Chemical Reactor Modeling of Oxy–Fuel Combustion Chamber for Semiclosed Combined Cycle

Abstract

This paper compares standard gas turbine combustion chambers and CO2-diluted oxy–fuel combustion chambers for a semiclosed combined cycle at a preliminary design level. To this end, simple chemical reactor networks, based on the well-stirred reactor plus plug flow reactor scheme, are analyzed using the Cantera package and the GRI 3.0 chemical kinetics mechanism. The focus is put on the CO consumption process and the final CO concentration. The behavior of this model suggests the use of the adiabatic equilibrium temperature to characterize the composition at any station inside the chamber and the incipient lean blow-out equilibrium temperature to fix the well-stirred reactor volume. This model is applied to a feasible design point of a power production cycle (combustion exit temperature 1600 K, combustion pressure 30 bar). The fuel is a natural gas with an 87% by volume CH4 content, the ASU stream is a 95% O2 gas, and the recirculated gas is an 82% CO2 gas. The residence times required for CO burnout are approximately 30% greater than those for air combustion for the same conditions, although the required lengths are much closer. The residence times and lengths would be reduced if the combustion exit temperature or the combustion pressure of the cycle was increased.

A review on combustion instabilities in energy generating devices utilizing oxyfuel combustion

“…Furthermore, at the same equivalence ratio, the CH 4 /O 2 flames blowoff at a longer residence time compared with the methane‐air flames, supporting the earlier observation for comparatively slower chemistry in the case of the oxy‐combustion mixture. This is also consistent with greater residence time (30% more time) required for CO burnout from oxy‐combustion in comparison with natural‐gas‐air combustion at the same conditions as reported by Timón et al 83 Consequently, the CH 4 /O 2 flames studied by Li et al 79 blowoff at a lower Damköhler number, Da, and at a higher equivalence ratio compared with that of CH 4 /air flames as shown in Figure 7. Similarly, in the case of non‐premixed C 3 H 8 /O 2 flames investigated numerically and experimentally by Abubakar et al, 80,84 the Da decreases with increasing CO 2 ‐dilution levels as shown in Figure 8.…”

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

“…4,5 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, 6,7 or turbine design. 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.…”

“…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 …”

Investigation of Oxy-Fuel Combustion through Reactor Network and Residence Time Data

“…A comparison between CRN-values and equilibrium predicted values is given in Table 7. The equilibrium values were calculated using the hypothesis of plug flow at a constant temperature, set at 1500 K. The results show that equilibrium CO content is more significant for O 2 /CO 2 conditions [4,24,65]. The higher CO emission for air combustion compared to oxyfuel combustion is attributed to the different mixing aspects highlighted in previous sections.…”

“…These early methodologies have been further employed in more recent works [20][21][22] which comprise the refinement for diffusion flames based on the work in [23]. Timón et al followed the example set by [17] in their work [24] comparing standard gas turbine combustion chambers and oxyfuel combustion for the Semi-Closed Oxyfuel Combustion Combined Cycle (SCOC-CC). The system was rigorously modeled from the technical point of view, and highlighted the different technical aspects to consider when designing oxyfuel combustion systems.…”