Pressurized Oxy-fuel Combustion Research Articles

Pressurized oxy-fuel combustion with sCO2 cycle and ORC for power production and carbon capture

The pressurization of oxy-fuel combustion presents the opportunity to recuperate more latent heat from the flue gas within the boiler. This study proposed a coal-fired pressurized oxy-fuel combustion plant coupled with the sCO2 Brayton cycle for simultaneous power production and carbon capture. Two configurations, i.e., sCO2 recuperator split and sCO2 bottom cycle, are conceived to fully exploit the flue gas heat from the boiler. Waste heat from various sources, including the air separation unit, the CO2 compression and purification unit and the sCO2 cycle, are recuperated by the organic Rankine cycle (ORC) to augment the net power efficiency. Sensitive analyses, including the turbine parameters, the recuperator split ratio, and the ORC parameters, are conducted to optimize the design and operation conditions of the plant. The plant net power efficiency ranges between 39.4 % and 42.9 %, inclusive of CO2 compression. The levelized cost of electricity (LCOE) is calculated, and the LCOE results are in the range of 101.60 $/MWh and 106.07 $/MWh for different configurations. These findings suggest the system's viability for future coal-fired plant with carbon capture.

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

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

Comparative study on process simulation and performance analysis in two pressurized oxy-fuel combustion power plants for carbon capture

Process simulation and analysis are demonstrated to provide significant benefits for pressurized oxy-fuel combustion systems. This study compares the performance of pressurized oxy-fuel combustion systems and a first-generation oxy-combustion system under the same standard conditions. On this basis, the increase in efficiency of pressurized oxy-fuel combustion systems is evaluated. Process simulation and analysis are carried out for the first-generation oxy-combustion system in a 600 MW supercritical primary intermediate reheat power plant without heat integration (Base Case) and with heat integration (Case A). The validity of the simulation results is then verified. Considering Case A as a benchmark model, the process simulations of a pressurized oxy-coal combustion system and a staged pressurized oxy-combustion system are performed. The simulation results are compared with results in other literature studies. Compared with the benchmark model, the results indicate that the gross generation efficiency of the pressurized oxy-coal combustion system is improved by 1.12 % (LHV), and the net generation efficiency is improved by 0.47 % (LHV). In addition, the gross generation efficiency of the staged pressurized oxy-combustion system is enhanced by 1.78 % (LHV), and the net generation efficiency is improved by 2.4 % (LHV) compared with the benchmark model.

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.

Towards a comprehensive understanding of PM1 formation in pressurized oxy-fuel combustion: A study comparing model predictions with experimental data

Oxy-fuel combustion is pivotal for fossil fuel power plants to attain net zero carbon emissions. While atmospheric pressure oxy-fuel combustion has garnered significant attention, its economic feasibility is questionable. This has led to the proposition of pressurized oxy-fuel combustion as a more economically viable alternative. A critical aspect, the formation of submicron ash aerosols (PM1), has implications for ash deposition in boilers and presents environmental concerns. Despite its significance, limited research exists on PM1 formation in this context. This study introduces a robust model, partitioned into combustion, vaporization, nucleation and condensation, and coagulation sub-models, to predict PM1 formation in pressurized oxy-fuel combustion. Key findings include: 1) Pressure escalation from 0.1 MPa to 1.5 MPa inhibits the CO formation and further reduces mineral vaporization ratio from 2.30 % to 0.12 %. 2) Elevated pressures decrease the critical nucleation diameter to about 5 nm, 4 nm, and 3 nm for pressures of 0.1 MPa, 0.8 MPa, and 1.5 MPa, respectively. 3) Coagulation primarily occurs within the diffusion layer around fuel particles, with its thickness diminishing as pressure increases. The model's predictions align closely with existing experimental data, underscoring its utility in understanding ash behavior in pressurized oxy-fuel combustion. Furthermore, this study not only bridges the knowledge gap in the field but also offers industry stakeholders a valuable tool to optimize combustion processes, mitigate environmental risks, and drive the transition towards more sustainable fossil fuel utilization.

Thermoeconomic investigation of pressurized oxy-fuel combustion integrated with supercritical CO2 Brayton cycle

Pressurization is expected to increase the power efficiency of oxy-fuel combustion plant. Supercritical CO2 (sCO2) Brayton cycle could yield higher thermal efficiencies at lower capital cost than the state-of-the-art steam-based power cycles. The coupling of pressurized oxy-fuel combustion and sCO2 cycle could potentially offer higher net power efficiency over its counterparts with CO2 capture. In this paper, pressurized oxy-fuel combustion was integrated with three different sCO2 Brayton cycle layouts, i.e., single reheated recompression, double reheated recompression, and intercooled recompression. The systems were analyzed from the perspective of thermodynamics and economics. The net power efficiencies for the three systems were 39.4%, 40.2%, and 41.3%, respectively. The effect of boiler pressure on the latent heat recovery of the flue gas was analyzed. In the sensitivity analysis, the influence of turbine inlet temperature, turbine inlet pressure, turbine inlet temperature, turbine outlet pressure, recirculated fan pressure boost, and the high-temperature recuperator (HTR) split ratio on the plant net power efficiency was assessed. Finally, the economic analysis was conducted. The levelized cost of electricity (LCOE) of the three systems were 103.18 $/MWh, 108.45 $/MWh, and 110.07 $/MWh, respectively. The results showed that the integrated systems were attractive as potential candidates for the coal-fired power generation with CO2 capture.

Reaction kinetics for high pressure hydrogen oxy-combustion in the presence of high levels of H2O and CO2

Novel shock tube experimental ignition delay time (IDT) data are provided to delineate the impact of high concentrations (45% by mole) of H2O and CO2 on IDTs of stoichiometric 4% H2. Ignition delay experiments were conducted using a high- and a low-pressure shock tube facility. High-pressure experiments were performed at pressures of 37-43.8 bar and temperatures of 1084-1242 K in four different bath gases, namely: Ar, 45%H2O/Ar, 30%H2O/15%CO2/Ar, and 45%CO2/Ar. Low-pressure experiments were conducted at 2.1-2.7 bar and 926-1198 K in Ar and 45%CO2/Ar bath gases. Impacts of non-ideal ignition phenomena that may occur in the presence of large amounts of H2O and CO2 were also analyzed. 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 presented. The mechanism is constructed from unadjusted kinetic rate parameters from theoretical / experimental elementary reaction rate determinations. The only adjusted rate in CanMECH 1.0 is the much disputed Ar-specific low-pressure-limit pre-exponential factor of H + O2 (+Ar) = HO2 (+Ar) within the uncertainty bounds of the source rate. Validity of CanMECH 1.0 is confirmed against shock tube IDT data of this work, as well as selected H2 and H2/CO shock tube IDT datasets from literature. The performance of the model is compared to Keromnes et al. model (Combust. Flame 160 (2013) 995-1011). CanMECH 1.0 outperformed Keromnes et al. for 16 datasets out of 26 and exhibited a similar performance for another two. In particular, CanMECH 1.0 outperformed Keromnes et al. in predicting shock tube IDTs for H2O- and CO2-laden reactive mixtures, as well as all IDT data at pressures of 17-43.8 bar, which are of distinct value to pressurized oxy-fuel combustion applications relevant to this work.

Influence of operating pressure on combustion and heat transfer in pressurized oxy-fuel combustion evaluated by numerical modeling

Pressurized oxy-fuel combustion (POFC) is an advanced-generation energy plant system that is used to capture and store carbon and can realize a high-efficiency generation cycle with increased heat transfer and minimized efficiency penalty. In this study, we conducted a numerical investigation to characterize the heat transfer, combustion reaction, and NOx emissions of a 0.1 MWth POFC system. In addition, the weighted-sum-of-gray-gases (WSGG) model was applied in the POFC conditions to precisely evaluate the radiative heat transfer based on a comparative analysis of various WSGG models. Both the measured and calculated results revealed that the temperature, including its peak value, decreased with the increasing pressure. Moreover, the average total heat recovery rate increased by approximately 0.2% upon increasing the pressure by 2 bar, and the proportion of the radiative heat transfer rate increased. Furthermore, the combustion reactions containing the O, H, and OH radicals were promoted with the increasing operating pressure, exhibiting a high peak value in a wide area. Consequently, the net reaction rates of the reactions involving HO2 and H2O2 increased with the pressure. Overall, NO was produced in the initial section of the oxy-flame, beyond which the oxidation reaction of NO with HO2 occurred to yield NO2, and the increasing pressure further promoted these reactions.

Thermal and kinetic analysis of pressurized oxy-fuel combustion of pulverized coal: An interpretation of combustion mechanism

• Pressurized oxy-fuel combustion performance of a typical bituminous coal is investigated. • The thermodynamics parameters and the most probabilistic kinetic model for the pressurized oxy-fuel combustion process are analyzed. • Elevating pressure can significantly improve the combustion performance of coal but the promotion effect gradually alleviates. • The ignition mechanism transforms from heterogeneous to homogeneous when the oxygen concentration reaches 50% at 0.5 MPa. Pressurized oxy-fuel combustion is one of the emerging clean technologies that can efficiently separate and recover CO 2 , and this combustion mechanism differs significantly from atmospheric air combustion. In this paper, the effects of reaction conditions such as total pressure, oxygen concentration and atmosphere gas composition on the combustion characteristics of Xinjiang Bostan coal were investigated using thermogravimetric methods. Furthermore, the thermodynamics parameters and the most probabilistic kinetic model for the pressurized oxy-fuel combustion process were explored. The results showed that the system pressure rising from 0.1 to 1 MPa could enhance the combustion process of coal; however, when the system pressure exceeds 0.5 MPa, the promoting effect is clearly weakened. The ignition mechanism transforms from heterogeneous to homogeneous when the oxygen concentration reaches 50% at 0.5 MPa. The mechanism functions of pressurized oxy-fuel combustion reaction varied as the reaction progressed. In addition, the rise of pressure and oxygen concentration correspond to the higher chemical reaction order of pulverized coal combustion and the pressure has less influence on the reaction mechanism than oxygen concentration. The results obtained may assist with the optimization of pressurized oxy-fuel combustion and guide its industrial applications.

Experimental study on devolatilization characteristics of lignite during pressurized oxy-fuel combustion: Effects of CO2 and H2O

Pressurized oxy-fuel combustion (POFC) is currently considered one of the advanced coal utilization technologies for large-scale CO2 capture but causes distinct coal conversion behavior, particularly more complicated and unclear with wet recycle. To explore coal conversion mechanisms and structural evolution of chars during the initial stage of POFC, lignite devolatilization was conducted in an isothermal horizontal tube furnace at 900 °C in individual and blending CO2 and H2O atmospheres (CO2/N2, H2O/N2, and H2O/CO2) under different pressures of 0.1 to 0.9 Mpa. The pore and chemical structures of resulting chars were characterized using N2 adsorption and Raman spectroscopy, and oxy-fuel combustion reactivities of chars were evaluated by thermogravimetry. The results indicate that coal char conversion in coexisting H2O/CO2 presents three different interactions of addition, synergy, and inhibition, corresponding to mesoporous surface area evolution of chars with partial and total pressures of H2O. CO2 chars primarily consist of micropores while chars formed in H2O-rich atmospheres contain more mesopores. These dominant micro-/mesopore numbers increase with CO2/H2O concentrations but decrease at 0.9 Mpa. The accelerated condensation of aromatic rings in chars induced by CO2 and H2O gasification also follows different pathways. H2O gasification dominates the carbon skeleton structure evolution of H2O/CO2 chars but the interaction between H2O/CO2 results in the complex variations of O-containing structures. CO2/N2 chars have the highest oxy-fuel combustion reactivities, follow by H2O/CO2 chars, and H2O/N2 char reactivities are the lowest. The combustion reactivities of H2O/CO2 chars show a more obvious attenuation trend than that of H2O/N2 chars and the disparities narrow with H2O concentration. Elevated total pressure decreases the reactivities of all chars along with the growth of aromatic ring sizes. The correlations between oxy-combustion reactivities and Raman band area ratios highlight the significance of the devolatilization stage to subsequent char combustion.

A ReaxFF study of the effect of pressure on the contribution of char-CO2 gasification to char conversion during pressurized oxy-fuel combustion

The effect of pressure on the contribution of char-CO2 gasification to char conversion during pressurized oxy-fuel combustion (POFC) at 10–25 bar was investigated using reactive force field molecular dynamics (ReaxFF MD) simulation. The results showed that char conversion rates under air (O2/N2), CO2/N2, and oxy-fuel (O2/CO2) atmospheres all increased with the increase of total pressure. Both the char-O2 oxidation under air atmosphere and char-CO2 gasification under CO2/N2 atmosphere followed the Langmuir-Hinshelwood (L-H) mechanism. The char reaction rates calculated by the L-H model based on the assumption of separate active sites and common active sites were compared with the ReaxFF MD simulation results under O2/CO2 atmosphere at different pressures. It was found that char-O2 oxidation competed with char-CO2 gasification under pressure of 10–15 bar, while the competition did not occur under pressure of 20–25 bar. The contribution of char-O2 oxidation and char-CO2 gasification to char conversion during char combustion in O2/CO2 atmosphere were quantitatively determined from the consumption of O2 and CO2. The char-O2 oxidation and char-CO2 gasification rates in O2/CO2 atmosphere at different char conversions were also examined. It indicated that the char-CO2 gasification rate was mainly controlled by the competition between char-CO2 gasification and char-O2 oxidation under low pressures, but was controlled by the partial pressure of CO2 under high pressures.

Experimental study and modelling of pressurized oxy-coal combustion: Effect of devolatilization conditions on the physical structure and combustion characteristics of char particles

Pressurized oxy-coal combustion has been regarded as a promising carbon capture and storage (CCS) technology, and the combustion characteristics of char particles under pressurized oxy-fuel combustion conditions have been extensively investigated. However, most previous studies used the char samples prepared under the atmospheric N2 condition rather than under the pressurized CO2 condition, which may lead to the misunderstanding of the combustion characteristics. In this study, the effects of devolatilization atmosphere and pressure on the physical structure of char particles were experimentally investigated. The char particles produced under different devolatilization conditions were then used for the oxy-char combustion experiments conducted in a fluidized bed with the operating pressure between 0.1 and 0.5 MPa. In view of the limitations of the experiment, an experimental verified particle-scale char combustion model was further used for predicting the char particle’s combustion reactivity and temperature, and the influence of physical structure on the combustion characteristics was analyzed. The results obtained from the experiments demonstrated that higher devolatilization pressure led to larger mean pore sizes and specific surface areas of char particles. The char particles obtained with CO2 atmosphere had larger specific surface areas but smaller mean pore sizes than those obtained with N2 atmosphere. Besides, increasing devolatilization pressure resulted in shorter burnout times of char particles. The simulation results showed that using the char samples prepared under the atmospheric N2 condition for the pressurized oxy-fuel combustion experiments led to the underestimations of char combustion reactivity and peak temperature.

Co-firing of coal and biomass under pressurized oxy-fuel combustion mode in a 10 kWth fluidized bed: Nitrogen and sulfur pollutants

Co-firing coal and biomass under pressurized oxy-fuel combustion (POFC) mode in fluidized beds is a novel and promising technology to capture CO2 at a low cost and with eco-friendly waste disposal. However, large knowledge gaps exist in combustion characteristics and pollutant generation owing to the tremendous lack of practices. Following our successful testing of co-firing coal and biomass under POFC mode in a10 kWth pressurized fluidized bed (PFB) [Chem. Eng. J. 2022, 431,133457], this study conducted a special and in-depth investigation of nitrogen and sulfur pollutants. Based on a comprehensive analysis of flue gas and solid residues, the effects of key operating parameters, such as combustion pressure (P), biomass blending ratio (Mb), and combustion temperature (T), on the emissions of gaseous and solid pollutants, transformation and distribution of nitrogen and sulfur, sulfur self-retention (SSR) process, and ash properties and potentials of deposition and agglomeration, were investigated. The results show that increase in P and Mb significantly reduces NOx, N2O, SO2, and CO emissions and improves the SSR efficiency. Notably, the pressurized and co-firing conditions have a synergistic effect on SO2 emission reduction. The T dependence of these products under POFC mode is clearly less than that under atmospheric oxy-fuel combustion mode. Within the typical operating temperature range of an oxy-fuel PFB, SSR occurs through the direct sulfation route. The ash and bed material have an overall low potential for slagging, fouling, and agglomeration, with no indication of ash-related problems during testing. This work will be helpful for the development of oxy-fuel co-firing in PFBs for CO2 capture.

Radiative heat transfer in splash and dilution zones of the pressurized oxy-fuel combustion CFB considering particle-dependent scattering

• The radiative heat transfer in the oxy-fuel combustion PCFB is investigated. • The radiative heat transfer considering particle-dependent scattering is studied. • The importance of particle concentration on radiative heat transfer is summarized. • The mechanism of radiative heat transfer action in different regions is revealed. Radiative heat transfer is dominant in splash and dilution zones of the oxy-fuel combustion pressurized circulating fluidized bed (PCFB). However, the particle radiation fields interact with each other due to the high particle concentration. Moreover, the particle concentration distribution, the flue gas components and pressure change drastically due to pressurized oxy-fuel combustion technology. In this paper, the radiative heat transfer in splash and dilution zones of the oxy-fuel combustion PCFB is investigated when particle-dependent scattering is considered. The results show that the maximum error of the particle radiation model is less than 1% in predicting the incident heat flux at the wall when particle-dependent scattering is considered. The particle concentration distribution has a significant impact on the radiative heat transfer in splash and dilution zones of oxy-fuel combustion PCFB. The simplified particle concentration distribution model cannot capture the zero-source term phenomenon in the core region and has a large error in the annular region. In addition, the mechanism and importance of the flue gas composition and pressure on the radiative heat transfer in splash and dilution zones of oxy-fuel combustion PCFB are analyzed.

Simulations on pressurized oxy-coal combustion and gasification by molecular dynamics method with ReaxFF

Pressurized oxy-fuel combustion (POFC) is recognized to have the potential to effectively capture CO2 with low cost and high efficiency. To investigate the chemical mechanism of oxy-fuel combustion and the effects of different operating parameters on combustion characteristics, a gasification reaction model and the pressurized oxy-fuel combustion model were constructed. A series of reactive molecular dynamics (MD) simulations were conducted on the POFC model using ReaxFF force field under the pressure of 0.2, 0.3 and 0.5 MPa, and with the temperature at 1600, 1800 and 2000 K, respectively. The activation energy for atmospheric oxy-fuel combustion was firstly calculated, in agreement with reported experimental results, which verified the accuracy of ReaxFF MD method. The results of gasification and combustion showed that both temperature and pressure positively affect coal decomposition and the combustion reaction rate. The conversion mechanism of C in coal to CO2 is a process with dehydrogenation, coal decomposition and oxidation reaction. Compared with atmospheric oxy-fuel combustion, the increase of pressure/density would accelerate the dehydrogenation reaction and the decomposition of coal structure, and improve the performance of coal combustion and promote the decomposition of coal molecule into smaller fragments, and further promote the releasing of CO2 and small fragments.

Co-firing of coal and biomass under pressurized oxy-fuel combustion mode: Experimental test in a 10 kWth fluidized bed

• Pressurized oxy-fuel combustion of coal/biomass in a fluidized bed is successful. • Stable, pressurized, oxy-fuel combustion mode using coal/biomass can be realized. • Increased pressure leads to higher combustion efficiency and CO 2 enrichment. • Increased pressure has the advantages of reducing CO, NO x , and SO 2 emissions. • Increased pressure makes the fly ash particles finer with surface more cracked. Pressurized oxy-fuel combustion (POFC) of solid fuels in fluidized beds possess the potential for CO 2 capture at low cost. However, the practical experience of oxy-coal combustion in pressurized fluidized beds (PFB) is still very limited, and there is a lack of attempts on the co-firing of coal and other fuels. In this study, the co-firing of coal and biomass in a POFC mode at a 10 kW th PFB was tested. The dynamic behaviors of the start-up process and combustion mode switching were investigated. The effects of key operating parameters, including combustion pressure ( P ), biomass blending ratio ( M b ), and excess oxygen coefficient ( α ), on the temperature distributions, CO 2 enrichment and conversion, pollutant emissions (CO, NO X , SO 2 ), and solid residues were methodically studied. The results show that the stable, pressurized, and oxy-fuel combustion mode with coal and biomass mixtures as fuels can be successfully realized in a fluidized bed. Increasing P and M b not only conduces to better temperature distribution, more CO 2 enrichment in flue gas, and higher combustion efficiency but also has the advantage of reducing NO x and SO 2 emissions by over 30%. In the oxy-fuel PFB, the positive effect of α on the combustion performance is more significant than that under atmospheric conditions. As P increases, the fly ash surface is more cracked, and the particle size distribution of fly ash decreases, while the bottom slag surface is smoother. Besides, the increase in P results in a decreased specific surface area and cumulative pore volume but an increased average pore diameter in fly ash.

Characterization of nitrogen and sulfur migration during pressurized coal pyrolysis and oxy-fuel combustion

In the present work, pressurized coal pyrolysis and oxy-fuel combustion experiments were carried out in a pressurized drop tube furnace to investigate the migration and transformation characteristics of nitrogen and sulfur. The pyrolysis experiments showed that high pyrolysis pressure inhibited the release of nitrogen and sulfur. The content of oxidized nitrogen (N-X), pyrite, sulfide, sulfoxide and sulfate in char decreased, while the content of pyridine nitrogen (N-6), pyrrole nitrogen (N-5), quaternary nitrogen (N-Q), thiophene and sulfone in char increased with the increase of pyrolysis pressure. The elevated pyrolysis temperature was conducive to the decomposition of nitrogen and sulfur-containing functional groups, and it also promoted the conversion of nitrogen and sulfur to functional groups with high stability such as N-Q and thiophene. The release of volatiles and the decomposition of nitrogen and sulfur-containing functional groups in coal were promoted by CO2 gasification. The increase of the total CO2 gasification pressure led to more nitrogen and sulfur remaining in char. During pressurized oxy-fuel combustion in O2/CO2 atmosphere, the emissions of NO, NO2 and SO2 were lower than those in air combustion. The emissions of NO, NO2 and SO2 gradually decreased with the increase of pressure at air and oxy-fuel atmospheres. The increase of temperature increased the emissions of NO and SO2 at different pressures, but the NO2 emission decreased at elevated temperature. In addition, the emissions of NO and NO2 increased, but the emission of SO2 decreased with the increase of oxygen concentration.

Influence of Operating Pressure on Combustion and Heat Transfer in Pressurized Oxy-Fuel Combustion Evaluated by Numerical Modeling

Influence of Operating Pressure on Combustion and Heat Transfer in Pressurized Oxy-Fuel Combustion Evaluated by Numerical Modeling

An improved low and high-temperature dimethyl ether kinetic model for the combustion atmospheres with high CO2 concentration

The Dimethyl ether (DME) kinetic model is significant to understand the DME combustion in the atmosphere containing high CO2 concentration, such as pressurized oxy-fuel combustion process and exhaust gas recirculation, and design the combustor. In this paper, the ignition delay times (IDTs) of DME were measured in a shock tube under the conditions of equivalence ratios of 0.5, 1 and 1.5, temperature ranges from 1007 K to 1340 K, and pressures of 2 and 11 atm. A detailed kinetic model of DME named as OXYDME was put forward based on the OXY-Aramco model, and was validated by the low and high temperature IDTs, laminar flame speeds, and species profiles measured in this work and those from literatures in atmospheres of O2/Ar/CO2, O2/N2, O2/N2/He/CO2 and O2/CO2. The OXYDME model was compared with OXY-Aramco, Liu-DME model in detail. The effects of CO2 on the DME ignition are very weak and not sensitive to the temperature and pressure. The reason for the weak effects of CO2 is that the chemical effects of CO2 promote ignition, which counteracts the inhibition effects caused by the physical properties of CO2. The chaperon effects of CO2 dominate the chemical effects. Meanwhile, the effects of the reactions with CO2 are very small.

Molecular insights into the role of char-bound hydrogen in char-NO reactions under high pressures: A reactive molecular dynamics simulation study

In the present work, the role of char-bound hydrogen in char-NO reaction under pressurized oxy-fuel combustion (POFC) conditions was studied using the reactive molecular dynamics (ReaxFF MD) simulations. The effects of char-bound hydrogen on the chemisorption of NO, formation of N2, kinetics of char-NO reaction, and structure of char at different pressures and temperatures were investigated. The results show that the char-bound hydrogen hindered the chemisorption of NO, and inhibited the generation of CN. The role of char-bound hydrogen in the chemisorption of NO weakened with the increase in pressure. Considerable amount of H2O was generated during the reaction of NO with H-containing char, which proves that char-bound hydrogen provided another channel for the conversion of NO to N2, especially at high pressures. The activation energies of the chemisorption of NO and the formation of N2 during the reaction of NO with H-containing char were determined to be 174 and 126 kJ/mol, respectively. The ReaxFF MD simulation results were in good agreement with previous experimental and DFT values. The char-bound hydrogen increased the activation energies of the chemisorption of NO and the formation of N2 by 40% and 29%, respectively. The role of char-bound hydrogen in char gasification and char structure were also examined. The char-bound hydrogen reduced the consumption of char, and CO was the main product from char gasification. The results of the O/C and N/C ratios of char indicate that char-bound hydrogen had little effect on the desorption of CO. By analyzing the dynamic evolution of char structure, it is found that char-bound hydrogen inhibited N-down chemisorption of NO.