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This study focuses on the emission characteristics of NOx under oxy-fuel combustion conditions. A comparative analysis with air combustion was performed. NOx emission, control measures and influence factors under different working conditions were studied. Experiments were carried out on a 3-MWth test platform and a laboratory platform. The 'π'-type furnace was adopted, with the furnace width of 2.6 m, depth of 2.0 m and height of 10.5 m for the 3-MWth coal-fired boiler. NOx emissions at different oxygen concentrations and different air distribution were investigated; the effects of H2O and CO2 concentration on denitrification efficiency and SO2/SO3 conversion rate were explored. Experiment results suggest that, compared with air combustion, NO concentration (volume basis) at the furnace outlet under oxy-fuel combustion is higher than that of air combustion, but the amount of NOx emissions in the discharged gas significantly decrease compared to the air combustion conditions. In addition, the formation of NOx can be effectively controlled through staged combustion. Furthermore, the selective catalytic reduction (SCR) denitrification efficiency and the conversion rate of SO2 to SO3 decreases when the CO2 concentration and the H2O content increase, indicating that CO2 and H2O have an adverse effect on the performance of the catalyst. Additionally, compared with CO2 concentration, H2O content has a greater effect on catalyst performance. [ABSTRACT FROM AUTHOR]

Abstract By using the concept of weighted sum of four gray particles and spectrum k -distribution (WSGP-SK), a non-gray radiative property model for unburnt char particles is developed. Based on the carbon burnout kinetic model for structure during oxidation, and the linear mixed approximation theory for complex index of refraction, spectral radiative properties of unburnt char particles are first calculated as function of the burnout ratio by Mie theory. Referring to the full spectrum k -distribution model, k -distribution is applied to reorder absorption and scattering efficiencies of particles. Then, weighting factors and efficiency factors of the non-gray radiative property model are directly obtained from Gaussian integral points of k -distribution. The model is validated against the benchmark solutions of line-by-line (LBL) model. Maximum relative errors of this model are 3% and 15% for radiative heat fluxes and source terms in non-isothermal inhomogeneous particulate media, respectively. The assumption of linearly varying radiative properties with burnout ratio (Lockwood et al. 1986) will result in a predicted deviation of 53% for radiative source terms. Results also show that this non-gray model is remarkably better than the Planck mean method. Moreover, a satisfactory comparison with LBL solutions is achieved in the gas and particle mixture by combining the non-gray WSGG-SK model (Guo et al. 2015). As a radiation sub-model, this non-gray radiative property model can significantly improve prediction accuracy of radiative heat transfer in oxy-fuel combustion. [ABSTRACT FROM AUTHOR]

Oxy‐fuel combustion in coal‐fired plants has become one of the most promising technologies for carbon capture and storage (CCS). Because of the obvious difference between the oxy‐fuel combustion medium (O2/CO2) and air in the atmosphere (O2/N2), the characteristics of combustion, heat transfer, etc., under oxy‐fuel combustion have changed greatly from those under air combustion. In this paper, computational fluid dynamics (CFD) simulation was used to investigate pulverized coal combustion in a 200 MWe tangentially fired oxy‐fuel combustion boiler. Improved models for the gas radiative properties and chemical reaction mechanisms were incorporated into the CFD code. Both conventional air‐fired and oxy‐fuel combustion were operated. Different flue gas recycling patterns (dry recycling and wet recycling) were also investigated. The temperature distribution in the furnace, the temperature field, and the CO concentration field in each scheme were analyzed, this being relevant to the design of oxy‐fuel combustion boilers. It was found that combustion could form a good tangential circle and stable temperature field in the furnace either under air‐fired or oxy‐fule combustion conditions. The temperature under oxy‐fuel combustion was lower than with air combustion. The burnout rate under the air condition was lower than that with the oxy‐fuel combustion condition. With oxy‐fuel combustion, it is necessary to pay special attention to the slagging tendency of the primary combustion zone in the furnace. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights • Detailed mechanisms are evaluated under oxy-fuel conditions for the first time. • A new 22-species reduced mechanism is proposed for oxy-fuel combustion. • Our proposed mechanism is better than other global and skeletal mechanisms. • The prediction of CO under oxy-fuel combustion is significantly improved. • Chemical effects of CO 2 are discussed to identify dominant reactions. Abstract The chemical kinetics under oxy-fuel combustion is significantly different from that of conventional air-combustion due to the effect of the high CO 2 concentration. Although previous studies have made substantial achievement in reaction mechanisms for air-combustion, their performance under oxy-fuel conditions is still unknown. This study proposes a new 22-species, 19-step reduced mechanism for methane oxy-fuel combustion, developed using comprehensive mechanism evaluation, reduction, and validation methods. First, through quantitative error evaluation against a large experimental data set, for the first time we find that USC-Mech II obtains the best overall predictions among seven detailed combustion mechanisms in oxy-fuel conditions, particularly for the prediction of CO concentration. This detailed mechanism is then thoroughly simplified (including both skeletal and time-scale reduction) with error control under both atmospheric and pressurized oxy-fuel conditions. The obtained reduced mechanism is systematically validated using the detailed mechanism and the relative errors are found to be less than 10%. Relative to other mechanisms, this specially developed reduced mechanism for oxy-fuel combustion not only has minimal species, but also significantly improves the prediction of CO formation. The chemical influence of CO 2 under oxy-fuel conditions is further discussed to identify dominant elementary reactions for CO formation, which is important for future development of methane oxy-fuel combustion. [ABSTRACT FROM AUTHOR]

The configurations of burner streams under oxy-fuel combustion are highly affected by its increased initial oxygen level. In this study, an air combustion and oxy-fuel combustion compatible configuration strategy for burner streams is proposed for a 200 MW e tangentially fired boiler, by aid of numerical simulation. Firstly, to achieve a momentum of primary and secondary streams that is similar to that of air combustion, the tertiary stream is switched-off in oxy-fuel combustion. In addition, the opposing tangential primary stream technology is suggested to reduce the gas temperature deviation in the upper furnace, which affects the quality of the steam and the safe operation of the boiler. For the present study, the appropriate opposing tangential angle is 5°–7° relative to the original primary stream design, and the ratio of opposing tangential momentum flow moment should be controlled at the low limit of 0.8 to decrease gas temperature deviation. To achieve a supported flame by the secondary stream, the momentum of the bottom secondary stream in oxy-fuel combustion should not be less than that in air combustion. The study illustrates for the first time that, the key design features of tangentially fired burners under oxy-fuel combustion. Although there are significant changes in the oxidant volume, oxidant composition, and chemical reaction under oxy-fuel combustion conditions, the design criteria of oxy-fuel tangentially fired boiler, in terms of momentum of the primary stream, momentum of the bottom secondary stream, and momentum ratio and momentum flow moment ratio of the secondary stream to primary stream, are consistent with those under air combustion. [ABSTRACT FROM AUTHOR]

Oxy-fuel combustion has different combustion and heat transfer characteristics from those of air-combustion, due to the high concentration of CO 2 and H 2 O in the flue gas. This study investigated the heat transfer characteristics in a 35 MW oxy-combustion large pilot plant. The experimental and numerical investigations are carried out with a sub-bituminous coal. The gas temperature, exhaust emission, and heat transfer are measured in conventional air-combustion and oxy-fuel conditions with wet and dry flue gas recycle. Detailed numerical studies of combustion and heat transfer are performed with a modified radiative property model and global reaction mechanism. The results are in good agreement with the experimental data. The effects of char and ash on radiative heat transfer are investigated. The experimental and numerical results show that although the peak temperature decreases, the heat transfer in membrane-wall and superheater in oxy-fuel combustion is slightly greater than that in air-combustion. The absorption coefficient ratios of particle to gas are approximately 2.5 and 2.4 in air-combustion and oxy-fuel combustion. The particle radiation dominates the radiative heat transfer in the pulverized coal combustion, which has a significant influence on the temperature level and distribution. [ABSTRACT FROM AUTHOR]

This paper reports on the recent experimental and numerical results from a 35 MW front wall-fired large pilot boiler. The boiler features a first-of-its-kind compatible design of oxy-fuel combustion and conventional air combustion (air-combustion). A sub-bituminous coal is used as fuel in the experiment. Wet and dry flue gas recycle oxy-fuel conditions are investigated, while air-combustion is also examined for reference. Measured in-furnace temperature, species concentration, exhaust emission, and transferred heat to membrane-wall and superheater are compared between oxy-fuel and air-combustion. Detailed numerical studies of combustion and heat transfer are performed using in-house developed sub-models for oxy-fuel condition, including a radiative property model and a global reaction mechanism. The predicted results agree well with the experimental data. The experimental and numerical results show that stable oxy-fuel combustion is achieved in the 35 MW large pilot boiler. Importantly, the oxy-fuel combustion and air-combustion can operate well with the especially designed burner system at similar heat loads in the experiment. Moreover, similar average temperatures and heat flux distributions are achieved under wet and dry flue gas recycle oxy-fuel conditions with an initial O 2 concentration of 28% in the oxidant. Transferred heat to membrane-wall and superheater in oxy-fuel combustion is slightly greater than in air-combustion. Furthermore, the flue gas recycle ratio significantly influences the heat transfer in oxy-fuel combustion. Increasing the recycle ratio from 0.71 to 0.73 reduces the transferred heat to membrane-wall by approximately 6%, while that of superheaters increases by approximately 4%. The selection of the optimized recycle ratio is a trade-off between boiler performance and flame stability of the burner system. [ABSTRACT FROM AUTHOR]

Oxy-fuel technology has been considered as a feasible way to achieve the reduction of CO 2 emission. In this article, an oxy-fuel combustion process model was developed using a 3 MW th oxy-fuel combustion test facility as prototype. Both steady state and dynamic model were developed using Aspen Plus and Aspen Plus Dynamics, respectively. The steady state model was validated with test data based on mass balance and energy balance. By defining several typical periods of time which could characterize the dynamic features of the control actuators and the responses of heat transfer and fluid flow processes, the combination of these periods of time was used to reflect the dynamic responses of the system and the simulation results were compared to the test results showing good agreement with the experimental results. Based on the validated dynamic model, transient analysis of typical operation parameters have been performed and the relationships of various inputs and output response have been investigated. All of these results will be helpful to the facility operations and the control system design. [ABSTRACT FROM AUTHOR]

In recent years, oxy-fuel combustion in coal-fired plants has become one of the most promising technologies for carbon capture and storage (CCS). Compared with air-fired combustion, high concentrations of CO 2 and H 2 O in the flue gas cause a remarkable change in the pulverized coal combustion and heat transfer characteristics in furnace. In this study, improved models for the gas radiative properties and chemical reaction mechanisms were incorporated into the computational fluid dynamics (CFD) code to simulate a 200 MW e tangentially fired utility boiler, which is expected to operate at full load under both conventional air-fired and oxy-fuel combustion. Different flue gas recycle patterns: dry recycle and wet recycle, were also investigated. The results indicate that, stable combustion is achieved by a compatible burner design in both air-fired and oxy-fuel combustion. In the oxy-fuel combustion, the flue gas peak temperature and wall heat flux decrease and high CO concentration appears in the burner region, resulted from higher heat capacity of CO 2 and chemical effect of CO 2 (Liu et al., 2003, Glarborg and Bentzen, 2008). Based on the comparison of the wet recycle and dry recycle, it shows the wet recycle has more advantages than dry recycle. This study indicates a slight increase in total heat transfer, when the oxygen concentration in oxidant increases from 23% to 29%, consistent with the results of Vattenfall and Callide pilot scale oxy-combustion plant. Thus, compared with air-fired combustion, the full load of a boiler may decrease by 5–10% under oxy-fuel combustion. [ABSTRACT FROM AUTHOR]

There has been little research on volatile releasing characteristics of pulverized coals under moderate or intense low-oxygen dilution (MILD) oxy-combustion (MO) conditions. For the first time, volatile releasing characteristics of bituminous coal and semi-anthracite under both MILD air-combustion (MA) and MO conditions were investigated using a flat-flame assisted entrained flow reactor. Both heating rate (~105 K/s) and residence time (65 ms) were carefully selected to mimic the conditions in typical industrial boilers. The combustion processes and properties of the volatiles were characterized through direct observation and char analysis. The results showed that the lower diffusion rate of the volatile in CO2 resulted in the decreasing of the volatile envelope flame size and a longer volatile burnout time (more than 20%). For bituminous coal (volatile content of 25%), the lower amount of apparent volatile yield under MO conditions reduced the heating value of the volatile. For semi-anthracite coal (volatile content of 7%), the short devolatilization time led to char-CO2 gasification reaction, which increased the apparent volatile yield and the heating value of the volatile by 47% and the volatile-N by 19%. This paper indeed provided new insight into the MILD oxy-combustion of solid fuels. [ABSTRACT FROM AUTHOR]

• A certain amount CaCO 3 exists under oxy-fuel combustion. • The viscosity of fly ash particles was higher under oxy-fuel combustion. • The particles were stickier and more easily coalesced under oxy-fuel combustion. • The slagging trend under oxy-fuel combustion was greater. Global warming has attracted extensive attention due to increasing CO 2 emissions. Oxy-fuel combustion has become an important topic in the domain of energy saving and emission reduction due to its high efficiency in CO 2 reduction. The slagging characteristics of coal ash under oxy-fuel combustion conditions are the premise for the successful application of this technology. In this study, we relied on a tubular furnace and flat flame-assisted entrained flow reactor to test coal ash under different atmospheres. The slagging trend of Shenhua coal under oxy-fuel combustion, including its melting point, mineral species, particle size, and morphology, was analyzed. A comparative analysis of different ash samples obtained from different experimental platforms was also conducted. Results showed that the oxy-fuel combustion atmosphere exerted a minimal effect on the melting point of Shenhua coal ash. Moreover, a high oxygen concentration corresponded to a relatively high melting point of ash. Ca existed in the form of CaO under air combustion, and a certain amount of undecomposed CaCO 3 appeared under oxy-fuel combustion. Given the same oxygen concentration, the average particle size under oxy-fuel combustion was smaller than that under air combustion. Moreover, particle adhesiveness was stronger and particles more easily gathered under oxy-fuel combustion than under air combustion. Particle aggregation was also more obvious under oxy-fuel combustion than under air combustion. Therefore, the slagging trend under oxy-fuel combustion was obviously higher than that under air combustion. [ABSTRACT FROM AUTHOR]

• LES-SWF well predicts oxy-flame characteristics across a wide Re range. • Higher Re reduces radial flame size, enhancing effects of vortex on reaction zone. • Increasing Re weakens the beneficial effect of preferential diffusion of H 2. • Adverse effect of CO 2 on combustion increases with increasing Re. Due to differences in the physical and chemical properties of CO 2 and N 2 , along with a reduction in the momentum ratio between oxidant and fuel streams, the local extinction of oxy-fuel flames is significantly more pronounced compared to conventional air–fuel flames, which poses challenges in the design and operation of oxy-fuel burners. This study further validates the species-weighted flamelet/progress variable (FPV) model proposed in previous work [Jiang et al., 2023], particularly in oxy-fuel flames characterized by highly local extinction. Large eddy simulations were conducted on the Sandia oxy-fuel jet diffusion flame at various Reynolds numbers. The predictions are systematically compared with experimental data, and the influence of Reynolds number on local extinction is thoroughly analyzed. The results demonstrate that the numerical simulation effectively predicts mean temperature, species mass fractions, differential diffusion parameters (Z HC), and local extinction in oxy-fuel jet flames across a wide range of Reynolds numbers. The errors in predicted mean temperature and mass fractions exhibit a slight increase with rising Reynolds numbers, yet remain below 15 %. As the Reynolds number increases from 12,000 to 18,000, the predicted peak Z HC decreases by 30 %, and the beneficial effect of preferential diffusion of H 2 weakens, while the adverse effect of CO 2 on combustion becomes stronger. [ABSTRACT FROM AUTHOR]

• NO x formation in staged oxy-combustion has been numerically studied. • The fuel staged mode reduces NO concentration in furnace outlet by 5.6%. • Oxygen-fuel two-way staged mode reduces NO concentration in furnace outlet by 17%. • The NO formation pathway of HCN → NCO → NO is suppressed, and NO reduction pathway of NO → HCN is enhanced in staged oxy-combustion. In this study, high-fidelity simulations are conducted on a 35 MW pulverized coal oxy-fuel boiler to investigate NO x formation characteristics under staged oxy-fuel combustion, including both fuel-staged and oxygen-fuel two-way staged modes. Detailed volatile components are considered by using the chemical percolation devolatilization model. A skeletal reaction mechanisms consisting of 35 species developed for fuel-NO x formation under oxy-fuel conditions are employed for the gas phase combustion and NO x modeling. The radiative property models are also optimized for oxy-fuel combustion. The results show that in the fuel-staged mode, a reduction atmosphere is established in the reburning zone to reduce the NO x concentration in the flue gas. A reduction of 5.6% in the average NO concentration at the furnace outlet is observed relative to the baseline oxy-fuel case. Moreover, the application of oxygen-fuel two-way staged combustion leads to a further reduction in NO x formation. The average NO concentration at the furnace outlet is decreased by 17% compared to the baseline oxy-fuel case. Pathway analysis indicates a reduction in the NO formation pathway involving HCN → NCO → NO, while the NO reduction pathway of NO → HCN is enhanced. [ABSTRACT FROM AUTHOR]

This study systematically investigates the detailed mechanism of nitrogen oxides (NO x ) in CH 4 and CH 4 /H 2 jet flames with O 2 /CO 2 hot coflow. After comprehensive validation of the modeling by experiments of Dally et al. [Proc. Combust. Inst. 29 (2002) 1147–1154]; the effects of CO 2 replacement of N 2 , mass fraction of oxygen in the coflow ( Y O 2 ), and mass fraction of hydrogen in the fuel jet ( Y H 2 ) on NO formation and destruction are investigated in detail. For methane oxy-fuel combustion, the NNH route is found to control the NO formation at Y O 2 ≤ 3%, while both NNH and N 2 O-intermediate routes dominate the NO production at 3% < Y O 2 < 10%. When Y O 2 ≥ 10%, NO is obtained mainly from thermal mechanism. Moreover, in the oxy-combustion of methane and hydrogen fuel blends with Y O 2 = 3%, with hydrogen addition the contribution of the NNH and prompt routes increases, while that of the N 2 O-intermediate route decreases. Furthermore, the chemical effect of CO 2 is significant in reducing NO in both oxy-combustion of methane with Y O 2 ≤ 3% and combustion of methane and hydrogen fuel blends with Y H 2 ≤ 10%. [ABSTRACT FROM AUTHOR]

This paper optimizes global reaction mechanisms under the MILD ( Moderate and Intensive Low-oxygen Dilution ) oxy-combustion combustion. Seven global mechanisms are compared and validated with two detailed mechanisms under the oxy-fuel combustion, MILD air-combustion, and MILD oxy-combustion conditions. The ability of these global models to capture the combustion process under different conditions is compared first using computational fluid dynamics (CFD) simulations of both the MILD oxy-combustion in a laboratory-scale furnace and non-premixed turbulent jet open flames, and later using a plug flow reactor (PFR) approach. Experiments of the MILD oxy-combustion are also carried out for the mechanism validation. The detailed comparison shows that the present optimized global mechanism significantly improves the prediction of temperatures, equilibrium concentrations of major species, and the peak CO concentration, relative to other global mechanisms, for the MILD oxy-combustion. The present refined mechanism is an appropriate global reaction mechanism for methane MILD oxy-combustion, if the computational cost of detailed reaction mechanism is unaffordable. [ABSTRACT FROM AUTHOR]

Particle radiation characteristics have a strong wavelength-dependence. However, the gray particle assumption is widely used for coal combustion simulations, which cannot reflect the non-gray radiative property of the particles. In this study, based on the measured complex index of refraction from literatures (Gupta and Wall, 1985, Goodwin and Mitchner, 1989, and Lohi et al., 1992), a new non-gray particle radiative property model for fly ash is proposed by combining the features of full-spectrum k -distribution (FSK) model with the weighted sum of gray gases (WSGG) model. Four gray particles with different absorption and scattering efficiencies are used to replace the non-gray particles, for which absorption efficiency, scattering efficiency and weighting factor are directly obtained from the k -distribution, with model parameters obtained based on rational polynomials. Simultaneously, a gray particle model based on the Planck’s law is also obtained for comparison. The new model is systematically validated by comparing the radiative source terms and radiative heat fluxes, with those predicted by the line-by-line (LBL) integration of Mie-data in a one-dimensional plane-parallel slab system. The maximum relative error of radiative source term is 8% for the new non-gray radiative property model, 13% for Planck mean coefficients, 14% for modified Johansson model (Johansson, 2017), and 18% for empirical-constant model in non-isothermal inhomogeneous particle media, respectively. Combining the new non-gray radiative property model with the non-gray formulation of WSGG-SK model (Guo et al., 2015), the prediction accuracy is further validated by LBL solutions in the gas and particle mixture. Moreover, the contribution of gases and particles to radiative heat transfer is discussed at different path lengths, which shows the accuracy of the particle radiative property model determines the prediction accuracy of the radiative heat transfer in large-scale furnace. [ABSTRACT FROM AUTHOR]

A flamelet/progress variable (FPV) model accounting for the differential diffusion (DD) effects is proposed and applied to large eddy simulation (LES) of turbulent oxy-fuel flames (Sevault et al. 2012). Based on tabulations with the detailed molecular diffusion and the equal diffusion (ED) assumption, a species-weighted flamelet (SWF) model is developed to represent the DD effects. The influences of combustion progress, mixture fraction, and turbulence on variable Lewis numbers are incorporated into the model. The model assessments are first conducted on a laminar coflow flame, showing that the effect of DD on temperature and species is accurately captured, in that the importance of DD is seen in the laminar flame. Subsequently the model is implemented in a fully coupled LES of oxy-fuel jet flames. The LES results show that DD plays an important role in the reaction zone and regions near the fuel nozzle, and its effect decreases farther downstream, consistent with the experimental observations. The LES with the SWF model yields good predictions on the mean temperature and major species at the fuel-rich side while slight deviation (less than 6%) at the fuel-lean side. In comparison, LES with the original unity Lewis numbers flamelet model (Pierce et al. 2004) predicts a full extinction because of neglecting the DD characteristics, while the variable Lewis number flamelet model provides the maximum deviation of 26% because of ignoring the ED characteristics produced by turbulent disturbance. The trend and location of localized extinction of oxy-fuel flame are also well predicted using the SWF model. [ABSTRACT FROM AUTHOR]

Accurate assessment of the structural characteristics and reactivity of coal char is crucial for the design of burners. Chars from low-volatile coal were prepared under O 2 /N 2 (ON) and O 2 /CO 2 (OC) conditions in a flat-flame assisted entrained flow reactor, with bituminous coal as a reference. Both the heating rate and residence time were carefully selected to mimic the conditions used in actual industrial boilers. The physical-chemical structures and reactivities of all chars were characterized using Raman and FTIR spectrometers and thermogravimetric analysis. The physical structure results indicated that a high CO 2 content inhibited the char yield and specific surface area of chars from low-volatile anthracite coal, while, for chars from high-volatile bituminous coal, CO 2 increased the char yield and specific surface area. For chemical structures, the degree of disorder in the carbon skeleton structures and active functional group contents of all chars prepared under OC conditions were greater than those of chars prepared under ON conditions. Moreover, the apparent reactivity results demonstrated that the physical structure characteristics of coal char played a leading role in the apparent reactivity under investigative conditions. • Chars were prepared in a flat-flame reactor under O 2 /N 2 and O 2 /CO 2 conditions. • Chars were analyzed for their physical-chemical structures and apparent reactivity. • The presence of CO 2 reduced the degree of order of the chars. • Physical structure characteristics of coal char dominated the apparent reactivity. [ABSTRACT FROM AUTHOR]

Control system design is one of the key elements which need to be studied before commercial implementation of oxy-fuel power plants. Among others, the control strategy for flue gas recycle process should be firstly considered as it is one of the major differences between oxy-fuel combustion and traditional power plants. In this paper, a dynamic model combined with exergy analysis was firstly proposed to design the control system and evaluate the performance of potential control schemes for flue gas recycle process. The dynamic model had been extensively validated using static and dynamic data from a 3 MW th oxy-fuel combustion facility. Based on the dynamic model, the characteristics of the flue gas recycle system was investigated and two possible control configurations, RR (recycle valve coupled with recycle fan) and SR (stack valve combined with recycle fan), were proposed. The control performances of the two candidates were tested in three typical types of disturbances usually occurred in the operation and further evaluated from the perspective of exergy efficiency. It was shown that both control loops could maintain the target variables (flue gas recycle ratio and recycled flue gas pressure) stable in the disturbances, while the total exergy destruction of flue gas recycle system in RR is 2.4%, 1.7% and 0.6% higher than that in SR during the disturbance tests, respectively. The exergy-based control strategy selection method proposed in this paper provides good insight to obtain the optimum control method for other subsystems in the power plant. [ABSTRACT FROM AUTHOR]

Oxy-fuel combustion has become one of the most promising technologies for carbon capture and storage (CCS) in coal-fired plants. Radiative properties of combustion gases in oxy-fuel combustion are significantly different from those found in air-fired due to the change of the gas composition. A few modified weighted-sum-of-gray-gases (WSGG) models had been proposed to consider the wide H 2 O to CO 2 ratio for oxy-fuel combustion in recent years. As most of the models are validated using simple homogenous benchmark, the applicability of such models to non-homogeneous media is questionable. In this paper, based on the up-to-date HITEMP 2010 database, we obtain new parameters of WSGG model for oxy-fuel combustion by combining the features of full-spectrum k -distribution (FSK) model with WSGG model, in which the weighting factors and absorption coefficients are directly obtained from the k -distribution, and the polynomial expression of absorption coefficient is improved. The new parameters of WSGG model are extensively validated by comparing the radiative source terms and radiative heat fluxes, predicted with the line-by-line (LBL) model integration of HITEMP 2010 database at a one-dimensional slab system. The predictions by different parameters of WSGG model from the literature are also included in comparison. The investigative cases include the non-isothermal and/or non-homogeneous gas mixture. The maximum relative error of heat fluxes is 11.2% for the new parameters, 33.5% for Yin model (Yin et al., 2010) and 23.0% for Johansson model (Johansson et al., 2011) in non-isothermal non-homogeneous gas mixture. The results show the new parameters can significantly improve the prediction accuracy in non-isothermal non-homogeneous CO 2 /H 2 O mixture. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the effects of H 2 O addition on pulverized coal oxy-MILD (moderate or intense low oxygen dilution) combustion based on our previous study, in which only O 2 /CO 2 was treated as oxidizer. While in the present study, the initial H 2 O mole fraction in oxidizer is varied at a constant oxygen level (30% by volume) to represent four typical oxy-fuel operations, i.e. ideal dry recycle (0% H 2 O + 70% CO 2 ), practical dry recycle (5% H 2 O + 65% CO 2 ), wet recycle (15% H 2 O + 55% CO 2 ) and oxy-steam (70% H 2 O + 0% CO 2 ). It is revealed that, with the addition of H 2 O, the internal recirculation rate (K V ) as well as the coal ignition is improved, however, due to the difference in physical effects between CO 2 and H 2 O, the temperature peak is likewise promoted. CO 2 is preferred than H 2 O to moderate the flame temperature and realize uniform temperature distribution under MILD combustion. Higher H 2 and lower CO formations are obtained by adding H 2 O because of the competing char gasification reactions between CO 2 and H 2 O under in-furnace low oxygen condition of MILD combustion. H 2 O addition tends to suppress the volatiles-N conversion while accelerate the char-N conversion in the upper furnace, respectively, and reduce the final NO emission by enhanced H 2 formation. Moreover, H 2 O addition is beneficial to increasing heat transfer in both radiative and convective forms. [ABSTRACT FROM AUTHOR]

MILD (Moderate or Intense Low-oxygen Dilution) combustion is a novel technology to reduce NO X emission from combustion. With the development of this technology, it is expected to combine this technology with oxy-fuel combustion to jointly control the pollutants from fossil fuel combustion. The present paper investigates the combustion characteristics of coal under oxy-MILD operation with the aid of CFD simulations. A seven-step global reaction mechanism is used for modeling coal combustion involving gaseous volumetric reaction and particle surface reaction. The predicted results using the adopted models for the reference case agree well with the experimental results. It is revealed that, the combustion temperature level increases with the enhancement of initial oxygen concentration because of the reduced injection momentum and promoted heat release. The in-furnace CO formation increases but the final CO emission reduces when enhancing the oxygen concentration under oxy-MILD combustion. Moreover, oxy-MILD combustion shows a greater potential on NO X formation reduction than air-MILD combustion, and this potential is promoted at higher initial oxygen concentration. [ABSTRACT FROM AUTHOR]

To fulfill its commitment to carbon emission reduction and peak carbon emission in 2030, China is expected to conduct large-scale carbon capture and storage deployment in future decades, considering the dominant role of coal-based energy for power generation. As an important carbon emission mitigation technology, oxy-fuel combustion will play a significant role in this process. Meanwhile, the water scarcity in China is also worthy of attention, especially in coal-rich areas which are usually water-scarce. The development and implementation of coal-based carbon capture and storage technology may exacerbate the water shortage situation in these regions. Considering this background, a correct analysis of the water use of oxy-fuel combustion power plants is of great importance, before implementing the large-scale deployment of carbon capture and storage. Therefore, this study aims to assess the life-cycle water consumption of a 600 MW oxy-fuel combustion power plant, retrofitted from a typical 600 MW coal-fired power plant in China. Based on a tiered hybrid method, the direct and indirect water consumption of a typical oxy-combustion CCS project is evaluated. Results show that 4.63 L of water is used for capturing 1 kg of carbon dioxide, while the calculated water intensity for power generation is 3.79 L/kWh. The operation and maintenance processes dominate the total water consumption, in which the cooling mode exerts a great influence on life cycle water consumption. Once-through cooling has lower water consumption than recirculating cooling in the retrofitted oxy-combustion power plant. If we compare water consumption with other power generation technologies, the water intensity of oxy-combustion carbon capture and storage power production is lower than that of bio-power, but beyond that of solar photovoltaic and wind power. Moreover, based on the thermal power production in China in 2017 and the water use calculated in this study, transforming all the thermal power plants to oxy-combustion systems is hardly feasible as the induced water withdrawal will account for 17.26%–827.19% of the total industrial water budget in 2030. Further regional analysis indicates that even to achieve 10 Gt of carbon dioxide abatement, Shanxi province will encounter great difficulties due to reduced water availability. • The life cycle water consumption for the oxyfuel CCS system is 4.63 L/kg CO 2. • The operation & maintenance dominates the life cycle water consumption. • Retrofitting of the thermal power plant increases water consumption by 16%–26%. • Shanxi province encounters water limitation in oxy-combustion CCS development. [ABSTRACT FROM AUTHOR]

Although fuel-NO formation is significant for the combustion of pulverized coal, biomass, and heavy distillate fuels, its mechanism has not been systematically validated under air and oxy-fuel combustion. This is the first study that quantitatively evaluates detailed fuel-NO mechanisms against large experimental datasets from a jet stirred reactor (JSR) under both air and oxy-fuel combustion. The mechanism with the best overall performance is thoroughly reduced and validated. A skeletal fuel-NO mechanism including only 35 species is obtained using methods of directed relation graph with error propagation (DRGEP), DRGEP-aided sensitivity analysis, and computational singular perturbation. The skeletal mechanism is comprehensively validated and agrees well with the detailed mechanism and experiments predicting the ignition delay, temperatures, and concentrations of important species in JSRs, laminar flame speeds, and flame extinction under both air and oxy-fuel combustion. Moreover, the skeletal mechanism is successfully applied to the finite-rate modeling of moderate or intense low-oxygen dilution (MILD) combustion of pulverized coal. Unlike conventional semi-empirical post-processing modeling of fuel-NO production, the fuel-NO calculation in this study is coupled with coal combustion by using the well-validated skeletal mechanism. A highly precise in-furnace distribution of fuel-NO critical precursors (i.e., NH 3 and HCN) and detailed fuel-NO reaction pathway under the MILD combustion are obtained. • Detailed mechanisms for fuel-NO are evaluated for the first time. • A 35-species skeletal fuel-NO mechanism is obtained. • Skeletal mechanism agrees well with detailed mechanism and experiments. • Mechanism is used in finite-rate modeling of coal combustion for NO formation. • Skeletal mechanism is suitable for fuel-NO under air and oxy-fuel conditions. [ABSTRACT FROM AUTHOR]

• A certain amount CaCO 3 exists under oxy-fuel combustion. • Fe is more likely to react with Si, Ca, Al. • Slagging tendency of Shenhua coal is predicted by different indexes. • Slagging tendency under oxy-fuel combustion is obviously higher. CO 2 capture and storage technology plays an important role in global carbon emission reduction, and oxy-fuel combustion is one of the key future technologies. The slagging and deposition characteristics of ash under oxy-fuel combustion restrict the competitiveness and development of this technology. In this study, an ash sample of Shenhua coal was obtained in a flat flame-assisted entrained flow reactor under different conditions, and an X-ray diffraction, X-ray fluorescence probe, and scanning electron microscope–energy dispersive spectrometer were used. The slagging tendency under oxy-fuel combustion was thoroughly analyzed. Results showed that the characteristics of the ash samples obtained under oxy-fuel and air combustion varied. Obvious differences existed in the mineral characteristics and relative content, and these may have affected the slagging characteristics. The presence of Ca in ash was mainly in the form of CaO, and Fe was likely to react with Si, Ca, Al, and other minerals. Compounds with low melting points were generated under oxy-fuel combustion, indicating that the slagging tendency was aggravated. Moreover, the slagging tendency of Shenhua coal in different atmospheres was predicted with common and viscosity slagging indexes, and the result was consistent with the experimental ones. The sphericity of the ash samples obtained under oxy-fuel combustion was better than that of the samples under air combustion. [ABSTRACT FROM AUTHOR]

• CFD results of a swirl oxy-coal flame are compared with detailed experiment. • Nonlinear variation particle radiative property is first used in oxy-coal modeling. • Contributions of gas and particle radiation are illustrated in oxy-coal flame. • Constant model ten times over-predicts the particle absorption after burnout. This paper reports a comprehensive computational fluid dynamics simulation of the IFRF's swirling oxy-fuel flame with pulverized coal using wet flue gas recycle. Special attention is given to the influence of particle radiative property model. Based on the burnout rate of pulverized coal, a recent proposed nonlinear conversion-dependent particle radiative property model (Guo et al., 2018) is used in the simulations. The influences of the high CO 2 concentration on the sub-models are also considered in detail. The gas-phase global reaction mechanism, kinetic parameters of char oxidation and gasification, and gas radiative property model are modified for oxy-fuel condition. The results show the prediction results agree well with the measurements, in terms of the temperature and composition of the flue gas. The particle radiation has an important effect on the flame temperature. Even in the small furnace studied here (optical length is approximately 1.6 m), the radiation in the flame zone is still dominated by particle radiation. Linear variation assumption (Yin et al., 2015) under-predicts the particle absorption in combustion zone. Ignoring the effect of burnout rate on particle radiative property will 10 times over-predict the particle absorption after burnout. [ABSTRACT FROM AUTHOR]