Oxy-fuel Combustion Technology Research Articles

Simplified mathematical model of oxy-fuel combustion of municipal solid waste in the grate furnace: effect of different flue gas recirculation rates and comparison with conventional mode

Bioenergy carbon capture technology (BioCCS or BECCS) plays a key role in the European Green Deal, which aims to decarbonize industry and energy sectors, resulting in the production of energy with negative CO2 emissions. Due to the biogenic origin of carbon contained in municipal solid waste (MSW), the application of carbon capture in waste incinera-tion plants can be classified as BioCCS. Thus, this technology has attracted scientists' attention recently since it reduces excessive waste and emissions of carbon dioxide. Currently, there are four incineration plants in the Netherlands, Norway and Japan, in which CO2 capture is implemented; however, they are based on the post-combustion technique since it is the most mature method and not requires many changes in the system. Nevertheless, the separation of CO2 from the flue gas flow, which contains mostly nitrogen, is complex and causes a large drop in the total performance of the system. Oxy-fuel combustion technology involves the replacement of air as an oxidizer into high purity oxygen and recirculated exhaust gas. As a result, CO2-rich gas is produced that is practically ready for capture. The main goal of the study is to develop a math-ematical model of oxy-waste combustion to answer the research questions, such as how the composition of oxidant that is supplied to the process affects the combustion performance. The model includes all important processes taking place within the chamber, such as pyrolysis, char burnout and gas combustion over the grate. The results of the work will contribute to the development of oxy-waste incineration plants and will be useful for design purposes.

NO Emission Characteristics of Pulverized Coal Combustion in O2/N2 and O2/H2O Atmospheres in a Drop-Tube Furnace.

Oxy-steam combustion is a new oxy-fuel combustion technology. This paper focuses on the NO emission characteristics during the combustion of SF (Shen Fu) coal in O2/N2 and O2/H2O mixtures. Experiments were performed in a drop-tube furnace. Combustion tests were carried out in O2/N2 and O2/H2O atmospheres for various O2 concentrations (21%, 30%, 40%, and 60%) at different temperatures (1173 K, 1273 K, and 1373 K). In addition, combustion experiments at different excess oxygen ratios (λ) were conducted in O2/N2 and O2/H2O atmospheres. The influences of the atmosphere, oxygen concentration, temperature, and excess oxygen ratio on NO emissions were analyzed. The results show that the NO concentrations of SF coal combustion in the 21% O2/79% H2O atmosphere were much lower than those in the 21% O2/79% N2 atmosphere at the three temperatures considered. This was because a large amount of NO was decomposed during the SF coal combustion in the O2/H2O atmospheres. The reasons for the decomposition of NO include the selective non-catalytic reaction (SNCR) mechanism and char's important role as a catalyst for the destruction of NO, either directly or by reacting with CO or H2. In oxy-steam combustion, the NO concentrations significantly increased with the increase in the oxygen concentration from 21 vol.% to 60 vol.% and the temperature from 1173 K to 1373 K. The excess oxygen ratio (λ) slightly impacted the NO emissions in the O2/H2O atmosphere.

Combustion behavior of solid waste fuels in the vertical tube reactor under different oxy-fuel environments

Oxy-fuel combustion technology has been recognized as one of the promising ways for cost-effective CO2 capture. The co-combustion characteristics of flax straw biomass/bituminous coal mixture (FS/BC) and flax straw biomass/sewage sludge mixture (FS/SS) under air, oxy-fuel (21%/79% O2/CO2) and oxygen-enriched oxy-fuel (30%/70% and 40%/60% O2/CO2) conditions were investigated in the vertical tube reactor. In particular, the study focused on the burning characteristics, the effect of blending ratio, and flue gas emissions. The findings indicated that flax straw biomass exhibited superior ignition performance compared to its blends with sewage sludge and bituminous coal. A higher O2 concentration from 21% to 40 led to a reduction in ignition delay time by 4s at 850 ℃ and by up to 10s at 950 ℃. Moreover, char combustion time was reduced by 50% for FS/SS blends due to the lower fixed carbon content compared to FS/BC blends. Additionally, increasing the O2 concentration resulted in lower emissions of CO by ∽40% and N2O by ∽45% for both blends. However, this also led to a slight increase in SO2 and NO emissions by ∽15% and ∽26%, respectively. The optimal conditions for the tested samples in oxy-fuel environment were found to be 30% O2/70 CO2, which enhanced combustion performance while lowering flue gas emissions.

Energy and Economic Assessment of Oxy-Fuel Combustion CO2 Capture in Coal-Fired Power Plants

Oxy-fuel combustion technology replaces air with a mixture of pure O2 and recycled flue gas for coal combustion, which leads to difficulties in the waste heat recovery of flue gas in the boiler tail of coal-fired power plants. This paper proposes a new integration scheme for waste heat recovery of flue gas in coal-fired power plants with oxy-fuel combustion CO2 capture. By introducing an oxygen preheater, a recycled flue gas preheater, and a low-pressure economizer, the waste heat of flue gas is fully recovered to preheat oxygen, recycled flue gas, and feed water, respectively. The proposed scheme simultaneously ensures the safe operation of the recycled fan and improves the thermal performance of the coal-fired power plants. Compared to the air combustion configuration, the boiler’s efficiency and gross power efficiency in the oxy-fuel combustion configuration are increased by 0.42% and 1.29%, respectively. Due to power consumption for the added equipment, the net power efficiency is reduced by 10.41%. A techno-economic analysis shows that the cost of electricity for oxy-fuel combustion in coal-fired power plants has increased from USD 46.45/MWh to USD 80.18/MWh, and the cost of the CO2 avoided reaches USD 43.24/t CO2.

Comparison of Water- and Amine-Based Carbon Capture Processes for Air and Oxyfuel Combustion Technologies

Comparison of Water- and Amine-Based Carbon Capture Processes for Air and Oxyfuel Combustion Technologies

Numerical investigation of the oxy-fuel combustion in the fluidized bed using macroscopic model supported by CFD-DDPM

Oxy-fuel combustion (OFC) presents a promising strategy for reducing carbon emissions from coal combustion. Traditional multiphase flow models (MFM) used for OFC simulations face challenges in integration and optimization with systems like carbon capture and electrolysis. Constructing a cost-effective and versatile macroscopic model simulation is critical for the industrial application of OFC. This study employs CFD-DDPM to obtain fluid dynamics parameters and couples heat and mass transfer models to construct macroscopic model of OFC based on a fluidized bed. Through calculations of OFC using both the macroscopic model and CFD-DDPM, molar fractions of O2, CO2, NO, and SO2 under various combustion conditions were found consistent with experimental measurements. Predictions under Recirculated Flue Gas (RFG) conditions showed comparable O2 and CO2 molar fractions at 30 % O2 & RFG, with the macroscopic model achieving 10.3 % and 69.3 %, versus 6.9 % and 72 % in CFD-DDPM. This demonstrates the ability of a macroscopic model to predict the design of the OFC in the fluidized bed. Importantly, the computational time of the macroscopic model is over 99 % shorter than that of CFD-DDPM. Consequently, employing a rapid simulation based on the macroscopic model method enables efficient simulation of OFC systems and facilitates the integration of oxygen combustion systems with other technologies like electrolysis. This approach provides valuable guidance for the development and application of OFC technology.

CFD modeling investigation of oxy-fuel combustion application in an industrial-scale FCC regenerator

The increase in atmospheric CO2 concentration and its consequential impact on climate change have elicited increased public concern. The refinery units including fluid catalytic cracking (FCC) generate substantial quantities of CO2. To mitigate the emission from the FCC process, oxy-fuel combustion has emerged as a prospective carbon capture and storage technology. This study presents the first trial for the modeling investigation of a 70 kt/a industrial FCC regenerator under the scenario of retrofitting it with oxy-fuel combustion technology. Employing the Eulerian-Eulerian model, a CFD model integrating heat transfer and coke combustion reactions has been established. The detailed hydrodynamics, temperature, and species concentration distribution inside the regenerator are obtained under both air-firing and oxy-firing conditions, which are further compared to exploit the possibility of oxy-fuel combustion retrofitting. As has been found, decreases in gas temperature and carbon conversion rate were observed for 21 % O2/79 % CO2 atmosphere in comparison to the air reference case due to the differences in gas properties between N2 and CO2. This discrepancy resulted in a drop of 17 K in dilute phase temperature and 2 K in dense phase temperature. The bed density also exhibited a large with the oxy-firing conditions, with notable observations revealing a lower bed density below a height of 4.2 m, transitioning to a higher density above said height. Sensitivity analysis was also conducted for three principal operating parameters, including superficial gas velocity, oxygen partial pressure, and catalyst circulation rate. An increase of oxygen partial pressure to 27 % or a decrease of the catalyst circulation rate to 20.7 kg/s proved effective in achieving the same temperature profile and even a slightly better carbon conversion in comparison to air-firing regeneration.

Low-carbon optimal dispatch strategy of power systems considering the combined operation of oxy-fuel combustion and electric hydrogen production

ABSTRACT Oxy-fuel combustion technology offers a promising solution for achieving nearly zero carbon dioxide emissions from coal-fired units, presenting a viable path toward low-carbon dispatch. This study establishes a simulation model for the low-carbon operation of power systems, focusing on the integrated operation of an oxy-fuel combustion plant and electric hydrogen production. By incorporating oxygen generated from electric hydrogen production into the oxy-fuel combustion plant, the primary objective is to minimize system operation costs. Through simulation analysis and verification, a comparative scenario is constructed to evaluate performance. The simulation results indicate that the joint operation approach yields significant benefits. In comparison to separate operation, the joint operation strategy leads to a reduction of approximately 7.38% in total system costs, 18.79% in operating costs, and 23.56% in carbon emissions. This integrated approach not only achieves lower carbon emissions but also results in reduced overall system costs.

Determination of the optimal total oxygen concentration and oxygen partitioning ratio based on the heat transfer characteristics of oxy-coal combustion in a swirl burner

Oxy-coal combustion is an attractive option for CO2 capture from coal-fired power plants due to high carbon capture efficiency and favorable economic performance. It is critical for the operation of the power plants to maintain similar heat transfer characteristics by rationalizing the partitioning strategy of the oxidant streams when retrofitting coal-fired power plants with oxy-fuel combustion technology. In the present work, the oxy-coal combustion characteristics under various total oxygen concentrations XO2,total of 21 %–32 % and oxygen partitioning ratio conditions in a 100 kW vertical swirl burner were numerically investigated by using computational fluid dynamics (CFD) models. And the effects of the XO2,total and oxygen partitioning ratio on the heat transfer characteristics of oxy-coal combustion were numerically simulated to quantitatively obtain the optimal oxygen supply partitioning strategy for the retrofitting of coal-fired power plants. Then the flame structure, heat transfer flux, and char burnout rate at different oxygen partitioning ratios between the primary and secondary streams were systematically analyzed to further determine the optimal oxygen partitioning ratio. The results showed that the maximum flue gas temperature Tmax increased by 220 K and the total heat transfer flux on the furnace wall increased by 42 % when the XO2,total was increased from 21 % to 32 %, respectively. Under oxy-coal combustion conditions, the Tmax at the XO2,total of 32.4 % was consistent with that under air combustion condition, while the total heat transfer flux at the XO2,total of 29.4 % matched with that under air combustion condition. Moreover, the total heat transfer flux and the flame length were increased by 17.3 % and 46.3 %, respectively, as the oxygen concentration of the primary stream XO2,Pri was increased from 6.5 % to 45 % at the XO2,total of 29 %. More importantly, the total heat transfer flux at the XO2,Pri of 31.9 % under oxy-coal combustion condition matched with that under air combustion condition. The optimal total oxygen concentration and oxygen partitioning ratio of oxy-coal combustion based on the heat transfer characteristics were quantitatively determined, which gave an important reference for the oxy-coal combustion retrofitting of traditional coal-fired power plants.

Investigation on the integration of supercritical CO2 cycle with natural gas oxy-fuel combustion power plant

The utilization of LNG cold energy is promising to offset the energy penalty of oxy-fuel combustion technology and achieve efficient carbon emissions reduction. In this paper, natural gas oxy-fuel power systems utilizing LNG cold energy are investigated. Supercritical and transcritical CO2 cycles are adopted to deeply recover flue gas waste heat. Results show that the thermal efficiency of the supercritical CO2 recompression cycle is 6% higher than that of the regenerative cycle, whereas the net power output of the recompression cycle is lower. With transcritical CO2 cycle as the secondary subsystem, the efficiency of both integrated systems is enhanced by approximately 9%. Meanwhile, 95% CO2 is captured with the power consumption of 0.07 kWh/kg-CO2. The total investment costs of the integrated regenerative and recompression cycle are 53.96 M$ and 54.62 M$. The levelized cost of electricity of the two integrated systems is 3.21 $/MWh and 3.24 $/MWh, indicating great financial availability. Therefore, applying supercritical and transcritical CO2 cycles contributes to efficient energy conversion and carbon capture. The research could provide meaningful information on the oxy-fuel combustion power system integrated with supercritical and transcritical CO2 cycles from thermodynamic and economic insights.

Review on thermal-science fundamental research of pressurized oxy-fuel combustion technology

Review on thermal-science fundamental research of pressurized oxy-fuel combustion technology

Numerical study on combustion characteristics of ammonia mixture under different combustion modes

Ammonia, an emerging carbon-free fuel, exhibits promising potential within the energy field. Nevertheless, it faces challenges such as unstable combustion and high NOx emissions that necessitate resolution. In this paper, numerical simulation methods are used to compare the combustion characteristics under different modes. Furthermore, the numerical research is carried out by adding ammonia gas in different combustion modes. The results indicated that regardless of the combustion mode, induction of ammonia elicits a significant surge in NOx emissions, but the combustion characteristics of different combustion modes are different. When ammonia is introduced into conventional combustion mode, ignition is significantly delayed. It is proved that the excess enthalpy combustion technology is effective in facilitating the combustion of ammonia mixtures. However, excess enthalpy combustion temperature will lead to elevate NO emissions. In contrast, MILD combustion and oxy-fuel MILD combustion technologies effectively suppress NO formation within ammonia mixtures. This is because in MILD combustion mode, the reaction rate becomes slow, which inhibits the formation of NO.

Energy efficiency analysis and optimization of a pressurized oxy-fuel circulating fluidized bed combustion system

The commercial application of oxy-fuel combustion technology is limited by energy deduction which is caused by addition of air separation unit (ASU) and carbon dioxide compression and purification unit (CPU). Pressurized circulating fluidized bed (CFB) oxy-fuel combustion technology is one option to improve the net electric generation efficiency. In this research, a series of simulations and optimizations were carried out to analyze the energy efficiency of a pressurized oxy-fuel combustion system. The boiler structure and heat exchange surface arrangement under different pressure were calculated. The cross-sectional area of the furnace and tail flue were both reduced up to 10 % of the original size and the floor space of the boiler was considered to be the lowest at 1.1 MPa. The energy efficiency and exergy analysis were used to explore the influence of pressure on the net efficiency and the optimization potential of system. The net electric generation efficiency reached a maximum value of 24.16 % at 1.1 MPa, which is 5.4 % higher than that at atmospheric pressure. Finally, four parameters, i.e. preheat temperature, oxygen concentration, ASU outlet oxygen purity and CPU compressor outlet pressure, were optimized to improve the system net efficiency to 26.67 %, 29.04 %, 25.87 % and 24.36 %, respectively.

Air and oxy-fuel combustion characteristics of coal gangue and weathered coal blends

Oxy-fuel combustion technology is suggested as one of the promising technologies for capturing CO2. The combustion characteristics of blends of a coal gangue and a weathered coal under air (21% O2/79% N2), oxy-fuel (20% O2/80% CO2) and oxygen-enriched oxy-fuel (40% O2/60% CO2) conditions were studied using a thermogravimetric analysis (TGA) technique operating at heating rate 10 oCmin−1 to a final temperature 900 °C, focussing on the effect of blending ratio and atmosphere. While the differential thermogravimetric (DTG) profiles of coal gangue in the three different atmospheres were very similar, the weathered coal showed a sharp peak in the temperature range 400–440 °C under oxygen-enriched oxy-fuel condition, which was different from DTG curves under air and oxy-fuel conditions. The blending of the coal gangue into the weathered coal gradually diminished this peak. The negligible deviations between the experimental DTG curves and theoretical DTG curves indicated that interactions were absent for all the coal gangue/weathered coal mixtures under air and oxy-fuel conditions. The obvious interactions between coal gangue and weathered coal were observed under oxygen-enriched oxy-fuel condition and the interaction may be related to thermal effect. The interactions increased as the increasing weathered coal ratio in blends and increasing oxygen concentration under oxy-fuel conditions.

Pressurized oxy-fuel combustion of pulverized coal blended with wheat straw: Thermochemical characterization and synergetic effect

Pressurized oxy-fuel combustion is recognized as the second generation of oxy-fuel combustion technology that can facilitate carbon capture and reduce energy consumption, while coal and biomass combustion is also an effective way to decrease carbon emissions. This study innovatively integrates these two clean combustion technologies and investigates the effects of pressure and blending ratio on the combustion characteristics (ignition, combustion rate, volatile combustion, semi-coke combustion, burnout) of coal, biomass and their blends using an advanced magnetic levitation HPTGA. The results show that pressurization can improve the combustion rate of coal and biomass, but it will cause ignition delay when system pressure exceeds 0.5 MPa. The effect of pressure on combustion characteristics is both facilitative and inhibitive, in terms of reaction kinetics, pressurization can significantly promote combustion but it also plays a role in inhibiting oxygen diffusion, the competition between the two effect leads to an optimum value of pressure in the combustion performance of the blends, which is about 1 MPa. Biomass is more sensitive to pressure than coal, and pressurization changes the ignition mode of biomass. In addition, a new synergy index is defined to quantify the synergistic effect of the whole co-combustion process. Pressurization could suppress both catalytic and non-catalytic mechanisms in the co-combustion process, and different sensitivities of biomass and coal to pressurization lead to more significant differences in combustion time and temperature interval compared with normal pressure, all these factors contribute to negative synergistic effect under pressurization.

Flamelet LES of oxy-fuel swirling flames with different O[formula omitted]/CO[formula omitted] ratios using directly coupled seamless multi-step solid fuel kinetics

Oxy-fuel combustion, in combination with carbon capture technologies, has generated significant interest since it has a high potential for rapid CO2 cutbacks for newly built and retrofitted coal-fired power plants. Although research and development of oxy-fuel combustion technologies have been advancing recently, the combustion of solid fuels in an oxygen–carbon dioxide environment is not yet fully understood. In particular, the oxygen content in the recirculated flue gas is an adjustable parameter in oxy-fuel combustion. This work aims to analyze its impact on the thermo-chemical conversion by applying a recently developed approach for accurately predicting pulverized solid fuel combustion to a range of oxy-fuel swirl flames. The employed modeling framework builds upon a detailed solid fuel kinetic mechanism that seamlessly describes the entire solid conversion process. For the description of the gas phase, a combined flamelet modeling approach with large-eddy simulation is applied. This previously introduced high-fidelity framework (Nicolai et al., 2022) was applied to three operating points in a pilot-scale facility, for which in-reactor data is available. The overall model, combined the available experimental data, is employed for the three operating points with different oxidizer O2/CO2 ratios to give deeper insights into combustion. In particular, the influence of the local oxygen partial pressure on the solid fuel conversion is analyzed in detail.

Oxy-fuel combustion of pulverized coal in an industrial boiler with a tangentially fired furnace

Numerical studies of the processes of oxy-fuel combustion of pulverized coal (PC) in an industrial boiler BKZ 500–140–1 (with a capacity of about 400 MW) were carried out in this work. The proposed comprehensive mathematical model was tested based on data from a full-scale experiment (2.4 MW laboratory stand) of oxy-fuel combustion of PC. The conducted comparison has shown a good agreement of the calculation results with the experimental data. A detailed comparative analysis of the effect of the operating modes of the BKZ 500–140–1 industrial boiler during oxy-fuel combustion of coal on physical and chemical processes and the level of harmful emissions (NOx, CO2) was performed for the first time. The effect of oxygen concentration and CO2/H2O ratio in the blast on the processes of ignition and combustion of fuel in a nitrogen-free environment has been studied. It is shown that when nitrogen in the blast composition is replaced with flue gases without changing the oxygen concentration in the boiler under study, the average temperature in the furnace volume declines, as well as the average heat flux at the walls decreases from 87.35 to 70.32 kW/m2. To achieve the standard operating parameters of the BKZ 500–140–1 industrial boiler, it is necessary to increase the oxygen concentration in the blast from 15.4 to 19.7 vol.% (i.e. by 28%). The implementation of the oxy-fuel combustion technology on a steam boiler leads to a decrease in the NOx concentration in flue gases from 480 to 273 mg/m3.

Oxyfuel Cofiring Characteristics of Biomass with Ultralow Volatile Carbon-Based Fuels

Biomass from agricultural production is a renewable energy source with a high-volatile content. Semicoke (SC) and gasification residual carbon, which are ultralow volatile carbon-based fuels (LVFs), are by-products of the coal chemical industry, which are over capacity and urgently need to be cleanly and effectively consumed. Biomass and LVFs exhibit complementary fuel characteristics, particularly the volatile content, which can potentially be coprocessed efficiently. Furthermore, oxyfuel combustion technology can not only realize carbon dioxide (CO2) capture and benefit from carbon neutrality, but also effectively reduce NOx emissions. The cocombustion of biomass and ultralow volatile fuel under oxyfuel conditions can both use individual benefits and effectively control pollutant emissions. However, the cofiring characteristics and interaction mechanisms of LVF with biomass in an oxyfuel atmosphere are yet to be fully understood. In this study, three ultralow volatile fuels and one typical biomass were selected to explore the oxyfuel cocombustion characteristics via thermogravimetric experiments. The experimental results indicated that blending with wheat straw (WS) improved the overall combustion performance, the ignition point was close to that of WS, and the burnout temperature was close to the average value of the two individual fuels. An increase in the oxygen content can effectively enhance the combustion feature of ultralow volatile fuels while it has little effect on the burnout performance of biomass. In the presence of high-content CO2, the decomposition of carbonate in ultralow volatile fuel is impeded and the decomposition temperature is slightly increased. The present investigation can promote the efficient co-utilization of inferior LVFs and biomass, which also benefits CO2 capture, carbon neutrality, and even negative carbon emissions.

CFD-aided optimization of the decomposition kinetics of cement raw meals under high CO2 concentrations

Oxy-fuel combustion technology is a promising option for CO2 capture in the cement industry, as the cement raw meal decomposes to generate large amounts of CO2. Exploring the decomposition kinetics of raw meal under high CO2 concentrations is crucial for the design and operation optimization of precalciners. In this work, a new method is proposed to obtain the decomposition kinetics of cement raw meals. First, a real decomposition atmosphere, including the temperature and CO2 concentration in an actual precalciner, is simulated in an electric-heated down firing furnace (E-DFF), and the decomposition characteristics of raw meal at various temperatures (850–1050 °C) and CO2 concentrations (0–90 vol%) are investigated. Second, a detailed decomposition model of raw meal under high CO2 concentrations is developed, and this model considers gas adsorption and surface reactions, structural changes due to solid product formation, gas diffusion around the particle and particle temperature changes due to heat transfer and endothermic reactions. Third, the prediction model of raw meal decomposition is implemented into CFD software, and the kinetic parameters are determined via a CFD-aided optimization method in which a direct search algorithm is used to accelerate the optimization process. Finally, the optimized kinetics are verified over wide ranges of temperatures, residence times, and CO2 concentrations. The simulation results agree well with the experimental data, indicating that the developed model and obtained kinetic parameters could be applied for the application of oxy-fuel combustion technology in the cement industry.

A new insight on the NO-CO reaction at the electronic level: homogeneous, E-R, and L-H mechanisms.

Carbonaceous surface, as one of the major carriers in coal combustion, was found to exert great influence on the nitric oxide with carbon monoxide (NO-CO) reaction. Although there have been some studies addressing the NO-CO reaction, the inherent mechanism remains obscure. In this work, some updated mechanisms with details were proposed at the electronic level. Using density functional theory calculations, the preferred pathways were identified with three channels consisting of homogeneous, Eley-Rideal (E-R), and Langmuir-Hinshelwood (L-H) heterogeneous reactions. The reasons for the difference in energy barrier among the three mechanisms were revealed by analyzing the chemical bond and electronic transfer. Results show that among these channels, the NO-CO reaction is more likely to occur along the E-R mechanism, due to its lower energy barrier of the rate-determining step. Compared to the L-H mechanism, there is a higher degree of electronic localization between NO molecules at the initial stage of the E-R mechanism. As a result, the NO dimer formation of the E-R mechanism has a lower energy barrier than that of the L-H mechanism. Meanwhile, a large number of electrons floods into the N-N, N-O, and O-O bonds of NO dimer in the homogeneous reaction, which certainly gets more difficult for the dissociation of O atoms in the gas phase. Accordingly, the following stage of N2 formation in the homogeneous reaction has a higher energy barrier than that in both the E-R and L-H reactions. Compared to the L-H mechanism, the E-R mechanism exhibits a lower degree of electronic localization between N2O and carbonaceous surface, suggesting that the interfacial interaction in the E-R mechanism is weaker. As a result, N2 is easier to remove from the carbonaceous surface in the E-R mechanism than in the L-H mechanism. To sum up, the results deepen the knowledge about the NO-CO reaction, which will help to further develop the oxy-fuel combustion technology.