically, the mechanisms considered were GRI-Mech 3.0, USC-II, San Diego 204-10-04, NUIG-I, and NUIG-III. The set of mechanisms was modeled in Cantera and compared against the literature data closest to the application range. The high pressure data set included autoignition delay time in nitrogen and argon diluents up to 85 atm and laminar flame speed in helium diluent up to 60 atm. The high carbon dioxide data set included laminar flame speed with 70% carbon dioxide diluent and the carbon monoxide species profile in an isothermal reactor with up to 95% carbon dioxide diluent. All mechanisms performed adequately against at least one dataset. Among the evaluated mechanisms, USC-II has the best overall performance and is preferred over the other mechanisms for use in the preliminary design of supercritical oxy-combustors. This is a significant distinction; USC-II predicts slower kinetics than GRI-Mech 3.0 and San Diego 2014 at the combustor conditions expected in a recompression cycle. Finally, the global pathway selection method was used to reduce the USC-II model from 111 species, 784 reactions to a 27 species, 150 reactions mechanism. Performance of the reduced mechanism was verified against USC-II over the range relevant for high inlet temperature supercritical oxy-combustion.

Molecular Dynamics Study of Combustion Reactions in Supercritical Environment. Part 3: Boxed MD Study of CH3 + HO2 → CH3O + OH Reaction Kinetics

“…8 Although several kinetic models for the methane combustion mechanism were developed, none of them was designed for oxy-combustion specifically. 9,10 These mechanisms involve a large number of elementary reactions, and some of them may be altered by the presence of carbon dioxide in large concentrations and high pressures. 11 Recently we extended our efforts toward development and validation of kinetic mechanisms specific for oxy-fuel combustion.…”

“…Oxy-fuel combustion technology, where CO 2 replaces nitrogen as diluent to control the flame temperature, holds a great promise of increased energy efficiency, reduced nitroxide pollution, , and an opportunity for carbon sequestration. , In many studies the standard combustion mechanisms are presumed to be valid at CO 2 -reach conditions for data interpretation and modeling the flame composition, , or turbine design . Although several kinetic models for the methane combustion mechanism were developed, none of them was designed for oxy-combustion specifically. , These mechanisms involve a large number of elementary reactions, and some of them may be altered by the presence of carbon dioxide in large concentrations and high pressures …”

Features of methane-hydrogen mixtures combustion in oxy-fuel power cycle combustion chamber

“…According to the data presented in [12][13][14], the most adequate patterns for simulating the combustion under non-standard conditions are: As expected, the normal flame propagation rate (figure 4) increases with an increase in the hydrogen fraction in the fuel. When the carbon dioxide content in the combustion zone is 30% of the total amount, the entire curve lies below the selected range.…”

“…The main goal is to determine the СН 4 /H 2 ratio in the fuel and the СО 2 diluent amount. The initial data for determining the fuel and oxidizer flow rates that are required to heat the working medium to the initial cycle temperature are shown in table 1 [13]. The media heat capacity values at the given temperature and pressure values have been taken from the REFPROF database.…”

Natural Gas-Oxygen Combustion in a Super-Critical Carbon Dioxide Gas Turbine Combustor

“…The analysis results provide a conclusion on the necessity to change the combustor inlet oxygen-fuel mixture velocity and the diluent content (γ -CO2 / (CO2 + O2)) that provide the flame stability and complete burn-out. The combustor envelope dimensions are similar to the traditional gas turbines [10][11][12].…”