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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 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]

Abstract: In this paper, entropy generation in hydrogen-enriched ultra-lean counter-flow methane–air non-premixed combustion confined by planar opposing jets is investigated for the first time. The effects of the effective equivalence ratio and the volume percentage of hydrogen in fuel blends on entropy generation are studied by numerically evaluating the entropy generation equation. The lattice Boltzmann model proposed in our previous work, instead of traditional numerical methods, is used to solve the governing equations for combustion process. Through the present study, five interesting features of this kind of combustion, which are quite different from that reported in previous literature on entropy generation analysis for hydrogen-enriched methane–air combustion, are revealed. The total entropy generation number can be approximated as a linear increasing function of the volume percentage of hydrogen in fuel mixture and the effective equivalence ratio for all the cases under the present study. [Copyright &y& Elsevier]

Abstract: A simple lattice Boltzmann model is developed for two-dimensional combustion simulations. In this model the time step and the fluid particle speed can be adjusted dynamically, depending on the “particle characteristic temperature”. The algorithm is still a simple process of hopping from one grid point to the next, the same as the standard lattice Boltzmann method. Therefore the outstanding advantages of the standard lattice Boltzmann method are retained in this model besides better numerical stability. Excellent agreement between the present results and other numerical or experimental data shows that this scheme is an efficient numerical method for practical combustion simulations. [Copyright &y& Elsevier]

Abstract: A novel coupled lattice Boltzmann model is developed for two- and three-dimensional low Mach number combustion simulations, in which the fluid density can bear sharp changes. Different to the hybrid lattice Boltzmann scheme [O. Filippova, D. Hanel, A novel lattice BGK approach for low Mach number combustion, J. Comput. Phys. 158 (2000) 139], this scheme is strictly pure lattice Boltzmann style (i.e., we solve the flow, temperature, and concentration fields using the lattice Boltzmann method only); different to the non-coupled lattice Boltzmann scheme [K. Yamamoto, X. He, G.D. Doolen, Simulation of combustion field with lattice Boltzmann method, J. Stat. Phys. 107 (2002) 367], the fluid density in this model is coupled directly with the temperature. In this model the time step and the fluid particle speed can be adjusted dynamically, depending on the “particle characteristic temperature”. And the algorithm is still a simple process of hopping from one grid point to the next, the same as the standard lattice Boltzmann method. Therefore the outstanding advantages of the standard lattice Boltzmann method are retained in this model besides better numerical stability. Excellent agreement between the present results and other numerical or experimental data shows that this scheme is an efficient numerical method for practical combustion simulations. [Copyright &y& Elsevier]

NH 3 is a carbon-free fuel with good storage and transport characteristics. Applying Moderate or Intense Low-oxygen Dilution (MILD) combustion to NH 3 /syngas blended fuel is expected to achieve clean and low-carbon combustion. This work explores the impacts of changing the NH 3 /syngas ratio and O 2 content in co-flow on the combustion characteristics and the NO x formation and transformation mechanisms. As the proportion of NH 3 increases, the flame is gradually lifted, while the rise of H 2 in syngas reduces the lifted height. As the O 2 proportion is increased to 15%, almost the entire computational domain is transformed from MILD to high-temperature combustion when the ratio of NH 3 to syngas is 3:7. NH that is derived from the decomposition of NH 3 participates more actively in the consumption process of NO and N 2 O. N radicals are more likely to generate N 2 when O 2 content in hot co-flow increases. [Display omitted] • Higher NH 3 ratio results in a shorter flame length and higher flame lifted-height. • The MILD combustion boundary of NH 3 /syngas mixed fuel is depicted. • The increase in syngas promotes the consumption of NH 3. • Detailed NH 3 conversion routes of NH 3 /syngas in JHC burner are explored. • Patterns of NO formation routes with the rise of NH 3 and O 2 ratio are revealed. [ABSTRACT FROM AUTHOR]

This study investigated the effect of the H 2 fraction on reaction dynamics and NO x formation in a premixed NH 3 /H 2 /air jet flame within a hot coflow (JHC) through numerical simulations. We found that even a small mole fraction of H 2 (e.g., X H2, F = 5%) significantly enhances the ignition of the premixed NH 3 /air flame. However, the presence of H 2 markedly intensifies the main combustion reactions only when X H2, F ≥ 30%, resulting in a sharp increase in temperature and heat release rate. Moreover, as X H2, F increases, the NO x emission first increases until X H2, F = 75% and then decreases. Without any H 2 addition, a high emission of unburned NH 3 occurs in the pure NH 3 JHC flame. On the other hand, when X H2, F ≥ 50%, the emissions of unburned H 2 and OH increase rapidly due to extremely high temperatures. Notably, maintaining X H2, F between 5% and 20% minimizes the emissions of NO x , NH 3 , H 2 , and OH. Furthermore, the preferential diffusion of H 2 plays a key role in enhancing the production of active radicals (OH, O, and H), thereby significantly boosting the initiation and combustion reactions of NH 3 /H 2 blended fuel. [Display omitted] • Effect of H 2 addition on the premixed NH 3 /H 2 /air jet flames is investigated. • A small amount of H 2 (5%) in the fuel notably enhances the ignition of NH 3 flame. • H 2 significantly boosts major combustion reactions only when its proportion ≥30%. • Optimal H 2 proportion is 5%–20% to reduce emissions of NO x , unburned NH 3 and H 2. • Preferential diffusion of H 2 greatly enhances the ignition and combustion reactions. [ABSTRACT FROM AUTHOR]

Hydrogen fuel has significant potential for various applications under MILD combustion conditions. This study investigates the impact of H 2 mass fraction (ranging from 10 % to 100 %) on the structure of the combustion zone and the emission rules of NO x in the JHC burner utilizing the detailed mechanism GRI-Mech 2.11. A contraction of the reaction zone and a decrease in the ignition delay is observed when the H 2 ratio increases. Increasing H 2 concentration results in the gradual loss of MILD combustion characteristics in the reaction area, and the downstream region gradually transforms to High Temperature Combustion. The MILD reaction volume at Y O2 = 6 % is only 69 % compared to that at Y O2 = 3 %. Higher Y O2 has a more significant impact on the relative increment of NO emissions. The NNH route consistently predominates, and increasing H 2 ratio amplifies the production of thermal NO x and weakens the NO-reburning mechanism. • Transition of reaction area from MILD to HTC is observed in pure hydrogen cases. • The boundary of pure hydrogen fuel under MILD combustion conditions is depicted. • Contributions of different NO formation routes under MILD conditions are conducted. • Trend of NO generation pathways with changing hydrogen ratio is revealed. [ABSTRACT FROM AUTHOR]

The NO mechanism under the moderate or intense low-oxygen dilution (MILD) combustion of syngas has not been systematically examined. This paper investigates the NO mechanism in the syngas MILD regime under the dilution of N 2 , CO 2 , and H 2 O through counterflow combustion simulation. The syngas reaction mechanism and the counterflow combustion simulation are comprehensively validated under different CO/H 2 ratios and strain rates. The effects of oxygen volume fraction, CO/H 2 ratio, pressure, strain rate, and dilution atmosphere are systematically investigated. For all the MILD cases, the contribution of the prompt and NO-reburning routes to the overall NO emission is less than 0.1% due to the lack of CH 4 in fuel. At atmospheric pressure, the thermal route only accounts for less than 20% of the total NO emission because of the low reaction temperature. Moreover, at atmospheric pressure, the contribution of the NNH route to NO emission is always larger than 55% in the N 2 atmosphere. The N 2 O-intermediate route is enhanced in CO 2 and H 2 O atmospheres due to the increased third-body effects of CO 2 and H 2 O through the reaction N 2 + O (+M) ↔ N 2 O (+M). Especially in the H 2 O atmosphere, the N 2 O-intermediate route contributes to 60% NO at most. NO production is reduced with increasing CO/H 2 ratio or pressure, mainly due to decreased NO formation from the NNH route. Importantly, a high reaction temperature and low NO emission are simultaneously achieved at high pressure. To minimize NO emission, the reactions should be operated at high values of CO/H 2 ratios (i.e., >4) and pressures (e.g., P > 10 atm), low oxygen volume fractions (e.g., X O2 < 15%), and using H 2 O as a diluent. This study provides a new fundamental understanding of the NO mechanism of syngas MILD combustion in N 2 , CO 2 , and H 2 O atmospheres. • The NNH route dominates NO formation in N 2 atmosphere under atmospheric pressure. • The N 2 O-intermediate route is enhanced in CO 2 and H 2 O atmospheres. • Increasing CO/H 2 ratio reduces NO formation from NNH and N 2 O-intermediate routes. • High pressure increases the combustion temperature while inhibits the NO formation. • The prompt and NO-reburning routes are negligible due to the absence of CH 4. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, entropy generation in non-premixed hydrogen versus heated air counter-flow combustion confined by planar opposing jets is investigated for the first time. The effects of the volume percentage of hydrogen in fuel mixture and the inlet Reynolds number (corresponding to the global stretch rate) on entropy generation are studied by numerical evaluating the entropy generation equation. The lattice Boltzmann model proposed in our previous work, instead of traditional numerical methods, is used to solve the governing equations for combustion process. Through the present study, three interesting features of this kind of combustion, which are quite different from that reported in previous literature on entropy generation analysis for diffusion hydrogen-air flames, are revealed. Moreover, it is observed that the whole investigated domain can be divided into two parts according to the predominant irreversibilities. The total entropy generation number can be approximated as a linear increasing function of the volume percentage of hydrogen in fuel mixture and the inlet Reynolds number for all the cases under the present study. It is very interesting that most characteristics in this kind of diffusion combustion also can be found in its premixed counterpart investigated in our previous work. Especially, the critical Reynolds numbers determining the order of the predominant irreversibilities in this type of diffusion flame are same as its premixed counterpart, although the flow and scalar fields between them are quite different. [Copyright &y& Elsevier]

Abstract: The emission of mercury by coal-fired power plants has become a recent concern on the part of the electric utility industry. Knowledge of mercury kinetic mechanisms is imperative for the research of predicting mercury transformation and finding its effective control methods in coal combustion flue gas. Near the end of the flue gas path, mercury exists as a combination of elemental vapor and HgCl2 vapor. HgCl2 is more likely to be removed from the flue gas. Thus, the degree of oxidation is considered to be a critical factor that tends to reduce emission. In the present work, the microcosmic kinetic mechanisms of reactions between mercury and oxidizing species were investigated by ab initio calculations of quantum chemistry. The geometry optimizations of reactants, transition states, intermediates and products were made by the quantum chemistry MP2 method at SDD basis function level. All molecule energies were calculated at QCISD(T)/SDD level and corrected with zero point energy. The activation energies and heat of reactions were calculated. The reaction rate constants were calculated from transition state theory (TST). The performance of the ab initio calculations of quantum chemistry was assessed through comparisons with the literature data. The comparisons showed that the ab initio calculations of quantum chemistry were in agreement with the literature data. The results showed that quantum chemistry was an effective means for investigating kinetic mechanism of mercury interaction with combustion-generated flue gas. [Copyright &y& Elsevier]

[Display omitted] • A benchmark model to evaluate the performance of pressurized oxy-coal systems is developed. • The performance and process characteristics of two pressurized oxy-coal systems are compared. • Detailed analysis of the factors affecting the pressurized oxy-coal efficiency is conducted. • The efficiency increases of two pressurized oxy-coal systems are obtained and analyzed. 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. [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]

• Ignition process is controlled by both mixing and chemistry for all jet flames. • Flow mixing greatly affects both ignition and stabilization of low-oxygen flames. • Rich-side reactions are much slower than lean-side and are far from equilibrium. • Premixing of fuel jet and coflow before ignition is crucial for low-oxygen flames. • Low-oxygen flames develop by autoignition versus high-oxygen ones by propagation. This study numerically investigates the ignition and evolution of CH 4 jet flames in a hot coflow (JHC) using large eddy simulation (LES). Three coflow oxygen fractions are carefully selected to compare moderate or intense low-oxygen dilution (MILD, Y O2,C = 6 % and 9 %) and high temperature combustion (HTC, Y O2,C = 23.3 %). Systematic investigations are performed on flame ignition, lift-off, reaction progress, and stabilization mechanisms. The results show that for the MILD cases, both the ignition process and final stable flame are controlled by turbulent mixing and chemistry in a state far from chemical equilibrium. In contrast, the reactions are much stronger for HTC, and the final flame is controlled by chemistry through equilibrium reactions. Moreover, for all three cases, the reactions always progress more rapidly at the lean side than at the rich side; thus, autoignition dominates the former, whereas flame propagation is more important for the latter. In addition, the premixing of fuel and oxidant prior to main reactions is crucial for realizing MILD combustion; therefore, the flame is lifted and stabilized by the autoignition of partially premixed reactants in the fuel-lean region. In contrast, the final HTC flame attaches to the burner exit and is stabilized by both the lean-side autoignition and rich-side flame propagation. For all three cases, the lean-side and stoichiometric flames adopt the nonpremixed mode, whereas the rich-side reactions are in the premixed mode, except for the flame base. [ABSTRACT FROM AUTHOR]

• NH 3 flame has much lower temperature rise and larger reaction zone than CH 4. • NO x emission of NH 3 flame is two orders higher than CH 4 at equivalence ratio < 1. • NO x emissions of both flames increase rapidly with coflow oxygen concentration. • NO x emission mainly comes from NO while N 2 O is important at low temperature. • MILD combustion can reduce the NO x emission of NH 3 flame by 1–2 orders. Moderate or intense low-oxygen dilution (MILD) combustion is suitable for solving the problems of unstable flames and high NO x emissions (E NO x) of ammonia fuels; however, studies on this are rare. This paper numerically investigates the MILD combustion characteristics of a premixed NH 3 /air jet flame in hot coflow (JHC) under different jet equivalence ratios (Φ J), coflow temperatures (T C), and oxygen levels (X O2,C). For comparison, similar CH 4 /air MILD-JHC flame characteristics are calculated. The results show that the NH 3 flame generally has a lower temperature increase and heat release, as well as a larger reaction zone, than CH 4. This suggests that the NH 3 flame can develop into a MILD regime more easily than CH 4. E NO x of the NH 3 flame is two orders of magnitude higher than that of CH 4 flame at all T C and X O2,C values for Φ J < 1. At Φ J > 1, E NO x of the NH 3 flame rapidly decreases to nearly zero, but unburned NH 3 emissions (E NH3) and H 2 emissions (E H2) are significantly high (∼1000 ppm) and the combustion efficiency is low. Moreover, E NO x increases rapidly (gradually) with X O2,C (T C), whereas E NH3 and E H2 are considerably low at T C ≥ 1300 K and X O2,C ≥ 1% for the NH 3 flame. E NO x primarily originates from NO; however, N 2 O is also important at low Φ J and T C values. Therefore, considering E NO x , E NH3 , E H2 and the burning efficiency, the optimal conditions for NH 3 MILD combustion are Φ J = 1, T C ≥ 1500 K, and X O2,C = 1%–3%. In addition, compared with conventional flames, NH 3 MILD combustion can reduce E NO x by one to two orders of magnitude. [ABSTRACT FROM AUTHOR]

NO-reburning technology can effectively decrease NO x emissions during combustion. Despite extensive studies have been conducted on NO reburning under traditional combustion, homogeneous NO-reburning characteristics have not been systematically examined in flameless combustion (FLC). This study performs a systematic comparative investigation of homogeneous NO-reburning for the first time via experiments and simulations in a 20-kW furnace. The influences of combustion mode, air-preheating temperature (T a), and equivalence ratio (Φ) are studied in detail. The experimental results show that FLC can improve NO-reduction efficiency by more than 35% compared to swirl flame combustion (SFC). Moreover, the results also show that reducing T a from 723 K to 573 K can enhance NO-reburning during FLC, while the NO-reburning is insensitive to Φ in the range of 0.65–0.89. Furthermore, a detailed numerical simulation that couples the eddy-dissipation concept model and a well-verified skeletal mechanism for NO-reburning is validated and performed, to further reveal the reduction pathways of NO. By combining flameless combustion with NO-reburning, this study confirms the preponderance of flameless combustion under low-temperature air conditions (T a ≤ 573 K) for considerable NO reduction by reburning. The results offer novel fundamental insights into the homogeneous NO-reburning characteristics. • Homogeneous NO-reburning in flameless combustion is studied for the first time. • Flameless combustion can improve the NO reduction efficiency by more than 35%. • Reducing the air preheat-temperature enhances NO-reburning of flameless combustion. • Reaction pathways of NO reduction for swirl and flameless combustion are revealed. [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]

In this paper, theoretical analysis and experimental studies are carried out to analyze the intrinsic kinetic properties of coal char oxidation based on a thermo-gravimetric analyzer (TGA). A one-dimensional oxidation model of the char particles' layer is established to consider various diffusion resistances, including external, inter-particle layer, and intra-particle diffusion in the crucible during TGA experiments. The model is validated (1) with the effective factor results calculated by the Thiele modulus formula; (2) with the present TGA experimental data. Then, the oxidation process of coal char in TGA under different crucible loading positions, particle thicknesses, oxygen concentrations, and heating rates, is inverted by the model. The results show that the external diffusion in the crucible significantly affects the char oxidation process. The external diffusion resistance increases with increasing the stagnation zone. The inter-particle layer resistance enhances with thickening particle thickness. The influence of diffusion resistance can be diminished as much as possible by filling the bottom of the crucible with inertia alumina particles. Further non-isothermal TGA experiments and kinetic analysis of a bituminous coal char confirm that the activation energy obtained by the optimized method (168.3 kJ/mol) is much higher than that obtained by the conventional method (134.1 kJ/mol). • Model considering external, inter-particle, intra-particle diffusion is developed. • Factors affecting the diffusion processes in the TGA experiment are investigated. • Inert particle filling is an effective method to avoid crucible external diffusion. • A much higher active energy of 168.3 kJ/mol for a bituminous char is obtained. [ABSTRACT FROM AUTHOR]

• Pilot-test of MILD combustion of solid waste blend is realized for the first time. • The burnout rates of solid waste blend MILD combustion are higher than 95%. • The fuel-NO emission of MILDC-AS combustion is reduced by 54%. • MILD combustion reduces the PM 2.5 emissions of biomass blend fuel by 50%. The treatment of solid waste through incineration has become an important development trend. A solid waste blend (sawdust and residual char) is studied experimentally in a tubular-furnace reactor and a 200-kW pilot-scale furnace under moderate or intense low-oxygen dilution (MILD) combustion conditions. The effects of temperature and oxygen concentration on NO release characteristics are examined in the tubular-furnace reactor. The pilot-scale furnace experiments include the conventional flame combustion using a swirl nozzle (CFC-S), MILD combustion using symmetrical dual straight nozzles (MILDC-SD), and MILD combustion using an asymmetrical single straight nozzle (MILDC-AS). The tubular-furnace reactor results indicate that the NO released from solid waste blend mainly originates from fuel-NO under medium temperature and low oxygen environments. The pilot-scale furnace results demonstrate that stable combustion of the solid waste blend can be achieved under three co-combustion conditions. Compared to CFC-S, the MILDC-AS combustion of solid waste blend inhibits the fuel-NO and PM 2.5 emissions by 54% and 50%, respectively. The burnout rates of solid waste blend MILD combustion exceed 95%. This study not only extends the fuel adaptability of MILD combustion to solid waste blend, but also proves the suppression influence of MILD combustion on fuel nitrogen and PM 2.5 emissions. [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]

The behaviour of mercury is investigated in a 35 MW th large pilot boiler of oxyfuel combustion with dry and wet flue gas recycle (FGR). The mercury species in fly ash particles as well as the involved reaction mechanism are systematically investigated. The results suggest that higher concentration of gas–phase mercury (Hg g ) is contained in oxyfuel combustion flue gas. The conversion of Hg g to particulate associated mercury (Hg p ) is enhanced in oxyfuel combustion. Different mercury species are presented in fly ash collected from air and oxyfuel combustion: trigonal red HgS is the main mercury species in air combustion; mercury bound to organic matter (Hg–OM) and trigonal red HgS are both dominant in the samples from oxyfuel combustion. The prominent difference is the significantly increase of Hg–OM in oxyfuel combustion atmosphere. The oxyfuel combustion atmosphere would favor the formation of oxygen–rich functional groups, especially the C O group, which is responsible for the adsorption of mercury and formation of Hg–OM in fly ash. [ABSTRACT FROM AUTHOR]

Accurate assessment of coal char oxidation kinetics is essential for the design of efficient combustion systems; nonetheless currently, there is little research on this aspect under moderate or intense low-oxygen dilution (MILD) oxy-fuel (MO) conditions. In this study, experimental and modeling studies were conducted for analyzing the intrinsic kinetic properties of coal char oxidation under MILD air-combustion (MA) and MO conditions based on thermogravimetric analysis (TGA). The experimental conditions were improved to minimize various diffusion resistances in the crucible during the TGA experiments. Under the optimal conditions of TGA experiments, the reactivity differences of coal char under the MA and MO atmospheres were small. Both nonlinear model-fitting and linear model-free analysis methods were used to analyze kinetic parameters of coal char oxidation. The results showed that the random pore model correlated the best with the experimental results. The activation energies of coal char under the optimal conditions in MA and MO atmospheres (i.e., 104.4 kJ/mol and 98.2 kJ/mol, respectively) were much higher than those obtained by the conventional method. The reaction orders of coal char oxidation in MA and MO atmospheres were close to 1.0, and the specific values were affected by the diffusion effect and background atmosphere. [Display omitted] • TGA experimental method is optimized by minimizing various diffusion resistances. • Kinetics of coal char in MA and MO atmospheres have been studied by the new method. • Kinetic parameters obtained by the new method exhibit obvious improvements. [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]

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]

Co-firing residual char and pulverized coal can apply the residual char in pulverized coal combustion equipment, whose difficulties lie in poor ignition performance and low burnout efficiency. For the first time, residual char and bituminous coal fuel blend is experimentally co-fired under moderate or intense low-oxygen dilution (MILD) conditions. MILD co-combustion is achieved with low-temperature preheating air in a pilot-scale furnace. The co-firing experiments include swirl low-NO flame combustion, MILD combustion through symmetrical secondary air jets, and MILD combustion through an asymmetrical secondary air jet. The pilot-scale tests reveal that MILD co-combustion through the asymmetrical single nozzle achieves the lowest peak temperature and the most uniform distributions of temperature, heat flux, and gas compositions in the furnace. The NO emission of MILD co-combustion through the asymmetrical air jet is decreased by 57% compared with swirl low-NO flame co-combustion. The burnout rate of MILD co-combustion through the asymmetrical air jet reaches 94%. Considering more uniform in-furnace distribution, lower NO emission, and higher burnout rate, MILD combustion through the asymmetrical single nozzle shows more obvious advantages than that through symmetrical air nozzles. Overall, the present study further widens the fuel flexibility of MILD combustion even to residual char fuel blend. • Co-firing residual char under MILD combustion is realized for the first time. • MILD co-combustion of residual char can reduce fuel-NO emission by at least 54%. • Fuel flexibility of MILD combustion is even expanded to residual char fuel blend. [ABSTRACT FROM AUTHOR]

A Lattice-Boltzmann model coupled with boundary method is proposed for the hydrodynamic resolved simulation of a single char particle combustion. A pure lattice Boltzmann scheme with multi distribution functions is presented for this low Mach reactive flows. Real varying thermodynamic and transport properties are considered, and the fluid density can bear significant change depending on the varying temperature and species concentrations. The recently proposed boundary-thickening based direct forcing-immersed boundary method is extended to implement the boundary conditions of velocity, temperature, and species concentrations at the char particle surface. Two heterogeneous reactions at particle surface and one homogeneous reaction in fluid are adopted to describe the combustion. The Stefan flow near the particle surface caused by the heterogeneous reactions is also considered. A satisfactory agreement can be found between the present simulation results and the previous experimental and numerical results. Three flame modes of a char particle combustion and the transition mechanisms between them are investigated. Furthermore, the effect of hydrodynamic interaction and the oxygen concentration in O 2 /CO 2 atmosphere on particle combustion behavior are explored in detail. The present work establishes the foundation for the efficient simulations of particle combustion with size change and motion. • IB-LBM is developed for particle combustion with varying thermodynamic and transport properties. • Results are validated by comparing with previous experiments and simulations. • Particle combustion behaviors in O 2 /N 2 and in O 2 /CO 2 atmosphere are compared. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, entropy generation in hydrogen enriched ultra-lean counter-flow methane–air premixed combustion confined by planar opposing jets is investigated for the first time. The effects of the effective equivalence ratio and volume percentage of hydrogen in fuel blends on entropy generation are studied by numerical evaluating the entropy generation equation. The lattice Boltzmann model proposed in our previous work, instead of traditional numerical methods, is used to solve the governing equations for combustion process. Through the present study, four interesting features of this kind of combustion, which are quite different from that reported in previous literature on entropy generation analysis for hydrogen enriched methane–air combustion, are revealed. For a given effective equivalence ratio, the total entropy generation number can be approximated as a linear increasing function of the volume percentage of hydrogen in fuel blends for all cases investigated in the present study. [Copyright &y& Elsevier]

Abstract: In order to reduce the CO2 emission from the coal-fired power plants, O2/CO2 recycle combustion (Oxy-combustion) technique has been proposed through combining a conventional combustion process with a cryogenic air separation process. The technique is capable of enriching CO2 concentration and then allowing CO2 sequestration in an efficient and energy-saving way. Taking into account the CO2 taxation and CO2 sale, the paper evaluates the economic feasibility of Oxy-combustion plants retrofitted from two typical existing conventional coal-fired power plants (with capacities of 2×300MW and 2×600MW, respectively) with Chinese data. The cost of electricity (COE) and the CO2 avoidance cost (CAC) are also considered in the evaluation. The COE of the retrofitted Oxy-combustion plant is nearly the same as that of the corresponding conventional plant if the unit price of CO2 sale reaches 17–22$/t (different cases). The CAC of the retrofitted 2×300MW Oxy-combustion plant is 1–3$/t bigger than that of the retrofitted 2×600MW Oxy-combustion plant. Supercritical plants are more economical and appropriate for Oxy-combustion retrofit. The result indicates that Oxy-combustion technique is not only feasible for CO2 emission control based on existing power plants but is also cost-effective. [Copyright &y& Elsevier]

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]

• New experiments on NO reduction under CO 2 atmosphere are performed in a JSR. • There is a critical equivalence ratio to achieve the maximum NO reduction. • The maximum NO reduction is achieved at Φ ≈ 1.4 and 1300 K in CO 2 atmosphere. • The maximum NO reduction is about 63% when the initial CH 4 /NO ratio is 20. • The optimum condition for NO reburning of oxy-fuel combustion is obtained. This paper presents new experimental results on NO reduction by CH 4 under both N 2 and CO 2 atmospheres in a jet-stirred rector (JSR). The experiments are simulated using an updated reaction mechanism, and simulations are consistent with experiments. Both experiments and simulations suggest that there is a critical equivalence ratio (Φ) to achieve the maximum NO reduction at a fixed reaction temperature (T), and the critical Φ is increased with the increase of T. The maximum NO reduction in the CO 2 atmosphere is achieved at T ≈ 1300 K, Φ ≈ 1.4, and CH 4 /NO ratio = 20 with a maximum reduction efficiency of 63%. When the CH 4 /NO ratio ≤5, relative to the N 2 atmosphere, the NO reburning in the CO 2 atmosphere is reduced by around 40%–60% at temperatures above 1100 K. Interestingly, at 1100 K the maximum NO reduction does not occur at fuel-rich environments but at Φ ≈ 0.7 due to the low reactivity to produce hydrocarbon radicals at low temperatures. Moreover, at 1300 K, as CO 2 concentration increases from 30% to 60%, the critical Φ is reduced from 1.4 to 1.2 and the NO reduction efficiency is reduced by around 7% owing to the enhanced inhibition of CH 4 oxidation. To improve reburning in oxy-fuel combustion, it is recommended to operate reburn zone at moderate temperatures (i.e., 1300–1400 K), the critical Φ (e.g., Φ ≈ 1.4 if T = 1300 K), long residence times (τ ≥ 2 s), and large reburning fuel/NO ratio (≥15). [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]