Combustion characteristics of lignite-fired oxy-fuel flames

Hjärtstam, Stefan; Andersson, Klas; Johnsson, Filip; Leckner, Bo G

doi:10.1016/j.fuel.2009.05.011

Cited by 98 publications

(36 citation statements)

References 14 publications

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“…In contrast, our previous paper shows the role of CO 2 was to advance CH 4 oxidation during fuel-rich O 2 /CO 2 combustion where the concentrations of reactants were high because R3 became insignificant under fuel-rich condition, and R1 produced an abundance of OH radicals that were more active than the H radicals in hydrocarbon reactions in the specific temperature range (12,13) . In addition to this, the total hydrocarbon in oxy-fuel coal combustion was lower than that in air combustion in some literature (1,2) . Therefore, further investigations are needed in hydrocarbon oxidation process under O 2 /CO 2 environments.…”

Section: Journal Of Thermal Science and Technologymentioning

confidence: 68%

“…typically coal, a large part of the fuel conversion occurs in the gas phase, and hydrocarbon oxidation plays an important role in combustion process (1)(2)(3)(4) . CH 4 is not only a natural gas component but also one of the major volatile matter released from coal.…”

Section: Journal Of Thermal Science and Technologymentioning

confidence: 99%

“…Further, the CO from the O 2 /CO 2 combustion is higher than that in air combustion, because R1 and R2 produce CO, as shown in previous literature (5) . CO 2 Figure 4(a). Acetylene has long been regarded as a dominant mass source for soot growth (16) .…”

Section: Journal Of Thermal Science and Technologymentioning

confidence: 99%

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Experimental and Kinetic Studies of Chemical Role of CO2 in Hydrocarbon Oxidation during Fuel-Rich O2/CO2 Combustion

Watanabe

Kiatpanachart

Okazaki

2013

JTST

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Experimental and kinetic studies of the chemical role of CO 2 in hydrocarbon reactions were conducted in a fuel-rich CH 4 flat flame with air ratios varying from 0.60 to 0.74. Unburned hydrocarbons (CH 4 , C 2 H 2 , C 2 H 4 , and C 2 H 6 ) in O 2 /CO 2 combustion were found to be lower than those in air combustion. The differences in the CH 4 oxidation characteristics between the air and O 2 /CO 2 combustion were caused by the chemical role of CO 2 in the reaction R1 (CO 2 + H → CO + OH), R2 (CH 2 (S) + CO 2 → CH 2 O + CO), and higher third body efficiencies of CO 2 at an air ratio (= 0.62 where the concentrations of reactants were high. The role of CO 2 in R1, R2, and the higher third body efficiencies of CO 2 decreased the rate of CH 4 oxidation during the early stage of combustion, where O 2 was present. Even though R2 did not directly compete with the main chain branching reaction R3 (H + O 2 → H + OH) for H radicals, like R1 did, R2 changed the hydrocarbon reaction pathway, thereby decreasing the rate of R4 (CH 3 + HO 2 → CH 3 O + OH) which had negative sensitivity in CH 4 oxidation. However, we found that R1 and R2 advance CH 4 oxidation in the last stage of combustion where O 2 was mostly consumed. This is attributed to the fact that the reactions R1 and R2 were able to advance without the presence of O 2 , and that R1 produced OH radicals that were active in hydrocarbon oxidation in the specific temperature range and R2 enhanced hydrocarbon oxidation when the rate of R4 was insignificant. Although R1 was the dominant reaction to reduce unburned hydrocarbons in the O 2 /CO 2 combustion, the role of R2 was significant at  = 0.62. Meanwhile, when the air ratio was 0.74 where concentrations of reactants were relatively low, the chemical role of CO 2 is to only decrease the rate of CH 4 oxidation due to the presence of an excessive amount of O 2 .

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Section: Journal Of Thermal Science and Technologymentioning

confidence: 68%

Section: Journal Of Thermal Science and Technologymentioning

confidence: 99%

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Experimental and Kinetic Studies of Chemical Role of CO2 in Hydrocarbon Oxidation during Fuel-Rich O2/CO2 Combustion

Watanabe

Kiatpanachart

Okazaki

2013

JTST

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“…The more recently published large mechanisms have used lower rates for reaction of NO with CO to form N atoms and so Reaction 1 should be considered a global reaction. In addition, Skreiberg et al (2004) state that they do not expect that CO under reducing conditions causes a significant reduction in NO below 1400 K. Hjärtstam et al (2007) reporting on the same experiments as Andersson et al (2007) note that stack CO emissions were comparable between air and oxy-fuel cases even when very high levels of CO existed in the oxy-fuel flames. They also report improved attachment of the flame with increasing oxygen concentration in the oxy-fuel cases.…”

Section: Review Of No X Formation In Oxy-combustionmentioning

confidence: 98%

A Mechanistic Investigation of Nitrogen Evolution and Corrosion with Oxy-Combustion

Tree

Mackrory²,

Fletcher³

2008

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A premixed, staged, down-fired, pulverized coal reactor and a flat flame burner were used to study the evolution of nitrogen in coal contrasting differences in air and oxy-combustion. In the premixed reactor, the oxidizer was staged to produce a fuel rich zone followed by a burnout zone. The initial nominal fuel rich zone stoichiometric ratio (S.R.) of 0.85 selected produced higher NO reductions in the fuel rich region under oxy-combustion conditions. Air was found to be capable of similar NO reductions when the fuel rich zone was at a much lower S.R. of 0.65. At a S.R. of 0.85, oxy-combustion was measured to have higher CO, unburned hydrocarbons, HCN and NH 3 in the fuel rich region than air at the same S.R. There was no measured difference in the initial formation of NO. The data suggest devolatilization and initial NO formation is similar for the two oxidizers when flame temperatures are the same, but the higher CO 2 leads to higher concentrations of CO and nitrogen reducing intermediates at a given equivalence ratio which increases the ability of the gas phase to reduce NO. These results are supported by flat flame burner experiments which show devolatilization of nitrogen from the coal and char to be similar for air and oxy-flame conditions at a given temperature. A model of premixed combustion containing devolatilization, char oxidation and detailed kinetics captures most of the trends seen in the data. The model suggests CO is high in oxy-combustion because of dissociation of CO 2 . The model also predicts a fraction (up to 20%, dependent on S.R.) of NO in air combustion can be formed via thermal processes with the source being nitrogen from the air while in oxy-combustion equilibrium drives a reduction in NO of similar magnitude. The data confirm oxy-combustion is a superior oxidizer to air for NO control because NO reduction can be achieved at higher S.R. producing better char burnout in addition to NO from recirculated flue gas being reduced as it passes back through the flame.4

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“…Likewise, Rehfeldt et al (Rehfeldt, Kuhr, Ehmann, Bergins, Scheffknecht, Maier and Wu 2009) found significantly higher CO concentration in the fuel-rich flame region of oxy-Lausitz lignite coal combustion using a 0.5 MW th pilot scale test facility. Moreover, Andersson et al (Andersson, Johansson, Johnsson andLeckner 2008, Andersson andJohnsson 2007) and Hjartstam et al (Hjartstam, Andersson, Johnsson and Leckner 2009) measured the CO concentrations in a 100 kW th test facility using propane or lignite coal fuels, and they observed consistently higher CO concentrations in the combustion zone near the burner under oxy-fuel conditions than under air-fired conditions when the combustion temperatures are maintained the same. The higher CO in the flame region is expected to affect the pollutant formation processes.…”

Section: Introductionmentioning

confidence: 97%

Modeling CO₂Chemical Effects on CO Formation in Oxy-Fuel Diffusion Flames Using Detailed, Quasi-Global, and Global Reaction Mechanisms

Chen

Ghoniem

2014

Combustion Science and Technology

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Interest in oxy-fuel combustion as one of the leading carbon capture technologies has grown significantly in the past two decades. Experimental studies have shown higher CO concentration in oxy-fuel diffusion flames than in traditional air-fuel flames of both gaseous and solid fuels. The higher CO concentration changes the flame profiles, and it may have impacts on pollutants formation. This paper presents a numerical study regarding the chemical effects of CO 2 on CO formation in the flame region, and their modeling approaches in CFD simulations. Equilibrium calculation confirms higher CO concentration associated with fuel-rich stoichiometry in CO 2 diluted combustion environment.One-dimensional counter flow diffusion flame simulation using detailed reaction mechanisms reveals

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Combustion characteristics of lignite-fired oxy-fuel flames

Cited by 98 publications

References 14 publications

Experimental and Kinetic Studies of Chemical Role of CO<sub>2</sub> in Hydrocarbon Oxidation during Fuel-Rich O<sub>2</sub>/CO<sub>2</sub> Combustion

Experimental and Kinetic Studies of Chemical Role of CO<sub>2</sub> in Hydrocarbon Oxidation during Fuel-Rich O<sub>2</sub>/CO<sub>2</sub> Combustion

A Mechanistic Investigation of Nitrogen Evolution and Corrosion with Oxy-Combustion

Modeling CO₂Chemical Effects on CO Formation in Oxy-Fuel Diffusion Flames Using Detailed, Quasi-Global, and Global Reaction Mechanisms

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Combustion characteristics of lignite-fired oxy-fuel flames

Cited by 98 publications

References 14 publications

Experimental and Kinetic Studies of Chemical Role of CO<sub>2</sub> in Hydrocarbon Oxidation during Fuel-Rich O<sub>2</sub>/CO<sub>2</sub> Combustion

Experimental and Kinetic Studies of Chemical Role of CO<sub>2</sub> in Hydrocarbon Oxidation during Fuel-Rich O<sub>2</sub>/CO<sub>2</sub> Combustion

A Mechanistic Investigation of Nitrogen Evolution and Corrosion with Oxy-Combustion

Modeling CO2Chemical Effects on CO Formation in Oxy-Fuel Diffusion Flames Using Detailed, Quasi-Global, and Global Reaction Mechanisms

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Product

Resources

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Modeling CO₂Chemical Effects on CO Formation in Oxy-Fuel Diffusion Flames Using Detailed, Quasi-Global, and Global Reaction Mechanisms